全文获取类型
收费全文 | 3630篇 |
免费 | 83篇 |
国内免费 | 30篇 |
专业分类
化学 | 2887篇 |
晶体学 | 48篇 |
力学 | 57篇 |
数学 | 176篇 |
物理学 | 575篇 |
出版年
2022年 | 24篇 |
2021年 | 29篇 |
2020年 | 31篇 |
2019年 | 37篇 |
2018年 | 23篇 |
2017年 | 31篇 |
2016年 | 42篇 |
2015年 | 66篇 |
2014年 | 78篇 |
2013年 | 262篇 |
2012年 | 164篇 |
2011年 | 223篇 |
2010年 | 124篇 |
2009年 | 102篇 |
2008年 | 189篇 |
2007年 | 193篇 |
2006年 | 214篇 |
2005年 | 200篇 |
2004年 | 178篇 |
2003年 | 191篇 |
2002年 | 193篇 |
2001年 | 43篇 |
2000年 | 51篇 |
1999年 | 54篇 |
1998年 | 40篇 |
1997年 | 37篇 |
1996年 | 51篇 |
1995年 | 50篇 |
1994年 | 43篇 |
1993年 | 28篇 |
1992年 | 28篇 |
1991年 | 25篇 |
1990年 | 29篇 |
1989年 | 35篇 |
1988年 | 34篇 |
1987年 | 26篇 |
1986年 | 25篇 |
1985年 | 46篇 |
1984年 | 46篇 |
1983年 | 27篇 |
1982年 | 55篇 |
1981年 | 39篇 |
1980年 | 54篇 |
1979年 | 58篇 |
1978年 | 41篇 |
1977年 | 29篇 |
1976年 | 23篇 |
1975年 | 23篇 |
1974年 | 25篇 |
1973年 | 18篇 |
排序方式: 共有3743条查询结果,搜索用时 15 毫秒
71.
The conjugate addition reactions of BHA alkenoates with organolithiums in toluene or toluene-hexane at −78 °C were mediated by the chiral ligands 1 and 2 to give the corresponding 3-substituted alkanoates in high ees and high yields. The two ligands are complementary each other, 1 is effective for phenyl- and vinyllithiums to give the adducts in 64–93% ee, while 2 is effective for butyl- and ethyllithiums to give the adducts in 91–99% ee. 相似文献
72.
Hara K Wang ZS Sato T Furube A Katoh R Sugihara H Dan-Oh Y Kasada C Shinpo A Suga S 《The journal of physical chemistry. B》2005,109(32):15476-15482
We have developed oligothiophene-containing coumarin dyes fully functionalized for dye-sensitized nanocrystalline TiO(2) solar cells (DSSCs). DSSCs based on the dyes gave good performance in terms of incident photon-to-current conversion efficiency (IPCE) in the range of 400-800 nm. A solar energy-to-electricity conversion efficiency (eta) of 7.4% was obtained with a DSSC based on 2-cyano-3-[5'-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)-[2,2']bithiophenyl-5-yl]acrylic acid (NKX-2677) under simulated AM 1.5G irradiation (100 mW cm(-2)) with a mask: short-circuit current density (J(sc)) = 13.5 mA cm(-2); open-circuit voltage (V(oc)) = 0.71 V; fill factor (FF) = 0.77. Transient absorption spectroscopy measurements indicated that electron injection from NKX-2677 to the conduction band of TiO(2) is very rapid (<100 fs), which is much faster than the emission lifetime of the dye (1.0 ns), giving a highly efficient electron injection yield of near unity. 相似文献
73.
Akira Akimoto Toshir
Yoshida 《Journal of polymer science. Part A, Polymer chemistry》1972,10(4):993-1000
Polymerization of vinyl chloride by the ternary catalyst system of VOCl3–AIRnCl3–n complexing agent was investigated. It was suggested that the formation of a polar complex (or charge-transfer complex) between AlRnCl3–n and the complexing agent participated in the polymerization of vinyl chloride. In the copolymerization of vinyl chloride with propylene with the present catalyst system, it was more difficult to incorporate the propylene unit in the copolymer than with a typical radical catalyst. 相似文献
74.
Twenty one methyl 5-phenoxy-2-furancarboxylates prepared from the reaction of methyl 5-nitro-2-furan-carboxylate with phenoxides via displacement of the nitro group. In the reaction of potassium 2-nitrophen-oxide with methyl 5-nitro-2-furancarboxylate at 110°-120°, 2,2′-dinitrodiphenyl ether was obtained as a main product. 相似文献
75.
The determination of nanometer thick layers of poly(methyl methacrylate) coated on to the surface of poly(ethylene terephthalate) film has been investigated by high resolution pyrolysis gas chromatography without sample pretreatment or modification of the instrumentation used. A good linear relationship was observed between the quantity of the characteristic pyrolysate and the thickness of the poly(methyl methacrylate) layer; the detection limit was sufficient to enable the quantitation of poly(methyl methacrylate)-to-poly(ethylene terephthalate) film thickness ratios of 1:20000 in composite materials. 相似文献
76.
