全文获取类型
收费全文 | 9683篇 |
免费 | 39篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 36篇 |
综合类 | 2篇 |
化学工业 | 497篇 |
金属工艺 | 36篇 |
机械仪表 | 58篇 |
建筑科学 | 174篇 |
矿业工程 | 15篇 |
能源动力 | 69篇 |
轻工业 | 237篇 |
水利工程 | 12篇 |
石油天然气 | 22篇 |
无线电 | 237篇 |
一般工业技术 | 400篇 |
冶金工业 | 7513篇 |
原子能技术 | 28篇 |
自动化技术 | 390篇 |
出版年
2021年 | 18篇 |
2019年 | 23篇 |
2017年 | 22篇 |
2016年 | 28篇 |
2015年 | 22篇 |
2014年 | 37篇 |
2013年 | 145篇 |
2012年 | 72篇 |
2011年 | 117篇 |
2010年 | 96篇 |
2009年 | 83篇 |
2008年 | 116篇 |
2007年 | 107篇 |
2006年 | 114篇 |
2005年 | 81篇 |
2004年 | 85篇 |
2003年 | 86篇 |
2002年 | 82篇 |
2001年 | 60篇 |
2000年 | 59篇 |
1999年 | 246篇 |
1998年 | 2168篇 |
1997年 | 1236篇 |
1996年 | 825篇 |
1995年 | 462篇 |
1994年 | 411篇 |
1993年 | 460篇 |
1992年 | 103篇 |
1991年 | 130篇 |
1990年 | 121篇 |
1989年 | 132篇 |
1988年 | 140篇 |
1987年 | 142篇 |
1986年 | 126篇 |
1985年 | 128篇 |
1984年 | 52篇 |
1983年 | 68篇 |
1982年 | 88篇 |
1981年 | 82篇 |
1980年 | 89篇 |
1979年 | 48篇 |
1978年 | 51篇 |
1977年 | 200篇 |
1976年 | 367篇 |
1975年 | 55篇 |
1974年 | 44篇 |
1973年 | 34篇 |
1972年 | 26篇 |
1971年 | 17篇 |
1970年 | 17篇 |
排序方式: 共有9726条查询结果,搜索用时 0 毫秒
61.
D Crenesse B Fossat F Craffa P Chaland J Porthe-Nibelle JC Poiree J Gugenheim 《Canadian Metallurgical Quarterly》1994,31(6):540-548
Isolated hepatocytes from the rat were used to assess the maintenance of liver cell function in relation to the composition of the preservation medium. After separation by collagenase, they were incubated in Krebs-Ringer-Bicarbonate medium (KRB), Euro-Collins (EC), or University of Wisconsin (UW) solutions. Potassium influx, cell volume, and transaminase release were measured in cells freshly separated from control livers or from livers preserved in vitro up to 12 h in these media or having undergone orthotopic liver transplantation (OLT). While ion exchange levels were retained in all media, cells shrank significantly in UW but were able to restore their volume after 3 h of liver preservation. With regard to in vivo conditions, UW appears to be the best medium to prevent edema and to maintain more stable potassium exchange and enzyme production. These results are of value for liver transplantation in humans. 相似文献
62.
Apoptosis in the failing human heart 总被引:1,自引:0,他引:1
G Olivetti R Abbi F Quaini J Kajstura W Cheng JA Nitahara E Quaini C Di Loreto CA Beltrami S Krajewski JC Reed P Anversa 《Canadian Metallurgical Quarterly》1997,336(16):1131-1141
BACKGROUND: Loss of myocytes is an important mechanism in the development of cardiac failure of either ischemic or nonischemic origin. However, whether programmed cell death (apoptosis) is implicated in the terminal stages of heart failure is not known. We therefore studied the magnitude of myocyte apoptosis in patients with intractable congestive heart failure. METHODS: Myocardial samples were obtained from the hearts of 36 patients who underwent cardiac transplantation and from the hearts of 3 patients who died soon after myocardial infarction. Samples from 11 normal hearts were used as controls. Apoptosis was evaluated histochemically, biochemically, and by a combination of histochemical analysis and confocal microscopy. The expression of two proto-oncogenes that influence apoptosis, BCL2 and BAX, was also determined. RESULTS: Heart failure was characterized morphologically by a 232-fold increase in myocyte apoptosis and biochemically by DNA laddering (an indicator of apoptosis). The histochemical demonstration of DNA-strand breaks in myocyte nuclei was coupled with the documentation of chromatin condensation and fragmentation by confocal microscopy. All these findings reflect apoptosis of myocytes. The percentage of myocytes labeled with BCL2 (which protects cells against apoptosis) was 1.8 times as high in the hearts of patients with cardiac failure as in the normal hearts, whereas labeling with BAX (which promotes apoptosis) remained constant. The near doubling of the expression of BCL2 in the cardiac tissue of patients with heart failure was confirmed by Western blotting. CONCLUSIONS: Programmed death of myocytes occurs in the decompensated human heart in spite of the enhanced expression of BCL2; this phenomenon may contribute to the progression of cardiac dysfunction. 相似文献
63.
