全文获取类型
收费全文 | 9864篇 |
免费 | 2042篇 |
国内免费 | 2971篇 |
专业分类
测绘学 | 1034篇 |
大气科学 | 2206篇 |
地球物理 | 2189篇 |
地质学 | 5051篇 |
海洋学 | 1607篇 |
天文学 | 358篇 |
综合类 | 989篇 |
自然地理 | 1443篇 |
出版年
2024年 | 70篇 |
2023年 | 179篇 |
2022年 | 509篇 |
2021年 | 602篇 |
2020年 | 488篇 |
2019年 | 592篇 |
2018年 | 565篇 |
2017年 | 534篇 |
2016年 | 616篇 |
2015年 | 579篇 |
2014年 | 675篇 |
2013年 | 773篇 |
2012年 | 790篇 |
2011年 | 790篇 |
2010年 | 769篇 |
2009年 | 706篇 |
2008年 | 731篇 |
2007年 | 655篇 |
2006年 | 564篇 |
2005年 | 468篇 |
2004年 | 376篇 |
2003年 | 324篇 |
2002年 | 347篇 |
2001年 | 336篇 |
2000年 | 251篇 |
1999年 | 291篇 |
1998年 | 208篇 |
1997年 | 197篇 |
1996年 | 173篇 |
1995年 | 157篇 |
1994年 | 112篇 |
1993年 | 106篇 |
1992年 | 81篇 |
1991年 | 51篇 |
1990年 | 40篇 |
1989年 | 45篇 |
1988年 | 28篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 6篇 |
1983年 | 10篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1958年 | 4篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
161.
结构动力反应分析的三阶显式方法 总被引:14,自引:6,他引:14
本通过对传统动力反应分析方法的总结,阐明了建立隐式和显式方法的一般思路及数学本质,提出了使用系统位移反向向量三阶导数的隐工和实用显式积分方法-3阶显式方法,分析了该显式方法的精度和稳定性,并对建立更高阶隐式和显式方法以及方法的精度和稳定性作了初步讨论。最后,通过算例对本方法、献[1]方法和经典的常平均加速度法(隐式方法、视为精确解)的精度和稳定性进行了比较分析。结果表明,本方法具有明显的优点。 相似文献
162.
163.
Wang Yan Diao Guiling Zhang Sichang Wang Qincai Liu Yunqing Zhu Zhenxing Zhang Yanqing 《中国地震研究》2002,16(4):363-368
Several earthquakes with Ms≥5.0 occurred in the Datong seismic region in 1989,1991 and 1999,The precise focus location of the earthquake sequence was made by the records of the remote sensing seismic station network in Datong.Using that data together with macro-intensity distribution and focal mechanism solutions,we analyze the difference among three subsequences.The results show that the focal fault of the 1999 Ms 5.6 earthquake was a NWW-trending left-lateral strike-slip fault.It is 16km long and 12km wide.It developed at the depth of 5km and is nearly vertical in dip.The two previous earthquake subsequences,however,were generated by activity along NNE-trending right-lateral strike-slip fault.It can be found that the rupture directioin of the 1999 earthquake has changed.It is generally found that a rupture zone has more than two directions and has different strength along these two directions.The complicate degree of focal circumstance is related to the type of earthquake sequences.There is the NE-trending Dawangcun fault and the NW-trending Tuanbu fault in the seismic region,but no proof indicates a connection between focal faults and these two tectonic faults.The feature that focal faults of three subsequences are strike-slip is different from that of the two tectonic faults.It is suggested that the 1999 earthquake subsequence was possibly generated by a new rupture. 相似文献
164.
多矿物岩石流变规律的研究进展及存在问题 总被引:4,自引:2,他引:4
总结了近年来由多种矿物组成的岩石的流变规律的研究,阐述了多矿物岩石流变性质研究的意义和进展,再从实验和理论两个方面,详细论述了目前最具代表性的三种理论模型,算术平均方法、几何平均方法和能量极小方法,最后,指出这方面研究仍然存在的问题和进一步研究的方向。 相似文献
165.
