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   18340篇
  免费   3013篇
  国内免费   1823篇
电工技术   1926篇
综合类   2615篇
化学工业   1237篇
金属工艺   705篇
机械仪表   1217篇
建筑科学   1308篇
矿业工程   481篇
能源动力   793篇
轻工业   754篇
水利工程   749篇
石油天然气   720篇
武器工业   243篇
无线电   2429篇
一般工业技术   1839篇
冶金工业   445篇
原子能技术   142篇
自动化技术   5573篇
  2024年   106篇
  2023年   375篇
  2022年   689篇
  2021年   800篇
  2020年   818篇
  2019年   721篇
  2018年   655篇
  2017年   770篇
  2016年   772篇
  2015年   928篇
  2014年   1289篇
  2013年   1235篇
  2012年   1596篇
  2011年   1467篇
  2010年   1197篇
  2009年   1271篇
  2008年   1103篇
  2007年   1264篇
  2006年   1099篇
  2005年   947篇
  2004年   704篇
  2003年   616篇
  2002年   469篇
  2001年   374篇
  2000年   361篇
  1999年   301篇
  1998年   220篇
  1997年   179篇
  1996年   141篇
  1995年   125篇
  1994年   117篇
  1993年   86篇
  1992年   74篇
  1991年   59篇
  1990年   59篇
  1989年   38篇
  1988年   22篇
  1987年   27篇
  1986年   21篇
  1985年   11篇
  1984年   9篇
  1983年   8篇
  1982年   11篇
  1981年   7篇
  1980年   10篇
  1979年   7篇
  1977年   3篇
  1975年   2篇
  1955年   1篇
  1951年   4篇
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
51.
A three-dimensional solution of the direct problem of heat conduction when a linear pulsed heat source acts in the plane of contact of two semibounded bodies is presented. The solution is obtained by the method of finite differences. An example of the modeling is considered. __________ Translated from Izmeritel’naya Tekhnika, No. 10, pp. 42–45, October, 2007.  相似文献   
52.
This paper presents an adaptive Hopfield neural network (AHNN) based methodology, where the slope of the activation function is adjusted, for finding approximate Pareto solutions for the multi-objective optimization problem of emission and economic load dispatch (EELD). We have placed emphasis on finding solutions quickly, rather than the global Pareto solutions, so that our algorithm can be employed in large on-line power systems where variations in load are quite frequent. To enable faster convergence, adaptive learning rates have been developed by using energy function and applied to the slope adjustment method. The proposed algorithm has been tested on selected IEEE bus benchmark systems. The convergence of AHNN is found to be nearly 50% faster than the non-adaptive version.  相似文献   
53.
It is very common to find meta-analyses in which some of the studies compare 2 groups on continuous dependent variables and others compare groups on dichotomized variables. Integrating all of them in a meta-analysis requires an effect-size index in the same metric that can be applied to both types of outcomes. In this article, the performance in terms of bias and sampling variance of 7 different effect-size indices for estimating the population standardized mean difference from a 2 × 2 table is examined by Monte Carlo simulation, assuming normal and nonnormal distributions. The results show good performance for 2 indices, one based on the probit transformation and the other based on the logistic distribution. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
54.
介绍了集团变分法的集团概率变量、配置熵等统计分析的理论基础及Helmholtz自由能的描述模型.提出了巨势及相对化学势的几何分析理论.讨论了应用集团变分法和巨势分析理论进行相平衡计算的过程,并分析了同结构平衡相图计算的若干实例.  相似文献   
55.
A detection-theoretic analysis of the auditory localization of dual-impulse stimuli is described, and a model for the processing of spatial cues in the echo pulse is developed. Although for over 50 years "echo suppression" has been the topic of intense theoretical and empirical study within the hearing sciences, only a rudimentary understanding of its mechanisms has emerged. In this article, psychometric functions and results from matching studies are used in developing a model that specifies the perceived position of the echo pulse as a normal deviate, with an expectation that is a logistic function of the echo delay and a variance that depends on interaural time difference. Loss of information in the echo event is quantified as a decline in the efficiency with which the binaural system receives information from the lag impulse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
56.
A significant part of the theory of one-dimensional linear shift-invariant systems is based on the concept of weighting function (or impulse response): the output is the convolution of the weighting function with the input. This paper introduces the concept of linear translation-invariant systems and uses this notion in studying impulse response, z-transforms, and transfer functions for multidimensional systems.  相似文献   
57.
Hydrolysis of Fe(OH)SO4 was carried out in the presence of metallic iron in order to prevent the formation of iron(III) oxides with strongly bonded sulphate. Under the conditions of the experiment, the products were found to be mixtures of ?-Fe2O3 and α-FeOOH. The occluded sulphate, if any, could be easily washed out with water. The hydrolysis reaction passes through an equilibrium state before coming to completion. The entropy with enthalpy of the hydrolysis corresponding to the equilibrium state were found to be 4 e.u. and 0·5 kJ/mol, respectively. The activation energy of the hydrolysis reaction was found to be 21 kJ/mol.  相似文献   
58.
环境试验与可靠性试验的关系   总被引:1,自引:1,他引:0  
从环境试验和可靠性试验的相关标准入手,详细论述了两者之间的相互关系与区别:互为补充,互为依存,共同发展,共同为保障产品的环境适应性和使用可靠性发挥作用。最后阐述了加强自然环境试验的重要性,它是检验实验结果的基本标准。  相似文献   
59.
波动方程正演模型及应用   总被引:2,自引:0,他引:2  
本采用声波方程,通过四阶有限差分近似,实现了复杂地质构造零炮距的数值模拟。中同时展示实际应用效果。  相似文献   
60.
    
In diethyl ether extracts from celeriac (Apium graveolens L. var.rapaceum) all four stereoisomers of (3a–7a)-cis-3-butylhexahydrophthalide were found to be present. The analyses were carried out by means of GC, enantioselective GC and GC-MS. The assignment of the relative configuration of the diastereomers3 and4 was accomplished by NOE difference spectroscopy.
  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