全文获取类型
收费全文 | 46893篇 |
免费 | 8441篇 |
国内免费 | 24602篇 |
专业分类
化学 | 46014篇 |
晶体学 | 891篇 |
力学 | 2956篇 |
综合类 | 1482篇 |
数学 | 8518篇 |
物理学 | 20075篇 |
出版年
2024年 | 432篇 |
2023年 | 1497篇 |
2022年 | 1803篇 |
2021年 | 1851篇 |
2020年 | 1496篇 |
2019年 | 1960篇 |
2018年 | 1355篇 |
2017年 | 1900篇 |
2016年 | 2097篇 |
2015年 | 2271篇 |
2014年 | 3783篇 |
2013年 | 3669篇 |
2012年 | 3676篇 |
2011年 | 3766篇 |
2010年 | 3580篇 |
2009年 | 4018篇 |
2008年 | 4753篇 |
2007年 | 4098篇 |
2006年 | 4287篇 |
2005年 | 3735篇 |
2004年 | 3988篇 |
2003年 | 2926篇 |
2002年 | 1907篇 |
2001年 | 1900篇 |
2000年 | 1582篇 |
1999年 | 1636篇 |
1998年 | 1204篇 |
1997年 | 1073篇 |
1996年 | 945篇 |
1995年 | 965篇 |
1994年 | 919篇 |
1993年 | 870篇 |
1992年 | 901篇 |
1991年 | 765篇 |
1990年 | 735篇 |
1989年 | 675篇 |
1988年 | 328篇 |
1987年 | 210篇 |
1986年 | 122篇 |
1985年 | 110篇 |
1984年 | 53篇 |
1983年 | 50篇 |
1982年 | 16篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1963年 | 1篇 |
1959年 | 9篇 |
1951年 | 3篇 |
1934年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
The First Intramolecular Charge Transfer Transition Based on 2-Ureido-4[1H]-pyrimidinone Binding Module 总被引:1,自引:0,他引:1
The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported. 相似文献
162.
The first hyperpolarizabilities of a series of novel azulenic-barbituric acid chromophores have been studied by using 12 excitation wavelengths, ranging from 900 to 1907 nm. The dispersion relation of the first hyperpolarizabilities of chromophores holds the same tendency as the experimental results. In addition, the static first hyperpolarizability β0 of molecules was calculated by means of the Sum-Over-States (SOS) expression and the two-level formula respectively. The results show that these molecules possess large static first hyperpolarizabilities and the, β0 value increases as the donor or acceptor strength enhances; the distorted degree of molecules has also an important influence on the β0 value. 相似文献
163.
Solid Phase Synthesis of 2-Substituted 1,3-Oxazin-6-ones Using Resin-bound Cyclic Malonic Acid Ester
A facile solid phase synthesis of 2-substituted 1,3-oxazin-6-ones using polymer-supported Meldrum‘s acid has been reported. Reaction of the resin-bound cyclic malonic acid ester with triethyl orthoformate and subsequent double substitution with amide, afforded the corresponding polymer-supported acylaminomethylene cyclic malonic acid ester, which upon thermal treatment led to 1, 3-oxazin-6-ones in good yields and with high purity. 相似文献
164.
The adsorption of asymmetrical triblock copolymers from a non-selective solvent on solid surface has been studied by using Scheutjens-Fleer mean-field theory and Monte Carlo simulation method on lattice model. The main aim of this paper is to provide detailed computer simulation data, taking A8-kB20Ak as a key example, to study the influence of the structure of copolymer on adsorption behavior and make a comparison between MC and SF results. The simulated results show that the size distribution of various configurations and density-profile are dependent on molecular structure and adsorption energy. The molecular structure will lead to diversity of adsorption behavior. This discrepancy between different structures would be enlarged for the surface coverage and adsorption amount with increasing of the adsorption energy. The surface coverage and the adsorption amount as well as the bound fraction will become larger as symmetry of the molecular structure becomes gradually worse. The adsorption layer becomes thicker with increasing of symmetry of the molecule when adsorption energy is smaller but it becomes thinner when adsorption energy is higher. It is shown that SF theory can reproduce the adsorption behavior of asymmetrical triblock copolymers. However, systematic discrepancy between the theory and simulation still exists.The approximations inherited in the mean-filed theory such as random mixing and the allowance of direct back folding may be responsible for those deviations. 相似文献
165.
Ming Zhao WANG Guan Liang CAI Ling XIA Jun Jian YAO Hong Yan CHEN Zhao Xing MENG Bo Li LIUDepartment of Chemistry Beijing Normal University Beijing Chemical Defense Institute PLA Beijing 《中国化学快报》2004,15(4):495-497
The crystal structures of two potential tumor imaging agents and therapeutic agents -copper(Ⅱ) complexes with salicylidene-tyrosinato Schiff base and nitrogen-donor chelating Lewis base, [Cu(sal-tyr)(bipy)] 1 and [Cu(sal-tyr)(phen)]2CH3OH 2 are presented. Our work is helpful to get deep understanding of novel 64Cu tumor imaging agents and therapeutic agents. 相似文献
166.
167.
通过对非饱和土非线性本构方程和场方程的线性化,推导出了非饱和土的线性本构方程和场方程,把线性方程表示为与Biot饱和多孔介质方程相似的形式;证明了Darcy定律对非饱和土的适用性;说明了Biot饱和多孔介质方程是这些线性方程的特征。所有这些都表明用混合理论处理非饱和土本构问题的正确性。 相似文献
168.
晶体微观结构是晶体材料在特定物理条件下其多个能量极小平衔态在空间形成的某种微尺度的规则分布.几何非线性的连续介质力学理论可以用能量极小化原理来解释晶体微观结构的形成,并用Young测度来刻画平衡态各变体在空间的概率分布.定性的理解与定量地分析和计算晶体材料的微观结构对于发展和改进高级晶体功能材料,如形状记忆合金、铁电体、磁至伸缩材料等,有重要的意义.本文回顾了近年来晶体微观结构数值计算方面的最新进展.介绍了计算晶体微观结构的几种数值方法及有关的数值分析结果。 相似文献
169.
170.
教学大纲要求物理教学要注重能力的培养。所谓能力,它包括知识和方法两方面的内容。然而,长期以来,在教学中都只重视知识,而忽视了方法。纵观物理学发展的整个过程,可以看到,物理学的发展不仅是知识不断积累的过程,也是方法不断更新的过程,所以物理学既是一门结构严谨的自然科学,又是一门带有方法论性质的理论科学。 相似文献