全文获取类型
收费全文 | 116588篇 |
免费 | 5837篇 |
国内免费 | 5697篇 |
专业分类
化学 | 23970篇 |
晶体学 | 416篇 |
力学 | 4591篇 |
综合类 | 692篇 |
数学 | 12391篇 |
物理学 | 22083篇 |
综合类 | 63979篇 |
出版年
2024年 | 260篇 |
2023年 | 912篇 |
2022年 | 1982篇 |
2021年 | 1999篇 |
2020年 | 2158篇 |
2019年 | 1966篇 |
2018年 | 1752篇 |
2017年 | 2155篇 |
2016年 | 2403篇 |
2015年 | 2788篇 |
2014年 | 5098篇 |
2013年 | 5751篇 |
2012年 | 5945篇 |
2011年 | 6549篇 |
2010年 | 5241篇 |
2009年 | 6613篇 |
2008年 | 6921篇 |
2007年 | 8304篇 |
2006年 | 7402篇 |
2005年 | 6257篇 |
2004年 | 5470篇 |
2003年 | 5512篇 |
2002年 | 5494篇 |
2001年 | 4362篇 |
2000年 | 3849篇 |
1999年 | 3138篇 |
1998年 | 2721篇 |
1997年 | 1940篇 |
1996年 | 1822篇 |
1995年 | 1617篇 |
1994年 | 1521篇 |
1993年 | 1203篇 |
1992年 | 1219篇 |
1991年 | 954篇 |
1990年 | 819篇 |
1989年 | 718篇 |
1988年 | 587篇 |
1987年 | 504篇 |
1986年 | 347篇 |
1985年 | 277篇 |
1984年 | 251篇 |
1983年 | 145篇 |
1982年 | 197篇 |
1981年 | 185篇 |
1980年 | 125篇 |
1979年 | 162篇 |
1978年 | 131篇 |
1977年 | 124篇 |
1976年 | 79篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
通过对行动不便者在居住小区内的户外生活实态及障碍的调查研究,总结出行动不便者对户外居住环境的需求和意愿,为使无障碍居住环境设计提供理论依据。 相似文献
922.
杨学江 《无锡职业技术学院学报》2007,6(3):72-73
前不久,笔者对我院即将毕业的第一届科技日语专业学生进行了一次问卷调查,旨在掌握、了解首届学生的学习状况,提高教学质量和效果,满足社会和学生的需求。该文针对教学存在的问题进行了分析研究,并提出了改进措施。 相似文献
923.
The authors give error estimates, a Voronovskaya-type relation, strong converse results and saturation for the weighted approximation of functions on the real line with Freud weights by Bernstein-type operators. 相似文献
924.
We develop an effective numerical method of studying large-time properties of reversible reaction-diffusion systems of type
A + B ↔ C with initially separated reactants. Using it we find that there are three types of asymptotic reaction zones. In particular
we show that the reaction rate can be locally negative and concentrations of species A and B can be nonmonotonic functions
of the space coordinate x, locally significantly exceeding their initial values.
Received 6 June 2002 / Received in final form 20 January 2003 Published online 7 May 2003 相似文献
925.
年龄相关的种群扩散系统的最优分布控制 总被引:5,自引:1,他引:4
本文讨论年龄相关的种群扩散系统的最优分布控制 ,证明了最优分布控制的存在性 ,得到了分布控制为最优的充分必要条件及确定最优控制的最优性组 . 相似文献
926.
A. A. Kuznetsova V. I. Mikhailenko A. Yu. Popovskii 《Journal of Applied Spectroscopy》2004,71(5):648-653
Two types of absorption centers, one being related to monomers and the other to dimers, have been revealed by the method of statistical analysis of the normalized absorption spectra of a superthin interlayer of nitrobenzene of variable thickness formed on activated surfaces of quartz and barium fluoride and measured for different thicknesses of the interlayer. On a decrease in the interlayer thickness the concentration of dimers increases. 相似文献
927.
Periodic, self-consistent, density functional theory (GGA-PW91) calculations are performed for both surface and subsurface atomic hydrogen on and in Ni(1 1 1). At a low coverage (θ=0.25 ML), the binding energies (BEs) of a hydrogen atom in surface fcc, subsurface octahedral (first layer), and subsurface octahedral (second layer) sites are −2.89, −2.18, and −2.11 eV, respectively. The activation energy barriers for hydrogen diffusion from the surface to the first subsurface layer and from the first to the second subsurface layer are estimated to be 0.88 and 0.52 eV, respectively. In the entire coverage range studied, hydrogen occupies surface fcc and hcp sites and subsurface octahedral sites. In addition, the magnitude of the BE per hydrogen atom and the magnetization of the nickel slabs both decrease as hydrogen coverage increases. Vibrational frequencies of hydrogen at various surface and subsurface sites are calculated and are in reasonable agreement with experimental data. A phase stability calculation with a 2 × 2 surface unit cell shows that a p(2 × 2)-2H overlayer structure (θ=0.5 ML) and a p(1 × 1)-1H structure (θ=1.0 ML) are stable at low hydrogen pressures, in agreement with numerous experimental results. A very large increase in pressure is required to populate subsurface sites. After such an increase occurs, the first subsurface layer is filled completely. 相似文献
928.
Enrique Casanovas 《Mathematical Logic Quarterly》2003,49(5):475-478
We prove a property of generic homogeneity of tuples starting an infinite indiscernible sequence in a simple theory and we use it to give a shorter proof of the Independence Theorem for Lascar strong types. We also characterize the relation of starting an infinite indiscernible sequence in terms of coheirs. 相似文献
929.
930.
Ching-Hua Kuo 《Analytica chimica acta》2003,482(1):47-58
An efficient micellar electrokinetic chromatography (MEKC) method has been developed for the analysis of nine anthraquinones and bianthrones in rhubarb. A chemometric approach was used to search for the optimum conditions of separation. Those factors which were found to be significant with a screening design were further optimized with a central composite face-centered (CCF) design. Acetonitrile concentration was found to be the most influential, not only in resolution, but also in analysis time and peak asymmetry. With the optimized conditions: 15 mM sodium tetraborate/15 mM sodium dihydrogenphosphate buffer, 30 mM sodium deoxycholate, pH 8.6, 17 vol.% acetonitrile and 28 kV, nine tested analytes were baseline-separated within 14 min. The method was validated to analyze the rhubarb material. Solid-phase extraction (SPE) was manipulated to remove interfering substances. Five anthraquinones and two glycosidic bianthrones were detected and quantificated. The method should be suitable for determining these major active principles in rhubarb crude drugs. 相似文献