全文获取类型
收费全文 | 1353篇 |
免费 | 41篇 |
国内免费 | 15篇 |
专业分类
化学 | 999篇 |
晶体学 | 16篇 |
力学 | 14篇 |
数学 | 81篇 |
物理学 | 299篇 |
出版年
2023年 | 9篇 |
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 15篇 |
2019年 | 21篇 |
2018年 | 16篇 |
2017年 | 14篇 |
2016年 | 32篇 |
2015年 | 20篇 |
2014年 | 35篇 |
2013年 | 59篇 |
2012年 | 90篇 |
2011年 | 70篇 |
2010年 | 52篇 |
2009年 | 40篇 |
2008年 | 65篇 |
2007年 | 62篇 |
2006年 | 74篇 |
2005年 | 86篇 |
2004年 | 66篇 |
2003年 | 66篇 |
2002年 | 66篇 |
2001年 | 39篇 |
2000年 | 29篇 |
1999年 | 21篇 |
1998年 | 10篇 |
1997年 | 28篇 |
1996年 | 15篇 |
1995年 | 8篇 |
1994年 | 30篇 |
1993年 | 14篇 |
1992年 | 11篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 24篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1979年 | 19篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1975年 | 10篇 |
1974年 | 6篇 |
1973年 | 9篇 |
排序方式: 共有1409条查询结果,搜索用时 46 毫秒
61.
Iida T Satoh H Maeda K Yamamoto Y Asakawa K Sawada N Wada T Kadowaki C Itoh T Mase T Weissman SA Tschaen D Krska S Volante RP 《The Journal of organic chemistry》2005,70(23):9222-9229
[Reaction: see text]. The synthesis of neuropeptide Y antagonist 1, currently under clinical investigation for the treatment of obesity, is described. The convergent synthesis from trans-spirolactone carboxylic acid intermediate 2a and aminopyrazole 3 is predicated on a stereoselective route to the former. The coupling reaction of ethyl 4-oxocyclohexanecarboxylate (10a) with lithiated isonicotinamide 11 was investigated in detail, but even optimized conditions only provided a 45:55 ratio of trans:cis isomers (12a:12b). While selective crystallization schemes were developed to isolate the thermodynamically less stable trans isomer 2a, improved stereocontrol was subsequentially achieved by the application of ketene chemistry. The ketene formation and quench was investigated under a variety of conditions aimed at maximizing the trans:cis ratio. Reacting a mixture of carboxylic acids 2a and 2b with POCl3 in THF, followed by concomitant addition of tert-butyl alcohol in the presence of TMEDA at 35 degrees C provided a 4:1 ratio of trans:cis tert-butyl esters (18a:18b) via in situ ketene formation. Ester hydrolysis, followed by selective crystallization of undesired 2b as the HCl salt, led to isolation of 2a in 47% overall yield. Aminopyrazole intermediate 3 was synthesized via the condensation reaction of 2-fluorophenylhydrazine hydrochloride (4a) with acrylonitrile derivative 5 in 65-70% yield. Coupling of advanced intermediates 2a and 3b via activation with thionyl chloride gave a 92% yield of 1. 相似文献
62.
Ayae Sugawara Akira Oichi Hiroko Suzuki Yuzo Shigesato Toshihiro Kogure Takashi Kato 《Journal of polymer science. Part A, Polymer chemistry》2006,44(17):5153-5160
Assembled structures of calcium carbonate (CaCO3) nanocrystals have been examined for polymer/CaCO3 thin-film composites synthesized through a self-organization process inspired by biomineralization. For the crystallization of CaCO3, a thin-film matrix of chitosan has been used as a polymeric substrate. When the matrix is immersed into a supersaturated aqueous solution of CaCO3 containing 1.4 × 10−3 wt % poly(aspartate) (PAsp), thin-film crystals of CaCO3 are formed spontaneously. Three kinds of disklike films have been observed under a polarizing optical microscope. Electron diffraction analyses of each film have revealed that one is aragonite, displaying radial orientation of the c axes, and the others are vaterite, exhibiting different orientations. Detailed observation by scanning electron microscopy has clarified that these films are assemblies of crystalline particles 10–20 nm in size. The thin-film composites have been obtained over a PAsp concentration range of 4.4 × 10−4 to 1.0 × 10−2 wt %. Vaterite formation becomes dominant when the concentration of PAsp is increased. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5153–5160, 2006 相似文献
63.
