全文获取类型
收费全文 | 5678篇 |
免费 | 178篇 |
国内免费 | 28篇 |
专业分类
化学 | 4078篇 |
晶体学 | 47篇 |
力学 | 144篇 |
综合类 | 1篇 |
数学 | 322篇 |
物理学 | 1292篇 |
出版年
2021年 | 58篇 |
2020年 | 66篇 |
2019年 | 65篇 |
2018年 | 56篇 |
2017年 | 50篇 |
2016年 | 127篇 |
2015年 | 114篇 |
2014年 | 127篇 |
2013年 | 267篇 |
2012年 | 312篇 |
2011年 | 331篇 |
2010年 | 190篇 |
2009年 | 162篇 |
2008年 | 312篇 |
2007年 | 306篇 |
2006年 | 318篇 |
2005年 | 296篇 |
2004年 | 282篇 |
2003年 | 238篇 |
2002年 | 244篇 |
2001年 | 152篇 |
2000年 | 132篇 |
1999年 | 91篇 |
1998年 | 73篇 |
1997年 | 55篇 |
1996年 | 65篇 |
1995年 | 54篇 |
1994年 | 52篇 |
1993年 | 60篇 |
1992年 | 66篇 |
1991年 | 47篇 |
1990年 | 41篇 |
1989年 | 50篇 |
1988年 | 49篇 |
1987年 | 46篇 |
1986年 | 40篇 |
1985年 | 97篇 |
1984年 | 91篇 |
1983年 | 26篇 |
1982年 | 58篇 |
1981年 | 45篇 |
1980年 | 48篇 |
1979年 | 88篇 |
1978年 | 58篇 |
1977年 | 69篇 |
1976年 | 59篇 |
1975年 | 41篇 |
1974年 | 31篇 |
1973年 | 21篇 |
1972年 | 22篇 |
排序方式: 共有5884条查询结果,搜索用时 296 毫秒
61.
62.
63.
M. Takagaki K. Ono S-I. Masunaga Y. Kinashi Y. Sakurai T. Kobayashi S-I. Miyatake N. Hashimoto 《Journal of Radioanalytical and Nuclear Chemistry》2001,247(2):389-392
Quantitative determination of ppb-order 10B was carried out in a small number of cultured tumor cells by particle tracks by the 10B(n,)7Li reactions using solid state nuclear track detector (SSNTD) for boron neutron capture therapy research. The detection limit of 10B concentration in tumor cells is less than 1·10-3 ppm under our experimental conditions which permits the quantitative determination of 10B in a small number of boronated tumor cells (105/ml = ca. 0.1 mg). Boron quantities in tumor cells determined were well compatible with the tumor cell killing effects of boron neutron capture therapy. 相似文献
64.
Relative concentrations of nine isomers of Ca at C82 derived from the C82 isolated-pentagon-rule satisfying cages are computed in a wide temperature interval. The computations are based on the Gibbs energy constructed from partition functions supplied with molecular parameters from density functional theory calculations. Five structures show significant populations at higher temperatures: C2v > Cs > C2 > C3v > Cs. The computed relative stabilities agree well with available observations. 相似文献
65.
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
66.
Vascular dilatory action of the Chinese crude drug. II. Effects of scoparone on calcium mobilization 总被引:1,自引:0,他引:1
J Yamahara G Kobayashi H Matsuda M Iwamoto H Fujimura 《Chemical & pharmaceutical bulletin》1989,37(2):485-489
Further experiments were conducted to examine the effect of scoparone (6,7-dimethoxycoumarin), a coumarin derivative found in the Chinese crude drug "Capillaris Flos," on calcium mobilization. Scoparone does not affect Ca2+ influx through the voltage-dependent channel due to membrane depolarization. Its inhibitory action may be dependent not only on the inhibition of Ca2+ release from sarcoplasmic reticulum but also on the inhibition of extracellular Ca2+ influx through the receptor-operated channel. 相似文献
67.
Jinghua Zhang Toshiko Nagahama Hiroki Ohwaki Yasuhiro Ishibashi Yuji Fujita Sunao Yamazaki 《Analytical sciences》2004,20(1):37-43
To understand the cause of discoloration of the sea laver "nori," which is found in the Ariake Sea, the concentrations of pigments and elements in the normal and discolored laver samples were determined. In the discolored samples, a decrease in all of the pigments, chlorophyll a and carotenoids, and proteinous pigments, phycobiliproteins, was clearly observed. This was accompanied by a decrease in the content of Fe, Zn, Mn, Cu, and P. Good correlations between these elements and chlorophyll a, as well as between these elements and phycobiliproteins, were confirmed, indicating that, in addition to the deficiency of nitrogen and phosphorus, the deficiency of trace elements (Fe, Zn, Mn, and Cu), which are specifically required for photosynthesis, could be a reason for the discoloration of nori. The cause of elemental deficiency is also discussed. 相似文献
68.
The enantio-controlled synthesis of trans-4,5-benzhydrindan-1-ones was achieved by means of a stereoselective [4+2] cycloaddition of o-quinodimethanes generated by a thermal cleavage of benzocyclobutene derivatives as a key step. The chiral substrates of the thermal reaction were synthesized by a diastereoselective Grignard addition to the chiral O-isopropylideneglyceroketones connected to a benzocyclobutene ring, which were simply prepared from D-mannitol as a chiral source. This approach can provide a new efficient access to A-nor B-aromatic steroidal compounds. 相似文献
69.
[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
70.
Several transition metal salts were found to catalyze aza-Michael reactions of enones with carbamates efficiently. The catalytic activity was strongly dependent on the nature of the metal salts. While conventional Lewis acids such as BF(3).OEt(2), AlCl(3), or TiCl(4) showed lower activity, group 7-11 transition metal salts in higher oxidation states such as ReCl(5), Fe(ClO(4))(3).9H(2)O, RuCl(3).nH(2)O, OsCl(3).3H(2)O, RhCl(3).nH(2)O, PtCl(4).5H(2)O, or AuCl(3).H(2)O exhibited higher catalytic activity. [reaction: see text] 相似文献