全文获取类型
收费全文 | 1407篇 |
免费 | 30篇 |
国内免费 | 3篇 |
专业分类
化学 | 1202篇 |
晶体学 | 16篇 |
力学 | 14篇 |
数学 | 15篇 |
物理学 | 193篇 |
出版年
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 18篇 |
2015年 | 25篇 |
2014年 | 27篇 |
2013年 | 77篇 |
2012年 | 59篇 |
2011年 | 68篇 |
2010年 | 50篇 |
2009年 | 31篇 |
2008年 | 64篇 |
2007年 | 76篇 |
2006年 | 90篇 |
2005年 | 102篇 |
2004年 | 79篇 |
2003年 | 75篇 |
2002年 | 69篇 |
2001年 | 19篇 |
2000年 | 25篇 |
1999年 | 19篇 |
1998年 | 13篇 |
1997年 | 20篇 |
1996年 | 25篇 |
1995年 | 8篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 17篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 25篇 |
1983年 | 11篇 |
1982年 | 24篇 |
1981年 | 27篇 |
1980年 | 34篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1976年 | 12篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1969年 | 8篇 |
1968年 | 12篇 |
1967年 | 11篇 |
排序方式: 共有1440条查询结果,搜索用时 125 毫秒
31.
The vertical ionization potentials of difluoramine are calculated by perturbation corrections to Koopmans' theorem. The calculation shows that difluoraimine has three overlapping bands between 15 and 16 eV. The calculated results compare well with the experimental values. The photoelectron spectrum of difluoramine is compared with that of OF2 and CH2F2. 相似文献
32.
Tsutomu Kagiya Masatsugu Izu Masakazu Hatta Takehisa Matsuda Kenichi Fukui 《Journal of polymer science. Part A, Polymer chemistry》1967,5(5):1129-1135
N,N′-Dipropionylethylenediamine was synthesized by the ring-opening addition reaction of 2-ethyl-2-imidazoline with propionic acid at 220°C. By applying this reaction to polymerization, polyamides were synthesized by the ring-opening polyaddition reaction at 220°C. of 1,4-bis(imidazoline-2-yl)butane with adipic acid, succinic acid, sebacic acid, and terephthalic acid. The reaction product of 1,4-bis(imidazoline-2-yl)butane with adipic acid, which was proposed to be nylon 26, was compared with an authentic sample of nylon 26 and shown to possess a very similar infrared spectrum and melting point. 相似文献
33.
Masatomo Iwao Toshiro TakeuchiNaotaka Fujikawa Tsutomu FukudaFumito Ishibashi 《Tetrahedron letters》2003,44(24):4443-4446
A highly efficient route to 3,4-diarylpyrrole marine alkaloids has been developed using Hinsberg-type pyrrole synthesis and palladium-catalyzed Suzuki cross-coupling of the 3,4-dihydroxypyrrole bis-triflate derivatives as key reactions. Based on this approach, formal syntheses of permethyl storniamide A and ningalin B, and a total synthesis of lamellarin G trimethyl ether have been achieved. 相似文献
34.
Hirakawa Y Suzuto M Ohnishi H Shingaki T Eyring EM Tokunaga M Masujima T 《The Analyst》2003,128(6):676-680
The nano-kinetic movement of a single DNA molecule was observed and analyzed by a newly developed video-microscope system with an optical fiber, called a pin-fiber video scope. A single lambda-DNA molecule was put in focus using fiber-illumination, and the stretching and shrinking motion was measured. The molecule's kinetics were analyzed by numerical calculations and are discussed. A photocleavage phenomenon of DNA molecules was also visualized by the pin-fiber video scope. The new video-microscope system has the potential to observe and analyze the nano-kinetics of a single molecule. 相似文献
35.
Kimura T Yoshino M Yamane T Yamato M Tobita M 《Langmuir : the ACS journal of surfaces and colloids》2004,20(14):5669-5672
A diamagnetic particle with magnetic susceptibilities chi3 < chi2 = chi1 < 0 was subjected to a rotating magnetic field to obtain an alignment of the chi3 axis (the smallest susceptibility axis) in the direction perpendicular to the plane of the rotating magnetic field. A polymer short fiber, whose fiber axis coincides with the chi3 axis, was suspended in a fluid with the same density, and then a rotating magnetic field generated by a rotation of a pair of permanent magnets was applied. The fiber axis, rotating following the applied field, finally ended up with an alignment perpendicular to the plane of the rotating magnetic field. The experimental data on the time course of the alignment was in good agreement with the numerical calculation based on the equation of rotation. 相似文献
36.
