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   554447篇
  免费   6489篇
  国内免费   1775篇
电工技术   10132篇
综合类   442篇
化学工业   81776篇
金属工艺   22077篇
机械仪表   17759篇
建筑科学   12261篇
矿业工程   3180篇
能源动力   15333篇
轻工业   41709篇
水利工程   5971篇
石油天然气   10707篇
武器工业   23篇
无线电   65926篇
一般工业技术   111739篇
冶金工业   105200篇
原子能技术   12479篇
自动化技术   45997篇
  2021年   5057篇
  2020年   3799篇
  2019年   4899篇
  2018年   8271篇
  2017年   8300篇
  2016年   8803篇
  2015年   5645篇
  2014年   9330篇
  2013年   26604篇
  2012年   14974篇
  2011年   20268篇
  2010年   16151篇
  2009年   18269篇
  2008年   18697篇
  2007年   18481篇
  2006年   16413篇
  2005年   14838篇
  2004年   14107篇
  2003年   14032篇
  2002年   13129篇
  2001年   13121篇
  2000年   12486篇
  1999年   13020篇
  1998年   33263篇
  1997年   23066篇
  1996年   17795篇
  1995年   13170篇
  1994年   11738篇
  1993年   11578篇
  1992年   8508篇
  1991年   8026篇
  1990年   7844篇
  1989年   7580篇
  1988年   7227篇
  1987年   6358篇
  1986年   6138篇
  1985年   6978篇
  1984年   6383篇
  1983年   5856篇
  1982年   5306篇
  1981年   5521篇
  1980年   5032篇
  1979年   5026篇
  1978年   5013篇
  1977年   5678篇
  1976年   7533篇
  1975年   4317篇
  1974年   4076篇
  1973年   4145篇
  1972年   3436篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
891.
892.
An a posteriori (off-line) approach to the simultaneous detection and identification of quasi-periodic fragments in a numerical sequence using their segments is analyzed. The solution of the problem is proposed for the case when the number of the desired fragments is known. The following assumptions are made. (i) Each desired fragment of the numerical sequence coincides with an element of the given alphabet of the reference sequences that have equal lengths (i.e., number of elements). (ii) Only a segment (part) of the desired fragment can be processed; unprocessable parts of the fragment are interpreted as lost data. (iii) The numbers of the elements in the sequence that correspond to the beginning of the desired fragment and the boundaries of the segment in the fragment represent deterministic (rather than random) quantities; the boundaries of the segments are different for different fragments; and the desired fragments are quasi-periodic in the sequence. (iv) Gaussian uncorrelated noise impedes the observation of the sequence that contains quasi-periodic segments of the reference sequences. It is demonstrated that the essence of the problem under study lies in the verification of a set of hypotheses on the mean value of a random Gaussian vector (the power of this set exponentially increases with an increase in the dimension of the vector—the sequence length). An effective a posteriori algorithm that provides for maximum-likelihood detection and identification is validated. The estimates of the time and space complexity are related to the parameters of the problem. The results of the numerical simulation are presented. This work was supported by the Russian Foundation for Basic Research, project no. 03-01-00036 and 06-01-00058. Aleksandr V. Kel’manov. Born April 25, 1952. Graduated from Izhevsk State Technical University in 1974. Received candidate’s degree in 1980 and doctoral degree in 1994. Leading researcher of the Sobolev Institute of Mathematics, Siberian Division, Russian Academy of Sciences. Scientific interests: mathematical methods for pattern recognition; discrete optimization; effective algorithms for the analysis and recognition of random sequences; algorithms for the solution of applied problems; and methods and algorithms for the processing, recognition, and synthesis of voice signals. Author of more than 120 papers. Sergei A. Khamidullin. Born March 28, 1952. Graduated from Novosibirsk State University in 1974. Received candidate’s degree in 1997. Senior researcher of the Sobolev Institute of Mathematics, Siberian Division, Russian Academy of Sciences. Scientific interests: mathematical methods for pattern recognition; discrete optimization; effective algorithms for the analysis and recognition of random sequences; algorithms for the solution of applied problems; and methods and algorithms for the processing, recognition, and synthesis of voice signals. Author of more than 80 papers.  相似文献   
893.
This paper presents a simplified analytical model of a silicon-controlled-rectifier based, load-commutated inverter driven, commutatorless series motor to predict its speed-current, torque-current and torque-speed characteristics. The model has been formulated, keeping in view the steady state equivalent circuit of a conventional DC series motor. The proposed analytical expressions relating torque and current with speed are found to follow an inverse law and that relating torque and current is found to be parabolic, as is expected in a "series" machine. The drive has been implemented, loaded with a DC generator and experimentally similar characteristics have been obtained, as predicted by the analytical model. The characteristics obtained experimentally are seen to follow the ones, predicted by the analytical model closely  相似文献   
894.
It is established that bismuth crystals under the simultaneous action of a constant magnetic field and current pulses exhibit a correlation between the microhardness and the mobility of twinning dislocations. It is shown that application of the external fields favors translation of the twinning dislocations along the twin-matrix boundaries.  相似文献   
895.
Manufacture of polyvinyl chloride (PVC) in western Europe for all applications is now almost 4 m tonnes and the UK accounts for about 400 kt of this.The aim of this paper is to illustrate the relative importance of PVC as a packaging material where, in the UK for example, for food packaging it accounts for almost 40 kt (10%) of the PVC used.The different types of PVC packaging material—bottles, foil, cling film and cap sealing—and their method of manufacture are described, together with the range of food packaging applications in which they are used. The physical properties of PVC are described and, additionally, its cost and competitiveness with other materials are compared. The chemical nature of PVC compositions arising from the addition of heat stabilisers and plasticisers to achieve the desired properties is also described, with particular reference to heat stability.With the VCM toxicity issue now behind us, and PVC polymer with a maximum level of 1 ppm vinyl chloride monomer (VCM) being supplied for food packaging, PVC must be the most stringently controlled and thoroughly researched material for food packaging. Recent developments in polymerisation technology and polymer manufacture, which have enabled this level to be achieved, are briefly described.The current situation on the global migration issue, on which attention is currently focused, not only for plasticised PVC, but also other packaging materials as well, is briefly reviewed.  相似文献   
896.
The microscopic structures of PLZT(7.9/70/30 and x/65/35, x = 7 or 8) ceramics were studied by means of transmission electron microscopy. The presence of micro-regions in PLZTs was first verfied.  相似文献   
897.
898.
899.
The indirect immunofluorescent technique was used to study the distribution of the ascitic fluid antigen (AgD) on histological sections from surgical specimens of gastric and colon tumours from proximal to distal lines of resection. AgD was found in gastric tumours exceptionally in the tumour area and in colon cancer--both in the tumour stroma and in surrounding histologically normal mucosa.  相似文献   
900.
We describe a compositional framework, together with its supporting toolset, for hardware/software co-design. Our framework is an integration of a formal approach within a traditional design flow. The formal approach is based on Interval Temporal Logic and its executable subset, Tempura. Refinement is the key element in our framework because it will derivefrom a single formal specification of the system the software and hardware parts of the implementation, while preserving all properties of the system specification. During refinement simulation is used to choose the appropriate refinement rules, which are applied automatically in the HOL system. The framework is illustrated with two case studies. The work presented is part of a UK collaborative research project between the Software Technology Research Laboratory at the De Montfort University and the Oxford University Computing Laboratory.  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