全文获取类型
收费全文 | 4341篇 |
免费 | 80篇 |
国内免费 | 24篇 |
专业分类
化学 | 3049篇 |
晶体学 | 47篇 |
力学 | 56篇 |
数学 | 205篇 |
物理学 | 1088篇 |
出版年
2023年 | 20篇 |
2021年 | 37篇 |
2020年 | 48篇 |
2019年 | 55篇 |
2018年 | 39篇 |
2017年 | 23篇 |
2016年 | 57篇 |
2015年 | 69篇 |
2014年 | 66篇 |
2013年 | 179篇 |
2012年 | 181篇 |
2011年 | 245篇 |
2010年 | 106篇 |
2009年 | 147篇 |
2008年 | 244篇 |
2007年 | 241篇 |
2006年 | 242篇 |
2005年 | 215篇 |
2004年 | 202篇 |
2003年 | 178篇 |
2002年 | 186篇 |
2001年 | 136篇 |
2000年 | 110篇 |
1999年 | 75篇 |
1998年 | 55篇 |
1997年 | 63篇 |
1996年 | 58篇 |
1995年 | 44篇 |
1994年 | 59篇 |
1993年 | 64篇 |
1992年 | 76篇 |
1991年 | 60篇 |
1990年 | 51篇 |
1989年 | 58篇 |
1988年 | 47篇 |
1987年 | 57篇 |
1986年 | 50篇 |
1985年 | 64篇 |
1984年 | 57篇 |
1983年 | 40篇 |
1982年 | 33篇 |
1981年 | 44篇 |
1980年 | 32篇 |
1979年 | 54篇 |
1978年 | 45篇 |
1977年 | 27篇 |
1976年 | 35篇 |
1975年 | 30篇 |
1974年 | 32篇 |
1973年 | 25篇 |
排序方式: 共有4445条查询结果,搜索用时 15 毫秒
31.
32.
Nishimiya N Yamaguchi Y Ohrui Y Suzuki M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(3):493-504
The mirror gap of a Fabry-Perot interferometer was stabilized with two laser diodes; one locked to the line frequency 385,243,555.14445 MHz of the F=3<--1 in 5D(3/2)<--5S(1/2) (87Rb) and the other to the 385,284,566.3663 MHz of the F=4<--2 in 5D(5/2)<--5S(1/2) (87Rb) [Opt. Commun. 102 (1993) 432]. The length of the mirror gap was adjusted to generate the zero-cross points simultaneously at both of the two line positions. The fringe signals obtained from an interferometer thus stabilized can be used as frequency markers having accuracies of the order of 10(10) depending on the finesse of the interferometer used. Based on measurement using Cs D1 hyperfine lines reported by Udem et al. [Phys. Rev. Lett. 82 (1999) 3568], the uncertainty of markers in the region 50 THz apart from the reference lines is +/- 5 MHz. 相似文献
33.
Junji Furukawa Eiichi Kobayashi Morio Nakamura 《Journal of polymer science. Part A, Polymer chemistry》1974,12(12):2789-2799
The effect of ultraviolet irradiation on the terpolymerization was investigated. In the terpolymerizations of sulfur dioxide–butene-1–acrylonitrile, sulfur dioxide–butene-1–n-butyl acrylate, and maleic anhydride–allyl chloride–acrylonitrile systems, the composition of the terpolymers prepared under ultraviolet irradiation was different from those prepared in the dark. The unit content of sulfur dioxide and butene-1 or of maleic anhydride and allyl chloride in the terpolymer increased under ultraviolet irradiation. The nature of the growing end under ultraviolet irradiation is supposed to be the same as that of the dark polymerization on the basis of the same solvent effect on the terpolymer composition, the rate of polymerization and the molecular weight of polymer. The experimental results suggest that the complex between sulfur dioxide and butene-1 or maleic anhydride and allyl chloride might be excited by ultraviolet light and the excited complex may participate in the terpolymerization. 相似文献
34.
Yoshiharu Yamane Yozo Nakamura Hiroyuki Okamoto Hiroshi Ooshima Jyoji Kato 《Applied biochemistry and biotechnology》1995,50(3):317-322
Effects of pH and dissolved oxygen concentration on batchwise riboflavin production by a 5-fluorouracil (5-FU)-resistant mutant
ofArthrobacter sp. were investigated. The reaction was carried out in a jar fermentor. The optimal pH of culture medium was around 7.3.
Dissolved oxygen concentration was almost constant during fermentation at 600 rpm of agitation rate. Production of riboflavin
reached a maximum of 160 mg/L after 70 h fermentation under the agitation rate of 600 rpm, aeration rate of 1.0 L/min, and
pH 7.0. 相似文献
35.
