全文获取类型
收费全文 | 2844篇 |
免费 | 133篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 29篇 |
综合类 | 2篇 |
化学工业 | 793篇 |
金属工艺 | 60篇 |
机械仪表 | 62篇 |
建筑科学 | 92篇 |
矿业工程 | 4篇 |
能源动力 | 93篇 |
轻工业 | 171篇 |
水利工程 | 15篇 |
石油天然气 | 7篇 |
无线电 | 271篇 |
一般工业技术 | 586篇 |
冶金工业 | 399篇 |
原子能技术 | 12篇 |
自动化技术 | 382篇 |
出版年
2023年 | 23篇 |
2022年 | 51篇 |
2021年 | 84篇 |
2020年 | 61篇 |
2019年 | 65篇 |
2018年 | 72篇 |
2017年 | 57篇 |
2016年 | 86篇 |
2015年 | 57篇 |
2014年 | 72篇 |
2013年 | 156篇 |
2012年 | 143篇 |
2011年 | 158篇 |
2010年 | 130篇 |
2009年 | 107篇 |
2008年 | 145篇 |
2007年 | 131篇 |
2006年 | 105篇 |
2005年 | 95篇 |
2004年 | 93篇 |
2003年 | 67篇 |
2002年 | 72篇 |
2001年 | 57篇 |
2000年 | 57篇 |
1999年 | 42篇 |
1998年 | 77篇 |
1997年 | 53篇 |
1996年 | 50篇 |
1995年 | 50篇 |
1994年 | 40篇 |
1993年 | 39篇 |
1992年 | 32篇 |
1991年 | 24篇 |
1990年 | 28篇 |
1989年 | 24篇 |
1988年 | 22篇 |
1987年 | 24篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 21篇 |
1983年 | 27篇 |
1982年 | 17篇 |
1981年 | 21篇 |
1979年 | 13篇 |
1978年 | 24篇 |
1977年 | 21篇 |
1976年 | 22篇 |
1975年 | 17篇 |
1974年 | 17篇 |
1973年 | 15篇 |
排序方式: 共有2978条查询结果,搜索用时 15 毫秒
81.
82.
Mixture model for face-color modeling and segmentation 总被引:11,自引:0,他引:11
In this paper, we propose a general methodology for face-color modeling and segmentation. One of the major difficulties in face detection and retrieval is partial face extraction due to highlights, shadows and lighting variations. We show that a mixture-of-Gaussians modeling of the color space, provides a robust representation that can accommodate large color variations, as well as highlights and shadows. Our method enables to segment within-face regions, and associate semantic meaning to them, and provides statistical analysis and evaluation of the dominant variability within a given archive. 相似文献
83.
K. T. Jacob 《Journal of Materials Science》1980,15(9):2167-2174
The phase diagram of the Cr-W-O system at 1000° C was established by metallographic and X-ray identification of the phases present after equilibration in evacuated silica capsules. Two ternary oxide phases, CrWO4 and Cr2WO6 were detected. The oxygen potential over the three-phase mixtures, W+Cr2O3 s+CrWO4, WO2.90+CrWO4+Cr2WO6 and Cr2O3+CrWO4+Cr2WO6, were measured by solid state cells incorporating Y2O3 stabilized ZrO2 electrolyte and Ni+NiO reference electrode. The Gibbs' energies of formation of the two ternary phases can be represented by the following equations $$\begin{gathered} W(s) + \tfrac{1}{2} Cr_2 O_3 (s) + \tfrac{5}{4} O_2 (g) \to CrWO_4 (s) \hfill \\ \Delta G^0 = - 172 047 + 48.725T ( \pm 230) cal mol^{ - 1} \hfill \\ Cr_2 O_3 (s) + WO_3 (s) \to Cr_2 WO_6 (s) \hfill \\ \Delta G^0 = - 3 835 + 0.235{\rm T} ( \pm 500) cal mol^{ - 1} \hfill \\ \end{gathered}$$ 相似文献
84.
Xiaozhen Mou Jisha Jacob Xinxin Lu Steven Robbins Shulei Sun Joseph D. Ortiz 《Journal of Great Lakes research》2013
Studies on the bacterial communities in Lake Erie have been largely focused on cyanobacteria. To characterize the community structure of the other bacteria, we examined the 16S rRNA gene content of free-living (FL) and particle-associated (PA) bacterioplankton populations in Sandusky Bay (SD) and adjacent waters in the Western Basin (WB) of Lake Erie. A comprehensive survey of nutrients and other limnological variables was also performed in parallel. A total of 18,569 of 16S rRNA V6 pyrotag sequences were recovered, which were affiliated with 64 unique bacterial orders within 14 phyla. FL bacteria were composed differently from PA ones and contained significantly more Actinomycetales. In addition, FL bacteria were taxonomically more diverse. Despite the distinct environmental conditions, compositional variation was insignificant between bacteria in the SD and WB samples. 相似文献
85.
