全文获取类型
收费全文 | 1816篇 |
免费 | 73篇 |
国内免费 | 15篇 |
专业分类
化学 | 1391篇 |
晶体学 | 10篇 |
力学 | 43篇 |
综合类 | 1篇 |
数学 | 146篇 |
物理学 | 313篇 |
出版年
2022年 | 13篇 |
2021年 | 20篇 |
2020年 | 30篇 |
2019年 | 25篇 |
2018年 | 30篇 |
2017年 | 25篇 |
2016年 | 56篇 |
2015年 | 50篇 |
2014年 | 48篇 |
2013年 | 83篇 |
2012年 | 119篇 |
2011年 | 90篇 |
2010年 | 73篇 |
2009年 | 59篇 |
2008年 | 122篇 |
2007年 | 113篇 |
2006年 | 116篇 |
2005年 | 124篇 |
2004年 | 93篇 |
2003年 | 75篇 |
2002年 | 70篇 |
2001年 | 29篇 |
2000年 | 24篇 |
1999年 | 27篇 |
1998年 | 22篇 |
1997年 | 11篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1982年 | 22篇 |
1981年 | 15篇 |
1980年 | 16篇 |
1979年 | 28篇 |
1978年 | 14篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1975年 | 14篇 |
1974年 | 8篇 |
1972年 | 7篇 |
1970年 | 9篇 |
1969年 | 9篇 |
1967年 | 7篇 |
1966年 | 6篇 |
排序方式: 共有1904条查询结果,搜索用时 31 毫秒
81.
A fully functionalized ABCD ring moiety of gambierol, a marine polycyclic ether toxin, was synthesized by the use of the oxiranyl anion strategy and reductive cycloetherification of a beta,delta-dihydroxy ketone. 相似文献
82.
Tachibana Y Otsuka K Terabe S Arai A Suzuki K Nakamura S 《Journal of chromatography. A》2003,1011(1-2):181-192
A robust and simple interface for microchip electrophoresis-mass spectrometry (MCE-MS) was developed using a spray nozzle connected to the exit of the separation channel of the microchip. The spray nozzle was attached to the microchip using a polyether ether ketone screw without adhesive, thus allowing easy replaced. Sample injection and electrophoretic separation was performed by control of the voltage only. The analysis of a few basic drugs was performed using the optimized MCE-MS system. The separation was improved by using a high-viscosity separation buffer and a spray nozzle with a small bore size. This system was also applied to the separation of peptides and protein-trypsin digests. Sample adsorption was minimized by adding acetonitrile to the separation buffer when using a quartz microchip. 相似文献
83.
Hiroki FurutaToyohisa Takase Hisafumi HayashiRyoji Noyori Yuji Mori 《Tetrahedron》2003,59(49):9767-9777
An efficient method has been developed for the synthesis of trans-fused tetrahydropyrans with angular methyl groups adjacent to the ring oxygen. The procedure involves the coupling reaction of a sulfonyl-stabilized oxiranyl anion with an appropriate triflate followed by 6-endo cyclization, and is effective for the construction of 6/6- and 6/7/6-cyclic ether ring systems with sterically congested 1,3-diaxial methyl groups. 相似文献
84.
A stereocontrolled linear synthesis of the ABCDEF-ring system of yessotoxin and adriatoxin, diarrhetic shellfish toxins, is described. Iterative application of a tetrahydropyran synthesis by reaction of the alkylation of a sulfonyl-stabilized oxiranyl anion followed by 6-endo cyclization of a 4,5-epoxy alcohol led to the synthesis of the trans-fused hexacyclic ether system, and the seven-membered E ring was constructed by ring expansion reaction. 相似文献
85.
