全文获取类型
收费全文 | 22961篇 |
免费 | 3189篇 |
国内免费 | 2892篇 |
专业分类
化学 | 16991篇 |
晶体学 | 271篇 |
力学 | 694篇 |
综合类 | 111篇 |
数学 | 450篇 |
物理学 | 5251篇 |
综合类 | 5274篇 |
出版年
2024年 | 73篇 |
2023年 | 271篇 |
2022年 | 1075篇 |
2021年 | 959篇 |
2020年 | 974篇 |
2019年 | 784篇 |
2018年 | 649篇 |
2017年 | 743篇 |
2016年 | 1022篇 |
2015年 | 921篇 |
2014年 | 1107篇 |
2013年 | 1832篇 |
2012年 | 1351篇 |
2011年 | 1230篇 |
2010年 | 1061篇 |
2009年 | 1207篇 |
2008年 | 1310篇 |
2007年 | 1432篇 |
2006年 | 1329篇 |
2005年 | 1203篇 |
2004年 | 1135篇 |
2003年 | 1077篇 |
2002年 | 814篇 |
2001年 | 695篇 |
2000年 | 710篇 |
1999年 | 613篇 |
1998年 | 572篇 |
1997年 | 453篇 |
1996年 | 382篇 |
1995年 | 381篇 |
1994年 | 333篇 |
1993年 | 236篇 |
1992年 | 215篇 |
1991年 | 155篇 |
1990年 | 130篇 |
1989年 | 123篇 |
1988年 | 103篇 |
1987年 | 68篇 |
1986年 | 64篇 |
1985年 | 55篇 |
1984年 | 34篇 |
1983年 | 11篇 |
1982年 | 21篇 |
1981年 | 27篇 |
1980年 | 25篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1975年 | 10篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
郑重德 《西南民族学院学报(自然科学版)》1994,20(4):369-371
在HOH角弯曲柔度极大的条件下,计算得到了能完全准确预测D_2O分子简正频率的H_2O分子柔度,并讨论了H_2O分子的简正模式。 相似文献
72.
Thermal, spectroscopic and electrical properties of lead pyrophosphate glass prepared by melt quenching have been examined.
A model based on the structural disproportionation of the P2O
7
4−
ions has been proposed and is shown to consistently explain all the observations. The equilibrium of various anionic species
has been discussed on the basis of their electronegativities which are in turn related to their basicities.
Communication No. 129 from the Materials Research Centre 相似文献
73.
经过多年的探伤实验,总结出两种快速制作距离波幅曲线的方法。 相似文献
74.
75.
There is a high correlation between molecular surface area (TSA) of triorganotin and triorganolead compounds and their toxicity towards a bacterium (Escherichia coli) and an alga (Selenastrum capricornutum). Parallel attempts to correlate other Group IVA organometals incorporating silicon or germanium were unsuccessful. It was further demonstrated, however, that a high correlation was obtainable between certain series of compounds with the same organic substituent but different metal centers involving all Group IVA elements. In both instances, the inability to obtain a quantitative structure-activity relationship (QSAR) for all systems studied appears to be a function of the solubility of the compounds. While organotin TSA values have been found to correlate well with their toxicities toward various organisms, this study clearly suggests that this type of QSAR can be readily extended to include other organometal systems, provided that there is no solubility problem and the toxicity is a function of the hydrophobicity of the organometal compounds. 相似文献
76.
SHIMIZU Jun EDA Hiroshi 《厦门大学学报(自然科学版)》2002,(Z1)
This study aims to reduce the work-affected layer of the machined surface by carrying out the grinding at the speed over static pr o pagation speed of plastic wave of ductile materials and also aims to clarify suc h super high-speed machining mechanism.This paper reports on the result obtain ed through the molecular dynamics simulations and experiments on the super-spee d grinding below and beyond static propagation speed of aluminum.From the simul ation results,it is verified that the plastic deformation ... 相似文献
77.
Tatiana B. Mikenas Vladimir A. Zakharov Lyudmila G. Echevskaya Mikhail A. Matsko 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5057-5066
The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl2/MgCl2‐Al(i‐Bu)3 (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl2/MgCl2‐Al(i‐Bu)3 has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl2/MgCl2‐Al(i‐Bu)3 has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007 相似文献
78.
The grain boundary is an interface and the surface tension is one of its important thermodynamic properties. In this paper,
the surface tension of the ∑9 grain boundary for α-Fe at various temperatures and pressures is calculated by means of Computer
Molecular Dynamics (CMD). The results agree satisfactorily with the experimental data. It is shown that the contribution of
entropy to surface tension of grain boundary can be ignored.
The project supported by the National Natural Science Foundation of China and the Science Foundation of Chinese Academy of
Sciences. 相似文献
79.
80.
运用多种密度泛函理论 (DFT)和从头算 (abinitio)方法研究了草酰胺顺、反异构体的分子几何构型 ,结果表明Beck88交换函数与LYP非局域相关函数形成杂化的DFT方法B3LYP与MP2方法计算结果比较吻合。在此基础上选择B3LYP方法对草酰胺分子电子结构、红外光谱和前线分子轨道组成进行了系统研究 ;与实验事实对比分析了气态草酰胺分子中配位原子的反应活性 相似文献