全文获取类型
收费全文 | 385129篇 |
免费 | 13447篇 |
国内免费 | 6333篇 |
专业分类
电工技术 | 12202篇 |
技术理论 | 9篇 |
综合类 | 8805篇 |
化学工业 | 62883篇 |
金属工艺 | 22790篇 |
机械仪表 | 18460篇 |
建筑科学 | 13637篇 |
矿业工程 | 7289篇 |
能源动力 | 7392篇 |
轻工业 | 18972篇 |
水利工程 | 6806篇 |
石油天然气 | 20282篇 |
武器工业 | 1073篇 |
无线电 | 35348篇 |
一般工业技术 | 81464篇 |
冶金工业 | 39373篇 |
原子能技术 | 13510篇 |
自动化技术 | 34614篇 |
出版年
2022年 | 6275篇 |
2021年 | 8516篇 |
2020年 | 6486篇 |
2019年 | 6275篇 |
2018年 | 9554篇 |
2017年 | 10271篇 |
2016年 | 10091篇 |
2015年 | 8202篇 |
2014年 | 11753篇 |
2013年 | 17835篇 |
2012年 | 15809篇 |
2011年 | 17968篇 |
2010年 | 14973篇 |
2009年 | 15597篇 |
2008年 | 15603篇 |
2007年 | 14743篇 |
2006年 | 12959篇 |
2005年 | 11219篇 |
2004年 | 9638篇 |
2003年 | 9386篇 |
2002年 | 9353篇 |
2001年 | 8740篇 |
2000年 | 8140篇 |
1999年 | 7151篇 |
1998年 | 9436篇 |
1997年 | 7674篇 |
1996年 | 6110篇 |
1995年 | 5123篇 |
1994年 | 4647篇 |
1993年 | 4537篇 |
1992年 | 4070篇 |
1991年 | 4039篇 |
1990年 | 4096篇 |
1989年 | 3937篇 |
1988年 | 3741篇 |
1987年 | 3681篇 |
1986年 | 3500篇 |
1985年 | 3617篇 |
1984年 | 3516篇 |
1983年 | 3409篇 |
1981年 | 3303篇 |
1980年 | 3336篇 |
1979年 | 3565篇 |
1978年 | 3783篇 |
1977年 | 3772篇 |
1976年 | 4225篇 |
1975年 | 3521篇 |
1974年 | 3591篇 |
1973年 | 3613篇 |
1972年 | 3305篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
Quasi-static stress fields for a crack inclined to the property gradation in functionally graded materials 总被引:3,自引:0,他引:3
Summary. Quasi-static stress fields for a crack inclined to the direction of property gradation in functionally graded materials (FGMs)
are obtained through an asymptotic analysis coupled with Westergaard's stress function approach. The elastic modulus of the
FGM is assumed to vary exponentially along the gradation direction. The mode mixity due to the inclination of the property
gradient is accommodated in the analysis through superposition of opening and shear modes. The first four terms in the expansion
of the stress field are derived to explicitly bring out the influence of nonhomogeneity on the structure of the stress field.
Using these stress field contours of constant maximum shear stress, constant maximum principal stress, constant first stress
invariant and constant out of plane displacement are generated, and the effect of inclination of the property gradation direction
on these contours is discussed.
Received September 22, 2002
Published online: May 20, 2003
The financial support of National Science Foundation (NSF) under grant no. CMS 99000138 is gratefully acknowledged. 相似文献
23.
24.
基于多相滤波器的信道化接收机及其应用研究 总被引:16,自引:0,他引:16
本文主要研究了应用多相滤波技术的信道化接收机建模问题。在给定信道频谱划分方案下,推导了基于多相 滤波器的信道化接收机数学模型。并由此模型设计了一个四信道模拟系统。最后用仿真实验结果验证了模型的正确性。 相似文献
25.
V. N. Tsygankov V. V. Safonov A. I. Kozlov V. P. Gavrilov 《Inorganic Materials》2003,39(10):1076-1078
The GeO2–NiO system is studied in the stability range of Ni2GeO4 by temperature-dependent resistivity measurements, in combination with x-ray diffraction, differential thermal analysis, and thermogravimetry. The resistivity of the starting mixtures and heat-treated samples is measured in the composition range 55–90 mol % NiO. The effect of air humidity on the resistivity of the samples is examined. 相似文献
26.
首次对茂金属聚丙烯(miPP)/齐格勒-纳塔聚丙烯(ziPP)共混体系的流动性进行了系统的研究。研究发现,在miPP/ziPP共混体系中,miPP含量的变化改变了共混体系的相结构,这种相结构会随着温度和剪切速率的变化而产生明显的变化,从而改变了体系的流动性能,且该共混体系在不同剪切速率下的流动曲线可以分别通过两个模型进行模拟。 相似文献
27.
It is often required to detect a long weak signal in Gaussian noise, and frequently, the exact form of that signal is parameterized but not known. A bank of matched filters provides an appropriate detector. However, in some practical applications, there are very many matched filters, and most are quite long. The consequent computational needs may render the classical bank-of-filters approach infeasibly expensive. One example, and our original motivation, is the detection of chirp gravitational waves by an Earth-based interferometer. In this paper, we provide a computational approach to this problem via sequential testing. Since the sequential tests to be used are not for constant signals, we develop the theory in terms of average sample number (ASN) for this case. Specifically, we propose two easily calculable expressions for the ASN: one a bound and the other an approximation. The sequential approach does yield moderate computational savings, but we find that by preprocessing the data using short/medium fast Fourier transforms (FFTs) and an appropriate sorting of these FFT outputs such that the most informative samples are entered to a sequential test first, quite high numerical efficiency can be realized. The idea is simple but appears to be quite successful: Examples are presented in which the computational load is reduced by several orders of magnitude. The FFT is an example of an energy-agglomerating transform, but of course, there are many others. The point here is that the transform need not match the sought signal exactly in the sense that all energy becomes confined to a single sample; it is enough that the energy becomes concentrated, and the more concentrated the better. 相似文献
28.
主要对各国3G许可证与使用技术标准的抽绑政策.各国对2G/3G网络漫游的管制规定。以及3G网络之间共享的种类及实施方式等方面做了详尽的讲解,并进行比较和分析。 相似文献
29.
Thomy V. Dubois L. Vanoverschelde C. Sozanski J.P. Pribetich J. 《IEEE sensors journal》2004,4(6):772-778
This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented. 相似文献
30.