全文获取类型
收费全文 | 23528篇 |
免费 | 518篇 |
国内免费 | 18篇 |
专业分类
电工技术 | 231篇 |
综合类 | 17篇 |
化学工业 | 2741篇 |
金属工艺 | 244篇 |
机械仪表 | 362篇 |
建筑科学 | 933篇 |
矿业工程 | 42篇 |
能源动力 | 467篇 |
轻工业 | 2034篇 |
水利工程 | 269篇 |
石油天然气 | 29篇 |
无线电 | 1810篇 |
一般工业技术 | 2525篇 |
冶金工业 | 9395篇 |
原子能技术 | 168篇 |
自动化技术 | 2797篇 |
出版年
2023年 | 70篇 |
2022年 | 161篇 |
2021年 | 288篇 |
2020年 | 145篇 |
2019年 | 212篇 |
2018年 | 287篇 |
2017年 | 264篇 |
2016年 | 288篇 |
2015年 | 261篇 |
2014年 | 418篇 |
2013年 | 706篇 |
2012年 | 722篇 |
2011年 | 978篇 |
2010年 | 674篇 |
2009年 | 717篇 |
2008年 | 753篇 |
2007年 | 703篇 |
2006年 | 601篇 |
2005年 | 586篇 |
2004年 | 539篇 |
2003年 | 493篇 |
2002年 | 441篇 |
2001年 | 359篇 |
2000年 | 334篇 |
1999年 | 587篇 |
1998年 | 3223篇 |
1997年 | 1895篇 |
1996年 | 1240篇 |
1995年 | 720篇 |
1994年 | 667篇 |
1993年 | 723篇 |
1992年 | 234篇 |
1991年 | 254篇 |
1990年 | 243篇 |
1989年 | 260篇 |
1988年 | 267篇 |
1987年 | 188篇 |
1986年 | 171篇 |
1985年 | 221篇 |
1984年 | 142篇 |
1983年 | 107篇 |
1982年 | 127篇 |
1981年 | 140篇 |
1980年 | 108篇 |
1979年 | 95篇 |
1978年 | 87篇 |
1977年 | 238篇 |
1976年 | 348篇 |
1975年 | 85篇 |
1974年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
M Hessing D Kanters H Takeya C van 't Veer TM Hackeng S Iwanaga BN Bouma 《Canadian Metallurgical Quarterly》1993,317(3):228-232
Human C4b-binding protein (C4BP) functions as a cofactor to factor I in the degradation of C4b and accelerates the decay rate of the C4b2a complex. In this study we describe a monoclonal antibody directed against the alpha-chain of C4BP that inhibits the binding of C4b to C4BP. In order to identify the structural domain of the alpha-chain of C4BP that interacts with C4b, tryptic fragments of C4BP were generated. Amino acid sequence analysis of the fragments revealed that the residues Ser333-Arg356 of the alpha-chain of C4BP contain the epitope of this antibody, and as a consequence, that this part of the alpha-chain of C4BP is likely to be involved in the interaction with C4b. 相似文献
82.
BACKGROUND: Monocytic tissue factor (TF), initiating the extrinsic blood coagulation pathway, is often upregulated under septic or inflammatory conditions. The complex activating mechanism remains largely unclear and no effective strategy has been firmly established. In this study, we used a model monocytic cell line (human leukemic THP-1 promonocytes) to address (1) the nature of TF activation in response to bacterial endotoxin and (2) the application of anti-inflammatory cytokines in relieving monocytic hypercoagulation. RESULTS: TF in THP-1 cells was substantially activated by exposure to bacterial endotoxin (LPS; 5 micrograms/ml) for 6 h. Human recombinant IL-4 (500 ng/ml) and IL-10 (500 ng/ml) inhibited TF activation induced by LPS. To determine if these cytokines depressed LPS recognition resulting in such inhibition, we employed an anti-CD14 mAb (UCHM-1; Sigma Chemical) to address the role of CD14 in LPS transmembrane signaling. LPS-induced TF activation was depressed by 35% upon inclusion of the anti-CD14 mAb (1:10 dilution). This antibody alone mimicked TF activation which accounted for 35% of the LPS-induced TF activation, suggesting the activating role of CD14 ligation. In addition, the anti-CD14 mAb elicited the production of nitric oxide (NO) which was found to be independent of TF activation. NO production could serve as an independent index for monitoring LPS recognition. IL-4 depressed the anti-CD14 mAb-induced TF activation as well as NO elicitation, indicating the blockade of CD14 ligation. In contrast, IL-10 showed differential inhibitory activities. TF activation induced by either LPS or anti-CD14 mAb was inhibited by IL-10 which did not show any inhibition on NO elicitation under these conditions. In a separate approach, neither IL-4 nor IL-10 inhibited phorbol ester-induced NO elicitation. More direct evidence came from an epifluorescent demonstration showing that IL-4 blocked binding of FITC-conjugated LPS and anti-CD14 mAb to THP-1 cells. CONCLUSIONS: Taken together, the results suggest that LPS action in relation to TF activation consists of CD14-independent and -dependent signaling including CD14 ligation. We also showed that anti-inflammatory cytokines (IL-4 and -10) significantly depressed TF activation. IL-4 antagonized CD14-dependent LPS recognition leading to the depression in TF activation. 相似文献
83.
