全文获取类型
收费全文 | 2413篇 |
免费 | 304篇 |
国内免费 | 403篇 |
专业分类
测绘学 | 206篇 |
大气科学 | 404篇 |
地球物理 | 539篇 |
地质学 | 957篇 |
海洋学 | 279篇 |
天文学 | 212篇 |
综合类 | 131篇 |
自然地理 | 392篇 |
出版年
2024年 | 10篇 |
2023年 | 34篇 |
2022年 | 93篇 |
2021年 | 138篇 |
2020年 | 103篇 |
2019年 | 124篇 |
2018年 | 141篇 |
2017年 | 126篇 |
2016年 | 164篇 |
2015年 | 171篇 |
2014年 | 165篇 |
2013年 | 176篇 |
2012年 | 173篇 |
2011年 | 182篇 |
2010年 | 156篇 |
2009年 | 146篇 |
2008年 | 154篇 |
2007年 | 131篇 |
2006年 | 103篇 |
2005年 | 92篇 |
2004年 | 54篇 |
2003年 | 55篇 |
2002年 | 48篇 |
2001年 | 50篇 |
2000年 | 38篇 |
1999年 | 29篇 |
1998年 | 18篇 |
1997年 | 30篇 |
1996年 | 35篇 |
1995年 | 16篇 |
1994年 | 12篇 |
1993年 | 18篇 |
1992年 | 12篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 11篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1980年 | 4篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1969年 | 3篇 |
排序方式: 共有3120条查询结果,搜索用时 187 毫秒
181.
Igor A. Dmitrenko Dorothea Bauch Sergey A. Kirillov Nikolay Koldunov Peter J. Minnett Vladimir V. Ivanov Jens A. Hölemann Leonid A. Timokhov 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(4):513-527
Inflow of Atlantic water (AW) from Fram Strait and the Barents Sea into the Arctic Ocean conditions the intermediate (100–1000 m) waters of the Arctic Ocean Eurasian margins. While over the Siberian margin the Fram Strait AW branch (FSBW) has exhibited continuous dramatic warming beginning in 2004, the tendency of the Barents Sea AW branch (BSBW) has remained poorly known. Here we document the contrary cooling tendency of the BSBW through the analysis of observational data collected from the icebreaker Kapitan Dranitsyn over the continental slope of the Eurasian Basin in 2005 and 2006. The CTD data from the R.V. Polarstern cruise in 1995 were used as a reference point for evaluating external atmospheric and sea-ice forcing and oxygen isotope analysis. Our data show that in 2006 the BSBW core was saltier (by ~0.037), cooler (by ~0.41 °C), denser (by ~0.04 kg/m3), deeper (by 150–200 m), and relatively better ventilated (by 7–8 μmol/kg of dissolved oxygen, or by 1.1–1.7% of saturation) compared with 2005. We hypothesize that the shift of the meridional wind from off-shore to on-shore direction during the BSBW translation through the Barents and northern Kara seas results in longer surface residence time for the BSBW sampled in 2006 compared with samples from 2005. The cooler, more saline, and better-ventilated BSBW sampled in 2006 may result from longer upstream translation through the Barents and northern Kara seas where the BSBW was modified by sea-ice formation and interaction with atmosphere. The data for stable oxygen isotopes from 1995 and 2006 reveals amplified brine modification of the BSBW core sampled downstream in 2006, which supports the assumption of an increased upstream residence time as indicated by wind patterns and dissolved oxygen values. 相似文献
182.
