全文获取类型
收费全文 | 30120篇 |
免费 | 5013篇 |
国内免费 | 4204篇 |
专业分类
化学 | 21748篇 |
晶体学 | 379篇 |
力学 | 1992篇 |
综合类 | 299篇 |
数学 | 3613篇 |
物理学 | 11306篇 |
出版年
2024年 | 55篇 |
2023年 | 495篇 |
2022年 | 926篇 |
2021年 | 927篇 |
2020年 | 1043篇 |
2019年 | 1084篇 |
2018年 | 967篇 |
2017年 | 929篇 |
2016年 | 1460篇 |
2015年 | 1405篇 |
2014年 | 1799篇 |
2013年 | 2210篇 |
2012年 | 2605篇 |
2011年 | 2762篇 |
2010年 | 2032篇 |
2009年 | 2011篇 |
2008年 | 2244篇 |
2007年 | 2006篇 |
2006年 | 1870篇 |
2005年 | 1645篇 |
2004年 | 1245篇 |
2003年 | 1019篇 |
2002年 | 1136篇 |
2001年 | 855篇 |
2000年 | 731篇 |
1999年 | 614篇 |
1998年 | 463篇 |
1997年 | 382篇 |
1996年 | 393篇 |
1995年 | 350篇 |
1994年 | 265篇 |
1993年 | 208篇 |
1992年 | 209篇 |
1991年 | 193篇 |
1990年 | 162篇 |
1989年 | 140篇 |
1988年 | 121篇 |
1987年 | 87篇 |
1986年 | 65篇 |
1985年 | 59篇 |
1984年 | 37篇 |
1983年 | 32篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 5篇 |
1978年 | 16篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
A periodic one-dimensional four-state hopping model is proposed. In the model, the substeps betweenarbitrary adjacent states are unequal, and an explicit solution of the master equation is first obtained for the probabilitydistribution as a function of the time and position for any initial distribution with all the transients included. Next, thetransient behaviors in the initial period of time and the characteristic time to reach the steady state for the molecularmotor are discussed. Finally, we compare the steady state results to experiments and illustrate qualitatively the kineticbehaviors of a molecular motor under external load F. 相似文献
122.
123.
124.
This paper is to investigate the approximate confidence limits of the reliability performances (such as failure rate, reliability function and average life) for a cold standby series system. The Bayesian approximate upper confidence limit of failure rate is obtained firstly, and next Bayesian approximate lower confidence limits for reliability function and average life are presented. The expressions for calculating Bayesian lower confidence limits of the reliability function and average life are also obtained, and an illustrative example is examined numerically by means of the Monte-Carlo simulation. Finally, the accuracy of confidence limits is discussed. 相似文献
125.
126.
Controlling the gain shape of Er^3+—doped fluorozirconate fibre amplifier by a coherent field
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We proposed a four-level system to explore the quantum interference effects on optical amplification.We found that the gain of the probe.including positions and values of gain peaks,can be adjusted by changing the coherent field and the incoherent pumping.At the same time,we can also modify the absorption profile of electromagnetically induced transparency by the incoherent pump.The results provide a method to flatten the gain of Erbium-doped fibre amplifiers. 相似文献
127.
Yong Lee Kazuhiko Hosomi Hiroyuki Uchiyama Toshio Katsuyama Shinya Kominami Tomoyoshi Mishima 《Optical Review》2003,10(1):38-42
An InGaAsP slab-type asymmetric-coupled-waveguide-based dispersion compensator with a mode selector has been designed and fabricated. The mode selector is necessary to select either a symmetric [with a positive group-velocity dispersion (GVD)] or antisymmetric (with a negative GVD) supermode. These supermodes exist simultaneously in the dispersion-compensation region of the device. Pulse-compression experiments were used to test the dispersion compensator, evaluating the function of the mode selector. A theoretical study of the experimental results shows that the mode selector obtains a very strong selectivity (nearly 100%) for the antisymmetric supermode. 相似文献
128.
完全Rees矩阵半群的分解及性质 总被引:1,自引:0,他引:1
用等价关系Q^~出了完全Rees矩阵半群的一种分解.而且得到了它的每个Q^~一类的表示. 相似文献
129.
130.
Yong‐Jin Kim Jin‐Woong Kim Jung‐Eun Lee Jee‐Hyun Ryu Junoh Kim Ih‐Seop Chang Kyung‐Do Suh 《Journal of polymer science. Part A, Polymer chemistry》2004,42(22):5627-5635
Mesoporous polymer microspheres with gold (Au) nanoparticles inside their pores were prepared considering their surface functionality and porosity. The Au/polymer composite microspheres prepared were characterized by transmission electron microscope (TEM), X‐ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) techniques. The results showed that the adsorption of Au nanoparticles could be increased by imparting the pore structure and surface‐functional groups into the supporting polymer microspheres (in this study, poly (ethylene glycol dimethacrylate‐co‐acrylonitrile) and poly (EGDMA‐co‐AN) system). Above all, from this study, it was established that the porosity of the polymer microspheres is the most important factor that determines the distribution and adsorption amount of face‐centered cubic (fcc) Au nanoparticles in the final products. Our study showed that the continuous adsorption of Au nanoparticles with the aid of the large surface area and surface interaction sites formed more favorably the Au/polymer composite microspheres. The BET measurements of Au/poly(EGDMA‐co‐AN) composite microspheres reveals that the adsorption of Au nanoparticles into the pores kept the pore structure intact and made it more porous. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5627–5635, 2004 相似文献