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   12016篇
  免费   1119篇
  国内免费   948篇
测绘学   539篇
大气科学   1365篇
地球物理   3369篇
地质学   5301篇
海洋学   888篇
天文学   1410篇
综合类   411篇
自然地理   800篇
  2023年   72篇
  2022年   192篇
  2021年   199篇
  2020年   172篇
  2019年   247篇
  2018年   725篇
  2017年   650篇
  2016年   568篇
  2015年   384篇
  2014年   448篇
  2013年   565篇
  2012年   985篇
  2011年   774篇
  2010年   460篇
  2009年   510篇
  2008年   425篇
  2007年   418篇
  2006年   447篇
  2005年   1038篇
  2004年   1056篇
  2003年   823篇
  2002年   334篇
  2001年   229篇
  2000年   207篇
  1999年   195篇
  1998年   183篇
  1997年   186篇
  1996年   166篇
  1995年   115篇
  1994年   86篇
  1993年   113篇
  1992年   91篇
  1991年   86篇
  1990年   71篇
  1989年   64篇
  1988年   56篇
  1987年   60篇
  1986年   63篇
  1985年   49篇
  1984年   54篇
  1983年   57篇
  1982年   50篇
  1981年   40篇
  1980年   35篇
  1979年   39篇
  1978年   22篇
  1977年   29篇
  1976年   26篇
  1975年   28篇
  1973年   26篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
This paper systematically analyzes and proves the favorable factors of utilizing the ports and the railways in Northeast China for the Asia-Europe land bridge transportation. It will be more beneficial to Dalian Port and HaDa (Harbin-Dalian) and Binzhou (Harbin-Manzhouli) railways in Northeast China to the Siberia railway in Russia than 1) to other ports and the corresponding railways in China, 2) to the Nakhodka Port in Russia and the corresponding railways and 3) to the Chongjin Port in North Korea and the corresponding railways. This paper also puts forward the reform measures to adopt the ports and the railways in the northeast region in China for the land bridge transportation and the problems in transportation policies and management systems.  相似文献   
3.
A spectacular change in the lower corona on the south-west limb has been found in solar images taken by the Yohkoh soft X-ray telescope. The event is characterized by a large topological change in magnetic field and a large intensity decrease observed after the X1. 1/1B flare on 9 November, 1991. A coronal mass ejection (CME) was observed by the Mark III K-coronameter (MK3) at the HAO/Mauna Loa Observatory. Both the MK3 (white-light) and soft X-ray observations showed that one leg of this CME was located above the flare site. An interplanetary shock associated with this event was observed by Pioneer Venus Orbiter, and, possibly, by IMP-8.Also Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309, U.S.A.  相似文献   
4.
Book reviews     
Howard  R. F.  van den Oord  G. H. J.  Švestka  Z. 《Solar physics》1996,169(1):225-227
  相似文献   
5.
中国古生教授学会微体古生物学分会举行代表大会和学术年会中国古竽物学会微体古物学分会第五次会员代表大分暨第六次不术年会于1996年1月24日到30日在福州市召开。来自全国地质、石油、煤炭的和产、科研和大学的100多位代表参加了这次大会和学术研讨。大会共...  相似文献   
6.
7.
In this paper, we present a new method to estimate, for each turbulent layer labelled i , the horizontal wind speed   v ( h i )  , the standard deviation of the horizontal wind speed fluctuations  σ v ( hi )  and the integrated value of   C 2 n   over the thickness  Δ hi   of the turbulent layer   C 2 n ( hi )Δ hi   , where   hi   is the altitude of the turbulent layer. These parameters are extracted from single star scintillation spatiotemporal cross-correlation functions of atmospheric speckles obtained within the generalized mode. This method is based on the simulated annealing algorithm to find the optimal solution required to solve the problem. Astrophysics parameters for adaptive optics are also calculated using   C 2 n ( hi )  and   v ( hi )  values. The results of other techniques support this new method.  相似文献   
8.
An empirical kinematic method developed by Hakamada and Akasofu (1982) is calibrated on the basis of a one-dimensional MHD solution. The calibrated results are used to simulate the stream-stream interaction and the background corotating structure in a simple situation and also during 22 November–6 December 1977. The solar wind disturbances caused by solar activities during this period are then introduced into the above background stream in simulating the heliospheric disturbance event which was observed by an aligned set of spacecraft at distances between 0.6 and 1.6 a.u. The observations and the simulated results are satisfactory, and a little more refinement in the simulation could reconstruct reasonably well the data by filling the data gaps in the solar wind speed, the density and the IMF magnitude.  相似文献   
9.
10.
We have developed a method for analytically solving the porous medium flow equation in many different geometries for horizontal (two‐dimensional), homogeneous and isotropic aquifers containing impermeable boundaries and any number of pumping or injection wells located at arbitrary positions within the system. Solutions and results are presented for rectangular and circular aquifers but the method presented here is easily extendible to many geometries. Results are also presented for systems where constant head boundary conditions can be emulated internal to the aquifer boundary. Recommendations for extensions of the present work are briefly discussed. Copyright © 2003 John Wiley & Sons, Ltd.  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