全文获取类型
收费全文 | 61778篇 |
免费 | 18972篇 |
国内免费 | 1462篇 |
专业分类
化学 | 69430篇 |
晶体学 | 193篇 |
力学 | 2918篇 |
综合类 | 75篇 |
数学 | 4478篇 |
物理学 | 5118篇 |
出版年
2024年 | 477篇 |
2023年 | 4882篇 |
2022年 | 2116篇 |
2021年 | 3261篇 |
2020年 | 5635篇 |
2019年 | 3073篇 |
2018年 | 2965篇 |
2017年 | 1061篇 |
2016年 | 6626篇 |
2015年 | 6644篇 |
2014年 | 6159篇 |
2013年 | 6546篇 |
2012年 | 4502篇 |
2011年 | 2273篇 |
2010年 | 4470篇 |
2009年 | 4399篇 |
2008年 | 1844篇 |
2007年 | 1438篇 |
2006年 | 706篇 |
2005年 | 560篇 |
2004年 | 433篇 |
2003年 | 343篇 |
2002年 | 365篇 |
2001年 | 230篇 |
2000年 | 221篇 |
1999年 | 230篇 |
1998年 | 172篇 |
1997年 | 228篇 |
1996年 | 252篇 |
1995年 | 296篇 |
1994年 | 216篇 |
1993年 | 317篇 |
1992年 | 195篇 |
1991年 | 153篇 |
1988年 | 175篇 |
1982年 | 143篇 |
1981年 | 176篇 |
1980年 | 206篇 |
1979年 | 209篇 |
1978年 | 219篇 |
1977年 | 335篇 |
1976年 | 394篇 |
1975年 | 478篇 |
1974年 | 501篇 |
1973年 | 325篇 |
1972年 | 455篇 |
1971年 | 416篇 |
1970年 | 625篇 |
1969年 | 459篇 |
1968年 | 502篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Elimination of matrix effects for headspace solid-phase microextraction of important volatile compounds in red wine using a novel coating 总被引:2,自引:0,他引:2
In this paper, hydroxy-terminated silicone oil-butyl methacrylate-divinylbenzene (OH-TSO-BMA-DVB) copolymer was first synthesized and used as stationary phase with the aid of γ-methacryloxypropyltrimethoxylsilane (KH-570) as bridge in solid-phase microextraction (SPME) using sol–gel method and cross-linking technique. It has high extraction efficiency for both polar alcohols and fatty acids and nonpolar esters in comparison with commercial PDMS, PDMS-DVB and PA fibers. A simple and sensitive headspace SPME-gas chromatography (HS-SPME-GC) method using the novel fiber was presented for the simultaneous analysis of both polar alcohols and fatty acids and nonpolar esters in wine. To check the matrix effects, various model wine matrices, including distilled water; 11.5% ethanol/water (v/v) solution; a concentrated synthetic wine; a ‘volatile-free’ wine and a real wine were investigated in detail. Matrix effects were compensated for by using internal standard method and selecting the ‘volatile-free’ wine as working standard. The method presented in this study showed satisfactory linearity, precision, detection limits and accuracy. The recoveries obtained ranged from 85.87 to 104.2%, and the relative standard deviation values were below 9%. The results obtained indicated that the present method is a validated and accurate procedure for the simultaneous determination of both polar and nonpolar aroma compounds in wine. 相似文献
112.
