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   954408篇
  免费   35657篇
  国内免费   18287篇
电工技术   32634篇
技术理论   49篇
综合类   26744篇
化学工业   151178篇
金属工艺   44536篇
机械仪表   41322篇
建筑科学   41140篇
矿业工程   15170篇
能源动力   25239篇
轻工业   72244篇
水利工程   13197篇
石油天然气   35452篇
武器工业   3039篇
无线电   107429篇
一般工业技术   156415篇
冶金工业   130842篇
原子能技术   16566篇
自动化技术   95156篇
  2023年   6719篇
  2022年   13506篇
  2021年   19479篇
  2020年   14528篇
  2019年   13725篇
  2018年   18482篇
  2017年   19707篇
  2016年   19434篇
  2015年   20166篇
  2014年   27755篇
  2013年   49129篇
  2012年   39411篇
  2011年   47606篇
  2010年   40228篇
  2009年   40972篇
  2008年   41351篇
  2007年   40389篇
  2006年   38484篇
  2005年   33967篇
  2004年   27146篇
  2003年   25422篇
  2002年   24175篇
  2001年   23051篇
  2000年   22144篇
  1999年   23185篇
  1998年   41127篇
  1997年   30023篇
  1996年   24163篇
  1995年   18497篇
  1994年   16118篇
  1993年   14833篇
  1992年   11102篇
  1991年   10062篇
  1990年   9815篇
  1989年   9288篇
  1988年   8624篇
  1987年   7348篇
  1986年   7183篇
  1985年   7799篇
  1984年   7266篇
  1983年   6605篇
  1982年   5952篇
  1981年   6156篇
  1980年   5675篇
  1979年   5704篇
  1978年   5533篇
  1977年   6088篇
  1976年   7941篇
  1975年   4832篇
  1973年   4593篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Network fault identification is an important network management function, which is closely related to fault management and has an impact on other network management functions such as configuration management, and performance management. This paper investigates fault surveillance and fault identification mechanisms for a transparent optical network in which data travels optically from the source node to the destination node without going through any optical-to-electrical (O/E) or electrical-to-optical (E/O) conversion. Mechanisms and algorithms are proposed to detect and isolate faults such as fiber cuts, laser, receiver, or router failures. These mechanisms allow nonintrusive device monitoring without requiring any prior knowledge of the actual protocols being used in the data transmission  相似文献   
72.
The three-dimensional structure of glutathione S-transferase from Arabidopsis thaliana has been solved at 2.2 A resolution (Reinemer et al., 1996). The enzyme forms a dimer of two identical subunits. The structure shows a new G-site architecture and a novel and unique dimer interface. Each monomer of the protein forms a separate G-site. Therefore, the requirements on the dimer interface are reduced. As a consequence, the interactions between the monomers are weaker and residues at the dimer interface are more variable. Thus, the dimer interface looses its relevance for a classification of plant glutathione S-transferases and the formation of heterodimers becomes even more difficult to predict.  相似文献   
73.
74.
75.
Malignant bone pain: pathophysiology and treatment   总被引:1,自引:0,他引:1  
2-acetyl aminofluorene (AAF) reacts in acidic conditions with nitrous fume yielding N-nitroso-AAF (N-NO-AAF), as previously described, that exerts more toxic and mutagenic effects than its parental compound. In this study, the effect of sodium nitrite (NaNO2) on the tumorigenicity of AAF in rats fed with AAF and NaNO2 was observed. Wistar rats were divided into five groups: group I served as control; group II were treated with NaNO2 (0.3%); group III was given 0.02% AAF alone; groups IV and V received both AAF and NaNO2 (0.2 and 0.3% respectively) in their diet for 12 weeks. At the end of the experiment, all rats in groups III, IV and V developed early stage phenomena of hepatocellular carcinoma, including hepatomegaly with variable-sized foci and neoplastic nodules. Severe damage was observed in the rats treated with AAF and NaNO2. Feeding of AAF (0.02%) for 3 months elevated the levels of c-Fos, c-Jun and c-Myc proteins in the rat livers. The AAF-induced c-Jun, c-Fos and c-Myc expressions were significantly magnified (P < 0.001) by NaNO2. These data confirmed that the strengthening of AAF-induced hepatocarcinogenesis by NaNO2 should be associated with its enhancing effect on the AAF-induced increases in the expressions of c-Jun, c-Fos and c-Myc.  相似文献   
76.
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features  相似文献   
77.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications  相似文献   
78.
Uses a Markov process to model a real-time expert system architecture characterized by message passing and event-driven scheduling. The model is applied to the performance evaluation of rule grouping for real-time expert systems running on this architecture. An optimizing algorithm based on Kernighan-Lin heuristic graph partitioning for the real-time architecture is developed and a demonstration system based on the model and algorithm has been developed and tested on a portion of the advanced GPS receiver (AGR) and manned manoeuvring unit (MMU) knowledge bases  相似文献   
79.
80.
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