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   287600篇
  免费   3066篇
  国内免费   817篇
电工技术   5030篇
综合类   162篇
化学工业   45405篇
金属工艺   11895篇
机械仪表   8606篇
建筑科学   6848篇
矿业工程   1835篇
能源动力   6734篇
轻工业   25918篇
水利工程   3190篇
石油天然气   7087篇
武器工业   16篇
无线电   31448篇
一般工业技术   56930篇
冶金工业   51361篇
原子能技术   7532篇
自动化技术   21486篇
  2021年   2098篇
  2018年   3672篇
  2017年   3623篇
  2016年   3903篇
  2015年   2465篇
  2014年   4230篇
  2013年   12022篇
  2012年   6827篇
  2011年   9212篇
  2010年   7565篇
  2009年   8642篇
  2008年   8929篇
  2007年   8813篇
  2006年   7826篇
  2005年   7309篇
  2004年   6800篇
  2003年   6553篇
  2002年   6627篇
  2001年   6497篇
  2000年   6177篇
  1999年   6229篇
  1998年   14749篇
  1997年   11029篇
  1996年   8566篇
  1995年   6525篇
  1994年   5914篇
  1993年   5787篇
  1992年   4481篇
  1991年   4441篇
  1990年   4288篇
  1989年   4306篇
  1988年   4255篇
  1987年   3598篇
  1986年   3595篇
  1985年   4161篇
  1984年   3965篇
  1983年   3621篇
  1982年   3422篇
  1981年   3558篇
  1980年   3423篇
  1979年   3365篇
  1978年   3445篇
  1977年   3923篇
  1976年   5037篇
  1975年   3158篇
  1974年   3007篇
  1973年   3025篇
  1972年   2651篇
  1971年   2473篇
  1970年   2104篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
The advantages and disadvantages of using a high-pressure pneumatic pump at porcelain and insulator works are discussed. The testing results of a prototype pump are described.  相似文献   
942.
We consider ad hoc wireless networks that use directional antennas and have limited energy resources. To explore quantitatively the advantage offered by the use of directional antennas over the case of omnidirectional antennas, we consider the case of connection-oriented multicast traffic. Building upon our prior work on multicasting algorithms, we introduce two protocols that exploit the use of directional antennas and evaluate their performance, We observe significant improvement with respect to the omnidirectional case, in terms of both energy efficiency and network lifetime. Additionally, we show that further substantial increase in the network's lifetime can be achieved by incorporating a simple measure of a node's residual energy into the node's cost function.  相似文献   
943.
Methods are proposed for obtaining the elastic and absorbed components of deformation and mechanical work expended in the region of a nondestructive mechanical effect from the stress-strain diagrams or by calculated prediction. The closeness of the values of the absorbed and correspondingly the elastic components obtained with the measured or predicted stress-strain diagram totally confirm the satisfactory reliability of modeling the physicomechanical properties of a fibre in the form of an integral equation in which the nonlinear-hereditary kernel analytically reflects the activating character of the mechanical effect combined with the concept of the deformation-time analogy in normalized form [5].  相似文献   
944.
The relative yield of delayed neutrons and the half-life of their precursor nuclei in fissioning of 233U, 235U, and 239Pu by epithermal neutrons are measured on a setup which is based on a KG-2.5 electrostatic accelerator. The experimental samples are irradiated in a polyethylene cube, one face of which is irradiated by a neutron beam consisting of T(p, n)3He neutrons. A procedure is developed for averaging the group parameters of delayed neutrons from different series of measurements, taking account of their correlation. A comparative analysis of the data of this work and in ENDF/BVI in terms of the average half-life of the precursor nuclei of the delayed neutrons and using the dependence of the reactivity on the asymptotic period of the reactor is performed.It is shown that the data of this work agree, to within the uncertainty limits, with the recommended experimental data and differ substantially from the ENDF/BVI data.  相似文献   
945.
Stabilization of the trajectories of a linear discrete system closed by dynamic feedback under interval uncertainty of the equations of motion and observation is studied. Sufficient conditions of stabilizability are formulated. Results of numerical experiments are given.  相似文献   
946.
We demonstrate a strategy for implementation a quantum full adder in a spin chain quantum computer. As an example, we simulate a quantum full adder in a chain containing 201 spins. Our simulations also demonstrate how one can minimize errors generated by non-resonant effects.  相似文献   
947.
The conventional application of reduction factors to response spectrum analysis results is inappropriate for the abutment shear forces, which are based on elastic action. On the other hand, adopting the unreduced values from the elastic dynamic analysis does not achieve equilibrium among the abutment shear forces, deck inertia forces, and reduced pier forces. A simplified method is here proposed for the assessment of the shear on the abutments, documented by comparison with response spectrum and time history nonlinear analyses for several bridge configurations. For the analyzed configuration of the bridge with an internal movement joint, the response spectrum analysis underestimates the shear on the abutment for low values of the abutment flexibility and overestimates it when the stiffness of the abutments becomes higher than that of the piers. In all the case studies analyzed, the proposed method approximates the time history results better than the response spectrum.  相似文献   
948.
949.
950.
The goal of the present studies was to construct and validate a short form of the 50-item Smoking Consequences Questionnaire (SCQ; T. H. Brandon & T. B. Baker, 1991), a measure of smoking outcome expectancies. In Study 1, a 21-item short form (S-SCQ) was derived from a sample of 107 young adults previously treated for substance abuse. In Study 2, the measure was cross-validated on 125 adolescents in treatment for substance abuse. Confirmatory factor analyses revealed good model fit and factorial invariance for the 4 S-SCQ subscales across both samples. Validation analyses on each sample found that subscale scores generally correlated significantly with smoking-related variables. The present studies provide initial evidence for the utility of the S-SCQ when used with young adults and adolescents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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