全文获取类型
收费全文 | 48435篇 |
免费 | 2060篇 |
国内免费 | 59篇 |
专业分类
电工技术 | 294篇 |
综合类 | 90篇 |
化学工业 | 7757篇 |
金属工艺 | 808篇 |
机械仪表 | 805篇 |
建筑科学 | 1348篇 |
矿业工程 | 98篇 |
能源动力 | 869篇 |
轻工业 | 5665篇 |
水利工程 | 386篇 |
石油天然气 | 219篇 |
武器工业 | 5篇 |
无线电 | 2372篇 |
一般工业技术 | 7463篇 |
冶金工业 | 16450篇 |
原子能技术 | 222篇 |
自动化技术 | 5703篇 |
出版年
2023年 | 362篇 |
2022年 | 384篇 |
2021年 | 944篇 |
2020年 | 776篇 |
2019年 | 730篇 |
2018年 | 1568篇 |
2017年 | 1556篇 |
2016年 | 1604篇 |
2015年 | 1159篇 |
2014年 | 1473篇 |
2013年 | 2853篇 |
2012年 | 2466篇 |
2011年 | 2324篇 |
2010年 | 1839篇 |
2009年 | 1639篇 |
2008年 | 1882篇 |
2007年 | 1631篇 |
2006年 | 1232篇 |
2005年 | 1032篇 |
2004年 | 961篇 |
2003年 | 875篇 |
2002年 | 761篇 |
2001年 | 483篇 |
2000年 | 500篇 |
1999年 | 847篇 |
1998年 | 5215篇 |
1997年 | 3056篇 |
1996年 | 2045篇 |
1995年 | 1157篇 |
1994年 | 990篇 |
1993年 | 989篇 |
1992年 | 258篇 |
1991年 | 320篇 |
1990年 | 271篇 |
1989年 | 279篇 |
1988年 | 257篇 |
1987年 | 236篇 |
1986年 | 248篇 |
1985年 | 265篇 |
1984年 | 189篇 |
1983年 | 145篇 |
1982年 | 190篇 |
1981年 | 212篇 |
1980年 | 219篇 |
1979年 | 139篇 |
1978年 | 142篇 |
1977年 | 338篇 |
1976年 | 740篇 |
1975年 | 99篇 |
1973年 | 85篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
101.
102.
A de Meester C Six P Henin C Scavée R Luwaert JM Chaudron 《Canadian Metallurgical Quarterly》1996,89(12):1673-1676
The authors report the case of a 32 year old woman who was shot with a shotgun. Acute inferior wall infarction was detected fortuitously on electrocardiography and coronary angiography showed occlusion of the right coronary artery with lead shot. The single coronary lesion, absence, of other cardiac complications (haemopericardium, cardiac perforation, ...) and the favourable outcome with conservative medical treatment has not been previously reported to the authors' knowledge. 相似文献
103.
M González Cabré 《Canadian Metallurgical Quarterly》1996,18(6):279-282
The activity of N-acetyltransferase (NAT) and catalase was measured in the tissues of placenta, full venous blood and full umbilical cord blood in 141 complicated pregnancies. The control group consisted of 34 physiological pregnancies. The enzymes activity was marked by use of biochemical methods. It has been shown that NAT and catalase is the most active in the group of physiological pregnancies. The decrease of NAT and catalase in venous and umbilical cord blood is correlated with the decrease of the activity these enzymes in placenta. 相似文献
104.
105.
B Marchou N Picot P Chavanet JC Auvergnat M Armengaud P Devilliers JE Cerisier FN Marié JL Excler 《Canadian Metallurgical Quarterly》1993,11(14):1383-1385
To determine whether a 3-week hepatitis B (HB) vaccination could achieve protective immunity, 89 healthy non-immunized young adults received three doses of 20 micrograms each of HBs antigen (GenHevac B, Pasteur) and were randomly assigned to schedule A (n = 44): two doses at day 0, one dose at day 21; or schedule B (n = 45): one dose at days 0, 10 and 21. Seroprotection rates (anti-HBs > or = 10 mIU ml-1) for groups A and B respectively were: 23 and 40% at day 21; and 77 and 91% at day 82 (not significant). Anti-HBs geometric mean titres were higher in group B than in group A (p < 0.05) at days 21 (6.4 versus 3.8) and 82 (77.6 versus 33.5). One year after primary vaccination, the seroprotection rate remained as high as 90% in the vaccinees of group B; after boosting all vaccinees had protective levels of anti-HBs antibodies. Thus 3-week HB vaccination with GenHevac B allowed early and durable protective immunity. 相似文献
106.
