全文获取类型
收费全文 | 329852篇 |
免费 | 3446篇 |
国内免费 | 931篇 |
专业分类
化学 | 165090篇 |
晶体学 | 5374篇 |
力学 | 15532篇 |
综合类 | 7篇 |
数学 | 38465篇 |
物理学 | 109761篇 |
出版年
2021年 | 3126篇 |
2020年 | 3334篇 |
2019年 | 3764篇 |
2018年 | 5204篇 |
2017年 | 5441篇 |
2016年 | 7371篇 |
2015年 | 4140篇 |
2014年 | 7034篇 |
2013年 | 15939篇 |
2012年 | 12396篇 |
2011年 | 14843篇 |
2010年 | 11019篇 |
2009年 | 10922篇 |
2008年 | 13241篇 |
2007年 | 13203篇 |
2006年 | 12153篇 |
2005年 | 10537篇 |
2004年 | 9845篇 |
2003年 | 8693篇 |
2002年 | 8681篇 |
2001年 | 10401篇 |
2000年 | 7657篇 |
1999年 | 5968篇 |
1998年 | 4973篇 |
1997年 | 4811篇 |
1996年 | 4481篇 |
1995年 | 3865篇 |
1994年 | 3823篇 |
1993年 | 3702篇 |
1992年 | 4099篇 |
1991年 | 4309篇 |
1990年 | 4099篇 |
1989年 | 4011篇 |
1988年 | 3782篇 |
1987年 | 3921篇 |
1986年 | 3687篇 |
1985年 | 4632篇 |
1984年 | 4689篇 |
1983年 | 3887篇 |
1982年 | 3976篇 |
1981年 | 3702篇 |
1980年 | 3656篇 |
1979年 | 3919篇 |
1978年 | 3918篇 |
1977年 | 3911篇 |
1976年 | 3885篇 |
1975年 | 3679篇 |
1974年 | 3617篇 |
1973年 | 3651篇 |
1972年 | 2605篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Direct Addition of Amides to Glycals Enabled by Solvation‐Insusceptible 2‐Haloazolium Salt Catalysis
Yuya Nakatsuji Yusuke Kobayashi Yoshiji Takemoto 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(40):14253-14257
The direct 2‐deoxyglycosylation of nucleophiles with glycals leads to biologically and pharmacologically important 2‐deoxysugar compounds. Although the direct addition of hydroxyl and sulfonamide groups have been well developed, the direct 2‐deoxyglycosylation of amide groups has not been reported to date. Herein, we show the first direct 2‐deoxyglycosylation of amide groups using a newly designed Brønsted acid catalyst under mild conditions. Through mechanistic investigations, we discovered that the amide group can inhibit acid catalysts, and the inhibition has made the 2‐deoxyglycosylation reaction difficult. Diffusion‐ordered two‐dimensional NMR spectroscopy analysis implied that the 2‐chloroazolium salt catalyst was less likely to form aggregates with amides in comparison to other acid catalysts. The chlorine atom and the extended π‐scaffold of the catalyst played a crucial role for this phenomenon. This relative insusceptibility to inhibition by amides is more responsible for the catalytic activity than the strength of the acidity. 相似文献
122.
123.
Avanesyan V. T. Provotorov P. S. Stozharov V. M. Sychev M. M. Eruzin A. A. 《Optics and Spectroscopy》2021,129(11):1196-1199
Optics and Spectroscopy - The optical absorption spectra of zinc oxide (ZnO) thin films formed by reactive cathode sputtering are studied. The observed absorption of light in the region of photon... 相似文献
124.
Saleh Z. M. Nasser H. Özkol E. Günöven M. Abak K. Canli S. Bek A. Turan R. 《Journal of nanoparticle research》2015,17(10):1-12
Journal of Nanoparticle Research - Plasmonic interfaces consisting of silver nanoparticles of different sizes (50–100&;nbsp;nm) have been processed by the self-assembled dewetting... 相似文献
125.
126.
127.
Dorovskikh S. I. Stabnikov P. А. Zelenina L. N. Sysoev S. V. Morozova N. B. 《Russian Journal of General Chemistry》2021,91(10):1977-1983
Russian Journal of General Chemistry - Thermogravimetry, differential scanning calorimetry, and flow methods were used to investigate thermal properties of a series of cobalt(II)... 相似文献
128.
Braikova A. M. Matveiko N. P. Protasov S. K. 《Russian Journal of General Chemistry》2021,91(13):2774-2778
Russian Journal of General Chemistry - The technical legal acts that regulate the quality and safety parameters of mineral waters out were analyzed. Seven samples of mineral waters produced in... 相似文献
129.
João Marcos G. Barbosa Milenna K. Fernandes Rodrigues Lurian C. David Taynara C. e Silva Danielly A. Fortuna Lima Naiara Z. Pereira Emmanuel B. D'Alessandro Anselmo E. de Oliveira Paulo H. Jorge da Cunha Maria Clorinda S. Fioravanti Nelson R. Antoniosi Filho 《Biomedical chromatography : BMC》2020,34(11):e4935
An innovative volatolomic approach employs the detection of biomarkers present in cerumen (earwax) to identify cattle intoxication by Stryphnodendron rotundifolium Mart., Fabaceae (popularly known as barbatimão). S. rotundifolium is a poisonous plant with the toxic compound undefined and widely distributed throughout the Brazilian territory. Cerumen samples from cattle of two local Brazilian breeds (‘Curraleiro Pé-Duro’ and ‘Pantaneiro’) were collected during an experimental intoxication protocol and analyzed using headspace (HS)/GC–MS followed by multivariate analysis (genetic algorithm for a partial least squares, cluster analysis, and classification and regression trees). A total of 106 volatile organic metabolites were identified in the cerumen samples of bovines. The intoxication by S. rotundifolium influenced the cerumen volatolomic profile of the bovines throughout the intoxication protocol. In this way, it was possible to detect biomarkers for cattle intoxication. Among the biomarkers, 2-octyldecanol and 9-tetradecen-1-ol were able to discriminate all samples between intoxicated and nonintoxicated bovines. The cattle intoxication diagnosis by S. rotundifolium was accomplished by applying the cerumen analysis using HS/GC–MS, in an easy, accurate, and noninvasive way. Thus, the proposed bioanalytical chromatography protocol is a useful tool in veterinary applications to determine this kind of intoxication. 相似文献
130.
Chandrachood Pranav S. Jadhav Amol R. Garud Dinesh R. Deshpande Nirmala R. Puranik Vedavati G. Kashalkar Rajashree V. 《Research on Chemical Intermediates》2020,46(12):5219-5230
Research on Chemical Intermediates - A series of quinoxaline derivatives were efficiently synthesized by convenient and simple procedure in excellent yields using 1 wt.% of titanium silicate (TS-1)... 相似文献