全文获取类型
收费全文 | 2232篇 |
免费 | 87篇 |
国内免费 | 540篇 |
专业分类
化学 | 1568篇 |
晶体学 | 16篇 |
力学 | 453篇 |
综合类 | 2篇 |
数学 | 197篇 |
物理学 | 623篇 |
出版年
2024年 | 4篇 |
2023年 | 78篇 |
2022年 | 54篇 |
2021年 | 68篇 |
2020年 | 73篇 |
2019年 | 59篇 |
2018年 | 45篇 |
2017年 | 79篇 |
2016年 | 66篇 |
2015年 | 50篇 |
2014年 | 88篇 |
2013年 | 115篇 |
2012年 | 106篇 |
2011年 | 213篇 |
2010年 | 139篇 |
2009年 | 198篇 |
2008年 | 185篇 |
2007年 | 216篇 |
2006年 | 164篇 |
2005年 | 117篇 |
2004年 | 97篇 |
2003年 | 118篇 |
2002年 | 79篇 |
2001年 | 75篇 |
2000年 | 65篇 |
1999年 | 55篇 |
1998年 | 61篇 |
1997年 | 38篇 |
1996年 | 26篇 |
1995年 | 22篇 |
1994年 | 23篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1988年 | 14篇 |
1987年 | 11篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有2859条查询结果,搜索用时 31 毫秒
41.
42.
The relaxation properties of water saturated in porous core are discussed and the distribution of proton transverse relaxation time and bi-exponential model of longitudiual relaxation time are obtained, which provide an illustration for two-model of fluids saturated in porous media. The cutoff value of T_1 based on relaxation specific property of fluids in porous core is adopted to improve the correlation between permeability and ?4T1b2. 相似文献
43.
44.
Summary A new expression which permits the prediction of the net retention volumes in gas chromatography with column packings of coated
porous polymers is reported. The porous polymers Chromosorb 101 and Chromosorb 102 were used as supports and squalane, Ethofat
and Carbowax 20M as stationary phases at three different column temperatures of 80°C, 100°C and 150°C. Several organic compounds
of various polarity were used as test compounds and the net retention volumes, VNtheor, have been calculated according to this new expression. The VNtheor values were compared with the experimental net retention volumes, VNexp, and it was found that the difference between these two values is dependent on the type of compound and column packing. Nevertheless,
the elution order could be predicted in most cases. 相似文献
45.
Katarzyna Samson Anna Klisiska Irena Gressel Barbara Grzybowska 《Reaction Kinetics and Catalysis Letters》2002,77(2):309-315
VOx/TiO2 and MoOx/TiO2 catalysts with the addition of Re (Re/V or Mo = 0.5) were synthetized and tested in oxidative dehydrogenation of propane and in reduction by propane. XPS measurements showed depletion of the surface in Re. The Re additive does not affect the total conversion of propane, but increases the selectivity to propene. The effect is more pronounced for the MoOx/TiO2 catalyst. The increase in the selectivity to propene is accompanied with the increase in the reducibility of the catalysts. 相似文献
46.
The Incorporation of Titania into Modified Silicates for Solar Photodegradation of Aqueous Species 总被引:2,自引:0,他引:2
Lowell R. Matthews David Avnir Alexander D. Modestov Srinivasan Sampath Ovadia Lev 《Journal of Sol-Gel Science and Technology》1997,8(1-3):619-623
A new class of sol-gel-derived photocatalytic materials has been synthesized and used in solar-assisted photodegradation studies. The materials are comprised of a homogeneous dispersion of commercial TiO2 powder into silica and organically modified silicate (Ormosil) hosts. The efficiency of the photocatalytic properties of these TiO2-containing materials was determined by their relative performance in the solar photodecomposition of aqueous rhodamine B. The improved adsorption properties of the modified materials compared to commercial TiO2 increase the photodecomposition rate and the buoyancy properties, although excess hydrophobicity decreases the wetted section of the catalyst and its photocatalytic performance. These materials can be used as floatable catalysts for solar-assisted water purification. 相似文献
47.
徐灿 《高等学校化学学报》1997,18(6):943-946
利用XeCl准分子激光烧蚀多种硅氧多孔结构材料,在负离子通道测得丰富的「(SiO2)nX」^-负离子团簇,并讨论了多孔网结构和表面活性基团的分布对激光能量的吸收,传输及团簇产生的重要作用。 相似文献
48.
K. E. Collins M. L. M. M. Granja R. G. Pereira Filho T. A. Anazawa I. C. S. F. Jardim 《Chromatographia》1997,45(1):99-103
Summary Poly(methyloctylsiloxane) (PMOS), sorbed into the pores of HPLC silica particles by solvent evaporation, can function as a
useful stationary phase for reversed-phase chromatography. The present work addresses the question of how the PMOS is distributed
in the pores. Measurements of the surface area (BET, N2) of a series of partially loaded samples (0–40% PMOS, m/m) using a typical batch of HPLC silica (10 μm irregular particles
with 6 nm pores) show that the specific surface area of the samples decreases linearly with the specific loading (mass of
PMOS per gram of silica). This result is not consistent with a “film” model in which the PMOS is deposited uniformly on the
pore walls, but is consistent with a model in which long segmented “plugs” of PMOS are deposited within the pore system.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
49.
50.
Summary On-line coupled HPLC-GC has been used for the fractionation and analysis of polychlorobiphenyls (PCB) according to their planarity.
HPLC elution with porous graphitic carbon (PGC) as stationary phase, enables fractionation of PCB into classes according to
the amount ofortho-substitution, which is related to congener toxicity. This is a preliminary step before GC analysis, which enables complete
separation of PCB congeners according to vapour pressure. Conditions for HPLC-HRGC coupling were optimised, in particular
the appropriate proper HPLC solvent was selected, because it determines eluent strength and selectivity and the transfer conditions.
Different solvent were studied—n-hexane, dichloromethane, benzene, toluene, and their mixtures.
Samples containing PCB standards and the commercial mixtures Aroclor 1242 and 1254 were analysed. Dichloromethane-n-hexane, 1:1, was selected as mobile phase for separation of poly-ortho from mono-ortho PCB; benzene-dichloromethane 30:70 resulted in the best separation of the most retained non-ortho-substituted PCB. Under these conditions the co-solvent trapping procedure, performed by adding 4% ethylbenzene as co-solvent,
was used as transfer technique to overcome the drawback of losses of volatile congeners.
Appropriate analysis conditions were successfully used to fractionate the technical PCB formulations Aroclor 1242 and 1254. 相似文献