Martin Menzies Dan Bosence Hamed A. El-Nakha Salah Al-Khirbash Mohamed A. Al-Kadasi Abdulkarim Al Subbary 《地学学报》1990,2(4):340-350
This paper analyses new field and radiometric age data on the timing of extension, sedimentation and magmatism related to the opening of the Red Sea. The first evidence of widespread extension is found in synsedimentary fissures in the fluviatile to shallow marine Tawilah Formation of Cretaceous to early Tertiary age. The first indication of magmatism is the eruption of alkaline basalts (43.5–21.2 Ma) on to marine and non-marine sandstones of lower to middle Tertiary age. The lack of an angular unconformity at the sediment-basalt contact, over a period of 25 Myr, corroborates a diachronous relationship between the Tawilah sandstones and the Yemen Volcanics. These data also indicate that the onset of volcanism in Yemen was in the Eocene, as is the case in Ethiopia and Saudi Arabia. A passive rifting model is supported by early extension and sedimentation followed by syn- and post-tectonic magmatism. 相似文献
183.
Hypothesis of possible superconductivity of the iced matter of the rings of Saturn (based on the data of Voyager and Pioneer
space missions) allow us to explain many phenomena which have not been adequately understood earlier. Introducing into planetary
physics force of magnetic levitation of the superconducting iced particle of the rings, which interact with magnetosphere
of the planet, becomes to be possible to explain origin, evolution, and dynamics of the rings; to show how the consequent
precipitation of the rings’ matter upon the planet was concluded; how the rings began their rotation; how they were compressed
by the magnetic field into the thin disc, and how this disc was fractured into hundreds of thousands of separated rings; why
in the ring B do exist “spokes”; why magnetic field lines have distortion near by ring F; why there is a variable azimuth brightness of the ring A; why the rings reflected radio waves so efficiently; why exists strong electromagnetic radiation of the rings in the 20.4
kHz–40.2 MHz range and Saturnian kilometric radiation; why there is anomalous reflection of circularly polarized microwaves;
why there are spectral anomalies of the thermal radiation of the rings; why the matter of the various rings does not mix but
preserves its small-scale color differences; why there is an atmosphere of unknown origin nearby the rings of Saturn; why
there are waves of density and bending waves within Saturn’s rings; why planetary rings in the solar system appear only after
the Belt of Asteroids (and may be the Belt of Asteroids itself is a ring for the Sun); why our planet Earth has no rings of
its own. 相似文献
184.
The Earth's crust faults and lineaments group in clusters with predominant N-S and E-W (System I) and NW-SE and NE-SW (System II) directions. The earthquake epicenters of the Benioff seismofocal zones follow the same regularities. In other words, seismofocal zones (epicenters of earthquakes) constitute a part of the regular network of the Earth's crust and lithosphere faults and lineaments. Mathematical modeling of stress distribution in the lithosphere due to a change of the Earth's ellipsoid compression showed that the principal stresses σ1 and σ2 are oriented in N-S and E-W directions, while corresponding shear stresses τ are oriented in NE-SW and NW-SE directions. It is shown that the secular deceleration of the Earth's rotation can be a reasonable mechanism for the change of Earth's ellipsoid compression and, consequently, for the origin of the regular system of faults and lineaments described above. 相似文献
185.
温度和盐度对埋栖性双壳类泥蚶(Tegillarca granosa) 呼吸、排泄的影响 总被引:1,自引:0,他引:1
在人工条件下采用静水封闭呼吸瓶的方法研究了温度、盐度对泥蚶(Tegillarca granosa)呼 吸、排泄的影响, 并综合分析了温度、盐度交互作用对呼吸、排泄的影响程度, 为泥蚶基础生物学研 究积累了资料。结果表明, 在设定的不同温度条件下泥蚶耗氧率变化范围0.63-4.47mg/(g·h), 单因 素方差分析结果显示4 个盐度条件下泥蚶耗氧率的差异均极显著(P<0.01); 排氨率的变化范围 123.11-955.68μg/(g·h), 排氨率受温度的影响也均极显著(P<0.01); 经回归发现, 在温度13-31℃ 范 围内, 耗氧率和排氨率均与温度的变化呈显著的指数相关。除温度为18℃ 时, 其它各温度条件下, 不同盐度梯度间的耗氧率差异不显著(P>0.05), 盐度对排氨率影响的变化趋势不一致。在温度 (13-31℃)和盐度(18-28)时, 温度和盐度对耗氧率、排氨率的影响均存在交互作用, 耗氧率(Y)、排 氨率(Y)与温度(T)和盐度(S)之间的二元线性回归关系为Y=a+bT+cS+dT×S.泥蚶呼吸排泄的O:N 比 在4.50-13.07 之间, 平均值为7.16.泥蚶呼吸排泄的代谢活动受温度、盐度的影响显著。 相似文献
186.
