全文获取类型
收费全文 | 1607篇 |
免费 | 31篇 |
国内免费 | 8篇 |
专业分类
化学 | 1228篇 |
晶体学 | 18篇 |
力学 | 11篇 |
数学 | 53篇 |
物理学 | 336篇 |
出版年
2023年 | 11篇 |
2022年 | 10篇 |
2021年 | 8篇 |
2020年 | 21篇 |
2019年 | 17篇 |
2018年 | 17篇 |
2017年 | 17篇 |
2016年 | 22篇 |
2015年 | 18篇 |
2014年 | 28篇 |
2013年 | 92篇 |
2012年 | 69篇 |
2011年 | 81篇 |
2010年 | 66篇 |
2009年 | 54篇 |
2008年 | 85篇 |
2007年 | 95篇 |
2006年 | 94篇 |
2005年 | 67篇 |
2004年 | 82篇 |
2003年 | 57篇 |
2002年 | 61篇 |
2001年 | 33篇 |
2000年 | 26篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 17篇 |
1996年 | 19篇 |
1995年 | 17篇 |
1994年 | 15篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1987年 | 7篇 |
1986年 | 18篇 |
1985年 | 29篇 |
1984年 | 28篇 |
1983年 | 9篇 |
1982年 | 22篇 |
1981年 | 19篇 |
1980年 | 26篇 |
1979年 | 22篇 |
1978年 | 23篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1975年 | 18篇 |
1974年 | 14篇 |
1973年 | 18篇 |
排序方式: 共有1646条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
Enantioselective Michael addition reactions of tertiary nucleophile precursors, such as substituted malononitriles and cyclic 1,3-diketones, can be successfully activated by the metal complexes derived from R,R-DBFOX/Ph chiral ligand and cationic metal salts. With this method, the enantioselective tertiary/quaternary and quaternary/quaternary carbon–carbon bond formations can be achieved. Use of alcohol solvents is essential for the success, and ,β-unsaturated amides of 3,5-dimethylpyrazole are much better acceptors than those of 2-oxazolidinone. 相似文献
46.
Shin-ichi OhsugiKiyoharu Nishide Keiji OonoKazunori Okuyama Masato FudesakaSumiaki Kodama Manabu Node 《Tetrahedron》2003,59(42):8393-8398
Development of the odorless dodecyl methyl sulfide (Dod-S-Me, 1) as an alternative for dimethyl sulfide (DMS) and new odorless methods for the Corey-Kim and Swern oxidations are described. These reactions have been developed with a view toward green chemistry, utilizing Dod-S-Me (1) and common solvents instead of dichloromethane. 相似文献
47.
Yamamoto Y Yamamoto A Furuta SY Horie M Kodama M Sato W Akiba KY Tsuzuki S Uchimaru T Hashizume D Iwasaki F 《Journal of the American Chemical Society》2005,127(42):14540-14541
The oxidized octaethyltetraphenylporphyrin (1, OETPP) and the corresponding newly prepared octaisobutyltetraphenylporphyrin (3, OisoBuTPP) could be isolated from the reaction of OETPPLi2 (or OisoBuTPPLi2) with SOCl2. The X-ray analysis and the characteristic UV-vis spectra of 1 and 3 revealed that these are the first examples of 16 pi nonaromatic porphyrins. 相似文献
48.
Tetsuo Suami Hiroaki Sasai Kazuhiro Matsuno Nobuo Suzuki Yoshimasa Fukuda Osamu Sakanaka 《Tetrahedron letters》1984,25(40):4533-4536
Tunicamycins and their eight analogs have been synthesized by condensation of a N-acetyl-D-glucosamine derivative and an anomeric chloride of tunicaminyl uracil, followed by deprotections and N-acylation. 相似文献
49.
The synthesis of a novel reagent, 2-[2-(8-hydroxyquinolyl)azo]-1-naphthol (HQAN), is described. The acidity constants of the reagent and its reactions with various metal ions are reported. The HQAN reagent forms a soluble calcium chelate in 50% (v/v) dioxane/ water at pH > 8.5 (? = 24 000 l mol?1 cm t-1 at 570 nm). It also forms chelates with magnesium, other alkaline earth metals, and ivalent Mn, Fe, Ni, Cu, Zn, Cd and Pb. These interferences (except for Mn) can be avaoided by pH adjustment or by adding masking agents, and a very simple procedure for the determination of calcium in potable waters is obtained. 相似文献
50.
We have plotted electropherograms in capillary zone electrophoresis (CZE) as a function of the quantity of electric charge (Q) in order to eliminate the dependency of the analyte peak areas, as well as that of the migration times, upon both the capillary temperature and the applied voltage. The procedure is based on an idea of a migration index (MI) and an adjusted migration index (AMI) which were originally proposed by Lee and Yeung. The value of Q is measured accurately and calculated easily because it is given by a product of the electrophoretic current and the migration times, where the index MI is derived by dividing the value of Q by the effective volume of the capillary. By calculating the CZE peak area from the newly plotted electropherogram, improvement in precision in quantitative analysis is expected. Concerning AMI, careful treatment is required in its application to analyte peaks whose migration time is close to that of the neutral marker. Experimental data and discussions concerning the migration indices are presented. 相似文献