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   322857篇
  免费   3544篇
  国内免费   831篇
电工技术   5035篇
综合类   2569篇
化学工业   50288篇
金属工艺   13984篇
机械仪表   10358篇
建筑科学   7562篇
矿业工程   1945篇
能源动力   6239篇
轻工业   28303篇
水利工程   3724篇
石油天然气   5425篇
武器工业   32篇
无线电   34103篇
一般工业技术   60542篇
冶金工业   47896篇
原子能技术   6196篇
自动化技术   43031篇
  2021年   2116篇
  2019年   2025篇
  2018年   17671篇
  2017年   16547篇
  2016年   13452篇
  2015年   2815篇
  2014年   4107篇
  2013年   10347篇
  2012年   9203篇
  2011年   17489篇
  2010年   14612篇
  2009年   12629篇
  2008年   14148篇
  2007年   15250篇
  2006年   6991篇
  2005年   7199篇
  2004年   6910篇
  2003年   6732篇
  2002年   6185篇
  2001年   5648篇
  2000年   5552篇
  1999年   5354篇
  1998年   12618篇
  1997年   8919篇
  1996年   6899篇
  1995年   5338篇
  1994年   4746篇
  1993年   4632篇
  1992年   3680篇
  1991年   3410篇
  1990年   3594篇
  1989年   3473篇
  1988年   3313篇
  1987年   2895篇
  1986年   2932篇
  1985年   3373篇
  1984年   3219篇
  1983年   2892篇
  1982年   2738篇
  1981年   2822篇
  1980年   2719篇
  1979年   2625篇
  1978年   2684篇
  1977年   2949篇
  1976年   3805篇
  1975年   2368篇
  1974年   2243篇
  1973年   2376篇
  1972年   1970篇
  1971年   1860篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models  相似文献   
42.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions.  相似文献   
43.
The capacitive idling converters derived from the Cuk, SEPIC, Zeta, and flyback topologies allow soft commutation of power switches without the need for additional circuitry, making it possible to increase the switching frequency while maintaining high efficiency  相似文献   
44.
45.
We present the design of E-kernel, an embedding kernel on the Victor V256 message-passing partitionable multiprocessor, developed for the support of program mapping and network reconfiguration. E-kernel supports the embedding of a new network topology onto Victor's 2D mesh and also the embedding of a task graph onto the 2D mesh network or the reconfigured network. In the current implementation, the reconfigured network can be a line or an even-size ring, and the task graphs meshes or tori of a variety of dimensions and shapes or graphs with similar topologies. For application programs having these task graph topologies and that are designed according to the communication model of E-kernel, they can be run without any change on partitions connected by the 2D mesh, line, or ring. Further, E-kernel attempts the communication optimization of these programs on the different networks automatically, thus making both the network topology and the communication optimization attempt completely transparent to the application programs. Many of the embeddings used in E-kernel are optimal or asymptotically optimal (with respect to minimum dilation cost). The implementation of E-kernel translated some of the many theoretical results in graph embeddings into practical tools for program mapping and network reconfiguration in a parallel system. E-kernel is functional on Victor V256. Measurements of E-kernel's performance on V256 are also included  相似文献   
46.
This research was supported under project No. 6.02.02/128-93 as part of the state scientific-technical program on future information technologies and systems by the Ukrainian State Committee, of Science and Technology.  相似文献   
47.
48.
49.
Carstensen and Rhodes1 have suggested that when, in stability programs, assays cannot be performed immediately after the protocol-designated storage time, then freezing them until such a time when assays can be performed would be a reasonable manner to retain the protocol schedule. They caution, however, that such a procedure may not be valid for dissolution data. The article to follow deals with real-time data showing that such a process is feasible for Nalidixic Acid tablets (and presumably for other tablets as well), and that, furthermore, the dissolution pattern would seem to be “frozen” as well.  相似文献   
50.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period  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