全文获取类型
收费全文 | 62026篇 |
免费 | 12156篇 |
国内免费 | 20980篇 |
专业分类
化学 | 45041篇 |
晶体学 | 2647篇 |
力学 | 4778篇 |
综合类 | 2203篇 |
数学 | 10319篇 |
物理学 | 30174篇 |
出版年
2024年 | 173篇 |
2023年 | 717篇 |
2022年 | 2224篇 |
2021年 | 2199篇 |
2020年 | 2184篇 |
2019年 | 2142篇 |
2018年 | 2030篇 |
2017年 | 2901篇 |
2016年 | 2239篇 |
2015年 | 3180篇 |
2014年 | 3872篇 |
2013年 | 5049篇 |
2012年 | 5138篇 |
2011年 | 5608篇 |
2010年 | 5371篇 |
2009年 | 5545篇 |
2008年 | 6183篇 |
2007年 | 5529篇 |
2006年 | 5426篇 |
2005年 | 4475篇 |
2004年 | 3491篇 |
2003年 | 2548篇 |
2002年 | 2513篇 |
2001年 | 2531篇 |
2000年 | 2627篇 |
1999年 | 1678篇 |
1998年 | 892篇 |
1997年 | 680篇 |
1996年 | 655篇 |
1995年 | 618篇 |
1994年 | 606篇 |
1993年 | 582篇 |
1992年 | 563篇 |
1991年 | 390篇 |
1990年 | 362篇 |
1989年 | 367篇 |
1988年 | 318篇 |
1987年 | 259篇 |
1986年 | 228篇 |
1985年 | 174篇 |
1984年 | 164篇 |
1983年 | 143篇 |
1982年 | 111篇 |
1981年 | 83篇 |
1980年 | 75篇 |
1979年 | 89篇 |
1978年 | 28篇 |
1977年 | 20篇 |
1965年 | 35篇 |
1959年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 656 毫秒
151.
根据耦合非线性薛定谔方程 ,本文研究了偏振模色散如何影响各种码型的频谱 ,分析了滑频滤波器和固定滤波器对偏振模色散的补偿作用。研究结果表明 :偏振模色散对不同码型的频谱影响是不一样的 ,对色散管理孤子的频谱影响最大 ,产生新的频率分量也最多 ,而且每个新频率分量都较强 ,比入射频谱展宽许多 ;滑频滤波器和固定滤波器对偏振模色散都具有补偿作用 ,使最大可传输距离成倍增加 ,两种滤波器对偏振模色散的补偿作用相差较小 ;但是对色散管理孤子系统中的偏振模色散补偿效果最佳。 相似文献
152.
153.
Based on the algebraic entanglement measure proposed [G. Vidal et al., Phys. Rev. A 65 (2002) 032314],we study the entanglement evolution of both pure quantum states and mixed ones of 2-qutrit system in a symmetrybroken environment consisting of a fermionic bath. Entanglement of states will decrease or remain constant under the influence of environment, and the class of states which remain unchanged has been found out. 相似文献
154.
Pyroelectricity and Spontaneous Polarization in [111] Oriented 0.955 Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 Single Crystals 下载免费PDF全文
We report that the measurements of the pyroelectric current of the pre-poled [111]-oriented 0.955 Pb(Zn1/3Nb2/3) O3-0.045 PbTiO3 (PZN-4.5%PT) single crystals can shed some light on the phase transition and spontaneous polarization characters of this material in a similar way to measures of remanent polarization and dielectric properties. The pyroelectric current is measured and the corresponding spontaneous polarization is calculated as a function of temperature with various poling fields added during cooling the sample from 200℃ to room temperature. Critical electric field of 0.061 k V/cm is found to be essential to induce the intermediate ferroelectric orthorhombic phase between the ferroelectric rhombohedral and tetragonal phases. Below the critical field, the polarization increases almost linearly with the increase of poling field. At the critical field, the polarization at 30OC increases abruptly from 14μC/cm^2 for a poling field of O.06kV/cm to 29.5μC/cm^2 for a poling field of 0.061 kV/cm, and afterwards, increases slowly and saturates to 31 μC/cm^2 for poling fields beyond 0.55 kV/cm. 相似文献
155.
Xiao Qi ZHENG Yong Hui WANG Qing Xiang GUO* Li YANG You Cheng LIU Department of Chemistry University of Science Technology of China Hefei National Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 《中国化学快报》2003,(8)
As artificial enzymes, the binding constants of cyclodextrins (CDs) and their substrates are expected to be high1. For this purpose, many kinds of bridged cyclodextrin dimers2 whose two cyclodextrins are linked by various spacers have been constructed. It was of interest to make the dimers, whose binding constants would exceed 108dm3/mol3. Up to date, the bridged cyclodextrin dimers have been extensively studied as enzyme models and as molecular receptors4-6. Recently, we synthesized a brid… 相似文献
156.
157.
Yu‐Hsiang Hu Chuh‐Yung Chen Chen‐Chien Wang Yao‐Hui Huang Shao‐Ping Wang 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4976-4993
The bulk polymerization of styrene initiated by ?‐caprolactam (CL) and n‐dodecyl mercaptan (RSH) has been explored. This novel polymerization system shows living characteristics. For example, the molecular weight of the resulting polymers increases with conversion, and the system has the ability to form diblock copolymers and so forth. The polymer chain end contains thiol and lactam structures, which we have investigated with Fourier transform infrared, 1H NMR, and 13C NMR techniques. Electron spin resonance spectra and theoretical calculations by the Hartree–Fock methods have been used to examine the mechanism. The results reveal that the initial polymerization starts from thiol via a chain‐transfer reaction, and the propagation proceeds by the insertion of a monomer between the terminal group and the intermediate structure of lactam. Finally, the polymerization kinetics have been examined. The polymerization rate varies linearly with the concentration of CL and RSH, and this confirms the mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4976–4993, 2004 相似文献
158.
介绍了一台10mm口径两级双程离轴放大系统,实现了对5mm×5mm口径光束的激光放大,耦合系统采用高功率LDA紧密侧面直接抽运棒状Nd:YLF方式。分析并实验研究了在不同抽运电流、放大脉冲与放大器LDA抽运时刻的不同延时及不同注入能量条件下,放大系统及光束每次放大时放大特性的规律。实验得到:在放大系统5mm×5mm软光阑处注入1.58mJ能量时,放大系统可输出129.2mJ能量,能量提取效率达到19.5%,满足该系统的设计指标。 相似文献
159.
160.