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   260714篇
  免费   3237篇
  国内免费   823篇
电工技术   5152篇
综合类   330篇
化学工业   37424篇
金属工艺   10280篇
机械仪表   8497篇
建筑科学   6115篇
矿业工程   1077篇
能源动力   6414篇
轻工业   23017篇
水利工程   2563篇
石油天然气   3910篇
武器工业   68篇
无线电   34744篇
一般工业技术   50183篇
冶金工业   46547篇
原子能技术   5425篇
自动化技术   23028篇
  2021年   2074篇
  2019年   2053篇
  2018年   3506篇
  2017年   3565篇
  2016年   3769篇
  2015年   2351篇
  2014年   4086篇
  2013年   11333篇
  2012年   6610篇
  2011年   8913篇
  2010年   7011篇
  2009年   7882篇
  2008年   8708篇
  2007年   8632篇
  2006年   7822篇
  2005年   7146篇
  2004年   6895篇
  2003年   6741篇
  2002年   6378篇
  2001年   6473篇
  2000年   6177篇
  1999年   6254篇
  1998年   14242篇
  1997年   10269篇
  1996年   8114篇
  1995年   6414篇
  1994年   5714篇
  1993年   5586篇
  1992年   4558篇
  1991年   4216篇
  1990年   4052篇
  1989年   3784篇
  1988年   3634篇
  1987年   3175篇
  1986年   3070篇
  1985年   3611篇
  1984年   3389篇
  1983年   3038篇
  1982年   2854篇
  1981年   2953篇
  1980年   2766篇
  1979年   2654篇
  1978年   2502篇
  1977年   2946篇
  1976年   3555篇
  1975年   2318篇
  1974年   2313篇
  1973年   2319篇
  1972年   1849篇
  1971年   1745篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Performance properties are established for the dissemination by flooding of a database that is initially distributed among the nodes of a communications network. An example of this general process is the dissemination of network status information as a component of the adaptive routing mechanism in a network like Arpanet. Bounds are given on the progress of the dissemination process at a sequence of times before the completion of the process, whereas earlier results only bounded the time until completion. The present bounds further extended earlier analysis by treating the diameter explicitly as a parameter. Specialized versions of the bounds are given for k-connected networks. The bounds yield a recognition property whereby a node can recognize that it has received the entire database without having a priori knowledge of the size of the database. An earlier assumption about a fixed time for correct message transmission over any edge is relaxed to assume only an upper bound on these transmission times  相似文献   
102.
This paper presents results of reliability investigation of 20 V N-Drift MOS transistor in 0.13 μm CMOS technology. Due to high performances required for CMOS applications, adding high voltage devices becomes a big challenge to guarantee the reliability criteria. In this context, new reliability approaches are needed. Safe Operating Area are defined for switch, Vds limited and Vgs limited applications in order to improve circuit designs. For Vds limited applications, deep doping dose effects in drift area are investigated in correlation to lifetime evaluations based on device parameter shifts under hot carrier stressing. To further determine the amount and locations of hot carriers injections, accurate 2D technological and electrical simulations are performed and permit to select the best compromise between performance and reliability for N-Drift MOS transistor.  相似文献   
103.
104.
The US Centers for Disease Control and Prevention (CDC) created the Public Health Information Network to advance fully capable, interoperable information systems in public health organizations. PHIN prioritizes public health information systems' functional requirements, capabilities, performance measures, and operational characteristics while letting the architects of those systems choose enabling approaches, methods, and concepts to meet the requirements. PHIN also provides a certification process for public health administrators to evaluate their information infrastructure's quality. The certification process is important because affected organizations often depend on certification for continued funding.  相似文献   
105.
A construction of a globally asymptotically stable time-invariant system which can be destabilized by some integrable perturbation is given. Besides its intrinsic interest, this serves to provide counterexamples to an open question regarding Lyapunov functions.  相似文献   
106.
When we test boards, we usually think in terms of traditional electrical test (in-circuit, flying probe) and nonelectrical test (optical, x-ray). This Orebro University article develops an alternative, connectionless technique based on scanning the electromagnetic field generated by active on-board devices. Could this make it into industry as an additional diagnostic tool?.  相似文献   
107.
An algorithm, 'phylogenetic scanning', is described for mapping gene conversion events where comparative DNA sequence data are available from different species. In this algorithm, sets of hypothetical phylogenetic trees are constructed that describe possible sequence relationships due to gene conversions in different species lineages; these trees are then evaluated by the principle of parsimony at intervals in the sequence alignment. When used to map gene conversion events that occurred between the pair of gamma-globin genes of higher primates, the algorithm gives results nearly identical to those obtained using a tedious manual approach. Suggestions are also provided for adaptation of this procedure to the analysis of other recombination events.  相似文献   
108.
109.
An investigation of the effect of reaction conditions on product distribution in the skeletal isomerisation reaction of linear butenes has been carried out. The main reaction routes over ferrierite have been identified. Beside the main product isobutene, major by-product formation occurs. The unwanted reactions include dimerisation of butene to form octenes, hydrogen transfer yielding small amounts of saturated C3 and C4 hydrocarbons and disproportionation producing propene and pentenes. The most abundant by-products were pentene and propene, though these were not formed in equimolar amounts as could be expected. Oligomerisation experiments of propene over ferrierite produced large amounts of butene and pentene, revealing the presence of adsorbed nonene. The cracking of this surface species to hexene and propene is the most likely reaction route for the excess propene formation. This additional path to propene formation operates mainly at temperatures above 623 K.  相似文献   
110.
The Metaflow architecture, a unified approach to maximizing the performance of superscalar microprocessors, is introduced. The Metaflow architecture exploits inherent instruction-level parallelism in conventional sequential programs by hardware means, without relying on optimizing compilers. It is based on a unified structure, the DRIS (deferred-scheduling, register-renaming instruction shelf), that manages out-of-order execution and most of the attendant problems. Coupling the DRIS with a speculative-execution mechanism that avoids conditional branch stalls results in performance limited only be inherent instruction-level parallelism and available execution resources. Although presented in the context of superscalar machines, the technique is equally applicable to a superpipelined implementation. Lightning, the first implementation of the Metaflow architecture, which executes the Sparc RISC instruction set is described  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