全文获取类型
收费全文 | 19287篇 |
免费 | 3175篇 |
国内免费 | 2955篇 |
专业分类
化学 | 15123篇 |
晶体学 | 261篇 |
力学 | 1022篇 |
综合类 | 264篇 |
数学 | 2349篇 |
物理学 | 6398篇 |
出版年
2024年 | 19篇 |
2023年 | 279篇 |
2022年 | 424篇 |
2021年 | 526篇 |
2020年 | 685篇 |
2019年 | 710篇 |
2018年 | 565篇 |
2017年 | 543篇 |
2016年 | 975篇 |
2015年 | 919篇 |
2014年 | 1190篇 |
2013年 | 1469篇 |
2012年 | 1687篇 |
2011年 | 1796篇 |
2010年 | 1341篇 |
2009年 | 1298篇 |
2008年 | 1486篇 |
2007年 | 1255篇 |
2006年 | 1122篇 |
2005年 | 925篇 |
2004年 | 856篇 |
2003年 | 721篇 |
2002年 | 886篇 |
2001年 | 700篇 |
2000年 | 535篇 |
1999年 | 426篇 |
1998年 | 288篇 |
1997年 | 215篇 |
1996年 | 245篇 |
1995年 | 191篇 |
1994年 | 180篇 |
1993年 | 172篇 |
1992年 | 122篇 |
1991年 | 121篇 |
1990年 | 71篇 |
1989年 | 73篇 |
1988年 | 55篇 |
1987年 | 49篇 |
1986年 | 46篇 |
1985年 | 44篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1959年 | 13篇 |
1958年 | 11篇 |
1957年 | 15篇 |
1956年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Cheng‐Ho Chen Chih‐Chun Teng Ming‐Shyong Tsai Fu‐Su Yen 《Journal of Polymer Science.Polymer Physics》2006,44(15):2145-2154
A Haake torque rheometer equipped with an internal mixer is used to study the influence of the amount of sodium montmorillonite (Na+‐MMT) and organically modified MMT (O‐MMT) on X‐ray diffraction (XRD), morphology, and mechanical characteristics of rigid poly (vinyl chloride) (PVC)/Na+‐MMT and PVC/O‐MMT nanocomposites, respectively. Results of XRD and transmission electron microscopy (TEM) indicate that MMT is partially encapsulated and intercalated in the rigid PVC/Na+‐MMT nanocomposites. However, results of XRD and TEM show MMT is partially intercalated and exfoliated in the rigid PVC/O‐MMT nanocomposites. Tensile strength, yield strength, and elongation at break of the rigid PVC/MMT nanocomposites were improved simultaneously with adding 1–3 wt % Na+‐MMT or O‐MMT with respect to that of pristine PVC. However, the addition of Na+‐MMT or O‐MMT should be kept as not more than 3 wt % to optimize the mechanical properties and the processing stability of the rigid PVC/MMT nanocomposites. SEM micrographs of the fractured surfaces of the rigid PVC/Na+‐MMT and PVC/O‐MMT nanocomposites both before and after tensile tests were also illustrated and compared. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2145–2154, 2006 相似文献
172.
This study describes the preparation of polypyrrole (PPy)/multiwalled carbon nanotube (MWNT) composites by in situ chemical oxidative polymerization. Various ratios of MWNTs, which served as hard templates, were first dispersed in aqueous solutions with the surfactant cetyltrimethylammonium bromide to form micelle/MWNT templates and overcome the difficulty of MWNTs dispersing into insoluble solutions of pyrrole monomer, and PPy was then synthesized via in situ chemical oxidative polymerization on the surface of the templates. Raman spectroscopy, Fourier transform infrared (FTIR), field‐emission scanning electron microscopy (FESEM), and high‐resolution transmission electron microscopy (HRTEM) were used to characterize the structure and morphology of the fabricated composites. Structural analysis using FESEM and HRTEM showed that the PPy/MWNT composites were core (MWNT)–shell (PPy) tubular structures. Raman and FTIR spectra of the composites were almost identical to those of PPy, supporting the idea that MWNTs served as the core in the formation of a coaxial nanostructure for the composites. The conductivities of these PPy/MWNT composites were about 150% higher than those of PPy without MWNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1413–1418, 2006 相似文献
173.
The electrochemical behavior of gatifloxacin (GTFX) and its interaction with natural calf thymus DNA (ctDNA) is investigated by differential pulse voltammetry (DPV) on a carbon paraffined electrode. According to the suggested electrochemical equation, a binding constant of 1.7058 x 10(5) (mol L(-1))(-1) and binding sizes s = 3.09 (base pairs) of GTFX with ctDNA are obtained by nonlinear fit analysis of electrochemical data. The results demonstrate that GTFX has the properties of an intercalative binder. 相似文献
174.
Positive Steady States of a Prey-predator Model with Diffusion and Non-monotone Conversion Rate 总被引:1,自引:0,他引:1
Rui PENG Ming Xin WANG Wen Van CHEN 《数学学报(英文版)》2007,23(4):749-760
In this paper, we study the positive steady states of a prey-predator model with diffusion throughout and a non-monotone conversion rate under the homogeneous Dirichlet boundary condition. We obtain some results of the existence and non-existence of positive steady states. The stability and uniqueness of positive steady states are also discussed. 相似文献
175.
Many sets of the soliton and periodic travelling wave solutions for the quadratic χ^(2) nonlinear system are obtained by the Backlund transformation and the trial method. The property of the propagation for some travelling waves is investigated. 相似文献
176.
热效应对光折变晶体两波耦合的特性影响的理论分析 总被引:3,自引:1,他引:2
用一种模型对两波耦合进行了分析,导出了强度相位的解析式,对影响两波耦合的参数进行了理论分析。分析了对BaTiO3光折变晶体的两波耦合的测量结果。 相似文献
177.
从实验上探讨了掺Nd^3+的氟化物玻璃光纤正向双程超荧光基本特性,包括输入-输出特性、输出-带宽特性以及输出-波长(激发)特性。并给出了理论上的拟合公式,实验表明利用氟化物玻璃光纤有望获得性能优异的有应用前景的低相干度集成化光源。 相似文献
178.
This paper presents some results of the relation between wavelet transform and fractal transform. The wavelet transform of the attractor of fractal transform posseses translational and scale invariance. So we speed the fractal image encoding by testing the invariance of the wavelet transform appropriate for image encoding. The classfication scheme of range blocks by wavelet transform is given in this paper. 相似文献
179.
180.
JiŘí Kvapil Josef Kvapil Bohumil Perner Michal Košelja Helena Jelínková 《Czechoslovak Journal of Physics》1990,40(11):1283-1287
The methods of growing YAG:Nd crystals with a flat interface and YAP:Nd crystals with a sharp conical interface are described. The form of the interface was controlled by the He and H2O content in the reducing atmosphere composed mainly of Ar and H2 as well as by axial temperature gradient above the melt level. The crystals of 120–180 mm in length were machined to the high-quality slabs. 相似文献