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   90552篇
  免费   1595篇
  国内免费   596篇
测绘学   1970篇
大气科学   6086篇
地球物理   17520篇
地质学   32547篇
海洋学   8319篇
天文学   20772篇
综合类   240篇
自然地理   5289篇
  2022年   646篇
  2021年   1099篇
  2020年   1182篇
  2019年   1342篇
  2018年   2705篇
  2017年   2498篇
  2016年   2909篇
  2015年   1497篇
  2014年   2779篇
  2013年   4866篇
  2012年   3074篇
  2011年   3964篇
  2010年   3607篇
  2009年   4566篇
  2008年   3975篇
  2007年   4061篇
  2006年   3765篇
  2005年   2738篇
  2004年   2657篇
  2003年   2441篇
  2002年   2441篇
  2001年   2071篇
  2000年   2076篇
  1999年   1618篇
  1998年   1692篇
  1997年   1532篇
  1996年   1316篇
  1995年   1311篇
  1994年   1122篇
  1993年   1070篇
  1992年   1007篇
  1991年   1018篇
  1990年   980篇
  1989年   862篇
  1988年   799篇
  1987年   925篇
  1986年   820篇
  1985年   994篇
  1984年   1119篇
  1983年   1095篇
  1982年   1004篇
  1981年   950篇
  1980年   842篇
  1979年   803篇
  1978年   772篇
  1977年   649篇
  1976年   652篇
  1975年   638篇
  1974年   610篇
  1973年   680篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
52.
53.
Transverse secondary circulations involving surface convergence, observed in a well-mixed estuary in North Wales, are made visible by the collection of surface material along an axial line which extends continuously for many kilometres through the estuary. The circulation and axial convergence, however, are seen only during the flood phase of the tide and no similar behaviour has been observed during the ebb phase.Convergent circulations in the estuary are associated with small but steady transverse density gradients in the cross-section, produced by non-uniform advection of the longitudinal gradient through the channel. A diagnostic model, using measured mean distributions of cross-sectional density, indicates surface transverse velocities (~0.1 ms?1) similar to those observed in the estuary. The model further predicts appreciable transverse divergent currents at a fractional depth of 0.75: a prediction which has been tested in the estuary using a vertical array of accurately resolving current direction indicators.  相似文献   
54.
The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ~2 × 105 g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ~0.04 at 1.25 μm and ~0.05 at 2.2 μm.  相似文献   
55.
Summary. A method of synthetic seismogram computation for teleseismic SV -waves is developed in order to treat quantitatively SV -waves in problems of body wave source inversion and source—receiver structure studies. The method employs WKBJ theory for a generalized ray in a vertically inhomogeneous half-space and the propagator matrix technique for waves in near-surface homogeneous layers. Wavenumber integration is done along the real axis of the wavenumber plane and anelasticity is included by using complex velocity in all regions of the earth model. The near-surface source structure is taken into account in the computation for the case of the shallow source by allowing a point source to be located in the homogeneous layers. Source and receiver area structures are also allowed to differ. A general moment tensor point source is considered.  相似文献   
56.
57.
We describe a procedure for the numerical modelling of astronomical interferometers, with particular relevance to far-infrared and submillimetre wavelengths. The scheme is based on identifying a set of modes that carry power from the sky to the detector. The procedure is extremely general, and can be used to model scalar or vector fields, in any state of coherence and polarization, the only limitation being that the propagation of a coherent field through the system be described by an integral transform, a constraint that is in practise always met.
We present simulations of ideal, multimode two-dimensional interferometers, and show that the modal theory reproduces the correct behaviour of both Michelson and Fizeau interferometers. We calculate simulated visibility data for a multimode bolometric Michelson interferometer, with a synthesized source, and produce a dirty map, recovering the original source with the usual artefacts associated with interferometers.  相似文献   
58.
I briefly present the Organizing Committee's and my own motivation for organizing this workshop, and I suggest a few key questions for which we will try to find possible answers in the coming days. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
59.
60.
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