全文获取类型
收费全文 | 6381篇 |
免费 | 239篇 |
国内免费 | 25篇 |
专业分类
化学 | 4139篇 |
晶体学 | 49篇 |
力学 | 166篇 |
综合类 | 1篇 |
数学 | 795篇 |
物理学 | 1495篇 |
出版年
2023年 | 43篇 |
2022年 | 35篇 |
2021年 | 75篇 |
2020年 | 103篇 |
2019年 | 93篇 |
2018年 | 54篇 |
2017年 | 59篇 |
2016年 | 171篇 |
2015年 | 162篇 |
2014年 | 193篇 |
2013年 | 244篇 |
2012年 | 329篇 |
2011年 | 394篇 |
2010年 | 212篇 |
2009年 | 181篇 |
2008年 | 336篇 |
2007年 | 320篇 |
2006年 | 328篇 |
2005年 | 309篇 |
2004年 | 246篇 |
2003年 | 186篇 |
2002年 | 200篇 |
2001年 | 138篇 |
2000年 | 119篇 |
1999年 | 94篇 |
1998年 | 74篇 |
1997年 | 71篇 |
1996年 | 96篇 |
1995年 | 102篇 |
1994年 | 92篇 |
1993年 | 99篇 |
1992年 | 68篇 |
1991年 | 64篇 |
1990年 | 63篇 |
1989年 | 64篇 |
1988年 | 39篇 |
1987年 | 46篇 |
1986年 | 42篇 |
1985年 | 38篇 |
1984年 | 43篇 |
1983年 | 39篇 |
1982年 | 36篇 |
1980年 | 47篇 |
1978年 | 34篇 |
1977年 | 39篇 |
1975年 | 40篇 |
1968年 | 52篇 |
1967年 | 119篇 |
1966年 | 112篇 |
1965年 | 71篇 |
排序方式: 共有6645条查询结果,搜索用时 46 毫秒
41.
The carbobenzyloxy (cbz) protecting group is evaluated for it's potential to enhance the resolution of chiral amine enantiomers using high-performance liquid chromatography (HPLC) and supercritical fluid chromatography (SFC). A series of cbz derivatives of commercially available racemates was prepared and analyzed by enantioselective chromatography using a variety of mobile phases and polysaccharide and Pirkle-type chiral stationary phases (CSPs). The cbz-derivatized product consistently demonstrated enhanced chiral resolution under HPLC and SFC conditions. Improved selectivity and resolution combined with an automated preparative HPLC or SFC system can lead to the rapid generation of highly purified enantiomers of desirable starting materials, intermediates or final products. 相似文献
42.
The palladium-catalyzed arylation of rac-(E)-3-acetoxy-1,3-diphenylprop-1-ene with arylboronic acids was studied under controlled microwave irradiation conditions. A variety of different catalysts, bases, and solvents were explored in order to achieve optimum yields in the shortest possible reaction times. The best isolated yields were obtained using Pd2(dba)3·CHCl3/PPh3 as the catalytic system, potassium phosphate monohydrate as the base, and toluene/H2O as a solvent system. Microwave irradiation using 5 mol % of the palladium catalyst for 90 s (max. temp 170 °C) generally afforded the cross-coupling products in good to excellent yields. 相似文献
43.
The hydrogen-deuterium exchange of H-2 in 4-pyrimidone, a number of 1- and 3-alkyl-4-pyrimidones and several of their thione analogs in deuterium oxide at moderate temperatures is reported. This reaction is apparently not susceptible to acid or base catalysis. Cations of the 4-pyrimidones were found not to exchange H-2 at all in acid media. Catalytic amounts of bases do not alter the exchange rates whereas more concentrated alkali decompose the pyrimidone. However, 1,4(3,4)-dihydro-1,3-dimethyl-4-oxopyrimidinium iodide (and its 6-methyl analog) exchange H-2 quite rapidly in neutral deuterium oxide, almost instantly when triethylamine is added as a catalyst, and very slowly in dilute solutions of deuterium chloride in deuterium oxide. Mechanisms are proposed to account for these phenomena. 相似文献
44.
Cyclo-heptane, -octane, -decane, -dodecane and -octadecane have been fluorinated in the vapour phase with cobaltic fluoride. The perfluorocarbons obtained revealed varying degrees of skeletal rearrangements. Thus, cycloheptane gave perfluoro-cycloheptane and -methylcyclohexane; cyclooctane gave at least eight fluorocarbons including-bicyclo(3,3,0)octane and -cyclooctane; cyclodecane gave a complex mixture from which were isolated perfluoro cis- and trans-bicyclo(4,4,0)decanes but no perfluorocyclodecane; cyclododecane and cyclooctadecane gave complex fluorocarbon mixtures in which none of the fluorocarbons with the original cycloalkene skeleton could be detected.Tetradecafluorobicyclo(3,3,0)octane gave dodecafluorobicyclo (3,3,0)oct-1(5)-ene and decafluorobicyclo(3,3,0)octa-di-1(5), 2-ene when pyrolysed over iron gauze.The fluorination of cyclooctane also afforded 1-pentadecafluorocyclooctane which was dehydrofluorinated to tetradecafluorocyclooctene. This was converted to a range of derivatives including dodecafluorosuberic acid, 1,2-dichlorotetradecafluorocyclooctane, 1-methoxy tridecafluorocyclooctene and tetradecafluorocyclooctanone. 相似文献
45.
46.
I. Bauer 《Fresenius' Journal of Analytical Chemistry》1967,231(6):464
Ohne Zusammenfassung 相似文献
47.
Ohne Zusammenfassung7. Mitt.:Hermann Schmid undG. Bauer, Mh. Chem.96, 1508 (1965); dort ältere Mitt. dieser Reihe zitiert. 相似文献
48.
The adsorption, diffusion and desorption of chlorine on and from stoichiometric, reduced and partially reduced (defective) rutile TiO2{110} are investigated using ab initio density functional theory (DFT) calculations. Theoretical results are compared with experimental investigations, and microkinetic simulations based on DFT values are then used to verify the diffusion mechanisms assumed in the experimental investigations. 相似文献
49.
50.
Hae‐Jeong Lee Christopher L. Soles Da‐Wei Liu Barry J. Bauer Wen‐Li Wu 《Journal of Polymer Science.Polymer Physics》2002,40(19):2170-2177
X‐ray reflectivity has been used to determine the mass uptake of probe molecules in porous thin films supported on thick silicon wafers. The adsorption occurs by capillary condensation when the films are exposed to probe vapor at controlled partial vapor pressures. The probe solvent partial pressure was varied by mixing saturated air and dry air at constant temperature or by changing sample temperature at a constant vapor concentration. Pore size distribution in the films can be calculated from the probe uptake with typical porosimetric approaches such as the application of the Kelvin equation to convert partial pressure into pore size. For illustration, the pore size distribution of three different nanoporous thin films, the primary candidate of ultra‐low‐k interlevel dielectrics in the next generation of integrated circuit chips, was determined with this technique. These samples represent different generations of low‐k dielectrics developed by industry. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2170–2177, 2002 相似文献