首页 | 官方网站   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   112906篇
  免费   1614篇
  国内免费   893篇
地球科学   115413篇
  2022年   559篇
  2021年   982篇
  2020年   1097篇
  2019年   1193篇
  2018年   4353篇
  2017年   4121篇
  2016年   3895篇
  2015年   1781篇
  2014年   2883篇
  2013年   5055篇
  2012年   3764篇
  2011年   6011篇
  2010年   5248篇
  2009年   6397篇
  2008年   5556篇
  2007年   5883篇
  2006年   3903篇
  2005年   3325篇
  2004年   3204篇
  2003年   3163篇
  2002年   2790篇
  2001年   2395篇
  2000年   2277篇
  1999年   1851篇
  1998年   1943篇
  1997年   1872篇
  1996年   1550篇
  1995年   1542篇
  1994年   1339篇
  1993年   1214篇
  1992年   1137篇
  1991年   1094篇
  1990年   1187篇
  1989年   1029篇
  1988年   934篇
  1987年   1104篇
  1986年   988篇
  1985年   1240篇
  1984年   1348篇
  1983年   1279篇
  1982年   1229篇
  1981年   1083篇
  1980年   1021篇
  1979年   937篇
  1978年   906篇
  1977年   861篇
  1976年   822篇
  1975年   787篇
  1974年   784篇
  1973年   772篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The first integrals of motion of the restricted planar circular problem of three bodies are constructed as the formal power series in r1/2, r being the distance of a moving particle from the primary. It is shown that the coefficients of these series are trigonometric polynomials of an angular variable. Some particular solutions have been found in a closed form. The proposed method for constructing the formal integrals can be generalized to a spatial problem of three bodies.  相似文献   
72.
The equation of motion of a rigid body in Kovaleveskaya case is reduced to a plane motion. By using the method of small parameters introduced by Poincaré, the existence of a periodic solution is established.  相似文献   
73.
ABSTRACT. Although considerable attention has been paid to the record of temperature change over the last few centuries, the range and rate of change of atmospheric circulation and hydrology remain elusive. Here, eight latitudinally well-distributed (pole-equator-pole), highly resolved (annual to decadal) climate proxy records are presented that demonstrate major changes in these variables over the last 2000 years. A comparison between atmospheric 14C and these changes in climate demonstrates a first-order relationship between a variable Sun and climate. The relationship is seen on a global scale.  相似文献   
74.
Progress in the introduction of coulometry for the analysis of total carbon dioxide (TCO2) in marine waters is described. An extractor—stripper removes CO2 that is measured coulometrically by the quantity of electricity (coulombs) used to electrogenerate OH? ions for the titration of the acid formed by the reaction of CO2 and ethanolamine. The equivalence point is detected photometrically with thymolphthalein as the indicator, and Faraday's Law relates coulombs to equivalents of titrant generated and CO2 determined so that there are no standard curves needed or titrants to standardize or store. Accuracy was determined by adding gelatin capsules containing 100–1500 μg C of pure CaCO3 into the stripper, and accuracies of better than ± 1 μg C were achieved. The best precision for natural seawater (± 1 standard error) of ± 0.5 μmol l?1 was found for 17 samples of Bermuda coastal waters having a mean TCO2 of 2007.2 μmol l?1 (0.05% CV). Sources of error and precautions are discussed. This method, which has been used successfully at sea, can be used to study a variety of marine phenomena involving TCO2.  相似文献   
75.
76.
77.
Evidence was found that uptake of lead from seawater in both model and natural systems by the leaves of the seagrass Zostera muelleri does occur for live, dead and scraped leaves at all the lead concentrations tested. Positive uptake of lead was measured using the three analytical techniques of radio-tracer, differential pulse anodic stripping voltammetry and atomic absorption spectrometry; similar uptake profiles were obtained for each technique. Profiles always showed an initial rapid uptake phase followed by a gradual transition to a plateau phase at which an approximate equilibrium between lead attached to seagrass and free ionic lead in seawater was reached. The presence of active lead uptake processes was indicated in experiments which attempted to remove lead from leaves by a chelating agent.  相似文献   
78.
The existence of prolonged periods of abnormally low solar activity (such as the Maunder minimum) is explained within the framework of Leighton's model of a solar cycle with a hypothetical internal magnetic field of the Sun taken into account.  相似文献   
79.
BV light curves of the eclipsing binary UV Leo obtained at the Kryonerion Astronomical Station of the National Observatory of Athens, Greece, are analyzed. The analysis is based on a Roche configuration with two spots on the secondary surface. The elements of the two components of the system are calculated and the spot characteristics are given.  相似文献   
80.
The spectra of active galaxies and their nuclei are rich in emission and absorption line features. A major aim of present research is the development of self-consistent hydrodynamic models for the production of the line-forming regions. We here review such modelling and stress the central role played by shock phenomena induced by winds and explosions on scales ranging from the circumstellar to the intergalactic.  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-23

京公网安备 11010802026262号