全文获取类型
收费全文 | 5297篇 |
免费 | 371篇 |
国内免费 | 77篇 |
专业分类
化学 | 3927篇 |
晶体学 | 62篇 |
力学 | 138篇 |
综合类 | 3篇 |
数学 | 350篇 |
物理学 | 1265篇 |
出版年
2024年 | 5篇 |
2023年 | 52篇 |
2022年 | 75篇 |
2021年 | 141篇 |
2020年 | 128篇 |
2019年 | 160篇 |
2018年 | 114篇 |
2017年 | 110篇 |
2016年 | 207篇 |
2015年 | 190篇 |
2014年 | 246篇 |
2013年 | 354篇 |
2012年 | 429篇 |
2011年 | 526篇 |
2010年 | 304篇 |
2009年 | 278篇 |
2008年 | 388篇 |
2007年 | 301篇 |
2006年 | 335篇 |
2005年 | 294篇 |
2004年 | 228篇 |
2003年 | 157篇 |
2002年 | 166篇 |
2001年 | 92篇 |
2000年 | 78篇 |
1999年 | 58篇 |
1998年 | 50篇 |
1997年 | 43篇 |
1996年 | 30篇 |
1995年 | 31篇 |
1994年 | 24篇 |
1993年 | 24篇 |
1992年 | 12篇 |
1991年 | 19篇 |
1990年 | 17篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有5745条查询结果,搜索用时 15 毫秒
101.
Young-a Lee Sang Myung jung Shin Won kang Ok-sang Jung 《Transition Metal Chemistry》2004,29(7):710-713
A facile procedure for synthesizing the mono(hydroxo)tris(carboxylato)platinum(IV) species has been achieved. The reaction of [PtII(OH)2(dmpda)] (dmpda=2,2-dimethyl-1,3-propanediamine) with a 30% aqueous solution of H2O2 in the presence of a carboxylic acid produces a stable [PtIV(OOCR)3(OH)(dmpda)] (R=Me, Et) complex in high yield. The crystal structures of [PtIV(OOCMe)3(OH)(dmpda)] . H2O (triclinic P1 bar, a=8.761(2) Å, b=9.245(3) Å, c=10.659(2) Å, =106.25(2)°, =93.90(2)°, =98.92(2)°, V=813.1(3) Å3, Z=2, R= 0.0474) and [PtIV(OOCEt)3(OH)(dmpda)] (monoclinic P21/c, a=12.777(4) Å, b=10.514(2) Å, c=14.971(3) Å, =107.40(2)°, V=1919.2(8) Å3, Z=4, R=0.0611) show that the hydroxyl group has been selectively positioned at an axial site. The intramolecular hydrogen bond between the OH and C=O moiety exists (O(H)...=C, 2.83 Å for [PtIV(OOCMe)3(OH)(dmpda)] · H2O; 2.72 Å for [PtIV(OOCEt)3(OH)(dmpda)]. Formation of the axial-mono(hydroxo)tris(carboxylato)platinum(IV) species may be ascribed to a combination of `reactive-equatorial effects' with `cis-addition' in the carboxylic acid. 相似文献
102.
103.
Seung‐Chul Choi Jaejung Ko Sang Ook Kang Won‐Sik Han Ki‐Young Choi 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(3):m85-m87
The copper(II) ion in the syn–anti carboxylate‐bridged one‐dimensional zigzag chain title complex, {[Cu(C16H18N3O2)]ClO4}n, exhibits a distorted trigonal–bipyramidal environment. Two N atoms and one carboxylate O atom of the ligand form the basal plane, while the axial positions are filled by an N atom of the ligand and one O atom belonging to the carboxylate group of an adjacent molecule. The crystal packing is enhanced by C—H⋯O(perchlorate) hydrogen bonds. 相似文献
104.
Top layers of γ-Al2O3 composite membranes have been modified by the silane coupling technique using phenyltriethoxysilane for improving the separation factor of CO2 to N2. The separation efficiency of the modified membranes was strongly dependent upon the hydroxylation tendency of the support materials and the amount of the special functional group (i.e. phenyl radical) which was coupled onto a top layer. The separation factor through the TiO2 supported γ-Al2O3 membrane was found to be fairly enhanced by silane coupling, but in case of the -Al2O3 supported membrane was not. The CO2/N2 separation factor through the modified γ-Al2O3/TiO2 composite membrane is 1.7 at 90°C and ΔP = 2 × 105 Pa for the binary mixture containing 50 vol% CO2. The separation factor is proportional to the CO2 concentration in the gas mixture, and the modified membrane is stable up to 100°C. The main mechanism of the CO2 transport through the modified γ-Al2O3 layer is known to be a surface diffusion. 相似文献
105.
Ketones react with an array of aldehydes in dioxane at 80 °C in the presence of a catalytic amount of RuCl2(PPh3)3 along with KOH to give the corresponding α-alkylated ketones in moderate to good yields. A reaction pathway involving base-catalyzed cross-aldol reaction between ketones and aldehydes to form α,β-unsaturated ketones and regioselective reduction of carbon-carbon double bond of α,β-unsaturated ketones is proposed for this catalytic process. 相似文献
106.
