全文获取类型
收费全文 | 460篇 |
免费 | 46篇 |
国内免费 | 68篇 |
专业分类
化学 | 372篇 |
晶体学 | 5篇 |
力学 | 14篇 |
综合类 | 6篇 |
数学 | 77篇 |
物理学 | 100篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 10篇 |
2021年 | 23篇 |
2020年 | 10篇 |
2019年 | 16篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 21篇 |
2014年 | 17篇 |
2013年 | 43篇 |
2012年 | 17篇 |
2011年 | 21篇 |
2010年 | 21篇 |
2009年 | 22篇 |
2008年 | 31篇 |
2007年 | 29篇 |
2006年 | 14篇 |
2005年 | 10篇 |
2004年 | 18篇 |
2003年 | 16篇 |
2002年 | 46篇 |
2001年 | 36篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1982年 | 5篇 |
1980年 | 3篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1971年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有574条查询结果,搜索用时 0 毫秒
91.
Dao Huy Bich 《International Journal of Non》2011,46(9):1195-1204
This paper presents an analytical approach to investigate the non-linear axisymmetric response of functionally graded shallow spherical shells subjected to uniform external pressure incorporating the effects of temperature. Material properties are assumed to be temperature-independent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of constituents. Equilibrium and compatibility equations for shallow spherical shells are derived by using the classical shell theory and specialized for axisymmetric deformation with both geometrical non-linearity and initial geometrical imperfection are taken into consideration. One-term deflection mode is assumed and explicit expressions of buckling loads and load-deflection curves are determined due to Galerkin method. Stability analysis for a clamped spherical shell shows the effects of material and geometric parameters, edge restraint and temperature conditions, and imperfection on the behavior of the shells. 相似文献
92.
Heterogeneity of biological materials, such as bone, tooth, and mollusc shells, plays a key role in determining their mechanical performance (e.g. the strength, damage tolerance, etc.). Here, we quantify heterogeneities in elasticity and inelasticity of bovine cortical bone between 100 nm and a few microns and identify a characteristic length scale (λc) of approximately 200 nm. Below λc the mechanical heterogeneity of bone is pronounced and exhibits a strong nonlinear size-dependence, while above λc the heterogeneity is much less. Such size-dependent heterogeneity benefits the mechanical performance of bone since it not only promotes the energy dissipation at nanoscale, but also suppresses heterogeneity-induced stress concentration and strain localization at larger length scales. This is one of the possible mechanisms functioning at multiple length scales that make bone a well-designed tough natural material. Utilizing experimentally measured data, systematic computational simulations were carried out, showing that the heterogeneity in inelasticity, rather than elasticity, plays a dominant role in promoting energy dissipation during deformation. Possible parameters that determine the inelasticity heterogeneity (e.g. mean value and standard deviation of heterogeneous yield stress) and therefore affect energy dissipation are investigated under typical deformation modes of bone. The analysis presented suggests that there exists an optimum ratio of macroscopic strength to elastic modulus for improving energy dissipation under tension. All these findings are of great value to the design and synthesis of improved bio-inspired composites. 相似文献
93.
广山药中16种元素的分析比较 总被引:21,自引:1,他引:21
用原子吸收法和分光光度法测定了5个产地的广山药及怀山药中16种元素的含量,并进行了比较。发现广山药及怀山药中均含有Mn,Fe,Zn,Ca,Cu,Mg,P,Se等元素,5个产地的广山药中的Cu/Zn值均低于正常人血清的Cu/Zn,这些元素可能是怀山药,广山药具有补脾养胃,生津益肺,补肾涩精,治疗糖尿病等功效的物质基础之一;广山药长期作为山药的一个品种同等入药,食用是有科学根据的;广山药,怀山药中含有一定量的As,Hg。 相似文献
94.
Laser Raman spectrometry with a fibre-optic system is used to monitor the concentrations of ethanol, glucose and fructose at various stages of an alcoholic fermentation process. For evaluation of the data, cross-correlation and multivariate least-squares procedures are compared; the latter gives the best results. Ethanol, glucose and fructose can be determined remotely with a precision of ca. 10 g l?1 (10–15%). 相似文献
95.
96.
Di Rong CHEN Dao Hong XIANG 《数学学报(英文版)》2007,23(4):705-710
We present a concrete method of constructing multiresolution analysis on interval. The method generalizes the corresponding results of Cohen, Daubechies and Vial [Appl. Comput. Harmonic Anal., 1(1993), 54-81]. By the use of the subdivision operator, the expressions of the constructed functions are more compact. Furthermore, the method reveals more clearly some properties of multiresolution analysis with certain approximation order. 相似文献
97.
Dao Rong LI Ling Na SUN Chang Wen HU 《中国化学快报》2006,17(8):1089-1092
TiO2 is widely used as photocatalyst because of its optical and electronic properties, low cost, chemical stability, non-toxicity and applicability to the treatment of a large variety of pollutants1. The activities of photocatalyst were influenced by the … 相似文献
98.
99.
Alargenumberofadditionsto[6O]fullerenehavebeeninvestigated.However,mostoftheworkhaveconcentratedontheformationofthemono-additionproductS0f[60]fullerene'-Thedevelopment0fselechveroutestomultipleadductShascurrentlybecomethefrontierinthechendstryof[60]fuIlerene'~'.FollowingtheaPplicahonoftether-directedremotefunctionalizati0ntotheregi0specificformati0nofthedi-andtriadductSof[60]fullerene,F.Diederichetal6alsodescribed'awayforthedirectdifunctionalizationof[60]fullerenebasedonacyclizationreachono… 相似文献
100.
Wolfgang Oppolzer Christian Chapuis Guo Mao Dao Daniel Reichlin Thierry Godel 《Tetrahedron letters》1982,23(46):4781-4784
Starting from (R)-(+)- and from (S)-(?)-camphor the chiral alcohols , and have been prepared; their acrylates II underwent TiCl2(OR)2-promoted Diels-Alder additions to cyclopentadiene giving efficiently in a predictable manner either the (2R)- or the (2S)-adducts III with up to virtually quantitative asymmetric induction. 相似文献