全文获取类型
收费全文 | 1938篇 |
免费 | 76篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 25篇 |
综合类 | 2篇 |
化学工业 | 475篇 |
金属工艺 | 53篇 |
机械仪表 | 37篇 |
建筑科学 | 56篇 |
矿业工程 | 9篇 |
能源动力 | 58篇 |
轻工业 | 168篇 |
水利工程 | 10篇 |
石油天然气 | 2篇 |
无线电 | 137篇 |
一般工业技术 | 350篇 |
冶金工业 | 291篇 |
原子能技术 | 17篇 |
自动化技术 | 327篇 |
出版年
2023年 | 15篇 |
2022年 | 24篇 |
2021年 | 34篇 |
2020年 | 28篇 |
2019年 | 43篇 |
2018年 | 61篇 |
2017年 | 61篇 |
2016年 | 64篇 |
2015年 | 57篇 |
2014年 | 72篇 |
2013年 | 126篇 |
2012年 | 102篇 |
2011年 | 143篇 |
2010年 | 101篇 |
2009年 | 109篇 |
2008年 | 106篇 |
2007年 | 82篇 |
2006年 | 54篇 |
2005年 | 69篇 |
2004年 | 42篇 |
2003年 | 50篇 |
2002年 | 41篇 |
2001年 | 23篇 |
2000年 | 31篇 |
1999年 | 22篇 |
1998年 | 62篇 |
1997年 | 46篇 |
1996年 | 61篇 |
1995年 | 19篇 |
1994年 | 27篇 |
1993年 | 31篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 19篇 |
1981年 | 9篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 16篇 |
1976年 | 24篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 8篇 |
排序方式: 共有2017条查询结果,搜索用时 15 毫秒
51.
Benoît Valiron 《New Generation Computing》2013,31(1):1-26
This paper is the second part of a series of two articles on quantum computation. If the first part was mostly concerned with the mathematical formalism, here we turn to the programmer’s perspective. We analyze the various existing models of quantum computation and the problem of the stability of quantum information. We discuss the needs and challenges for the design of a scalable quantum programming language. We then present two interesting approaches and examine their strengths and weaknesses. Finally, we take a step back, and review the state of the research on the semantics of quantum computation, and how this can help in achieving some of the goals. 相似文献
52.
A protective layers were prepared on a magnesium electrode by treatment in different solutions and times after modification in 0.15 M HCl for 20 seconds. The corrosion of magnesium coated protective layer with different compounds was studied by using potential-time, current-potential curves and AC impedance spectra. The coatings morphology depends on the treating bath compositions and immersion times. The protective efficiencies of the surface layers were calculated by using corrosion rates obtained by extrapolation of Tafel zones of current-potential curves to the corrosion potential and by using Stern-Geary equation with polarization resistance from impedance spectra. 相似文献
53.
Sezai K��t��k S��leyman Bolat Kemal ?zt��rk ?enol Akbulut Ekrem Yanmaz 《Journal of Superconductivity and Novel Magnetism》2011,24(1-2):471-474
The flame-quench-melt-growth (FQMG) method was used for the preparation of bulk YBa2Cu3O7?x (Y123). Both the superconducting and nonsuperconducting regions changing with thickness of superconducting sample were determined by X-ray diffraction (XRD) patterns and also observed at micrographs taken by the polarized optical microscope. It was observed that superconducting forming ratio which was examined for different thicknesses of the sample ranging from 6.54 to 1.58 mm strongly enhanced. This means that a region near the top surface of the sample contains more superconducting phase than the other regions. These observations would be helpful in designing and manufacturing the practical applications of YBCO systems. 相似文献
54.
Andres Castellanos‐Gomez Magdalena Wojtaszek Nikolaos Tombros Nicolás Agraït Bart J. van Wees Gabino Rubio‐Bollinger 《Small (Weinheim an der Bergstrasse, Germany)》2011,7(17):2491-2497
By mechanical exfoliation, it is possible to deposit atomically thin mica flakes down to single‐monolayer thickness on SiO2/Si wafers. The optical contrast of these mica flakes on top of a SiO2/Si substrate depends on their thickness, the illumination wavelength, and the SiO2 substrate thickness, and can be quantitatively accounted for by a Fresnel‐law‐based model. The preparation of atomically thin insulating crystalline sheets will enable the fabrication of ultrathin, defect‐free insulating substrates, dielectric barriers, or planar electron‐tunneling junctions. Additionally, it is shown that few‐layer graphene flakes can be deposited on top of a previously transferred mica flake. Our transfer method relies on viscoelastic stamps, as used for soft lithography. A Raman spectroscopy study shows that such an all‐dry deposition technique yields cleaner and higher‐quality flakes than conventional wet‐transfer procedures based on lithographic resists. 相似文献
55.
