全文获取类型
收费全文 | 1440篇 |
免费 | 24篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 92篇 |
地球物理 | 300篇 |
地质学 | 524篇 |
海洋学 | 114篇 |
天文学 | 282篇 |
综合类 | 4篇 |
自然地理 | 147篇 |
出版年
2020年 | 12篇 |
2018年 | 14篇 |
2017年 | 20篇 |
2016年 | 19篇 |
2015年 | 16篇 |
2014年 | 27篇 |
2013年 | 51篇 |
2012年 | 27篇 |
2011年 | 33篇 |
2010年 | 55篇 |
2009年 | 47篇 |
2008年 | 45篇 |
2007年 | 47篇 |
2006年 | 57篇 |
2005年 | 39篇 |
2004年 | 42篇 |
2003年 | 56篇 |
2002年 | 45篇 |
2001年 | 19篇 |
2000年 | 25篇 |
1999年 | 26篇 |
1998年 | 19篇 |
1997年 | 22篇 |
1996年 | 31篇 |
1995年 | 19篇 |
1994年 | 28篇 |
1993年 | 24篇 |
1992年 | 22篇 |
1991年 | 17篇 |
1990年 | 25篇 |
1989年 | 23篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 26篇 |
1985年 | 36篇 |
1984年 | 44篇 |
1983年 | 34篇 |
1982年 | 33篇 |
1981年 | 31篇 |
1980年 | 32篇 |
1979年 | 31篇 |
1978年 | 27篇 |
1977年 | 21篇 |
1976年 | 19篇 |
1975年 | 21篇 |
1974年 | 20篇 |
1973年 | 25篇 |
1972年 | 11篇 |
1971年 | 15篇 |
1970年 | 13篇 |
排序方式: 共有1475条查询结果,搜索用时 15 毫秒
941.
942.
A complete Mars year of measurements of atmospheric water vapor in the south arctic have been obtained from the Viking Orbiters. Analysis of the observations indicates that, except for the south remnant cap, the southern hemisphere of Mars is devoid of any substantial reservoirs of water in contact with the atmosphere, and that, in the summer time, the top layer of soil is desiccated. Small amounts of water ice are incorporated into the annual CO2 cap; this water is released at the cap margin when it retreats in the spring. The first global dust storm resulted in heating of the south arctic atmosphere and a transport of water in from the equatorial region. The second global dust storm had a negligible effect on atmospheric water vapor; the dust contained little water. 相似文献
943.
Is seagrass an important nursery habitat for the Caribbean spiny lobster,panulirus argus,in Florida?
Donald C. Behringer Mark J. Butler IV William F. Herrnkind John H. Hunt Charles A. Acosta William C. Sharp 《新西兰海洋与淡水研究杂志》2013,47(1):327-337
Caribbean spiny lobster (Panulirus argus) settle preferentially in macroalgal‐covered hard‐bottom habitat, but seagrass is more prevalent in Florida (United States) and the Caribbean, so even low settlement of lobsters within seagrass could contribute substantially to recruitment if post‐settlement survival and growth were high. We tested the role of seagrass and hard‐bottom habitats for P. argus recruitment in three ways. We first explored possible density‐dependent regulation of early benthic juvenile lobster survival within cages deployed in seagrass and hard‐bottom habitats. Second, we compared settlement and survival of P. argus in both habitats, by comparing the recovery of microwire‐tagged early benthic juveniles from patches of seagrass and hard‐bottom. Finally, we assessed the relative abundance of juvenile lobsters in each habitat by deploying artificial structures in seagrass sites and compared these data with data from similar deployments of artificial structures in hard‐bottom habitat in other years. More early benthic juvenile lobsters were recovered from cages placed in hard‐bottom than in seagrass, but mortality of the early benthic life stage was high in both habitats. In regional surveys, the mean number of lobsters recovered from artificial shelters deployed within seagrass was lower than in any year that we sampled hard‐bottom, indicating that fewer lobsters reside naturally in seagrass, particularly large juveniles >40 mm carapace length. The greater abundance (and likely survival) of juvenile P. argus that we observed in hard‐bottom habitat as opposed to seagrass, combined with previous studies demonstrating that postlarval P. argus are attracted to, settle in, and metamorphose more quickly in red macroalgae, confirm that macroalgae‐dominated hard‐bottom habitat appears to be the preferred and more optimal nursery for Caribbean spiny lobster. 相似文献
944.
Wavelengths of clean atmospheric water lines, and some solar lines, in the wavelength interval 10750 Å to 10900 Å have been measured to an accuracy approaching ± 1 mÅ. Strengths and wavelengths have been measured for all atmospheric water lines with absorption coefficients > 5 × 10–4 cm–1 gm–1 cm–2 at 280K, that lie within 15 Å of the He I 10830 Å featur of the stronger He component is affected by a weak water line which reduces atmospheric transmission by nearly 1 % with 10 mm precipitable water in the line of sight.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
945.
946.
