全文获取类型
收费全文 | 2238篇 |
免费 | 324篇 |
国内免费 | 258篇 |
专业分类
化学 | 1708篇 |
晶体学 | 23篇 |
力学 | 124篇 |
综合类 | 17篇 |
数学 | 232篇 |
物理学 | 716篇 |
出版年
2024年 | 2篇 |
2023年 | 53篇 |
2022年 | 79篇 |
2021年 | 89篇 |
2020年 | 104篇 |
2019年 | 96篇 |
2018年 | 74篇 |
2017年 | 75篇 |
2016年 | 102篇 |
2015年 | 113篇 |
2014年 | 125篇 |
2013年 | 151篇 |
2012年 | 211篇 |
2011年 | 231篇 |
2010年 | 149篇 |
2009年 | 126篇 |
2008年 | 141篇 |
2007年 | 124篇 |
2006年 | 116篇 |
2005年 | 102篇 |
2004年 | 100篇 |
2003年 | 52篇 |
2002年 | 58篇 |
2001年 | 27篇 |
2000年 | 36篇 |
1999年 | 47篇 |
1998年 | 44篇 |
1997年 | 28篇 |
1996年 | 33篇 |
1995年 | 22篇 |
1994年 | 27篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 22篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有2820条查询结果,搜索用时 15 毫秒
941.
Wei Xu Guifa Zhai Dr. Yuanzhen Liu Yuan Li Yanrong Shi Prof. Kui Hong Dr. Hui Hong Prof. Peter F. Leadlay Prof. Zixin Deng Prof. Yuhui Sun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(20):5595-5598
Detailed analysis of the modular Type I polyketide synthase (PKS) involved in the biosynthesis of the marginolactone azalomycin F in mangrove Streptomyces sp. 211726 has shown that only nineteen extension modules are required to accomplish twenty cycles of polyketide chain elongation. Analysis of the products of a PKS mutant specifically inactivated in the dehydratase domain of extension-module 1 showed that this module catalyzes two successive elongations with different outcomes. Strikingly, the enoylreductase domain of this module can apparently be “toggled” off and on : it functions in only the second of these two cycles. This novel mechanism expands our understanding of PKS assembly-line catalysis and may explain examples of apparent non-colinearity in other modular PKS systems. 相似文献
942.
Bingbing Deng Lian Shen Yangai Liu Tao Yang Manshu Zhang Renjie Liu Zhaohui Huang Minghao Fang Xiaowen Wu 《中国化学快报》2017,28(12):2281-2284
A novel porous silicon was synthesized through a magnesiothermic reduction method of molecular sieve for the first time, the porous silicon was used as anode material, which shows a high initial specific capacity of 2018.5 mAh/g with current density of 0.1 A/g. 相似文献
943.
Zhao Dong Jie Xiong Jianliang Zhai Tusheng Zhang 《Journal of Functional Analysis》2017,272(1):227-254
944.
Positive semidefinite rank (PSD-rank) is a relatively new complexity measure on matrices, with applications to combinatorial optimization and communication complexity. We first study several basic properties of PSD-rank, and then develop new techniques for showing lower bounds on the PSD-rank. All of these bounds are based on viewing a positive semidefinite factorization of a matrix M as a quantum communication protocol. These lower bounds depend on the entries of the matrix and not only on its support (the zero/nonzero pattern), overcoming a limitation of some previous techniques. We compare these new lower bounds with known bounds, and give examples where the new ones are better. As an application we determine the PSD-rank of (approximations of) some common matrices. 相似文献
945.
H. R. Marasi H. Afshari M. Daneshbastam C. B. Zhai 《Journal of Contemporary Mathematical Analysis (Armenian Academy of Sciences)》2017,52(1):8-13
In this paper we study the existence and uniqueness of positive solutions for nonlinear fractional differential equation boundary value problems by using new fixed point results of mixed monotone operators on cones. 相似文献
946.
