全文获取类型
收费全文 | 809篇 |
免费 | 20篇 |
国内免费 | 19篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 46篇 |
地球物理 | 189篇 |
地质学 | 201篇 |
海洋学 | 234篇 |
天文学 | 121篇 |
综合类 | 4篇 |
自然地理 | 42篇 |
出版年
2021年 | 6篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 20篇 |
2015年 | 11篇 |
2014年 | 19篇 |
2013年 | 30篇 |
2012年 | 25篇 |
2011年 | 38篇 |
2010年 | 34篇 |
2009年 | 46篇 |
2008年 | 38篇 |
2007年 | 42篇 |
2006年 | 49篇 |
2005年 | 39篇 |
2004年 | 57篇 |
2003年 | 27篇 |
2002年 | 23篇 |
2001年 | 24篇 |
2000年 | 18篇 |
1999年 | 13篇 |
1998年 | 22篇 |
1997年 | 13篇 |
1996年 | 18篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 19篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 7篇 |
1971年 | 3篇 |
1970年 | 2篇 |
排序方式: 共有848条查询结果,搜索用时 15 毫秒
51.
The Current System in the Yellow and East China Seas 总被引:18,自引:1,他引:18
During the 1990s, our knowledge and understanding of the current system in the Yellow and East China Seas have grown significantly
due primarily to new technologies for measuring surface currents and making high-resolution three-dimensional numerical model
calculations. One of the most important new findings in this decade is direct evidence of the northward current west of Kyushu
provided by satellite-tracked surface drifters. In the East China Sea shelf region, these recent studies indicate that in
winter the Tsushima Warm Current has a single source, the Kuroshio Branch Current in the west of Kyushu, which transports
a mixture of Kuroshio Water and Changjiang River Diluted Water northward. In summer the surface Tsushima Warm Current has
multiple sources, i.e., the Taiwan Warm Current, the Kuroshio Branch Current to the north of Taiwan, and the Kuroshio Branch
Current west of Kyushu. The summer surface circulation pattern in the East China Sea shelf region changes year-to-year corresponding
to interannual variations in Changjiang River discharge. Questions concerning the Yellow Sea Warm Current, the Chinese Coastal
Current in the Yellow Sea, the current field southwest of Kyushu, and the deep circulation in the Okinawa Trough remain to
be addressed in the next decade.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
52.
53.
A pattern of slick streaks winding into a spiral, known as a spiral eddy, was identified in 5 images taken by the ERS-1/2
synthetic aperture radar (SAR) in Mutsu Bay (Japan); dynamic and kinematic models of these spiral eddies have been proposed.
Common characteristics of the five spiral eddies are: 1) an eddy diameter of about 15 km; 2) their location in the western
part of the bay; and 3) their cyclonic direction of rotation. Moreover, the wind conditions over the bay were common: prior
to acquiring the images, a strong easterly wind continued blowing for more than one day. The wind field on the bay is known
to be orographically steered and has strong windstress vorticity, which generates cyclonic circulation. The diameter and location
of the circulation simulated with a numerical ocean model corresponded well to those of the identified spiral eddies. Based
on these facts, we propose a dynamic model for the movement of a slick streak, and a kinematic model for the formation of
a spiral eddy. We have assumed calm air, a microlayer and seawater with a cyclonic circulation in the dynamic model. The balance
of forces is established in the microlayer among the frictional force from the seawater, the frictional force from the calm
air, the gravitational force, and the Coriolis force. As a result, the velocity vector of the microlayer deflects slightly
towards the center of the cyclonic circulation. We have assumed a point source of the microlayer in the kinematic model. The
shapes of a slick streak simulated with the models agree well with the identified patterns in the SAR images. 相似文献
54.
Wataru Takahashi Hiroshi Kawamura Takuo Omura Ken Furuya 《Journal of Oceanography》2009,65(5):647-656
A multi-spectral classification scheme is proposed to identify water with red tide(s) using satellite ocean color imagery
obtained by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The study area was the eastern Seto Inland Sea in Japan,
where serious red tides frequently occur. “Background Ocean Colors” (BOCs hereafter), or colors of water around a red tide
or those of the water before/after a red tide, are calculated as the monthly climatological average of normalized water-leaving
radiances (nLw) with 0.01 degree spatial resolution with SeaWiFS imagery. Criteria for detecting red-tide pixels are established
from analyses of characteristics of the nLws (in the 443, 490, 510, and 555 nm bands) anomalies from BOCs and the nLw spectra
together with the red-tide records in Osaka Bay. The proposed scheme can efficiently indicate the presence or absence of red
tides for independent match-ups with 83% accuracy. Additional validations of specific events indicate that the algorithm performed
well in the study area. These results suggest that the scheme is appropriate to detect red tides in the optically complex
coastal water of the eastern Seto Inland Sea. 相似文献
55.
