全文获取类型
收费全文 | 725篇 |
免费 | 113篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 6篇 |
综合类 | 31篇 |
化学工业 | 129篇 |
金属工艺 | 10篇 |
机械仪表 | 22篇 |
建筑科学 | 147篇 |
矿业工程 | 4篇 |
能源动力 | 27篇 |
轻工业 | 9篇 |
水利工程 | 2篇 |
石油天然气 | 4篇 |
无线电 | 133篇 |
一般工业技术 | 283篇 |
冶金工业 | 3篇 |
原子能技术 | 5篇 |
自动化技术 | 47篇 |
出版年
2024年 | 6篇 |
2023年 | 53篇 |
2022年 | 16篇 |
2021年 | 43篇 |
2020年 | 54篇 |
2019年 | 63篇 |
2018年 | 43篇 |
2017年 | 42篇 |
2016年 | 42篇 |
2015年 | 26篇 |
2014年 | 41篇 |
2013年 | 47篇 |
2012年 | 24篇 |
2011年 | 18篇 |
2010年 | 31篇 |
2009年 | 35篇 |
2008年 | 20篇 |
2007年 | 29篇 |
2006年 | 24篇 |
2005年 | 17篇 |
2004年 | 20篇 |
2003年 | 22篇 |
2002年 | 12篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 7篇 |
排序方式: 共有862条查询结果,搜索用时 31 毫秒
1.
P. G. Muzykov Y. I. Khlebnikov S. V. Regula Y. Gao T. S. Sudarshan 《Journal of Electronic Materials》2003,32(6):505-510
To establish fast, nondestructive, and inexpensive methods for resistivity measurements of SiC wafers, different resistivity-measurement
techniques were tested for characterization of semi-insulating SiC wafers, namely, the four-point probe method with removable
graphite contacts, the van der Pauw method with annealed metal and diffused contacts, the current-voltage (I-V) technique,
and the contactless resistivity-measurement method. Comparison of different techniques is presented. The resistivity values
of the semi-insulating SiC wafer measured using different techniques agree fairly well. As a result, application of removable
graphite contacts is proposed for fast and nondestructive resistivity measurement of SiC wafers using the four-point probe
method. High-temperature van der Pauw and room-temperature Hall characterization for the tested semi-insulating SiC wafer
was also obtained and reported in this work. 相似文献
2.
文章对国内外开展微区薄层电阻测试的方法进行了综述,特别对改进范德堡四探针技术方法的测试原理、测试过程与测试结果进行了论述与分析,对微区电阻测试方法的进一步发展提出了一种可操作的方法,并研制出新型四探针测试样机。 相似文献
3.
Many-Body Terms in van der Waals Cohesion Energy of Nanotubes 总被引:2,自引:0,他引:2
We have developed a model for the calculation of van der Waals force for layered systems with axial symmetry. Our result can be applied to compute the cohesion of a carbon nanotube to a substrate, the cohesion between nanotubes, and between shells of multiwall nanotubes. We have obtained unusal power laws for the distance dependence of the many-body van der Waals potential. 相似文献
4.
In general, this paper deals with general nonlinear oscillations of a nonconservative and single degree-of-freedom system with odd nonlinearity and, in particular, it presents accurate higher-order analytical approximate solutions to van der Pol damped nonlinear oscillators having odd nonlinearity and the Rayleigh equation. By combining the linearization of the governing equation with harmonic balancing and the method of averaging, we establish accurate analytical approximate solutions for the general weakly damped nonlinear systems. Unlike the classical harmonic balance method, simple linear algebraic equations instead of nonlinear algebraic equations are obtained upon linearization prior to harmonic balancing. The combination of these two methods results in very accurate transient response of the periodic solution. In addition and for the first time, this paper also presents a method for deducing fourth-, fifth- and higher-order linearized governing equations from the lower-order equations without the requirement of formulating the problem from the first principle. Three examples including the van der Pol damped nonlinear oscillator are presented to illustrate the excellent agreement with approximate solution using the exact frequency. 相似文献
5.
6.
On the Predominant Electron-Donicity of Polar Solid Surfaces 总被引:2,自引:0,他引:2
The reasons for the predominant electron-donicity of almost all solid polar surfaces and its implications are discussed in this paper. By contact angle or interfacial tension measurements, the electron-accepting as well as the electron-donating properties of polar liquids can be ascertained, through the interplay between their energies of adhesion and cohesion. For the solid-liquid interface, direct interfacial tension measurements are not possible, but indirectly, solid/liquid interfacial tensions of polar systems can be obtained by contact angle measurement. However, as the energy of cohesion of a solid does not influence the contact angle formed by a liquid drop placed upon its surface, one can only measure the solid surface'ks residual polar property, manifested by the energy of adhesion between solid and liquid. This residual polar property is of necessity the dominant component; in most cases this turns out to be its electron donicity. When, by means of contact angle measurements with polar liquids, both electron-accepting and electron-donating potentials are found on a polar solid, it is most likely still partly covered with a polar liquid: usually water. The amount of residual water of hydration of a polar solid follows from its polar (Lewis acid-base) surface tension component (γAB). The degree of orientation of the residual water of hydration on a polar solid can be expressed by the ratio of the electron-donating to electron-accepting potentials (γ⊖/γ⊕), measured on the hydrated surface. 相似文献
7.
The crystalline complex between poly(γ-methyl l-glutamate) (PMLG) and dimethyl phthalate (DMP) has been formed in films cast from a solution in dichloroethane. It has the stoichiometry of 1 mol of DMP to three or four residues of PMLG and shows two definite characteristics in X-ray diffraction patterns; one is the large hexagonal unit cell with the edge of around 28 Å and another the ‘extra’ 5.07 Å meridional reflection which can not be interpreted by a PMLG α-helical conformation. The structural examination for the films with various DMP contents is carried out by X-ray, viscoelastic, and d.s.c. measurements and the following structure is proposed for the crystalline complex. Four PMLG are associated to form a group which is hexagonally packed and DMP molecules, located in the gaps between groups, form a specific favourable helical structure along PMLG chains in which the van der Waals stacking of benzene rings of DMP is significant. 相似文献
8.
9.
以范·德·拉恩的比例理论为例,对建筑理论研究的目的和方法进行了探讨,结论是:建筑理论研究的根本目的,是从自然规律中提取若干可以指导实践的基本原则或者"法则";为了获得这些法则,人们通常采用的是隐喻和分类,类比和还原等基本策略;在最指实的地方,往往可以得到一种禅宗所说的"顿悟",从这个意义上说,任何真正的建筑理论都不是以神秘主义为直接目标的. 相似文献
10.
本文研究了不确定Van der Pol混沌系统的同步问题,并进行了基于规则的模糊逻辑控制器(FLC)的控制。首先寻找主从Van der Pol混沌系统满足Lyapunov稳定性理论的条件,在此基础上建立模糊规则,设计模糊控制器,实现不确定混沌系统的同步。通过不确定VanderPol混沌系统的两组仿真结果,验证了模糊同步控制方法具有很好的鲁棒性。最后为了进一步验证该方法的有效性,本文在相同条件下,利用反馈控制的方法实现不确定主从VanderPol混沌系统的同步,然后再将此方法的仿真结果与本文的模糊同步控制方法的仿真结果在稳态误差及同步所需时间这两个方面进行对比分析。分析结果验证了本文同步方法的可行性及有效性。 相似文献