Yoshitaka Ogiwara Yuji Kimura Zenjiro Osawa Hitoshi Kubota 《Journal of polymer science. Part A, Polymer chemistry》1977,15(7):1667-1675
Effects of ferric chloride (FeCl3) on photodegradation of high-density polyethylene (PE) were investigated by using ESR and infrared spectrometry. In the system with irradiation at light of λ > 220 nm, PE irradiated at 77°K yielded an 8-line spectrum, the intensity of which was markedly weakened by using FeCl3 with the sample, indicating a distinct depression of radical formation. On the other hand, PE with the use of FeCl3 yielded radicals under irradiation only with light of λ > 300 nm, showing a singlet spectrum with a line width of 15 gauss. For photooxidized PE, almost the same effect of FeCl3 was observed. On irradiation at room temperature, PE samples with and without FeCl3 showed a singlet spectrum with line widths of 15 and 25 gauss, respectively. On the other hand, the unsaturated double bond contained in a small amount in PE sample was observed by infrared study to be decreased with photoirradiation; however, the decrease was sharply depressed with the addition of FeCl3 to the sample. The degradation of carbonyl group in a photooxidized sample was markedly affected by photoirradiation, and the decay was obviously reduced for the sample on addition of FeCl3. It is concluded that FeCl3 works upon photodegradation of PE to enhance the Norrish type II reaction and to accelerate the formation of unsaturated double bond in the chain. 相似文献
86.
Hattori S Wada Y Yanagida S Fukuzumi S 《Journal of the American Chemical Society》2005,127(26):9648-9654
The electron self-exchange rate constants of blue copper model complexes, [(-)-sparteine-N,N'](maleonitriledithiolato-S,S')copper ([Cu(SP)(mmt)])(0/)(-), bis(2,9-dimethy-1,10-phenanthroline)copper ([Cu(dmp)(2)](2+/+)), and bis(1,10-phenanthroline)copper ([Cu(phen)(2)](2+/+)) have been determined from the rate constants of electron transfer from a homologous series of ferrocene derivatives to the copper(II) complexes in light of the Marcus theory of electron transfer. The resulting electron self-exchange rate constant increases in the order: [Cu(phen)(2)](2+/+) < [Cu(SP)(mmt)](0/)(-) < [Cu(dmp)(2)](2+/+), in agreement with the order of the smaller structural change between the copper(II) and copper(I) complexes due to the distorted tetragonal geometry. The dye-sensitized solar cells (DSSC) were constructed using the copper complexes as redox couples to compare the photoelectrochemical responses with those using the conventional I(3)(-)/I(-) couple. The light energy conversion efficiency (eta) values under illumination of simulated solar light irradiation (100 mW/cm(2)) of DSSCs using [Cu(phen)(2)](2+/+), [Cu(dmp)(2)](2+/+), and [Cu(SP)(mmt)](0/)(-) were recorded as 0.1%, 1.4%, and 1.3%, respectively. The maximum eta value (2.2%) was obtained for a DSSC using the [Cu(dmp)(2)](2+/+) redox couple under the light irradiation of 20 mW/cm(2) intensity, where a higher open-circuit voltage of the cell was attained as compared to that of the conventional I(3)(-)/I(-) couple. 相似文献
87.
A zwitterionic trichloroplatinum(II) complex PtCl3(4,4′-bpy-N-nBu) (1) was prepared by an aqueous reaction of [4,4′-bpy-N-nBu]Cl with K2PtCl4, and was characterized by 1H-n.m.r. and IR spectroscopy as well as elemental analysis. Dissolving (1) into dmso-d
6 at 25 °C yields a mixture of the complexes, cis-PtCl2(4,4′-bpy-N-nBu)(dmso-d
6) (2-cis), trans-PtCl2(4,4′-bpy-N-nBu)(dmso-d
6) (2-trans), [4,4′-bpy-N-nBu]Cl and PtCl2(dmso-d
6)2. Ratio of the products in the dmso-d
6 solution changed depending on the temperature and the total concentration of the complexes. These compounds are in equilibrium
via isomerization reaction between (2-cis) and (2-trans) and via displacement reaction of the alkylbipyridinium ligand of
(2-cis) and (2-trans) with dmso-d
6 to form [4,4′-bpy-N-nBu]Cl and PtCl2(dmso-d
6)2. 相似文献
88.
89.
Yuji Liu 《Journal of Applied Mathematics and Computing》2012,38(1-2):195-208
Sufficient conditions for the existence of solutions of nonlinear boundary value problems for higher order functional difference equations with p-Laplacian are established by using the continuation theorem. The result is proved without using the monotonicity of B i (i=0,1). We allow f to be at most linear, superlinear or sublinear in obtained results. 相似文献
90.