Chuanzhou Tao Lei Sun Bin Wang Zhou Liu Yadong Zhai Xiulian Zhang Dahua Shi Weiwei Liu 《Tetrahedron letters》2017,58(4):305-308
Efficient copper-catalyzed cross-coupling reactions of non-activated alkyl chlorides, including primary, secondary, and tertiary alkyl chlorides, with phenyl Grignard reagents were achieved. Preparation of phenylmagnesium bromide in 2-methyltetrahydrofuran is critical for the success of the reaction. This protocol expands the synthetic toolbox for the construction of CC bonds of non-activated primary, secondary, and tertiary alkyl chlorides via copper-catalyzed cross-coupling. 相似文献
947.
Photonic microwave phase shifter/modulator based on a nonlinear optical loop mirror incorporating a Mach-Zehnder interferometer 总被引:1,自引:0,他引:1
We realize a novel photonic microwave phase shifter/modulator based on a nonlinear optical loop mirror incorporating a Mach-Zehnder interferometer. A near-linear phase shifter exceeding 180 degrees and a phase modulation with 2.5 Gbit/s baseband signal are obtained for a 10 GHz microwave signal by this proposed device. 相似文献
948.
The aggregation of dyes is of considerable importance in relating to their functions and applications. In this paper, we have investigated the regulation on the aggregation and morphology of two cyanine dyes, 3,3'-disulfopropyl-4,5,4',5'-dibenzo-9-methylthiacarbocyanine triethylammonium salt (MTC) and 3,3'-disulfopropyl-4,5,4',5'-dibenzo-9-phenylthiacarbocyanine triethylammonium salt (PTC), using a series of gemini amphiphiles (bis(2'-heptadecyl-3'-ethylimidazolium)-1,n-alkane dibromide, abbreviated as Gn, n=2, 4, 6, 8, 10). It has been found that both of the dyes could be adsorbed onto the monolayers of the gemini amphiphiles through the electrostatic and pi-pi interaction and stacked into H- or J-aggregate. The spacer of the gemini amphiphile showed good control over the aggregation of MTC: H-aggregate was favored when gemini amphiphiles with short spacer were applied, while J-aggregation was preferred in the case of longer spacer. Only J-aggregate was observed for PTC on gemini monolayer, regardless of the structure of the gemini amphiphiles. Interesting morphologies were observed for all the gemini/dye complex monolayers. Network structure and nanofibers were formed for the gemini/MTC films transferred below the plateau surface pressure and close to the collapse pressure, respectively. The ability of the complex monolayers to form nanofibers strongly depended on the component amphiphiles, G2>G4>G6, and no nanofibers were observed for G8/MTC and G10/MTC after the collapse. Only squared domains were observed for gemini/PTC monolayers. When both G2 and G10 were mixed, an individual control of the gemini amphiphiles over the aggregation of MTC in the complex monolayers was observed. The relationship among the spacer, dye structure, and aggregation was revealed. 相似文献
949.
950.
A simple and compact fluorescence detection system for capillary electrophoresis and its application to food analysis 下载免费PDF全文
Haiyun Zhai Kaisong Yuan Zuanguang Chen Zhenping Liu Zihao Su 《Electrophoresis》2015,36(20):2509-2515
A novel fluorescence detection system for CE was described and evaluated. Two miniature laser pointers were used as the excitation source. A Y‐style optical fiber was used to transmit the excitation light and a four‐branch optical fiber was used to collect the fluorescence. The optical fiber and optical filter were imported into a photomultiplier tube without any extra fixing device. A simplified PDMS detection cell was designed with guide channels through which the optical fibers were easily aligned to the detection window of separation capillary. According to different requirements, laser pointers and different filters were selected by simple switching and replacement. The fluorescence from four different directions was collected at the same detecting point. Thus, the sensitivity was enhanced without peak broadening. The fluorescence detection system was simple, compact, low‐cost, and highly sensitive, with its functionality demonstrated by the separation and determination of red dyes and fluorescent whitening agents. The detection limit of rhodamine 6G was 7.7 nM (S/N = 3). The system was further applied to determine illegal food dyes. The CE system is potentially eligible for food safety analysis. 相似文献