Spectroscopic characterization of effective components anthraquinones in Chinese medicinal herbs binding with serum albumins 总被引:2,自引:0,他引:2
Bi S Song D Kan Y Xu D Tian Y Zhou X Zhang H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(1-3):203-212
The interactions of serum albumins such as human serum albumin (HSA) and bovine serum albumin (BSA) with emodin, rhein, aloe-emodin and aloin were assessed employing fluorescence quenching and absorption spectroscopic techniques. The results obtained revealed that there are relatively strong binding affinity for the four anthraquinones with HSA and BSA and the binding constants for the interactions of anthraquinones with HSA or BSA at 20 degrees C were obtained. Anthraquinone-albumin interactions were studied at different temperatures and in the presence of some metal ions. And the competition binding of anthraquinones with serum albumins was also discussed. The Stern-Volmer curves suggested that the quenching occurring in the reactions was the static quenching process. The binding distances and transfer efficiencies for each binding reactions were calculated according to the F?ster theory of non-radiation energy transfer. Using thermodynamic equations, the main action forces of these reactions were also obtained. The reasons of the different binding affinities for different anthraquinone-albumin reactions were probed from the point of view of molecular structures. 相似文献
113.
114.
Kebin Zhou Hongde Chen Qun Tian Dixin Shen Xiaobai Xu 《Reaction Kinetics and Catalysis Letters》2002,77(1):65-72
Pd/LaFe0.8Co0.2O3 was found to be more active than the Pd/Al2O3 catalyst in propane oxidation. Activity and the oxidation state of palladium were strongly affected by the redox ratio (S) of reactants. Higher propane conversion could be obtained under rich conditions at higher temperatures, contributing to steam reforming. The presence of excess steam would bring about inhibition and oscillation. 相似文献
115.
A new fluorescent compound based on calix[4] arene skeleton was synthesized.Its complexation ability with transition metal ions,such as Fe^3 ,Co^2 ,Ni^2 ,Cu^2 ,Zn^2 and Ag^ ,Was investigated by UV-vis and fluorescent spectra. 相似文献
116.
Synthesis and Characterization of Novel Orange-emitting Iridium(Ⅲ) Complexes with Diphenylquinoline Ligands Containing Fluorinated Substituent 总被引:1,自引:0,他引:1
Xiao Wei ZHANG Chu Luo YANG Zhong An LI Lin Na ZHU Jin Gui QIN Jia GAO Dong Ge MA 《中国化学快报》2006,17(3):411-414
Three new cyclometalated iridium(m) complexes based on ligands of diphenylquinoline with fluorinated subsfituents were prepared, and characterized by elemental analysis (EA), ^1H NMR, and mass spectroscopy (MS). The photophysical and electrophosphorescent properties of the complexes were briefly discussed. 相似文献
117.
118.
二氧化碳多相催化加氢的新进展 总被引:4,自引:0,他引:4
就近年来关于CO2活化、几个重要的CO2多相催化加氢反应及廉价氢的供给的研究进展进行综述。参考文献34篇。 相似文献
119.
Vladimir Rapić Prof. Dr. Karl Schlögl Brigitte Steinitz 《Monatshefte für Chemie / Chemical Monthly》1977,108(4):767-780
Starting from optically active methylferrocene-- and--carboxylic acids (1 a and1 b) of known absolute configuration and enantiomeric purity about 15 chiral ferrocenes (of each isomeric series— and ) were obtained by suitable ligand transformations. Thereby (almost) all possible chiral combinations of the ligands CH3, COOH (COO–), COOCH3, CN and NH2 (NH3
+) were accessible which are necessary for a potential test of approximations of chirality functions for compounds with basic symmetry C5v. The chiroptical properties of these disubstituted ferrocenes are recorded.Preliminary tests using a shortened Ansatz revealed large discrepancies between calculated () and found [M]D-values. Possible reasons for this failure are discussed.
61. Mitt. über Ferrocenderivate
39. Mitt.:A. Meyer, H. Neudeck undK. Schlögl, Chem. Ber.110, 1403 (1977).
60. Mitt.:V. Rapi, K. Schlögl undB. Steinitz, J. Organometal. Chem.94, 87 (1975). 相似文献
61. Mitt. über Ferrocenderivate
39. Mitt.:A. Meyer, H. Neudeck undK. Schlögl, Chem. Ber.110, 1403 (1977).
60. Mitt.:V. Rapi, K. Schlögl undB. Steinitz, J. Organometal. Chem.94, 87 (1975). 相似文献
120.