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   832696篇
  免费   9653篇
  国内免费   2048篇
电工技术   15445篇
综合类   723篇
化学工业   127938篇
金属工艺   33281篇
机械仪表   26505篇
建筑科学   18614篇
矿业工程   5419篇
能源动力   22555篇
轻工业   64722篇
水利工程   9610篇
石油天然气   18222篇
武器工业   46篇
无线电   93304篇
一般工业技术   168317篇
冶金工业   149997篇
原子能技术   19158篇
自动化技术   70541篇
  2021年   7983篇
  2020年   6162篇
  2019年   7375篇
  2018年   12566篇
  2017年   12686篇
  2016年   13382篇
  2015年   8582篇
  2014年   14320篇
  2013年   39191篇
  2012年   22543篇
  2011年   30723篇
  2010年   24536篇
  2009年   27552篇
  2008年   28058篇
  2007年   27667篇
  2006年   24249篇
  2005年   21920篇
  2004年   20922篇
  2003年   20689篇
  2002年   19671篇
  2001年   19282篇
  2000年   18300篇
  1999年   18576篇
  1998年   45422篇
  1997年   32210篇
  1996年   25004篇
  1995年   18902篇
  1994年   16911篇
  1993年   16709篇
  1992年   12496篇
  1991年   11896篇
  1990年   11757篇
  1989年   11344篇
  1988年   10779篇
  1987年   9732篇
  1986年   9370篇
  1985年   10697篇
  1984年   9732篇
  1983年   9102篇
  1982年   8277篇
  1981年   8446篇
  1980年   7895篇
  1979年   7955篇
  1978年   7792篇
  1977年   8792篇
  1976年   11174篇
  1975年   6899篇
  1974年   6620篇
  1973年   6725篇
  1972年   5684篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Bulletin of Engineering Geology and the Environment - It has been found that during construction of the dam, prior to the filling of the reservoir, compaction and loading of the rocks under the...  相似文献   
92.
The growth of algae and occurrence of algal “blooms” in a number of different waters are described.They cover the period 1930–1940 when only natural phosphates would be present.The waters were drawn from either protected catchments or from a fully treated domestic supply.Spasmotic blooms in a fully treated domestic supply suggest that the mechanism which “triggers” the start of an algal bloom may be neither nutrient concentration nor the concentration of organic matter.It is considered that the pH, alkalinity, carbon dioxide equilibrium condition is a major factor, not only in promoting, but also in maintaining algal blooms.  相似文献   
93.
The computer model developed has been used successfully for studying the large pipe-bending problem frequently encountered in offshore structural engineering. The pipe-soil interaction is modelled by using the Coulomb friction law. The modified finite element approach coupled with a modified tangent stiffness procedure is used to handle the nonlinearities (geometric and material, etc.) in the problem. The material nonlinearity has been considered both by the plastic-hinge method and by an elastic-plastic method. Before studying the practical problems, sufficient check problems were analysed and a good agreement was found between theoretically exact solutions and the results obtained from the developed computer model.  相似文献   
94.
Isotropic multistory buildings are the ones characterized by the property: all load‐resisting planar frames have proportional lateral stiffness matrices. In the present paper it is proved that the modal analysis of an N‐story isotropic asymmetric, torsionally coupled, building (a problem of order 3N) can be separated into two independent sub‐problems: (a) a sub‐problem that corresponds to a single‐story asymmetric, torsionally coupled, building (a problem of order 3); and (b) a sub‐problem that corresponds to an N‐story, torsionally uncoupled, planar frame (a problem of order N). It is also demonstrated that the orientation of peak modal seismic forces of the building is independent of the orientation of seismic excitation, which affects only their size. The separation provides a better insight into the structural behavior of asymmetric multistory buildings under earthquake ground motion. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
95.
The weatherability of the basalts in the Capivara Dam site, Rio Paranapanema, São Paulo State, Brazil, has been studied by means of saturation-drying tests. A great number of samples have disaggre — gated intensively with production of fines. The behavior of these rocks is related to their petrography, especially to their content in expansive clay minerals. These studies were performed in order to obtain data for the utilization of this material as rock fill, including ripraps.  相似文献   
96.
In cooperation with Mayor Daley's Committee to investigate the McCormick Place Fire, Underwriters' Laboratories tested the effectiveness of automatic sprinkler systems in a simulated exhibition hall having ceiling heights of 30 ft and 50 ft. The results may prove surprising to some who doubt the value of sprinklers in high-ceilinged structures, such as McCormick Place. Fire Protection Department Underwriters' Laboratories, Inc.  相似文献   
97.
Rolling Dynamic Compaction(RDC),which is a ground improvement technique involving non-circular modules drawn behind a tractor,has provided the construction industry with an improved ground compaction capability,especially with respect to a greater influence depth and a higher speed of compaction,resulting in increased productivity. However,to date,there is no reliable method to predict the effectiveness of RDC in a range of ground conditions. This paper presents a new and unique predictive tool developed by means of artificial neural networks(ANNs) that permits a priori prediction of density improvement resulting from a range of ground improvement projects that employed 4-sided RDC modules;commercially known as"impact rollers". The strong coefficient of correlation(i.e. R0.86) and the parametric behavior achieved in this study indicate that the model is successful in providing reliable predictions of the effectiveness of RDC in various ground conditions.  相似文献   
98.
To assess the dose of UV light needed to achieve specified levels of Giardia spp. cysts and Cryptosporidium spp. oocysts inactivation in drinking water, a Bayesian meta-analysis is used to analyze experimental data from several studies. Of the 20 studies identified by an extensive data collection effort, 14 (five reported experiments on Giardia and nine on Cryptosporidium) were selected for analysis based on a set of criteria. A substantial amount of the log inactivation data are reported as greater than a given inactivation level (i.e., censored data). The Bayesian hierarchical modeling approach used in this study not only properly addresses the common concerns in a meta-analysis but also provides a robust method for incorporating censored data. Different statistical models will result in different estimates of the UV doses needed to achieve a specific inactivation level. The Bayesian approach allows us to present the uncertainty in terms of risk, which is better suited for supporting US EPA in developing regulations.  相似文献   
99.
Trace element analysis of Cretan wines and wine products   总被引:2,自引:0,他引:2  
The object of this research is to investigate the ways and the degree of contamination of Cretan grapes from the area of Chania and their alcoholic products, with the elements aluminium, arsenic, cadmium, copper, chromium, iron, lead, manganese, nickel and zinc. Fifteen samples of grapes were collected and used for the production of experimental wines from rinsed and unrinsed grapes. A microwave furnace was used for the digestion and dissolution of the experimental wines, the precipitates that originated in these wines, as well as the wines of the corresponding producers. The analyses of all mentioned samples as well as 34 local alcoholic distillates were performed using total reflection X-ray fluorescence and graphite furnace atomic absorption spectrometry. The concentrations for all the elements that were determined were almost in all cases, well below the maximum permissible levels by the Greek and the European Union legislation.  相似文献   
100.
This paper presents the global activities of the World Road Association (PIARC) in the area of fire and life safety in road tunnels. It traces the organizational structure in the form of technical committees, its publications, current activities and concludes with a summary as to the position of the organization with regard to fire and life safety in tunnels.  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