Shinichi Yamabe Tsutomu Minato Yoshihiro Osamura 《International journal of quantum chemistry》1980,18(1):243-250
A general way for drawing the state correlation diagram and seeking the reaction path is presented. If a high-symmetry reacting system is given, its least-motion path that maintains the symmetry is primarily examined. For a given state, it is judged whether the least-motion path is symmetry allowed or forbidden. If allowed, it is called the direct process. If forbidden, the symmetry imposed on the system should be relaxed, resulting in the mixing of MO 's. Then, the energy barrier of the avoided crossing for some excited states is removed and the possible reaction path is found. After this procedure, the symmetry-allowed paths may be sought by the geometry optimization with a suitable wave function. By the use of such a procedure, the dissociation of diazomethane and (3H-)diazirine is found to proceed via the Cs and C2 symmetries. 相似文献
37.
The effects of cation symmetry and packing on the mixed-valence state of binuclear ferrocene derivatives are discussed separately by using chiral isomers and racemic modification of 1',1' "-bis(2-phenylbutyl)-1,1' '-biferrocenium pentaiodide. The pentaiodide anion has a polymeric structure and is composed of triiodide anion and iodine molecule units. The (R,S) isomer having an inversion center shows a detrapped-valence state even at 78 K. On the other hand, the (R,R) and the (S,S) isomers having no inversion center show a trapped-valence state at room temperature. The racemic modification, however, consisting of the (R,R) and the (S,S) isomers shows a perfect detrapped-valence state at room temperature. This finding shows that the packing effect overcomes the effect of cation asymmetry. 相似文献
38.
Tsutomu Yokozawa Jun Takagi Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》1989,27(1):291-299
Spontaneous copolymerization of cyclic ketene acetal, 2-methylene-4-phenyl-1,3-dioxolane ( I ) with common electrophilic vinyl monomers, such as methyl α-cyanoacrylate (MCA), acrylonitrile (AN), and methyl methacrylate (MMA) were investigated to further explore zwitterion polymerization method with cyclic ketene acetals. In the reaction of I with MCA and AN, spontaneous copolymerization took place at ambient temperature. The copolymers of I with MCA gave low molecular weight polymers, but copolymers obtained with I and AN were high molecular weight polymers. In the reaction of I and MMA, high molecular weight copolymer was obtained only at temperatures above 80°C. Thus, obtained polymers were not the alternating copolymers and possessed high I content in all the cases. From the above results, macrozwitterionic mechanism was suggested as discussed. 相似文献
39.
Hisao Yokota Masatsune Kondo Tsutomu Kagiya Kenichi Fukui 《Journal of polymer science. Part A, Polymer chemistry》1968,6(2):435-446
The kinetic behavior on the polymerization of formaldehyde with and without acidic catalyst, in liquid carbon dioxide, in the temperature range of 30 to 50°C. was investigated. In the polymerization without catalyst both the polymer yield and the degree of polymerization increased with reaction time and also with rising temperature. With acidic catalyst, such as acetic acid and dichloroacetic acid, both the polymer yield and the degree of polymerization increased more than that in the polymerization without catalyst. The overall rate of polymerization with and without acidic catalyst was expressed by the first-order rate equation with respect to monomer concentration. From the results it was concluded that the polymerizations belonged to a type of successive polymerization with rapid initiation and no termination. The rate constant and the activation energy of each elementary process of polymerization were estimated on the basis of the results. 相似文献
40.
When glassy carbon fibres are used, alkali and alkaline earth metal ions are adsorbed in the micropores which are created or activated by oxidative treatment of the fibres. The average pore radius was estimated to be 2 nm by nitrogen adsorption experiments. Uptake was studied with a flow system consisting of a flow-through carbon-fibre electrode; a dropping mercury electrode at the end of the flow line monitored changes in the metal ion concentrations. The ions were taken up at negative potentials and released at positive potentials. The amount taken up increased in the sequence Na+ < Li+ < H+, suggesting that the ions were desolvated before entering the pore system. 相似文献