全文获取类型
收费全文 | 61919篇 |
免费 | 1496篇 |
国内免费 | 708篇 |
专业分类
测绘学 | 2025篇 |
大气科学 | 4881篇 |
地球物理 | 13074篇 |
地质学 | 22456篇 |
海洋学 | 4978篇 |
天文学 | 13088篇 |
综合类 | 374篇 |
自然地理 | 3247篇 |
出版年
2021年 | 531篇 |
2020年 | 552篇 |
2019年 | 600篇 |
2018年 | 1842篇 |
2017年 | 1726篇 |
2016年 | 1955篇 |
2015年 | 1137篇 |
2014年 | 1740篇 |
2013年 | 3135篇 |
2012年 | 2346篇 |
2011年 | 2661篇 |
2010年 | 2091篇 |
2009年 | 2678篇 |
2008年 | 2308篇 |
2007年 | 2277篇 |
2006年 | 2285篇 |
2005年 | 2445篇 |
2004年 | 2372篇 |
2003年 | 2142篇 |
2002年 | 1639篇 |
2001年 | 1427篇 |
2000年 | 1370篇 |
1999年 | 1137篇 |
1998年 | 1061篇 |
1997年 | 1147篇 |
1996年 | 961篇 |
1995年 | 938篇 |
1994年 | 893篇 |
1993年 | 754篇 |
1992年 | 726篇 |
1991年 | 737篇 |
1990年 | 745篇 |
1989年 | 696篇 |
1988年 | 662篇 |
1987年 | 751篇 |
1986年 | 635篇 |
1985年 | 820篇 |
1984年 | 847篇 |
1983年 | 854篇 |
1982年 | 808篇 |
1981年 | 678篇 |
1980年 | 723篇 |
1979年 | 609篇 |
1978年 | 574篇 |
1977年 | 551篇 |
1976年 | 499篇 |
1975年 | 492篇 |
1974年 | 524篇 |
1973年 | 522篇 |
1972年 | 336篇 |
排序方式: 共有10000条查询结果,搜索用时 158 毫秒
951.
We develop and apply visualization and quantification methods to reconstruct hydrothermal plumes in 3D from acoustic images and to make the first direct measurements from the reconstructions of scalar properties that describe the behavior of two buoyant plumes discharging from adjacent black smoker chimneys. The actual behavior is then compared to that predicted by a classic simple buoyant plume model. The images are reconstructed as isointensity surfaces of backscatter from particulate matter suspended in the plumes. The measurements pertinent to the role of the plumes as agents of dispersal of heat and mass into the ocean include change with height of diameter, particle distribution, dilution, centerline attitude, surface protrusions, and connectivity. The protrusions are the surface expression of eddies and appear to follow a bifurcating helical flow pattern that resemble simulation of the naturally forced flow of coherent vortex rings as the eddies rise with the buoyant plume. These direct measurements and the derived entrainment coefficient are generally consistent with behavior predicted by the simple buoyant plume model and support engulfment by vortex shedding as a primary mechanism for entrainment of surrounding seawater. Deviations from predicted buoyant plume behavior are diagnostic of particle dynamics. 相似文献
952.
Wang Tan K. McIntosh Kirk Nakamura Yosio Liu Char-Shine Chen How-Wei 《Marine Geophysical Researches》2001,22(4):265-287
A wide-angle seismic survey, combining ocean-bottom seismometers (OBS) and multi-channel seismic (MCS) profiling, was implemented
in the southwestern Ryukyu subduction zone during August and September 1995. In this paper, we present the data analysis of
eight OBSs and the corresponding MCS line along profile EW9509-1 from this experiment. Seismic data modeling includes identification
of refracted and reflected arrivals, initial model building from velocity analysis of the MCS data, and simultaneous and layer-stripping
inversions of the OBS and MCS arrivals. The velocity-interface structure constructed along profile EW9509-1 shows that the
northward subduction of the Philippine Sea Plate has resulted in a northward thickening of the sediments of the Ryukyu Trench
and the Yaeyama accretionary wedge north of the trench. The boundary between the subducting oceanic crust and the overriding
continental crust (represented by a velocity contour of 6.75 km/s) and a sudden increase of the subducting angle (from 5 degrees
to 25 degrees) are well imaged below the Nanao Basin. Furthermore, velocity undulation and interface variation are found within
the upper crust of the Ryukyu Arc. Therefore, the strongest compression due to subduction and a break-off of the slab may
have occurred and induced the high seismicity in the forearc region.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
953.
