全文获取类型
收费全文 | 3530篇 |
免费 | 135篇 |
国内免费 | 14篇 |
专业分类
化学 | 3013篇 |
晶体学 | 24篇 |
力学 | 23篇 |
数学 | 195篇 |
物理学 | 424篇 |
出版年
2023年 | 15篇 |
2022年 | 23篇 |
2021年 | 36篇 |
2020年 | 37篇 |
2019年 | 47篇 |
2018年 | 30篇 |
2017年 | 38篇 |
2016年 | 68篇 |
2015年 | 71篇 |
2014年 | 82篇 |
2013年 | 186篇 |
2012年 | 189篇 |
2011年 | 231篇 |
2010年 | 129篇 |
2009年 | 142篇 |
2008年 | 239篇 |
2007年 | 250篇 |
2006年 | 212篇 |
2005年 | 213篇 |
2004年 | 159篇 |
2003年 | 155篇 |
2002年 | 119篇 |
2001年 | 60篇 |
2000年 | 81篇 |
1999年 | 53篇 |
1998年 | 53篇 |
1997年 | 61篇 |
1996年 | 52篇 |
1995年 | 34篇 |
1994年 | 31篇 |
1993年 | 43篇 |
1992年 | 25篇 |
1991年 | 24篇 |
1990年 | 27篇 |
1989年 | 24篇 |
1988年 | 25篇 |
1987年 | 24篇 |
1986年 | 12篇 |
1985年 | 49篇 |
1984年 | 40篇 |
1983年 | 14篇 |
1982年 | 25篇 |
1981年 | 33篇 |
1980年 | 31篇 |
1979年 | 41篇 |
1978年 | 26篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 19篇 |
1974年 | 25篇 |
排序方式: 共有3679条查询结果,搜索用时 15 毫秒
971.
Tadashi Nakata Takaaki Kuwabara Yōichirō Tani Takeshi Oishi 《Tetrahedron letters》1982,23(9):1015-1016
()-Oudemansin has been synthesized starting from -cinnamaldehyde by a route involving the stereoselective Zn(BH4)2 reduction of β-keto ester. 相似文献
972.
Both the enantiomers of sclerosporin and sclerosporal were synthesized from (-)-carvone. (4R,9R,10S)-(+)-Sclerosporin and (4R,9R,10S)-(-)-sclerosporal were identified as the natural enantiomers by a comparison of their CD-spectra. An intramolecular Diels-Alder route was proved to be an efficient method of preparing sufficient amounts of (+)- for the biological study. 相似文献
973.
Terutaka Watanabe Takeshi Wada Masaaki Takehisa Sueo Machi 《Journal of polymer science. Part A, Polymer chemistry》1974,12(8):1609-1618
The radiation-induced polymerization of ethylene in cyclohexane was carried out in a reactor of 100 ml capacity under a range of temperature of 25–150°C, dose rate of 4.1 × 104–2.9 × 105 rad/hr, pressure of 200 kg/cm2, and amount of cyclohexane of 20–90 ml. The polymerization was found to proceed at a steady state from the beginning. The polymerization rate is maximum at ca. 50 ml of cyclohexane. The dose rate exponent of the polymerization rate was 0.6 at every temperature from 25 to 150°C. The polymer molecular weight is in the range of 103–104, independent of dose rate, and decreases with increasing amount of cyclohexane. The molecular weight distribution is unimodal and narrow. Kinetic analysis of these results indicates that the polymerization proceeds via a simple scheme of homogeneous polymerization and the polymer molecular weight was determined by the chain transfer reaction which takes place mostly with cyclohexane. The unimodal and narrow molecular weight distribution is also consistent with the homogeneous polymerization scheme. 相似文献
974.
Fumio Hamazu Sumio Akashi Tatsuya Koizumi Toshikazu Takata Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》1993,31(4):1023-1028
Various p-substituted benzyl p-hydroxyphenyl methyl sulfonium salts ( 2 ) were synthesized and their initiator activities were evaluated in bulk polymerization of glycidyl phenyl ether (PGE). The order of the activity was found to be 2b (X = CH3) > 2a (X = H) ≈ 2c (X = Cl) > 2d (X = NO2), indicating that the introduction of an electron-donating group enhanced the activity. In Hammett's plots, the logarithm of the ratio of the polymerization rates (log kx/kH) was correlated with σ+ρ better than with σp and a negative ρ+ value (-1.18) was obtained. Reaction of 2a with benzyl mercaptan mainly gave dibenzyl sulfide and p-hydroxyphenyl methyl sulfide. The obtained results seemed to demonstrate that the OH group of the aryl group yielded no proton as initiator for the polymerization, whereas the benzyl group caused the polymerization, which was initiated by the corresponding benzyl cation formed by C? S bond cleavage. © 1993 John Wiley & Sons, Inc. 相似文献
975.
Mochizuki D Shimojima A Imagawa T Kuroda K 《Journal of the American Chemical Society》2005,127(19):7183-7191
A novel methodology for constructing molecularly ordered silica nanostructures with two-dimensional (2-D) and three-dimensional (3-D) networks has been developed by using a stepwise process involving silylation of a layered silicate octosilicate with alkoxytrichlorosilanes [ROSiCl(3), R = alkyl] and subsequent reaction within the interlayer spaces. Alkoxytrichlorosilanes react almost completely with octosilicate, bridging two closest Si-OH (or -O(-)) sites on the silicate layers, to form new five-membered rings. The unreacted functional groups, Si-Cl and Si-OR, are readily hydrolyzed by the posttreatment with a water/dimethyl sulfoxide (DMSO) or water/acetone mixture, leading to the formation of two types of silicate structures. The treatment with a water/DMSO mixture produced a unique crystalline 2-D silicate framework with geminal silanol groups, whereas a water/acetone mixture induced hydrolysis and subsequent condensation between adjacent layers to form a new 3-D silicate framework. The 2-D structure is retained by the presence of DMSO molecules within the swelled interlayer spaces and is transformed to a 3-D silicate upon desorption of DMSO. The structural modeling suggests that both of the 3-D silicates contain new cagelike frameworks where solvent molecules are trapped even at high temperature (up to 380 degrees C, in the case of acetone). Both 2-D and 3-D silica structures are quite different from known layered silicates and zeolite-like materials, indicating the potential of the present approach for precise design of various silicate structures at the molecular level. 相似文献
976.
