全文获取类型
收费全文 | 11181篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 11篇 |
化学工业 | 182篇 |
金属工艺 | 11篇 |
机械仪表 | 27篇 |
建筑科学 | 21篇 |
能源动力 | 25篇 |
轻工业 | 145篇 |
水利工程 | 4篇 |
无线电 | 73篇 |
一般工业技术 | 179篇 |
冶金工业 | 10418篇 |
原子能技术 | 16篇 |
自动化技术 | 80篇 |
出版年
2021年 | 8篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 17篇 |
2015年 | 8篇 |
2014年 | 17篇 |
2013年 | 42篇 |
2012年 | 39篇 |
2011年 | 39篇 |
2010年 | 25篇 |
2009年 | 15篇 |
2008年 | 32篇 |
2007年 | 35篇 |
2006年 | 34篇 |
2005年 | 30篇 |
2004年 | 33篇 |
2003年 | 42篇 |
2002年 | 20篇 |
2001年 | 18篇 |
2000年 | 23篇 |
1999年 | 306篇 |
1998年 | 3377篇 |
1997年 | 1975篇 |
1996年 | 1207篇 |
1995年 | 688篇 |
1994年 | 543篇 |
1993年 | 648篇 |
1992年 | 71篇 |
1991年 | 139篇 |
1990年 | 118篇 |
1989年 | 137篇 |
1988年 | 152篇 |
1987年 | 110篇 |
1986年 | 103篇 |
1985年 | 67篇 |
1984年 | 22篇 |
1983年 | 21篇 |
1982年 | 64篇 |
1981年 | 61篇 |
1980年 | 75篇 |
1979年 | 9篇 |
1978年 | 30篇 |
1977年 | 203篇 |
1976年 | 475篇 |
1975年 | 15篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1965年 | 6篇 |
1955年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
JH Viles JB Mitchell SL Gough PM Doyle CJ Harris PJ Sadler JM Thornton 《Canadian Metallurgical Quarterly》1996,242(2):352-362
The aqueous solution structure of the cyclic pentapeptide cyclo(-Ser-D-Leu-Asp-Val-Pro-) has been determined by two-dimensional 1H-NMR spectroscopy, combined with a conformational search and distance-geometry calculations. As many as five conformers in slow exchange were observed, and the rate of interconversion between components was measured from the build-up rates of exchange peaks. NMR data allowed the structures of the two predominant conformers to be determined. The major component (66%) contained a cis-proline as part of a type-VIa2 beta-turn encompassing residues Asp-Val-cis-Pro-Ser. The second component (16%) contained only trans-amide bonds, and a type-VIII beta-turn formed by residues Val-Pro-Ser-D-Leu. These structures are discussed in relation to the (phi, psi), space available to the cyclic pentapeptide, determined by a conformational search, and in relation to previously published cyclic-pentapeptide structures. The molecule exhibits activity in a scintillation-proximity assay for the inhibition of the interaction between the integrin very-late antigen-4 (VLA-4; alpha 4 beta 1) and vascular-cell-adhesion molecule-1 (VCAM-1). The structure/activity relationship of the LDV sequence is discussed and related to the recently published X-ray structure of VCAM-1. The relevance of the work to the design of anti-inflammatory drugs is discussed. 相似文献
43.
Earlier studies have established that mutant strains of Azotobacter vinelandii that do not synthesize ferredoxin I (AvFdI) overexpress another protein designated Protein X (Morgan, T. V., Lundell, P. J., and Burgess, B. K. (1988) J. Biol. Chem. 263, 1370-1375). This protein has now been purified using two-dimensional gel electrophoresis as an assay. The purified protein is a monomer with M(r) approximately 29,000 which degrades slowly to a specific M(r) approximately 22,000 form when stored in solution. The native protein is bright yellow and contains noncovalently attached FAD that is reduced by either dithionite or NADPH without formation of a stable semiquinone. Titration with NADP+/NADPH gives an E0' value of approximately -327 mV versus SHE. Because this E0' is so close to that of the NADP+/NADPH couple it is not clear if Protein X is an NADPH oxidase or an NADP+ reductase in vivo. Comparison of the NH2-terminal sequence and other properties of Protein X with those of other proteins, suggests that it is likely to be related to the Escherichia coli ferredoxin NADP+ reductase (the fpr gene product), and affinity chromatography shows that Protein X binds specifically to AvFdI. 相似文献
44.
JM Samet 《Canadian Metallurgical Quarterly》1994,86(24):1813-1814
45.
46.
RM Bionta G Blewitt CB Bratton D Casper A Ciocio R Claus M Crouch ST Dye S Errede GW Foster W Gajewski KS Ganezer M Goldhaber TJ Haines TW Jones D Kielczewska WR Kropp JG Learned JM LoSecco J Matthews HS Park LR Price F Reines J Schulz S Seidel E Shumard D Sinclair HW Sobel JL Stone L Sulak R Svoboda G Thornton van der Velde JC C Wuest 《Canadian Metallurgical Quarterly》1987,36(1):30-36
47.
48.
Patients with ulcerative colitis are usually non- or ex-smokers in contrast to Crohn's disease where smoking is common. Abnormalities of quantity and quality of intestinal mucus have been postulated in the pathogenesis of these diseases. It is possible that smoking habit may exert its effects via changes in mucus in inflammatory bowel disease. We have therefore studied incorporation of N-acetylglucosamine into synthesized colonic mucin in explants from 85 controls with normal colonoscopic appearances and histology, including 27 smokers and 58 nonsmokers, 36 patients with ulcerative colitis and 19 with ileocolonic Crohn's disease over 24 h in tissue culture. Incorporation of N-acetylglucosamine into normal explants was 31.3 +/- (SD) 7.1 dpm/microgram biopsy protein, incorporation was increased in patients with active Crohn's disease (mean 41.2 +/- (SD) 10.4 dpm/microgram biopsy protein, p = 0.003), decreased in inactive ulcerative colitis (mean 24.1 +/- 7.8 dpm/microgram biopsy protein, p = 0.0006) but normal in active ulcerative colitis (mean 35.0 +/- 13.8 dpm/microgram biopsy protein, p = 0.44). No significant relationship was found between cigarette smoking habits and mucus synthesis in controls with normal mucosa (nonsmokers, n = 58, mean 31.0 +/- (SD) 7.52 dpm/microgram biopsy protein; smokers, n = 27, mean 31.8 +/- (SD) 6.1 dpm/microgram biopsy protein, p = 0.9). This study shows that mucus glycoprotein synthesis is reduced in inactive ulcerative colitis, rising to normal levels in active disease and that synthesis is increased in Crohn's disease. There is no effect of smoking on mucus synthesis by control biopsies suggesting that the differences seen in inflammatory bowel disease are not related to cigarette smoking. 相似文献
49.
Concentrations of 11 trace elements were determined in 56 control and 98 Alzheimer's disease (AD) olfactory bulb, olfactory tract, olfactory trigone, piriform cortex and amygdala specimens by instrumental neutron activation analysis. Iron and zinc were significantly elevated and bromine was significantly depleted in olfactory regions of AD patients, compared with normal age-matched control subjects. Elevated iron could possibly play a role in neuronal degeneration in AD by enhancing reactive free radical formation. 相似文献
50.