全文获取类型
收费全文 | 9433篇 |
免费 | 1839篇 |
国内免费 | 2683篇 |
专业分类
化学 | 7644篇 |
晶体学 | 294篇 |
力学 | 676篇 |
综合类 | 352篇 |
数学 | 1251篇 |
物理学 | 3738篇 |
出版年
2024年 | 24篇 |
2023年 | 164篇 |
2022年 | 317篇 |
2021年 | 352篇 |
2020年 | 405篇 |
2019年 | 388篇 |
2018年 | 343篇 |
2017年 | 436篇 |
2016年 | 453篇 |
2015年 | 516篇 |
2014年 | 628篇 |
2013年 | 780篇 |
2012年 | 811篇 |
2011年 | 856篇 |
2010年 | 657篇 |
2009年 | 765篇 |
2008年 | 785篇 |
2007年 | 664篇 |
2006年 | 640篇 |
2005年 | 609篇 |
2004年 | 458篇 |
2003年 | 412篇 |
2002年 | 454篇 |
2001年 | 444篇 |
2000年 | 362篇 |
1999年 | 241篇 |
1998年 | 143篇 |
1997年 | 82篇 |
1996年 | 89篇 |
1995年 | 97篇 |
1994年 | 90篇 |
1993年 | 101篇 |
1992年 | 67篇 |
1991年 | 45篇 |
1990年 | 45篇 |
1989年 | 36篇 |
1988年 | 31篇 |
1987年 | 27篇 |
1986年 | 30篇 |
1985年 | 17篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 11篇 |
1960年 | 2篇 |
1959年 | 5篇 |
1957年 | 5篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
31.
Yousong Gu Dayong ZhangXiaoyuan Zhan Zhen JiYue Zhang 《Journal of magnetism and magnetic materials》2006
Series of [FePt(4min)/Fe(tFe)]10 multilayers have been prepared by RF magnetron sputtering and post-annealing in order to optimize their magnetic properties by structural designs. The structure, surface morphology, composition and magnetic properties of the deposited films have been characterized by X-ray diffractometer (XRD), Rutherford backscattering (RBS), scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX) and vibrating sample magnetometer (VSM). It is found that after annealing at temperatures above 500 °C, FePt phase undergoes a phase transition from disordered FCC to ordered FCT structure, and becomes a hard magnetic phase. X-ray diffraction studies on the series of [FePt/Fe]n multilayer with varying Fe layer thickness annealed at 500 and 600 °C show that lattice constants change with Fe layer thickness and annealing temperature. Both lattice constants a and c are smaller than those of standard ones, and lattice constant a decreases as Fe layer deposition time increases. Only a slight increase in grain size was observed as Fe layer decreased in samples annealed at 500 °C. However, the increase in grain size is large in samples annealed at 600 °C. The coercivities of [FePt/Fe]n multilayers decrease with Fe layer deposition time, and the energy product (BH)max reaches a maximum in the samples with Fe layer deposition time of 3 min. Comparison of magnetic properties with structure showed an almost linear relationship between the lattice constant a and the coercivities of the FePt phase. 相似文献
32.
We study the domain of existence of a solution to a Riemann problem for the pressure gradient equation in two space dimensions. The Riemann problem is the expansion of a quadrant of gas of constant state into the other three vacuum quadrants. The global existence of a smooth solution was established in Dai and Zhang [Z. Dai, T. Zhang, Existence of a global smooth solution for a degenerate Goursat problem of gas dynamics, Arch. Ration. Mech. Anal. 155 (2000) 277-298] up to the free boundary of vacuum. We prove that the vacuum boundary is the coordinate axes. 相似文献
33.
34.
基于VAGUE集多准则决策的模糊TOPSIS方法 总被引:3,自引:0,他引:3
给出了V AGUE集之间距离的新定义,在此基础上,提出一个基于V AGUE集多准则决策的模糊TOP-S IS方法,它为决策系统提供了一个有用的工具,并通过例子阐明本文方法的有效性. 相似文献
35.
36.
37.
X-ray emission spectra for L-shell of Li-like aluminium ions are simulated by using the flexible atomic code based on the collisional radiative model. Atomic processes including radiative recombination, dielectronic recombination, collisional ionization and resonance excitation from the neighbouring ion (Al^9+ and Al^11+ ) charge states of the target ion (Al^10+) are considered in the model. In addition, the contributions of different atomic processes to the x-ray spectrum are analysed. The results show that dielectronic recombination, radiative recombination, collisional ionization and resonance excitation, other than direct collisional excitation, are very important processes. 相似文献
38.
39.
Zhong‐Zhen Yu Mingshu Yang Qingxin Zhang Chungui Zhao Yiu‐Wing Mai 《Journal of Polymer Science.Polymer Physics》2003,41(11):1234-1243
Nylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with an alkyl ammonium surfactant pretreated montmorillonite (MMT). The thermal stability of the organic MMT powders was measured by thermogravimetric analysis. The decomposition of the surfactant on the MMT occurred from 200 to 500 °C. The low onset decomposition temperature of the organic MMT is one shortcoming when it is used to prepare polymer nanocomposites at high melt‐compounding temperatures. To provide greater property enhancement and better thermal stability of the polymer/MMT nanocomposites, it is necessary to develop MMT modified with more thermally stable surfactants. The dispersion and spatial distribution of the organic MMT layers in the nylon‐66 matrix were characterized by X‐ray diffraction. The organic MMT layers were exfoliated but not randomly dispersed in the nylon‐66 matrix. A model was proposed to describe the spatial distribution of the organic MMT layers in an injection‐molded rectangular bar of nylon‐66/organic MMT nanocomposites. Most organic MMT layers were oriented in the injection‐molding direction. Layers near the four surfaces of the bar were parallel to their corresponding surfaces; whereas those in the bulk differed from the near‐surface layers and rotated themselves about the injection‐molding direction. The influence of the spatial distribution of the organic MMT on crystallization of nylon‐66 was also investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1234–1243, 2003 相似文献
40.