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   107567篇
  免费   1801篇
  国内免费   857篇
测绘学   2399篇
大气科学   7649篇
地球物理   21083篇
地质学   38813篇
海洋学   9602篇
天文学   24263篇
综合类   271篇
自然地理   6145篇
  2022年   663篇
  2021年   1134篇
  2020年   1231篇
  2019年   1393篇
  2018年   2875篇
  2017年   2686篇
  2016年   3203篇
  2015年   1658篇
  2014年   3055篇
  2013年   5505篇
  2012年   3342篇
  2011年   4400篇
  2010年   3959篇
  2009年   5076篇
  2008年   4416篇
  2007年   4457篇
  2006年   4255篇
  2005年   3088篇
  2004年   3032篇
  2003年   2869篇
  2002年   2844篇
  2001年   2476篇
  2000年   2492篇
  1999年   1981篇
  1998年   1996篇
  1997年   1909篇
  1996年   1654篇
  1995年   1629篇
  1994年   1401篇
  1993年   1303篇
  1992年   1251篇
  1991年   1279篇
  1990年   1258篇
  1989年   1134篇
  1988年   1048篇
  1987年   1239篇
  1986年   1123篇
  1985年   1323篇
  1984年   1515篇
  1983年   1465篇
  1982年   1344篇
  1981年   1276篇
  1980年   1147篇
  1979年   1106篇
  1978年   1099篇
  1977年   970篇
  1976年   928篇
  1975年   903篇
  1974年   934篇
  1973年   995篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
911.
Summary The effect of thickening of the crustal layer in mountainous region on the dispersion curve of Love waves has been studied. Perturbation method has been applied to obtain the modified frequency equation for Love waves through the surface of separation between a semi-infinite material and a layer the thickness of which abruptly increases throughout a certain length of the path. The effect is to decrease the phase velocity of the waves particularly in the low period range. It has been pointed out that by proper study, the amount of thickening may be obtained.  相似文献   
912.
913.
914.
915.
916.
A scheme is presented for the identification and classification of chlorite and related minerals in sediments which is mainly based on X-ray characteristics of the orginal sample and the sample heated at 350°C and treated with K+ and with glycerol. Examples are given. It is emphasized that additional data about clay mineral genesis, electron microscopy, infrared spectroscopy and chemical analyses are needed for the ordening of a certain mineral in the proposed scheme. Many names of minerals so far found to occur in the clay separate of sediments proved to be synonymous (52 of a total of 88) and thus should be abandoned. They only give confusion and needlessly increase the many difficulties which already exist in the identification, classification and quantitative determination of this complicated group of minerals of about 36 well defined specimens which may be found in sediments.  相似文献   
917.
Radio noise observations at frequencies of 0·700 Mc and 2·200 Mc were made at altitudes between 3000 and 11,000 km from a Blue Scout Jr. high-altitude rocket probe on 30 July 1963. A steady background flux of (7·5−3+6) × 10−19 W m−2)(c/s)−1 at 0·700 Mc and (1·8+1.0−0.5 × 10−19 W m−2 (c/s)−1 at 2·200 Mc was observed. Assuming a galactic origin of the observed fluxes at both frequencies, the averaged sky brightnesses are b(0·700 Mc) = (6−3+5) × 10−20 W m−2 (c/s)−1 sr−1b(2·200 Mc) = (1.4+1.0−0.5 × 10−20 W m−2 (c/s)−1 sr−1 The observed brightness at 2·200 Mc is in reasonable agreement with the results of other observers. The apparent brightness at 0·700 Mc is, however, greater than was expected from previous observations. An alternative source of the 0·700 Mc flux in the terrestrial exosphere, as well as characteristics of several noise bursts observed during the flight, is briefly discussed.  相似文献   
918.
Summary Simultaneous measurements of wind, air temperature, and humidity profiles as well as of evaporation, presented byTakahashi (1958), were compared with relevant formulae suggested by turbulence theory. Satisfactory agreement could be achieved if, near the sea surface, the influence of molecular diffusion and, at higher levels, the effect of thermal stratification on the profiles were taken into account in addition to a suitable reduction of the value of evaporation obtained by means of a floating pan.The chief results of this report have been presented on 27th April 1962 to the Tenth Yearly Meeting of theSocietà Italiana di Geofisica e Meteorologia (Genova: 26–28 April 1962).  相似文献   
919.
Summary The paper deals with the disturbances in an infinite slab of finite thickness, the medium being homogeneous, isotropic and perfectly elastic.  相似文献   
920.
Summary Correlation between some physical and chemical variables, measured at 28 stations of the United States Weather Bureau Network, and seasonal and annual frequencies of precipitation, has been attempted with the aim of gaining insight into the bearing of such variables, on occurrence of precipitation. — Concurrent trends of frequencies with local temperature functions, altitude parameters, precipitable water vapour increments, and some chemical species have been found.Contribution of the «Centro Nucleazione Aerosoli» of the National Research Council of Italy, Via Vettore 4 (Monte Sacro),Roma.  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