全文获取类型
收费全文 | 25184篇 |
免费 | 5193篇 |
国内免费 | 7319篇 |
专业分类
化学 | 19138篇 |
晶体学 | 818篇 |
力学 | 1740篇 |
综合类 | 963篇 |
数学 | 3601篇 |
物理学 | 11436篇 |
出版年
2024年 | 54篇 |
2023年 | 319篇 |
2022年 | 898篇 |
2021年 | 927篇 |
2020年 | 974篇 |
2019年 | 1001篇 |
2018年 | 878篇 |
2017年 | 1125篇 |
2016年 | 1063篇 |
2015年 | 1360篇 |
2014年 | 1602篇 |
2013年 | 2065篇 |
2012年 | 2127篇 |
2011年 | 2234篇 |
2010年 | 2135篇 |
2009年 | 2179篇 |
2008年 | 2352篇 |
2007年 | 2068篇 |
2006年 | 2016篇 |
2005年 | 1805篇 |
2004年 | 1327篇 |
2003年 | 967篇 |
2002年 | 932篇 |
2001年 | 885篇 |
2000年 | 960篇 |
1999年 | 628篇 |
1998年 | 387篇 |
1997年 | 300篇 |
1996年 | 250篇 |
1995年 | 251篇 |
1994年 | 206篇 |
1993年 | 199篇 |
1992年 | 191篇 |
1991年 | 145篇 |
1990年 | 125篇 |
1989年 | 120篇 |
1988年 | 109篇 |
1987年 | 100篇 |
1986年 | 76篇 |
1985年 | 50篇 |
1984年 | 62篇 |
1983年 | 63篇 |
1982年 | 39篇 |
1981年 | 34篇 |
1980年 | 42篇 |
1979年 | 22篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1975年 | 6篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
基于FPGA并行处理的实时图像相关速度计 总被引:3,自引:1,他引:2
研究制作了一种采用高速线阵CCD的实时相关速度计,其测量数据的输出速率可达每秒一万次。针对以往光学相关测速方法的问题进行了讨论,探讨了适合FPGA并行处理的算法,制作了高速线阵CCD摄像机及其处理装置。通过实验验证了系统的可行性和可实现性。 相似文献
32.
33.
贝克曼Allegra^TM 21R型超高速离心机开机后,操作面板上出现错误代码“28”,离心机不旋转。离心机的电机采用无刷感应驱动,由电机驱动电源模块BSMl0GD60DN2驱动离心机的电机。故障是由于电源模块BSMl0GD60DN2损坏引起的。采用东芝三相桥式IGBT电源模块MG25Q6ES42代替BSMl0GD60DN2,并更换已烧毁的栅极电阻后。开机试验,仪器恢复正常。 相似文献
34.
Hydrodynamic Properties of Fe3O4 Kerosene-Based Ferrofluids with Narrow Particle Size Distribution
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We investigate the hydrodynamic properties of Fe3O4 kerosene-based ferrofluids with narrow particle size distribution. The ferrofluids are synthesized by improving chemical coprecipitation technique. A narrow distribution of 8.6-10.8nm particle sizes is obtained from the magnetization curve with the free-form model based on the Bayesian inference theory. The fitting result is consistent with average particle size obtained from x-ray diffraction. With the increase of applied magnetic field and magnetic particle concentration, apparent viscosity of ferrofluids increases. At concentration 4.04%, the type of flow for the ferrofluid transforms from Newtonian to Bingham plastic fluid as the applied magnetic field increases. 相似文献
35.
36.
37.
YBa2Cu3O7-x (YBCO) bulk is one of the most important high temperature superconducting materials for magnetic levitation applications, because it has a high magnetic irreversibility field Hirr at liquid nitrogen temperature, and can grow into large grains. The levitation force of YBCO bulk is proportional to the critical current density (Jc) and grain radius (r)[1], so higher Jc and r are appreciated for YBCO bulks to achieve higher levitation force. Now single-domain YBCO bulks up to s… 相似文献
38.
ZHU Yabin ZHOU Yueliang LIU Zhen WANG Shufang CHEN Zhenghao U Huibin YANG Guozhen XlAO Ling Ren Hongtao JIAO Yulei Zheng Minghui 《中国科学G辑(英文版)》2004,47(2):165-172
The irreversibility field (Hirr) of Y-based superconductor is much higher than that of Bi-based superconductor. Y-based superconductor is capable of maintaining stable electrical currents in high magnetic field and electric field, so it is a better suited mate-rial for electric-current applications. Commonly, the Y-based tapes comprise a YBCO thick film deposited on a flexible substrate, typically with an intermediate buffer layer, and an overcoat of noble metal. In this process, the interm… 相似文献
39.
This paper is devoted to a detailed theoretical study of an ion pair SN2 reaction LiNCO+CH3F in the gas phase and in solution at the level of MP2(full)/6-31+G**//HF/6-31+G**. Two possible reaction mechanisms, inversion and retention, are discussed. There are eight possible reaction pathways. The inversion mechanism is more favorable no matter in the gas phase or in solution based on analyses of the transition structures. Methyl isocyanate should form preferentially in the gas phase and more stable methyl cyanate is the main product in solution. The retardation of the reaction in solvents was attributed to the difference in solvation in the separated reactants and in the transition state. 相似文献
40.
Comparing with the exact solutions of the model system of one and two particles coupled to an axial rotor, the quality of the semi classical tilted axis cranking approximation is investigated. Extensive comparisons of the energies and M1 and E2 transition probabilities are carried out for the lowest bands. Very good agreement is found, except near band crossings. Various recipes to take into account finite K within the frame of the usual principal axis cranking are included into the comparison. A set of rules is suggested that permits to construct the excited bands from the cranking configurations, avoiding spurious states. 相似文献