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   18395篇
  免费   4177篇
  国内免费   5885篇
测绘学   1706篇
大气科学   3293篇
地球物理   5179篇
地质学   10948篇
海洋学   3267篇
天文学   1307篇
综合类   1282篇
自然地理   1475篇
  2024年   57篇
  2023年   230篇
  2022年   520篇
  2021年   666篇
  2020年   738篇
  2019年   923篇
  2018年   803篇
  2017年   851篇
  2016年   878篇
  2015年   1023篇
  2014年   1340篇
  2013年   1202篇
  2012年   1315篇
  2011年   1404篇
  2010年   1257篇
  2009年   1416篇
  2008年   1325篇
  2007年   1564篇
  2006年   1496篇
  2005年   1254篇
  2004年   1196篇
  2003年   1012篇
  2002年   799篇
  2001年   663篇
  2000年   675篇
  1999年   631篇
  1998年   608篇
  1997年   475篇
  1996年   410篇
  1995年   349篇
  1994年   332篇
  1993年   224篇
  1992年   214篇
  1991年   149篇
  1990年   103篇
  1989年   125篇
  1988年   68篇
  1987年   51篇
  1986年   26篇
  1985年   21篇
  1984年   7篇
  1983年   5篇
  1982年   5篇
  1981年   9篇
  1980年   5篇
  1977年   2篇
  1976年   7篇
  1973年   4篇
  1971年   2篇
  1954年   15篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
对武汉区域气象中心并行计算机系统进行了详细地介绍,分析了并行计算机体系结构、网络和存储系统特点;给出了在并行计算机SP上实现数值预报业务并行化的部分结果;对数值预报模式在串、并行编程环境下的结果进行了分析比较。  相似文献   
72.
介绍当今确定天文大地垂偏差的新仪器-CCD自动天体测量仪和确定两点间高程异常差的新方法,该方法用单极坐标代替繁琐的双极坐标进行计算,讨论了天文重力水准的误差及垂线偏差非线性影响等问题,估计在不久的将来,用这一手段施测山区似大地水准面的精度可望达到厘米级。  相似文献   
73.
通过对影响能见度的因素的分析,提出了一种能见度预报方法-综合分析法,极大地提高了能见度的预报准确率。  相似文献   
74.
Dark energy has a dramatic effect on the dynamics of the Universe, causing the recently discovered acceleration of the expansion. The dynamics are also central to the behaviour of the growth of large-scale structure, offering the possibility that observations of structure formation provide a sensitive probe of the cosmology and dark energy characteristics. In particular, dark energy with a time-varying equation of state can have an influence on structure formation stretching back well into the matter-dominated epoch. We analyse this impact, first calculating the linear perturbation results, including those for weak gravitational lensing. These dynamical models possess definite observable differences from constant equation of state models. Then we present a large-scale numerical simulation of structure formation, including the largest volume to date involving a time-varying equation of state. We find the halo mass function is well described by the Jenkins et al. mass function formula. We also show how to interpret modifications of the Friedmann equation in terms of a time-variable equation of state. The results presented here provide steps toward realistic computation of the effect of dark energy in cosmological probes involving large-scale structure, such as cluster counts, the Sunyaev–Zel'dovich effect or weak gravitational lensing.  相似文献   
75.
Mainly, the author focuses on Baumgarte's method and its applications in satellite, asteroid, stellar and planetary problems. In the paper arguments are given for the use of energy relations for stabilization in the elliptical two-body problem. Stabilizing properties of Baumgarte's equations and others are discussed. A simple approach is proposed for stabilizing the equations of almost circular motion. By using Baumgarte's technique, the author derives stabilized equations of perturbed restricted three-body problem. It is shown experimentally that stabilization in the problems mentioned above can raise the accuracy of numerical integration by several orders.  相似文献   
76.
In this paper a slightly different approach is proposed for the process of determining the functions S m and H m * of the algorithm of the canonical version of Hori method. This process will be referred to as integration theory of the mth order equation of the method. It will be shown that the ordinary differential equation with an auxiliary parameter t * as independent variable, introduced through Hori auxiliary system, can be replaced by a partial differential equation in the time t. In this way, the mth order equation of the algorithm assumes a form very similar to the one of other perturbation methods. In virtue of this new approach of the integration theory for Hori method, Lagrange's variational equations introduced by Sessin are revised. As an example, the Duffing equation is solved through this new approach.  相似文献   
77.
用电测深研究地电断面、寻找隐伏多金属矿体时,以往采用ρ_s(或η_s)等值线断面图进行地质推断解释,因受浅源信号的干扰,效果差。本文提出了采用ρ_s(或η_s)差值法,能排除浅源干扰信号,反映出地电断面的相对变化,突出了深部微弱信息,取得了较好的地质解释效果。  相似文献   
78.
79.
Geoff Kite 《水文研究》1993,7(2):227-233
Using current meters to estimate flows in fast mountain streams is difficult and inaccurate. The salt dilution method offers an easier and more accurate alternative. The method has been used for many years but is time consuming and messy because of the need to mix chemical solutions and measure chemical concentrations in the field. A computer program has been developed which uses a laptop computer to calculate the mixing length and the mass of salt needed. The program controls the conductivity measurements and calculates the streamflow directly in the field. The development of this program is described and examples are presented of the application of the method in the Rocky Mountains of Alberta and British Columbia.  相似文献   
80.
为了给公路设计部门提供选线依据,运用瞬变电磁法在山西境内的某两条高速公路隧道工程设计线路段上进行探测,以查明下覆不良地质构造的发育情况.通过对瞬变电磁法的探测能力进行理论上的讨论,对不同地电断面情况下的异常体电磁响应的定性分析,得出用瞬变电磁法探测不良地质体的可行性结论.经过资料处理,查出不良地质构造赋存的位置,解释结果与钻探资料完全吻合.  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