全文获取类型
收费全文 | 6679篇 |
免费 | 215篇 |
国内免费 | 45篇 |
专业分类
化学 | 4187篇 |
晶体学 | 26篇 |
力学 | 275篇 |
数学 | 1406篇 |
物理学 | 1045篇 |
出版年
2023年 | 30篇 |
2022年 | 51篇 |
2021年 | 140篇 |
2020年 | 146篇 |
2019年 | 118篇 |
2018年 | 114篇 |
2017年 | 87篇 |
2016年 | 245篇 |
2015年 | 188篇 |
2014年 | 230篇 |
2013年 | 398篇 |
2012年 | 441篇 |
2011年 | 462篇 |
2010年 | 241篇 |
2009年 | 275篇 |
2008年 | 410篇 |
2007年 | 398篇 |
2006年 | 339篇 |
2005年 | 318篇 |
2004年 | 307篇 |
2003年 | 236篇 |
2002年 | 180篇 |
2001年 | 88篇 |
2000年 | 69篇 |
1999年 | 65篇 |
1998年 | 65篇 |
1997年 | 73篇 |
1996年 | 104篇 |
1995年 | 50篇 |
1994年 | 65篇 |
1993年 | 44篇 |
1992年 | 66篇 |
1991年 | 46篇 |
1990年 | 44篇 |
1989年 | 48篇 |
1988年 | 40篇 |
1987年 | 36篇 |
1986年 | 38篇 |
1985年 | 55篇 |
1984年 | 48篇 |
1983年 | 50篇 |
1982年 | 56篇 |
1981年 | 31篇 |
1980年 | 42篇 |
1979年 | 30篇 |
1978年 | 35篇 |
1977年 | 30篇 |
1976年 | 27篇 |
1974年 | 19篇 |
1973年 | 18篇 |
排序方式: 共有6939条查询结果,搜索用时 62 毫秒
11.
12.
R. Pizzoferrato L. Lagonigro T. Ziller A. Di Carlo R. Paolesse F. Mandoj A. Ricci C. Lo Sterzo 《Chemical physics》2004,300(1-3):217-225
We study the infrared emission at 1.54 μm of an organolanthanide complex, Er(III)-tetraphenylporphyrin [Er(TPP)acac], both as a result of direct optical excitation and via energy transfer from host π-conjugate polymers of type poly(arylene–ethynylene) [PAE]. In the first case, the emission of the neat complex is characterized in inert transparent materials and a value of the quantum yield at 1.54 μm φIR=4×10−4 is measured. Then, fluorescence resonance transfer is investigated in blends of Er(TPP)acac with PAEs by monitoring the quenching of the polymer fluorescence along with the enhancement of both the visible emission of the ligand and the near-infrared band of Er3+. These different procedures allow a detailed analysis of the transfer efficiency within a specific implementation of the Förster model for polymeric donors. The experimental values of the critical radius R0, ranging from 1.3 to 2.5 nm for the different blends, are in good agreement with theory for a wide interval of the physical and spectroscopic parameters. This suggests that other mechanisms for excitation transfer do not play a significant role in these materials. 相似文献
13.
Robert Jerrard Alberto Montero Peter Sternberg 《Communications in Mathematical Physics》2004,249(3):549-577
We establish the existence of locally minimizing vortex solutions to the full Ginzburg-Landau energy in three dimensional simply-connected domains with or without the presence of an applied magnetic field. The approach is based upon the theory of weak Jacobians and applies to nonconvex sample geometries for which there exists a configuration of locally shortest line segments with endpoints on the boundary.Research partially supported by NSERC grant number 261955 相似文献
14.
Alberto Plaza Sonia Piacente Angela Perrone Arafa Hamed Cosimo Pizza Giuseppe Bifulco 《Tetrahedron》2004,60(52):12201-12209
Stemmosides C and D, two novel pregnane glycosides characterized by an unusual C-17 side chain were isolated from the pericarps of Solenostemma argel. In addition, stemmoside D displays an uncommon 14β proton configuration, apparently being the first pregnane isolated from plants known to have a 15 keto, cis CD ring junction. Their structures have been established by ESIMS and NMR experiments. The relative configuration of the molecules was determined using a strategy based on the simulation of 1H, 13C, and J coupling NMR parameters. DFT calculations of 1H and 13C chemical shifts, and of the 1H homonuclear spin–spin coupling constants were performed with the mPW1PW91 functional using the 6-31G(d,p) basis set on the fully optimized geometries of all the possible stereoisomers. 相似文献
15.
Alberto Mariani Simone Bidali Stefano Fiori Marco Sangermano Giulio Malucelli Roberta Bongiovanni Aldo Priola 《Journal of polymer science. Part A, Polymer chemistry》2004,42(9):2066-2072
By combining frontal polymerization and radical‐induced cationic polymerization, it was possible to cure thick samples of an epoxy monomer bleached by UV light. The effect of the relative amounts of cationic photoinitiator and radical initiator was thoroughly investigated and was related to the front's velocity and its maximum temperature. The materials obtained were characterized by quantitative conversion also in the deeper layers, not reached by UV light. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2066–2072, 2004 相似文献
16.
17.
Alberto Elduque José Marí a Pé rez 《Proceedings of the American Mathematical Society》1997,125(8):2207-2216
Composition algebras with a unit element constitute a well-known class of algebras. In this paper, those composition algebras with a one-sided unit element are characterized and examples are given of arbitrary infinite dimension.
18.
19.
Roger Alberto 《Journal of organometallic chemistry》2007,692(6):1179-1186
This article will emphasize the particular role of organometallic radiopharmaceutical chemistry, namely the need for syntheses from water and the emerging implications for other (bio)organometallic fields. After some basic insights into the different directions of bioorganometallic chemistry, some facets of the [M(CO)3]+ (M = Tc, Re) moiety are reviewed and discussed in the respective context. The mechanism for the synthesis of [M(OH2)3(CO)3]+ which is still little understood, will be touched. The formation of additional M-C bonds is exemplified with cyclopentadienyl chemistry, the potential impact on targeted molecular imaging with the labelling of amino acids and the reactivity towards essential biomolecules such as guanine is shown. Future perspectives and implications for organometallic radiopharmaceutical chemistry will close this article. 相似文献
20.
Franca M. Cordero Francesco De Sarlo Alberto Brandi 《Monatshefte für Chemie / Chemical Monthly》2004,40(2):649-669
The review outlines the various different azaheterocycles available from 5-spirocyclopropane isoxazolidines. These compounds can be regarded as versatile direct precursors of tetrahydro-, dihydropyridone and azetidinone derivatives. The current scope and limitations, and the selectivity aspects of the different processes are discussed therein. 相似文献