Masahiko Miyauchi Yoshinori Kawaguchi Akira Harada 《Journal of inclusion phenomena and macrocyclic chemistry》2004,50(1-2):57-62
-Cyclodextrin having cinnamamide at 6- or 3-positions (6-CiNH--CD, 3-CiNH--CD) and -cyclodextrin with cinnamamide on 6-position (6-CiNH--CD) have been prepared. Supramolecular structures were formed in the solid state or aqueous solutions and characterized by measurements of NMR and vapor pressure osmometry (VPO). The results indicate that 6-CiNH--CD formed insoluble supramolecular polymers in the solid state, while 6-CiNH--CD and 3-CiNH--CD formed supramolecular complexes in aqueous solutions. 6-CiNH--CD was found to form a dimer in an aqueous solution. 3-CiNH--CD formed intermolecular complexes to give supramolecular polymers. The differences of the position of guest part on cyclodextrins caused to give a variety of supramolecular structures in aqueous solutions. 相似文献
77.
Ito F Ikoma T Akiyama K Watanabe A Tero-Kubota S 《The journal of physical chemistry. B》2005,109(18):8707-8717
We have studied the magnetic field effects (MFEs) on the charge-transfer fluorescence and transient photocurrent of a 1,2,4,5-tetracyanobenzene-doped poly(N-vinylcarbazole) film, which reflect the recombination and escape yields of the carriers, respectively. The recombination yield dependence of the external magnetic field (B) clearly shows two types of the MFEs, growth with increasing B due to the hyperfine mechanism (HFM) and a negative dip due to the level-crossing mechanism (LCM). On the other hand, the escape yield indicates complementary MFEs with a sharp decrease in yield with increasing B and then a positive dip. Simultaneous observation of the HFM- and LCM-MFEs proves the stepwise hole-hopping mechanism rather the long-range hole-jumping one. The quantitative analysis of the recombination and escape MFEs is performed using the stochastic Liouville equations (SLE) for a one-dimensional lattice model in which the stepwise hole hops take place between the nearest neighbor carbazole units with spin conservation. The SLE analysis provides the recombination and hole transfer rate constants of 7.0 x 10(7) and 4.5 x 10(8) s(-1), respectively. The boundary site number for the ion pairs in the one-dimensional model is estimated by the best fit to the experimental results. The interionic distance of the boundary ion pair in the one-dimensional model including eight sites agrees with the thermalization distance in the Onsager model. Hence, it is concluded that the elementary processes in the Onsager model applied to molecular amorphous solids are the stepwise hole hops rather than a long-range hole jump. 相似文献
78.
Ken-ichi Sato Shoji Akai Akira Yoshitomo Yoshimitsu Takai 《Tetrahedron letters》2004,45(44):8199-8201
The merits of an indirect protecting method for hydroxyl groups using allyl groups via allyloxycarbonyl groups in the synthesis of antennary β-d-mannopyranosyl disaccharides from β-d-galactopyranosyl disaccharides were studied. Regioselective allyloxycarbonylation and conversion reactions involving simultaneous double SN2 nucleophilic substitution at C-2′ and C-4′ of benzyl O-[β-d-galactopyranosyl]-(1-4)-3,6-di-O-benzyl-2-deoxy-2-N-phthalimido-β-d-glucopyranoside were examined for comparison with the direct allylation method. The required β-d-mannopyranosyl disaccharide having proper protecting groups was obtained using this indirect method in 52% yield. In contrast, the reported direct allylation method using methyl O-(β-d-galactopyranosyl) disaccharide gave the corresponding β-d-mannopyranosyl disaccharide in only 7.5% yield. 相似文献
79.
Norio Tsubokawa Akira Kogure 《Journal of polymer science. Part A, Polymer chemistry》1991,29(5):697-702
The surface grafting onto inorganic ultrafine particles, such as silica, titanium oxide, and ferrite, by the reaction of acid anhydride groups on the surfaces with functional polymers having hydroxyl and amino groups was examined. The introduction of acid anhydride groups onto inorganic ultrafine particle was achieved by the reaction of hydroxyl groups on these surfaces with 4-trimethoxysilyltetrahydrophthalic anhydride in toluene. The amount of acid anhydride groups introduced onto the surface of ultrafine silica, titanium oxide, and ferrite was determined to be 0.96, 0.47, and 0.31 mmol/g, respectively, by elemental analysis. Functional polymers having terminal hydroxyl or amino groups, such as diol-type poly(propylene glycol) (PPG), and diamine-type polydimethylsiloxane (SDA), reacted with acid anhydride groups on these ultrafine particles to give polymer-grafted ultrafine particles: PPG and SDA were considered to be grafted onto these surfaces with ester and amide bond, respectively. The percentage of grafting increased with increasing acid anhydride group content of the surface: the percentage of grafting of SDA (Mn = 3.9 × 103) onto silica, titanium oxide, and ferrite reaching 64.7, 33.7, and 24.1%, respectively. These polymer-grafted ultrafine particles gave a stable colloidal dispersion in organic solvents. 相似文献
80.
Akira Masuoka 《Proceedings of the American Mathematical Society》1996,124(3):735-737
We give an algebraic version of a result of G. I. Kac, showing that a semisimple Hopf algebra of dimension , where is a prime and , over an algebraically closed field of characteristic 0 contains a non-trivial central group-like. As an application we prove that, if , is isomorphic to a group algebra.