全文获取类型
收费全文 | 3089篇 |
免费 | 164篇 |
国内免费 | 13篇 |
专业分类
化学 | 2262篇 |
晶体学 | 11篇 |
力学 | 132篇 |
数学 | 341篇 |
物理学 | 520篇 |
出版年
2023年 | 30篇 |
2022年 | 59篇 |
2021年 | 60篇 |
2020年 | 68篇 |
2019年 | 68篇 |
2018年 | 48篇 |
2017年 | 37篇 |
2016年 | 91篇 |
2015年 | 88篇 |
2014年 | 104篇 |
2013年 | 152篇 |
2012年 | 223篇 |
2011年 | 262篇 |
2010年 | 130篇 |
2009年 | 147篇 |
2008年 | 232篇 |
2007年 | 218篇 |
2006年 | 224篇 |
2005年 | 213篇 |
2004年 | 176篇 |
2003年 | 149篇 |
2002年 | 125篇 |
2001年 | 60篇 |
2000年 | 36篇 |
1999年 | 21篇 |
1998年 | 21篇 |
1997年 | 20篇 |
1996年 | 28篇 |
1995年 | 14篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 33篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1897年 | 2篇 |
排序方式: 共有3266条查询结果,搜索用时 15 毫秒
81.
P. E. Sulewski E. Bucher N. Stücheli C. S. Oglesby K. Friemelt M. Vögt J. R. Baumann Ch. Kloc 《Applied Physics A: Materials Science & Processing》1992,54(1):79-83
Recently, an anomalously large redshift of the absorption edge with electric field was claimed for -GaSe1–x
S
x
layered crystals. We have studied Bridgman grown -GaSe crystals as well as vapor transport grown -GaS, and 2H-WSe2. While we have observed a shift in the absorption edge for -GaSe similar to that reported in previous work, our results demonstrate that the redshift arises from Joule heating, and is thus temperature induced, rather than intrinsic. For -GaS, much larger resistivities virtually eliminate Joule heating, and our measurements of the electric field induced absorption edge shift yield an estimated upper limit of approximately 0.04 meV · cm/kV for a field of 2.4×103 kV/cm, in good agreement with the theoretical value expected for the Franz-Keldysh effect.Also at University of Konstanz 相似文献
82.
83.
Magic numbers in the magnetic properties of gadolinium clusters 总被引:1,自引:0,他引:1
84.
Michel F Thomas F Hamman S Saint-Aman E Bucher C Pierre JL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(17):4115-4125
Galactose oxidase (GO) is an enzyme that catalyzes two-electron oxidations. Its active site contains a copper atom coordinated to a tyrosyl radical, the biogenesis of which requires copper and dioxygen. We have recently studied the properties of electrochemically generated mononuclear Cu(II)-phenoxyl radical systems as model compounds of GO. We present here the solution chemistry of these ligands under various copper and dioxygen statuses: N(3)O ligands first chelate Cu(II), leading, in the presence of base, to [Cu(II)(ligand)(CH(3)CN)](+) complexes (ortho-tert-butylated ligands) or [(Cu(II))(2)(ligand)(2)](2+) complexes (ortho-methoxylated ligands). Excess copper(II) then oxidizes the complex to the corresponding mononuclear Cu(II)-phenoxyl radical species. N(2)O(2) tripodal ligands, in the presence of copper(II), afford directly a copper(II)-phenoxyl radical species. Addition of more than two molar equivalents of copper(II) affords a Cu(II)-bis(phenoxyl) diradical species. The donor set of the ligand directs the reaction towards comproportionation for ligands possessing an N(3)O donor set, while disproportionation is observed for ligands possessing an N(2)O(2) donor set. These results are discussed in the light of recent results concerning the self-processing of GO. A path involving copper(II) disproportionation is proposed for oxidation of the cross-linked tyrosinate of GO, supporting the fact that both copper(I) and copper(II) activate the enzyme. 相似文献
85.
