全文获取类型
收费全文 | 545194篇 |
免费 | 7750篇 |
国内免费 | 1546篇 |
专业分类
电工技术 | 9799篇 |
综合类 | 567篇 |
化学工业 | 83094篇 |
金属工艺 | 20378篇 |
机械仪表 | 15594篇 |
建筑科学 | 14271篇 |
矿业工程 | 2415篇 |
能源动力 | 15161篇 |
轻工业 | 48827篇 |
水利工程 | 5361篇 |
石油天然气 | 9383篇 |
武器工业 | 38篇 |
无线电 | 61180篇 |
一般工业技术 | 105323篇 |
冶金工业 | 105742篇 |
原子能技术 | 10685篇 |
自动化技术 | 46672篇 |
出版年
2022年 | 3424篇 |
2021年 | 5333篇 |
2020年 | 3742篇 |
2019年 | 4832篇 |
2018年 | 8211篇 |
2017年 | 7980篇 |
2016年 | 8384篇 |
2015年 | 5966篇 |
2014年 | 9832篇 |
2013年 | 25399篇 |
2012年 | 15542篇 |
2011年 | 21465篇 |
2010年 | 16742篇 |
2009年 | 18603篇 |
2008年 | 19180篇 |
2007年 | 18695篇 |
2006年 | 16326篇 |
2005年 | 14973篇 |
2004年 | 14266篇 |
2003年 | 14003篇 |
2002年 | 13198篇 |
2001年 | 13167篇 |
2000年 | 12180篇 |
1999年 | 12950篇 |
1998年 | 33161篇 |
1997年 | 23220篇 |
1996年 | 17738篇 |
1995年 | 13291篇 |
1994年 | 11549篇 |
1993年 | 11236篇 |
1992年 | 8141篇 |
1991年 | 7606篇 |
1990年 | 7442篇 |
1989年 | 7225篇 |
1988年 | 6631篇 |
1987年 | 5923篇 |
1986年 | 5810篇 |
1985年 | 6478篇 |
1984年 | 6092篇 |
1983年 | 5332篇 |
1982年 | 5047篇 |
1981年 | 5143篇 |
1980年 | 4825篇 |
1979年 | 4743篇 |
1978年 | 4531篇 |
1977年 | 5447篇 |
1976年 | 7096篇 |
1975年 | 3906篇 |
1974年 | 3646篇 |
1973年 | 3738篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A diagonal coordinate representation for Volterra filters is developed and exploited to derive efficient Volterra filter implementations for processing carrier based input signals. In the diagonal coordinate representation, the output is expressed as a sum of linear filters applied to modified input signals. Hence, linear filtering methods are employed to implement the nonlinear filter on a baseband version of the input. Downsampling is then used to reduce computational complexity. The same approach is employed to develop efficient implementations for processing continuous-time carrier-based signals, pulse amplitude-modulated signals, and frequency division multiplexed input signals 相似文献
992.
Tsuji M. Shigesawa H. Frezza F. Lampariello P. Oliner A.A. 《Antennas and Propagation, IEEE Transactions on》1998,46(7):1047-1055
For pt.II ibid., vol.46, no.7, p.1042-46. The article describes the measurements that verify the validity of the theoretical expressions for this new type of antenna. Measurements were made both at millimeter wavelengths (40 to 60 GHz) and in the X-band (8 to 12 GHz) frequency range and of two different quantities: the propagation wavenumbers β and α and radiation patterns. Comparisons were made with numerical values obtained from the theoretical expressions derived in parts I and II and very good agreement was found in all cases 相似文献
993.