S. M. Jeong S.-B. Park S.-S. Hong C.-S. Seo S.-W. Park 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(2):349-356
Summary The
electrolytic reduction of U3O8 powder was carried out
using LiCl-Li2O molten salt in a 20-kg U3O8
batch cell to verify the feasibility of the process. As the current passes the
cell, the decomposition of Li2O and the reduction of U3O8
occur simultaneously in a cathode assembly and oxygen gas evolvs at the anode.
The results from a 20-kg U3O8 scale cell were compared
with data obtained from a bench scale cell. The results suggest a successful
demonstration of this process, exhibiting a reduction conversion of U3O8
of more than 99% in a batch.</p>
</p> 相似文献
107.
Koketsu M Choi SY Ishihara H Lim BO Kim H Kim SY 《Chemical & pharmaceutical bulletin》2002,50(12):1594-1596
This study reports depigmenting potency of 1,3-selenazol-4-one derivatives, which would be based upon the finding of direct inhibition to mushroom tyrosinase. 1,3-Selenazol-4-one derivatives exhibited inhibitory effect on dopa oxidase activity of mushroom tyrosinase. In this study, inhibitory effects of six kinds of 1,3-selenazol-4-one derivatives (A, B, C, D, E and F) on mushroom tyrosinase were investigated. Compounds at a concentration of 500 microM exhibited 33.4-62.1% of inhibition on dopa oxidase activity of mushroom tyrosinase. Their inhibitory effects were higher than that of kojic acid (31.7%), a well known tyrosinase inhibitor. 2-(4-Methylphenyl)-1,3-selenazol-4-one (A) exhibited the strongest inhibitory effect among them dose-dependently and in competitive inhibition manner. 相似文献
108.
Ahn YH Park EJ Cho K Kim JY Ha SH Ryu SH Yoo JS 《Rapid communications in mass spectrometry : RCM》2004,18(20):2495-2501
The enrichment of phosphopeptides using immobilized metal ion affinity chromatography (IMAC) and subsequent mass spectrometric analysis is a powerful protocol for detecting phosphopeptides and analyzing their phosphorylation state. However, nonspecific binding peptides, such as acidic, nonphosphorylated peptides, often coelute and make analyses of mass spectra difficult. This study used a partial chemical tagging reaction of a phosphopeptide mixture, enriched by IMAC and contaminated with nonspecific binding peptides, following a modified beta-elimination/Michael addition method, and dynamic mass analysis of the resulting peptide pool. Mercaptoethanol was used as a chemical tag and nitrilotriacetic acid (NTA) immobilized on Sepharose beads was used for IMAC enrichment. The time-dependent dynamic mass analysis of the partially tagged reaction mixture detected intact phosphopeptides and their mercaptoethanol-tagged derivatives simultaneously by their mass difference (-20 Da for each phosphorylation site). The number of new peaks appearing with the mass shift gave the number of multiply phosphorylated sites in a phosphopeptide. Therefore, this partial chemical tagging/dynamic mass analysis method can be a powerful tool for rapid and efficient phosphopeptide identification and analysis of the phosphorylation state concurrently using only MS analysis data. 相似文献
109.
Won Young Jung Seung Hee Baek Seong Soo Park Gun-Dae Lee Euh Duck Jeong Hyun Gyu Kim Seong-Soo Hong 《Reaction Kinetics and Catalysis Letters》2007,91(2):233-240
The nanosized titania and TiO2/SiO2 particles were prepared by the microwave-hydrothermal method. The effect of physical properties TTIP/TEOS ratio and calcination
temperature has been investigated. The major phase of the pure TiO2 particle is of the anatase structure, and a rutile peak was observed above 800°C. In TiO2/SiO2 particles, however, no significant rutile phase was observed, although the calcination temperature was 900°C. No peaks for
the silica crystal phase were observed at either silica/titania ratio. The crystallite size of TiO2/SiO2 particles decreases as compared to pure TiO2 at high calcination temperatures. The TiO2/SiO2 particles show higher activity on the photocatalytic decomposition of orange II as compared to pure TiO2 particles. 相似文献
110.
Aromatic molecular "clips" bearing two symmetrically bound platinum moieties have been prepared. The molecular "clip" 4 readily self-assembled with linear linkers such as 4,4'-bipyridyl, 1,4-bis[2-(4-isocyano-3,5-diisopropylphenyl)ethynyl]benzene, and nicotinic acid to form molecular rectangles. The overall dimensions of the rectangle 7 were 7.3 Angstroms x 15.3 Angstroms. The molecular "clip" also self-assembled with tritopic pyridyl and isocyanide ligands to form trigonal prismatic frameworks. The characterization of the supramolecules by multinuclear NMR, electrospray mass spectrometry, and X-ray crystal structures is also reported. 相似文献