全文获取类型
收费全文 | 232376篇 |
免费 | 17811篇 |
国内免费 | 9342篇 |
专业分类
电工技术 | 12691篇 |
技术理论 | 24篇 |
综合类 | 14412篇 |
化学工业 | 39375篇 |
金属工艺 | 13401篇 |
机械仪表 | 14723篇 |
建筑科学 | 17802篇 |
矿业工程 | 7587篇 |
能源动力 | 6516篇 |
轻工业 | 13710篇 |
水利工程 | 3662篇 |
石油天然气 | 16826篇 |
武器工业 | 1671篇 |
无线电 | 25490篇 |
一般工业技术 | 27789篇 |
冶金工业 | 12939篇 |
原子能技术 | 2313篇 |
自动化技术 | 28598篇 |
出版年
2024年 | 1016篇 |
2023年 | 3859篇 |
2022年 | 6591篇 |
2021年 | 9273篇 |
2020年 | 7207篇 |
2019年 | 6098篇 |
2018年 | 6857篇 |
2017年 | 7671篇 |
2016年 | 6858篇 |
2015年 | 9003篇 |
2014年 | 11417篇 |
2013年 | 13488篇 |
2012年 | 14446篇 |
2011年 | 15749篇 |
2010年 | 13598篇 |
2009年 | 12901篇 |
2008年 | 12559篇 |
2007年 | 12034篇 |
2006年 | 12543篇 |
2005年 | 10909篇 |
2004年 | 7365篇 |
2003年 | 6330篇 |
2002年 | 5533篇 |
2001年 | 4948篇 |
2000年 | 5513篇 |
1999年 | 6528篇 |
1998年 | 5516篇 |
1997年 | 4515篇 |
1996年 | 4233篇 |
1995年 | 3545篇 |
1994年 | 2851篇 |
1993年 | 1981篇 |
1992年 | 1554篇 |
1991年 | 1248篇 |
1990年 | 942篇 |
1989年 | 747篇 |
1988年 | 541篇 |
1987年 | 340篇 |
1986年 | 282篇 |
1985年 | 198篇 |
1984年 | 143篇 |
1983年 | 116篇 |
1982年 | 126篇 |
1981年 | 98篇 |
1980年 | 71篇 |
1979年 | 36篇 |
1978年 | 26篇 |
1977年 | 20篇 |
1976年 | 35篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
M Liu 《Canadian Metallurgical Quarterly》1994,50(4):2925-2928
82.
83.
C-reactive protein (CRP) is a prototypic acute phase protein in human and rabbit. Although it is structurally and functionally conserved from invertebrate to human, there are species-specific differences in patterns of expression and putative function. To further investigate the biological significance, regulation, and evolution of CRP, we isolated Xenopus CRP and subsequently derived and sequenced corresponding cDNA and the genomic clones. The structure and expression of Xenopus CRP were also compared to those of the other CRPs. Analyses of the amino acid sequence and the nucleotide sequence reveal that the mature Xenopus CRP is a 222-amino acid protein preceded by a 16-residue signal peptide. During development, Xenopus CRP is expressed, only when the liver appears, and therefore is not likely to play a role in early embryonic development. Compared to other species, Xenopus CRP is present at an intermediate low level of < 1 microgram/ml in the normal serum. Unlike human and rabbit CRP, Xenopus CRP is not induced by turpentine or heatshock treatment. The heatshock consensus sequence (Woo, P., Korenberg, J. R., and Whitehead, A. S. (1985) J. Biol. Chem. 265, 4136-4142) are not present in the Xenopus CRP gene. It is suggested that Xenopus CRP represents a transitional period in CRP evolution when host defenses switched from primitive innate immunity to a much more complex immune system. The constitutive functions of CRP gradually became less essential as the result of the development of a complex immune system. 相似文献
84.
Complements in serum and middle ear effusion were determined in 20 patients with secretory otitis media, and compared with those in the normal controls. The C5 and C1-INH in serum of the patients were significantly higher. On the contrary, C9 and B factor (Bf) were significantly lower, and the circulatory immunocomplex was also higher. In patients with secretory otitis media, the middle ear effusion levels of C3, C4 and C5 were significantly lower, and Bf and immunocomplex were significantly higher than those in serum. The results suggest that the ability of complements in clearing immunocomplex is low. Therefore, the immunocomplex may deposit in the mucosa of the middle ear. Thus the permeability of capillary will be increased, and the middle ear effusion occurs. 相似文献
85.
86.
Qing Zhong Liu 《Microwave Theory and Techniques》1992,40(2):329-337
Unified analytical expressions have been derived for calculating the resonant frequencies, transimpedance and equivalent input noise current densities of the four most widely used tuned optical receiver front ends built with FETs and p-i-n diodes. A more accurate FET model has been used to improve the accuracy of the analysis. The Miller capacitance has been taken into account, and its impact on the performances of the tuned front ends has been demonstrated. The accuracy of the expressions has been verified by Touchstone simulations. The agreement between the calculated and simulated performances of the front ends is very good. The expressions can be used to investigate the performances of different tuned front ends in a very simple way and provide a good starting point for further computer optimizations of the front ends 相似文献
87.
紫杉醇的全合成困难,许多工作还只能停留在实验室的模型化合物上。作者以思想实验方法提出了:先以D-A反应形成A环和C环,然后用两步形成B环,最后形成D环,以此完成紫杉醇母核的全合成。 相似文献
88.
89.
90.