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   4388篇
  免费   199篇
  国内免费   12篇
电工技术   99篇
综合类   26篇
化学工业   700篇
金属工艺   97篇
机械仪表   111篇
建筑科学   191篇
矿业工程   10篇
能源动力   180篇
轻工业   401篇
水利工程   34篇
石油天然气   17篇
武器工业   1篇
无线电   735篇
一般工业技术   810篇
冶金工业   479篇
原子能技术   43篇
自动化技术   665篇
  2023年   32篇
  2022年   58篇
  2021年   83篇
  2020年   67篇
  2019年   72篇
  2018年   109篇
  2017年   135篇
  2016年   123篇
  2015年   108篇
  2014年   172篇
  2013年   314篇
  2012年   238篇
  2011年   261篇
  2010年   202篇
  2009年   209篇
  2008年   216篇
  2007年   186篇
  2006年   184篇
  2005年   132篇
  2004年   133篇
  2003年   114篇
  2002年   111篇
  2001年   79篇
  2000年   80篇
  1999年   96篇
  1998年   202篇
  1997年   140篇
  1996年   84篇
  1995年   76篇
  1994年   65篇
  1993年   81篇
  1992年   47篇
  1991年   27篇
  1990年   34篇
  1989年   22篇
  1988年   21篇
  1987年   20篇
  1986年   12篇
  1985年   15篇
  1984年   20篇
  1983年   15篇
  1982年   13篇
  1981年   21篇
  1980年   15篇
  1979年   12篇
  1977年   19篇
  1976年   19篇
  1975年   17篇
  1974年   12篇
  1973年   10篇
排序方式: 共有4599条查询结果,搜索用时 31 毫秒
21.
We have employed polyclonal antibodies to a peptide sequence of bovine steroidogenic acute regulatory (StAR) protein and human placental 3beta-hydroxysteroid dehydrogenase (3beta-HSD) to determine the localisation and distribution of these proteins in rat and bovine adrenal glands. Immunohistochemical staining demonstrated the presence of StAR protein in the zona glomerulosa (ZG), zona fasciculata (ZF), zona reticularis (ZR) and in the medulla of both species. For 3beta-HSD, immunostaining was observed in the ZG, ZF and ZR of the rat adrenal and was absent in the medulla. Immunoblotting experiments showed intense bands for StAR protein (30 kDa, 37 kDa) in the mitochondria of bovine ZG, ZF and medulla and a less intense band (30 kDa) in the microsomes. In rat ZG and ZF/R mitochondria only the 30 kDa protein was present. For 3beta-HSD, an intense band (42 kDa) was found in microsomes and mitochondria of rat and bovine ZG and ZFR. A very faint signal for 3beta-HSD was seen in adrenal medulla. In conclusion, StAR (or a closely related) protein is present throughout the adrenal gland in rat and bovine species in contrast to 3beta-HSD which is confined to the steroidogenic zones. The possible function of StAR protein in the adrenal medulla merits investigation.  相似文献   
22.
The tone sense multiaccess with partial collision detection (TSMA/PCD) protocol is particularly suitable for a packet satellite system serving an area with a dense population of earth stations. By incorporating a narrowband ground radio channel for broadcasting busy ones, the earth stations are able to avoid packet collisions by sensing for the absence of busy tones before transmitting packets. Partial collision detection capability can also be achieved. Single-tone TSMA/PCD gives 97% of the carrier-sense multiaccess with collision detection (CSMA/CD) throughput when N=10 tones are used, while for multitone and slot-by-slot announcement TSMA/PCD protocols only N=8 and N=2, respectively, are sufficient to drive the system to the CSMA/CD performance  相似文献   
23.
As opposed to the analytic approach used in the modern theory of optimal filtering, a synthetic approach is presented. The signal/sensor data, which are generated by either computer simulation or actual experiments, are synthesized into a filter by training a recurrent multilayer perceptron (RMLP) with at least one hidden layer of fully or partially interconnected neurons and with or without output feedbacks. The RMLP, after adequate training, is a recursive filter optimal for the given structure, with the lagged feedbacks carrying the optimal conditional statistics at each time point. Above all, it converges to the minimum variance filter as the number of hidden neurons increases. We call such an RMLP a neural filter. Simulation results show that the neural filters with only a few hidden neurons consistently outperform the extended Kalman filter and even the iterated extended Kalman filter for the simple nonlinear signal/sensor systems considered.  相似文献   
24.
Osteomyelitis in uncommon locations can present unusual diagnostic difficulties. A patient with primary sternal osteomyelitis who presented with pain over the right supraclavicular area and a radiologic picture of a pleural-based right upper lung mass is discussed. A triple-phase bone scan was consistent with the diagnosis, and a needle aspiration of the mass revealed a staphylococcal abscess. Percutaneous drainage of the contiguous abscess and a prolonged course of antibiotic therapy cured the infection.  相似文献   
25.
26.
The Mn0.23Ga1.85S3 phase belongs to the solid solution ф0, stable at low temperature in the Ga2S3MnS system. It is hexagonal superstructure of the wurtzite, with the Ga2S3α′ type (a = 6.397 A?; c = 18.027 A?Z = 6; space groupe P61 or P65). Its crystal structure has been refined by the least squares method to a final R = 0.06 with 323 independant reflections. This structure is closely related to Ga2S3 α described by Hahn and Frank, and differs only by the partial occupation of the vacant metal site of Ga2S3 by Mn atoms in statistical disorder.  相似文献   
27.
28.
In this paper we consider two performance modelling techniques from the perspectives of model construction, generation of an underlying continuous time Markov process, and the potential for reduction in the Markov process. Such careful comparison of modelling techniques allows us to appreciate the strengths and weaknesses of different approaches, and facilitates cross-fertilization between them. In the present case we take a characteristic of one formalism, functional rates in Stochastic Automata Networks, and introduce it to the other formalism, Performance Evaluation Process Algebra. We investigate the benefits of this cross-fertilization, particularly from the perspectives of Markov process generation and reduction.  相似文献   
29.
This paper tests the assertion that experienced contractors are more competitive than inexperienced contractors by measuring the effect of experience on bidding competitiveness for building contracts procured by a regular client. Contractors are grouped into experienced and inexperienced contractors, and two levels of contractors’ experience are identified: (1) bidding experience only and (2) bidding plus construction experience. Results of two-sample t tests show that experienced contractors are more competitive than inexperienced contractors. Contractors’ competitiveness in respect of school contracts and other contracts are further compared in evaluating the relationship between the project type and experience effect. Experienced contractors are, on average, more competitive in competing for school contracts. It emerges that the factor of project type familiarity amplifies the experience effect. A comparison of experienced contractors’ competitiveness in bidding for (1) new building works and (2) alteration and extension works shows that the effect of experience would be more significant when contract works packages are highly standardized.  相似文献   
30.
The General Packet Radio Service (GPRS) provides a packet switched data service for mobile users. However, the existing GPRS specification does not provide the push mechanism and it is difficult to support GPRS services such as call termination (incoming call) for wireless voice over IP (VoIP). Based on the short message service, this paper proposes a push mechanism for GPRS supporting private IP addresses. Our approach does not need to modify the existing GPRS structure.  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