全文获取类型
收费全文 | 1286篇 |
免费 | 275篇 |
国内免费 | 206篇 |
专业分类
化学 | 941篇 |
晶体学 | 10篇 |
力学 | 78篇 |
综合类 | 9篇 |
数学 | 165篇 |
物理学 | 564篇 |
出版年
2024年 | 5篇 |
2023年 | 33篇 |
2022年 | 46篇 |
2021年 | 61篇 |
2020年 | 78篇 |
2019年 | 55篇 |
2018年 | 53篇 |
2017年 | 57篇 |
2016年 | 62篇 |
2015年 | 57篇 |
2014年 | 85篇 |
2013年 | 117篇 |
2012年 | 131篇 |
2011年 | 112篇 |
2010年 | 82篇 |
2009年 | 67篇 |
2008年 | 86篇 |
2007年 | 86篇 |
2006年 | 79篇 |
2005年 | 60篇 |
2004年 | 36篇 |
2003年 | 43篇 |
2002年 | 34篇 |
2001年 | 28篇 |
2000年 | 29篇 |
1999年 | 22篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 22篇 |
1995年 | 11篇 |
1994年 | 19篇 |
1993年 | 10篇 |
1992年 | 20篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1970年 | 1篇 |
1965年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有1767条查询结果,搜索用时 937 毫秒
131.
Reactions of indoles and α,β-unsaturated ketones could be effectively catalyzed by using 10 mol % gallium triiodide to give the corresponding Michael adducts in good to excellent yields. 相似文献
132.
133.
In this paper, we study an age-structured reaction-diffusion-advection population model. First, we use a non-densely defined operator to the linear age-structured reaction-diffusion-advection population model in a patchy environment. By spectral analysis, we obtain the asynchronous exponential growth of the population model. Then we consider nonlinear death rate and birth rate, which all depend on the function related to the generalized total population, and we prove the existence of a steady state of the system. Finally, we study the age-structured reaction-diffusion-advection population model in non-autonomous situations. We give the comparison principle and prove the eventual compactness of semiflow by using integrated semigroup. We also prove the existence of compact attractors under the periodic situation. 相似文献
134.
本文应用Normal Form理论和退化向量场的普适开折理论研究了参数激励与强迫激励联合作用下非线性振动系统的余维2退化分叉,用Melnikov方法讨论了全局分叉的存在性. 相似文献
135.
建筑物内火灾烟羽流和顶蓬射流诱发的空气运动盐水模拟实验研究 总被引:3,自引:0,他引:3
盐水在清水中的扩散与火灾烟气在空气中的蔓延相似,因而可用盐水的扩散来模拟火灾烟气的蔓延;同样地,由于盐水的扩散而导致的环境清水的运动也可用来模拟烟气蔓延诱发的空气运动。基于这一原理,本文用实验的方法,研究了建筑物内初起火灾产生的烟羽流和顶蓬射流所诱发的空气运动,并对走廊空气层生长规律和运动特性进行了初步的测量和分析。所得结果基本合理,对建筑物通风排烟及疏散通道设计有帮助,从而为建筑火灾环境空气的运动的实验研究开辟了新的思路,也为火灾区域模拟提供了实验依据 相似文献
136.
Nonequilibrium thermodynamics of pseudoelasticity 总被引:2,自引:0,他引:2
Solid-solid phase transitions often exhibit hystereses, and a hysteresis indicates energy dissipation. Pseudoelasticity refers to a hysteretic loadingunloading characteristic observed in the stress-induced martensitic transformation of shape memory alloys.This paper describes the thermodynamic model ofideal pseudoelasticity, a largely schematized adaptation of the experimental observations, and it reviews the works of other authors on thermodynamics of pseudoelasticity. Different approaches vary widely and we have chosen to put them into perspective by contrasting their assumptions and predictions against those of ideal pseudoelasticity.Ideal pseudoelasticity receives support from the experimental results of Fu [1] and its thermodynamic properties have been exploited by Huo [2]. The model makes use of an analytical ansatz proposed by Müller [3] in which the hysteresis is assumed to be due to the presence of a coherency energy in solid phase mixtures. This model permits the study of stability of the equilibrium states and the calculation of the energy dissipation or entropy production during the phase transition: The equilibrium states of a phase mixture are found to be unstable in load-controlled processes and the dissipated energy is related to the coherency coefficient.We also discuss some open problems concerning the states inside the hysteresis loop and the formation of interfaces. 相似文献
137.
