全文获取类型
收费全文 | 120631篇 |
免费 | 31604篇 |
国内免费 | 32891篇 |
专业分类
化学 | 77823篇 |
晶体学 | 3336篇 |
力学 | 8448篇 |
综合类 | 2099篇 |
数学 | 17154篇 |
物理学 | 76266篇 |
出版年
2024年 | 572篇 |
2023年 | 1180篇 |
2022年 | 2576篇 |
2021年 | 2428篇 |
2020年 | 2542篇 |
2019年 | 2913篇 |
2018年 | 2757篇 |
2017年 | 4290篇 |
2016年 | 3526篇 |
2015年 | 4616篇 |
2014年 | 5016篇 |
2013年 | 7243篇 |
2012年 | 7864篇 |
2011年 | 9638篇 |
2010年 | 13277篇 |
2009年 | 13742篇 |
2008年 | 8238篇 |
2007年 | 7096篇 |
2006年 | 6700篇 |
2005年 | 6508篇 |
2004年 | 6365篇 |
2003年 | 4877篇 |
2002年 | 4737篇 |
2001年 | 5009篇 |
2000年 | 4435篇 |
1999年 | 3639篇 |
1998年 | 2694篇 |
1997年 | 2352篇 |
1996年 | 2614篇 |
1995年 | 3069篇 |
1994年 | 3124篇 |
1993年 | 3196篇 |
1992年 | 2742篇 |
1991年 | 2311篇 |
1990年 | 1973篇 |
1989年 | 2086篇 |
1988年 | 2035篇 |
1987年 | 1293篇 |
1986年 | 1311篇 |
1985年 | 931篇 |
1984年 | 1060篇 |
1983年 | 458篇 |
1982年 | 970篇 |
1981年 | 801篇 |
1980年 | 817篇 |
1979年 | 586篇 |
1978年 | 550篇 |
1977年 | 641篇 |
1976年 | 1050篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
S. Aravinda N. Shamala Rituparna S. Roy P Balaram 《Journal of Chemical Sciences》2003,115(5-6):373-400
An overview of the use of non-protein amino acids in the design of conformationally well-defined peptides, based on work from
the author’s laboratory, is discussed. The crystal structures of several designed oligopeptides illustrate the useα-aminoisobutyric acid (Aib) in the construction of helices, D-amino acids in the design of helix termination segments andDPro-Xxx segments for nucleating ofβ-hairpin structures.β- andγ-amino acid residues have been used to expand the range of designed polypeptide structures.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
92.
The paper discusses the relationship between weights and control vertices of two rational NURBS curves of degree two or three with all weights larger than zero when they represent the same curve parametrically and geometrically, and gives sufficient and necessary conditions for coincidence of two rational NURBS curves in non-degeneracy case. 相似文献
93.
Let Cld
AW
(X) be the hyperspace of nonempty closed subsets of a normed linear space X with the Attouch–Wets topology. It is shown that the space Cld
AW
(X) and its various subspaces are AR's. Moreover, if X is an infinite-dimensional Banach space with weight w(X) then Cld
AW
(X) is homeomorphic to a Hilbert space with weight 2
w(X). 相似文献
94.
本文根据Ляпунов的稳定性理论,研究了陀螺系统在非线性耗散力与非线性保守力作用下的稳定性问题,得到了非线性陀螺系统的稳定准则.结果表明:线性系统的稳定准则也同样适用于非线性系统,从而推广了KTC定理的应用范围. 相似文献
95.
Based on phase space delay-coordinate reconstruction of a chaotic dynamics system, we propose a local prediction of chaotic time series using a support vector machine (SVM) to overcome the shortcomings of traditional local prediction methods. The simulation results show that the performance of this proposed predictor for making onestep and multi-step prediction is superior to that of the traditional local linear prediction method and global SVM method. In addition, it is significant that its prediction performance is insensitive to the selection of embedding dimension and the number of nearest neighbours, so the satisfying results can be achieved even if we do not know the optimal embedding dimension and how to select the number of nearest neighbours. 相似文献
96.
An investigation on nonconnectedness of numerical range for monic matrix polynomials L(λ) is undertaking here. The distribution of eigenvalues of L(λ) to the components of numerical range and some other algebraic properties are also presented. 相似文献
97.
Mass distributions of fragments in the low-energy fission of nuclei from 187Ir to 213At have been analysed. This analysis has shown that shell effects in symmetric-mode fragment mass yields from the fission of pre-actinide nuclei could be described if one assumes the existence of two strongly deformed neutron shells in the arising fragments with neutron numbers N1 ≈ 52 and N2 ≈ 68. A new method has been proposed for quantitatively describing the mass distributions of the symmetric fission mode for pre-actinides with A ≈ 180–220. 相似文献
98.
We show that an electron confined to a single finite parabolic quantum well in crossed electric and magnetic fields can behave as a double quantum well system. The magnetic field is parallel to the heterostructure layers and the electric field is perpendicular to those. For a suitable choice of both fields and quantum well width, the electron can be confined to a double quantum well effective potential that is very similar to the electronic potential model for diatomic molecules. The double quantum well spectrum is calculated using a numerical algorithm based on semiclassical methods. A physical interpretation of this quantum system is given based on the analogy to the electrons bound to diatomic molecules. 相似文献
99.
Hans-Rudolf Buser Michael Oehme Walter Vetter Bernd Luckas 《Fresenius' Journal of Analytical Chemistry》1993,347(12):502-512
Summary Conventional electron ionization (EI) mass spectrometry (MS) and MS/MS techniques were applied to the analysis of two abundant octa and nonachlorobornanes isolated from seals of the Baltic sea and originating from technical toxaphene. The exact sterical structures of the two compounds were previously determined using nuclear magnetic resonance (NMR) spectroscopy by two independent research groups. The MS and MS/MS data generated in this study allowed partial structure elucidation of these polychlorobornanes, in particular revealing the distribution of the Cl substituents between the six-membered carbon ring, the bridge and the bridgehead in the parent bornane structure. Fragmentation of the six-membered carbon ring and the bridge by retro-Diels-Alder (RDA) and related mechanisms was discovered by studying specific parent/daughter ion transitions. The detailed fragmentation pathways formulated may be applicable to the structure elucidation of other toxaphene congeners and the monitoring of strategic transitions is highly selective for the detection of these compounds in technical toxaphene and in environmental samples. 相似文献
100.
1IntroductionThebrainofmankindhasmanycognitivefunctionssuchaslearning,asociationandoptimizationetc..Theneuronisthemostfoundam... 相似文献