全文获取类型
收费全文 | 80664篇 |
免费 | 5389篇 |
国内免费 | 3813篇 |
专业分类
化学 | 4640篇 |
晶体学 | 55篇 |
力学 | 2761篇 |
综合类 | 629篇 |
数学 | 11462篇 |
物理学 | 8648篇 |
综合类 | 61671篇 |
出版年
2024年 | 123篇 |
2023年 | 432篇 |
2022年 | 818篇 |
2021年 | 1010篇 |
2020年 | 1076篇 |
2019年 | 906篇 |
2018年 | 916篇 |
2017年 | 1289篇 |
2016年 | 1498篇 |
2015年 | 1875篇 |
2014年 | 3720篇 |
2013年 | 3464篇 |
2012年 | 4338篇 |
2011年 | 5167篇 |
2010年 | 4324篇 |
2009年 | 4615篇 |
2008年 | 5246篇 |
2007年 | 6749篇 |
2006年 | 5823篇 |
2005年 | 5550篇 |
2004年 | 4874篇 |
2003年 | 4214篇 |
2002年 | 3406篇 |
2001年 | 2800篇 |
2000年 | 2235篇 |
1999年 | 2038篇 |
1998年 | 1615篇 |
1997年 | 1503篇 |
1996年 | 1342篇 |
1995年 | 1193篇 |
1994年 | 1009篇 |
1993年 | 876篇 |
1992年 | 739篇 |
1991年 | 688篇 |
1990年 | 595篇 |
1989年 | 477篇 |
1988年 | 441篇 |
1987年 | 299篇 |
1986年 | 189篇 |
1985年 | 97篇 |
1984年 | 54篇 |
1983年 | 32篇 |
1982年 | 37篇 |
1981年 | 41篇 |
1980年 | 28篇 |
1979年 | 29篇 |
1978年 | 16篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
Reported here is an analytical method enabling the stereochemical resolution of a new antianginal compound possessing two stereogenic centers, leading to four stereoisomers. Only one of these isomers is currently under development as a novel antianginal agent and consequently, the other three isomers are considered as unwanted chiral impurities. Therefore, an enantioselective method is required in order to check its enantiomeric purity. This paper presents a method exploiting the high efficiency of capillary electrophoresis and the complexing properties of cyclodextrins to achieve the separation of the four stereoisomers of this weakly basic compound (pKa = 7.4). For this purpose, the combination of a neutral cyclodextrin, hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD), and an anionic cyclodextrin, carboxymethyl-beta-cyclodextrin (CM-beta-CD), was added to the separation buffer running in an uncoated silica capillary. After selection of the suitable cyclodextrin system, satisfactorily separation conditions were as follows: 30 mM phosphate buffer (pH 6.4) containing 10 mM of HP-gamma-CD and 10 mM of CM-beta-CD, running voltage +30 kV. The resulting run time and resolutions were respectively about 17 min and between 1.95 and 2.84. Linearity curves (0.993 < r2 < 0.998) are also shown. 相似文献
933.
本文设计并合成了良好水溶性的赖氨酸修饰壳聚糖,并对制备工艺进行了优化.产物通过红外(FTIR)和核磁(1H-NMR)进行了表征,并将其作为壳层材料制备了赖氨酸修饰壳聚糖磁性超微载体.通过光电能谱(XPS)、透射(TEM)、激光粒度仪、X射线衍射(XRD)、磁性能测试(VSM)对载体进行了表征.结果表明,制备的赖氨酸修饰壳聚糖磁性超微载体表面带有大量的氨基(-NH2),粒径分布较为均一(100nm左右),形貌较为规则,并具有良好的超顺磁性,因而该载体具有更加良好的性能. 相似文献
934.
J. A. Azizi D. Dollimore P. J. Dollimore G. R. Heal P. Manley W. A. Kneller W. Jin Yong 《Journal of Thermal Analysis and Calorimetry》1993,40(2):831-847
In this study a relationship between the surface and textural properties of carbon blacks and the gasification process induced thermally in air is noted. A temperature jump method was used to follow the gasification in air and to establish the relevant Arrhenius parameters. This can be associated with the activity of ‘basal’ plane carbon atoms as well as ‘edge’ carbon atoms at the surface. This is based on a model of carbon black structure consisting of the irregular packing of small graphite carbon structures. The carbon black surface was measured using a single measurement of adsorption based essentially on the BET volumetric method. The carbon black surface had a rate of oxidation per unit are which clearly indicated that the lower area carbon blacks had a predominately active area of ‘edge’ atoms at the surface while the surface of the higher area carbon blacks had a predominate amount of ‘basal’ plane graphite carbon atoms. 相似文献
935.
936.
937.
Hydrodynamic properties for a class of nondiffusive particle systems are investigated. The method allows one to study local equilibria for a class of asymmetric zero-range processes, and applies as well to other models, such as asymmetric simple exclusion and misanthropes. Attractiveness is an essential ingredient. The hydrodynamic equations present shock wave phenomena. Preservation of local equilibrium is proven to hold away from the shocks. The problem of breakdown of local ergodicity at the shocks, which was investigated by D. Wick in a particular model, remains open in this more general setup. 相似文献
938.
We consider the equilibrium dynamics of a system consisting of a spin interacting with an ideal Fermi gas on the lattice , 3. We present two examples: when this system is unitarily equivalent to an ideal Fermi gas or to a spin in an ideal Fermi gas without interaction between them. 相似文献
939.
本文用变分过渡态理论,首次对无鞍点的释能反应O+CS→CO+S、O+CO→CO+O和S+CS→CS+S进行了动力学研究,考察了反应动力学瓶颈区性质,计算了反应的速度常数,并将O+CS反应的速度常数值与实验值及经典轨迹计算结果进行了比较,三者基本相符. 相似文献
940.
本文通过对锌(Ⅱ)—硫氰酸盐—孔雀绿体系溶剂浮选过程的考察,提出了待测Zn~(2+)离子从水相被输送到有机相,可以用吸附机理和粘附机理来解释;同时还对影响锌溶剂浮选的主要因素:溶液的pH,气泡的大小和气体流速等进行了讨论。 相似文献