全文获取类型
收费全文 | 8306篇 |
免费 | 505篇 |
国内免费 | 45篇 |
专业分类
电工技术 | 160篇 |
综合类 | 12篇 |
化学工业 | 2188篇 |
金属工艺 | 249篇 |
机械仪表 | 221篇 |
建筑科学 | 295篇 |
矿业工程 | 15篇 |
能源动力 | 475篇 |
轻工业 | 808篇 |
水利工程 | 77篇 |
石油天然气 | 164篇 |
无线电 | 898篇 |
一般工业技术 | 1558篇 |
冶金工业 | 411篇 |
原子能技术 | 48篇 |
自动化技术 | 1277篇 |
出版年
2024年 | 22篇 |
2023年 | 164篇 |
2022年 | 360篇 |
2021年 | 431篇 |
2020年 | 308篇 |
2019年 | 363篇 |
2018年 | 487篇 |
2017年 | 363篇 |
2016年 | 370篇 |
2015年 | 277篇 |
2014年 | 341篇 |
2013年 | 710篇 |
2012年 | 415篇 |
2011年 | 505篇 |
2010年 | 396篇 |
2009年 | 393篇 |
2008年 | 332篇 |
2007年 | 242篇 |
2006年 | 260篇 |
2005年 | 187篇 |
2004年 | 163篇 |
2003年 | 185篇 |
2002年 | 144篇 |
2001年 | 110篇 |
2000年 | 121篇 |
1999年 | 106篇 |
1998年 | 147篇 |
1997年 | 84篇 |
1996年 | 75篇 |
1995年 | 59篇 |
1994年 | 54篇 |
1993年 | 54篇 |
1992年 | 40篇 |
1991年 | 36篇 |
1990年 | 26篇 |
1989年 | 36篇 |
1988年 | 41篇 |
1987年 | 46篇 |
1986年 | 34篇 |
1985年 | 36篇 |
1984年 | 30篇 |
1983年 | 32篇 |
1982年 | 22篇 |
1981年 | 25篇 |
1980年 | 30篇 |
1978年 | 28篇 |
1977年 | 25篇 |
1976年 | 33篇 |
1975年 | 21篇 |
1973年 | 19篇 |
排序方式: 共有8856条查询结果,搜索用时 0 毫秒
31.
Educational research over the past three years has intensified such that the context of learning resources needs to be properly modeled. Many researchers have described and even mandated the use of ontologies in the research being conducted, yet the process of actually connecting one or more ontologies to a learning object has not been extensively discussed. This paper describes a practical model for associating multiple ontologies with learning objects while making full use of the IEEE LOM specification. The model categorizes these ontologies according to five major categories of context based on the most popular fields of study actively being pursued by the educational research community: Thematic context, Pedagogical context, Learner context, Organizational context, and Historical/Statistical context. 相似文献
32.
33.
A El?i 《Canadian Metallurgical Quarterly》1994,50(12):8882-8884
34.
Lentils, rice and their blend (Koshary) were cooked by traditional Egyptian methods. Cooking resulted in slight changes in the total nitrogen, as well as in the non-protein nitrogen (NPN), ether extract and crude fibre of the three products, compared with raw grains. In contrast, significant decreases were found in the mineral elements, indicating losses through leaching, on washing and cooking. The mineral composition of lentils' cooking liquor confirmed this. 相似文献
35.
36.
Mohammed Nurul Afsar Hua Chi 《Journal of Infrared, Millimeter and Terahertz Waves》1994,15(7):1161-1179
The room temperature application of sapphire as window material at higher frequencies is not feasible since its absorption coefficient increases almost linearly with increasing frequency in the millimeter wavelength region. At cryogenic temperature the absorption coefficient value decreases only by a few factors (factor of 2 to 3) in the 90 – 200 GHz region. The earlier reported temperature squared dependence (decrease) in the absorption coefficient or the loss tangent value is totally absent in our broad band continuous wave data we are reporting here (at 6.5 K, 35K, 77K and 300K) and one we reported at conferences earlier. Our results are verified by another technique. We utilize our precision millimeter wave dispersive Fourier transform spectroscopic techniques at room temperature and at cryogenic temperatures The extra high resistivity single crystal compensated silicon is no doubt the lowest loss material available at room temperature in the entire millimeter wavelength region At higher millimeter wave frequencies an extra high resistivity silicon window or an window made with extra high resistivity silicon coated with diamond film would certainly make a better candidate in the future. A single free standing synthetic diamond window seems to have higher absorption coefficient values at millimeter wavelength region at this time although it is claimed that it possesses good mechanical strength and higher thermal conductivity characteristics. It certainly does not rule out the use of diamond film on a single crystal high resistivity silicon to improve its mechanical strength and thermal conductivity 相似文献
37.
Modified tracking loop for DS spread spectrum systems 总被引:1,自引:0,他引:1
A nonconventional pseudo-noise (PN) code tracking loop for direct sequence (DS) spread spectrum systems is presented. It solves problems of component imbalance while maintaining hardware simplicity.<> 相似文献
38.
The effect of matrix microcracking on the stiffnesses of a carbon-fibre/SiC-matrix woven composite is studied by means of an ultrasonic method. It provides the whole set of the stiffness tensor coefficients which are inaccessible by classical strain measurements and which are required to identify anisotropic damage. The induced anisotropy depends on the loading direction. If a tensile solicitation in a fibre direction leads to stiffnesses decreases without any rotation of principal axes, a tensile solicitation of 45° from a fibre direction creates microcracks with a predominant orientation that does not coincide with the elastic symmetry axes, and induce a fully anisotropic elastic degradation. 相似文献
39.
O Soetens M Crabeel B El Moualij C Duyckaerts F Sluse 《Canadian Metallurgical Quarterly》1998,258(2):702-709
In this work we have characterised the transport of L-arginine and L-ornithine into mitochondria isolated from a wild-type Saccharomyces cerevisiae strain and an isogenic arg11 knock-out mutant. The Arg11 protein (Arg11p) is a mitochondrial carrier required for arginine biosynthesis [Crabeel, M., Soetens, O., De Rijcke, M., Pratiwi, R. & Pankiewicz, R. (1996) J. Biol. Chem. 271, 25011-25019]. Reconstitution experiments have confirmed that it is an L-ornithine carrier also transporting L-arginine and L-lysine by order of decreasing affinity, but not L-histidine [Palmieri, L., De Marco, V., Iacobazzi, V., Palmieri, F., Runswick, M. & Walker, J. (1997) FEBS Lett. 410, 447-451]. Evidence is presented here that the mitochondrial inner membrane contains an L-arginine and L-ornithine transporting system distinct from Arg11p, in keeping with the arginine leaky phenotype of arg11 knock-out mutants. The newly characterised carrier, which we propose to name Bac1p (basic amino acid carrier), behaves as an antiporter catalysing the electroneutral exchange of the basic amino acids L-arginine, L-lysine, L-ornithine and L-histidine and displays the highest affinity for L-arginine (Km of 30 microM). L-Arginine uptake has a pH optimum in the range of 7.5-9 and is inhibited by several sulphydryl reagents, by pyridoxal 5'-phosphate and by cations. 相似文献
40.