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   566853篇
  免费   6307篇
  国内免费   986篇
电工技术   10531篇
综合类   470篇
化学工业   90068篇
金属工艺   23338篇
机械仪表   18498篇
建筑科学   12533篇
矿业工程   4314篇
能源动力   14431篇
轻工业   45771篇
水利工程   6950篇
石油天然气   14964篇
武器工业   39篇
无线电   60294篇
一般工业技术   116256篇
冶金工业   95560篇
原子能技术   14700篇
自动化技术   45429篇
  2021年   5482篇
  2020年   4040篇
  2019年   5269篇
  2018年   9201篇
  2017年   9409篇
  2016年   9837篇
  2015年   6034篇
  2014年   10245篇
  2013年   26100篇
  2012年   15775篇
  2011年   21087篇
  2010年   16968篇
  2009年   18818篇
  2008年   19067篇
  2007年   18765篇
  2006年   16285篇
  2005年   14742篇
  2004年   14008篇
  2003年   13690篇
  2002年   13246篇
  2001年   12850篇
  2000年   12329篇
  1999年   12011篇
  1998年   27649篇
  1997年   20038篇
  1996年   15627篇
  1995年   12005篇
  1994年   10859篇
  1993年   10612篇
  1992年   8332篇
  1991年   8102篇
  1990年   7990篇
  1989年   7763篇
  1988年   7478篇
  1987年   6747篇
  1986年   6533篇
  1985年   7390篇
  1984年   6700篇
  1983年   6439篇
  1982年   5777篇
  1981年   5896篇
  1980年   5633篇
  1979年   5733篇
  1978年   5663篇
  1977年   6178篇
  1976年   7685篇
  1975年   5108篇
  1974年   4903篇
  1973年   4980篇
  1972年   4279篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Bulletin of Engineering Geology and the Environment - Information about distribution of elastic wave propagation velocities Vp, Vs in the subsurface zone of a soil mass can be obtained rapidly and...  相似文献   
72.
A method of evaluating the stress-strain state of frozen soils, which takes into account the existence of elastoviscoplastic and temperature deformations over time under variable external effects, is described. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 10–13, July–August, 1997.  相似文献   
73.
74.
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   
75.
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   
76.
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   
77.
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   
78.
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   
79.
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   
80.
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   
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