Hiroshi Ishida Yutaka W. Watanabe Joji Ishizaka Toshiya Nakano Naoki Nagai Yuji Watanabe Akifumi Shimamoto Nobuhiro Maeda Michimasa Magi 《Journal of Oceanography》2009,65(2):179-186
Our analysis of the last three decades of retrospective data of vertical distributions and size composition of chlorophyll-a
(Chl-a) over the western North Pacific has revealed significant changes of three indices related to Chl-a during summer season,
as follows: (1) decreasing linear trend of the proportion of Chl-a in surface layer to that of the whole water column by 0.4
and 2.3% year−1 in the subtropical area along 137°E (STA137) during 1972 to 1997 and in the Kuroshio Extension area along 175°E (KEA175) during 1990 to 2001; (2) increasing linear trend of the depth of subsurface Chl-a maximum (DCM) by 0.4 and 2.6 m year−1 in STA137 and KEA175; and (3) decreasing linear trend of larger-size Chl-a (>3 μm) by 0.1 and 2.5% year−1 in STA137 and KEA175, respectively. Water density (σ
θ
) at 75 m depth had also decreased by 0.006 and 0.05 year−1 in STA137 and KEA175, respectively. The ratio of biogenic opal to biogenic CaCO3 in the sinking flux decreased by 0.015 year−1 in the subtropical region from 1997 to 2005. These findings may indicate that the subsurface chlorophyll maximum is deepening
and larger phytoplankton such as diatoms has been decreasing during the past decade, associated with the decreasing density
of surface water caused by warming in the western North Pacific, especially in the summer. 相似文献
56.
Yasutaka Terakado Hiroshi Shimizu Akimasa Masuda 《Contributions to Mineralogy and Petrology》1988,99(1):1-10
Initial Nd and Sr isotopic ratios were obtained for middle Miocene igneous rocks as well as for related rocks from the Outer Zone of Southwest Japan to investigate the petrogenesis of acidic magmas and their relation to a peculiar tectonic environment bearing on the back-arc spreading of the Japan Sea. On the
Nd-
Sr diagram, data points for the acidic rocks fall in the –
Nd, +
Sr quadrant occupying different positions from those for sedimentary and old crustal rocks, and seem to define several subparallel lines which extend towards the lower-righthand sedimentary field. The S-type acidic rocks occupy an intermediate position between I-type rocks and sedimentary ones, a fact suggesting mixing of an igneous component and a sedimentary one. The linear mixing trend observed on the
Nd-
Sr diagram can be attained in the restricted case that the igneous component has similar Sr/Nd concentration ratios to that of the sedimentary one, which implies an intermediate to acidic composition for the igneous component. Inconsistency between the elemental and isotopic variations observed may be reconciled by considering that mixing, probably in the relatively deep part of the crust, might have occured prior to chemical differentiation processes. The episodic igneous activity and the high heat energy required to melt such materials involving sedimentary rocks may be explained by a model in which a hot mantle region probably corresponding to the rising part of the mantle convection supplied the heating energy to the Outer Zone of Southwest Japan when passing beneath Southwest Japan in the course of movement of the hot rising part from the Shikoku basin areas to the Japan Sea area. 相似文献
57.
Tadashi Akamatsu Kiyoshi Fujino Mineo Kumazawa Akio Fujimura Manabu Kato Hiroshi Sawamoto Takamitsu Yamanaka 《Physics and Chemistry of Minerals》1988,16(2):105-113
Synthetic (Mg0.51, Mn0.49)2SiO4 olivine samples are heat-treated at three different pressures; 0, 8 and 12 GPa, all at the same temperature (~500° C). X-ray structure analyses on these single crystals are made in order to see the pressure effect on cation distribution. The intersite distribution coefficient of Mg and Mn in M1 and M2 sites, K D = (Mn/Mg) M1/(Mn/Mg) M2, of these samples are 0.192 (0 GPa), 0.246 (8 GPa) and 0.281 (12 GPa), indicating cationic disordering with pressure. The small differences of cell dimensions between these samples are determined by powder X-ray diffraction. Cell dimensions b and c decrease, whereas a increases with pressure of equilibration. Cell volume decreases with pressure as a result of a large contraction of the b cell dimension. The effect of pressure on the free energy of the cation exchange reaction is evaluated by the observed relation between the cell volume and the site occupancy numbers. The magnitude of the pressure effect on cation distribution is only a fifth of that predicted from the observed change in volume combined with thermodynamic theory. This phenomenon is attributed to nonideality in this solid solution, and nonideal parameters are required to describe cation distribution determined in the present and previous experiments. We use a five-parameter equation to specify the cationic equilibrium on the basic of thermodynamic theory. It includes one energy parameter of ideal mixing, two parameters for nonideal effects, one volume parameter, and one thermal parameter originated from the lattice vibrational energy. The present data combined with some of the existing data are used to determine the five parameters, and the cation distribution in Mg-Mn olivine is described as a function of temperature, pressure, and composition. The basic framework of describing the cationic behavior in olivine-type mineral is worked out, although the result is preliminary: each of the determined parameters is not accurate enough to enable us to make a reliable prediction. 相似文献
58.
