全文获取类型
收费全文 | 112270篇 |
免费 | 7871篇 |
国内免费 | 10017篇 |
专业分类
化学 | 43006篇 |
晶体学 | 640篇 |
力学 | 9759篇 |
综合类 | 1668篇 |
数学 | 37799篇 |
物理学 | 37286篇 |
出版年
2024年 | 164篇 |
2023年 | 993篇 |
2022年 | 2120篇 |
2021年 | 2230篇 |
2020年 | 2365篇 |
2019年 | 2621篇 |
2018年 | 2271篇 |
2017年 | 2651篇 |
2016年 | 2903篇 |
2015年 | 2504篇 |
2014年 | 3805篇 |
2013年 | 7714篇 |
2012年 | 4381篇 |
2011年 | 5027篇 |
2010年 | 4240篇 |
2009年 | 6177篇 |
2008年 | 6879篇 |
2007年 | 7332篇 |
2006年 | 6585篇 |
2005年 | 5554篇 |
2004年 | 5013篇 |
2003年 | 5171篇 |
2002年 | 5256篇 |
2001年 | 4114篇 |
2000年 | 3980篇 |
1999年 | 3496篇 |
1998年 | 3354篇 |
1997年 | 2520篇 |
1996年 | 2242篇 |
1995年 | 1967篇 |
1994年 | 1892篇 |
1993年 | 1533篇 |
1992年 | 1534篇 |
1991年 | 1144篇 |
1990年 | 1004篇 |
1989年 | 843篇 |
1988年 | 754篇 |
1987年 | 637篇 |
1986年 | 557篇 |
1985年 | 603篇 |
1984年 | 596篇 |
1983年 | 310篇 |
1982年 | 474篇 |
1981年 | 517篇 |
1980年 | 380篇 |
1979年 | 379篇 |
1978年 | 307篇 |
1977年 | 292篇 |
1976年 | 213篇 |
1973年 | 152篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
P. Staszczuk J. C. Bazan M. Błachnio D. Sternik N. J. Garcia 《Journal of Thermal Analysis and Calorimetry》2006,86(1):57-68
This paper presents possible applications of thermal analysis, sorptometry
and porosimetry to study physico-chemical properties of Na- and La-montmorillonite
samples, especially for determination of total surface heterogeneity. The
quasi-isothermal thermogravimetric (Q-TG) mass loss and its first derivative
(Q-DTG) curves with respect to temperature and time obtained during programmed
liquid thermodesorption under quasi-isothermal conditions have been used to
study adsorbed layers and heterogeneous properties of the Na- and La-montmorillonites.
Calculations of the desorption energy distribution functions by analytical
procedure using mass loss Q-TG and differential mass loss Q-DTG curves of
thermodesorption under quasi-isothermal conditions of polar and non-polar
liquid vapours preadsorbed on a material surface are presented. Parameters
relating to porosity of samples were determined by sorptometry, mercury porosimetry
and atomic force microscopy (AFM). From nitrogen sorption isotherms from sorptometry
and porosimetry methods, the fractal dimensions of montmorillonites have been
calculated. Moreover, a new approach is proposed to calculate fractal dimensions
of materials obtained from Q-TG curve; this is compared with values obtained
by the above methods. The total heterogeneous properties (energy distribution
function and pore-size distribution functions) of samples studied were estimated.
The radius and pore volume of the tested samples calculated on the basis of
thermogravimetry, sorptometry and porosimetry techniques were compared and
good correlations obtained. 相似文献
992.
Circular high-performance thin-layer chromatography (HPTLC) has been used to differentiate a series of twelve tricyclic neuroleptics, using both normal phase and reverse phase procedures. The use of normal phase systems also allows the resolution of geometric isomers of chlorprothixene, clopenthixol and flupenthixol. Thirteen sulphonamides and Trirnethoprim may also be distinguished using HPTLC. 相似文献
993.
Two predicative theories for superheating limits of a boiling liquid are considered in this work. In the nucleation picture, classical homogeneous nucleation theory is used to calculate superheating temperature at various pressures. In spinodal decomposition picture, stability limits are taken as the superheating temperature. A perturbed-hard chain equation of state was developed and used for the purpose of calculating mechanical stability limit. Calculations are done for the case of normal hexane at different pressures and compared with experimental results. Classical nucleation theory gives good prediction at negative and smaller pressures. While near critical pressure, spinodal picture seems to be more accurate. 相似文献
994.
