全文获取类型
收费全文 | 3321篇 |
免费 | 184篇 |
国内免费 | 121篇 |
专业分类
化学 | 2637篇 |
晶体学 | 2篇 |
力学 | 110篇 |
综合类 | 10篇 |
数学 | 404篇 |
物理学 | 463篇 |
出版年
2024年 | 29篇 |
2023年 | 331篇 |
2022年 | 107篇 |
2021年 | 70篇 |
2020年 | 113篇 |
2019年 | 193篇 |
2018年 | 137篇 |
2017年 | 146篇 |
2016年 | 107篇 |
2015年 | 93篇 |
2014年 | 159篇 |
2013年 | 187篇 |
2012年 | 132篇 |
2011年 | 156篇 |
2010年 | 129篇 |
2009年 | 153篇 |
2008年 | 133篇 |
2007年 | 155篇 |
2006年 | 113篇 |
2005年 | 107篇 |
2004年 | 121篇 |
2003年 | 46篇 |
2002年 | 42篇 |
2001年 | 36篇 |
2000年 | 25篇 |
1999年 | 31篇 |
1998年 | 28篇 |
1997年 | 21篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 4篇 |
1986年 | 19篇 |
1985年 | 23篇 |
1984年 | 27篇 |
1983年 | 24篇 |
1982年 | 16篇 |
1981年 | 79篇 |
1980年 | 69篇 |
1979年 | 20篇 |
1978年 | 26篇 |
1977年 | 31篇 |
1976年 | 28篇 |
1975年 | 35篇 |
1974年 | 28篇 |
1973年 | 26篇 |
1968年 | 7篇 |
排序方式: 共有3626条查询结果,搜索用时 172 毫秒
101.
Yong-Dong Li Hao Zhao Nan Zhang 《International Journal of Solids and Structures》2013,50(22-23):3610-3617
The purpose of the present work is to study the mixed mode fracture of a piezoelectric–piezomagnetic composite with two un-coaxial cracks parallel to the interface and each in a layer. Methods of generalized dislocation simulation, Green’s function, Cauchy singular integral equation and Lobatto–Chebyshev collocation are combined together to get the numerical results of mechanical strain energy release rate (MSERR). Three kinds of effects are revealed by parametric studies, i.e., the free-surface effect, the shielding effect and the interference effect, and they are used to interpret the characteristics of COD and MSERR curves. In addition, the effects of shear loading, magnetic loading and electric loading on MSERR are also disclosed, respectively, by varying the corresponding loading factor. 相似文献
102.
Abstract Organic-inorganic composites (OICs) were prepared via the in-situ polymerization of an organically (phenyl) substituted trialkoxysilane, phenyltriethoxysilane (PhTEOS), in the presence of poly(vinyl acetate) (PVAc). The mechanical reinforcement above T g previously observed in OICs of unfunctionalized organic polymers such as PVAc with acid catalyzed in-situ polymerized tetraalkoxysilane was not observed when the tetraalkoxysilane was replaced with PhTEOS. Although both systems are optically transparent and both exhibit a high degree of hydrogen bonding between the carbonyl of PVAc and the residual hydroxyls of the silicate, the polymerization of the alkoxide is different. The tetra-functional alkoxide polymerizes to form a load-supporting silicate network, leading to a high plateau in the tensile modulus above T g, whereas the trifunctional alkoxide reacts to form primarily low molecular weight oligomers. These increase the T g of the PVAc but do not provide mechanical reinforcement. 相似文献
103.
We present a generalization of a family of points on , the Diamond ensemble, containing collections of N points on with very small logarithmic energy for all . We extend this construction to the real projective plane and we obtain upper and lower bounds with explicit constants for the Green and logarithmic energy on this last space. 相似文献
104.
Martin Sweeney Michael Gurry Lee-Ann J. Keane Fawaz Aldabbagh 《Tetrahedron letters》2017,58(36):3565-3567
Environmentally-friendly and cost effective hydrogen peroxide in ethyl acetate was used to prepare in high yields pyrrolo[1,2-a]benzimidazoles from commercial o-(pyrrolidin-1-yl)anilines without the requirement for organic-aqueous extraction and chromatography. Six, seven and eight membered ring-fused analogues were similarly obtained in high yields with methanesulfonic acid required for the pyrido[1,2-a]benzimidazole. Anti-tumour benzimidazolequinone derivatives were obtained in high yield via the cyclization of 3,6-dimethoxy-2-(cycloamino)anilines. 相似文献
105.
This study presents a two-step synthesis of nanoparticles and the stabilization process of Ag ions in the matrix of NaCl nanocrystals. Ag+ ions are incorporated to NaCl with a new and attractive method that can be easily used for the different types of alkaline halides. The nanoparticles with predominant size found between 10 and 15 nm were stabilized on the surface and/or interior of NaCl nanocrystals using, in the first stages, the ionic-exchange property of zeolite A4. The optical properties of the materials were characterized through optical absorption, leading to well defined absorption bands located in the wave length values between 217–275 nm and 350–770 nm approximately, for Ag+ and AgNp, respectively. The antibacterial property of Ag ions and nanoparticles stabilized in NaCl was analyzed against gram-negative Escherichia Coli and Klebsiella bacteria. In order to quantify the antibacterial effect of Ag ions and nanoparticles the inhibition ratio was used as a parameter on the bacteria colonies grown in culture medium by conventional methods. Ag+ ions that were stabilized in NaCl nanocrystals show a mayor inhibition ratio in contact with Klebsiella bacteria, conversely Ag nanoparticles showed better results in contact with E. coli. 相似文献
106.
Malik Abdul Waseem ShireenAnjali Srivastava Arjita SrivastavaRahila I.R. Siddiqui 《Tetrahedron letters》2014
Reusable [bmIm]OH was found to be a highly efficient renewable homogenous catalyst for the rapid and convenient synthesis of benzoxazine-4-one derivatives from o-iodobenzoic-acid and benzonitrile at 75 °C in moderate to good yields. This methodology provides a facile and straightforward path to construct other related heterocycles in an eco-compatible fashion. 相似文献
107.
108.
109.
Matteo Cepale 《Journal of Difference Equations and Applications》2017,23(10):1707-1736
A Liouville–Green (or WKB) asymptotic approximation theory is developed for a class of almost-diagonal (‘asymptotically diagonal’) linear second-order matrix difference equations. Rigorous and explicitly computable bounds for the error terms are obtained, the asymptotics being made with respect to both, the index and some parameter affecting the equation. The case of the associated inhomogeneous equations is also considered in detail. Some examples and a number of applications are presented for the purpose of illustration. 相似文献
110.
发展了一种经济、简单的海蛎壳粉负载的CuCl2异相催化剂OSP-CuCl2,用来催化醛-炔-胺之间的A3偶联反应.OSP-CuCl2容易通过简单的方法从海蛎壳粉以及CuCl2制备,且显示出高的催化活性以及良好的可循环回收性.在微波辅助以及无溶剂条件下,以OSP-CuCl2为催化剂,能够以高产物收率制备出一系列炔胺类化合物.OSP-CuCl2可通过简单的过滤方式进行回收,并至少可循环使用6次.初步放大实验表明,炔胺类化合物能够以150 mmol的规模制备(87%收率). 相似文献