84.
School-based condom distribution programs have generated considerable controversy across the country. In the present study 249 sexually active African American adolescents who did (n = 119) and did not (n = 130) use a condom during their initial sexual experience were compared to assess whether condom use at the onset of sexual activity was associated with later differences in sexual behavior. The results indicated that youths who used a condom from the onset of sexual activity were more likely to have used a condom in the most recent intercourse occasion, less likely to be diagnosed with a sexually transmitted disease (STD) or to combine substance use with sexual activity, endorsed more positive attitudes toward condoms, and were older when they initiated sexual activity. The findings have implications for condom availability programs and indicate that initial condom use was not associated with earlier onset of sexual activity and was associated with higher rates of precautionary behavior among sexually active minority adolescents. 相似文献
85.
86.
87.
Measuring knowledge transfer between fields of science 总被引:4,自引:2,他引:2
Rinia Ed J. van Leeuwen Thed N. Bruins Eppo E. W. van Vuren Hendrik G. van Raan Anthony F. J. 《Scientometrics》2002,54(3):347-362
In this paper we report on the results of an exploratory study of knowledge exchange between disciplines and subfields of
science, based on bibliometric methods. The goal of this analysis is twofold. Firstly, we consider knowledge exchange between
disciplines at a global level, by analysing cross-disciplinary citations in journal articles, based on the world publication
output in 1999. Among others a central position of the Basic Life Sciences within the Life Sciences and of Physics within
the Exact Sciences is shown. Limitations of analyses of interdisciplinary impact at the journal level are discussed. A second
topic is a discussion of measures which may be used to quantify the rate of knowledge transfer between fields and the importance
of work in a given field or for other disciplines. Two measures are applied, which appear to be proper indicators of impact
of research on other fields. These indicators of interdisciplinary impact may be applied at other institutional levels as
well.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
88.
Aard J. Groen Petra C. De WeerdNederhof Inge C. Kerssensvan Drongelen Rob A.J. Badoux Gerard P.H. Olthuis 《Creativity & Innovation Management》2002,11(1):2-16
In this paper we describe a framework for analysing the creation and justification of Research & Development. The 4S framework is developed for analysing the scope, scale, skills and social network aspects of Research & Development value. The framework is based on social system theory, a process contingency model, and recent Research & Development metrics. We present a first empirical assessment based on a workshop using the 4S framework for leveraging Research & Development. Results that assist in the assessment of value creation utilising R & D within networks are very relevant in high tech industries. The multi–dimensional process approach of this framework seems promising for understanding and managing R&D value creation, but needs further operationalisation. Case studies are described and a Dutch network on leveraging R&D has been initiated. 相似文献
89.
A diagonal coordinate representation for Volterra filters is developed and exploited to derive efficient Volterra filter implementations for processing carrier based input signals. In the diagonal coordinate representation, the output is expressed as a sum of linear filters applied to modified input signals. Hence, linear filtering methods are employed to implement the nonlinear filter on a baseband version of the input. Downsampling is then used to reduce computational complexity. The same approach is employed to develop efficient implementations for processing continuous-time carrier-based signals, pulse amplitude-modulated signals, and frequency division multiplexed input signals 相似文献
90.