Ago H Imamura S Okazaki T Saito T Yumura M Tsuji M 《The journal of physical chemistry. B》2005,109(20):10035-10041
Single-walled carbon nanotubes (SWNTs) with a narrow diameter distribution are synthesized by thermal chemical vapor deposition (CVD) of methane over Fe/MgO catalyst on the basis of parametric study considering Fe loading, reaction temperature and time, methane concentration, and structure of a support material. We found that the porous MgO support gives the SWNTs with a narrow diameter distribution with the mean diameter and standard deviation of 0.93 and 0.06 nm, respectively, only when the Fe loading and reaction temperature are relatively low. The higher Fe loading and/or the higher reaction temperature enlarged the nanotube diameter, forming double-walled carbon nanotubes (DWNTs) in addition to SWNTs. This result indicates that only the diameter of Fe nanoparticles determines the growth of either SWNTs or DWNTs on the MgO support. The fluorescence and absorption spectra of the nanotube dispersion in D(2)O solution with sodium dodecyl sulfate (SDS) were studied to identify their chirality distribution. The fluorescence of the uniform-diameter SWNTs indicates the formation of the near armchair structures. On the other hand, the SWNTs synthesized over the catalyst with a high Fe loading, 3 wt %, showed a wide chirality distribution including the near zigzag structure. The synthesis of the SWNTs with a narrow diameter distribution could be applied to the selection of SWNTs with a specific chirality based on postsynthesis separation. 相似文献
977.
Vadim A. Soloshonok Takeshi Yamada Hisanori Ueki Tanner K. Cook Anatolii V. Soloshonok Yasufumi Ohfune 《Tetrahedron》2006,62(26):6412-6419
This paper presents a practical and efficient asymmetric synthesis of enantiomerically pure 4-aminoglutamic acids using a quite unusual methylene dimerization of chiral nucleophilic glycine equivalents with dichloromethane under phase-transfer catalysis (PTC) conditions. From a synthetic standpoint, the reported procedure is highly operationally convenient and scalable as it does not require any chromatographic purification of the intermediate products. 相似文献
978.
Mao-Peng Lin Tomiki Ikeda Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》1992,30(12):2569-2576
Vinylether was used as a cationically polymerizable moiety and incorporated into sidechain of polymers as copolymers of vinyloxyethyl methacrylate (VEM) and styrene (St). Photoirradiation of the copolymers containing a small amount of benzyl(4-hydroxyphenyl) methylsulfonium salt (BSS) resulted in a high crosslinking density as evidenced by a low degree of swelling, which is ascribed to the high reactivity of the vinyloxy moieties. The sensitivity of this photoreaction is significantly high because of a large kinetic chain length of the cationic polymerization of vinylethers, while copolymers of glycidyl methacrylate and St showed crosslinking to much less extent when irradiated under the same condition. The ability of other sulfonium salts, (4-hydroxyphenyl) methyl(4-nitrobenzyl) sulfonium salt and (4-hydroxyphenyl) methyl(1-naphthylmethyl)sulfonium salt, to induce photocrosslinking was also examined. © 1992 John Wiley & Sons, Inc. 相似文献
979.
Morikawa MA Yoshihara M Endo T Kimizuka N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(5):1574-1578
alpha-Helical peptide microcapsules were prepared by the emulsion-templated self-assembly of amphiphilic poly(gamma-benzyl L-glutamate)s (PBLG) 1. By mixing solutions of 1 in dichloromethane (in the form of a sodium salt) with water, oil-in-water emulsions were obtained. Spontaneous stripping of the dichloromethane phase caused a decrease in the diameter of the microdroplets and finally stable microcapsules formed. The microcapsules contain an inner aqueous phase as observed by confocal laser scanning microscopy (CLSM). Binding of hydrophobic pyrene molecules to the polypeptide shell was also demonstrated. The present polypeptide microcapsules are stable even after drying in air and they would serve as supramolecular vehicles for both hydrophobic and water-soluble molecules. 相似文献
980.
Takeshi Furuya Tetsuya Ishikawa Toshitaka Funazukuri Yoshihiro Takebayashi Satoshi Yoda Katsuto Otake Tohru Saito 《Fluid Phase Equilibria》2007
The reduction of sulfur content in gasoline and diesel fuel is a great environmental concern to reduce the motor vehicle emissions. Oxidative desulfurization using acetonitrile biphasic system has received much attention in recent years. The oxidative desulfurization can be oxidized the unreactive sulfur contents in the hydrodesulfurization and removed effectively. For the oxidative desulfurization process design and development, liquid–liquid equilibria (LLE) for acetonitrile biphasic systems are needed as fundamental information. In our previous work, LLE for acetonitrile + n-octane and + n-decane systems have been reported. In this work, therefore, LLE for acetonitrile + n-hexadecane system was measured. Furthermore, NRTL equation was applied to correlate the LLE for these three acetonitrile + n-alkane systems. 相似文献