M. S. Han S. R. Hahn H. C. Kwon Y. Bin T. W. Kang J. H. Leem Y. B. Hou H. C. Jeon J. K. Hyun Y. T. Jeoung H. K. Kim J. M. Kim T. W. Kim 《Journal of Electronic Materials》1998,27(6):680-683
Double-crystal x-ray rocking curve (DCRC) and secondary-ion mass-spectroscopy (SIMS) measurements have been performed to investigate the effect of rapid thermal annealing on the interdiffusion behavior of Hg in HgTe/CdTe superlattices grown on Cd0.96Zn0.04Te (211)B substrates by molecular beam epitaxy. The sharp satellite peaks of the DCRC measurements on a 100-period HgTe/CdTe (100Å/100Å) superlattice show a periodic arrangement of the superlattice with high-quality interfaces. The negative direction of the entropy change obtained from the diffusion coefficients as a function of the reciprocal of the temperature after RTA indicates that the Hg diffusion for the annealed HgTe/CdTe superlattice is caused by an interstitial mechanism. The Cd and the Hg concentration profiles near the annealed HgTe/CdTe superlattice interfaces, as measured by SIMS, show a nonlinear behavior for Hg, originating from the interstitial diffusion mechanism of the Hg composition. These results indicate that a nonlinear interdiffusion behavior is dominant for HgTe/CdTe superlattices annealed at 190°C and that the rectangular shape of HgTe/CdTe superlattices may change to a parabolic shape because of the intermixing of Hg and Cd due to the thermal treatment. 相似文献
994.
Buffer analysis has traditionally relied heavily on the use of traffic models with short range (exponentially decaying) autocorrelation, e.g. Poisson and Markov modulated Poisson processes. Recent literature has suggested the presence of traffic with slowly (hyperbolically) decaying autocorrelation functions; these sources collectively and individually seem to be exhibiting the phenomenon of long range dependence (LRD). Furthermore, it has been claimed that this sort of traffic may exhibit behaviour, when buffered, that is advantageous in that a smaller buffer may be required than would be the case with non-LRD traffic. This phenomenon has been named the crossover effect, and the authors quantify its relevance to ATM networking, using simulation studies of a homogenous mix of chaotic sources. These show that there is a crossover effect, but the key finding is that this effect is much nearer to a buffer length of zero than was predicted by previous theoretical studies, actually occurring at a value so low that it has no practical significance 相似文献
995.
In reference to the above-titled paper by R.A. DeMillo and A.J. Offutt (see ibid., vol.17, no.9, p.900-10, Sept. 1991), the commenter rates that he and M.R. Woodward (1985) implemented a system for FORTRAN-77 programs that integrates weak mutation and data flow analysis. He reports here that experiments have been carried out by them (1986), using the system to compare the error exposing ability of weak mutation, data flow, and control flow testing strategies 相似文献
996.
The paper presents a review of results concerning the aspartic proteinase cathepsin D and its role in tumor invasion and metastasis. Special attention was paid to the clinical prognostic value of cathepsin D determination in the breast cancer cytosol. 相似文献
997.
Ivo M. Babuka Rodolfo Rodriguez 《International journal for numerical methods in engineering》1993,36(4):539-567
This paper addresses the problem of assessing the quality of an a posteriori error estimate of a finite element solution. An error estimate based on local L2-projections is analysed in the case of translation-invariant meshes. It is shown that for general meshes this technique does not lead to an asymptotically exact estimator. The problem is analysed in detail in the one-dimensional setting. It is shown that an asymptotically exact estimator is not the optimal one when the solution is not sufficiently smooth. An optimal estimator for adaptively constructed meshes is given. Finally, a general mathematical framework for the quality assessment of estimators is introduced. 相似文献
998.
L Struillou M Fiks-Sigaud JH Barrier E Blat G Magadur-Joly 《Canadian Metallurgical Quarterly》1993,60(7-8):524-526
The authors report an exceedingly rare complication of rheumatoid arthritis, i.e. acquired hemophilia due to anti-factor VIII autoantibody production. Treatment with intravenous immune globulin ensured control of hemorrhagic manifestations by inducing a transient rise in factor VIII level. 相似文献
999.
It was found, that To?pa Peat Preparation (TPP) administered to healthy volunteers in doses of 100-300 mg/day during 14 days evoked the stimulation of the phagocytic and bactericidal activity of the granulocytes. The dose of 600 mg/day causes only a transient and insignificant increase of phagocytic and bactericidal properties of the granulocytes. 相似文献
1000.