全文获取类型
收费全文 | 3302篇 |
免费 | 95篇 |
国内免费 | 13篇 |
专业分类
化学 | 2477篇 |
晶体学 | 34篇 |
力学 | 39篇 |
数学 | 157篇 |
物理学 | 703篇 |
出版年
2022年 | 12篇 |
2021年 | 20篇 |
2020年 | 37篇 |
2019年 | 50篇 |
2018年 | 40篇 |
2017年 | 19篇 |
2016年 | 61篇 |
2015年 | 55篇 |
2014年 | 70篇 |
2013年 | 163篇 |
2012年 | 161篇 |
2011年 | 187篇 |
2010年 | 111篇 |
2009年 | 95篇 |
2008年 | 167篇 |
2007年 | 161篇 |
2006年 | 157篇 |
2005年 | 161篇 |
2004年 | 132篇 |
2003年 | 140篇 |
2002年 | 138篇 |
2001年 | 90篇 |
2000年 | 87篇 |
1999年 | 59篇 |
1998年 | 36篇 |
1997年 | 41篇 |
1996年 | 32篇 |
1995年 | 25篇 |
1994年 | 35篇 |
1993年 | 42篇 |
1992年 | 38篇 |
1991年 | 48篇 |
1990年 | 47篇 |
1989年 | 32篇 |
1988年 | 42篇 |
1987年 | 45篇 |
1986年 | 36篇 |
1985年 | 66篇 |
1984年 | 54篇 |
1983年 | 23篇 |
1982年 | 40篇 |
1981年 | 38篇 |
1980年 | 27篇 |
1979年 | 37篇 |
1978年 | 38篇 |
1977年 | 43篇 |
1976年 | 35篇 |
1975年 | 24篇 |
1974年 | 22篇 |
1973年 | 31篇 |
排序方式: 共有3410条查询结果,搜索用时 421 毫秒
61.
Yoshio Ueno Yutaka Takeuchi Jinya Koshitani Takatoshi Yoshida 《Journal of heterocyclic chemistry》1981,18(3):645-647
4-Acyl-1,2-dimethyl-3H-phenothiazin-3-ones were prepared by the photochemical reaction of 1,2-dimethyl-3H-phenothiazin-3-one with aldehydes. The structures of the newly prepared compounds were determined by elemental analysis, spectroscopic methods (ir, nmr and ms) and comparison with a sample prepared by an alternate route. 相似文献
62.
63.
[reaction: see text] We have developed an efficient copper-catalyzed allylation of carbonyl derivatives using allyl(2-pyridyl)silanes, in which the strong directing effect of the 2-pyridyl group was observed. A useful synthesis and allylation of substituted allyl(2-pyridyl)silanes is also described. 相似文献
64.
Yoshida H. Yang M. Masaka K. Houshito Y. Mashiko K. Nakamura S. 《Journal of Thermal Analysis and Calorimetry》2002,70(3):703-711
Phase transition behavior of polyesters derived from 2,7-phenanthrene dicarbonic acid diethylester and alkanediols with even
methylene carbon number was investigated by the simultaneous DSC-XRD method. The smectic A phase was observed on cooling from
the molten state. The transition entropy from the isotropic state to the smectic A phase was about 9.0 J mol-1 K-1, which depended on the methylene carbon number. The linear expansion coefficients, based on the (001) spacing of the crystalline
phase at room temperature, were 1.3·10-4 K-1 (crystalline phase), 5.7·10-4 K-1 (crystallization region), 1.7·10-3 K-1 (smectic A phase) during cooling, and 1.5·10-4 K-1 (crystalline phase), and 1.0·10-3K-1(melting region) on heating.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
65.
Hiroshi Suda Masatoahi Motoi Masatoshi Fujii Shigeyoshi Kanoh Hiroshi Yoshida 《Tetrahedron letters》1979,20(47):4565-4568
Enantioselective reductions of prociral ketones with chiral hydride reagent prepared from optically active 2,2′-diamino-6,6′-dimethylbiphenyl and lithium aluminum hydride were accomplished in O.Y. more than 50%. 相似文献
66.
