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   79874篇
  免费   726篇
  国内免费   598篇
测绘学   1909篇
大气科学   5010篇
地球物理   15188篇
地质学   28945篇
海洋学   7310篇
天文学   19139篇
综合类   296篇
自然地理   3401篇
  2022年   672篇
  2021年   1089篇
  2020年   1184篇
  2019年   1284篇
  2018年   2640篇
  2017年   2477篇
  2016年   2901篇
  2015年   1415篇
  2014年   2680篇
  2013年   4184篇
  2012年   2927篇
  2011年   3635篇
  2010年   3299篇
  2009年   4039篇
  2008年   3527篇
  2007年   3693篇
  2006年   3372篇
  2005年   2252篇
  2004年   2222篇
  2003年   2122篇
  2002年   2015篇
  2001年   1854篇
  2000年   1695篇
  1999年   1298篇
  1998年   1342篇
  1997年   1288篇
  1996年   1066篇
  1995年   1068篇
  1994年   937篇
  1993年   813篇
  1992年   808篇
  1991年   815篇
  1990年   877篇
  1989年   689篇
  1988年   713篇
  1987年   733篇
  1986年   641篇
  1985年   844篇
  1984年   910篇
  1983年   807篇
  1982年   774篇
  1981年   684篇
  1980年   685篇
  1979年   633篇
  1978年   649篇
  1977年   531篇
  1976年   495篇
  1975年   504篇
  1974年   450篇
  1973年   507篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Expressions for the variation of shock strength and its propagation in non-ideal fluids are presented by using the method developed by Whitham. The effects of the presence of rotation, rotation and magnetic field on the strength and propagation velocity of shock waves have been discussed separately. Finally, the effects of the presence of gravitation on the shock strength and on propagation velocity have been studied.  相似文献   
152.
Geomagnetism and Aeronomy - A global dynamic model of the F2 layer of the ionosphere GDMF2 is designed to calculate foF2 in both quiet and geomagnetically disturbed conditions. The term...  相似文献   
153.
The existing data on findings of unaltered volcanic glasses in the Paleozoic (from Late Ordovician to Late Devonian inclusive) volcanic strata of the Ural fold belt are systematized. These glasses have compositions that correspond to tholeiitic basalts, potassic alkaline basaltoids, andesites, and rhyolites. Relic portions of glasses of cenotypal appearance are preserved in thick glassy crusts of pillow lava flows, in fragments among hyaloclastites, in bombs from tuffs, and in extrusive bodies and dykes. Chemical analysis showed that the amount of dissolved water was low (1–1.3 wt %) in the primary tholeiitic magma and higher (8–10 wt %) in the magma that formed island-arc hyalobasalts, potassic alkaline basaltoids, andesites and rhyolites.  相似文献   
154.
Izvestiya, Atmospheric and Oceanic Physics - The natural variability of regional climatic conditions poses certain difficulties in detecting global climate change at a local scale. The question...  相似文献   
155.
In the context of the general linear theory, we consider the propagation of an internal tide across a frontal zone overyling an oceanic ridge. For a uniformly stratified ocean, the solution was derived using Riemann's technique. The dependences of the generated internal wave amplitudes on the stratification parameters and bottom topography were determined. We have found that wave disturbances of high intensity inside and in the neighbourhood of the ridge may be concentrated in raytype areas. An increase of the horizontal density gradient in the frontal zone results in a perceptible deformation of these areas.Translated by Vladimir A. Puchkin.  相似文献   
156.
Preliminary results of a space experiment using the IKFS-2 infrared sounder (Meteor-M2 satellite) showed high-quality of measurements of spectra of the outgoing thermal radiation of the atmosphere–surface system and the adequacy of developed IR radiation atmospheric models in the 15-μm carbon gas absorption band used to recover the vertical profiles of the atmospheric temperature. Outgoing radiation spectra measured by IKFS-2 instruments make it possible to restore vertical temperature profiles with errors close to 1K in most of the 0–30 km high-altitude region, except for the lower troposphere and altitudes above 30 km, where these errors are close to 2–3K.  相似文献   
157.
The in vitro aryl hydrocarbon receptor (AhR) agonist potency of offshore produced water effluents, collected from the United Kingdom Continental Shelf, was determined using the dioxin responsive (DR)-chemically activated luciferase expression (CALUX) assay. Octadecylsilane (C18) solid phase extraction (SPE) extracts of produced water were exposed to DR-CALUX cells for 24 h in order to investigate the contribution in potency from compounds that are stable to metabolism by the CALUX cells during exposure. The stable AhR agonist potency determined over 24 h was highly variable and ranged from 1 to 430 ng TCDD TEQCALUX l−1. These data reflect the highly variable composition of produced water discharges from different production fields. It is recommended that further work be performed to characterise the full range of stable dioxin like AhR agonists present in offshore produced water discharges using techniques such as bioassay-directed analysis.  相似文献   
158.
159.
160.
Concentration of7Be has been measured in 15 air filters flown at 18·3 km in the latitudes 10 to 25°N and longitudes 80 to 96°W. Testing of nuclear weapons in atmosphere increased7Be considerably, on two occasions, above the expected cosmic-ray production level in the stratosphere. This provides evidence for the existence of interhemispheric mixing,via stratosphere.  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