全文获取类型
收费全文 | 1061篇 |
免费 | 97篇 |
国内免费 | 73篇 |
专业分类
化学 | 405篇 |
晶体学 | 16篇 |
力学 | 53篇 |
综合类 | 6篇 |
数学 | 305篇 |
物理学 | 446篇 |
出版年
2024年 | 3篇 |
2023年 | 13篇 |
2022年 | 17篇 |
2021年 | 16篇 |
2020年 | 28篇 |
2019年 | 27篇 |
2018年 | 29篇 |
2017年 | 22篇 |
2016年 | 41篇 |
2015年 | 32篇 |
2014年 | 45篇 |
2013年 | 131篇 |
2012年 | 65篇 |
2011年 | 75篇 |
2010年 | 45篇 |
2009年 | 91篇 |
2008年 | 82篇 |
2007年 | 73篇 |
2006年 | 43篇 |
2005年 | 51篇 |
2004年 | 42篇 |
2003年 | 32篇 |
2002年 | 33篇 |
2001年 | 22篇 |
2000年 | 18篇 |
1999年 | 21篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 17篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有1231条查询结果,搜索用时 406 毫秒
81.
Ping Chen Min LiuLing Wang Yin PooRui-xin Wu 《Journal of magnetism and magnetic materials》2011,323(23):3081-3086
We experimentally studied the frequency dependent complex permittivity ε and permeability μ of composite composed of carbonyl iron powder (CIP) and epoxy resin in the frequency range 1-18 GHz. We found that the intrinsic ε and μ of CIP extracted from the measured ε and μ of composites follow the classical Maxwell equations and the Landau-Lifshitz-Gilbert (LLG) equation, respectively. The dependences of ε and μ of composites on the volume fraction of CIP (vfCIP) were investigated using the two-exponent phenomenological percolation equation (TEPPE). We found that the TEPPE can fit the experimental results very well. Comparing the results of percolation parameters derived by experimental data at different frequencies, we show that the TEPPE is frequency independent for the composites at microwave frequencies. The results also show that the ε and μ spectrums of composites with definite vfCIP can be correctly calculated by combining the TEPPE with the theoretical models of intrinsic ε and μ. 相似文献
82.
The geometrical structures, relative stabilities, and electronic properties of bimetallic AunMg (n=1-8) clusters have been systematically investigated by means of first-principle density functional theory. The results show that the ground-state isomers have planar structures for n=1-7. Here, the calculated fragmentation energies, the second-order difference of energies, the highest occupied-lowest unoccupied molecular orbital energy gaps, and the hardness exhibit a pronounced odd-even alternation, manifesting that the clusters, especially Au2Mg, with even-number gold atoms have a higher relative stability. On the basis of natural population analysis, the charge transfer and magnetic moment are also discussed. 相似文献
83.
84.
Effect of looking backward on traffic flow in an extended multiple car-following model 总被引:1,自引:0,他引:1
In this paper, a new car-following model is proposed by incorporating the backward looking effect under certain conditions and multiple information of preceding cars in traffic flow. And the neutral stability condition of this model can be obtained by using the linear stability theory. Numerical simulation shows that the proposed model is theoretically an improvement over previous ones. 相似文献
85.
Rita Giuliano Claudio Macci Barbara Pacchiarotti 《Journal of Mathematical Analysis and Applications》2014
In this paper we study some sequences of weighted means of continuous real valued Gaussian processes. More precisely we consider suitable generalizations of both arithmetic and logarithmic means of a Gaussian process with covariance function which satisfies either an exponential decay condition or a power decay condition. Our aim is to provide limits of variances of functionals of such weighted means which allow the application of some large deviation results in the literature. 相似文献
86.
近来,林群从哲学的角度用公式相对真理/绝对真理=0.9阐述了微积分的内涵,并探究了计算数学、概率统计等学科领域乃至日常生活现象也同样蕴藏着该哲学公式.基于林群等在《概率论初步设想》中对大数定律和中心极限定理等概率统计学理论的哲学内涵分析,用一些数值算例展示概率统计学中这些常用理论所蕴含的这一哲学公式. 相似文献
87.
《Physics and Chemistry of Liquids》2012,50(3):335-339
The alkanols of three carbon length have been studied by dielectric methods during many years and they do not obey any theoretical model. These substances have the same chain length and have one, two or three dipoles per molecule, so their ability to form hydrogen bridges changes from one substance to other, and one can obtain information by comparative studies. In previous works, we have measured the thermal dependence of permittivity of these substances and analysed the results with an empirical modification of the Onsager equation. Now we shall analyse and compare the results using a different representation. In this representation, the data shows straight lines, whose slopes depend on the quantity of dipoles of each molecule encouraging the high quality of the fittings obtained with the three substances, and also that they behave in the same dielectric way with the rise of temperature. 相似文献
88.
Four Cl2O3 isomers have been calculated using density functional theory with B3P86 and B3LYP functionals and various basis sets. The energy hypersurfaces of Cl2O3 are very flat and the relative energies of the isomers which have hypervalent characters such as ClOCl(O)O and ClClO3 are strongly dependent on the basis sets. The stability for Cl2O3 isomers are in the order of (1)ClOOOCl(Cs), (2)ClOOOCl(C2), (3)ClClO3 and (4)ClOCl(O)O with ClOCl(O)O being most stable. We suggest that at least the cc-pV6Z(-ghi) basis set for Cl and the cc-pVTZ basis set for O are required to obtain reliable relative stabilities of Cl2O3 isomers with hypervalent characters. 相似文献
89.
用密度泛函理论方法研究了气相和水溶液中Gd(H2O)n^3+(n=8,9)化合物的结构和相对稳定性,其中水溶剂效应利用极化连续介质方法结合多种溶质空腔模型进行模拟.气相计算得到的化合物结构与实验观察结果一致.计算结果表明,在气相中9配位Gd(H2O)9^3+比8配位Gd(H2O)8^3+稳定,而在水溶液中稳定顺序刚好相反,这一结果不依赖于计算中采用的空腔模型种类,而且也与实验结果吻合.最后,通过采用各种空腔模型计算Gd^3+的水合自由能,并与实验值比较,发现当化合物只包含第一层配位水分子时,UA0、UAHF及UAKS空腔模型最适合研究Gd^3+在水溶液中的性质. 相似文献
90.
Zuliang Luo Weijun Kong Feng Qiu Meihua Yang Qian Li Riwei Wei Xiaoli Yang Jieping Qin 《Journal of separation science》2013,36(4):699-705
A simple and sensitive HPLC coupled with photodiode array (HPLC–PDA) method was developed for simultaneous determination of seven lignans in Justicia procumbens using relative response factors (RRFs). The chromatographic separation was performed on a Shiseido Capcell Pak C18 column (250 × 4.6 mm id, 5 μm), a gradient elution of acetonitrile/water, and a photodiode array detector. The column temperature was maintained at 35°C and the detection wavelength was set at 256 nm. Chinensinaphthol methyl ether was selected as the reference compound for calculating the relative response factors of the lignans. It has shown that the RRFs for lignans are quite similar at 256 nm of detection under different analytical conditions (different columns and HPLC instruments). Using RRFs, not every lignan is needed as a reference standard, making the method ideal for rapid, routine analysis, especially for those laboratories where lignans standards are not readily available. An economic and practicable HPLC method using RRFs was established for the determination of seven lignans in J. procumbens. This method not only can determine multiple indexes in traditional Chinese medicines (TCMs) simultaneously, but also resolve the problem of lacking of chemical standards. It will be a good quality evaluation method and pattern for TCMs. 相似文献