全文获取类型
收费全文 | 11845篇 |
免费 | 1840篇 |
国内免费 | 1466篇 |
专业分类
化学 | 6805篇 |
晶体学 | 146篇 |
力学 | 402篇 |
综合类 | 107篇 |
数学 | 1070篇 |
物理学 | 3364篇 |
无线电 | 3257篇 |
出版年
2024年 | 29篇 |
2023年 | 247篇 |
2022年 | 320篇 |
2021年 | 431篇 |
2020年 | 438篇 |
2019年 | 501篇 |
2018年 | 366篇 |
2017年 | 356篇 |
2016年 | 460篇 |
2015年 | 597篇 |
2014年 | 713篇 |
2013年 | 866篇 |
2012年 | 1032篇 |
2011年 | 1003篇 |
2010年 | 848篇 |
2009年 | 858篇 |
2008年 | 926篇 |
2007年 | 832篇 |
2006年 | 753篇 |
2005年 | 634篇 |
2004年 | 480篇 |
2003年 | 367篇 |
2002年 | 317篇 |
2001年 | 271篇 |
2000年 | 207篇 |
1999年 | 199篇 |
1998年 | 150篇 |
1997年 | 125篇 |
1996年 | 143篇 |
1995年 | 130篇 |
1994年 | 102篇 |
1993年 | 98篇 |
1992年 | 79篇 |
1991年 | 57篇 |
1990年 | 47篇 |
1989年 | 32篇 |
1988年 | 36篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 24篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 196 毫秒
81.
采用MTT比色法对体外培养的肿瘤细胞进行细胞毒作用实验,验证槲寄生蛋白注射液体外抗肿瘤效果.并且鉴定这种检测方法的有效性。实验结果表明槲寄生蛋白注射液有一定的体外抗肿瘤效果;MTT比色法是一种可用的体外细胞毒作用检测法,为新药品的开发提供了实验依据。 相似文献
82.
Chun-Ling Song Lin Xie Zun-Quan Xia 《Journal of Applied Mathematics and Computing》2004,15(1-2):323-331
A new topology in terms of order on fuzzy sets, revealing better the relationship between smooth topology and Chang’s fuzzy topology, is presented in the paper. Some basic properties are discussed. 相似文献
83.
The polycrystalline sample of layered compound FePS_3 has been investigated by using M?ssbauer spectroscopy (12K to 300K), magnetic susceptibility measurements, x-ray diffraction and FTIR spectroscopy. The antiferromagnetic order exists below T_N=120.5±1K. The M?ssbauer spectra below T_N indicate that the magnetization axis is perpendicular to the layer of FePS_3, and the divalent iron cations are in their high spin configurations. By fitting the hyperfine field parameters near the Néel temperature, we obtain information on the nature of magnetic interactions in the material. The results show that the magnetic coupling can be treated by the two-dimensional Ising model, and it can be interpreted on the basis of a crystal-field effect. 相似文献
84.
Zhihong Xia 《Journal of Differential Equations》2004,200(2):185-190
We give a simple proof of a classical result of MacMillan and Bartky (Trans. Amer. Math. Soc. 34 (1932) 838) which states that, for any four positive masses and any assigned order, there is a convex planar central configuration. Moreover, we show that the central configurations we find correspond to local minima of the potential function with fixed moment of inertia. This allows us to show that there are at least six local minimum central configurations for the planar four-body problem. We also show that for any assigned order of five masses, there is at least one convex spatial central configuration of local minimum type. Our method also applies to some other cases. 相似文献
85.
86.
PFC控制技术的一种改进方案 总被引:1,自引:0,他引:1
文章首先指出了目前PFC所用控制技术的缺陷,然后提出了一各改进方案,并从理论分析和仿真验证的角度证明了改进方案的可行性和先进性。 相似文献
87.
Extremely low frequencies (ELFs) are employed to transmit data from underground to the ground surface in the measurement-while-drilling electromagnetic (MWD-EM) telemetry system. Based on electromagnetic field theory, the present work is aimed at predicting the receivability of the signals at the surface. A unified analytic method that is suitable for vertical, directional, or horizontal wells is presented. Attenuation properties are examined for various parameters, including the Earth's conductivity, operating frequency and the length of the drill string. The frequency dependence of the receivability in reference to a noise level is illustrated for different depths of well and different cases. It is also demonstrated that the electric field distributions at the surface have the same features for the three types of well, and that the measurements should be carried out near the well heads for any type of well. A scale model experiment is made to test the authors' theoretical results. The measured data and the computed results are comparable 相似文献
88.
成形反射面天线的设计与综合是近年来卫星天线发展的一个热点问题 ,本文对日本、北美和欧洲成形反射面天线的技术发展和综合方法作了介绍和比较。 相似文献
89.
J. P. Bucher D. C. Douglass P. Xia B. Haynes L. A. Bloomfield 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,19(4):251-254
A new apparatus for measuring the magnetic properties of metal clusters has been constructed. The technique involves the conventional Stern-Gerlach deflection scheme together with modern pulsed laser vaporization source technology and time of flight mass spectrometry. High field seeking monodirectional deflections have been measured for cobalt clusters containing between 40 and 400 atoms. The measured magnetic moments per atom are found to be lower than the known values for the bulk. Special attention has been given to velocity measurements of the metal clusters and the carrier gas atoms in the beam. The residence time of the particles in the source cavity has been measured. 相似文献
90.
由于密码分析研究的进展及DES自身的弱点,原64比特的DES将不能作为数据加密的标准算法而长期存在。在原来工作的基础上,本文提出了256比特的分组密码方案。密码算法由基于混沌映射的数字滤波器构造。 相似文献