全文获取类型
收费全文 | 113300篇 |
免费 | 20932篇 |
国内免费 | 9851篇 |
专业分类
化学 | 92009篇 |
晶体学 | 1066篇 |
力学 | 5676篇 |
综合类 | 431篇 |
数学 | 11077篇 |
物理学 | 33824篇 |
出版年
2024年 | 305篇 |
2023年 | 1729篇 |
2022年 | 2968篇 |
2021年 | 3317篇 |
2020年 | 4371篇 |
2019年 | 5367篇 |
2018年 | 3679篇 |
2017年 | 3198篇 |
2016年 | 6843篇 |
2015年 | 6984篇 |
2014年 | 7592篇 |
2013年 | 9403篇 |
2012年 | 9896篇 |
2011年 | 9291篇 |
2010年 | 7518篇 |
2009年 | 7246篇 |
2008年 | 7199篇 |
2007年 | 6114篇 |
2006年 | 5440篇 |
2005年 | 4891篇 |
2004年 | 4010篇 |
2003年 | 3423篇 |
2002年 | 4068篇 |
2001年 | 3088篇 |
2000年 | 2753篇 |
1999年 | 2052篇 |
1998年 | 1463篇 |
1997年 | 1396篇 |
1996年 | 1379篇 |
1995年 | 1134篇 |
1994年 | 1000篇 |
1993年 | 809篇 |
1992年 | 719篇 |
1991年 | 625篇 |
1990年 | 542篇 |
1989年 | 409篇 |
1988年 | 353篇 |
1987年 | 289篇 |
1986年 | 255篇 |
1985年 | 218篇 |
1984年 | 151篇 |
1983年 | 110篇 |
1982年 | 83篇 |
1981年 | 69篇 |
1980年 | 65篇 |
1979年 | 34篇 |
1978年 | 30篇 |
1977年 | 40篇 |
1976年 | 30篇 |
1973年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Jiguo Yu Qiuju Bian Guizhen Liu Na Wang 《Journal of Applied Mathematics and Computing》2007,25(1-2):283-291
A simple graphG is said to be fractionaln-factor-critical if after deleting anyn vertices the remaining subgraph still has a fractional perfect matching. For fractionaln-factor-criticality, in this paper, one necessary and sufficient condition, and three sufficient conditions related to maximum matching, complete closure are given. 相似文献
102.
The universal condition for the formation of omnidirectional band gaps (OBG) in photonic crystal (PC) was derived with consideration
of permeability of the materials. And it was found that there are four kinds of PCs: one of them has no OBG, and one always
possesses OBG. For the other two kinds of PCs, there are OBG for only TM or TE waves respectively. Moreover, in all PCs, the
OBG can be broadened by decreasing the refractive index of the ambient medium or/and increasing the contrast between the wave
impedances of the component materials of the PC.
PACS 42.70.Qs; 71.20.Tx 相似文献
103.
104.
文章详细描述了航空兵机场塔台辅助指挥系统之通信分系统设计的特点与功能、硬件结构、软件设计原则以及接口通信协议等问题。该分系统设计已在航空兵塔台辅助指挥系统研究中得到应用 ,并达到了良好的控制效果。 相似文献
105.
光泽精化学发光体系的研究与应用 总被引:5,自引:0,他引:5
对光泽精化学发光体系的动力学性质、荧光光谱、化学发光光谱及化学发光机理进行研究和探讨。详细研究了光泽精 - H2 O2 - Co( )流动注射化学发光体系的最佳分析条件。结果表明 ,当光泽精 (L c)为 2 .5×10 - 5mol/L、H2 O2 为 0 .5 mol/L、Na OH为 0 .4 mol/L、CTMAB为 2 .0× 10 - 5mol/L时 ,测定 Co( )的校准曲线线性范围为 0 .0 5— 2 0 0μg/m L ,检出限为 0 .0 1μg/m L。对 10μg/m L Co( )连续测定 7次 ,相对标准偏差为 1.7%。 相似文献
106.
This paper proposes the Rice condition numbers for invariant subspace, singular sub-spaces of a matrix and deflating subspaces of a regular matrix pair. The first-order perturbation estimations for these subspaces are derived by applying perturbation expansions of orthogonal projection operators. 相似文献
107.
Kai-li Xiang 《计算数学(英文版)》2002,(2)
1. IntroductionWe consider a class of direct hybrid methods proposed in [11 for solving the second orderinitial value problemy" = f(t,y), y(0),y'(0) given (1.1)The basic method has the formandHere t. = nh and we define t.l.. = t. I aih, i = 1, 2 and n=0,1… 相似文献
108.
Sung‐Fu Hsu Tzong‐Ming Wu Chien‐Shiun Liao 《Journal of Polymer Science.Polymer Physics》2006,44(23):3337-3347
Poly(3‐hydroxybutyrate) (PHB)/layered double hydroxides (LDHs) nanocomposites were prepared by mixing PHB and poly(ethylene glycol) phosphonates (PEOPAs)‐modified LDH (PMLDH) in chloroform solution. Both X‐ray diffraction data and TEM micrographs of PHB/PMLDH nanocomposites indicate that the PMLDHs are randomly dispersed and exfoliated into the PHB matrix. In this study, the effect of PMLDH on the isothermal crystallization behavior of PHB was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. Isothermal crystallization results of PHB/PMLDH nanocomposites show that the addition of 2 wt % PMLDH into PHB induced more heterogeneous nucleation in the crystallization significantly increasing the crystallization rate and reducing their activation energy. By adding more PMLDH into the PHB probably causes more steric hindrance of the diffusion of PHB, reducing the transportation ability of polymer chains during crystallization, thus increasing the activation energy. The correlation among crystallization kinetics, melting behavior and crystalline structure of PHB/PMLDH nanocomposites can also be discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3337–3347, 2006 相似文献
109.
In this paper, the relation between synchronization and pattern formation in one-dimensional discrete and continuous open flow models is investigated in detail. Firstly a sufficient condition for globally asymptotical stability of lag/anticipating synchronization among lattices of these models is proved by analytic method. Then, by analyzing and simulating lag/anticipating synchronization in discrete case, three kinds of pattern of wave (it is called wave pattern) travelling in the lattices are discovered. Finally, a proper definition for these kinds of pattern is proposed. 相似文献
110.
In situ flying height testing technology is becoming more and more important in slider–disk interaction analysis and manufacturing quality control of disk drives and head-related components. Triple harmonic method is a quite promising choice for in situ flying height analysis, compared with other in situ methods reported up to now. This paper reports results of investigations on engineering issues of applying triple harmonic method for in situ flying height analysis. The paper reports results of analysis on the effects of various testing conditions on flying height testing repeatability and accuracy. Results suggest that working at reasonable high channel density and working on the ratio between third and first harmonics will be an advantage in terms of both flying height testing sensitivity and testing repeatability. Comparing with media thickness effect, the gap-length variation among different heads will be important if it is to study flying height difference among different heads and the testing is at high channel density. Also, it is suggested to work at AC erased track, in order to reduce the non-linearity caused by hard transition. 相似文献