全文获取类型
收费全文 | 865篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
化学 | 564篇 |
晶体学 | 3篇 |
力学 | 13篇 |
数学 | 74篇 |
物理学 | 241篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 19篇 |
2019年 | 10篇 |
2018年 | 11篇 |
2017年 | 13篇 |
2016年 | 22篇 |
2015年 | 10篇 |
2014年 | 19篇 |
2013年 | 44篇 |
2012年 | 38篇 |
2011年 | 35篇 |
2010年 | 31篇 |
2009年 | 25篇 |
2008年 | 51篇 |
2007年 | 55篇 |
2006年 | 46篇 |
2005年 | 35篇 |
2004年 | 55篇 |
2003年 | 22篇 |
2002年 | 27篇 |
2001年 | 35篇 |
2000年 | 30篇 |
1999年 | 22篇 |
1998年 | 13篇 |
1997年 | 13篇 |
1996年 | 17篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 4篇 |
排序方式: 共有895条查询结果,搜索用时 343 毫秒
101.
Iron-catalyzed sulfonyl radical formations from sulfonylhydrazides and oxidative addition to alkenes
Generation of sulfonyl radicals from sulfonylhydrazides has been achieved in the presence of a non-toxic iron catalyst and oxygen. The intermolecular addition of resultant sulfonyl radicals to alkenes affords β-hydroxysulfone compounds. 相似文献
102.
The room-temperature chemical transformation of spherical CdTe nanoparticles into anisotropic alloyed CdHgTe particles using mercury bromide in a toluene/methanol system at room temperature has been investigated. The resulting materials readily dissolved in toluene and exhibited a significant red-shift in the optical properties toward the infrared region. Structural transformations were observed, with electron microscopy showing that the CdTe nanoparticles were chemically attached ('welded') to other CdTe nanoparticles, creating highly complex anisotropic heterostructures which also incorporated mercury. 相似文献
103.
Yamaoka Y Taniguchi Y Yasuzuka S Yamamura Y Saito K 《The Journal of chemical physics》2011,135(4):044705
Quasi-binary (QB) picture of thermotropics, which regards a neat thermotropic liquid crystal as a binary system consisting of (semi)rigid core and molten alkyl chain, was assessed experimentally for the most famous (and representative) thermotropic mesogenic series nCB. By adding n-heptane as solvent, the smectic A phase was induced in 7CB-n-heptane system. Small angle x-ray diffraction showed that the QB picture holds not only in the phase behavior but also in the structure. It is suggested that the melting of 8CB and 9CB to isotropic liquid via smectic and nematic liquid crystals can be understood as a thermotropic-lyotropic crossover. 相似文献
104.
Imoto M Matsui Y Takeda M Tamaki A Taniguchi H Mizuno K Ikeda H 《The Journal of organic chemistry》2011,76(15):6356-6361
Observations show that nitroanilines exhibit an unusually high S(N)Ar reactivity with OH(-) in aqueous media in reactions that produce nitrophenols. S(N)Ar reaction of 4-nitroaniline (2a) in aqueous NaOH for 16 h yields 4-nitrophenol (4a) quantitatively, whereas a similar reaction of 4-nitrochlorobenzene (1a) gave 4a in 2% yield together with recovered 1a in 97%, suggesting that the leaving ability of the NH(2) group far surpasses that of Cl under these conditions. An essential feature of S(N)Ar reactions of nitroanilines is probably that the NH(2) leaving group participates in a hydrogen-bonding interaction with H(2)O. Density functional theory (DFT) calculations for a set of 4-nitroaniline, OH(-), and H(2)O suggest a possible formation of a Meisenheimer complex stabilized by hydrogen-bonding interactions and a six-membered ring structure. The results obtained here contrast with conventional S(N)Ar reactivity profiles in which nitroanilines are nearly unreactive with nucleophiles in organic solvents. 相似文献
105.
106.
Kenichi Hashizume Hiroyasu Ogiwara Hiroshi Taniguchi 《International Journal of Multiphase Flow》1985,11(5):643-658
Two-phase flow in horizontal pipe was analyzed with simplified models for annular and stratified flow. The velocity profiles for the liquid and gas phase were described with the Prandtl mixing length. From this analysis, the frictional pressure drop was calculated with the modified Baker map for flow pattern transition. The intermediate region, i.e. wavy flow, was interpolated between annular and stratified flow. Comparison of this analysis with existing experimental data of refrigerants showed good agreement. 相似文献
107.
Shigetoshi Tsubotani Yoshikazu Wada Kazuhide Kamiya Hisayoshi Okazaki Setsuo Harada 《Tetrahedron letters》1984,25(4):419-422
The structure of a new antibiotic thiotropocin is described. 相似文献
108.
Let {Xt} be a Gaussian ARMA process with spectral density fθ(λ), where θ is an unknown parameter. The problem considered is that of testing a simple hypothesis H:θ = θ0 against the alternative A:θ ≠ θ0. For this problem we propose a class of tests
, which contains the likelihood ratio (LR), Wald (W), modified Wald (MW) and Rao (R) tests as special cases. Then we derive the χ2 type asymptotic expansion of the distribution of T
up to order n−1, where n is the sample size. Also we derive the χ2 type asymptotic expansion of the distribution of T under the sequence of alternatives An: θ = θ0 + /√n, ε > 0. Then we compare the local powers of the LR, W, MW, and R tests on the basis of their asymptotic expansions. 相似文献
109.
Preliminary communicationPalladium-catalyzed carboxylation of aromatic compounds with carbon dioxide
Hiroshi Sugimoto Itaru Kawata Hiroshi Taniguchi Yuzo Fujiwara 《Journal of organometallic chemistry》1984,266(3):c44-c46
Carbon dioxide has been found to react with aromatic compounds such as benzene, anisole, furane, and thiophene to give aromatic acids in modest yields with palladium(II) salts as catalysts. The addition of t-BuOOH increases the yield. 相似文献
110.
The effect of pressure on the conformational equilibria between rotational isomers in solution has been studied by the infrared and Raman spectroscopy. The experimental volume changes for the transformation are explained theoretically by the three effects contributing to these volume changes, namely the overlap of the atoms with the internal rotation angle, the change of local packing of the solute and solvent, and the change of the electrostatic interaction with the solvent. The purpose of this paper is to review what is known about the volume changes for small molecules with internal rotation angles. 相似文献