全文获取类型
收费全文 | 37311篇 |
免费 | 1771篇 |
国内免费 | 26篇 |
专业分类
电工技术 | 166篇 |
综合类 | 10篇 |
化学工业 | 6017篇 |
金属工艺 | 445篇 |
机械仪表 | 574篇 |
建筑科学 | 842篇 |
矿业工程 | 52篇 |
能源动力 | 631篇 |
轻工业 | 5669篇 |
水利工程 | 312篇 |
石油天然气 | 130篇 |
武器工业 | 1篇 |
无线电 | 1096篇 |
一般工业技术 | 4436篇 |
冶金工业 | 14969篇 |
原子能技术 | 85篇 |
自动化技术 | 3673篇 |
出版年
2024年 | 69篇 |
2023年 | 282篇 |
2022年 | 319篇 |
2021年 | 771篇 |
2020年 | 686篇 |
2019年 | 712篇 |
2018年 | 1235篇 |
2017年 | 1207篇 |
2016年 | 1264篇 |
2015年 | 976篇 |
2014年 | 1147篇 |
2013年 | 2334篇 |
2012年 | 1824篇 |
2011年 | 1652篇 |
2010年 | 1325篇 |
2009年 | 1191篇 |
2008年 | 1204篇 |
2007年 | 1103篇 |
2006年 | 734篇 |
2005年 | 615篇 |
2004年 | 578篇 |
2003年 | 558篇 |
2002年 | 475篇 |
2001年 | 361篇 |
2000年 | 297篇 |
1999年 | 616篇 |
1998年 | 4984篇 |
1997年 | 2993篇 |
1996年 | 1844篇 |
1995年 | 1024篇 |
1994年 | 805篇 |
1993年 | 915篇 |
1992年 | 152篇 |
1991年 | 202篇 |
1990年 | 169篇 |
1989年 | 179篇 |
1988年 | 212篇 |
1987年 | 172篇 |
1986年 | 146篇 |
1985年 | 130篇 |
1984年 | 64篇 |
1983年 | 45篇 |
1982年 | 85篇 |
1981年 | 107篇 |
1980年 | 124篇 |
1978年 | 50篇 |
1977年 | 289篇 |
1976年 | 660篇 |
1975年 | 46篇 |
1973年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
This paper reviews the pathogenesis of Mycobacterium bovis infection in cattle, focusing on aspects relating to the host rather than the organism. A broad concept of pathogenesis has been considered and information is presented on sources and routes of infection, as well as the immune responses and pathology. In addition, data is presented on the excretion of M. bovis from tuberculous cattle. 相似文献
103.
104.
105.
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
106.
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
107.
JM Samet 《Canadian Metallurgical Quarterly》1994,86(24):1813-1814
108.
109.
RM Martín‐Aranda E Ortega‐Cantero ML Rojas‐Cervantes MA Vicente‐Rodríguez MA Baares‐Muoz 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(2):234-238
α,β‐Unsaturated nitriles have been synthesized by Knoevenagel condensation of a carbonylic compound with malononitrile, assisted by sonochemical irradiation. Two alkaline‐promoted clays (Li+‐ and Cs+‐exchanged saponites) have been employed as catalysts. The influence of the carbonylic compound (benzaldehyde or cyclohexanone) and the use of a solvent on the catalytic activity have been studied. Remarkable increase in the conversion values has been found when the reaction is activated by ultrasound, as compared with the thermal activation. In this green, solvent‐free procedure, α,β‐unsaturated nitriles have been produced in very high yields (97%) when the Cs+‐saponite is used as catalyst. Copyright © 2004 Society of Chemical Industry 相似文献
110.
Summary The nucleophilic substitution with C6H5SNa, at -30°C, is compared for five PVC samples with various contents of isotactic triads. The conversion curves consist of a very fast stage followed by a steady one. All the samples are found to behave in the same way except for the content of the structures involved in the fast period. This content is estimated by extrapolating the straight lines of the steady stages to zero time. The obtained values are found to be a linear function of the content of isotactic triads. The results, together with some earlier ones, allow for the content of the labile non-defect structures in PVC to be determined. 相似文献