Isotopic ratios and abundances of all REE in two Oklo ore samples have been measured. We have succeeded in developing a new method to estimate the neutron fluence, the conversion factor of uranium and the average neutron energy (or temperature) based on Gd and U isotopic ratios. This new calculation is found to be useful in evaluating those parameters for the natural nuclear reactors at Oklo. Comparison is made between the neutron fluence values evaluated by our new method employing Gd isotopes and a previous one [11] employing Sm and Nd isotopes. The relative agreement becomes better with the increase of fluence. A relationship between the abundances of fissiongenic nuclides of La, Ce, Nd, Sm, and Gd and their mass numbers is also presented. 相似文献
59.
Abstract Fossil whales in the very rare, primitive, extinct cetacean family Aetiocetidae are small, relict, toothed mysticetes that persisted into Late Oligocene time after more highly derived baleen-bearing mysticetes had already evolved. No known aetiocetid could be ancestral to baleen-bearing mysticetes, but aetiocetid morphology is in many ways intermediate between archaeocetes and baleen-bearing mysticetes, demonstrating the probable transitional steps passed through in the evolution of baleen-bearing mysticetes. Their discovery indicates that mysticetes evolved from Archaeocetes, and supports theories of the monophyly of Cetacea. Late Oligocene aetiocetids have been found on both sides of the North Pacific Ocean: on Vancouver Island, British Columbia, Canada; in Oregon and Washington, USA; in Baja California Sur, México; and the islands of Kyushu and Hokkaido, Japan. The most primitive North American aetiocetid, Chonecetus sookensis Russell, 1968, is from the early Late Oligocene Hesquiat Formation on Vancouver Island, British Columbia, Canada. A more derived, Late Oligocene species, Chonecetus goedertorum Barnes and Furusawa, new species, from the Late Oligocene Pysht Formation, Olympic Peninsula, Washington, has the primitive placental mammalian tooth count of 11/11. The type genus of the family, Aetiocetus Emlong, 1966, has as its type species, A. cotylalveus Emlong, 1966, known only from the Late Oligocene Yaquina Formation on the coast of Oregon. It has 11 upper teeth on each side of the rostrum. A more derived species, Aetiocetus weltoni Barnes and Kimura, new species, from a higher stratigraphic level in the Yaquina Formation, has a more posteriorly positioned cranial vertex and a tooth count of 11/12. We describe four new species of aetiocetids in three genera from the Late Oligocene Morawan Formation near Ashoro, Hokkaido, Japan. The most primitive, Ashorocetus eguchii Barnes and Kimura, new genus and species, has a primitive stage of cranial telescoping, and is closely related to Chonecetus Russell, 1968. Another, Morawanocetus yabukii Kimura and Barnes, new genus and species, in some ways intermediate between Chonecetus and Aetiocetus, has a suite of unique derived characters, including a much foreshortened brain case. The third, Aetiocetus tomitai Kimura and Barnes, new species, is the most primitive species of Aetiocetus yet discovered. The fourth, Aetiocetus polydentatus Sawamura, new species, the most derived species of Aetiocetus known, has a highly telescoped cranium, homodonty, polydonty and a dental count of 13–14/14–15. The fossil record now indicates considerable diversity in the family, with several different contemporaneous lineages in three new subfamilies: Chonecetinae, Morawanocetinae and Aetiocetinae. Aetiocetids are not known outside the North Pacific. Many Recent mysticetes are essentially cosmopolitan, and aetiocetids might have also been relatively widely dispersed. We suspect that with time their remains will be found around other ocean basins also. If so, then they may be potentially useful in trans-oceanic geological correlations. 相似文献
60.
Numerical study of the oxidation process of dimethylsulfide in the marine atmosphere 总被引:1,自引:0,他引:1
A box model, involving simple heterogeneous reaction processes associated with the production of non-sea-salt sulfate (nss-SO
4
2–
) particles, is used to investigate the oxidation processes of dimethylsulfide (DMS or CH3SCH3) in the marine atmosphere. The model is applied to chemical reactions in the atmospheric surface mixing layer, at intervals of 15 degrees latitude between 60° N and 60° S. Given that the addition reaction of the hydroxyl radical (OH) to the sulfur atom in the DMS molecule is faster at lower temperature than at higher temperature and that it is the predominant pathway for the production of methanesulfonic acid (MSA or CH3SO3H), the results can well explain both the increasing tendency of the molar ratio of MSA to nss-SO
4
2–
toward higher latitudes and the uniform distribution with latitude of sulfur dioxide (SO2). The predicted production rate of MSA increases with increasing latitude due to the elevated rate constant of the addition reaction at lower temperature. Since latitudinal distributions of OH concentration and DMS reaction rate with OH are opposite, a uniform production rate of SO2 is realized over the globe. The primary sink of DMS in unpolluted air is caused by the reaction with OH. Reaction of DMS with the nitrate radical (NO3) also reduces DMS concentration but it is less important compared with that of OH. Concentrations of SO2, MSA, and nss-SO
4
2–
are almost independent of NO
x
concentration and radiation field. If dimethylsulfoxide (DMSO or CH3S(O)CH3) is produced by the addition reaction and further converted to sulfuric acid (H2SO4) in an aqueous solution of cloud droplets, the oxidation process of DMSO might be important for the production of aerosol particles containing nss-SO
4
2–
at high latitudes. 相似文献