Benturquia N Couderc F Sauvinet V Orset C Parrot S Bayle C Renaud B Denoroy L 《Electrophoresis》2005,26(6):1071-1079
Serotonin or 5-hydroxytryptamine (5-HT) is a major neurotransmitter in the central nervous system. In this work, a method for analyzing 5-HT in brain microdialysis samples using a commercially available capillary electrophoresis (CE) system has been developed. A pH-mediated in-capillary preconcentration of samples was performed, and after separation by capillary zone electrophoresis, native fluorescence of 5-HT was detected by a 266 nm solid-state laser. The separation conditions for the analysis of 5-HT in standard solutions and microdialysates have been optimized, and this method has been validated on both pharmacological and analytical bases. Separation of 5-HT was performed using a 80 mmol/L citrate buffer, pH 2.5, containing 20 mmol/L hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and +30 kV voltage. The detection limit was 2.5 x 10(-10) mol/L. This method allows the in vivo brain monitoring of 5-HT using a simple, accurate CE measurement in underivatized microdialysis samples. 相似文献
86.
Amgoune A Thomas CM Roisnel T Carpentier JF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):169-179
A series of new alkoxy-amino-bis(phenols) (H2L 1-6) has been synthesized by Mannich condensations of substituted phenols, formaldehyde, and amino ethers or diamines. The coordination properties of these dianionic ligands towards yttrium, lanthanum, and neodymium have been studied. The resulting Group 3 metal complexes have been used as initiators for the ring-opening polymerization of rac-lactide to provide poly(lactic acid)s (PLAs). The polymerizations are living, as evidenced by the narrow polydispersities of the isolated polymers, together with the linear natures of number average molecular weight versus conversion plots and monomer-to-catalyst ratios. Complex [Y(L6){N(SiHMe2)2}(THF)] (17) polymerized rac-lactide to heterotactic PLA (Pr = 0.90 at 20 degrees C) and meso-lactide to syndiotactic PLA (Pr = 0.75 at 20 degrees C). The in situ formation of [Y(L6)(OiPr)(THF)] (18) from 17 and 2-propanol resulted in narrower molecular weight distributions (PDI = 1.06). With complex 18, highly heterotactic PLAs with narrow molecular weight distributions were obtained with high activities and productivities at room temperature. The natures of the ligand substituents were shown to have a significant influence on the degree of control of the polymerizations, and in particular on the tacticity of the polymer. 相似文献
87.
Xu X Zhao Z Song P Zhou G Xu J Deng P Bourdet G Chanteloup JC Zou JP Fulop A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(11-12):2444-2447
Infrared (1.2-1.6 microm) luminescence in a ytterbium aluminium garnet (YbAG) crystal, doped with Cr (0.05at.%) ions, was investigated under CW laser diode pumping (lambda=940 nm). The Cr4+ emission band was observed with its peak at 1.34 microm and measured to be about 1.3 times with respect to Yb3+ IR luminescence (lambda=1.03 microm). We demonstrate that for the excitation wavelength of 940 nm Yb3+ ions act as sensitizers of the 3B2(3T2)-3B1(3A2) emission of Cr4+ ions. This crystal is promising as a high-efficient system for tunable laser (1.2-1.6 microm) output. 相似文献
88.
The one-carbon elongation of aldoses to ketoses using iodomethyllithium as the key reagent in the homologation step is exemplified by the preparation of two carbohydrates of chemical and biological interests: d-manno-hept-2-ulose from d-mannose and l-fructose from l-arabinose. 相似文献
89.
Delajon C Gutberlet T Steitz R Möhwald H Krastev R 《Langmuir : the ACS journal of surfaces and colloids》2005,21(18):8509-8514
The coupling of lipid molecules to polymer components in a planar biomimetic model membrane made of a lipid bilayer (dimyristoylphosphatidylcholine) supported by polyelectrolyte multilayers is studied. The polyelectrolyte support was prepared by layer-by-layer deposition of positively charged poly(allylamine hydrochloride) (PAH) and negatively charged poly(sodium 4-styrenesulfonate) (PSS). Two polymer sample terminations were considered: positively charged (PAH-terminated) and negatively charged (PSS-terminated). Neutron reflectometry studies showed that, whereas positively charged samples did not favor the deposition of lipid, negatively charged samples allowed the deposition of a lipid bilayer with a thickness of approximately 5 nm. In the latter case, formation of polyelectrolyte layers after the deposition of the lipid layer was also possible. 相似文献
90.