首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   36413篇
  免费   6460篇
  国内免费   7974篇
测绘学   3320篇
大气科学   5826篇
地球物理   6550篇
地质学   19374篇
海洋学   4135篇
天文学   3421篇
综合类   2392篇
自然地理   5829篇
  2024年   134篇
  2023年   502篇
  2022年   1264篇
  2021年   1441篇
  2020年   1362篇
  2019年   1581篇
  2018年   1195篇
  2017年   1438篇
  2016年   1433篇
  2015年   1631篇
  2014年   2112篇
  2013年   2126篇
  2012年   2259篇
  2011年   2336篇
  2010年   2002篇
  2009年   2533篇
  2008年   2456篇
  2007年   2575篇
  2006年   2465篇
  2005年   2349篇
  2004年   2071篇
  2003年   1941篇
  2002年   1683篇
  2001年   1494篇
  2000年   1504篇
  1999年   1320篇
  1998年   1152篇
  1997年   822篇
  1996年   683篇
  1995年   586篇
  1994年   552篇
  1993年   479篇
  1992年   333篇
  1991年   293篇
  1990年   195篇
  1989年   151篇
  1988年   124篇
  1987年   75篇
  1986年   41篇
  1985年   33篇
  1984年   17篇
  1983年   12篇
  1982年   12篇
  1981年   10篇
  1980年   8篇
  1979年   6篇
  1978年   15篇
  1977年   5篇
  1976年   4篇
  1954年   7篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
151.
V838 Mon is the prototype of a new class of objects. Understanding the nature of its multistage outburst and similar systems is challenging. So far, several scenarios have been invoked to explain this group of stars. In this work, the planets-swallowing model for V838 Mon is further investigated, taking into account the findings that the progenitor is most likely a massive B-type star. We find that the super-Eddington luminosity during the eruption can explain the fast rising times of the three peaks in the optical light curve. We used two different methods to estimate the location where the planets were consumed. There is a nice agreement between the values obtained from the luminosities of the peaks and from their rising time-scale. We estimate that the planets were stopped at a typical distance of one solar radius from the centre of the host giant star. The planets-devouring model seems to give a satisfying explanation to the differences in the luminosities and rising times of the three peaks in the optical light curve of V838 Mon. The peaks may be explained by the consumption of three planets or alternatively by three steps in the terminal falling process of a single planet. We argue that only the binary merger and the planets-swallowing models are consistent with the observations of the new type of stars defined by V838 Mon.  相似文献   
152.
153.
154.
Wang Yanhui 《水文研究》1992,6(2):241-251
Black locust (Robina pseudoacacia) has become one of the most important shelter species in the loess area of northwest China. This paper summarizes recent research concerning its hydrological influence, including canopy interception, litter absorption capacity, its effect on rainfall kinetic energy, infiltration rates, surface runoff, soil moisture, and evapotranspiration, and its role in soil conservation. Several predictive models are listed. on the basis of existing results, optimum characteristics for an effective plantation are defined, and problems requiring further research are identified.  相似文献   
155.
156.
Galileo系统及其在中国的应用   总被引:9,自引:0,他引:9  
较详细地介绍了Galileo系统的全面体系结构、频率设计、服务内容及其广泛的应用范围,指出了它与GPS系统相比的优点,并对开发和增强Galileo系统在我国多层次、全方位的应用提出了建议。  相似文献   
157.
158.
The main reasons for the high content of inorganic N and its increase by several times in the Changjiang River and its mouth during the last 40 years were analysed in this work. The inorganic N in precipitation in the Changjiang River catchment mainly comes from gaseous loss of fertilizer N, N resulting from the increases of population and livestock, and from high temperature combustions of fossil fuels. N from precipitation is the first N source in the Changjiang River water and the only direct cause of high content of inorganic N in the Changjiang River and its mouth. The lost N in gaseous form and from agriculture non-point sources fertilizer comprised about 60% of annual consumption of fertilizer N in the Changjiang River catchment and were key factors controlling the high content of inorganic N in the Changjiang River mouth. The fate of the N in precipitation and other N sources in the Changjiang River catchment are also discussed in this paper.  相似文献   
159.
160.
Analysis of the RXTE slew data in October 1996 revealed a weak X-ray burst from the millisecond pulsar SAX J 1808.4-3658. The 3–20-keV energy spectrum of the source can be described by a power law with an index of 2.0 and a(3-to 20 keV) luminosity of ~1.4×1035 erg s?1 (the distance to the source was taken to be 2.5 kpc). Because of the short exposure time, we failed to detect weak pulsations at a frequency of 401 Hz in the source. The (2σ) upper limit of the pulse fraction is ~13%.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号