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   4733篇
  免费   133篇
  国内免费   3篇
电工技术   47篇
综合类   4篇
化学工业   1074篇
金属工艺   85篇
机械仪表   78篇
建筑科学   163篇
矿业工程   18篇
能源动力   130篇
轻工业   349篇
水利工程   66篇
石油天然气   19篇
无线电   265篇
一般工业技术   764篇
冶金工业   1184篇
原子能技术   30篇
自动化技术   593篇
  2021年   70篇
  2020年   42篇
  2019年   53篇
  2018年   64篇
  2017年   73篇
  2016年   75篇
  2015年   63篇
  2014年   104篇
  2013年   267篇
  2012年   140篇
  2011年   228篇
  2010年   196篇
  2009年   171篇
  2008年   198篇
  2007年   182篇
  2006年   197篇
  2005年   163篇
  2004年   145篇
  2003年   146篇
  2002年   117篇
  2001年   87篇
  2000年   87篇
  1999年   91篇
  1998年   126篇
  1997年   106篇
  1996年   103篇
  1995年   97篇
  1994年   101篇
  1993年   89篇
  1992年   90篇
  1991年   44篇
  1990年   66篇
  1989年   59篇
  1988年   60篇
  1987年   51篇
  1986年   53篇
  1985年   85篇
  1984年   78篇
  1983年   66篇
  1982年   53篇
  1981年   48篇
  1980年   39篇
  1979年   52篇
  1978年   51篇
  1977年   42篇
  1976年   50篇
  1975年   37篇
  1974年   38篇
  1973年   29篇
  1972年   31篇
排序方式: 共有4869条查询结果,搜索用时 15 毫秒
41.
Four actuarial instruments for the prediction of violent and sexual reoffending (the Violence Risk Appraisal Guide [VRAG], Sex Offender Risk Appraisal Guide [SORAG], Rapid Risk Assessment for Sex Offender Recidivism [RRASOR], and Static-99) were evaluated in 4 samples of sex offenders (N = 396). Although all 4 instruments predicted violent (including sexual) recidivism and recidivism known to be sexually motivated, areas under the receiver operating characteristic (ROC) were consistently higher for the VRAG and the SORAG. The instruments performed better when there were fewer missing items and follow-up time was fixed, with an ROC area up to .84 for the VRAG, for example, under such favorable conditions. Predictive accuracy was higher for child molesters than for rapists, especially for the Static-99 and the RRASOR. Consistent with past research, survival analyses revealed that those offenders high in both psychopathy and sexual deviance were an especially high-risk group. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
42.
Five parameters of postcessation smoking withdrawal variability derived from clinical data (T. M. Piasecki, D. E. Jorenby, S. S. Smith, M. C. Fiore, & T. B. Baker, 2003a, 2003b) were predicted from baseline measures and pharmacotherapy assignment. Smokers who were more dependent, older, and high in negative affect reported more severe withdrawal. Women, heavier smokers, and those with a history of depression reported more variable symptoms. Smokers treated with nicotine patch, bupropion, or both reported less severe withdrawal than did those given placebo, but medication did not affect the slope of symptoms over time, day-to-day variability of symptoms, or the size of acute changes in symptoms associated with lapses to smoking. Prior research has shown that these symptom facets predict later relapse: thus, current pharmacotherapies may aid cessation by diminishing withdrawal severity, but they do not affect all clinically important aspects of withdrawal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
43.
In order to help establish criteria for optimizing protocols for in vivo mutation studies, lacZ transgenic mice (Muta mouse) were treated with five consecutive daily doses of ethylnitrosourea (50 mg/kg), sampled at times up to 55 days after treatment, and mutant frequencies and DNA sequences determined for liver and bone marrow. In the bone marrow, the mutant frequency rose very rapidly in the first 5 days after treatment to 34 times the control frequency. Subsequently, there was a brood peak where the mutant frequency did not vary significantly, although it did appear to begin to decline after 45 days. In contrast, in the liver, the peak mutant frequency (11 times the control frequency) was not achieved until 35 days, after which there appeared to be a slow decline up to 55 days, which was not statistically significant. Once the maximum mutant frequency was reached, the mutation spectra in the two tissues were indistinguishable. In contrast to the G:C-->A:T transitions in 5'-CpG sites characteristic of untreated mice, A:T-->T:A transversions and A:T-->G:C transitions were prominent in both liver and bone marrow of ENU-treated mice, suggesting the involvement of unrepaired O2- and O4-ethylthymine adducts. In addition, G:C-->T:A transversions were induced in liver. This study demonstrates the possibility that although tissues may have different mutation fixation times, a single mutation fixation time equal to the longest time may be appropriate for in vivo mutation studies, provided that the mutation frequency does not decline appreciably after the peak is reached. This study also illustrates the necessity of ensuring that mutation characteristics are determined after optimal fixation has occurred.  相似文献   
44.
