全文获取类型
收费全文 | 23810篇 |
免费 | 656篇 |
国内免费 | 25篇 |
专业分类
电工技术 | 254篇 |
综合类 | 19篇 |
化学工业 | 4752篇 |
金属工艺 | 584篇 |
机械仪表 | 428篇 |
建筑科学 | 1017篇 |
矿业工程 | 173篇 |
能源动力 | 608篇 |
轻工业 | 1620篇 |
水利工程 | 283篇 |
石油天然气 | 208篇 |
武器工业 | 1篇 |
无线电 | 1704篇 |
一般工业技术 | 3788篇 |
冶金工业 | 5507篇 |
原子能技术 | 199篇 |
自动化技术 | 3346篇 |
出版年
2022年 | 170篇 |
2021年 | 279篇 |
2020年 | 220篇 |
2019年 | 292篇 |
2018年 | 324篇 |
2017年 | 330篇 |
2016年 | 404篇 |
2015年 | 318篇 |
2014年 | 499篇 |
2013年 | 1390篇 |
2012年 | 818篇 |
2011年 | 1033篇 |
2010年 | 834篇 |
2009年 | 848篇 |
2008年 | 969篇 |
2007年 | 1051篇 |
2006年 | 869篇 |
2005年 | 800篇 |
2004年 | 710篇 |
2003年 | 669篇 |
2002年 | 631篇 |
2001年 | 417篇 |
2000年 | 430篇 |
1999年 | 408篇 |
1998年 | 708篇 |
1997年 | 544篇 |
1996年 | 505篇 |
1995年 | 433篇 |
1994年 | 380篇 |
1993年 | 456篇 |
1992年 | 354篇 |
1991年 | 264篇 |
1990年 | 306篇 |
1989年 | 317篇 |
1988年 | 287篇 |
1987年 | 281篇 |
1986年 | 315篇 |
1985年 | 331篇 |
1984年 | 329篇 |
1983年 | 318篇 |
1982年 | 260篇 |
1981年 | 290篇 |
1980年 | 285篇 |
1979年 | 276篇 |
1978年 | 254篇 |
1977年 | 287篇 |
1976年 | 276篇 |
1975年 | 219篇 |
1974年 | 205篇 |
1973年 | 211篇 |
排序方式: 共有10000条查询结果,搜索用时 246 毫秒
71.
James A. Ward 《Information Systems Management》1997,14(1):62-65
The road to employee empowerment runs between true commitment on the one side and enforced compliance and chaos on the other. By following this column's guidelines, IS managers can steer their organizations to success and help free employees to be more creative in terms of both quality and productivity. 相似文献
72.
OBJECTIVE: The aim of this study was to evaluate both the importance of the screening strategy and the familial aggregation characteristics of families with hypercholesterolemic children. PATIENTS AND METHODS: Ninety-one families (369 subjects) with one hypercholesterolemic child were studied. In addition to clinical and general biochemical evaluation, lipids including apo A-I and B-100 were examined. LDL was quantified under ultracentrifugation. RESULTS: Among the 91 children studied, 10 (10.99%) suffered heterozygous hypercholesterolemia, while 81 (89.01%) suffered polygenic hypercholesterolemia. Following a diet, polygenic children exhibited normal lipid parameters. In heterozygous children a decrease of 19% for total cholesterol, 19.9% for LDL-cholesterol and 16.3% for apo B were observed. When starting the study, 77.5% of the family members thought that they had normal serum lipid values. At the end of the study it was confirmed that only 28% were really normolipemic, indicating that 49.4% of the individual did not know that they were suffering dyslipemia. The study also showed that fathers exhibited the highest incidence of hypercholesterolemia (80.2%) followed by brothers (65.6%) and mothers (61.5%). Therefore, 69.4% of the individuals studied exhibited dyslipemia. CONCLUSIONS: The screening strategy allows one to diagnose a high percentage (almost 50%) of individuals suffering hypercholesterolemia in families with a child previously diagnosed of this pathology. Moreover, in these families there is a high degree of familiar aggregation of dyslipemia. 相似文献
73.
