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   24459篇
  免费   1903篇
  国内免费   1004篇
电工技术   966篇
技术理论   1篇
综合类   2406篇
化学工业   3111篇
金属工艺   560篇
机械仪表   1024篇
建筑科学   2219篇
矿业工程   527篇
能源动力   507篇
轻工业   2348篇
水利工程   575篇
石油天然气   522篇
武器工业   156篇
无线电   1391篇
一般工业技术   3916篇
冶金工业   1318篇
原子能技术   237篇
自动化技术   5582篇
  2024年   88篇
  2023年   286篇
  2022年   442篇
  2021年   593篇
  2020年   666篇
  2019年   676篇
  2018年   620篇
  2017年   774篇
  2016年   845篇
  2015年   859篇
  2014年   1400篇
  2013年   1584篇
  2012年   1664篇
  2011年   1899篇
  2010年   1474篇
  2009年   1478篇
  2008年   1261篇
  2007年   1512篇
  2006年   1284篇
  2005年   1086篇
  2004年   998篇
  2003年   844篇
  2002年   728篇
  2001年   579篇
  2000年   480篇
  1999年   418篇
  1998年   398篇
  1997年   323篇
  1996年   256篇
  1995年   228篇
  1994年   192篇
  1993年   149篇
  1992年   122篇
  1991年   107篇
  1990年   106篇
  1989年   106篇
  1988年   98篇
  1987年   65篇
  1986年   61篇
  1985年   74篇
  1984年   83篇
  1983年   97篇
  1982年   96篇
  1981年   31篇
  1980年   36篇
  1979年   31篇
  1978年   24篇
  1977年   17篇
  1955年   19篇
  1954年   11篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
A review of the literature on the impact of sexual contacts between adults and boys reveals the existence of two principal outcomes: 1) some participants develop various disorders once in adulthood, such as behavioural problems, sexual disorders, or personality problems; 2) some participants do not present with any major disorders in the long run. These different outcomes may be associated with several moderating variables related to the sexual contacts, such as the level of coercion at the time of these contacts, the bond between the child and the adult, or the context of the sexual relation. However, the conclusions relating to the relations between early sexual contacts with adults and subsequent problems of adaptation in adulthood are difficult to determine. This is because of various methodological problems associated with relevant studies (i.e., definition of these contacts, nature of the sample, method evaluation, statistical analyses). In this article, we propose certain avenues of research that may help clarify this problem. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
3.
The focus of this paper lies in the practical aspects of voice over IP communication. VoIP configurations in the H.323 standard will be presented briefly. Following that, the fundamental protocol procedure of H.323 communication will be briefly explained. A further part of the paper will address the subject QoS (quality of service), and present the common measurement methods used in QoS. Results gained from experiments conducted in a VoIP environment will then follow. The investigations concentrate primarily on the load behavior of voice packets in relation to important parameters of this service. The results obtained are presented and evaluated in diagrams. The paper concludes with a summary.  相似文献   
4.
In this paper we present a numerical method for estimating the current state of a nonlinear control system. We use finite differences to discretize a modified version of the finite-time observer equations in James. The discretized equations are simple and easily programmed. The convergence and accuracy of the scheme is proved, and the scheme enjoys a number of important properties: availability of rate of convergence estimates, good robustness characteristics, and the ability to handle certain types of discontinuities in the observations. The major disadvantage is that the number of grid points required increases exponentially with the number of state dimensions.  相似文献   
5.
Work system improvements are implemented in various manufacturing processes to prevent problems caused by human errors. However, they are almost always applied to problems which have already occurred. This paper examines a method of identifying latent human errors existing within the work systems beforehand. A procedure for applying failure mode and effect analysis to this identification problem was defined based on over 1000 empirical errors: a work system decomposition criterion and fundamental error modes for listing latent human errors, and then applied to three practical manufacturing processes in order to evaluate its effectiveness.  相似文献   
6.
经济利润率是评价一个实际热力装置的主要指标之一。将有限时间热力学,非平衡量子统计理论和yong经济学相结合,导出了量子斯特林制冷机的最大利润率以及对应的性能界限,其结果与实际斯特林制冷机的优化设计和模型评估提供了一个最佳的预选方案。  相似文献   
7.
This work aims to compare numerical results obtained by using the Monte Carlo composition-PDF method and a presumed-β-PDF in order to reveal their effects on the prediction of flow and scalar fields in swirling confined methane diffusion flame. Using the intrinsic low dimensional manifolds method for modelling the chemistry and a second moment closure for the turbulence, it is shown that both PDF-methods provide a similar accuracy level of the prediction of mean quantities. While the presumed-β-PDF performs using reasonable computational efforts, the Monte Carlo-PDF allows to capture well the turbulence-chemistry interaction and strong finite-chemistry effects such as local extinction.  相似文献   
8.
应用统计控制图法,选用平均值——标准差、平均值——极差控制图法,控制24^#坝粘土填筑干密度值及施工偶然异常波动,早期提出警报,以保证土坝的施工质量。  相似文献   
9.
10.
Rainwater can collect in a lens-shaped region within the rock of a tropical island, and may be separated from the underlying salt water by a sharp interface. This paper presents a nonlinear theory for determining the shape of this interface. The island is assumed to be saturated with rain, and provision is made for the outflow of rain-water through the sides of the island. The effect of a bore well on the shape of the interface is investigated, and the problem is solved using a spectral method. An integral-equation method is also presented for the case when the island has infinite width.  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