全文获取类型
收费全文 | 3532篇 |
免费 | 223篇 |
国内免费 | 360篇 |
专业分类
化学 | 1384篇 |
晶体学 | 56篇 |
力学 | 27篇 |
综合类 | 6篇 |
数学 | 2078篇 |
物理学 | 564篇 |
出版年
2024年 | 5篇 |
2023年 | 17篇 |
2022年 | 29篇 |
2021年 | 43篇 |
2020年 | 53篇 |
2019年 | 76篇 |
2018年 | 76篇 |
2017年 | 70篇 |
2016年 | 60篇 |
2015年 | 63篇 |
2014年 | 91篇 |
2013年 | 255篇 |
2012年 | 163篇 |
2011年 | 263篇 |
2010年 | 236篇 |
2009年 | 254篇 |
2008年 | 289篇 |
2007年 | 322篇 |
2006年 | 255篇 |
2005年 | 172篇 |
2004年 | 155篇 |
2003年 | 147篇 |
2002年 | 98篇 |
2001年 | 103篇 |
2000年 | 89篇 |
1999年 | 75篇 |
1998年 | 71篇 |
1997年 | 69篇 |
1996年 | 56篇 |
1995年 | 79篇 |
1994年 | 65篇 |
1993年 | 50篇 |
1992年 | 40篇 |
1991年 | 30篇 |
1990年 | 29篇 |
1989年 | 25篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1974年 | 3篇 |
排序方式: 共有4115条查询结果,搜索用时 375 毫秒
161.
《Optimization》2012,61(1):77-94
In this article we study a recently introduced notion of non-smooth analysis, namely convexifactors. We study some properties of the convexifactors and introduce two new chain rules. A new notion of non-smooth pseudoconvex function is introduced and its properties are studied in terms of convexifactors. We also present some optimality conditions for vector minimization in terms of convexifactors. 相似文献
162.
163.
In this paper, our main attempt was to reduce Total Internal Reflection (TIR) happening at Indium Tin Oxide (ITO, nito = 1.8 + 0.01i) and Glass (nglass = 1.51) interface, which is due to ITO's higher index in comparison with Glass's, that makes light guided in ITO layer, 50% of generated light in Wight Organic Light Emitting Diodes (WOLED) are trapped in ITO layer; here we tried to reduce this portion of trapped light by implying 12-fold quasi-photonic crystal to the mentioned interface. With some gentle changes in 12-fold's structure we could reduce TIR in this interface to less than 9%. Also, far field results before and after adding the structure to WOLED were studied, which represents suitability of using this structure for lighting applications. 相似文献
164.
We present novel inorganic–organic hybrid catalyst to accomplish domino multi‐component reaction (MCR) for synthesis of 3‐amino‐2′‐oxospiro[benzo[c]pyrano[3,2‐a]phenazine‐1,3′‐indoline]‐2‐carbonitrile/carboxylate derivatives. This methodology offers remarkable development by easy production of H3PMo12O40/Hyd‐SBA‐15 in regard to solving the problem of using harsh catalysts, also it demonstrates to be impressive and environmentally friendly in term of low reaction times and high yields. 相似文献
165.
《Journal of Coordination Chemistry》2012,65(1-4):77-89
Abstract A steric effect in the carbon-skeleton rearrangement catalyzed by heptamethyl cobyrinate perchlorate, [Cob(II)7C1ester]C104, was investigated under electrochemical conditions. The controlled-potential electrolyses of alkyl halides having two carboxylic ester groups of different bulkiness on the same carbon atom, such as 2,2-bis(ethoxycarbonyl)-l-bromopropane, l-bromo-2-tert-butoxycarbonyl-2-ethoxy-carbonylpropane, l-bromo-2-cyclohexyloxycarbonyl-2-ethoxycarbonylpropane, and l-bromo-2-ethoxy-carbonyl-2-phenoxycarbonylpropane, were carried out in N,N-dimethylformamide, as catalyzed by [Cob(II)7C1ester]CIO4, to give the corresponding ester-migrated products in the dark at—1.5 V vs SCE in the presence of acetic acid and at—2.0 V vs SCE without acetic acid. As regards a correlation between bulkiness of an ester group and a migration aptitude, a smaller ester group tends to migrate to the adjacent carbon atom more readily than a larger one. The origin of such a steric effect is discussed with attention to the rate-determining step. 相似文献
166.
We introduce the concept of a pentagonal geometry as a generalization of the pentagon and the Desargues configuration, in the same vein that the generalized polygons share the fundamental properties of ordinary polygons. In short, a pentagonal geometry is a regular partial linear space in which for all points x, the points not collinear with the point x, form a line. We compute bounds on their parameters, give some constructions, obtain some nonexistence results for seemingly feasible parameters and suggest a cryptographic application related to identifying codes of partial linear spaces. 相似文献
167.
《Optimization》2012,61(2)
We consider robustness properties of second-order methods for the sliding mode control of nonlinear ordinary differential equations. A new approach is presented based on the theory of well-posed optimization problems. It is shown that the convergence of the real states of the control system to the ideal one is intimately related to Tykhonov well-posedness of suitably defined dynamic optimization problems. 相似文献
168.
Preparation,characterization and heterogeneous catalytic applications of GO/Fe3O4/HPW nanocomposite in chemoselective and green oxidation of alcohols with aqueous H2O2
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Graphene oxide ‐ Fe3O4 ‐ NH3+H2PW12O40 ‐ magnetic nanocomposite (GO/Fe3O4/HPW) was prepared by linking amino ‐ functionalized Fe3O4 nanoparticles (Fe3O4 ‐ NH2) on the graphene oxide (GO), and then grafting 12 ‐ tungstophosphoric acid (H3PW12O40) on the graphene oxide ‐ magnetite hybrid (GO ‐ Fe3O4 ‐ NH2). The obtained GO/Fe3O4/HPW nanocomposite was well characterized with different techniques such as FT ‐ IR, TEM, SEM, XRD, EDX, TGA ‐ DTA, AGFM, ICP and BET measurements. The used techniques showed that the graphene oxide layers were well prepared and the various stages of preparation of the GO/Fe3O4/HPW nanocomposites successfully completed. This new nanocomposite displayed excellent performance as a heterogeneous catalyst in the oxidation of alcohols with H2O2. The as ‐ prepared GO/Fe3O4/HPW catalyst was more stable and recyclable at least five times without significantly reducing its catalytic activity. 相似文献
169.
170.
《Quaestiones Mathematicae》2013,36(1):15-32
Abstract In this paper we define two concepts of prime ideals for Ω-groups. The first generalizes the definitions of prime ideal in rings, nearrings, Γ-rings, associative algebras and Lie algebras. The second generalizes a concept defined for groups by ??ukin ([21]). We show that both lead to radicals in the sense of Hoehnke ([10]). Furthermore in the case of rings, Γ-rings, abelian zero-symmetric nearrings and cubic rings these two definitions coincide, thus obtaining a new characterization for the prime ideal. Zero-symmetric Ω-groups are defined analogously to the nearring case and a new characterization in term of ideals is given. 相似文献