全文获取类型
收费全文 | 2236篇 |
免费 | 139篇 |
国内免费 | 198篇 |
专业分类
化学 | 1313篇 |
晶体学 | 7篇 |
力学 | 408篇 |
综合类 | 13篇 |
数学 | 289篇 |
物理学 | 543篇 |
出版年
2023年 | 28篇 |
2022年 | 44篇 |
2021年 | 75篇 |
2020年 | 73篇 |
2019年 | 55篇 |
2018年 | 43篇 |
2017年 | 53篇 |
2016年 | 65篇 |
2015年 | 41篇 |
2014年 | 60篇 |
2013年 | 147篇 |
2012年 | 119篇 |
2011年 | 89篇 |
2010年 | 89篇 |
2009年 | 123篇 |
2008年 | 143篇 |
2007年 | 155篇 |
2006年 | 131篇 |
2005年 | 113篇 |
2004年 | 118篇 |
2003年 | 101篇 |
2002年 | 76篇 |
2001年 | 90篇 |
2000年 | 74篇 |
1999年 | 64篇 |
1998年 | 59篇 |
1997年 | 54篇 |
1996年 | 34篇 |
1995年 | 33篇 |
1994年 | 26篇 |
1993年 | 22篇 |
1992年 | 19篇 |
1991年 | 25篇 |
1990年 | 22篇 |
1989年 | 17篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1979年 | 2篇 |
1978年 | 8篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有2573条查询结果,搜索用时 31 毫秒
31.
32.
33.
34.
35.
The reductions of several substituted acetophenones using supercritical 2-propanol were carried out to estimate the Hammett's reaction constant (ρ=0.33). Also, the reduction of acetophenone using supercritical deuteriated 2-propanol was carried out to determine the rate-determining step. The kinetic isotope effects were observed in the reduction using 2-deuterio-2-propanol (kH/kD=1.6) and O-deuterio-2-propanol (kH/kD=2.0). These findings suggest that the reaction proceeds via a cyclic transition state between acetophenone and 2-propanol similar to that of the Meerwein-Ponndorf-Verley reduction. 相似文献
36.
G. J. Dear D. N. Mallett D. M. Higton A. D. Roberts S. A. Bird H. Young R. S. Plumb I. M. Ismail 《Chromatographia》2002,55(3-4):177-184
Summary In this paper we investigate the potential of alkyl-bonded silica monolithic columns for the isolation and identification
of drug-related components in biological fluids. Up to 6 columns have been connected in series to produce a chromatographic
system with up to 40,000 plates. This high-resolution chromatography system has been coupled to both MS and NMR to enable
efficient detection and characterisation of drug-related components in biological fluids. The use of six coupled columns has
been shown to give enhanced resolution over a high quality silica particulate column packed with 3 μm material which exhibits
the same back pressure. The effect of volume and mass load on the performance of monolithic columns for semi-preparative chromatography
of biological fluids has also been investigated. In these studies it was possible to inject up to 100 mL of neat urine with
no loss of chromatographic performance. Furthermore, upon re-testing, the columns showed similar chromatographic performance.
Again several columns were serially connected, producing enhanced resolution in the semi-preparative mode. 相似文献
37.
J. Popplewell A. Al-Qenaie S. W. Charles R. Moskowitz K. Raj 《Colloid and polymer science》1982,260(3):333-338
The thermal conductivity of a number of ferrofluids consisting of colloidally dispersed Fe3O4 particles in diester, hydrocarbon, water and fluorcarbon carriers have been measured at 38°C. The variation in thermal conductivity with particle concentration is well described by Tareef's equation (1940). This has enabled the ratio of the physical to magnetic size to be determined and compared with estimates of the ratio obtained from electron micrographs and magnetic measurements.The fit between theory and experiment is particularly good for hydrocarbon carrier fluids giving the ratio of solid to magnetic radiusR
i/R
m=1.24±0.03 compared with the value obtained from magnetic data and electron micrographs of 1.19±0.07. The corresponding value from the fluids with a diester carrier ranges between 1.1<R
d/R
m<1.3 which is again consistent with microscopy and magnetic data.The application of a magnetic field of 0.1 T had no noticeable effect on the thermal conductivities of ferrofluids. 相似文献
38.
Optimisation of Supercritical Carbon Dioxide Systems for Complexation of Naproxen : Beta-Cyclodextrin 总被引:1,自引:0,他引:1
Susana Junco Teresa Casimiro Nuno Ribeiro Manuel Nunes Da Ponte Helena M. Cabral Marques 《Journal of inclusion phenomena and macrocyclic chemistry》2002,44(1-4):69-73
Supercritical carbon dioxide (scCO2)offers several attractive scenarios for thepharmaceutical processing as an alternativeto aqueous and organic solvents. In thiswork naproxen, a widely used non steroidalanti-inflammatory drug with analgesic andanti-inflammatory properties, was chosenas a model drug. Its complexation with cyclodextrinsimproves the rate and extent of dissolutionof the drug, increase its rate of absorption and mayreduce the unpleasant side-effects of the drug.The interest in using this supercritical technologyled us to develop an experimental unit for the useof supercritical CO2 as a processing medium forthe complexation of naproxen with beta cyclodextrin (CD). 相似文献
39.
聚乙烯塑料在连续超临界水反应器中的油化研究 总被引:1,自引:1,他引:1
在连续超临界水(SCW)反应器中考察了反应温度、停留时间和反应压力对聚乙烯(PE)降解油化的影响。实验结果表明,在120s、25MPa下,从500℃提高到550℃,液体收率呈现先升后降的趋势,在530℃达到最大值(79%);在520℃、25MPa下,随停留时间的延长,PE裂解程度加深,产物轻质化程度提高,导致液体收率降低,停留240s时,气体收率达到43%;反应压力对产物收率的影响较小,气、液产物中烯/烷比随反应压力的增加而增大。 相似文献
40.