全文获取类型
收费全文 | 2027篇 |
免费 | 36篇 |
国内免费 | 3篇 |
专业分类
化学 | 1274篇 |
晶体学 | 19篇 |
力学 | 28篇 |
综合类 | 1篇 |
数学 | 57篇 |
物理学 | 687篇 |
出版年
2023年 | 11篇 |
2021年 | 5篇 |
2020年 | 17篇 |
2019年 | 22篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 23篇 |
2015年 | 22篇 |
2014年 | 23篇 |
2013年 | 89篇 |
2012年 | 62篇 |
2011年 | 87篇 |
2010年 | 52篇 |
2009年 | 52篇 |
2008年 | 104篇 |
2007年 | 125篇 |
2006年 | 113篇 |
2005年 | 129篇 |
2004年 | 124篇 |
2003年 | 111篇 |
2002年 | 106篇 |
2001年 | 53篇 |
2000年 | 55篇 |
1999年 | 34篇 |
1998年 | 28篇 |
1997年 | 32篇 |
1996年 | 36篇 |
1995年 | 36篇 |
1994年 | 32篇 |
1993年 | 36篇 |
1992年 | 48篇 |
1991年 | 25篇 |
1990年 | 21篇 |
1989年 | 28篇 |
1988年 | 19篇 |
1987年 | 30篇 |
1986年 | 18篇 |
1985年 | 26篇 |
1984年 | 27篇 |
1983年 | 12篇 |
1982年 | 21篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 22篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 10篇 |
1973年 | 12篇 |
排序方式: 共有2066条查询结果,搜索用时 15 毫秒
111.
Tachi Y Aita K Teramae S Tani F Naruta Y Fukuzumi S Itoh S 《Inorganic chemistry》2004,43(15):4558-4560
A dicopper(I) complex supported by a novel asymmetric pentapyridine dinucleating ligand, consisting of tetradentate and tridentate metal-binding sites, has been synthesized and characterized. The dicopper(I) complex reacted with molecular oxygen at a low temperature to give an unprecedented mu-peroxo dicopper(II) complex presumably having a mu-eta1:eta2 binding mode, the spectroscopic features and the reactivity of which have been explored in detail. 相似文献
112.
The amino acid industry has been steadily expanding since monosodium glutamate was first marketed as a flavoring material in 1909. Its production has recently reached almost the 1 billion dollar level. Amino acids are produced by extraction from protein hydrolyzates, by fermentation with the aid of microorganisms, by enzymatic processes, and by chemical synthesis. To obtain natural L-amino acid, chemical synthesis generally requires two additional steps, i.e. optical resolution and racemization of the D isomer. The most important applications of amino acids include the fortification of plant food and feeds by supplementation of the deficient essential amino acid(s). Apart from their uses in the food industry, medical applications of amino acids (nutritional preparations and therapeutic agents) are becoming increasingly important. 相似文献
113.
Kazuo Itoh Masahiko Chikuma Hisashi Tanaka 《Fresenius' Journal of Analytical Chemistry》1988,330(7):600-604
Summary The hydride generation/atomic absorption spectrometry (AAS) with an automated flow system is useful for the routine analysis of selenium in environmental samples. This method is, however, subject to interferences from transition metal ions and other hydride forming ions. The conditions to minimize the interferences were established: the concentration of hydrochloric acid 6 mol/l; the concentration of tetrahydroborate 0.5%. Iron(III) chloride released the depression of selenium signals by metal ions such as copper(II) and bismuth(III). Selenium in several standard reference materials including sediment samples was determined by the present method and by fluorimetry with 2,3-diaminonaphthalene. The results obtained by the two methods agreed with an acceptable precision. This means that hydride generation/AAS offers good precision and accuracy in the determination of selenium in sediment samples as well as DAN fluorimetry. However, the former is much simpler in operation. The method was applied to the determination of selenium in estuarine sediments collected in Nagoya harbor and Ise Bay. The results can be used to assess the pollution state of these places.
Selenbestimmung in Sedimenten durch AAS mit Hydriderzeugung. Eliminierung von Störungen相似文献
114.
