全文获取类型
收费全文 | 117330篇 |
免费 | 20039篇 |
国内免费 | 12540篇 |
专业分类
化学 | 80385篇 |
晶体学 | 1441篇 |
力学 | 7625篇 |
综合类 | 745篇 |
数学 | 13524篇 |
物理学 | 46189篇 |
出版年
2024年 | 393篇 |
2023年 | 2254篇 |
2022年 | 3926篇 |
2021年 | 4283篇 |
2020年 | 4662篇 |
2019年 | 4534篇 |
2018年 | 3927篇 |
2017年 | 3645篇 |
2016年 | 5763篇 |
2015年 | 5546篇 |
2014年 | 6700篇 |
2013年 | 8663篇 |
2012年 | 10428篇 |
2011年 | 10798篇 |
2010年 | 7287篇 |
2009年 | 7051篇 |
2008年 | 7522篇 |
2007年 | 6835篇 |
2006年 | 6281篇 |
2005年 | 5259篇 |
2004年 | 3988篇 |
2003年 | 3161篇 |
2002年 | 3091篇 |
2001年 | 2535篇 |
2000年 | 2200篇 |
1999年 | 2347篇 |
1998年 | 2020篇 |
1997年 | 1847篇 |
1996年 | 2035篇 |
1995年 | 1609篇 |
1994年 | 1559篇 |
1993年 | 1261篇 |
1992年 | 1126篇 |
1991年 | 1049篇 |
1990年 | 832篇 |
1989年 | 591篇 |
1988年 | 492篇 |
1987年 | 404篇 |
1986年 | 395篇 |
1985年 | 339篇 |
1984年 | 259篇 |
1983年 | 173篇 |
1982年 | 154篇 |
1981年 | 115篇 |
1980年 | 81篇 |
1979年 | 54篇 |
1978年 | 41篇 |
1976年 | 38篇 |
1974年 | 51篇 |
1973年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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
52.
Qipeng Guo Fei Chen Ke Wang Ling Chen 《Journal of Polymer Science.Polymer Physics》2006,44(21):3042-3052
An amphiphilic poly(ethylene oxide)‐block‐poly(dimethylsiloxane) (PEO–PDMS) diblock copolymer was used to template a bisphenol A type epoxy resin (ER); nanostructured thermoset blends of ER and PEO–PDMS were prepared with 4,4′‐methylenedianiline (MDA) as the curing agent. The phase behavior, crystallization, hydrogen‐bonding interactions, and nanoscale structures were investigated with differential scanning calorimetry, Fourier transform infrared spectroscopy, transmission electron microscopy, and small‐angle X‐ray scattering. The uncured ER was miscible with the poly(ethylene oxide) block of PEO–PDMS, and the uncured blends were not macroscopically phase‐separated. Macroscopic phase separation took place in the MDA‐cured ER/PEO–PDMS blends containing 60–80 wt % PEO–PDMS diblock copolymer. However, the composition‐dependent nanostructures were formed in the cured blends with 10–50 wt % PEO–PDMS, which did not show macroscopic phase separation. The poly(dimethylsiloxane) microdomains with sizes of 10–20 nm were dispersed in a continuous ER‐rich phase; the average distance between the neighboring microdomains was in the range of 20–50 nm. The miscibility between the cured ER and the poly(ethylene oxide) block of PEO–PDMS was ascribed to the favorable hydrogen‐bonding interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3042–3052, 2006 相似文献
53.
In this paper we give a realization of some symmetric space G/K as a closed submanifold P of G. We also give several equivalent representations of the submanifold P. Some properties of the set gK∩P are also discussed, where gK is a coset space in G. 相似文献
54.
55.
56.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
57.
Theoretical and experimental investigations on the performance of micro-perforated -panel absorbers are reviewed in this paper. By reviewing recent research work, this paper reveals a relationship between the maximum absorption coefficient and the limit of the absorption frequency bandwidth. It has been demonstrated that the absorption frequency bandwidth can be extended up to 3 or 4 octaves as the diameters of the micro-holes decrease. This has become possible with the development of the technologies for manufacturing micro-perforated panels, such as laser drilling, powder metallurgy, welded meshing and electro-etching to form micrometer order holes. In this paper, absorption characteristics of such absorbers in random fields and in high sound intensity are discussed both theoretically and experimentally. A new absorbing structure based on micro-perforated-panel absorbers demonstrate experimentally high sound absorption capability. This review shows that the micro-perforated-panel absorber has potentials to be one of ideal absorbing materials in the 21st century. 相似文献
58.
In this paper, the dimension of the spaces of bivariate spline with degree less that 2r and smoothness order r on the Morgan-Scott triangulation is considered. The concept of the instability degree in the dimension of spaces of bivariate spline is presented. The results in the paper make us conjecture the instability degree in the dimension of spaces of bivariate spline is infinity. 相似文献
59.
60.