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   192033篇
  免费   18278篇
  国内免费   10157篇
电工技术   14219篇
技术理论   10篇
综合类   19935篇
化学工业   17790篇
金属工艺   7744篇
机械仪表   16257篇
建筑科学   26684篇
矿业工程   7645篇
能源动力   8042篇
轻工业   13475篇
水利工程   8383篇
石油天然气   12001篇
武器工业   2051篇
无线电   10428篇
一般工业技术   18437篇
冶金工业   7570篇
原子能技术   2604篇
自动化技术   27193篇
  2024年   721篇
  2023年   2242篇
  2022年   4762篇
  2021年   5667篇
  2020年   6011篇
  2019年   4968篇
  2018年   4916篇
  2017年   5882篇
  2016年   7127篇
  2015年   7477篇
  2014年   12446篇
  2013年   12331篇
  2012年   14456篇
  2011年   15882篇
  2010年   11383篇
  2009年   11586篇
  2008年   10850篇
  2007年   12921篇
  2006年   11241篇
  2005年   9469篇
  2004年   7986篇
  2003年   6857篇
  2002年   5532篇
  2001年   4562篇
  2000年   3824篇
  1999年   3187篇
  1998年   2737篇
  1997年   2289篇
  1996年   1880篇
  1995年   1532篇
  1994年   1397篇
  1993年   1046篇
  1992年   961篇
  1991年   700篇
  1990年   592篇
  1989年   502篇
  1988年   403篇
  1987年   274篇
  1986年   236篇
  1985年   221篇
  1984年   263篇
  1983年   246篇
  1982年   200篇
  1981年   99篇
  1980年   122篇
  1979年   75篇
  1978年   55篇
  1977年   46篇
  1976年   44篇
  1959年   33篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
冯久成 《人民黄河》1993,(10):14-16,56
通过对故县水库水文特征分析,论述了水库开发任务和要求。并根据水库的洪水、径流、泥沙特性,拟定了水库防洪运用的控制条件和运用方式,以及水库的兴利运用水位和原则。对水库工程的投资和效益作出了分析和评价。  相似文献   
992.
The strip element method (SEM) is used to investigate wave scattering by rectangular flaws in anisotropic laminated plates. The plates containing flaws are divided by junctions into domains in which the SEM is applied. For each domain, SEM equations are obtained which give a relationship between the traction and displacement vector on the vertical boundaries. A set of equations which gives a relationship between the traction and displacement vector on the junctions is then obtained by assembling the SEM equations for all the domains. This set of equations is solved by using the conditions on the junctions. Scattered wave fields in the frequency domain for isotropic and composite plates with rectangular flaws are computed and discussed in comparison with results for corresponding plates without flaws. A technique for determining the length of a rectangular flaw in a plate is also presented. The results presented in this paper are of importance and could be used in the characterization of flaws in anisotropic laminated plates.  相似文献   
993.
使用有限元程序SAP5对某新型导弹发射筒内的适配器的强度进行了计算。通过结果分析,找出了适配器危险应力点的分布规律,它对结构选型设计具有指导意义。  相似文献   
994.
The limit carrying capacity of gas pipelines having corrosion defects were evaluated by means of an improved FEM analysis, together with the ANSI/ASME defect judgement and an experimental verification. When compared with our past presentation at the proceedings of the CAPE'93 Colloquium (dealing with reproduced defects), this paper evaluates the remaining lifetime of a pipeline having natural faults. The new improved analysis includes geometrical nonlinearities leading to a modification of limit state parameters and thus matching better with actuality. This presented work was initiated by the firm of Trans-Gas in Prague after having had a pipeline inspected proving some parts of it as being heavily corroded. The task in hand was to determine the remaining pipeline lifetime with the view to at least a two-year period.  相似文献   
995.
