全文获取类型
收费全文 | 7638篇 |
免费 | 1287篇 |
国内免费 | 1281篇 |
专业分类
化学 | 6450篇 |
晶体学 | 69篇 |
力学 | 378篇 |
综合类 | 87篇 |
数学 | 904篇 |
物理学 | 2318篇 |
出版年
2024年 | 31篇 |
2023年 | 138篇 |
2022年 | 200篇 |
2021年 | 218篇 |
2020年 | 310篇 |
2019年 | 338篇 |
2018年 | 290篇 |
2017年 | 218篇 |
2016年 | 375篇 |
2015年 | 388篇 |
2014年 | 431篇 |
2013年 | 579篇 |
2012年 | 644篇 |
2011年 | 620篇 |
2010年 | 499篇 |
2009年 | 497篇 |
2008年 | 509篇 |
2007年 | 487篇 |
2006年 | 427篇 |
2005年 | 396篇 |
2004年 | 366篇 |
2003年 | 330篇 |
2002年 | 391篇 |
2001年 | 243篇 |
2000年 | 215篇 |
1999年 | 211篇 |
1998年 | 156篇 |
1997年 | 133篇 |
1996年 | 96篇 |
1995年 | 65篇 |
1994年 | 70篇 |
1993年 | 44篇 |
1992年 | 46篇 |
1991年 | 49篇 |
1990年 | 40篇 |
1989年 | 30篇 |
1988年 | 24篇 |
1987年 | 11篇 |
1986年 | 20篇 |
1985年 | 20篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1979年 | 6篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1968年 | 3篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Qi Wang Huaxiang Yang Zhiqiang Fan Hong Xu 《Journal of polymer science. Part A, Polymer chemistry》2004,42(5):1093-1099
Ethylisobutylaluminoxane (EBAO) and its analogues were synthesized by a reaction between an triethylaluminum (Et3Al)/triisobutylaluminum (i‐Bu3Al) mixture and 4‐fluorobenzeneboronic acid, phenylboronic acid, or n‐butaneboronic acid and subsequent hydrolysis with water. They were used as cocatalysts in ethylene polymerization catalyzed by an iron complex {[(ArN?C(Me))2C5H3N]FeCl2, where Ar is 2,6‐diisopropylphenyl}. Polyethylene with a high molecular weight and a narrow molecular weight distribution was prepared with modified EBAOs, and the performance of the iron complex at high polymerization temperatures was greatly improved. The activators for the iron complex also affected the polymerization activity and the molecular weight of the resultant polyethylene. It was suggested that the stereo and electronic effects of the substitute groups of aluminoxane contributed to the improved performance of the new activators. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1093–1099, 2004 相似文献
22.
Chin‐Ping Yang Sheng‐Huei Hsiao Che‐Yu Tsai Guey‐Sheng Liou 《Journal of polymer science. Part A, Polymer chemistry》2004,42(10):2416-2431
Two series of fluorinated polyimides were prepared from 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl ( 2 ) and 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐1,1′‐binaphthyl ( 4 ) with various aromatic dianhydrides via a conventional, two‐step procedure that included a ring‐opening polyaddition to give poly(amic acid)s, followed by chemical or thermal cyclodehydration. The inherent viscosities of the polyimides ranged from 0.54 to 0.73 and 0.19 to 0.36 dL/g, respectively. All the fluorinated polyimides were soluble in many polar organic solvents, such as N,N‐dimethylacetamide and N‐methylpyrrolidone, and afforded transparent and light‐colored films via solution‐casting. These polyimides showed glass‐transition temperatures in the ranges of 222–280 and 257–351 °C by DSC, softening temperatures in the range of 264–301 °C by thermomechanical analysis, and a decomposition temperature for 10% weight loss above 520 °C both in nitrogen and air atmospheres. The polyimides had low moisture absorptions of 0.23–0.58%, low dielectric constants of 2.84–3.61 at 10 kHz, and an ultraviolet–visible absorption cutoff wavelength at 351–434 nm. Copolyimides derived from the same dianhydrides with an equimolar mixture of 4,4′‐oxydianiline and diamine 2 or 4 were also prepared and characterized. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2416–2431, 2004 相似文献
23.
24.
非负矩阵与有向图的谱半径 总被引:2,自引:0,他引:2
本文给出非负矩阵的谱半径的上界、下界,由此给出有向图的谱半径的界. 相似文献
25.
26.
27.
28.
The distortion theorem for biholomorphic convex mappings in bounded symmetric domains are considered. Especially the distortion theorem for biholomorphic convex mappings in classical domain of type IV and two exceptional domains are given. 相似文献
29.
A method for determining accurate relative molecular masses and elemental compositions of several non-volatile and thermally labile organic compounds in the source cell was established. The experimental sequence included laser desorption/electron impact Fourier transform mass spectrometry and direct-mode observation over a narrow mass range. Perfluorotributylamine was used as internal calibrant. Errors were about 1 ppm. 相似文献
30.
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