Sir James Lighthill 《Journal of Engineering Mathematics》1996,30(1-2):35-78
Helical distributions of stokeslets can valuably model microbial locomotion through a fluid, and also the flow field generated, wherever a flagellum actively executes helical undulations (as in many single-celled algae and protozoa) or where (as in many bacteria) the action of rotary motors causes a passive structure of helical shape (which may be a flagellum or else the cell body itself) to rotate. Here, previous biomechanical studies of such modes of locomotion are extended to include analyses of three-dimensional flow fields. In some cases, a rotlet field (curl of a stokeslet) needs to be incorporated in the models. For example, spirochete swimming is modelled by combined helical distributions of stokeslets and rotlets; the computed flow field being confined to within distances of less than twice the radius of the cell body's helical shape from its axis, while including a powerful jet-like interior flow through the coils of the swimming spirochete. 相似文献
74.
The miswak chewing stick is an oral hygiene device used by the majority of people in Arab Gulf countries. Despite its widespread use, few studies demonstrated its benefits or applications as an alternative and convenient means for cleansing the teeth. This paper will examine the unique properties of the miswak chewing stick and its proper use. 相似文献
75.
James Lighthill 《Journal of Engineering Mathematics》1996,30(1-2):25-34
Lorentz [1] pioneered the representation of flows at very low Reynolds number by a surface distribution of stokeslets — whose strengths, nowadays, are computed by surface-velocity collocations. That method is here compared with a representation widely used in flagellar hydrodynamics, by a curvilinear distribution of stokeslets and dipoles along the flagellar centreline; with the velocity of each cross-section expressed as a centreline value of the combined fields of singularities beyond a certain cutoff distance. The latter is also a good representation, and offers moreover some computational advantages. This paper establishes the equivalence of the two representations, and identifies those properties of Stokes flows which make both the dipoles and the cutoff essential to that equivalence. 相似文献
76.
77.
Treatment of the addictions is changing. Psychosocial treatment programs and research projects have changed the way helping professionals view, treat, and prevent drug abuse. This article reviews the contributions included in this special series; they encompass several general issues facing psychologists who conduct treatment, research, and teaching in the field of addictive behaviors. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
78.
79.
The role of MHC class II in the presentation of Heligmosomoides polygyrus antigens has been investigated, using a number of T cell hybridomas produced in A and E positive and negative mice. By using fixed and irradiated antigen presenting cells (APC), further evidence has emerged, to support earlier data, that there can be differential processing requirements during the presentation of H. polygyrus antigens by A and E molecules. In concordance with these earlier observations, this work provides further evidence than individual T cells can respond to antigen when presented by more than one MHC molecule. Previously, this evidence has been restricted to individual MHC molecules of the same haplotype, but these data show that H. polygyrus produces antigens which can be presented by both syngeneic and allogeneic MHC molecules. These antigens do not appear to be synonymous with the previously described H. polygyrus superantigen, as presentation is restricted to specific MHC haplotypes. It is proposed that H. polygyrus may produce these antigenic molecules as part of its strategy to manipulate the host immune system. 相似文献
80.
Abstract: Environmental justice advocates have recently focused attention on cumulative exposure in minority neighborhoods due to multiple sources of pollution. This article uses U.S. EPA's National Air Toxics Assessment (NATA) for 1996 to examine environmental inequality in California, a state that has been a recent innovator in environmental justice policy. We first estimate potential lifetime cancer risks from mobile and stationary sources. We then consider the distribution of these risks using both simple comparisons and a multivariate model in which we control for income, land use, and other explanatory factors, as well as spatial correlation. We find large racial disparities in California's “riskscape” as well as inequalities by other factors and suggest several implications for environmental and land use policy. 相似文献