全文获取类型
收费全文 | 2304篇 |
免费 | 90篇 |
国内免费 | 19篇 |
专业分类
化学 | 1652篇 |
晶体学 | 10篇 |
力学 | 43篇 |
数学 | 478篇 |
物理学 | 230篇 |
出版年
2023年 | 14篇 |
2022年 | 11篇 |
2021年 | 38篇 |
2020年 | 43篇 |
2019年 | 44篇 |
2018年 | 22篇 |
2017年 | 20篇 |
2016年 | 65篇 |
2015年 | 39篇 |
2014年 | 50篇 |
2013年 | 76篇 |
2012年 | 109篇 |
2011年 | 105篇 |
2010年 | 54篇 |
2009年 | 80篇 |
2008年 | 131篇 |
2007年 | 106篇 |
2006年 | 104篇 |
2005年 | 95篇 |
2004年 | 89篇 |
2003年 | 93篇 |
2002年 | 93篇 |
2001年 | 40篇 |
2000年 | 62篇 |
1999年 | 36篇 |
1998年 | 49篇 |
1997年 | 54篇 |
1996年 | 48篇 |
1995年 | 35篇 |
1994年 | 44篇 |
1993年 | 32篇 |
1992年 | 26篇 |
1991年 | 36篇 |
1990年 | 24篇 |
1989年 | 22篇 |
1988年 | 31篇 |
1987年 | 24篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 42篇 |
1983年 | 27篇 |
1982年 | 35篇 |
1981年 | 32篇 |
1980年 | 27篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 10篇 |
1974年 | 8篇 |
排序方式: 共有2413条查询结果,搜索用时 312 毫秒
11.
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
12.
13.
14.
Paul A. Binding Patrick J. Browne Bruce A. Watson 《Journal of Mathematical Analysis and Applications》2004,291(1):246-261
Three inverse problems for a Sturm-Liouville boundary value problem −y″+qy=λy, y(0)cosα=y′(0)sinα and y′(1)=f(λ)y(1) are considered for rational f. It is shown that the Weyl m-function uniquely determines α, f, and q, and is in turn uniquely determined by either two spectra from different values of α or by the Prüfer angle. For this it is necessary to produce direct results, of independent interest, on asymptotics and oscillation. 相似文献
15.
This study presents a method of adaptive identification of parameters describing Sugeno fuzzy inference system in presence of bounded disturbances while maintaining the readability and interpretability of the fuzzy model during and after identification. This method do not require any a priori knowledge of a bound on the disturbance and noise and of a bound on the unknown parameters values. The method can be used for the robust and adaptive identification of slowly time varying nonlinear systems using fuzzy inference systems. The suggested method was used to build a fuzzy expert system that approximates the functional relationship between physical fitness and some of the measurable physiological parameters by their real measurements and opinion (human-experiences) of a medical expert. 相似文献
16.
17.
18.
19.
Abstract— Oxygen effects on the photocyclization of N-methyldiphenylamine to N-methylcarbazole were investigated in n-hexane, water, and aqueous surfactant solutions by steady state irradiations and flash photolysis measurements. The reaction sequence in micelles was found to involve the same intermediate steps as in homogeneous solutions. In aerated micellar solutions, the quantum yield of N-methylcarbazole is significantly higher than in n-hexane, while the rate constants of the unimolecular reaction steps show no solvent dependence. The bimolecular dehydrogenation of the intermediate 4a, 4b-dihydro-N-methylcarbazole by oxygen is enhanced in aqueous and micellar solutions, whereas the quenching rate of triplet intermediates by oxygen was not affected. The lesuhs are interpreted using a dispersed phase model of micellar solutions. Special 'micellar effects' need not be invoked since the dependence of the quantum yield on the solvent is shown to be due to the difference in the overall oxygen concentration. 相似文献
20.