GO Aspinall AG McDonald H Pang LA Kurjanczyk JL Penner 《Canadian Metallurgical Quarterly》1993,268(24):18321-18329
A water-soluble antigenic polysaccharide of high M(r) associated with the lipopolysaccharide has been isolated from phenol-water extraction of cells of Campylobacter coli serotype O:30. The polysaccharide and oligosaccharide degradation products formed on O-dephosphorylation and by periodate oxidation followed by reduction have been investigated by one- and two-dimensional 1H, 13C, and 31P NMR. It is concluded that the antigenic polysaccharide has a teichoic acid-like structure with a poly-Ribitol phosphate, [5-Ribitol-1-P]n, backbone with side chains at O-2 of O-(6-deoxy-beta-D-talo-heptopyranosyl)-(1-->4)-(2-acetylamino-2-deoxy-beta-D- glucopyranosyl) units. The structure is unusual in Gram-negative bacteria and is unique in possessing 6-deoxy-D-talo-heptose as a constituent sugar. Evidence for the relationship of the antigenic polysaccharide to the lipopolysaccharide of low M(r) is discussed. 相似文献
107.
Recent data have suggested the existence of at least two major classes of calcitonin gene-related peptide (CGRP) receptors in brain and peripheral tissues [Henke et al., Brain Res., 410 (1987) 404-408; Dennis et al., J. Pharmacol. Exp. Ther., 251 (1989) 718-725; ibid, 254 (1990) 123-128; Quirion et al., Ann. NY Acad. Sci., 657 (1992) 88-105]. However, little is currently known in the structure characteristics of CGRP receptors as cloning as yet to be reported. In the present study, the sensitivity of [125I]humanCGRP alpha binding to guanine nucleotides and temperature was investigated in guinea pig atria (prototypical CGRP1 tissue) guinea pig vas deferens (prototypical CGRP2 tissue) and in the rat brain and cerebellum (mixed assay). Binding isotherms of [125I]hCGRP alpha in those four tissue preparations were curvilinear and best fitted to a two-site model under most assay conditions. The high affinity binding component was highly temperature-sensitive and accounted, under experimental conditions, for up to 18% of the total population of receptors. Moreover, these high affinity sites were also highly sensitive to guanine nucleotides (Gpp(NH)p, 100 microM) in all preparations although to a different extend depending upon assay temperatures. Taken together, this suggests that the different CGRP receptor subtypes present in these tissue all belong to a G-protein coupled receptor family. 相似文献
108.
KK Doak CE Haas KJ Dunnigan RA Reiss JR Reiser J Huntress JL Altavela 《Canadian Metallurgical Quarterly》1998,18(3):637-645
In the absence of E1B, the 289-amino acid product of human adenovirus type 5 13S E1A induces p53-independent apoptosis by a mechanism that requires viral E4 gene products (Marcellus, R.C., J.C. Teodoro, T. Wu, D.E. Brough, G. Ketner, G.C. Shore, and P.E. Branton. 1996. J. Virol. 70:6207-6215) and involves a mechanism that includes activation of caspases (Boulakia, C.A., G. Chen, F.W. Ng, J. G. Teodoro, P.E. Branton, D.W. Nicholson, G.G. Poirier, and G.C. Shore. 1996. Oncogene. 12:529-535). Here, we show that one of the E4 products, E4orf4, is highly toxic upon expression in rodent cells regardless of the p53 status, and that this cytotoxicity is significantly overcome by coexpression with either Bcl-2 or Bcl-XL. Conditional expression of E4orf4 induces a cell death process that is characterized by apoptotic hallmark features, such as externalization of phosphatidylserine, loss of mitochondrial membrane potential, cytoplasmic vacuolation, condensation of chromatin, and internucleosomal DNA degradation. However, the wide-spectrum inhibitor of caspases, tetrapeptide zVAD-fmk, does not affect any of these apoptogenic manifestations, and does not alter the kinetics of E4orf4-induced cell death. Moreover, E4orf4 expression does not result in activation of the downstream effector caspase common to most apoptosis-inducing events, caspase-3 (CPP32). We conclude, therefore, that in the absence of E1A, E4orf4 is sufficient by itself to trigger a p53-independent apoptosis pathway that may operate independently of the known zVAD-inhibitable caspases, and that may involve an as yet uncharacterized mechanism. 相似文献
109.
110.