Surface‐Enhanced Raman Scattering Based on Controllable‐Layer Graphene Shells Directly Synthesized on Cu Nanoparticles for Molecular Detection
下载免费PDF全文
![点击此处可从《Chemphyschem》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hengwei Qiu Dr. Yanyan Huo Zhen Li Dr. Chao Zhang Peixi Chen Prof. Shouzhen Jiang Dr. Shicai Xu Prof. Yong Ma Prof. Shuyun Wang Hongsheng Li 《Chemphyschem》2015,16(14):2953-2960
Graphene shells with a controllable number of layers were directly synthesized on Cu nanoparticles (CuNPs) by chemical vapor deposition (CVD) to fabricate a graphene‐encapsulated CuNPs (G/CuNPs) hybrid system for surface‐enhanced Raman scattering (SERS). The enhanced Raman spectra of adenosine and rhodamine 6G (R6G) showed that the G/CuNPs hybrid system can strongly suppress background fluorescence and increase signal‐to‐noise ratio. In four different types of SERS systems, the G/CuNPs hybrid system exhibits more efficient SERS than a transferred graphene/CuNPs hybrid system and pure CuNPs and graphene substrates. The minimum detectable concentrations of adenosine and R6G by the G/CuNPs hybrid system can be as low as 10?8 and 10?10 M , respectively. The excellent linear relationship between Raman intensity and analyte concentration can be used for molecular detection. The graphene shell can also effectively prevent surface oxidation of Cu nanoparticles after exposure to ambient air and thus endow the hybrid system with a long lifetime. This work provides a basis for the fabrication of novel SERS substrates. 相似文献
138.
Inside Cover: Surface‐Enhanced Raman Scattering Based on Controllable‐Layer Graphene Shells Directly Synthesized on Cu Nanoparticles for Molecular Detection (ChemPhysChem 14/2015)
下载免费PDF全文
![点击此处可从《Chemphyschem》网站下载免费的PDF全文](/ch/ext_images/free.gif)
139.
Catalytic Performance of Graphite Oxide Supported Au Nanoparticles in Aerobic Oxidation of Benzyl Alcohol: Support Effect
下载免费PDF全文
![点击此处可从《化学物理学报(中文版)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Various Au/GO catalysts were prepared by depositing Au nanoparticles on thermally- and chemically-treated graphite oxide (GO) supports using a sol-immobilization method. The surface chemistry and structure of GO supports were characterized by a series of analytical techniques including X-ray photoelectron spectroscopy, temperature-programmed desorption and Raman spectroscopy. The results show that thermal and chemical treatments have large influence on the presence of surface oxygenated groups and the crystalline structure of GO supports. A strong support effect was observed on the catalytic activity of Au/GO catalysts in the liquid phase aerobic oxidation of benzyl alcohol. Compared to the amount and the type of surface oxygen functional groups, the ordered structure of GO supports may play a more important role in determining the catalytic performance of Au/GO catalysts. 相似文献
140.
弥散型核燃料元件热应力的计算模拟 总被引:2,自引:0,他引:2
针对弥散型燃料板的具体形状,选择了一种能够反映其实际变形特征的三维代表性体积单元作为研究对象;利用有限元法对其热力耦合行为进行了弹塑性分析,研究了热应力在燃料和基体中的分布特征. 相似文献