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   17053篇
  免费   1992篇
  国内免费   2948篇
测绘学   908篇
大气科学   2496篇
地球物理   3421篇
地质学   8210篇
海洋学   2368篇
天文学   1996篇
综合类   1033篇
自然地理   1561篇
  2024年   68篇
  2023年   221篇
  2022年   680篇
  2021年   888篇
  2020年   805篇
  2019年   862篇
  2018年   1079篇
  2017年   1003篇
  2016年   994篇
  2015年   755篇
  2014年   955篇
  2013年   1033篇
  2012年   1001篇
  2011年   1144篇
  2010年   1035篇
  2009年   947篇
  2008年   891篇
  2007年   934篇
  2006年   834篇
  2005年   461篇
  2004年   470篇
  2003年   492篇
  2002年   515篇
  2001年   477篇
  2000年   344篇
  1999年   374篇
  1998年   304篇
  1997年   313篇
  1996年   268篇
  1995年   264篇
  1994年   234篇
  1993年   199篇
  1992年   177篇
  1991年   124篇
  1990年   97篇
  1989年   118篇
  1988年   86篇
  1987年   64篇
  1986年   58篇
  1985年   44篇
  1984年   42篇
  1983年   41篇
  1982年   40篇
  1981年   24篇
  1980年   25篇
  1979年   30篇
  1978年   18篇
  1977年   22篇
  1976年   19篇
  1975年   22篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
101.
At pesent,it is very popular to estimate pile bearing capacity by use of empirical formula andphysical indexes of soil provided in the design codes for civil construction in China.This paper attempts toapply mechanical indexes of soil and semi-empirical formulas,which are based on soil mechanical theoriesand were summarized and presented by Meyerhof in 1976,to calculate the axial pile bearing capacity.Lo-ading test results of 24 single piles in Tianjin area have been collected and compared with the proposed cal-ulation approach.  相似文献   
102.
In this paper a numerical analysis method combining FEM incemental technique with limit analysis concept is proposed for the study of the static strength of offshore platform in collision. Large deformation and plasticity are accounted for and the limit yield surface expressed by generalized stress for a tubular section is derived. The modified stiffness matrix of space beam element is formulated by Plastic Node Method. The buckling behavior of beam columns can also be taken into account. It can trace the generation of plastic hinges during loading and finally the ultimate strength of offshore platform against collision is obtained.  相似文献   
103.
Shear Failure of a Clamped Dented Tubular Beam Under Lateral Impact   总被引:1,自引:0,他引:1  
- The shear failure of a rigid-plastic dented clamped tubular beam under the lateral impact of a mass is investigated. Both the denting and the impact point are in the middle span of the beam. It is assumed that denting does not spread during the shear sliding. Numerical results show that the axial force and lateral deflection of the beam are very small at the moment of the occurence of shear failure, which means that the finite deformation effect can be neglected in the shear failure analysis. Also, some aspects of the initial impact energy are investigated.  相似文献   
104.
采用金属络合物通式模型,在IBM-PC计算机上计算了不同pH(7.5~9.5)、碱度(2.3~2.5mmol dm~(-3))和加入不同浓度的铜离子(1.0×10~(-4)~1.0mg dm~(-3))条件下,海水培养液中铜的主要化学存在形式分配的百分数。还给出了计算机程序框图和主要化学存在形式含量的百分数随pH、碱度和铜浓度变化图。  相似文献   
105.
The basis, process and results of the demonstration of the main dimensions of a 75000t floating production and storage vessel are discussed in this paper. A simple but reliable orthogonal design method is applied in the main dimension optimization. The ideas of gradual approximation and feedback from various aspects are put into effect. During the demonstration, in order to make the model tally with the actual situation, the draft design is closely related to the computational analysis, so that the demonstration model can be verified at any time; the handling of the overall system is closely related to the research of each item, which is beneficial not only to the mastery of various regularities, but also to the balance of decisions. Finally, according to the computational results and the regularities obtained from analysis, the main dimensions are determined.  相似文献   
106.
This paper describes the study of a single-column structure used as well-head platform. In order to check the reliability of computation theory and programme, model tests have been carried out. The paper introduces the conclusion of tests and the dynamic properties of single-column platform are obtained.  相似文献   
107.
The plastic node method is reformulated by the variational principle and is applied to elasto-plastic finite element analysis of tubular joints, eventually including the effect of internal and external gussets, stiffener rings, etc., if necessary. Four different joints are studied here in detail for the elasto-plastic behavior, the strain at the hot spot, the strain concentration factor around the intersection line, and the propagation of the plastic region with loading up to collapse in order to determine the ultimate strength, safety factor, and development of the plastic field. The present results are in good agreement with the experimental results.  相似文献   
108.
Multi-directional irregular waves are simulated on the basis of the given directional spectrum using a double summation model, a single direction per frequency model and a single summation model. Their results are compared. It is shown that the single direction per frequency model proposed in this paper can generate a realistic wave field. The effects of the model parameters on the simulated results are also studied in this paper and corresponding suggestions are given.  相似文献   
109.
An empirical formula for estimating the overtopping discharge of wind-waves on a smooth-impermeable-simple slope dyke is derived through model tests in this paper, it can be adopted by related design departments in the determination of the crest elevation of the dyke.  相似文献   
110.
介绍了斜坡式防波堤砌石护面中的插砌条石和干砌块石在波浪作用下的力学图式及作用机理 ,重点给出考虑摩擦力作用时的砌石块体稳定厚度的计算公式 ,并结合工程实例验证了公式的适用性  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