Agrees with R. W. Motta et al's (see record 1994-04005-001) conclusion that there is little evidence that human figure drawings (HFDs) have any predictive validity or definitive clinical use in personality and intellectual assessment. Use of the HFD as a personality assessment tool is reviewed in the empirical literature. It is concluded that the only defensible ways that HFDs can be used involve hypothesis generating and testing under behavioral or cognitive-behavioral perspectives. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
64.
65.
BA Stankiewicz JC Hutchins R Thomson DE Briggs RP Evershed 《Canadian Metallurgical Quarterly》1997,11(17):1884-1890
Flash pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) was used to assess the quality and mechanism of protein preservation in the tissue of Iron Age bog bodies from Lindow, UK, and south-eastern Drenthe, The Netherlands. Abundant pyrolysis products of the fresh skin tissue, including 2,5-diketopiperazines of Pro-Gly, Pro-Ala, Pro-Val, Pro-Pro and Hyp, were readily assigned to specific amino acid or dipeptide moieties. Comparison of the pyrolysates of the bog-body tissues with that of modern samples revealed qualitative similarities suggesting good preservation of the collagen and non-collagenous proteins in the ancient tissues. Examination of the pyrolysates of samples of fresh calf skin, which had been treated with various vegetable tanning agents, clearly revealed markers of non-hydrolysable tannins including 1,2-benzenediol, 1,3-benzenediol and 1,2,3-benzenetriol, although chromatographic quality inevitably diminished with increasing functionalization of the compounds. Such markers were not detected in the pyrolysates of the bog-body tissues. Instead 4-isopropenylphenol, a characteristic pyrolysis product of Sphagnum moss, was detected in both solvent-extracted and base-treated samples of tissue. The presence of 4-isopropenylphenol in the pyrolysates of the bog-body tissues provides evidence that their preservation involves reactions of amino acids with sphagnum acid, and possibly other agents derived from the peat. The study constitutes the first chemical characterization of the pyrolysis products of modern and ancient collagen. 相似文献
66.
Tucker Joan S.; Friedman Howard S.; Tsai Catherine M.; Martin Leslie R. 《Canadian Metallurgical Quarterly》1995,10(1):3
Models of the relations between contact with pets and better health are examined in an archival prospective study using data derived from the longitudinal study initiated by Terman in 1921 (current N?=?343 men, 300 women) . In survival analyses of documented longevity, playing with pets in 1977 (M age?=?67 years) was not associated with mortality risk through 1991 for the total sample nor for those who were unmarried or those who were less satisfied with their human relationships. Playing with pets was not associated with health-prone attributes or healthy behaviors such as personality, social ties, education, and smoking. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
67.
With worldwide energy consumption rising, there is a need to reduce energy use of the housing stock. While this general idea is well-known, there is an overwhelming amount of product data and manufacturers claims through which the homebuilder or designer must sort to make informed selections of energy-efficient upgrades. The main objective of this research was to identify cost effective–energy efficient upgrades from a group of 16 commonly available choices, and rank them according to the most beneficial for the least cost. This study was conducted in Phoenix, Arizona, and included a sample of 30 production-style homes typical of the Phoenix metropolitan area. Energy-simulation software was used to perform energy evaluations and derive the benefits of each upgrade. The cost of each upgrade was obtained from a database of national average costs and from a local context. Differences in the selection of beneficial upgrades vary dramatically with the source of the cost information. This research provides a generic methodology that can be used by builders and designers to select appropriate energy-efficient upgrades for a given geographic area that will provide high operating benefits relative to the amount of capital investment. 相似文献
68.
69.
70.