全文获取类型
收费全文 | 41189篇 |
免费 | 4962篇 |
国内免费 | 3849篇 |
专业分类
化学 | 28962篇 |
晶体学 | 433篇 |
力学 | 1891篇 |
综合类 | 254篇 |
数学 | 4846篇 |
物理学 | 13614篇 |
出版年
2023年 | 499篇 |
2022年 | 663篇 |
2021年 | 1016篇 |
2020年 | 1218篇 |
2019年 | 1229篇 |
2018年 | 1092篇 |
2017年 | 965篇 |
2016年 | 1586篇 |
2015年 | 1548篇 |
2014年 | 1870篇 |
2013年 | 2792篇 |
2012年 | 2977篇 |
2011年 | 3227篇 |
2010年 | 2275篇 |
2009年 | 2276篇 |
2008年 | 2673篇 |
2007年 | 2488篇 |
2006年 | 2186篇 |
2005年 | 1922篇 |
2004年 | 1622篇 |
2003年 | 1442篇 |
2002年 | 1557篇 |
2001年 | 1154篇 |
2000年 | 990篇 |
1999年 | 866篇 |
1998年 | 663篇 |
1997年 | 591篇 |
1996年 | 622篇 |
1995年 | 568篇 |
1994年 | 471篇 |
1993年 | 385篇 |
1992年 | 360篇 |
1991年 | 356篇 |
1990年 | 316篇 |
1989年 | 269篇 |
1988年 | 211篇 |
1987年 | 202篇 |
1986年 | 187篇 |
1985年 | 272篇 |
1984年 | 268篇 |
1983年 | 195篇 |
1982年 | 205篇 |
1981年 | 172篇 |
1980年 | 165篇 |
1979年 | 142篇 |
1977年 | 163篇 |
1976年 | 147篇 |
1975年 | 124篇 |
1974年 | 120篇 |
1973年 | 119篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
991.
992.
The stoichiometry of the reaction between ferrocyanide and thorium, neodymium, uranyl ion and mercury(II) has been investigated. The first three give single products irrespective of the order of addition of the reagents, but the last does not. If mercury(II) is added to ferrocyanide Hg(2)Fe(CN)(6) is obtained, but if ferrocyanide is added to mercury(II) various cyanide complexes of mercury are formed. The K(sp) values for the precipitates are reported. 相似文献
993.
A new quantum chemical definition of oxidation number is proposed, in the present paper, as a direct generalization of the corresponding classical definition. According to the proposed general definition, the oxidation number can be calculated by use of molecular orbital data and a population analysis method or by use of other quantum chemical methods. For the practical calculation, we present a corresponding concrete calculation procedure within the framework of the maximum overlap population principle, which is very simple and very easy to use. The calculated numerical results are, on the whole, in good agreement with chemists' intuitive concepts of chemical bonding. 相似文献
994.
Cyrille Ceugniet Ltitia Lepetit Nancy Lauth De Viguerie Henry Jammes Nicole Peyrot Monique Rivire 《Journal of chromatography. A》1998,810(1-2):237-240
A high-performance liquid chromatographic (HPLC) procedure was developed to allow the rapid separation, in a single run, of a mixture of the main retinal isomers (all-trans, 13-cis, 9-cis), all-trans-retinol, and of the two major photooxygenated photoproducts (5,8-peroxyretinal and 5,6-epoxyretinal). The mixture was separated by HPLC on an octadecyl (ODS) column with 16% (v/v) diethyl ether in hexane as mobile phase and anthracene as the internal standard. A commercial type cosmetic formulation containing 0.05% all-trans-retinal was analyzed successfully for this analyte. 相似文献
995.
996.
DunWANG DeShengYU FangQIN LinFANG PingGONG 《中国化学快报》2004,15(1):19-22
Some new derivatives of 3-ethoxycarbonyl-6-bromo-5-hydroxyindoles were designedand prepared, their antiviral activity were determined in cell culture with virus cytopathic effect assay. The results showed compound Ⅶ b, Ⅶ h exhibited potential antiviral activity. 相似文献
997.
Highly concentrated, well-stable gold colloids can be prepared directly from an amine-bearing polyelectrolyte-HAuCl4 aqueous solution at room temperature. It is found that increasing molar ratio of polyelectrolyte to gold leads to increasing particle size. UV-vis spectra, transmission electron microscopy (TEM), and X-ray photoelectron spectra (XPS) were used to characterize the products thus formed. 相似文献
998.
[structure: see text] Platinum(II) terpyridyl acetylide complex (1) was incorporated into Nafion membranes as a photosensitizer, and the Nafion was immersed in an aqueous or organic solution of 7-dehydrocholesterol, alpha-pinene, or cyclopentadiene. This photosensitizer system can generate singlet oxygen ((1)O(2)) in high quantum yield to oxidize the alkenes in the solution outside the Nafion and can be easily removed from the reaction vessel at the end of the photooxidation. 相似文献
999.
Acid-catalysed reactions of tri-O-acetyl-D-glucal with benzotriazole, 5,6-dimethylbenzotriazole, 5,6-dichlorobenzotriazole and 6-chloropurine have been found to give anomeric mixtures of the corresponding 2′,3′-unsaturated N-glycosyl derivatives with the α-anomers preponderating. When tri-O-acetyl-D-galactal was used the 3′,4′,6′-tri-O-acetyl-α- and β-D-lyxo-hexopyranosyl nucleoside analogs were obtained. The conformation and anomeric configuration of all the N-glycosyl compounds obtained were assigned by NMR studies. 相似文献
1000.
The chiral phosphine‐oxazoline ligands 3 and 4 bearing 4‐alkoxymethyl substituents on the oxazoline ring with (R)‐configuration were prepared from L‐serine methyl ester in 66% and 33% yields, respectively. Along this synthetic pathway, the β‐hydroxylamides derived from L‐serine methyl ester and 2‐halobenzoyl chlorides were expediently converted to the corresponding oxazolines by using diethylaminosulfur trifluoride as the activation agent. Potassium diphenylphosphide was the reagent of choice for replacing the bromine atom on the phenyl ring, giving the desired oxazoline‐phosphine ligands 3 and 4 . Together with [Pd(η3‐allyl)Cl]2, ligands 3 and 4 induced an enantioselective allylic substitution reaction of 1,3‐diphenyl‐2‐pro‐penyl acetate by dimethyl malonate. Although ligands 3 and 4 exhibit the (R)‐configuration, differing from the (S)‐configuration of Pfaltz‐Helmchen‐Williams phosphine‐oxazoline ligands, all these ligands led to the same enantiotopic preference in the allylic substitution reaction. To facilitate the recovery and reuse of the phosphine‐oxazoline ligand, immobilization on Merrifield resin was attempted, albeit in low loading. 相似文献