全文获取类型
收费全文 | 3510篇 |
免费 | 138篇 |
国内免费 | 10篇 |
专业分类
化学 | 2763篇 |
晶体学 | 28篇 |
力学 | 47篇 |
数学 | 334篇 |
物理学 | 486篇 |
出版年
2023年 | 21篇 |
2022年 | 40篇 |
2021年 | 40篇 |
2020年 | 60篇 |
2019年 | 55篇 |
2018年 | 36篇 |
2017年 | 35篇 |
2016年 | 90篇 |
2015年 | 96篇 |
2014年 | 106篇 |
2013年 | 155篇 |
2012年 | 236篇 |
2011年 | 279篇 |
2010年 | 140篇 |
2009年 | 114篇 |
2008年 | 241篇 |
2007年 | 236篇 |
2006年 | 231篇 |
2005年 | 232篇 |
2004年 | 195篇 |
2003年 | 151篇 |
2002年 | 143篇 |
2001年 | 57篇 |
2000年 | 53篇 |
1999年 | 39篇 |
1998年 | 22篇 |
1997年 | 22篇 |
1996年 | 40篇 |
1995年 | 26篇 |
1994年 | 31篇 |
1993年 | 33篇 |
1992年 | 38篇 |
1991年 | 24篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 18篇 |
1984年 | 13篇 |
1982年 | 19篇 |
1981年 | 22篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1977年 | 14篇 |
1976年 | 17篇 |
1975年 | 14篇 |
1973年 | 11篇 |
1972年 | 14篇 |
1969年 | 9篇 |
排序方式: 共有3658条查询结果,搜索用时 31 毫秒
11.
Lisa A. Liotta Irene Medina Jennifer L. Robinson Po-Shen Pan Jennifer V.C. Johnston Fiona A. Curtis Shelli R. McAlpine 《Tetrahedron letters》2004,45(46):8447-8450
Described are the syntheses of 15 macrocyclic peptides designed to trap Holliday junctions (HJs) in bacteria during site-specific and homologous recombination. This leads to inhibiting bacterial growth. These second generation macrocycles were based on the C-2 symmetrical HJ. They were synthesized using a strategy that permits elucidation of the amino acid role in binding HJs. The syntheses of these macrocycles are an important step in the development of a new class of antibiotics. 相似文献
12.
Benjamin M. NugentAmie L. Williams E.N. PrabhakaranJeffrey N. Johnston 《Tetrahedron》2003,59(45):8877-8888
The complete scope of free radical-mediated vinyl amination is described, using 5-exo-trig cyclizations of vinyl radicals to the nitrogen of azomethines. The focus is primarily on N,N-dialkyl enamines since their nucleophilicity renders them the most challenging enamines to synthesize using redox conditions. These studies establish several encouraging precedents for the broader application of this strategy. 相似文献
13.
Thomas J. Delia Dennis P. Anderson Jennifer M. Schomaker 《Journal of heterocyclic chemistry》2004,41(6):991-993
In a continuation of our studies involving the nucleophilic displacement of one of the chlorines from 2,4,6‐trichloropyrimidine, we now report the initial displacement of one of the fluorine atoms from 2,4,6‐trifluoropyrimidine using both aliphatic and aromatic amines. The monosubstitution products favor 2‐substitution with ammonia and ethanolamine while aniline gave the 4‐substituted derivative as the preferred product. 相似文献
14.
Johnston CG Vestal JR 《Antarctic journal of the United States / National Science Foundation》1988,21(5):225-226
Photosynthetic activity of three cryptoendolithic microbial communities was studied under controlled conditions in the laboratory. In two of these communities, the dominant organisms were lichens, collected from Linnaeus Terrace and from Battleship Promontory. The third community, dominated by cyanobacteria, was collected from Battleship Promontory. Both sites are in the ice-free valleys of southern Victoria Land. Previous efforts have shown how physical conditions can influence metabolic activity in endolithic communities (Kappen and Friedmann 1983; Kappen, Friedmann, and Garty 1981; Vestal, Federle, and Friedmann 1984). Biological activity can also be strongly influenced by the chemical environment. Inorganic nutrients such as nitrate, ammonia, and phosphate are often limiting factors, so their effects on photosynthetic carbon-14 bicarbonate incorporation were investigated. Iron and manganese are two metals present in Linnaeus Terrace and Battleship Promontory sandstones, and their effects on photosynthesis were also studied. The results may add to our understanding of biogeochemical interactions within this unique microbial community. 相似文献
15.
16.
17.
18.
19.
Primus TM Kohler DJ Goodall MA Yoder C Mathies T Miller L Johnston JJ Vercauteren K 《Journal of AOAC International》2003,86(6):1144-1148
4,4'-Dinitrocarbanilide (DNC) was extracted from chicken, duck, goose, and snake eggs and isolated by reversed-phase liquid chromatography. DNC was detected by ultraviolet absorbance at 347 nm and quantitated by comparison with a calibration standard. Recoveries of DNC from fortified control chicken, duck, goose, and snake egg samples were determined for DNC levels of 0.16, 10, and 16 microg/g. The mean recoveries from chicken, duck, goose, and snake eggs were 92 +/- 4, 88 +/- 9, 87 +/- 7, and 95 +/- 6%, respectively. The method limits of detection for DNC in chicken, duck, goose, and snake eggs ranged from 0.015 to 0.035 microg/g. The reported method is much simpler than and equally efficient as previous methods developed for the determination of DNC residues in egg contents. 相似文献
20.