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   84620篇
  免费   4671篇
  国内免费   1067篇
电工技术   2273篇
技术理论   1篇
综合类   1483篇
化学工业   15801篇
金属工艺   3517篇
机械仪表   4690篇
建筑科学   3167篇
矿业工程   630篇
能源动力   3170篇
轻工业   5911篇
水利工程   601篇
石油天然气   1550篇
武器工业   119篇
无线电   13577篇
一般工业技术   15056篇
冶金工业   7332篇
原子能技术   1008篇
自动化技术   10472篇
  2024年   240篇
  2023年   983篇
  2022年   1584篇
  2021年   2507篇
  2020年   1801篇
  2019年   1750篇
  2018年   2136篇
  2017年   2216篇
  2016年   2522篇
  2015年   2316篇
  2014年   3394篇
  2013年   5264篇
  2012年   4939篇
  2011年   5846篇
  2010年   4557篇
  2009年   4797篇
  2008年   4400篇
  2007年   3806篇
  2006年   3706篇
  2005年   3191篇
  2004年   2772篇
  2003年   2529篇
  2002年   2476篇
  2001年   1877篇
  2000年   1775篇
  1999年   1822篇
  1998年   2821篇
  1997年   1933篇
  1996年   1675篇
  1995年   1324篇
  1994年   1016篇
  1993年   876篇
  1992年   676篇
  1991年   620篇
  1990年   520篇
  1989年   482篇
  1988年   415篇
  1987年   329篇
  1986年   299篇
  1985年   261篇
  1984年   232篇
  1983年   171篇
  1982年   178篇
  1981年   144篇
  1980年   142篇
  1979年   118篇
  1978年   98篇
  1977年   127篇
  1976年   168篇
  1975年   85篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
This study examined the predictive efficacy of 10 rationally derived, archivally coded variables for assessing reoffense risk among extrafamilial child molesters. Follow-up data on 111 child molesters who were discharged from the Massachusetts Treatment Center between 1960 and 1984 were used. Degree of sexual preoccupation with children, paraphilias, and number of prior sexual offenses predicted sexual recidivism. Juvenile and adult antisocial behavior, paraphilias, and low amount of contact with children predicted nonsexual victim-involved and violent recidivism. Area under the receiver-operating characteristic curves in all three analyses indicated discrimination that was substantially better than chance, ranging from .73 to .79. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
73.
Penalty interference of nonlinear propagation impairments and polarisation mode dispersion (PMD) caused signal distortions is experimentally investigated  相似文献   
74.
The widening of interest and scope of property management and maintenance has attracted a greater diversity of professional disciplines into facilities management. Dr Quah, coordinator of CIB W70 on Management, Maintenance and Modernization of Building facilities, expresses her personal views on the current fascination with the subject.  相似文献   
75.
76.
Numerous power utilities have installed advanced distributed temperature sensing (DTS) systems to measure the temperature of underground cables. This paper presents a general procedure for real-time assessment of underground cable ratings based on DTS. After the identification and location of hot spots on a cable, the cable installation data, load, and DTS-recorded temperature over a period of time are used to estimate soil thermal parameters and assess cable ratings under normal and overloading conditions. In order to accurately estimate soil thermal parameters, a combined technique of the finite-element method and gradient-based optimization is used. The technique was validated in the laboratory and applied to a rating assessment of a 230-kV/500-MVA cable circuit. The assessed continuous and emergency ratings are helpful in improving the operation of this circuit.  相似文献   
77.
Centralized and distributed automated guided vehicle system (AGVS) models for materials handling, and the model for part processing are integrated into a single coherent model. This formulation can be used to collectively schedule and control the entire flexible manufacturing system (FMS) as opposed to the traditional separate scheduling of part processing and material handling. The two AGVS models are based on Petri nets and can be directly used in the scheduling method that uses Petri nets for formulation and heuristic search for solution. This method employs a global search to seek the optimal operation of an entire FMS. Scheduling examples are presented and the method compares favorably with the results simulated using heuristic dispatch rules  相似文献   
78.
In this paper, we present a technique for using an additional parallel neural network to provide adaptive enhancements to a basic fixed neural network-based nonlinear control system. This proposed parallel adaptive neural network control system is applicable to nonlinear dynamical systems of the type commonly encountered in many practical position control servomechanisms. Properties of the controller are discussed, and it is shown that if Gaussian radial basis function networks are used for the additional parallel neural network, uniformly stable adaptation is assured and the approximation error converges to zero asymptotically. In the paper, the effectiveness of the proposed parallel adaptive neural network control system is demonstrated in real-time implementation experiments for position control in a servomechanism with asymmetrical loading and changes in the load  相似文献   
79.
In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p+-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF2-implanted device is much larger than that of the boron-implanted device  相似文献   
80.
Using ion exchange chromatography and an ATP-dependent actin precipitation step, we have isolated three myosin-I isozymes that, together, account for most of the K+EDTA-ATPase activity recovered from extracts of Dictyostelium. The two major myosin-I isozymes, present in approximately equal amounts, had apparent molecular masses of 125 kDa on SDS gels and have been identified by amino acid sequence analysis as the products of the Dictyostelium myosin-IB (DMIB) and myosin-ID (DMID) genes. DMIB, with a specific K+EDTA-ATPase activity 10-fold higher than DMID, was responsible for most of the activity in cell extracts. The third isozyme, present in low amounts, had an apparent molecular mass of 137 kDa on SDS gels and is too large to be the product of any of the known myosin-I genes. DMIB eluted from DE53 cellulose columns as two distinct peaks (II and III). Addition of the phosphatase inhibitor okadaic acid to the extraction buffer increased the fraction of DMIB recovered from growth phase cells in peak III from 35 to 70%. DMIB isolated from peak III, but not from peak II, displayed a significant level of actin-activated MgATPase activity. These results indicate that peak III represents a phosphorylated, actin-activatable form of DMIB.  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