This paper presents a numerical method to calculate the value function for a general discounted impulse control problem for piecewise deterministic Markov processes. Our approach is based on a quantization technique for the underlying Markov chain defined by the post jump location and inter-arrival time. Convergence results are obtained and more importantly we are able to give a convergence rate of the algorithm. The paper is illustrated by a numerical example. 相似文献
56.
Ş. Aydoğan M. Sağlam A. Türüt Y. Onganer 《Materials science & engineering. C, Materials for biological applications》2009,29(4):1486-1490
The current–voltage (I–V) characteristics of Polypyrrole(PPy)/p-Si/Al structure have been investigated as a function of temperature. A modified Norde function combined with conventional forward I–V method has been used to extract the junction parameters including the ideality factor, barrier height and series resistance. Norde function has been compared with the Cheung functions and it has been seen that there is a good agreement with both method for the barrier height values. However, the values of series resistance have very different especially towards to the lower temperatures. This is attributed to non-ideal I–V characteristics of the Au/PPy/p-Si/Al structure and non-pure Thermionic emission theory due to the low temperature effects. 相似文献
57.
Ass. Prof. Dr. Gulsun ?zyurt Ali Serhat ?zk��t��k Abdurrahman Polat 《Journal für Verbraucherschutz und Lebensmittelsicherheit》2011,6(2):167-174
The effects of rosemary extract addition on oxidative stability of cooked sea bream during frozen storage period were investigated. Sea bream fillets were fried, oven baked and grilled. Three groups with rosemary extract were also cooked by the same methods and cooked samples (with and without rosemary extract) were stored in ?18?°C for 4?months. After cooking procedures, the FFA formation was quite similar in fresh-raw and fried sea bream fillets, but significantly increased oven baked (0.31?C0.33% oleic acid) and grilled fillets (0.39?C0.40% oleic acid). The highest value of PV was also obtained from grilled fillets (1.18?C1.58?meq/kg). However, TBA values (1.92?mg MA/kg for fresh-raw fillet) did not increase in sea bream fillets after the frying and grilling procedure except oven baking without rosemary extract (2.41?mg MA/kg). A considerable increase in the FFA, PV and TBA was observed in all cooked groups during frozen storage period. The treated samples with rosemary extract generally showed slower PV and TBA formation than those of the untreated samples. However, the additions of rosemary extract have positive effect on sensory quality of baked sea bream. 相似文献
58.
The oxidative coupling of methane (OCM) has been found to be structure sensitive on La2O3 catalysts exhibiting different crystallite morphologies. Thin plates obtained by thermal decomposition of lanthanum nitrate at 650 °C are more selective on OCM reaction performed at 750 °C than the particles obtained by decomposition of the nitrate at 800 °C. It is assumed that the oxycarbonate observed is formed from the methane deep oxidation on the catalyst surface. This compound appears to act as an intermediate in the production of CO2 and is thus important hi the resulting selectivity. 相似文献
59.
Véronique Gauthier Benoît Cochepin Sylvain Dubois Dominique Vrel 《Journal of the American Ceramic Society》2006,89(9):2899-2907
Ti3 SiC2 is synthesized by self-propagating high-temperature synthesis (SHS) of elemental titanium, silicon, and graphite powders. The reaction paths and structure evolution are studied in situ during the SHS of the 3Ti+Si+2C mixture by time-resolved X-ray diffraction coupled with infrared thermography. The proposed reaction mechanism suggests that Ti3 SiC2 might be formed from Ti–Si liquid phase and solid TiC x . Finally, the effect of the powders starting composition on the Ti3 SiC2 synthesis is studied. For the investigated initial mixtures, TiC x is always formed as a major impurity together with the Ti3 SiC2 phase. 相似文献
60.
Differential retention of carbon, nitrogen and phosphorus in grassland soil profiles with long-term manure application 总被引:3,自引:0,他引:3
D. A. Angers M. H. Chantigny J. D. MacDonald P. Rochette D. Côté 《Nutrient Cycling in Agroecosystems》2010,86(2):225-229
Liquid hog manure (LHM) is a valuable source of nutrients for farm production. Long-term experimental plots that had received LHM applications of 0, 50, and 100 m3 ha?1 annually for 20 years were analyzed for total soil C, N and P storage. Applications increased total soil N and P by 1,200 kg N ha?1 and 850 kg P ha?1 at 100 m?3 LHM year?1, compared to the control treatment. However, C storage did not increase with LHM rates and was lower in the 50 m3 ha?1 LHM treatment (86 Mg C ha?1) than in the 0 or 100 m3 ha?1 treatments (100 Mg C ha?1). In addition to the limited quantities and high decomposability of the C supplied by LHM, it is hypothesized that LHM stimulated the mineralization of both native soil C and fresh root-derived material. This priming effect was particularly apparent in deeper soil horizons where the decomposability of native C may be limited by the supply of fresh C. This study indicates that while LHM can be a significant source of crop nutrients, it has limited capacity for maintaining or increasing soil C. 相似文献