全文获取类型
收费全文 | 1584篇 |
免费 | 65篇 |
国内免费 | 7篇 |
专业分类
化学 | 1311篇 |
晶体学 | 9篇 |
力学 | 14篇 |
数学 | 73篇 |
物理学 | 249篇 |
出版年
2023年 | 15篇 |
2022年 | 12篇 |
2021年 | 19篇 |
2020年 | 25篇 |
2019年 | 26篇 |
2018年 | 26篇 |
2017年 | 16篇 |
2016年 | 42篇 |
2015年 | 33篇 |
2014年 | 48篇 |
2013年 | 84篇 |
2012年 | 142篇 |
2011年 | 111篇 |
2010年 | 61篇 |
2009年 | 71篇 |
2008年 | 113篇 |
2007年 | 122篇 |
2006年 | 125篇 |
2005年 | 95篇 |
2004年 | 77篇 |
2003年 | 59篇 |
2002年 | 42篇 |
2001年 | 26篇 |
2000年 | 23篇 |
1999年 | 12篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1988年 | 12篇 |
1986年 | 6篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1971年 | 6篇 |
1969年 | 4篇 |
排序方式: 共有1656条查询结果,搜索用时 109 毫秒
91.
Hisashi Odani Masaki Uchikura Yukimasa Ogino Michio Kurata 《Journal of membrane science》1983,14(2):193-208
Diffusion and solution behavior of methanol vapor in two diblock copolymers, poly(2-vinylpyridine)—block—polyisoprene [P(2VPbI)] and poly(2-vinylpyridine)—block—polystyrene [P(2VPbS)], was studied by the weighing method at 25°C. The domain structure of films of both copolymers showed an alternating lamellar arrangement. Methanol is a good solvent for P2VP, but a nonsolvent for PI and PS. Methanol dissolved exclusively in the P2VP phase of the copolymers. For both copolymer systems, absorption and desorption processes of non-Fickian type were observed as characterized by a thickness anomaly. However, the magnitude of the deviations from purely Fickian behavior was small, and the integral diffusion coefficient, D?, was obtainable with reasonable accuracy. At low and medium concentrations, D? for P(2VPbI) was greater, by about one order of magnitude, than that for P2VP, while D? for P(2VPbS) was lower than that for P2VP. A similar trend was observed in plots of the permeability coefficient against the vapor pressure of methanol. The results indicate that the rubbery PI phase may facilitate the transport of penetrant molecules in the P(2VPbI) film. On the other hand, the glassy PS phase in the P(2VPbS) film merely interferes with the transport of methanol molecules. 相似文献
92.
93.
Tamejiro Hiyama Hiroyuki Saimoto Koji Nishio Masaki Shinoda Hajime Yamamoto Hitosi Nozaki 《Tetrahedron letters》1979,20(22):2043-2046
A new method is reported for constructing α-methylene-γ-butyrolactone moiety under neutral, anhydrous conditions. Olefin-dibromocarbene adducts are transformed to methyl 1-(N,N-dimethylaminomethyl)cyclopropanecarboxylates which in turn are treated with trimethylsilyl iodide and the crude products distilled to give the title compounds with high regio- and stereoselectivity. 相似文献
94.
95.
96.
Bunichiro Yamada Masaki Itahashi Takayuki Otsu 《Journal of polymer science. Part A, Polymer chemistry》1978,16(7):1719-1733
To obtain the optimum values of the monomer reactivity ratios for the copolymerization systems with largely different reactivities between both monomers, a nonlinear least-squares procedure which took into account the weights of experimental data, was proposed and discussed. The weights of the data were treated for the errors arisen from the amounts of monomers charged, the densities of monomers, the weights of copolymer formed, and the composition of copolymer. The least-squares procedure with the consideration of the weights was applicable to both differentiated equation and integrated equation derived by Lewis and Mayo. This procedure was applied to radical copolymerizations of α-substituted crotonic esters with styrene, and reasonable monomer reactivity ratios were obtained. It was noted that errors from the copolymer composition were more important than those from the other factors and that the use of the integrated equation was recommended even when the copolymers were isolated at low conversions. 相似文献
97.
Aizawa M Morikawa Y Namai Y Morikawa H Iwasawa Y 《The journal of physical chemistry. B》2005,109(40):18831-18838
The catalytic dehydration reaction processes of formic acid on a TiO2(110) surface at 350 K have been studied to visualize reaction intermediates and their dynamic behaviors by scanning tunneling microscopy. Three types of configurations of adsorbed formates on the surface were identified by their shapes and positions in STM images. Successive STM observations revealed transformations among the three configurations, i.e., bridge formate on a 5-fold coordinated Ti4+ row, bridge formate on an oxygen vacancy site with an oxygen atom of formate and on a 5-fold coordinated Ti4+ ion and with the other formate oxygen atom, and a monodentate formate on an oxygen vacancy site with an oxygen atom of formate. The decomposition of the monodentate formate to carbon monoxide and hydroxyl was also imaged, which is a rate-determining step in the catalytic dehydration of formic acid. Combined with first-principle DFT calculations, the overall reaction processes of the catalytic dehydration of formic acid on the surface have been elucidated. Oxygen vacancies on the surface that can be produced by dehydration of two hydroxyls in situ under the catalytic reaction conditions are essential for the reaction. 相似文献
98.
Ikuma N Tsue H Tsue N Shimono S Uchida Y Masaki K Matsuoka N Tamura R 《Organic letters》2005,7(9):1797-1800
[reaction: see text] Enantiomerically enriched samples of chiral cyclic nitroxides with a 4-hydroxyphenyl group on the stereogenic center bearing the NO radical group undergo unprecedented spontaneous racemization and/or epimerization in aprotic solvents, which can be well accounted for by the multistep equilibrations involving planar quinoid intermediates. 相似文献
99.
A systematic perturbation theory is developed for the ESR shift and is applied to the spin-1/2 Heisenberg antiferromagnetic chain with a general anisotropic exchange interaction. Using the Bethe ansatz technique, the resonance shift is obtained exactly for the whole range of temperature and magnetic field in the first order of the anisotropy. The obtained g shift strongly depends on magnetic fields at low temperature, showing a significant deviation from the previous classical result. 相似文献
100.
Norihiro?SadatoEmail author Hiroki?Yamada Tomohisa?Okada Masaki?Yoshida Takehiro?Hasegawa Ken-Ichi?Matsuki Yoshiharu?Yonekura Harumi?Itoh 《BMC neuroscience》2004,5(1):56