全文获取类型
收费全文 | 4436篇 |
免费 | 629篇 |
国内免费 | 508篇 |
专业分类
化学 | 3273篇 |
晶体学 | 42篇 |
力学 | 247篇 |
综合类 | 37篇 |
数学 | 509篇 |
物理学 | 1465篇 |
出版年
2024年 | 11篇 |
2023年 | 107篇 |
2022年 | 120篇 |
2021年 | 162篇 |
2020年 | 202篇 |
2019年 | 180篇 |
2018年 | 155篇 |
2017年 | 125篇 |
2016年 | 187篇 |
2015年 | 202篇 |
2014年 | 195篇 |
2013年 | 309篇 |
2012年 | 330篇 |
2011年 | 343篇 |
2010年 | 232篇 |
2009年 | 231篇 |
2008年 | 263篇 |
2007年 | 223篇 |
2006年 | 212篇 |
2005年 | 213篇 |
2004年 | 189篇 |
2003年 | 122篇 |
2002年 | 125篇 |
2001年 | 117篇 |
2000年 | 120篇 |
1999年 | 111篇 |
1998年 | 91篇 |
1997年 | 90篇 |
1996年 | 91篇 |
1995年 | 67篇 |
1994年 | 79篇 |
1993年 | 55篇 |
1992年 | 49篇 |
1991年 | 37篇 |
1990年 | 45篇 |
1989年 | 27篇 |
1988年 | 26篇 |
1987年 | 25篇 |
1986年 | 20篇 |
1985年 | 24篇 |
1984年 | 13篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1969年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有5573条查询结果,搜索用时 78 毫秒
21.
三种群食物链交错扩散模型的整体 总被引:1,自引:0,他引:1
本文应用能量估计方法和Gagliardo-Nirenberg型不等式证明了一类强耦合反应扩散系统整体解的存在性和一致有界性,该系统是带自扩散和交错扩散项的三种群Lotka-Volterra食物链模型.通过构造Lyapunov函数给出了该模型正平衡点全局渐近稳定的充分条件. 相似文献
22.
Leong‐Huat Gan Palaniswamy Ravi Bao Wei Mao Kam‐Chiu Tam 《Journal of polymer science. Part A, Polymer chemistry》2003,41(17):2688-2695
Polymerization of 2‐(diethylamino)ethyl methacrylate (DEAEMA) via homogeneous atom transfer radical polymerization under various reaction conditions is described. The effects of the initiators and solvents were examined. With 1,1,4,7,10,10‐hexamethyl triethylenetetramine/copper(I) chloride/p‐toluenesulfonyl chloride as the ligand/catalyst/initiator system in methanol, poly(DEAEMA) with a polydispersity index as low as 1.07 was synthesized. Kinetic studies demonstrated the polymerization was very well controlled and exhibited the living characteristic of the process. Well‐defined block copolymers of DEAEMA and tert‐butyl methacrylate (tBMA) were successfully synthesized. The copolymers could be synthesized with equally good results by starting with either p(DEAEMA) or p(tBMA) as the macroinitiators. However, only the macroinitiators terminated with chlorine should be used. The corresponding macroinitiators with bromine as a transferable group did not yield well‐defined copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2688–2695, 2003 相似文献
23.
In this paper, by the use of a fixed point theorem, many new necessary and sufficient conditions for the existence of positive solutions in C[0,1]∩C1[0,1]∩C2(0,1) or C[0,1]∩C2(0,1) are presented for singular superlinear and sublinear second-order boundary value problems. Singularities at t=0, t=1 will be discussed. 相似文献
24.
Positron-lifetime experiments have been carried out on two undoped n-type liquid encapsulated Czochralski (LEC)-grown InP samples with different stoichiometric compositions in the temperature range 10-300 K. For temperatures below 120 K for P-rich InP and 100 K for In-rich InP, the positron average lifetime began to increase rapidly and then leveled off, which was associated with the charge state change of hydrogen indium vacancy complexes from (VInH4)+ to (VInH4)0. This phenomenon was more obvious in P-rich samples that have a higher concentration of VInH4. The transformation temperature of approximately 120 K suggests that the complex VInH4 is a donor defect and that the ionization energy is about 0.01 eV. The ionization of neutral VInH4 accounted for the decrease of the positron average lifetime when the sample was illuminated with a photon energy of 1.32 eV at 70 K. These results provide evidence for hydrogen complex defects in undoped LEC InP. 相似文献
25.
26.
KunHuaLIN MaoPingSONG ChenXiaDU QiaoHongZHANG YangJieWU 《中国化学快报》2003,14(7):673-676
The cyclomercurated ferrocenylimines containing heterocyclic ring were prepared by the condensation of cyclomercuration of acylferrocene with the appropriate heterocyclic amine.This procedure provides an efficient method for the synthesis of cyclomerucurated ferrocenylimines containing heterocyclic ring which are difficultly synthesized by the conventional method.The reaction mechanism is proposed. 相似文献
27.
28.
29.
Yifeng Yu 《纯数学与应用数学通讯》2007,60(8):1111-1147
In the first part of this paper, we extend several results in Crandall, Evans, and Gariepy [11] and Crandall and Evans [10] to absolute minimizers of more general L∞ functionals. In the second part, we present some interesting connections between L∞ variational problems and weak KAM theory. As an application, we will advance the main result in Fathi and Siconolfi [17], i.e, the existence of a C1 subsolution of the Hamilton‐Jacobi equation. Moreover, we will propose a possible approximation of the projected Aubrey set by a variational approach that was first used by Evans in [14]. © 2007 Wiley Periodicals, Inc. 相似文献
30.
Iron oxide catalyst with spinel structure used for dehydrogenation of ethylbenzene is one kind of important catalyst in petrochemical industry. In this work several series of industrial catalyst were prepared with different components and different manufacturing processes. Mössbauer Spectroscopy has been used to determine the optimal components and the better manufacturing process for spinel structure formation. The results may prove useful for producing the industrial dehydrogenation catalyst with better catalytic property. 相似文献