全文获取类型
收费全文 | 4733篇 |
免费 | 133篇 |
国内免费 | 3篇 |
专业分类
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 |
出版年
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.
Harris Grant T.; Rice Marnie E.; Quinsey Vernon L.; Lalumière Martin L.; Boer Douglas; Lang Carol 《Canadian Metallurgical Quarterly》2003,15(3):413
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.
Piasecki Thomas M.; Jorenby Douglas E.; Smith Stevens S.; Fiore Michael C.; Baker Timothy B. 《Canadian Metallurgical Quarterly》2003,11(4):276
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.
GR Douglas J Jiao JD Gingerich LM Soper JA Gossen 《Canadian Metallurgical Quarterly》1996,28(4):317-324
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.
Douglas E. Olesen 《The Electricity Journal》1995,8(10)
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.
Structural Antecedents to Knowledge and Participation: Extending the Knowledge Gap Concept to Participation 总被引:1,自引:0,他引:1
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.
Douglas Walton 《Artificial Intelligence and Law》2006,14(3):177-239
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