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   260827篇
  免费   3230篇
  国内免费   823篇
电工技术   5134篇
综合类   332篇
化学工业   37408篇
金属工艺   10254篇
机械仪表   8495篇
建筑科学   6154篇
矿业工程   1079篇
能源动力   6403篇
轻工业   23040篇
水利工程   2564篇
石油天然气   3913篇
武器工业   68篇
无线电   34788篇
一般工业技术   50179篇
冶金工业   46577篇
原子能技术   5421篇
自动化技术   23071篇
  2021年   2070篇
  2019年   2058篇
  2018年   3490篇
  2017年   3556篇
  2016年   3752篇
  2015年   2331篇
  2014年   4071篇
  2013年   11333篇
  2012年   6616篇
  2011年   8929篇
  2010年   7026篇
  2009年   7875篇
  2008年   8722篇
  2007年   8647篇
  2006年   7829篇
  2005年   7162篇
  2004年   6919篇
  2003年   6755篇
  2002年   6390篇
  2001年   6483篇
  2000年   6184篇
  1999年   6259篇
  1998年   14251篇
  1997年   10280篇
  1996年   8117篇
  1995年   6419篇
  1994年   5715篇
  1993年   5591篇
  1992年   4554篇
  1991年   4219篇
  1990年   4050篇
  1989年   3782篇
  1988年   3628篇
  1987年   3172篇
  1986年   3066篇
  1985年   3611篇
  1984年   3387篇
  1983年   3031篇
  1982年   2853篇
  1981年   2960篇
  1980年   2765篇
  1979年   2650篇
  1978年   2504篇
  1977年   2945篇
  1976年   3556篇
  1975年   2319篇
  1974年   2312篇
  1973年   2321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
151.
152.
The biological decolorization of two industrial, spent textile reactive dyebaths was investigated using a suspended-growth, halophilic mixed culture fed with glucose. Dyebath I contained mainly Reactive Blue 19 (RB19), an anthraquinone dye, whereas dyebath II contained mainly Reactive Blue 21 (RB21), a phthalocyanine dye. Batch assays under anaerobic conditions with the two neutralized dyebaths resulted in 87 and 37% extent of decolorization for dyebaths I and II, respectively. The rate of glucose utilization and the extent of acetate production were impacted in the presence of each dyebath as compared to the control culture. However, dyebath decolorization occurred despite moderate culture inhibition. Reuse of a biologically renovated RB19-containing dyebath in the dyeing process resulted in reproducible but not identical cotton fabric shades as compared to a standard dyeing (i.e., control) using fresh water. This difference is attributed to a variable degree of RB19 aggregation during the dyeing process and is not related to the efficiency of the biodecolorization process. Further improvement of the redyeing efficiency will lead to the development of an in-plant, closed-loop decolorization system resulting in significant water conservation and minimization of textile pollutants such as salt and dyes.  相似文献   
153.
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   
154.
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   
155.
156.
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   
157.
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   
158.
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   
159.
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   
160.
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