Nishiyama Y Kaneda M Saito R Mori T Wada T Inoue Y 《Journal of the American Chemical Society》2004,126(21):6568-6569
In the enantiodifferentiating photoaddition of ROH (R = Me, Et, i-Pr) to 1,1-diphenylpropene sensitized by fructosyl 1,4-naphthalenedicarboxylate in supercritical carbon dioxide, the enantiomeric excess of photoadduct increased with increasing bulkiness of the alcohol at all pressures used, with an accompanying sudden jump at the critical density, for which the enhanced clustering of alcohol, particularly in the subcritical pressure region, was revealed to be responsible from the fluorescence spectral examinations. 相似文献
64.
65.
66.
Xiongchao Lin Keiko Ideta Jin Miyawaki Yusuke Nishiyama Isao Mochida Seong‐Ho Yoon 《Magnetic resonance in chemistry : MRC》2012,50(4):289-294
A general strategy of structural analysis of alumina silicate by combining various solid‐state NMR measurements such as single pulse, multi‐quantum magic angle spinning, double‐quantum homo‐nuclear correlation under magic angle spinning (DQ‐MAS), and cross‐polarization hetero‐nuclear correlation (CP‐HETCOR) was evaluated with the aid of high magnetic field NMR (800 MHz for 1H Larmor frequency) by using anorthite as a model material. The high magnetic field greatly enhanced resolution of 27Al in single pulse, DQ‐MAS, and even in triple‐quantum magic angle spinning NMR spectra. The spatial proximities through dipolar couplings were probed by the DQ‐MAS methods for homo‐nuclear correlations between both 27Al–27Al and 29Si–29Si and by CP‐HETCOR for hetero‐nuclear correlations between 27Al–29Si in the anorthite framework. By combining various NMR methodologies, we elucidated detailed spatial correlations among various aluminum and silicon species in anorthite that was hard to be determined using conventional analytical methods at low magnetic field. Moreover, the presented approach is applicable to analyze other alumina‐silicate minerals. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
67.
V. V. Kaminskii Toshihiro Kuzuya Shinji Hirai S. M. Solov’ev N. V. Sharenkova M. M. Kazanin 《Physics of the Solid State》2012,54(7):1345-1347
The electrical conductivity of SmS polycrystals has been studied in the temperature range 300?C870 K. It has been shown that, at 300 K ?? T ?? 700 K, the concentration of conduction electrons is determined by electron transfer from impurity donor levels, and at T > 700 K, by that from the samarium 4f levels. 相似文献
68.
Toshihiro Kasezawa Hideyoshi Horimai Hiroshi Tabuchi Tsutomu Shimura 《Optical Review》2016,23(6):997-1003
A new photovoltaic generation unit based on the application of holographic technologies called a Holo-Window is proposed in this work. The basic principle and the optical configuration used for the basic experimental unit are described. Suitable fabrication technology for a hologram with the broadband spectrum required to provide the appropriate sunlight capture capability is then discussed. Finally, a laboratory-prototype Holo-Window unit was developed and its performance was evaluated. 相似文献
69.
70.
Hong Xia Yoshio Hashimoto Toru Morita Toshihiro Hirai 《Journal of Polymer Science.Polymer Physics》2014,52(13):887-892
Few solvents are capable of dissolving polyketones (PKs). 1,1,1,3,3,3‐Hexafluoro‐2‐propanol (hexafluoroisopropanol, HFIP) is a better solvent than trifluoroethanol and m‐cresol. When HFIP was evaporated from a PK/HFIP solution, a porous cast‐film with a microparticle structure was formed because the isotactic PKs adopted a helical conformation, and convection during evaporation of the high polarity and low‐boiling‐point HFIP caused aggregation and rolling of the polymer molecules. The addition of plasticizer suppressed particle formation, improving the surface structure and mechanical properties of the film. In particular, the dielectric properties of the film improved significantly. This will enable PKs, which are rigid insulating materials, to be used as dielectric materials, broadening their range of applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 887–892 相似文献