全文获取类型
收费全文 | 1525589篇 |
免费 | 25603篇 |
国内免费 | 6986篇 |
专业分类
电工技术 | 34254篇 |
综合类 | 6485篇 |
化学工业 | 271616篇 |
金属工艺 | 64114篇 |
机械仪表 | 42742篇 |
建筑科学 | 47071篇 |
矿业工程 | 11374篇 |
能源动力 | 50220篇 |
轻工业 | 117936篇 |
水利工程 | 15496篇 |
石油天然气 | 37288篇 |
武器工业 | 136篇 |
无线电 | 196395篇 |
一般工业技术 | 287965篇 |
冶金工业 | 170409篇 |
原子能技术 | 33792篇 |
自动化技术 | 170885篇 |
出版年
2021年 | 15586篇 |
2020年 | 11852篇 |
2019年 | 14625篇 |
2018年 | 14856篇 |
2017年 | 14049篇 |
2016年 | 21066篇 |
2015年 | 17373篇 |
2014年 | 28773篇 |
2013年 | 87879篇 |
2012年 | 36176篇 |
2011年 | 48458篇 |
2010年 | 42208篇 |
2009年 | 50363篇 |
2008年 | 45362篇 |
2007年 | 42594篇 |
2006年 | 45610篇 |
2005年 | 39880篇 |
2004年 | 42440篇 |
2003年 | 42290篇 |
2002年 | 41341篇 |
2001年 | 38376篇 |
2000年 | 36638篇 |
1999年 | 35618篇 |
1998年 | 46954篇 |
1997年 | 40595篇 |
1996年 | 36345篇 |
1995年 | 31508篇 |
1994年 | 29562篇 |
1993年 | 29108篇 |
1992年 | 26536篇 |
1991年 | 23628篇 |
1990年 | 23874篇 |
1989年 | 22949篇 |
1988年 | 21449篇 |
1987年 | 19723篇 |
1986年 | 19187篇 |
1985年 | 22572篇 |
1984年 | 22691篇 |
1983年 | 20572篇 |
1982年 | 19426篇 |
1981年 | 19491篇 |
1980年 | 18096篇 |
1979年 | 18743篇 |
1978年 | 17922篇 |
1977年 | 17988篇 |
1976年 | 19542篇 |
1975年 | 16110篇 |
1974年 | 15646篇 |
1973年 | 15720篇 |
1972年 | 13209篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
861.
Wavelength conversion of optical signals over 20 nm is demonstrated using highly nondegenerate four-wave mixing in a semiconductor traveling-wave optical amplifier. This technique has the potential for extremely-high-speed operation and allows continuous tuning of both input and output wavelengths over the amplifier gain bandwidth. It is demonstrated that, even for such a large wavelength conversion range, it is possible to obtain conversion efficiencies in excess of -10 dB and high extinction ratios. The feasibility of the technique is demonstrated by system measurements at 622 Mb/s, showing a 1.1-dB power penalty at 10-9 bit error rate (BER) 相似文献
862.
The author points out that in the transmission-line-matrix (TLM) method, spurious reflection is encountered at the edge of the mesh. By transforming the infinite region exterior to a finite region and discretizing it by a second mesh, the magnitude of reflection is much reduced. Numerical results are presented together with an application 相似文献
863.
Ion beam assisted deposition (IBAD) of thin films is still a new technology with respect to the number of applications. A broader industrial application depends on the availability and versatility of facilities which are able to process various kinds of workpieces under appropriate conditions. Recently, IBAD facilities of the second generation were described in literature and are partially commercially available. In the present report such IBAD machines with their special features such as number and kind of ion sources and evaporators are described. Particularly, the set-up of the ALLIGATOR, a versatile IBAD device for coating complex workpieces under ion bombardment with a broad range of ion energies, is described. As an application example, recent results on the treatment of medical implants are discussed. In -vivo tests of coated cardiovascular stents showed that the deposited noble metal films were effective in influencing the corrosivity and thromboresistance of the implant 相似文献
864.
The thermal expansion of tellurides of germanium, bismuth, and intermetallic compounds is investigated over the temperature range 293-973 K.Belarusian Agricultural Technical University, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 5, pp. 612–616, May 1994. 相似文献
865.
Clive L. Dym 《工程教育杂志》1994,83(4):303-310
This paper describe a freshman course in engineering design that stresses the open-ended and ill-structured nature of design in a project-based context. The projects are chosen in part for their social context and utility. The projects are supplemented by lectures on design methodology and other topics related to engineering practice. Among the deliverables required of the students are proposals, progress reports, and written and oral presentations—the latter to an external design jury as part of a design competition. 相似文献
866.
A general (possibly asymmetric noncausal and/or nonminimum phase) 2D autoregressive moving average random field model driven by an independent and identically distributed 2D nonGaussian sequence is considered. The model is restricted to be invertible, i.e., system zeros are not allowed to lie on the unit bicircle. Three performance criteria are investigated for parameter estimation of the system parameters given only the output measurements (image pixels). The proposed criteria are functions of the higher order cumulant statistics of an inverse filter output. One of these criteria is novel and the others have been considered in past only for moving average inverses and without any analysis of their consistency. In the paper strong consistency of the proposed methods under the assumption that the system order is known is proved. The convergence of the proposed parameter estimators under overparametrization is also analyzed. Experimental results involving synthesized as well as real life textures are presented to illustrate the performance of two of the considered approaches. Experimental results of synthesis of 128x128 textures visually resembling several real life textures in the Brodatz album (and other sources) are presented. 相似文献
867.
J. Faleskog 《International Journal of Fracture》1993,68(2):99-126
Fracture mechanics tests have been performed in the upper shelf region of a steel on large surface cracked plate (SCT) specimens and on small compact tension (CT) specimens. Some of the SCT specimens were subjected to combined tension and bending in such a way that the loading was strongly non-proportional. Crack growth characteristics were compared between the specimens in order to assess possible influences of geometry and nonproportional loading. The differences observed could unambiguously be reduced to and correlated with differences in constraint. Constraint parameters were evaluated by detailed three-dimensional finite element computations and quantities for growing cracks were interpreted on the basis of deformation theory considerations, in analogy with the commonly used J
R-philosophy. It was noted that the initiation of ductile crack growth along a three-dimensional crack front appears to be independent of the degree of local constraint. However, the increase in toughness for a growing crack was markedly affected by the degree of local constraint. Some estimates of the constraints effects regarding stability considerations were also made. 相似文献
868.
869.
The indications and results of single and double lung transplantation are described on the basis of 66 operations performed by the authors and on the background of the world literature. Lung transplantation is considered a new and promising therapeutic mode for treating patients with end-stage pulmonary failure related to fibrosis, emphysema, infective conditions, and pulmonary hypertension yielding satisfactory early results. The long-term prognosis of patients undergoing lung transplantation, like that of any other organ transfer, remains guarded. 相似文献
870.