166.
167.
Soil sediment samples of 10 layers with a spacing of 10 cm each were collected in different floodplain zones adjacent to Huolin
River in the Xianghai Nature Reserve, and contents of total N, total P and organic matters were analyzed. The results showed
that contents of total N, total P and organic matters were generally decreasing with the increase of distance from sample
locations to the river channel, and contents of the three items were generally higher in the upper soil layer than that in
the lower soil layer. The content variations displayed how flooding functions influenced nutrient matter content variations
in floodplain soils since the flood inundation frequencies of the sample locations varied. The correlation analysis displayed
that there were remarkable relativities between total N, total P and organic matters within definite spatial distance from
the Huolin River channel. 相似文献
168.
Yao Chun-xial Li Bao-sheng Jin He-ling David Dian Zhang Yan Man-cun Zhu Yi-zhi Li Hou-xin Zhang Yu-hong Luo Kai-li 《地理学报(英文版)》2002,12(1):65-71
The paper makes some analyses on 11 trace elements in the Milanggouwan stratigraphical section in the Salawusu River valley,
which is regarded as a prototype geology-palaeoclimate record since 150 ka BP. The results show that the content and variation
of trace elements has experienced remarkably regular changes in the pace with coarse and fine sedimentary cycles of palaeo-aeolian
sands to its overlying fluvio-lacustrine facies or/and palaeosols. The trace elements with chemical properties of relatively
active (V, Sr, Cu, Ni, As) and relatively stable (P, Pb, Rb, Mn, Nb, Zr) are a manifestation of the corresponding 27 changeable
cycles between peak and valley values, appearing a multi-fiuctuational process line of relative gathering and migration since
then. The low numerical value distribution of these two types of trace elements in the aeolian sand facies represents erosion
and accumulation under wind force during the cold-dry climate. Whereas their enrichments in both fluvio-lacustrine facies
and palaeosols are related to the valley’s special low-lying physiognomic position between the Ordos Plateau and the Loess
Plateau under the warm and humid climate conditions. The above relatively migrated and gathered change of the trace elements
is the result of 27 climatic cycles of cold-dry and warm-humid, which is probably caused by repeated alternations of winter
monsoon and summer monsoon in the Mu Us Sandy Land influenced by the climate vicissitudes in northern hemisphere during glacial
and interglacial periods since 150 ka BP. 相似文献
169.
Based on energy balance equation and mass transfer equation, a general model to estimate actual evaporation from non-saturated
surfaces was derived. Making use of two concepts, “relative evaporation” and “relative drying power”, a relationship was established
to account for the departure from saturated conditions. Using this model, the actual evaporation (evapotranspiration) can
be calculated without the need of potential evaporation estimation. Furthermore, the model requires only a few meteorological
parameters that are readily and routinely obtainable at standard weather stations. Based on nearly 30 years data of 432 meteorological
stations and 512 hydrological stations in China, in combined with GIS, nine typical river basins were selected. Using the
data of the selected river basins, the model was tested. The results show that the actual evaporation rate can be estimated
with an error of less than 10% in most areas of China, except few years in the Yellow River Basin. 相似文献
170.
Through the study of mutual process between groundwater systems and eco-environmental water demand, the eco-environmental
water demand is brought into groundwater systems model as the important water consumption item and unification of groundwater’s
economic, environmental and ecological functions were taken into account. Based on eco-environmental water demand at Da’an
in Jilin province, a three-dimensional simulation and optimized management model of groundwater systems was established. All
water balance components of groundwater systems in 1998 and 1999 were simulated with this model and the best optimal exploitation
scheme of groundwater systems in 2000 was determined, so that groundwater resource was efficiently utilized and good economic,
ecologic and social benefits were obtained. 相似文献