1 .IntroductionEvery year ,Taiwanis subjectedtotwo or three typhoonintrusions in average which always causedisasters . Most of the disasters which occur around the coastal zone are due to seabed instability andcoastal structure destruction caused bytyphoo… 相似文献
954.
955.
Understanding regime shifts is important to management. Optimal allocation of fishery effort can be improved if it were known whether or not the regime was positive or negative. This determination is difficult because a high recruitment, when the stock is at a low level of abundance (or vice versa), may be the indication of the onset of a multidecadal regime shift, or just a chance occurrence. Accordingly, the determination of an increase or decrease in productivity from observations independent of those made directly on fish populations is important. 相似文献
956.
钝顶螺旋藻C-藻蓝蛋白和多管藻R-藻红蛋白的分离纯化及摩尔消光系数的测定 总被引:2,自引:1,他引:2
1993年11月~1994年1月用简单的羟基磷灰石柱层析法从多管藻中分 离纯化了R-藻红蛋白和从钝顶螺旋藻中纯化了C-藻蓝蛋白,它们的纯度(指可见 光部分的最大吸收与 280nm处吸收值之比)可分别达到 6(R-藻红蛋白)和 5. 5(C- 藻蓝蛋白)。由于不同藻种的同种藻胆蛋白的摩尔消光系数不同,所以应用凯氏定 氮法并结合可见光的吸收值测定了上述两种藻胆蛋白的摩尔消光系数,钝顶螺旋 藻C-藻蓝蛋白为1.853 × 106mol-1cm-1(620nm),多管藻R-藻红蛋白为1.796 × 106mol-1cm-1(498nm),为藻胆蛋白的浓度测定提供了方便。 相似文献
957.
A. B. Polonsky 《Physical Oceanography》1995,6(1):51-59
The equation for the turbulence kinetic energy balance as applied to the horizontally-inhomogeneous upper ocean layer encompassing the equatorial zone is analysed. A partial solution of the equation has been derived for the equilibrium conditions. Using the equatorial Atlantic as an example, the prime importance of considering the effect of horizontal heterogeneity in calculating the upper mixed layer thickness is shown.Translated by Vladimir A. Puchkin. 相似文献
958.
Amvrakikos Gulf is a Neogene basin, formed during a late extensional tectonic phase within the Plio-Quaternary period. It is a semienclosed embayment, separated from the Ionian Sea by a shallow (< 10 m) channel. The analysis of 3.5-kHz seismic reflection profiles shows that, during the last (Würm) glacial period, the parts of the Gulf that lie at water depths >41 m (below present sea level) were a paleo-lake while the rest were exposed to subaerial erosion. Subsequent offshore depositional sequences accumulated at rates of 1.2–2.3 m/ka. 相似文献
959.
R.H.M. Eertman C.L.F.M.G. Groenink B. Sandee H. Hummel A.C. Smaal 《Marine environmental research》1995,39(1-4)
The polycyclic aromatic hydrocarbons fluoranthene and benzo(a)pyrene significantly reduced the feeding rate of mussels. For both compounds the tissue concentration resulting in a 50% reduction of the clearance rate (TEC50) was calculated. At high tissue concentrations both aromatic compounds reduced the tolerance of mussels to aerial exposure, whereas at low tissue concentrations an improved response was noticed. The activities of the antioxidant enzymes Superoxide dismutase (SOD) and catalase were elevated only at low tissue concentrations of fluoranthene and benzo(a)pyrene. At the highest measured tissue concentrations the activity of both enzymes was reduced, possibly due to a narcotic effect. The reproductive success rate of mussels appeared to be affected negatively by the investigated hydrocarbons. The results of a pilot experiment indicate that mussels can be used also for the testing of contaminated sediments. 相似文献
960.
Nuclear activity on land and dumping of waste in the Siberian shelf seas mean that the Kara Sea is most likely to experience inputs of radioactivity. Industrial and other anthropogenic activities in the expansive Ob' and Yenisey watersheds also contribute organochlorines, heavy metals and oil to this region. Contaminant fate is influenced by the distribution of the river discharge and processes associated with ice formation and ocean currents. Although average conditions are important in the transport of pollutants, events such as storms and iceberg gouging may be critical in deciding the ultimate fate of dumped and released contaminants. 相似文献