全文获取类型
收费全文 | 8735篇 |
免费 | 299篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 103篇 |
综合类 | 7篇 |
化学工业 | 1610篇 |
金属工艺 | 174篇 |
机械仪表 | 191篇 |
建筑科学 | 473篇 |
矿业工程 | 19篇 |
能源动力 | 272篇 |
轻工业 | 921篇 |
水利工程 | 118篇 |
石油天然气 | 43篇 |
无线电 | 666篇 |
一般工业技术 | 1487篇 |
冶金工业 | 1731篇 |
原子能技术 | 61篇 |
自动化技术 | 1167篇 |
出版年
2023年 | 38篇 |
2022年 | 77篇 |
2021年 | 125篇 |
2020年 | 117篇 |
2019年 | 127篇 |
2018年 | 141篇 |
2017年 | 161篇 |
2016年 | 161篇 |
2015年 | 153篇 |
2014年 | 214篇 |
2013年 | 489篇 |
2012年 | 402篇 |
2011年 | 505篇 |
2010年 | 342篇 |
2009年 | 398篇 |
2008年 | 509篇 |
2007年 | 418篇 |
2006年 | 345篇 |
2005年 | 359篇 |
2004年 | 312篇 |
2003年 | 282篇 |
2002年 | 249篇 |
2001年 | 148篇 |
2000年 | 131篇 |
1999年 | 168篇 |
1998年 | 314篇 |
1997年 | 217篇 |
1996年 | 195篇 |
1995年 | 156篇 |
1994年 | 136篇 |
1993年 | 136篇 |
1992年 | 87篇 |
1991年 | 79篇 |
1990年 | 77篇 |
1989年 | 92篇 |
1988年 | 71篇 |
1987年 | 72篇 |
1986年 | 72篇 |
1985年 | 91篇 |
1984年 | 92篇 |
1983年 | 75篇 |
1982年 | 79篇 |
1981年 | 81篇 |
1980年 | 51篇 |
1979年 | 65篇 |
1978年 | 58篇 |
1977年 | 67篇 |
1976年 | 77篇 |
1975年 | 41篇 |
1974年 | 39篇 |
排序方式: 共有9043条查询结果,搜索用时 15 毫秒
71.
A specific radioimmunoassay for platelet-activating factor (PAF) sensitive in the range 10–1000 pg (0.02–2 pmoles) has been
developed. Detailed quantitative hapten inhibition studies showed specificity for the acetyl group at C-2 of PAF, a requirement
for the ether linkage at C-1 and some tolerance for substituents on the choline nitrogen. No significant cross-reactivity
was found with phosphatidylcholine and lysophosphatidylcholine or with lysoPAF.
Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl
Ether Lipids, Tokyo, Japan, May 1989. 相似文献
72.
73.
74.
JA Gogos M Morgan V Luine M Santha S Ogawa D Pfaff M Karayiorgou 《Canadian Metallurgical Quarterly》1998,95(17):9991-9996
Catechol-O-methyltransferase (COMT) is one of the major mammalian enzymes involved in the metabolic degradation of catecholamines and is considered a candidate for several psychiatric disorders and symptoms, including the psychopathology associated with the 22q11 microdeletion syndrome. By means of homologous recombination in embryonic stem cells, a strain of mice in which the gene encoding the COMT enzyme has been disrupted was produced. The basal concentrations of brain catecholamines were measured in the striatum, frontal cortex, and hypothalamus of adult male and female mutants. Locomotor activity, anxiety-like behaviors, sensorimotor gating, and aggressive behavior also were analyzed. Mutant mice demonstrated sexually dimorphic and region-specific changes of dopamine levels, notably in the frontal cortex. In addition, homozygous COMT-deficient female (but not male) mice displayed impairment in emotional reactivity in the dark/light exploratory model of anxiety. Furthermore, heterozygous COMT-deficient male mice exhibited increased aggressive behavior. Our results provide conclusive evidence for an important sex- and region-specific contribution of COMT in the maintenance of steady-state levels of catecholamines in the brain and suggest a role for COMT in some aspects of emotional and social behavior in mice. 相似文献
75.
We study non-linear behaviour in a model chemical reaction scheme (proposed by Sal?nikov), in which a single chemical species undergoes a two-stage, first-order decay process. The second stage is exothermic and has a temperature-dependent rate, and as a result, spontaneous oscillations in the temperature and the concentration of an intermediate chemical are known to be possible. An additional oscillation is imposed on the system by varying the ambient temperature in a sinusoidal manner. Primary resonance occurs when the forcing frequency coincides with the frequency of the natural oscillations in this scheme and an infinite sequence of super-and subharmonic resonances is also present. Chaos is possible for appropriate parameter values and may result either from the Feigenbaum period-doubling cascade, or else as a result of the Ruelle-Takens approach through quasi-periodicity. 相似文献
76.
The current study examined psychological and physical health outcomes of the written disclosure paradigm and the hypothesis that the principles of therapeutic exposure account for the beneficial effects of the paradigm. Participants were randomly assigned to either a written disclosure condition or a control condition. Reactivity to the writing sessions was examined using both subjective and physiological measures. Measures of psychological and physical health were completed before and 1 month after the sessions. Participants assigned to the disclosure condition reported fewer psychological and physical symptoms at follow-up compared with control participants, though reductions were clinically significant for only 1 outcome measure. Physiological activation to the 1st disclosure session was associated with reduced psychological symptoms at follow-up for disclosure participants. Subjective reports of emotional responding corresponded with physiological reactivity. Implications of these findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
77.
Brian McKenna 《Computer Fraud & Security》2004,2004(7):3
Public Key Infrastructure is staging a comeback, according to new research from European IT user association EEMA. 相似文献
78.
Brian Dipert 《电子设计技术》2003,10(8):52-62
DRAM供应商希望有朝一日一种产品大小规格能适应所有的应用要求,但各种各样的设备要求则与之相差甚远.DRAM用户也许更喜欢定制的芯片,但价格会格外昂贵.双方会在保持原则的同时作出足够的让步以达成顺利的交易么? 相似文献
79.
80.
Melamed Barbara G.; Matthews Karen A.; Routh Donald K.; Stabler Brian 《Canadian Metallurgical Quarterly》1986,5(3):181
This article introduces the current issue of Health Psychology. The call for early intervention to prevent adulthood health problems and the need to consider each period of children's lives within its developmental perspective are the main emphases in this special issue of the journal. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献