Transport phenomenon of three sulfonated azo dyes, C.I. Acid Red 88, C.I. Direct Yellow 12, and C.I. Direct Blue 15 into water-swollen cellulose membranes has been analyzed on the basis of parallel transport theory by surface and pore diffusion. Langmuir equation was applied into the mass balance equation to estimate dye concentration in the pores. The results were compared with the results obtained by applying Freundlich equation in our previous papers. The surface diffusivity (D
s) and the pore diffusivity (D
p) for the parallel diffusion model obtained by applying Langmuir equation agreed with those obtained by applying Freudlich equation. The theoretical concentration profiles for parallel diffusion calculated usingD
s andD
p coincided accurately with the experimental data when we applied either Langmuir or Freundlich equations. 相似文献
67.
Takeo Katami Tomokuni Hayakawa Masamichi Furukawa Shozo Shibata Tadashi Hara 《Analytica chimica acta》1986
An extraction-spectrophotometric method is described for the determination of traces of zinc with 2-[2-(3,5-dibromopyridyl)azo]-5-dimethylaminobenzoic acid. The reagent forms a stable, blue 1:2 zinc/reagent complex that can be extracted into chloroform. The apparent molar absorptivity of the zinc(II) complex is 1.26 × 105 l mol?1 cm?1 at 610 nm in chloroform. The reagent is relatively selective; interferences from cobalt, copper and nickel can be masked with dimethylglyoxime and aluminium and iron with a mixture of sodium fluoride and triethanolamine. The method is applied to the determination of zinc in coal fly ash and pond sediments with good precision and accuracy. 相似文献
68.
Patrícia P. C. Sartoratto I. Valria P. Yoshida 《Journal of polymer science. Part A, Polymer chemistry》1992,30(11):2333-2340
In this work several polyorganosilylenes were synthesized including homo-and copolymers containing SiMe2 and SiPh2 units. A Wurtz-type coupling reaction of the respective dichlorodiorganosilanes with sodium metal, varying the Ph2SiCl2/Me2SiCl2 ratio was the chosen synthesis method. Products with different characteristics for solubility, structure (cyclic or linear), composition, and molecular weight distribution could be obtained depending on the comonomer ratios employed. The polysilane derivatives were characterized by infrared spectroscopy (IR), proton nuclear magnetic resonance (1H-NMR), and gel permeation chromatography (GPC). Valuable information related to the comonomers' reactivities was obtained, such as molecular weight distribution, composition, and relationships between yields of soluble, insoluble, and cyclic materials of each polycondensation reaction. © 1992 John Wiley & Sons, Inc. 相似文献
69.
The structural change from the porphyrin free base to monoacid and diacid by successive protonation has been studied by the IR, visible and NMR spectroscopy. The results have indicated that the cation and anion of the porphyrin diacid are strongly associated through H-bonding. The far IR spectra show especially marked differences in the free base, monoacid, and diacid due to the changes of the inner core of the porphyrin ring. 相似文献
70.
Polymer-protected platinum/ruthenium colloidal dispersions were prepared by refluxing mixed solutions of hexachloroplatinic(IV) acid and ruthenium(III) chloride in a mixture of ethanol/water (1/1 v/v) in the presence of poly(N-vinyl-2-pyrrolidone). The electronic spectra and transmission electron micrographs suggested that the colloidal dispersions are almost composed of the mixture of the small monometallic Pt and Ru clusters over all the ratio of Pt/Ru compositions. Extended X-ray absorption fine structure analyses and high resolution electron microprobe analyses indicated that no Pt/Ru alloy clusters exist in the dispersions, and the aggregation occurs between small monometallic Pt clusters (diameter ca. 15 A) and partially oxidized Ru microclusters (diameter less than 10 A). Electron diffraction measurements also suggested that the diffraction pattern of aggregated Pt/Ru cluster particles prepared by the simultaneous reduction of Pt and Ru ions is the same as that of the physical mixture of the small monometallic Pt and Ru clusters separately prepared. Therefore, it can be concluded that the aggregated Pt/Ru cluster particles, with 10 to 60 A in diameter, are built up by small monometallic Pt clusters and partially oxidized Ru microclusters, and that Pt/Ru alloy clusters are not formed. 相似文献