全文获取类型
收费全文 | 5100篇 |
免费 | 108篇 |
国内免费 | 34篇 |
专业分类
化学 | 3506篇 |
晶体学 | 59篇 |
力学 | 73篇 |
数学 | 339篇 |
物理学 | 1265篇 |
出版年
2022年 | 35篇 |
2021年 | 39篇 |
2020年 | 45篇 |
2019年 | 73篇 |
2018年 | 52篇 |
2017年 | 36篇 |
2016年 | 70篇 |
2015年 | 104篇 |
2014年 | 93篇 |
2013年 | 303篇 |
2012年 | 255篇 |
2011年 | 284篇 |
2010年 | 166篇 |
2009年 | 187篇 |
2008年 | 283篇 |
2007年 | 314篇 |
2006年 | 307篇 |
2005年 | 263篇 |
2004年 | 206篇 |
2003年 | 185篇 |
2002年 | 209篇 |
2001年 | 111篇 |
2000年 | 129篇 |
1999年 | 81篇 |
1998年 | 50篇 |
1997年 | 52篇 |
1996年 | 84篇 |
1995年 | 49篇 |
1994年 | 38篇 |
1993年 | 56篇 |
1992年 | 74篇 |
1991年 | 51篇 |
1990年 | 54篇 |
1989年 | 49篇 |
1988年 | 66篇 |
1987年 | 48篇 |
1986年 | 55篇 |
1985年 | 79篇 |
1984年 | 71篇 |
1983年 | 34篇 |
1982年 | 53篇 |
1981年 | 46篇 |
1980年 | 48篇 |
1979年 | 44篇 |
1978年 | 42篇 |
1977年 | 52篇 |
1976年 | 27篇 |
1975年 | 36篇 |
1974年 | 32篇 |
1973年 | 33篇 |
排序方式: 共有5242条查询结果,搜索用时 15 毫秒
61.
62.
63.
Transition of the radial electric field by electron cyclotron heating in the CHS heliotron/torsatron
64.
[reaction: see text] A three-step route of converting allylsilanes to functionalized allenes was developed. Thermal decomposition of 1,1-dibromo-2-(silylmethyl)cyclopropanes, which were quantitatively prepared by treatment of allylsilane derivatives with CHBr3/KO(t)Bu, afforded substituted 2-bromo-1,3-butadienes with elimination of bromosilanes. The Pd-catalyzed reaction of the bromodienes with soft nucleophiles gave the allene derivatives. Previously inaccessible tri- and tetrasubstituted allenes can be prepared by this method as well. 相似文献
65.
Double C-C bond cleavage of a cyclopentadienyl ligand proceeded to titanacyclopentadienes when 2 equiv of nitriles were added and the resulting two-carbon unit and three-carbon unit were converted into a benzene derivative and a pyridine derivative, respectively, in one-pot. 相似文献
66.
N-Acyl-α-amino acids are synthesized by the amidocarbonylation of allylic alcohols catalyzed by homogeneous binary systems which consist of cobalt carbonyl and rhodium (or iron or palladium) complexes. 相似文献
67.
Koga T Taguchi K Kinoshita T Higuchi M 《Chemical communications (Cambridge, England)》2002,(3):242-243
A novel artificial protein with simple primary structure, poly(gamma-methyl-L-glutamate)-grafted polyallylamine, has been prepared and the resultant peptide has shown a unique property of pH-regulated conformation and morphology. 相似文献
68.
A method was developed for determination of total dietary fiber (TDF) in foods containing resistant maltodextrin (RMD) which includes nondigestible carbohydrates that are not fully recovered as dietary fiber by conventional TDF methods such as AOAC 985.29 or 991.43. Because the average molecular weight (MW) of RMD is 2000 daltons, lower MW soluble dietary fiber components do not precipitate in 78% ethanol; therefore, RMD is not completely quantitated as dietary fiber by current AOAC methods. The accuracy and precision of the method was evaluated through an AOAC collaborative study. Ten laboratories participated and assayed 12 test portions (6 blind duplicates) containing RMD. The 6 test pairs ranged from 1.5 to 100% RMD. The method consisted of the following steps: (1) The insoluble dietary fiber (IDF) and high MW soluble dietary fiber (HMWSDF) were determined by AOAC 985.29. (2) Ion exchange resins were used to remove salts and proteins contained in the AOAC 985.29 filtrates (including ethanol and acetone). (3) The amount of low MWRMD (LMWRMD) in the filtrates were determined by liquid chromatography. (4) The TDF was calculated by summation of the IDF, HMWSDF, and LMWRMD fractions having nondigestible carbohydrates with a degree of polymerization of 3 and higher. Repeatability standard deviations (RSDr) were 1.33-7.46%, calculated by including outliers, and 1.33-6.10%, calculated by not including outliers. Reproducibility standard deviations (RSDR) were 2.48-9.39%, calculated by including outliers, and 1.79-9.39%, calculated by not including outliers. This method is recommended for adoption as Official First Action. 相似文献
69.
A unique family of 1,3,8,10-tetrahydro-2,9-diazadibenzo[cd,lm]perylenes (THDAP) was prepared through a new synthetic strategy. Completion of the synthesis was achieved in several steps from commercially available perylene-3,4,9,10-tetracarboxylic dianhydride via reactions between 3,4,9,10-tetra(chloromethyl)perylene and primary amines. The successful use of a variety of primary amines in the reactions indicated that the synthetic approach provides a rich opportunity to produce new functionalized perylene derivatives. 相似文献
70.
γ-Butyrolactone (hereafter abbreviated GBL) is produced by the two-stage hydrogenation of maleic anhydride(MAH) in the liquid phase: the hydrogenation of MAH to succinic anhydride(SAH) in the first stage and the subsequent hydrogenation of SAH to GBL in the second stage. A novel ruthenium catalyst system consisting of Ru salts, trialkylphosphine and p-toluene sulfonic acid (p-TsOH) was found very effective for the hydrogenation of SAH affording GBL, which exhibited excellent catalyst performance, exceeding 97% selectivity for GBL and high activity. 相似文献