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   328468篇
  免费   21945篇
  国内免费   11662篇
电工技术   16078篇
技术理论   31篇
综合类   17478篇
化学工业   56213篇
金属工艺   19455篇
机械仪表   19672篇
建筑科学   23674篇
矿业工程   9672篇
能源动力   9255篇
轻工业   18818篇
水利工程   5119篇
石油天然气   21586篇
武器工业   2234篇
无线电   35136篇
一般工业技术   43922篇
冶金工业   22120篇
原子能技术   3581篇
自动化技术   38031篇
  2024年   1228篇
  2023年   4737篇
  2022年   8118篇
  2021年   11768篇
  2020年   8771篇
  2019年   7603篇
  2018年   8752篇
  2017年   9806篇
  2016年   8681篇
  2015年   11638篇
  2014年   14472篇
  2013年   18586篇
  2012年   18967篇
  2011年   21047篇
  2010年   18061篇
  2009年   17462篇
  2008年   16878篇
  2007年   16646篇
  2006年   17216篇
  2005年   15255篇
  2004年   10104篇
  2003年   8885篇
  2002年   8274篇
  2001年   7512篇
  2000年   7974篇
  1999年   9420篇
  1998年   8843篇
  1997年   7354篇
  1996年   6796篇
  1995年   5424篇
  1994年   4462篇
  1993年   3369篇
  1992年   2702篇
  1991年   2151篇
  1990年   1681篇
  1989年   1400篇
  1988年   1113篇
  1987年   919篇
  1986年   747篇
  1985年   640篇
  1984年   483篇
  1983年   419篇
  1982年   429篇
  1981年   381篇
  1980年   415篇
  1979年   365篇
  1977年   415篇
  1976年   629篇
  1975年   308篇
  1973年   311篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The fault-state detection approach for blackbox testing consists of two phases. The first is to bring the system under test (SUT) from its initial state to a targeted state t and the second is to check various specified properties of the SUT at t. This paper investigates the first phase for testing systems specified as observable nondeterministic finite-state machines with probabilistic and weighted transitions. This phase involves two steps. The first step transfers the SUT to some state t' and the second step identifies whether t' is indeed the targeted state t or not. State transfer is achieved by moving the SUT along one of the paths of a transfer tree (TT) and state identification is realized by using diagnosis trees (DT). A theoretical foundation for the existence and characterization of TT and DT with minimum weighted height or minimum average weight is presented. Algorithms for their computation are proposed.  相似文献   
52.
53.
54.
An innovative method for modelling biological processes under anaerobic conditions is presented and discussed. The method is based on titrimetric and off-gas measurements. Titrimetric data is recorded as the addition rate of hydroxyl ions or protons that is required to maintain pH in a bioreactor at a constant level. An off-gas analysis arrangement measures, among other things, the transfer rate of carbon dioxide. The integration of these signals results in a continuous signal which is solely related to the biological reactions. When coupled with a mathematical model of the biological reactions, the signal allows a detailed characterisation of these reactions, which would otherwise be difficult to achieve. Two applications of the method to the enhanced biological phosphorus removal processes are presented and discussed to demonstrate the principle and effectiveness of the method.  相似文献   
55.
Domain-Driven, Actionable Knowledge Discovery   总被引:1,自引:0,他引:1  
Data mining increasingly faces complex challenges in the real-life world of business problems and needs. The gap between business expectations and R&D results in this area involves key aspects of the field, such as methodologies, targeted problems, pattern interestingness, and infrastructure support. Both researchers and practitioners are realizing the importance of domain knowledge to close this gap and develop actionable knowledge for real user needs.  相似文献   
56.
A study of the trace elements emission (As, Se, Cd, Co, Cr, Cu, Zn, Hg, Tl, Pb, Ni, Sn, Sb, V, Mn and Fe) from pulverized coal combustion has been made at six heating and power stations situated in the Czech Republic. The amount of chlorine in coal has considerable influence on volatilization of some elements such as Zn, Cu, Pb, Hg and Tl, which is explained by the formation of thermodynamically stable compounds of these elements with chlorine. Generally, the affinities for Cl follows the order Tl > Cu > Zn > Pb > Co > Mn > Sn > Hg. The experimental data indicates enrichment of some of the trace toxic elements in the emissions (Cu, Zn, As, Se, Cd, Sn, Sb, Hg and Pb) and good agreement was obtained by thermodynamic equilibrium calculations with a few exceptions. In the case of Fe, Mn, Co, Cr and Sn calculated values are overestimated in the bottom ash and there are zero predicted amounts of these elements in the fly ash. In comparison, the results from experiments show up to 80% of these elements retained in fly ash. This implies that there exist additional steps leading to the enrichment by Fe, Mn, Co, Cr and Sn of small particles. Such mechanisms could include the ejection during devolatilization of small inorganic particles from the coal of bottom ash particles, or disintegration of the char containing these metals to small particles of fly ash. On the other hand, there are slightly overestimated or similar values of relative enrichment factors for As, V, Cu, Cd, Sb, Tl and Pb in the fly ashes and zero predicted values for bottom ashes. Our experimental results show about 5% or less of these elements are retained in bottom ashes, so they probably remain in the bottom ash inside unburned parts of coal. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
57.
58.
Time variation of drinking is substantial and has an effect on aggregate estimates of consumption. In this article it is shown that because of a considerable seasonal variation in consumption (+/- 20%) a serious bias in annual consumption estimates can be expected in surveys with a limited time frame. The present study analyzes drinking data collected in the general population of the Netherlands from March 1985 through December 1985 (including Christmas and New Year's Eve). Since it was expected that sensitivity to temporal fluctuations might not be equal for different methods of measurement, several indices of consumption were compared. Although the assessed seasonal effect varies indeed across types of measurement, across male and female subsample and across types of alcoholic beverage, the general tendency is for consumption to be highest in the spring season and lowest in the autumn. Sales figures fluctuate accordingly. It is evident that the risk of biased estimates is larger the shorter the time frame of the survey. Seasonal variation was highest in the frequency domain. Furthermore, exclusion from the time frame of collective holidays, during which people drink more often and more per occasion (viz., Christmas), increases the risk of biased estimates. Even estimates of abstention, but also regular heavy drinking among women, appear to vary considerably over the three seasons in this study. The main conclusion is that results of comparisons of survey data on drinking, particularly those over time, are more or less invalid if the respective time frames of the surveys do not correspond.  相似文献   
59.
In the absence of adequate autogenous vein for tibial artery bypass in limb salvage surgery, the use of prosthetic grafts with a distal anastomotic vein cuff or patch has shown promising results. Here, we describe how the Florester Internal Vessel Occluder (Meadox UK, Bedfordshire, UK) can facilitate the construction of a distal anastomotic vein cuff.  相似文献   
60.
The oxygen absorption process in highly aligned YBa2Cu3Ox samples in air and in pure oxygen was studied at several constant temperatures. The process can be expressed in two steps, a chemical reaction controlled step and a diffusion controlled step. The kinetic equations are as follows respectively:
(1 − at) ln(1 − at) + at = kDt

The activation energy was calculated using an Arrhenius equation. The technical conditions of heat treatment for oxygen absorption of highly aligned YBa2Cu3Ox crystals are discussed.  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