We estimated the energy barriers of proton transfers in the systems of (CF3SO3/H/SO3CF3)− and (CF3SO3/H/H2O/SO3CF3)− as models of a water-swollen Nafion membrane by an ab initio density functional quantum calculation method with consideration of the hydration effect. As a result, the proton transfer between the SO sites, which is accompanied by one water molecule, was found to be one of the proton-transfer mechanisms in the water-swollen Nafion membrane; that is, the surface diffusion mechanism was found to be important for the proton transfer in that membrane. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1905–1914, 2004 相似文献
115.
Room temperature chiral spiro ionic liquids 1 and 2 based on 1,2,3-triazolium salts, were synthesized via an intramolecular double Huisgen reaction. The preparation of the enantiomerically pure spiro triazolium salts was achieved by resolution by HPLC using a chiral stationary phase column and subsequent N-dialkylations of spiro triazoles 6 and 10. 相似文献
116.
Herein we report the production of enantiopure epoxides through biocatalysis using recombinant Escherichia coli cells expressing Rhodococcus sp. ST-10 styrene monooxygenase (SMO) and Leifsonia sp. S749 alcohol dehydrogenase (LSADH) genes are described. Rhodococcus sp. ST-10 SMO catalyzed the epoxidation of various alkenes, including styrene derivatives, vinyl pyridines, and linear alkenes, to give (S)-epoxides. NADH was regenerated by the reduction of NAD+ by LSADH with 2-propanol. The E. coli biocatalyst was used in an aqueous/organic biphasic reaction system and the reaction conditions were optimized. Under the optimized conditions, 170 mM of (S)-styrene oxide was obtained from styrene in the organic phase with excellent enantiomeric excess (99.8%). This biocatalytic process was used to synthesize various (S)-epoxides. 相似文献
117.
Kazuhiro Marumo Manabu Itoh Sungmin Kang Koichi Sakajiri Junji Watanabe 《Liquid crystals》2013,40(2):234-238
Galactose derivatives were explored as chiral dopants, effective for inducing chiral nematic liquid crystal (LC) phases. Galactose bearing O-isopropylidene substituents at the C3 and C4 and butoxybiphenyl substituents at the C2 and C6 positions exhibits a high helical twisting power (HTP) value of ?74.4 μm?1. Such a high HTP value for the galactose derivative is attributed to (1) linkage of the C3 and C4 carbons with the O-isopropylidene substituent, which places the C2 and C6 substitutes in a skew arrangement at a large angle and (2) enhancement of the affinity with the host nematic LCs by incorporating aromatic substituents at the C2 and C6 positions that are similar to those in the host. 相似文献
118.
Maki Sachiko Eiji Nishibori Shinobu Aoyagi Makoto Sakata Masaki Takata Mio Kondo Masaki Murata Ryota Sakamoto Hiroshi Nishihara 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(7):696-703
The title compound, [Fe2(C5H5)2(C40H22O2)] or 1,4‐(FcPh)2Aq [where FcPh is 2‐(4‐ferrocenylphenyl)ethynyl and Aq is anthraquinone], was synthesized in an attempt to obtain a new solvent‐incorporating porous material with a large void space. Thermodynamic data for 1,4‐(FcPh)2Aq show a phase transition at approximately 430 K. The crystal structure of solvent‐free 1,4‐(FcPh)2Aq was determined at temperatures of 90, 300 and 500 K using synchrotron powder diffraction data. A direct‐space method using a genetic algorithm was employed for structure solution. Charge densities calculated from observed structure factors by the maximum entropy method were employed for model improvement. The final models were obtained through multistage Rietveld refinements. In both phases, the structures of which differ only subtly, the planar Aq fragments are stacked alternately in opposite orientations, forming a one‐dimensional column. The FcPh arms lie between the stacks and fill the remaining space, leaving no voids. C—H...π interactions between the Ph and Fc fragments mediate crystal packing and stabilization. 相似文献
119.
Shuichi Hirata Kouichi Tanaka Katsuya Matsui Fernando Arteaga Arteaga Yasushi Yoshida Shinobu Takizawa Hiroaki Sasai 《Tetrahedron: Asymmetry》2013,24(19):1189-1192
The introduction of a 1,3-propanediamine unit at the 3-position of (S)-BINOL using a methylene spacer led to the formation of a chiral bifunctional organocatalyst for the aza-Morita–Baylis–Hillman (aza-MBH) reaction. The organocatalyst 1k mediated aza-MBH transformations with high chemical yields and with up to 82% ee. 相似文献