An algorithm that acts as a preprocessor to the straight ray algebraic reconstruction technique (ART) algorithm, for the purpose of dealing with nonrectangular scanning geometries, is described. The mathematics of ART in its elementary form is reviewed, showing how the discretization of the rectangular scanning space defines quantities in the projection matrix of the algorithm. A triangular discretization approach for the scanning space that allows nonrectangular or twisted plane geometries to be addressed is proposed, and the effect of this approach on the projection matrix is discussed. An algorithm for determining the projection matrix under these discretization conditions is described, followed by some commentary on its computer implementation. The performance of this preprocessor algorithm, working with standard ART, in reconstructing various synthetic images is demonstrated  相似文献   
45.
Technology developments on the horizon promise to transform the electricity industry far from its present shape and structure. But, just as technology has played a critical role in pushing the industry to its present thrust toward competition and vertical de-integration, a sensible technology policy can make a utility or power supplier a winmer tomorrow.  相似文献   
46.
47.
In new institutional economics, the variance in institutions explains differences in cross-country output per capita. Institutions may also explain how the supply of oil is affected within oil-producing countries. For example in the early 1970s, as nominal oil prices increased from $3 per barrel to $11 per barrel, a number of OPEC oil producers changed the institutional environment by nationalizing their oil production and putting under government control all petroleum-related capital and infrastructure. This affected oil supplies. Similar institutional changes may be happening again now that oil prices are rising. In particular, the newly democratic Russia may be following the same path. The Russian government has already effectively taken over control of much of the oil production capacity in the country and is still heavily involved in natural gas production. In this paper, we will look at the Russian upstream oil industry as it changed from central planning to a market-oriented sector and is now swaying toward re-nationalization. Some of the laws and institutional transitions will be detailed in order to elucidate what has taken place.  相似文献   
48.
This paper investigates relationships between community characteristics and levels of knowledge and participation examined at both the individual and the community levels. This research extends the knowledge gap concept to a parallel phenomenon, the participation gap. Results from the Social Capital Benchmark Survey 2000 showed that community density, education, and cohesion were significant positive predictors of knowledge but less consistent predictors of participation at the individual level. At the community level, relationships were even stronger, though cohesion was associated with higher mean levels of participation and reduced participation gaps, whereas population density was associated with lower levels of participation and increased gaps.  相似文献   
49.
In this paper it is shown how tools developed in argumentation theory and artificial intelligence can be applied to the development of a new dialectical analysis of the speech act of making a proposal in a deliberation dialogue. These tools are developed, modified and used to formulate dialogue pre-conditions, defining conditions and post-conditions for the speech act of making a proposal in a deliberation dialogue. The defining conditions set out what is required for a move in a dialogue to count as the making of a proposal by one of the parties. What is required are the conditions that (1) the move fit the requirements of the argumentation scheme for practical reasoning, and (2) the premises are propositions describing common goals of both parties or propositions that they reasonably consider means to achieve these goals. The analysis goes beyond the standard speech act approach by specifying not only the normative requirements for making a well-formed proposal, but also the requirements for responding to it by questioning or criticizing it, and the requirements for defending it.  相似文献   
50.
To improve the quality of life, man has learned to manufacture countless chemicals, pharmaceutical and biotechnological products, petroleum fuels, and numerous metal products. The processing of these products and their by-products has had a major impact on the environment. Tougher air and water quality standards have led to the development of new sealing systems that far exceed performance requirements for emission control. New seal technology has resulted in non-contacting non-leaking seals for conventional pumps handling difficult services. Design and application of this seal technology is presented in this article. Comparison of competing technologies is discussed and life cycle costs are given. Clearly, gas lubricated non-contacting seals for pumps are becoming the choice of sealing technologies for plant operators on difficult services. These systems are proving to be very economical.  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