A quantitative study on the community structure and biodiversity of free-living marine nematodes and their relationship with environmental factors in the northern South China Sea were carried out based... 相似文献
187.
基于Delft3D-Flow模块建立了象山港海域的三维斜压潮流数值模型,结合实测水文资料,研究了象山港的潮(余)流特征,对欧拉余流场的时空分布进行了定量的比较和分析,并与潮流测站计算分析得到的欧拉余流分布对比,很好的模拟了象山港的余流特征。结果表明:由湾外至湾顶,余流呈减小的趋势,湾外余流最大为33 cm/s,湾顶最小,余流平均仅5 cm/s。垂向上,表层余流大于底层余流,表层余流指向湾外,而底层余流则指向湾内。对比斜压、正压两种模式下的欧拉余流分布,可以看出湾顶附近主要受径流控制,两种模式得到的结果基本一致,口门至西沪港区域受径流和潮流的共同影响,斜压模式更准确地模拟出了水体层化和垂向余环流结构。 相似文献
188.
JIAO Haifeng ZHENG Dan YOU Zhongjie XU Nianjun LOU Dan HUANG Chengwei 《中国海洋大学学报(英文版)》2015,(2):375-384
Xiangshan bay is a narrow semi-closed bay and situated on the northwestern coast of the East China Sea. Over past decades, it has become to a major bay with intensive human activities, dense urbanized area, and poor water quality. The aim of this paper was to reveal the ecological status through the elucidation of the species composition, abundance, biomass and diversity of macrobenthos in this bay. Six intertidal sections were surveyed from January 2007 to November 2008 quarterly. Sections TG, HD and XH are located in the three inner bays, sections QJ and WS are located near the thermal power plants, and section XX is located at the outer part of Xiangshan Bay. Great variations in macrobenthos community were indentified, and the species composition of the community in the present study showed the dominance in the order of molluscs(bivalves and gastropods), crustaceans and others, and only few Polychaeta were recorded. Only three dominant species, Littorina brevicula, Ilyplax tansuiensis, and Cerithidea cingulata were collected in all the sections, and a total of 19 dominant species were recorded only in one section. Two-way ANOVA analyses of abundance indicated that there were significant differences among sections or seasons. Shannon-Wiener diversity index(H’) had its maximum(2.45) in section QJ, and minimum(1.76) in section TG. Multiple irregular k-dominance plots clearly showed that the study area was polluted and the macrobenthos community was under stress. We conclude that the macrobenthos of Xiangshan Bay have been disturbed by human activities, especially at the interior bay. 相似文献
189.
190.
黑龙江省耕地非农化的空间格局与重心曲线分析 总被引:1,自引:0,他引:1
为了揭示耕地非农化的空间格局与重心曲线,为耕地资源保护和利用政策制定提供决策支撑,该文以黑龙江省1980、1990、2000、2010、2015年土地利用数据为基础,运用GIS空间分析方法,引入重心模型分析黑龙江省耕地非农化的空间格局及重心曲线。研究结果表明:1980—2015年黑龙江省耕地非农化发展不平衡,4个时期耕地非农化面积呈波动增长的趋势;耕地非农化等级空间分布特征明显,等级较高的城市集中分布在西部地区;耕地非农化速度等级的重心曲线在空间分布上,具有从中心向边缘延伸的特点;耕地非农化围绕中心地区进行,其空间扩散路径在图形上呈现出一个回旋状。 相似文献