Islam Z Capatina D Ruff JP Das RK Trakhtenberg E Nojiri H Narumi Y Welp U Canfield PC 《The Review of scientific instruments》2012,83(3):035101
We present a pulsed-magnet system that enables x-ray single-crystal diffraction in addition to powder and spectroscopic studies with the magnetic field applied on or close to the scattering plane. The apparatus consists of a single large-bore solenoid, cooled by liquid nitrogen. A second independent closed-cycle cryostat is used for cooling samples near liquid helium temperatures. Pulsed magnetic fields close to ~30 T with a zero-to-peak-field rise time of ~2.9 ms are generated by discharging a 40 kJ capacitor bank into the magnet coil. The unique characteristic of this instrument is the preservation of maximum scattering angle (~23.6°) on the entrance and exit sides of the magnet bore by virtue of a novel double-funnel insert. This instrument will facilitate x-ray diffraction and spectroscopic studies that are impractical, if not impossible, to perform using split-pair and narrow-opening solenoid magnets. Furthermore, it offers a practical solution for preserving optical access in future higher-field pulsed magnets. 相似文献
86.
In this paper we propose a new unsupervised dimensionality reduction algorithm that looks for a projection that optimally preserves the clustering data structure of the original space. Formally we attempt to find a projection that maximizes the mutual information between data points and clusters in the projected space. In order to compute the mutual information, we neither assume the data are given in terms of distributions nor impose any parametric model on the within-cluster distribution. Instead, we utilize a non-parametric estimation of the average cluster entropies and search for a linear projection and a clustering that maximizes the estimated mutual information between the projected data points and the clusters. The improved performance is demonstrated on both synthetic and real world examples. 相似文献
87.
Jacob Theodore; Fagin Robert; Perry Joseph; Van Dyke Ruth A. 《Canadian Metallurgical Quarterly》1975,11(3):393
Upper-, middle-, and lower-class parents were asked to explain a proverb which had both "growth" and "stability" interpretations to their 11- and 16-yr-old sons. The growth interpretation was overwhelmingly endorsed by most parents. With 16-yr-olds, lower-middle-class parents continued to endorse the growth interpretation; most upper-class parents endorsed the stability interpretation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
88.
A young female with ulcerative colitis associated with positive direct and indirect Coombs reaction and severe autoimmune hemolytic anemia is reported. Cortisone was beneficial and total colectomy was promptly followed by subsidence of the hematologic defects. Review of the literature suggests that this complication of ulcerative colitis is uncommon. It basis is unclear. It seems to be expressed through the presence of a "warm" auto-antibody. Colectomy should be strongly considered when severe hemolysis is present but not when the Coombs test is positive alone without significant hemolysis. 相似文献
89.
The oxidative erosion of seven types of graphite has been investigated by heating in air at temperatures between 600 and 1000 K. The specimens include pyrolytic graphite, fine-grain graphites, carbon-fibre composites (CFC), and graphites doped with Si and Ti. The weight loss was measured using a microbalance, the surface morphology by scanning electron microscopy, and the composition of the surface layer by MeV ion beam techniques. Pyrolytic graphite is least affected by erosion, while pure and Si-doped CFCs erode particularly fast. Typical erosion rates for specimens with a surface area of ?4 cm2 are below 0.2 μg/m2 s at 600 K for all graphite types, and at 900 K range from 0.34 mg/m2 s for pyrolytic graphite to about 9 mg/m2 s for the strongest eroding types. The temperature dependence of the erosion rate of all types of graphite studied is well described by an activation energy of 1.7 eV. The erosion rates of these graphites are by far lower than the removal rates for deposited amorphous hydrocarbon layers. In contrast to all other types, the Ti-doped graphite absorbs a significant amount of oxygen reaching up to ?5% of its original mass. Once the oxygen uptake is saturated, it erodes with rates similar to those of the strongest eroding types. 相似文献
90.
Jacques Angel Alain Boissier Sylvain Lallemant Franois Leblanc Bertrand Pcout Jacob W. Lin James Tung 《Journal of the Society for Information Display》2003,11(3):533-538
Abstract— As the need for high‐resolution ultra‐low‐power bistable displays grows, it is important to rapidly implement the mass‐production manufacturing of BiNem® LCDs. The cost‐effective approach for BiNem® manufacturing is based on using STN manufacturing process technologies since BiNem® and STN displays have a similar internal structure. The key differences between BiNem® and STN displays from a manufacturing point of view will be discussed. We show that industrial STN manufacturing equipment can be used to produce BiNem® LCDs at competitive costs. Reflective e‐book display modules with VGA resolution are produced in the pilot‐production series. 相似文献