全文获取类型
收费全文 | 34897篇 |
免费 | 918篇 |
国内免费 | 33篇 |
专业分类
电工技术 | 329篇 |
综合类 | 38篇 |
化学工业 | 5687篇 |
金属工艺 | 380篇 |
机械仪表 | 477篇 |
建筑科学 | 1311篇 |
矿业工程 | 100篇 |
能源动力 | 621篇 |
轻工业 | 1895篇 |
水利工程 | 233篇 |
石油天然气 | 71篇 |
无线电 | 1822篇 |
一般工业技术 | 4512篇 |
冶金工业 | 14624篇 |
原子能技术 | 197篇 |
自动化技术 | 3551篇 |
出版年
2023年 | 214篇 |
2022年 | 359篇 |
2021年 | 567篇 |
2020年 | 338篇 |
2019年 | 432篇 |
2018年 | 535篇 |
2017年 | 464篇 |
2016年 | 633篇 |
2015年 | 558篇 |
2014年 | 749篇 |
2013年 | 1422篇 |
2012年 | 1163篇 |
2011年 | 1512篇 |
2010年 | 1077篇 |
2009年 | 1015篇 |
2008年 | 1149篇 |
2007年 | 1087篇 |
2006年 | 950篇 |
2005年 | 765篇 |
2004年 | 749篇 |
2003年 | 673篇 |
2002年 | 564篇 |
2001年 | 428篇 |
2000年 | 364篇 |
1999年 | 690篇 |
1998年 | 4035篇 |
1997年 | 2464篇 |
1996年 | 1607篇 |
1995年 | 1069篇 |
1994年 | 900篇 |
1993年 | 982篇 |
1992年 | 331篇 |
1991年 | 322篇 |
1990年 | 373篇 |
1989年 | 381篇 |
1988年 | 347篇 |
1987年 | 320篇 |
1986年 | 313篇 |
1985年 | 324篇 |
1984年 | 227篇 |
1983年 | 234篇 |
1982年 | 256篇 |
1981年 | 242篇 |
1980年 | 235篇 |
1979年 | 195篇 |
1978年 | 186篇 |
1977年 | 373篇 |
1976年 | 688篇 |
1975年 | 173篇 |
1974年 | 125篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
The expression of several markers of epithelial cell proliferation was analyzed to establish baseline data for future chemoprevention studies of oral premalignant lesions. Punch biopsies (n = 60) from three different sites of oral mucosa (bucca, lateral tongue, and the floor of the mouth) were obtained from 20 normal donors of both sexes. After formaldehyde fixation and paraffin embedding, immunohistochemistry was used to detect the proliferation markers Mib-1, cyclin D1, and centromere-associated protein CENP-F. Analysis of sections stained for the three markers showed similar patterns, i.e., a low labeling index (LI) in the basal layer and a high LI in the parabasal layer at all three intraoral sites. No proliferative activity was seen above the parabasal layer (superficial layer). All sites showed similar Mib-1 LI values for the proliferative markers. The tongue epithelium exhibited higher parabasal LIs of cyclin D1 and CENP-F than did the other two sites. No significant differences were detected between smokers and nonsmokers. The data from normal mucosa were compared with those from low (n = 30)- and high (n = 17)-grade dysplastic leukoplakias. The Mib-1 LI showed a very significant change, with a 9-fold increase in the basal layer LI in dysplastic leukoplakias. Cyclin D1 and CENP-F showed similar trends with increments of up to 7-fold in the basal layer of high-grade dysplasia. Although the proliferative activity of the parabasal layer was similar in normal and leukoplakic epithelia, the superficial layer showed a significant increment in proliferative activity mainly in high-grade leukoplakia. These studies suggest that proliferation markers in the basal and superficial cells of premalignant lesions may serve as surrogate end point biomarkers for chemoprevention trials. 相似文献
93.
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
94.
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
95.
JM Samet 《Canadian Metallurgical Quarterly》1994,86(24):1813-1814
96.
97.
Non-redundant data clustering 总被引:6,自引:6,他引:0
Data clustering is a popular approach for automatically finding classes, concepts, or groups of patterns. In practice, this
discovery process should avoid redundancies with existing knowledge about class structures or groupings, and reveal novel,
previously unknown aspects of the data. In order to deal with this problem, we present an extension of the information bottleneck
framework, called coordinated conditional information bottleneck, which takes negative relevance information into account by maximizing a conditional mutual information score subject to
constraints. Algorithmically, one can apply an alternating optimization scheme that can be used in conjunction with different
types of numeric and non-numeric attributes. We discuss extensions of the technique to the tasks of semi-supervised classification
and enumeration of successive non-redundant clusterings. We present experimental results for applications in text mining and
computer vision. 相似文献
98.
Neben der Gestaltung technischer Systeme zur Unterstützung des Wissensmanagements ist die Ausgestaltung organisatorischer
Ma?nahmen gleichbedeutend wichtig. 相似文献
99.
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
100.