To detect a lectin from soybean, an electrochemical procedure was developed by the use of a labeling of galactosamine. Because the lectin has binding sites to galactosamine, galactosamine labeled with daunomycin having electroactivity was prepared. When labeled galactosamine (LG) combines with lectin, the part of daunomycin is taken in the binding sites of the lectin and becomes electroinactive. Therefore, the concentration of the lectin can be estimated by measuring the peak current of the LG. On the other hand, a competitive reaction to the lectin of galactosamine and the LG makes a detection of galactosamine possible. This method has merit that does not require a separation procedure of the free LG from the bound one. An effect of length of spacer between daunomycin and galactosamine was also investigated. It was found that adsorption of reagent on the electrode increased due to introduction of the spacer. Furthermore, the electrode response of the LG was influenced by the type of the spacer. 相似文献
36.
Kozo Arai Atsushi Matsunaga Masaru Yoneyama Shoji Takigami Yoshio Nakamura Haydn E. Edwards Glyn O. Phillips 《Journal of polymer science. Part A, Polymer chemistry》1993,31(1):249-258
The reactions of heparin with 2,4,6-trinitrobenzenesulfonic acid (TNBS) were studied spectrometrically. Seven different commercial heparins were used in this study. The amino groups react with TNBS to form equimolar amounts of trinitrophenylated (TNP) amino groups and bisulfite ions. The TNP-amino groups further react with bisulfite ions to form the monosubstituted anionic sigma complex. The absorption spectrum with two maxima at approximately 350 nm and approximately 420 nm, characteristic of either the TNP-amino groups or the complex, was analyzed for the reaction of TNBS with heparin. It was shown that the reactivities of TNBS with amino groups from α-amino acid and hexosamine residues are greatly different. By combining the results of the reaction kinetics and the reaction of heparin with Sanger's reagent, the number of the α-amino groups and the free amino groups in hexosamine residues were determined. These data have been performed with a range of heparins from different commercial sources, of different activities and physical characteristics. No correlation was found between the free amino contents of these heparins and biological potency. © 1993 John Wiley & Sons, Inc. 相似文献
37.
[structure: see text]. All stereoisomers of a cyclic alkyne containing three helicene units, 1,12-dimethylbenzo[c]phenanthrene, are synthesized using a building block. Isomeric [3 + 3]cycloalkynes aggregate in organic solvents. Vapor pressure osmometry reveals dimer formation of (M,M,M)-[3 + 3]cycloalkynes in chloroform and benzene at concentrations above 2 mM. No higher aggregation is observed. The chirality of helicenes plays an important role in self-aggregation, and diastereomeric (M,P,M)-[3 + 3]cycloalkyne forms a dimer only above 15 mM. Aggregation of racemic (M,M,M)-[3 + 3]cycloalkyne or (M,P,M)-[3 + 3]cycloalkyne is much weaker than that of a single enantiomer. 相似文献
38.
[reaction: see text] Catalytic, enantioselective Mannich-type reactions of alpha-imino esters bearing readily removable substituents on nitrogen are described. Several N-carbamate-protected alpha-imino esters, which are readily prepared from 2-bromoglycine esters using a polymer-supported amine, reacted with silicon enolates to afford the desired adducts in high yields with high enantioselectivity using a copper(II)-diamine complex. Easy deprotection of the product amine and transformation to free alpha-amino acid derivatives have also been demonstrated. 相似文献
39.
Shuichi Nakamura 《Tetrahedron letters》2006,47(43):7599-7602
A catalytic enantioselective Strecker-type reaction to N-(2-pyridylsulfonyl)imines in the presence of chiral bis(oxazoline)s afforded the products with a high enantioselectivity. A dynamically induced new chiral center on the sulfur by discriminative coordination of a chiral Lewis acid to one of the sulfonyl oxygens efficiently controlled the enantioselectivity. 相似文献
40.
Kondo T Kaneko Y Taguchi Y Nakamura A Okada T Shiotsuki M Ura Y Wada K Mitsudo TA 《Journal of the American Chemical Society》2002,124(24):6824-6825
Pyranopyrandiones were prepared by a novel ruthenium-catalyzed carbonylative dimerization of cyclopropenones via C-C bond cleavage. For example, treatment of dipropylcyclopropenone with a catalytic amount of Ru3(CO)12 and NEt3 in THF under 15 atm of carbon monoxide at 140 degrees C for 20 h gave a novel functional monomer, 3,4,7,8-tetrapropylpyrano[6,5-e]pyran-2,6-dione, in an isolated yield of 81%. Unsymmetrically substituted pyranopyrandiones were also obtained by ruthenium-catalyzed carbonylative coupling of cyclopropenones with alkynes under similar reaction conditions. 相似文献