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   107484篇
  免费   2300篇
  国内免费   981篇
测绘学   2955篇
大气科学   7826篇
地球物理   22991篇
地质学   37703篇
海洋学   8977篇
天文学   23904篇
综合类   337篇
自然地理   6072篇
  2022年   595篇
  2021年   1077篇
  2020年   1202篇
  2019年   1255篇
  2018年   2882篇
  2017年   2714篇
  2016年   3458篇
  2015年   2094篇
  2014年   3256篇
  2013年   5772篇
  2012年   3502篇
  2011年   4546篇
  2010年   3945篇
  2009年   5192篇
  2008年   4613篇
  2007年   4419篇
  2006年   4155篇
  2005年   3320篇
  2004年   3258篇
  2003年   3015篇
  2002年   2899篇
  2001年   2632篇
  2000年   2514篇
  1999年   2047篇
  1998年   2152篇
  1997年   2095篇
  1996年   1665篇
  1995年   1685篇
  1994年   1485篇
  1993年   1336篇
  1992年   1237篇
  1991年   1185篇
  1990年   1258篇
  1989年   1140篇
  1988年   1019篇
  1987年   1227篇
  1986年   1068篇
  1985年   1311篇
  1984年   1470篇
  1983年   1379篇
  1982年   1333篇
  1981年   1183篇
  1980年   1066篇
  1979年   1017篇
  1978年   1026篇
  1977年   893篇
  1976年   853篇
  1975年   840篇
  1974年   810篇
  1973年   829篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
961.
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   
962.
Summary Equations for the motions in a galaxy which is controlled by gravitational forces and inertial effects are formulated. It is found that for the motions relative to the rotating system formulae analogous, and of similar form, to the geostrophic wind equations may be written. From these formulae and from the distribution of the relative gravitational potential in the disc of the galaxy, it is found that a spiral tendency in the mass distribution carries the implication of an inward flux of angular momentum by advective processes. This is to be compared with an outward flux through gravitational torques obtained in previous studies in which the writer participated.  相似文献   
963.
Summary A gradually cumulative error due to the use of the hydrostatic approximation is examined through consideration of a simple mathematical model taken from the classical theory of gravity waves. Two cases are chosen which differ solely in the circumstance that in one the hydrostatic assumption is made while in the other it is not. A large divergence of the results present in the later stages is then to be referred to the neglect of terms contained in the exact equation of motion for the vertical direction in one of the solutions. The inference is drawn that comparable phenomena might arise in the integration of the atmospheric equations over long time periods.  相似文献   
964.
Summary Argillaceous sediments of jurassic and lower cretaceous age in NW-Germany contain in several localities authigenous ZnS-polytypes. The crystals with a maximum height of 2 mm exhibit hexagonal-pyramidal and trigonal-pyramidal habit.With X-ray rotation and precession technique the following polytypes could be identified: Sphalerite (3 R = 3 C) 211, 411, 6H 9R, 12R, 15R and 21R.The 9 R-, 12 R- and 21 R-polytypes have not until now been described elsewhere.The structures of the new polytypes were determined as 9R=(21), 12R=(13) and 21R=(3112).Oriented intergrowths of R- and H-polytypes were frequently observed. From the intergrowth-phenomena arguments for the environmental conditions of formation can be deducted.[/p]  相似文献   
965.
966.
967.
968.
Резюме С помощью принятия простых кинематических предположений и на основании ω—уравнения выла определена конфигурация полос облаков в полностью окклюдированном циклоне без фронтов. Облачная система определяется полем скрытой теплоты, выделяемой в процессах конденсации. Полосы облаков теоретически представляют собой в основном листы синусоидальной спирали.

Address: Boční II, Praha 4-Spořilov.  相似文献   
969.
Summary According to the author the reason of the subsistence of the 11 years' sunspot cycle is to be found in the conjunction of the planets. As a result of the investigations it has been stated that from among the nine planets the joint tidal effect of Venus-Jupiter-Earth is a decisive factor in the variations of sunspot activity. The above three planets are every 10.4 years and 12.0 years respectively, in a close conjunction. The mean value (11.2 years) is in an almost full accordance with the average cycle-period. The fluctuations of the period of the cycle come from the fact that the planets' getting into approximately one line takes a different time within each cycle. This time delay is the cause of the stronger or weaker sunspot activity, and of the shorter or longer cycles.  相似文献   
970.
Gully erosion has for many years been a problem in Rhodesia1s Tribal Trust Lands. This paper describes how Soil Conservation Service staff, with no previous ground knowledge of these areas, used good quality 1/25,000 scale aerial photographs to measure the extent of the gully erosion and to pinpoint erosion “black spots.” This enabled quick and reliable estimates of the cost of reclamation work to be made without the need for time-consuming field survey. The survey method discussed is capable of wide application wherever gully erosion occurs and needs to be brought under control.  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