This paper is concerned with the problem of pipe whip, the dynamic response of a high pressure piping system subjected to an end force as the result of a pipe break which releases a jet of fluid from the broken section. Both experimental and theoretical results are presented concerning the dynamic elastic-plastic behaviour of cantilever pipes subjected to a transverse force pulse at the free end. Comparisons between experimental data and theoretical predictions are made for mild-steel pipes with outer diameter-to-thickness ratios of 19.5, 28 and 32. It is demonstrated that, for these geometries, the whipping pipes display three characteristically different responses, viz. elastic, plastic hardening behaviour for thick pipes, elastic, plastic hardening-softening behaviour for moderately thick pipes and elastic, plastic hardening-softening-collapse behaviour for thinner pipes. The experimental data taken from a series of high-speed films are compared with the predictions of the instantaneous shapes of the whipping pipes derived from both a rigid, perfectly-plastic, large deflection, dynamic beam model and a more comprehensive model which incorporates the effects of elasticity and plastic hardening and softening, the details of which are presented in the paper.  相似文献   
996.
高层结构几何非线性分析的QR法   总被引:3,自引:1,他引:2  
秦荣 《工程力学》1996,13(1):8-15
本文利用QR法分析高层建筑结构几何非线性问题,建立了新的计算格式。该法不仅未知量的数目少,精度高,而且输入简单,计算速度快,可以用微机分析复杂问题。  相似文献   
997.
岩心分析过程中的取心间隔并非完全相同,这就形成了非等间距的岩心分析数据。测井曲线的数据一般都是采样等间距的,为了使岩心数据与测井数据更好地进行匹配,对岩心分析数据进行插值处理,使分析数据形成等距的形式,然后对插值后的数据根据不同的测井曲线进行滤波,使得岩心分析数据与测井数据的分辨率相匹配,利用处理后的数据建立模型或数据分析才可得到较为准确的模型。克里金插值和分形插值均为非线性的数学插值方法,它们与一般的数学插值方法相比较,能更好地反映数据的内在分布规律。文中分别利用克里金插值和分形插值的理论对岩心数据的插值进行了深入的研究,根据两种插值方法的理论建立了相应的插值方法。经过对两种插值理论的实例对比分析,得到了两种非线性插值方法的优缺点,为进一步的深入研究奠定了一定基础。  相似文献   
998.
The adsorption and thermal analysis of 1-propanamine has been compared over MFI zeolites which contain H, Ga, and In cations. In the case of H+-containing materials, NH3 and propene are simultaneously desorbed above 600 K. This behavior, is well known and characteristic of the Hofmann elimination reaction. However, a distinctly different mode of reaction is observed in the case of Ga and In containing materials. NH3 is released below 600 K, propene and other products are released above 600 K, and a stable residue remains above 800 K. It is suggested that such behavior results from Lewis acid interactions of Ga or In cations with propanamine.On leave from the Bulgarian Academy of Sciences, Institute of Organic Chemistry.  相似文献   
999.
描述了二流量试井工艺的实现,从常规分析和双对数曲线拟合两上方面,给出了二流量试井的资料解释分析方法,分析认为二流量试井同样可以计算出正常关井测压力恢复(或压力降落)资料所解释的油藏及流体参数。这种试井方法不但可以减少因正常关井测压对产油量和注水量的影响,而且可以减缓因突然关、开井造成的套管变形或损坏。实践证明,该试井技术方法具有较好的经济效益和应用前景。  相似文献   
1000.
The present work quantifies the relations between the structure of a chemical reaction kinetic model, its valid parameter range, and the truncation error tolerance of the model. General methods are presented to solve the three important problems of valid parameter range analysis: (1) identification of the valid parameter range of a kinetic model, (2) estimation of the error tolerance required when applying a kinetic model over a specified parameter range, and (3) improvement of existing model generation algorithms to construct more robust models. Finally, the relationship between a model's structure, its valid parameter range, and the truncation error tolerance are illustrated by the flexibility-tolerance-model graph. The new methods are applied to pyrolysis of methane/ethane mixtures.  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