全文获取类型
收费全文 | 4098篇 |
免费 | 288篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 36篇 |
化学工业 | 1144篇 |
金属工艺 | 76篇 |
机械仪表 | 110篇 |
建筑科学 | 137篇 |
矿业工程 | 12篇 |
能源动力 | 162篇 |
轻工业 | 638篇 |
水利工程 | 36篇 |
石油天然气 | 19篇 |
无线电 | 291篇 |
一般工业技术 | 645篇 |
冶金工业 | 191篇 |
原子能技术 | 35篇 |
自动化技术 | 859篇 |
出版年
2024年 | 14篇 |
2023年 | 64篇 |
2022年 | 190篇 |
2021年 | 242篇 |
2020年 | 135篇 |
2019年 | 183篇 |
2018年 | 175篇 |
2017年 | 172篇 |
2016年 | 206篇 |
2015年 | 145篇 |
2014年 | 207篇 |
2013年 | 323篇 |
2012年 | 304篇 |
2011年 | 312篇 |
2010年 | 234篇 |
2009年 | 224篇 |
2008年 | 201篇 |
2007年 | 193篇 |
2006年 | 106篇 |
2005年 | 99篇 |
2004年 | 103篇 |
2003年 | 64篇 |
2002年 | 71篇 |
2001年 | 42篇 |
2000年 | 33篇 |
1999年 | 31篇 |
1998年 | 44篇 |
1997年 | 38篇 |
1996年 | 34篇 |
1995年 | 28篇 |
1994年 | 22篇 |
1993年 | 17篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1972年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有4391条查询结果,搜索用时 0 毫秒
1.
Effect of the Twisting Motion on the Nonunifornities of Transmyocardial Fiber Mechanics and Energy Demand A Theoretical Study 总被引:3,自引:0,他引:3
The contraction of the left ventricle (LV) is manifested by a distribution of strains and strain rates throughout the muscle thickness. Using a nested shell spheroidal model of the LV, which accounts for a fiber angle distribution from + 60°at the endocardium to ?60° at the epicardium, and the radial electrical activation pattern from the endocardium to the epicardium, it can be shown that endocardial layers undergo higher strains than the epicardial layers throughout the cardiac cycle, and higher length changes characterize the endocardial sarcomeres relative to the epicardial sarcomeres. However, the calculated nonuniformities in the sarcomeres' shortening are significantly moderated when the physiological twisting motion of the LV around the longitudinal axis is accounted for. Thus, the twisting motion of the heart is a basic mechanism by which the sarcomere function is maintained within its physiological range. 相似文献
2.
3.
Symbolic parametrization of curves 总被引:1,自引:0,他引:1
If algebraic varieties like curves or surfaces are to be manipulated by computers, it is essential to be able to represent these geometric objects in an appropriate way. For some applications an implicit representation by algebraic equations is desirable, whereas for others an explicit or parametric representation is more suitable. Therefore, transformation algorithms from one representation to the other are of utmost importance.We investigate the transformation of an implicit representation of a plane algebraic curve into a parametric representation. Various methods for computing a rational parametrization, if one exists, are described. As a new idea we introduce the concept of working with classes of conjugate (singular or simple) points on curves. All the necessary operations, like determining the multiplicity and the character of the singular points or passing a linear system of curves through these points, can be applied to such classes of conjugate points. Using this idea one can parametrize a curve if one knows only one simple point on it. We do not propose any new method for finding such a simple point. By classical methods a rational point on a rational curve can be computed, if such a point exists. Otherwise, one can express the coordinates of such a point in an algebraic extension of degree 2 over the ground field. 相似文献
4.
Leonardo Badia Andrea Baiocchi Alfredo Todini Simone Merlin Silvano Pupolin Andrea Zanella Michele Zorzi 《Wireless Communications, IEEE》2007,14(1):36-43
Multicellular networks based on the IEEE 802.16 standard appear to be very promising candidates to provide end users with broadband wireless access. However, they also pose interesting challenges in terms of radio resource management, where several design choices are not specified in the standard, intentionally left open to implementors. For this reason, we focus in this article on scheduling and resource allocation, and investigate how they could operate in a cross-layer fashion. In particular, we describe the principles of joint scheduling and resource allocation for IEEE 802.16 operating in AMC mode, and discuss the critical role played by physical layer considerations, especially intercell interference estimation and channel state awareness, in the obtained performance. This leads to identifying key open issues and possible general solutions 相似文献
5.
The authors present experimental results which indicate that a Dy 3+-doped Ga:La:S glass fibre amplifier may be operated efficiently at 1.3 μm with an optimum device length significantly shorter than a comparable Pr3+-doped glass fibre amplifier. Moreover, the efficiency exceeds that obtained from the Pr3+-doped ZBLAN devices currently available 相似文献
6.
7.
Performance improvement is reported resulting from incorporating a semiconductor laser amplifier (SLA) as a post-transmitter-amplifier in long-haul directly modulated optical systems operating in the 1.5 mu m region. This improvement arises from reduction of the chirp produced by the semiconductor laser as the signal passes through the SLA. Eye closure penalty improvements in excess of 5 dB are observed for an illustrative long-haul 4.8 Gbit/s system.<> 相似文献
8.
Javier Lara-Romero Rafael Maya-Yescas José Luis Rico-Cerda José Luis Rivera-Rojas Fernando Chiñas Castillo Matey Kaltchev 《Thin solid films》2006,496(2):463-468
The thermal decomposition of model extreme-pressure lubricant additives on clean iron was studied in ultrahigh vacuum conditions using molecular beam strategies. Methylene chloride and chloroform react to deposit a solid film consisting of FeCl2 and carbon, and evolve only hydrogen into the gas phase. No gas-phase products and less carbon on the surface are detected in the case of carbon tetrachloride. Dimethyl and diethyl disulfide react on clean iron to deposit a saturated sulfur plus carbon layer at low temperatures (∼600 K) and an iron sulfide film onto a Fe + C underlayer at higher temperatures (∼950 K). Methane is the only gas-phase product when dimethyl disulfide reacts with iron. Ethylene and hydrogen are detected when diethyl disulfide is used. 相似文献
9.
Leonardo Setti Pier Giorgio Pifferi Gaetano Lanzarini 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,64(1):41-48
A new mathematical model for n-alkane biodegradation in crude oil, heavy oil and paraffinic mixtures is described. The pattern of n-alkane degradation as a function of the inverse of hydrocarbon chain length reported in this paper can be considered as general behaviour for many aerobic n-alkane biodegradation processes. A new interpretation of n-alkane biodegradation as a function of surface tension, is given. A mathematical expression was obtained starting from the degradation values of n-alkane and relative surface tension, which is a parameter independent of fermentation conditions. An interesting parameter, b, was identified which represented the accelerating conversion factor for n-alkane biodegradation. The findings suggested that the n-alkane biodegradation. The findings suggested that he n-alkane biodegradation rate may be affected by the fermentation condition (agitation, aeration, etc.) and by the strain of microorganism, while the behaviour pattern of n-alkane degradation was essentially linked to the substrate characteristics (molecular structure, molecular weight and density). 相似文献
10.
On formalism and stability of switched systems 总被引:1,自引:1,他引:0
In this paper,we formulate a uniform mathematical framework for studying switched systems with piecewise linear partitioned state space and state dependent switching.Based on known results from the the... 相似文献