全文获取类型
收费全文 | 4499篇 |
免费 | 77篇 |
国内免费 | 22篇 |
专业分类
化学 | 3022篇 |
晶体学 | 67篇 |
力学 | 76篇 |
数学 | 281篇 |
物理学 | 1152篇 |
出版年
2022年 | 31篇 |
2021年 | 31篇 |
2020年 | 45篇 |
2019年 | 58篇 |
2018年 | 36篇 |
2017年 | 34篇 |
2016年 | 58篇 |
2015年 | 79篇 |
2014年 | 73篇 |
2013年 | 250篇 |
2012年 | 206篇 |
2011年 | 228篇 |
2010年 | 131篇 |
2009年 | 150篇 |
2008年 | 230篇 |
2007年 | 255篇 |
2006年 | 254篇 |
2005年 | 202篇 |
2004年 | 161篇 |
2003年 | 152篇 |
2002年 | 163篇 |
2001年 | 103篇 |
2000年 | 122篇 |
1999年 | 77篇 |
1998年 | 47篇 |
1997年 | 51篇 |
1996年 | 72篇 |
1995年 | 55篇 |
1994年 | 36篇 |
1993年 | 50篇 |
1992年 | 71篇 |
1991年 | 51篇 |
1990年 | 47篇 |
1989年 | 45篇 |
1988年 | 68篇 |
1987年 | 52篇 |
1986年 | 56篇 |
1985年 | 73篇 |
1984年 | 77篇 |
1983年 | 32篇 |
1982年 | 54篇 |
1981年 | 52篇 |
1980年 | 55篇 |
1979年 | 47篇 |
1978年 | 45篇 |
1977年 | 54篇 |
1976年 | 39篇 |
1975年 | 44篇 |
1974年 | 49篇 |
1973年 | 39篇 |
排序方式: 共有4598条查询结果,搜索用时 15 毫秒
931.
Yoshihiro Tsuda Kohshin Takahashi Takahiro Yamaguchi Syuichi Matsui Teruhisa Komura 《Journal of molecular catalysis. A, Chemical》1998,130(3):244-295
When a viologen-linked Mn(III)porphyrin complex with a short methylene-chain, in which a viologen is covalently linked by the methylene-chain into one phenyl group of 5,10,15,20-tetraphenylporphyrinatomanganese(III)chloride (Mn(III)(tpp)Cl), was used as a catalyst for a monooxygenation of cyclohexene in an air-equilibrated acetonitrile solution containing insoluble zinc powder as a reductant, more cyclohexene oxide was obtained as a single product than when Mn(tpp)Cl was used as a catalyst. Benzoic acid as a cleaving reagent of the dioxygen double-bond and 1-methylimidazole as a ligand to Mn porphyrin were further contained in the reaction mixture. This result implies that the viologen moiety in the viologen-linked Mn(III)porphyrin acted effectively as a mediator for electron transfer from zinc powder to the Mn(III)porphyrin moiety in the epoxidation cycle activating molecular dioxygen reductively. Though Mn(tpp)Cl was remarkably demetallated by H+ ion from benzoic acid during the epoxidation reaction in the mixed system of Mn(III)(tpp)Cl and viologen, the demetallation of the viologen-linked Mn porphyrin with the short methylene-chain was partly prevented because the reduction of a Mn(II)porphyrin-dioxygen adduct was easily caused by fast intramolecular electron-transfer between the two moieties of the viologen and the Mn porphyrin, proceeding the epoxidation cycle smoothly. 相似文献
932.
Ultrafine particles (UFP) of six kinds of FeNi alloys were synthesized by the method of hydrogen plasma reaction. The prepared UFP samples were examined by X-ray diffraction, electron transmission microscopy and magnetic measurement. The spherical FeNi UFP alloys with a mean particle size less than 35 nm can be prepared with a production rate much higher than by conventional methods. The phase constitution of UFP alloys is different from the equilibrium phase diagram owing to rapid condensation of evaporated metal gases. Although the magnetization for the UFP alloys has almost the same temperature dependence as that of the bulk alloys, the saturation magnetization remarkably decreases as the bulk alloys change into the UFP alloys. 相似文献
933.
T Kojima K Niigata T Fujikura S Tachikawa Y Nozaki S Kagami K Takahashi 《Chemical & pharmaceutical bulletin》1985,33(9):3766-3774
934.
935.
Keiko Takahashi Kenjiro Hattori 《Journal of inclusion phenomena and macrocyclic chemistry》1994,17(1):1-24
Cyclodextrins have great potential for exploitation as a useful tool for asymmetric induction. Many kinds of asymmetric reaction have been achieved in the presence of cyclodextrin under various conditions such as the solid phase, heterogeneous suspension or homogeneous aqueous or organic solution. Complexation is essential for asymmetric induction. What is necessary to improve CDs for greater asymmetric induction? 相似文献
936.
A joint-transform phase correlation is made by an extracted phase from the joint power spectrum using a phase-shifting Mach-Zehnder
interferometer with a wavelength-shifted laser diode (LD), and then by numerically Fourier-transforming a measured phase.
The algorithm in six steps is insensitive to the power changes in an LD. The phase correlator gives the best discrimination
performance. Discriminative multiple-object recognition is performed with no intermodulation noise and artifact noise-free
correlation by arranging the multiple objects in a regularly equal-spaced array. The experimental and numerical results are
shown. 相似文献
937.
938.
939.
Time-dependent density functional theory calculations have been performed for the excited states of psoralen, 5-methoxypsoralen, and 8-methoxypsoralen in systems and furan and pyrone monoadducts bonded to a thymine residue. The theoretical assignments to ultraviolet (UV) absorption spectra of isolated systems have been performed. The present calculations have clarified that the excitation energies of the first singlet excited (S1) state of monoadducts are blue-shifted compared with the isolated systems. It is shown that, in particular, the S1 excitation energy of the pyrone monoadduct is significantly blue-shifted and, therefore, the pyrone monoadduct is not excited by UV-A light (300-400 nm), which is used in the photochemotherapy. 相似文献
940.