全文获取类型
收费全文 | 25708篇 |
免费 | 4005篇 |
国内免费 | 2964篇 |
专业分类
化学 | 18590篇 |
晶体学 | 269篇 |
力学 | 1566篇 |
综合类 | 236篇 |
数学 | 3036篇 |
物理学 | 8980篇 |
出版年
2024年 | 53篇 |
2023年 | 496篇 |
2022年 | 694篇 |
2021年 | 824篇 |
2020年 | 975篇 |
2019年 | 994篇 |
2018年 | 799篇 |
2017年 | 812篇 |
2016年 | 1133篇 |
2015年 | 1131篇 |
2014年 | 1410篇 |
2013年 | 1732篇 |
2012年 | 2308篇 |
2011年 | 2311篇 |
2010年 | 1554篇 |
2009年 | 1400篇 |
2008年 | 1671篇 |
2007年 | 1545篇 |
2006年 | 1435篇 |
2005年 | 1206篇 |
2004年 | 885篇 |
2003年 | 776篇 |
2002年 | 759篇 |
2001年 | 661篇 |
2000年 | 554篇 |
1999年 | 543篇 |
1998年 | 460篇 |
1997年 | 412篇 |
1996年 | 456篇 |
1995年 | 374篇 |
1994年 | 307篇 |
1993年 | 256篇 |
1992年 | 246篇 |
1991年 | 232篇 |
1990年 | 184篇 |
1989年 | 162篇 |
1988年 | 118篇 |
1987年 | 101篇 |
1986年 | 105篇 |
1985年 | 95篇 |
1984年 | 69篇 |
1983年 | 58篇 |
1982年 | 47篇 |
1981年 | 37篇 |
1980年 | 36篇 |
1979年 | 24篇 |
1978年 | 26篇 |
1977年 | 29篇 |
1976年 | 29篇 |
1973年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
Chien-Hsin Cheng 《中国化学会会志》1994,41(1):33-38
Dynamic and static scattering of light was employed to investigate mixed micelles of two homologous anionic surfactants-sodium octyl sulfate and sodium hexadecyl sulfate, above the phase boundary temperature and critical micelle concentrations (cmc). The results indicate that the mixed micelles change from prolate to sphcrical as the molar ratio SOS/SHS increases from 1 to 8. Below 1 or above 8, the formation of micelles is due to one surfactant dissolving the other. 相似文献
25.
This paper through discussing subdifferentiability and convexity of convex functions shows that a Banach space admits an equivalent
uniformly [locally uniformly, strictly] convex norm if and only if there exists a continuous uniformly [locally uniformly,
strictly] convex function on some nonempty open convex subset of the space and presents some characterizations of super-reflexive
Banach spaces.
Supported by NSFC 相似文献
26.
27.
Gang Wang Xiulin Zhu Zhenping Cheng Jian Zhu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2912-2921
A series of (di)picolinic acids and their derivates are investigated as novel complexing tridentate or bidentate ligands in the iron‐mediated reverse atom transfer radical polymerization of methyl methacrylate in N,N‐dimethylformamide at 100 °C with 2,2′‐azobisisobutyrontrile as an initiator. The polymerization rates and polydispersity indices (1.32–1.8) of the resulting polymers are dependent on the structures of the ligands employed. Different iron complexes may be involved in iron‐mediated reverse atom transfer radical polymerization, depending on the type of acid used. 1H NMR spectroscopy has been used to study the structure of the resulting polymers. Chain‐extension reactions have been performed to further confirm the living nature of this catalytic system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2912–2921, 2006 相似文献
28.
Natural populations, whose generations are non-overlapping, can be modelled by difference equations that describe how the populations evolve in discrete time-steps. In the 1970s ecological research detected chaos and other forms of complex dynamics in simple population dynamics models, initiating a new research tradition in ecology. However, in former studies most of the investigations of complex population dynamics were mainly concentrated on single populations instead of higher dimensional ecological systems. This paper reports a recent study on the complicated dynamics occurring in a class of discrete-time models of predator–prey interaction based on age-structure of predator. The complexities include (a) non-unique dynamics, meaning that several attractors coexist; (b) antimonotonicity; (c) basins of attraction (defined as the set of the initial conditions leading to a certain type of an attractor) with fractal properties, consisting of pattern of self-similarity and fractal basin boundaries; (d) intermittency; (e) supertransients; and (f) chaotic attractors. 相似文献
29.
Bo Jin Xi Wang Jing Chen Feng Zhang Xinli Cheng Zhijun Chen 《Applied Surface Science》2006,252(16):5627-5631
The oxidation of SiGe film epitaxial grown on top of SOI wafers has been studied. These SiGe/SOI samples were oxidized at 700, 900, 1100 °C. Germanium atoms were rejected from SiGe film to SOI layer. A new Si1−xGex (x is minimal) layer formed at SiGe/Si interface. As the germanium atoms diffused, the new Si1−xGex (x is minimal) layer moved to Si/SiO2 interface. Propagation of threading dislocation in SiGe film to SOI substrate was hindered by the new SiGe/Si interface. Strain in SOI substrate transferred from SiGe film was released through dislocation nucleation and propagation inner. The relaxation of SiGe film could be described as: strain relaxed through strain equalization and transfer process between SiGe film and SOI substrates. Raman spectroscopy was used to characterize the strain of SiGe film. Microstructure of SiGe/SOI was observed by transmission electron microscope (TEM). 相似文献
30.
The structural evolution in amorphous silicon and germanium thin films has been investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis. The results established that the structure of as-deposited semiconductor films is of a high density of nanocrystallites embedded in the amorphous matrix. In addition, from ACF analysis, the structure of a-Ge is more ordered than that of a-Si. The density of embedded nanocrystallites in amorphous films was found to diminish with annealing temperature first, then to increase. The conclusions also corroborate well with the results of diminished medium-range order in annealed amorphous films determined previously by a variable coherence microscopy method. 相似文献