Thomas F. Brodasky 《Journal of separation science》1978,1(5):239-244
Two new acyltetramic acids related to streptolydigin have been isolated from fermentations of Streptomyces lydicus. The principal members of this complex were resolved by TLC on silica gel. However, the methods of detection, permanganate spray or bioautography, were not suitable for both crude fermentation broths and purified extracts. Gas chromatography is unsuitable for the detection of either underivatized or silylated streptolydigins. High performance liquid chromatography (HPLC) particularly on triethylaminoethyl cellulose is rapid and sensitive and is the method of choice for the analysis of both crude and purified samples. Using high performance liquid chromatography, two components were detected in the complex, which are not observed using any of the other chromatographic procedures. 相似文献
995.
Methyl methacrylate and butyl methacrylate were polymerized in oil-in-water microemulsions that were stabilized by sodium dodecyl sulphate (SDS). A poly(N-acetylethylenimine) (PNAEI) macromer was also included in the recipe, as a cosurfactant and a comonomer. Polymerizations were initiated by UV-irradiation. The average diameters of latex particles, obtained by STM, were in the range of 17-200 nm. The experimental data evidenced that the particle size was mainly dependent on the SDS/PNAEI ratio. Polymerization yields were around 75-85%. The synthesized copolymers have viscosity average molecular weights in the range of 2.1-2.4×106 and glass transition temperatures of 38.0-43.5°C, lower than those obtained without using PNAEI. The investigation by means of FTIR and 1H-NMR techniques revealed that PNAEI was incorporated into the nanoparticles. 相似文献
996.
Kozhevnikov I. S. Kovalev V. L. Rusinov O. N. Chupakhin 《Chemistry of Heterocyclic Compounds》2001,37(9):1136-1140
3-R-6-Phenyl-1,2,4-triazine 4-oxides react with cyclic -diketones (dimethylbarbituric acid, dimedone, and indan) in both acidic (substrate activation) and basic conditions (nucleophile activation) with formation of H-adducts, intermediates in the nucleophilic substitution of hydrogen (SN
H) in 3-R-5-Nu-4-hydroxy-6-phenyl-4,5-dihydro-1,2,4-triazines. Oxidative aromatisation of these intermediates or auto-aromatisation of acylated (benzoyl chloride) at the NOH -adducts with elimination of benzoic acid gave the corresponding substituted 1,2,4-triazine 4-oxides or 1,2,4-triazines. 相似文献
997.
Siavosh Mahboobi Andreas Sellmer Thomas Burgemeister Alexei Lyssenko Dieter Schollmeyer 《Monatshefte für Chemie / Chemical Monthly》2004,135(3):333-342
The synthesis of the naturally occurring and biologically active alkaloids 1 and 2, first isolated from the red ascidian Botryllus leachi by Duran et al. [1], is described and the structure proposed for Botryllazine B (1) is confirmed. The analytical data for 2-(p-hydroxybenzoyl)-4-(p-hydroxyphenyl)imidazole (2) are discussed and compared with the literature. With special emphasis of 1H NMR data the tautomerism of aroylimidazolemethanones is described. 相似文献
998.
S. B. Denisova E. G. Galkin V. T. Danilov Yu. I. Murinov 《Chemistry of Natural Compounds》2003,39(3):237-239
Simple sugars were isolated from the ethanol extract of Glycyrrhiza glabra L. root. The component composition of the carbohydrate fraction was established using GC-MS (gas-chromatographic separation and mass-spectrometric analysis). 相似文献
999.
L. A. Sviridova G. A. Golubeva S. V. Shorunov 《Chemistry of Heterocyclic Compounds》2006,42(9):1185-1189
3-Nitromethylpyrazolidine reacts with derivatives of unsaturated acids and reducing agents with the formation of polyfunctional
compounds of the pyrazolidine nucleus.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1365–1369, September, 2006. 相似文献
1000.
A simple and inexpensive equipment for the optical resolution of enantiomers (and separation of diastereomers) on triacetylcellulose in ethanol at elevated pressure is described. It involves a closed circuit of solvent (pump—column—detector—pump) allowing a continuous chromatography up to 16 cycles without stopping the flow or handling fractions.This useful and versatile method permitting also the determination of enantiomeric purities is illustrated by several examples of centro-, axial- and planarchiral arenes and metallocenes.Herrn Prof. Dr.U. Schmidt, Stuttgart, zum 60. Geburtstag gewidmet. 相似文献