全文获取类型
收费全文 | 17672篇 |
免费 | 3136篇 |
国内免费 | 2661篇 |
专业分类
化学 | 13511篇 |
晶体学 | 199篇 |
力学 | 1016篇 |
综合类 | 198篇 |
数学 | 2080篇 |
物理学 | 6465篇 |
出版年
2024年 | 41篇 |
2023年 | 270篇 |
2022年 | 494篇 |
2021年 | 575篇 |
2020年 | 697篇 |
2019年 | 651篇 |
2018年 | 568篇 |
2017年 | 512篇 |
2016年 | 887篇 |
2015年 | 905篇 |
2014年 | 1081篇 |
2013年 | 1298篇 |
2012年 | 1511篇 |
2011年 | 1638篇 |
2010年 | 1195篇 |
2009年 | 1172篇 |
2008年 | 1348篇 |
2007年 | 1181篇 |
2006年 | 1084篇 |
2005年 | 848篇 |
2004年 | 770篇 |
2003年 | 574篇 |
2002年 | 751篇 |
2001年 | 568篇 |
2000年 | 504篇 |
1999年 | 371篇 |
1998年 | 284篇 |
1997年 | 253篇 |
1996年 | 248篇 |
1995年 | 208篇 |
1994年 | 185篇 |
1993年 | 184篇 |
1992年 | 115篇 |
1991年 | 105篇 |
1990年 | 82篇 |
1989年 | 55篇 |
1988年 | 55篇 |
1987年 | 48篇 |
1986年 | 24篇 |
1985年 | 39篇 |
1984年 | 19篇 |
1983年 | 18篇 |
1982年 | 7篇 |
1981年 | 14篇 |
1980年 | 4篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1974年 | 3篇 |
1916年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Deng Shitao 《数学学报(英文版)》1989,5(3):223-234
ForH C
2 (,R) where 0 R
2n
,H (0)=0 and detH(0)0, the paper proves that there is a global Hopf bifurcation fromx=0 for Hamiltonian systemx=JH(x) iffJH(0)possesses purely imaginary eigenvalues. The work improves the corresponding result of J.C.Alexander and J. Yorke (Amer. J. Math., 100 (1978), 263–292). 相似文献
72.
73.
74.
A novel photothermal phase-shift spectroscopy configuration based on the retro-reflected beam interference has been developed and its operational principle is described. The weak absorption measurement ability of this technique is experimentally proven with a water/ethanol solution of standard Pyronine G dye and the limit of detection is found to be 1.8 x 10(-6) absorbance. Potential applications of the technique are discussed. 相似文献
75.
Yongcheng Liu Xin Chen Jianghong Qian Haiying Liu Zhengzhong Shao Jiaqi Deng Tongyin Yu 《Applied biochemistry and biotechnology》1997,62(2-3):105-117
The structure and properties of the blend of regenerated silk fibroin (RSF) and poly(vinyl alcohol) (PVA) were investigated.
The two polymers in the blend are in the state of phase segregation. Infrared (IR) spectra indicate that the RSF in the blend
maintains its intrinsic properties, thus, ethanol treatment can transfer silk I structure of RSF to silk II structure. The
water absorption property and mechanical property of the blend are improved in comparison with those of RSF. The blend maintains
the major merit of RSF, that is, it can immobilize glucose oxidase on the basis of the conformational transition from silk
I structure to silk II structure. The properties of the immobilized enzyme are examined. Moreover, the second generation of
glucose sensor based on the immobilized enzyme is fabricated and it has a variety of advantages including easy maintenance
of enzyme, simplicity of construction, fast response time and high stability. 相似文献
76.
Ju-Chun Huang Chien Hong Cheng Shyang Roeng Sheen Zhi Ling Lee Chien Ming Lei Maw Kuen Wu 《中国化学会会志》1996,43(2):139-143
The synthesis of bulk Y2Ba4Cu7O15-δ superconductor at atmospheric oxygen pressure via solid state sintering is reported. Temperature ranging from 860 to 890 °C as well as time interval over 2 to 15 days were used to investigate the formation of the Y2Ba4Cu7O15-δ phase. A time-temperature profile characterizing the conditions for the preparation of Y2Ba4Cu7O15-δ phase suggests the optimal condition to be sintering at 890 °C for over 10 days. Detailed results of X-ray diffraction, electrical resistivity, iodometric titration and magnetization measurements are described. 相似文献
77.
Isomeric structures and energies of three kinds of lithofluorosilylenoids, R2SiLiF (R = NH2, OH, F) were studied using theab initio molecular orbital theory. The calculations show that thermal stability of the three-membered ring structures of these three
kinds of silylenoids decreases in the order of substituents NH2 > OH > F because of the conjugation between NH2, OH or F and Si atom. The interaction of substituents R with Li atom makes R2SiLiF have a structure with two Li-A-Si-F (A = N, O, F) four-membered rings, which is the most stable of the isomers of each
of three kinds of silylenoids and whose stability decreases in the order of substituents F > OH > NH2. Inductive effect of substituents influences the thermal stability of the linear structure of silylenoids. 相似文献
78.
乳状液法制备憎液溶胶Ⅰ.BaCO_3均匀粒子的制备 总被引:1,自引:0,他引:1
均匀胶体粒子的形成,除与反应条件(反应物浓度、陈化时间和温度、介质种类等)有关外,反应体系的环境也影响最终产物的形态,《至结晶结构.气溶胶法和微乳液法正是利用微环境中的‘水池效应”;分别制备出球形亚微米和纳米级的均匀粒子[‘-‘]、这些方法与水解法和相转化法等方法比较,反应物浓度要大几个数量级,而反应时间却短很多,因而受到研究人员的关注.乳状液也能提供亚微米、微米及以上级的微环境,因此,可以应用O/W乳状液乳液中的聚合反应制备亲液的分散体系.然而,极少有关利用w/O乳状液制备僧液溶胶的报导问;最近… 相似文献
79.
YU Ming XU Qiang School of Materials Science Engineering East China University of Science Technology Shanghai China 《Chinese Journal of Reactive Polymers》2006,(1)
1. INTRODUCTIONThese years, HCFC-141b may be the most used blowing agent for its useful properties. But, because of its high global warming effect leading to the destruction of the ozone layer, production of HCFC141b has been forbidden. However, there are… 相似文献
80.