全文获取类型
收费全文 | 11141篇 |
免费 | 1333篇 |
国内免费 | 784篇 |
专业分类
化学 | 7947篇 |
晶体学 | 69篇 |
力学 | 826篇 |
综合类 | 98篇 |
数学 | 430篇 |
物理学 | 3888篇 |
出版年
2024年 | 15篇 |
2023年 | 90篇 |
2022年 | 308篇 |
2021年 | 302篇 |
2020年 | 356篇 |
2019年 | 296篇 |
2018年 | 314篇 |
2017年 | 409篇 |
2016年 | 458篇 |
2015年 | 431篇 |
2014年 | 522篇 |
2013年 | 722篇 |
2012年 | 742篇 |
2011年 | 621篇 |
2010年 | 527篇 |
2009年 | 498篇 |
2008年 | 546篇 |
2007年 | 583篇 |
2006年 | 590篇 |
2005年 | 466篇 |
2004年 | 457篇 |
2003年 | 410篇 |
2002年 | 354篇 |
2001年 | 291篇 |
2000年 | 310篇 |
1999年 | 348篇 |
1998年 | 280篇 |
1997年 | 296篇 |
1996年 | 231篇 |
1995年 | 221篇 |
1994年 | 177篇 |
1993年 | 141篇 |
1992年 | 149篇 |
1991年 | 118篇 |
1990年 | 125篇 |
1989年 | 106篇 |
1988年 | 94篇 |
1987年 | 74篇 |
1986年 | 51篇 |
1985年 | 43篇 |
1984年 | 45篇 |
1983年 | 24篇 |
1982年 | 27篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
171.
Terenina M. B. Misharina T. A. Krikunova N. I. Golovnya R. V. 《Russian Chemical Bulletin》2001,50(6):1032-1036
Capillary gas chromatography was applied to study the sorption of aliphatic ketones (C6—C11), including metamers, from aqueous solutions by corn starch cryotextures. The amount of ketones sorbed by cryotextures depends linearly on their concentrations in the initial sol. Equations describing the concentration dependence of sorption were proposed. The shape of sorption isotherms reflects the strength of sorption. The binding constants and the number of binding sites were determined for weakly sorbed ketones. The length of alkyl substituent and the position of the functional group are the crucial factors governing the sorption of ketones under conditions of excess binding sites. It was found that the degree of sorption increases with an increase in the carbon chain length from 6 to 9 carbon atoms. The presence of cooperation of binding sites for ketone sorption by cryotextures was demonstrated. The major part of ketones is sorbed irreversibly. This fact points to the formation of supramolecular complexes. Ketones with lower molecular masses are better sorbed by cryotextures than by native starch grains. 相似文献
172.
H. Balard M. Sidqi E. Papirer J. B. Donnet A. Tuel H. Hommel A. P. Legrand 《Chromatographia》1988,25(8):712-716
Summary The surface properties of silicas modified with – diols having between 4 and 16 carbon atoms were investigated by inverse gas chromatography. It is shown, that the value of the dispersive component of the surface energy does not change monotonously: a minimum value is recorded when the surface is covered by a monolayer of methylene groups. Further, when measuring the adsorption enthalpies of polar probes, an alternation of their H values is observed: grafts having an odd number of carbon atoms systematically show higher H values than the others. A trans-trans configuration of the grafted chains which allows optimum interactions is proposed, suggesting a preferential diesterification reaction of both terminal hydroxyl groups of odd diols. 相似文献
173.
174.
A method has been developed for highly sensitive determination of haloperidol in human serum involving a simple extraction procedure followed by gas chromatographic separation. Target components were separated from the extracting solvents with a Van den Berg type solventless sample injector before introduction Into a DB-1 capillary separation column. A surface ionization detector (SID), which has highly selective sensitivity for Substituted amines, was employed for quantitation using bromperidol as an internal standard. Chloroform proved to be the best extracting solvent, yielding a quantitative detection limit of 5 ng/ml (S/N = 2). Comparison of the response to target compounds obtained by the SID, FTD (flame thermionic detector), and FID (flame ionization detector) showed the SID to be superior. 相似文献
175.
建立了气相 质谱联用 (GC/MS)测定苯乙烯中阻聚剂对叔丁基邻苯二酚含量的方法。苯乙烯样品直接进样 ,通过毛细管柱 (HP 1,30m× 0 32mmi.d .× 0 2 5 μm)分离 ,由电子轰击 (EI)源于选择离子监测 (SIM)模式下进行检测。结果表明 ,对叔丁基邻苯二酚含量在 5mg/kg~ 5 0mg/kg时线性关系良好 (r2 =0 9987) ,回收率高 ;与美国材料测试标准ASTMD4 5 90中的分光光度测量法比较具有操作简捷、准确度高的特点。 相似文献
176.
J. U. Keller 《Adsorption》1995,1(4):283-290
The gas adsorbed on the inner surface of a highly porous material like activated carbon or zeolite can be measured by slow damped oscillations of a torsional pendulum. The physical principles and the theory of this method are outlined. Formulas are given relating the increase in mass due to adsorption to changes of the frequency and the logarithmic decrement of slow, damped rotational oscillations of the pendulum. Preliminary measurements of gas adsorption equilibria of nitrogen on activated carbon show that the ratio of the mass adsorbedm, to the mass of the adsorbentm
s
, can be determined by this method with mean absolute error |m/m
s
|0.04%.Dedicated to the memory of Joseph Kestin (1913–1993). 相似文献
177.
178.
氧化锌脱硫中氢和氧的双气氛效应及动力学研究 总被引:4,自引:0,他引:4
用热重法研究了氧化锌脱硫中氢氧的气氛效应以及氢氧共同存在下氧化锌脱硫的微观动力学行为。实验温区为200 ℃~320 ℃,氧化锌粒度为100目~120目。研究结果表明,在0%~40%的体积浓度范围内,氢可促进脱硫反应进行;氧则由于会引起氧化锌表面析硫使得脱硫过程随其浓度的变化复杂化。氢氧双气氛下,氧化锌脱硫动力学行为可用改良收缩核模型进行描述,表面反应活化能和固体扩散活化能分别为14.96 kJ/mol和46.77 kJ/mol。 相似文献
179.
气相色谱法研究配位化合物的热稳定性——ⅩⅢ.普鲁士蓝化合物的热分解及其加氢反应研究 总被引:2,自引:0,他引:2
普鲁士蓝化合物的热分解过程,可分为三个阶段:(1)脱水;(2)Fe3+还原至Fe2+;(3)C≡N-键的断裂。H2气中的热分解由于发生了一系列的加氢反应,分解产物及所对应的分解温度都不同于He气中的情况,其产物的种类增加,C≡N-键的断裂温度降低。普鲁士蓝化合物中,CN-呈典型的双端基配位,可看作是一种双金属配位的活化模型,与CN-呈单端基配位的K3[Fe(CN)6]相比,C≡N-键的活化程度增加,不仅断裂温度降低,且能发生更深度的加氢反应。 相似文献
180.
M. V. Kirov 《Journal of Structural Chemistry》2003,44(3):420-428
A nanostructural approach to analysis of proton ordering in gas hydrate cages has been worked out within the framework of the topological model of strong and weak H-bonds. The approach involves rejection of the periodic boundary conditions, decomposition of the H-bond net into spherical layers, and two-dimensional drawing of the structure of spherical (spheroidal) fragments in the form of conjugate Schlegel diagrams. To analyze proton ordering in the spherical fragments composed of gas hydrate voids, we used the simulated annealing procedure and the correlation extension method proposed earlier. 相似文献