全文获取类型
收费全文 | 6145篇 |
免费 | 93篇 |
国内免费 | 38篇 |
专业分类
化学 | 3985篇 |
晶体学 | 48篇 |
力学 | 191篇 |
数学 | 1125篇 |
物理学 | 927篇 |
出版年
2022年 | 33篇 |
2021年 | 38篇 |
2020年 | 55篇 |
2019年 | 45篇 |
2018年 | 46篇 |
2017年 | 43篇 |
2016年 | 85篇 |
2015年 | 87篇 |
2014年 | 103篇 |
2013年 | 298篇 |
2012年 | 289篇 |
2011年 | 338篇 |
2010年 | 179篇 |
2009年 | 165篇 |
2008年 | 320篇 |
2007年 | 318篇 |
2006年 | 313篇 |
2005年 | 296篇 |
2004年 | 270篇 |
2003年 | 224篇 |
2002年 | 222篇 |
2001年 | 116篇 |
2000年 | 92篇 |
1999年 | 72篇 |
1998年 | 72篇 |
1997年 | 68篇 |
1996年 | 94篇 |
1995年 | 67篇 |
1994年 | 70篇 |
1993年 | 71篇 |
1992年 | 84篇 |
1991年 | 78篇 |
1990年 | 63篇 |
1989年 | 72篇 |
1988年 | 52篇 |
1987年 | 51篇 |
1986年 | 49篇 |
1985年 | 95篇 |
1984年 | 103篇 |
1983年 | 77篇 |
1982年 | 103篇 |
1981年 | 83篇 |
1980年 | 89篇 |
1979年 | 81篇 |
1978年 | 87篇 |
1977年 | 81篇 |
1976年 | 72篇 |
1975年 | 85篇 |
1974年 | 67篇 |
1973年 | 79篇 |
排序方式: 共有6276条查询结果,搜索用时 0 毫秒
1.
2.
Graham Smith 《The Journal of the Operational Research Society》1989,40(9):761-770
Courses which teach discrete-event simulation are based on many different simulation languages. The requirements for a language to support teaching simulation are discussed. In particular, it is recommended that such languages separate into distinct modules those aspects of simulation which are taught as separate topics. Implementation of the separation is discussed. The SEESIM language, developed as a teaching aid, is described, and examples of its use are given. Straightforward use of SEESIM can be learned quickly, yet the language provides facilities for a staged introduction to advanced concepts of simulation. 相似文献
3.
4.
Amine boranes bearing hydrophobic substituents were used to reduce aryl ketones in competition with a methyl ketone. Their high stability in protic solvents combined with their ease of preparation made amine boranes useful compounds in the study of hydrophobically directed selective reductions. Several characteristics of the reducing agent were found to be important in determining the reaction selectivity, including available hydrocarbon surface area, degree of fluorination, and proximity of the hydrophobic group to the active hydrides. 相似文献
5.
6.
Stefan Pitsch Sebastian Wendeborn Ramanarayanan Krishnamurthy Armin Holzner Mark Minton Martin Bolli Christian Miculca Norbert Windhab Ronald Micura Michael Stanek Bernhard Jaun Albert Eschenmoser 《Helvetica chimica acta》2003,86(12):4270-4363
Pyranosyl‐RNA (‘p‐RNA’ ) is an oligonucleotide system isomeric to natural RNA and composed of the very same building blocks as RNA. Its generational, chemical, and informational properties are deemed to be those of an alternative nucleic acid system that could have been a candidate in Nature's evolutionary choice of the molecular basis of genetic function. We consider the study of the chemistry of p‐RNA as etiologically relevant in the sense that knowledge of its structural, chemical, and informational properties on the chemical level offers both a perspective and reference points for the recognition of specific structural assets of the RNA structure that made it the (supposedly) superior system among possible alternatives and, therefore, the system that became part of biology as we know it today. The paper describes the chemical synthesis of β‐d‐ (and L )‐ribopyranosyl‐(4′→2′)‐oligonucleotide sequences, presents a resume of their structural and chemical properties, and cautiously discusses what we may and may not have learned from the pyranosyl isomer of RNA with respect to the conundrum of RNA's origin. 相似文献
7.
Graham R. Knox Peter L. Pauson Debra Willison 《Journal of organometallic chemistry》1993,450(1-2):177-184
Phenylazoferrocene undergoes nickelation and palladation exclusively on the phenyl group. Lithium phenylazocyclopentadienide has been converted into derivatives of Mo, Mn, Fe, Ru and Rh. 相似文献
8.
9.
Emulsions of perfluorotributylamine (FTBA) and perflubron were evaluated for their utility in 19F echo planar imaging. Fluorine images of the emulsions were obtained in a phantom and two mice that had been predosed. Both agents, but particularly perflubron, show potential for fluorine echo planar studies because of the long spin-spin relaxation times of the CF3 resonances. High resolution thin slice images obtained in as little as 26.6 ms are presented. 相似文献
10.