Hongwu Xu Yusheng Zhao Donald D. Hickmott Nina J. Lane Sven C. Vogel Jianzhong Zhang Luke L. Daemen 《Physics and Chemistry of Minerals》2013,40(10):799-810
To study the structural behavior of brucite at high temperature, we conducted in situ neutron diffraction experiments of a deuterated brucite powder sample, Mg(OD)2, in the temperature range 313–583 K. The sample was stable up to 553 K, above which it started to decompose into periclase (MgO) and D2O vapor. Rietveld analyses of the obtained data were performed using both single-site and three-site split-atom hydrogen models. Our results show that with increasing temperature, unit-cell parameter c increases at a rate ~7.7 times more rapidly than a. This large anisotropy of thermal expansion is primarily due to rapid increase in the interlayer thickness along the c-axis on heating. The amplitudes of thermal vibration for Mg, O, and D increase linearly with increasing temperature; however, the rate of the increase for the lighter D is much larger. In addition, D vibrates anisotropically with a higher magnitude within the (001) plane, as confirmed by our first-principles phonon calculations. On heating, the interatomic distances between a given D and its associated O and D from the adjacent [MgO6] layer increase, whereas the O–D bond length decreases. This behavior suggests weakened D···O and D···D interlayer interactions but strengthened O–D bonding with increasing temperature. 相似文献
947.
E. Natasha Stavros John T. Abatzoglou Donald McKenzie Narasimhan K. Larkin 《Climatic change》2014,126(3-4):455-468
Seasonal changes in the climatic potential for very large wildfires (VLWF?≥?50,000 ac?~?20,234 ha) across the western contiguous United States are projected over the 21st century using generalized linear models and downscaled climate projections for two representative concentration pathways (RCPs). Significant (p?≤?0.05) increases in VLWF probability for climate of the mid-21st century (2031–2060) relative to contemporary climate are found, for both RCP 4.5 and 8.5. The largest differences are in the Eastern Great Basin, Northern Rockies, Pacific Northwest, Rocky Mountains, and Southwest. Changes in seasonality and frequency of VLWFs d7epend on changes in the future climate space. For example, flammability-limited areas such as the Pacific Northwest show that (with high model agreement) the frequency of weeks with VLWFs in a given year is 2–2.7 more likely. However, frequency of weeks with at least one VLWF in fuel-limited systems like the Western Great Basin is 1.3 times more likely (with low model agreement). Thus, areas where fire is directly associated with hot and dry climate, as opposed to experiencing lagged effects from previous years, experience more change in the likelihood of VLWF in future projections. The results provide a quantitative foundation for management to mitigate the effects of VLWFs. 相似文献
948.
Ya-Ting Lee Donald L. Turcotte John B. Rundle Chien-Chih Chen 《Pure and Applied Geophysics》2013,170(1-2):221-228
In this paper we consider the statistics of the aftershock sequence of the m = 7.65 20 September 1999 Chi–Chi, Taiwan earthquake. We first consider the frequency-magnitude statistics. We find good agreement with Gutenberg–Richter scaling but find that the aftershock level is anomalously high. This level is quantified using the difference in magnitude between the main shock and the largest inferred aftershock $ {{\Updelta}}m^{ *}. $ Typically, $ {{\Updelta}}m^{ *} $ is in the range 0.8–1.5, but for the Chi–Chi earthquake the value is $ {{\Updelta}}m^{ *} $ = 0.03. We suggest that this may be due to an aseismic slow-earthquake component of rupture. We next consider the decay rate of aftershock activity following the earthquake. The rates are well approximated by the modified Omori’s law. We show that the distribution of interoccurrence times between aftershocks follow a nonhomogeneous Poisson process. We introduce the concept of Omori times to study the merging of the aftershock activity with the background seismicity. The Omori time is defined to be the mean interoccurrence time over a fixed number of aftershocks. 相似文献
949.
Michael R. Helfert Kamlesh P. Lulla Victor S. Whitehead M. Justin Wilkinson Donald E. Williams Michael J.. McCulley 《国际地球制图》2013,28(3):65-79
Abstract Although high‐resolution microwave synthetic aperture radar (SAR) sensors possess all‐weather capability for mapping soil moisture from spaceborne platforms, continuous temporal and spatial monitoring of this important hydrological parameter has been relatively limited. However, the recent launch of operational SAR sensors aboard various satellites have made possible synoptic soil moisture monitoring a reality. Such systems operate over a wide range of frequencies, look angles, and polarization combinations, and thus show synergistic advantages when combined for estimating soil moisture patterns. Two soil moisture inversion algorithms have been developed using as inputs radar backscattering data at L, S, and C bands in the microwave frequency range. These models have been tested using radar image simulation with speckle added. It is observed that the neural network algorithm yields superior results in mapping actual soil moisture patterns over the linear statistical inversion technique, although both models show comparable errors in soil moisture estimation. We infer that using statistical estimation errors alone for comparison purposes may lead to erroneous conclusions regarding the advantages of one soil moisture inversion algorithm over another. 相似文献
950.
Given the level of contemporary technological accomplishment in computing, it is now possible to undertake image‐processing tasks on a variety of “smaller” systems. While a typical hardware configuration includes 24 bits of refresh memory for color. 8 bits each for red, green, and blue, it is feasible to construct color‐composite images comprised of three spectral bands of remotely sensed data using workstations configured with only a single eight‐bit graphics plane for color. Such systems are commonly available in colleges and universities, since they are less expensive than fully configured color workstations. 相似文献