全文获取类型
收费全文 | 8049篇 |
免费 | 194篇 |
国内免费 | 372篇 |
专业分类
化学 | 1608篇 |
晶体学 | 125篇 |
力学 | 71篇 |
综合类 | 4篇 |
数学 | 70篇 |
物理学 | 6737篇 |
出版年
2024年 | 5篇 |
2023年 | 65篇 |
2022年 | 74篇 |
2021年 | 57篇 |
2020年 | 97篇 |
2019年 | 112篇 |
2018年 | 134篇 |
2017年 | 196篇 |
2016年 | 265篇 |
2015年 | 248篇 |
2014年 | 686篇 |
2013年 | 483篇 |
2012年 | 339篇 |
2011年 | 790篇 |
2010年 | 529篇 |
2009年 | 613篇 |
2008年 | 553篇 |
2007年 | 639篇 |
2006年 | 462篇 |
2005年 | 338篇 |
2004年 | 279篇 |
2003年 | 248篇 |
2002年 | 226篇 |
2001年 | 226篇 |
2000年 | 146篇 |
1999年 | 173篇 |
1998年 | 162篇 |
1997年 | 73篇 |
1996年 | 81篇 |
1995年 | 48篇 |
1994年 | 35篇 |
1993年 | 34篇 |
1992年 | 22篇 |
1991年 | 22篇 |
1990年 | 30篇 |
1989年 | 16篇 |
1988年 | 17篇 |
1987年 | 23篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有8615条查询结果,搜索用时 62 毫秒
121.
Kenji Maeda Ross A. Miller Ali Shafiee Joseph D. Armstrong III 《Tetrahedron letters》2005,46(9):1545-1549
Highly diastereoselective (>20:1) bromo-lactonization of N-sulfonyl-2-allyl-2-phenylglycine methyl ester (11) was observed. Successive treatment of the chiral lactone with MeONa gave the desired (2S,4R)-4-hydroxy-2-phenylproline derivative in high yield without erosion of the diastereoselectivity. The starting chiral non-racemic compound (5) was prepared from the racemic 2-phenylglycine using a classical kinetic resolution (crystallization), an asymmetric phase transfer alkylation, and an enzyme-catalyzed kinetic resolution. 相似文献
122.
Monitoring nitrite with optical sensing films 总被引:1,自引:0,他引:1
Ali A. EnsafiA. Kazemzadeh 《Microchemical Journal》2002,72(2):193-199
A new, low-cost nitrite sensor was developed by immobilizing a direct indicator dye in an optical sensing film for food and environmental monitoring. This sensor was fabricated by binding Safranine O to a cellulose acetate film that had previously been subjected to an exhaustive base hydrolysis. The membrane has good durability (>12 months) and a short response time (<8 s). Nitrite can be determined for the range of 0.005-2.00 μg ml−1 with 3δ detection limits of 0.001 μg ml−1. The method is easy to perform and uses acetylcellulose as a carrier. The reagents used for the activity of the cellulose support are inexpensive, non-toxic and widely available. 相似文献
123.
124.
A laser-induced fluorescence microscopic system based on optical parametric oscillation has been constructed as a tunable detector for microchip analysis. The detection limit of sulforhodamine B (Ex. 520 nm, Em. 570 nm) was 0.2 mol, which was approximately eight orders of magnitude better than with a conventional fluorophotometer. The system was applied to the determination of fluorescence-labeled DNA (Ex. 494 nm, Em. 519 nm) in a microchannel and the detection limit reached a single molecule. These results showed the feasibility of this system as a highly sensitive and tunable fluorescence detector for microchip analysis. 相似文献
125.
Vesselin Dimitrov 《Journal of solid state chemistry》2005,178(3):831-846
A classification of binary oxide glasses has been proposed taking into account the values obtained on their refractive index-based oxide ion polarizability αO2−(n0), optical basicity Λ(n0), metallization criterion M(n0), interaction parameter A(n0), and ion's effective charges as well as O1s and metal binding energies determined by XPS. Four groups of oxide glasses have been established: glasses formed by two glass-forming acidic oxides; glasses formed by glass-forming acidic oxide and modifier's basic oxide; glasses formed by glass-forming acidic and conditional glass-forming basic oxide; glasses formed by two basic oxides. The role of electronic ion polarizability in chemical bonding of oxide glasses has been also estimated. Good agreement has been found with the previous results concerning classification of simple oxides. The results obtained probably provide good basis for prediction of type of bonding in oxide glasses on the basis of refractive index as well as for prediction of new nonlinear optical materials. 相似文献
126.
127.
The electrical and magnetic properties of the tetragonal phase SmCuOSe are reported as a function of the temperature. The optical properties were studied by means of diffuse reflectance spectrum in the UV-Vis range. The electrical resistivity measurements as well as diffuse reflectance spectrum show that SmCuOSe is a semiconductor with an optical band gap (Eg) of 2.6 eV. In this phase, Cu is at its monovalent oxidation state and, as such, it does not contribute to the total magnetic moment, whereas Sm is in its 3+ oxidation state, with a large VanVleck contribution due to the admixture of the fundamental state with higher energy levels. 相似文献
128.
Hongwei Liu Xiangdong Liu KeXue Yuan KeSong Hu Yutau Chen 《International Journal of Infrared and Millimeter Waves》1993,14(8):1693-1699
A five-channel grating spectrometer for use in millimeter wave band (25100GHz) is described with its design theory of optical path, and measured results of insertion loss and resolving power. 相似文献
129.
Copper(II) compounds catalyze the reaction of 1,1-diphenylethylene with diazoacetic acid ethylester. The main product is 2,2-diphenylcyclopropane carboxylic acid ethylester. The formation of the carbene dimerization products fumaric and maleic acid diethylester can be suppressed by the continuous addition of diazoacetic acid ester to 1,1-diphenylethylene.37 optically active ligands, partly new, were combined with copper(II)-acetate to givein-situ-catalysts. In five cases isolated copper complexes were used as catalysts. The best optical inductions in the formation of 2,2-diphenylcyclopro-pane carboxylic acid ethylester with up to 65.6% ee were achieved withSchiff base ligands, which derive from salicylaldehyde and amino alcohols, obtained from amino acid esters and phenylGrignard.
Prof. Dr.Karl Schlögl, Universität Wien, mit den besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
130.
杂氮硅三环是一类具有特殊生理活性的新型有机硅化合物,有关其合成及性质在近20年中已有大量报道。特别是当R为氯甲基时,该化合物的生理活性很高,用它制成的药膏已用来治疗脱发及伤口愈合。因此,1-氯甲基杂氮硅三环(Ⅰ)的分子结构引起了人们的关注,先后有人报道了(Ⅰ)及1-氯甲基-3,7-二甲基,1-氯甲基-3,7,10-三甲基 相似文献