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   6242篇
  免费   349篇
  国内免费   558篇
林业   611篇
农学   632篇
基础科学   392篇
  2153篇
综合类   2062篇
农作物   299篇
水产渔业   129篇
畜牧兽医   491篇
园艺   99篇
植物保护   281篇
  2024年   54篇
  2023年   145篇
  2022年   225篇
  2021年   212篇
  2020年   251篇
  2019年   279篇
  2018年   196篇
  2017年   309篇
  2016年   315篇
  2015年   260篇
  2014年   288篇
  2013年   355篇
  2012年   443篇
  2011年   412篇
  2010年   342篇
  2009年   310篇
  2008年   302篇
  2007年   423篇
  2006年   335篇
  2005年   251篇
  2004年   215篇
  2003年   152篇
  2002年   126篇
  2001年   120篇
  2000年   114篇
  1999年   68篇
  1998年   78篇
  1997年   89篇
  1996年   81篇
  1995年   61篇
  1994年   73篇
  1993年   60篇
  1992年   35篇
  1991年   32篇
  1990年   47篇
  1989年   25篇
  1988年   20篇
  1987年   17篇
  1986年   10篇
  1985年   4篇
  1984年   2篇
  1982年   4篇
  1981年   2篇
  1979年   2篇
  1978年   2篇
  1976年   2篇
  1955年   1篇
排序方式: 共有7149条查询结果,搜索用时 703 毫秒
41.
The subject matter of this paper is to analyze the stability of excavated high slope. On the base of typical engineering case in Wulong, Chongqing, the geological conditions and potential failure pattern of the high slope are discussed. Then, the limit equilibrium method and the stereographic projection method are used to synthetically analyze the stability of excavated high slope. As a result, it indicates that the stability of the high slope in insufficient and some retaining structures ought to be adopted for the high slope as soon as possible.  相似文献   
42.
43.
Based on analyzing about blasting mode of slope in the construction of road, the paper shows that pre splitting blasting is mostly suitable in the section of severely weathering soft rock with developed joints and fractures, introduced the laying out about the hole of pre splitting blasting that can apply in the high slope of the expressway in the section, and designed the parameter. The practice shows that it gained favourable effect by this method.  相似文献   
44.
We shall discuss the real opererating conditions of the mine fans . in the mine diagonal ventilation system and establish a set of mathematics model for analysing the real engineering to provide judgement for technical manage ment of mine ventilation.  相似文献   
45.
In this paper we concider the problem of stability of stochastic evolution systemsin Hilbert space drived by a cylindrical Brownian mothin. We regard the stochestic evolutionequation dXt = AXtdt +G(Xt)dBt as a deterministic system of the form dXt=AXtdt under randomperturbation,and obtain stability of its solution. It is shown that under certain assumptions,itsevolution solution and L2-contimuous evulution solution are exponertially stable.  相似文献   
46.
The mechanization of mining thinnest coal seam is a key program in the 7th five-year plan in Sichaan province, It is sponsored by The Scientific and Technieal Commission of Sichuan province. In this paper, the dynamic performance for the hydraulie servo-system of haulage party for SGW-150 shearer with coustant-power speed governing is analysed. It shows that the system designed by us is stability and reasonable for SGW-150 shearer.  相似文献   
47.
A structural optimization algorithm is performed for single-layer Kiewit reticulated dome by means of ANASYS. In the process of optimum design, the overall weight is taken as objective function; the stress constraints and stability constraints etc are considered. Meanwhile, the geometrical non-linearity is taken into account. Then the overall stability analysis for the optimized single-layer reticulated dome is operated. The results show that the optimization design is reliable.  相似文献   
48.
By virtue of some analysis techniques,it is proved that certain ishikawa iteration procdeure with errors are stable with respect to strongly pseudocontractive operators in real Banach space. A related result deals with stable iteration procedures for solution of the nonlinear equation of strongly accretive operators. The results presented extend and improve the corresponding by Osilike,Zeng, Chidume, Deng, Liu,et al.  相似文献   
49.
Analysis and Control on Roof Stability of Rock-salt Cavity   总被引:1,自引:0,他引:1  
Analysis and control on roof stability of rock-salt cavity are very important to ensure safety and benefit in production, build and use of repertorv of rock salt cavity. Dynamic balance process and instability process of rock-salt carity roof are studied, and instability mechanism of rock-salt cavity roof is studied with catastrophe theory, and the influencing factor are analyzed, which will be theoretical basis of rock-salt cavity stability control.  相似文献   
50.
由于对边坡强度参数统计特性考虑不全面,使得边坡可靠性指标计算值偏小,对应的失效概率偏大,常常超过10%,设计中难以采纳,造成地基可靠度规范的制定和执行进展缓慢。以某高速公路全风化花岗岩土质高边坡为工程背景,在分析土质参数统计特性的基础上,采用极限平衡理论和蒙特卡罗模拟法,系统地分析了土质强度参数的均值不定性、变异性、相关性、区间特性和空间变化性等对边坡稳定可靠性的影响。结果表明:土性参数的各种统计特性对边坡稳定可靠性均具有不同程度的影响。可靠性指标计算值随抽样距离的减小而增加,随c或φ均值的增大而增加,随c和φ的变异系数的增大而减小,随c和φ相关系数绝对值的增大而增加,考虑区间性后可靠性指标计算值也明显变大。即变异性对边坡稳定不利,而相关性、区间性和空间变化性对边坡稳定有利。因此,准确而全面地考虑土质参数的统计特性,尤其是在参数变异性和相关性的基础上加以考虑土性参数空间变化性和区间性会更加符合工程实际,且计算结果趋于安全,有利于地基可靠度规范的推广运用和边坡工程的安全评价。  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