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   595503篇
  免费   23429篇
  国内免费   12415篇
电工技术   22241篇
技术理论   4篇
综合类   14616篇
化学工业   86866篇
金属工艺   25767篇
机械仪表   23942篇
建筑科学   26185篇
矿业工程   6560篇
能源动力   16707篇
轻工业   57329篇
水利工程   7634篇
石油天然气   10391篇
武器工业   2026篇
无线电   77366篇
一般工业技术   96953篇
冶金工业   84425篇
原子能技术   7655篇
自动化技术   64680篇
  2023年   3506篇
  2022年   7087篇
  2021年   10398篇
  2020年   7581篇
  2019年   6980篇
  2018年   8950篇
  2017年   9981篇
  2016年   9432篇
  2015年   11221篇
  2014年   15624篇
  2013年   31502篇
  2012年   23898篇
  2011年   29155篇
  2010年   24654篇
  2009年   25592篇
  2008年   26455篇
  2007年   26182篇
  2006年   23600篇
  2005年   20478篇
  2004年   17579篇
  2003年   16421篇
  2002年   15853篇
  2001年   15569篇
  2000年   13835篇
  1999年   13718篇
  1998年   26604篇
  1997年   19620篇
  1996年   15706篇
  1995年   12395篇
  1994年   10926篇
  1993年   10129篇
  1992年   7697篇
  1991年   7258篇
  1990年   6755篇
  1989年   6439篇
  1988年   6092篇
  1987年   5042篇
  1986年   4963篇
  1985年   6056篇
  1984年   5663篇
  1983年   4878篇
  1982年   4541篇
  1981年   4511篇
  1980年   4260篇
  1979年   4110篇
  1978年   3786篇
  1977年   4564篇
  1976年   6121篇
  1975年   3131篇
  1974年   3019篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
71.
在英国伦敦多克兰斯轻便铁路刘易舍姆延长线(DLR-LWE)双隧道掘进工程中,在敏感建筑物下进行了补偿灌浆,以防止隧道开挖引起的过度沉降。但是,过度灌浆也会对隧道下部施加超越。介绍了由隧道掘进承包商所编辑的关于地面和建筑物沉降以及由补偿灌浆引起的隧道衬砌变形的详细现场监测数据。  相似文献   
72.
恢复城市水环境的自然生态   总被引:5,自引:0,他引:5  
为了确保城市社会经济的可持续发展,城市的水资源管理是重要的一环,而且,这项管理会逐步从防洪、水资源利用的量的管理向水质管理、空间管理和生态体系的保护等综合管理发展,其中恢复河流清澈、优美的自然生态,科学有效地建设城市水环境是个需要研究的大课题.  相似文献   
73.
Functional Properties and Food Applications of Rapeseed Protein Concentrate   总被引:1,自引:0,他引:1  
Rapeseed protein concentrate (RC), prepared with 2% hexameta-phosphate, was tested for its functionality and performance in some foods. The RC had good nitrogen solubility, fat absorption, emulsification, and whipping capacities but poor water absorption and gelling properties. It increased the emulsion stability, and protein but lowered the fat content of wieners. It also increased the cooking yield, reduced the shrinkage and tenderized meat patties. Results were similar to soybean isolate except for the poorer color and flavor. The cooking yield of RC supplemented wieners was less than the all-meat control and soybean-supplemented wieners. A 9% RC dispersion mixed with an equal volume of eggwhite produced a meringue of comparable stability and texture to that of eggwhite alone.  相似文献   
74.
J. Perahia comments on the paper by J. S. Hsu (see ibid., vol.16, p.192-7, 2001) and expands on the case of a two stator three phase squirrel cage induction machine where one stator housing is stationary and other stator housing is mounted on a worm gear assembly. The original author replies to the comments  相似文献   
75.
An investigation into the effects of pressure (helium gas) on the isothermal fluid behavior includes: (1) the effect of pressure on the rate of melting and coking as evidenced by the rate constants k(melt) and k(coke); (2) the effect of pressure on the energies of activation of melting and coking; (3) the effects of pressure on the characteristic times; (4) the effects of pressure on the maximum isothermal fluidity. Results from the effects of pressure on k(melt) revealed that it was generally the high total sulfur, low nitrogen, low reactives/mineral matter ratio, medium rank coals which show the greatest increase in k(melt), whereas the highest rank coals show the least decrease in k(coke). The energies of activation of melting and coking were not significantly affected by pressure. The investigation also reveals increases or decreases in the respective times of softening, maximum fluidity, resolidification and total time of fluid behavior under isothermal pressurized conditions. There appears the possibility that these shifts may be rank dependent. Additionally, the lower rank coals show the largest relative increase in their fluidities when subjected to pressure. Empirical relationships were derived in order to quantitatively predict the maximum isothermal fluidity for most (fluid) coals at a given pressure.  相似文献   
76.
77.
This paper demonstrates the use of computer simulation for topological design and performance engineering of transparent wavelength-division multiplexing metropolitan-area networks. Engineering of these networks involves the study of various transport-layer impairments such as amplifier noise, component ripple, chirp/dispersion, optical crosstalk, waveform distortion due to filter concatenation, fiber nonlinearities, and polarization effects. A computer simulation methodology composed of three main simulation steps is derived and implemented. This methodology obtains performance estimations by applying efficient wavelength-domain simulations on the entire network topology, followed by time-/frequency-domain simulations on selected paths of the network and finally Q-budgeting on an identified worst case path. The above technique provides an efficient tool for topological design and network performance engineering. Accurate simulation models are presented for each of the performance impairments, and the computer simulation methodology is used for the design and engineering of a number of actual metro network architectures  相似文献   
78.
In this work, a quantitative analysis is applied to resolve the newly reported polarity-dependent charge-to-breakdown (Q/sub BD/) data from thick oxides of 6.8 nm down to ultrathin oxides of 1.9 nm. Three independent sets of Q/sub BD/ data, i.e., n/sup +/poly/NFET stressed under inversion and accumulation, and p/sup +/ poly/PFET under accumulation are carefully investigated. The Q/sub BD/ degradation observed for p-type anodes, either poly-Si or Si-substrate, can be nicely understood with the framework of maximum energy released by injected electrons. Thus, this work provides a universal and quantitative account for a variety of experimental observations in the time-to-breakdown (T/sub BD/) and Q/sub BD/ polarity-dependence of oxide breakdown.  相似文献   
79.
We have studied the optical power losses due to multiple curvatures in polymethylmetacrylate (PMMA) plastic optical fibers (POFs) of different numerical apertures (NAs) and attenuation. The fibers were tested for several configurations in order to assess the influence of different types of curved-to-straight fiber transitions in the amount of power radiation. We found that losses are below the standards for all tested fiber types, and thus, they are a suitable choice for local area network (LAN) applications. In addition, our results revealed the presence of modal interactions as confirmed using an experimental procedure to estimate the mode coupling strength for the same fibers.  相似文献   
80.
威维霍抽水蓄能电站对昆士兰电网及其业主塔朗能源公司起着重要作用。  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