全文获取类型
收费全文 | 4102篇 |
免费 | 115篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 65篇 |
综合类 | 13篇 |
化学工业 | 991篇 |
金属工艺 | 85篇 |
机械仪表 | 88篇 |
建筑科学 | 241篇 |
矿业工程 | 18篇 |
能源动力 | 98篇 |
轻工业 | 577篇 |
水利工程 | 22篇 |
石油天然气 | 4篇 |
无线电 | 377篇 |
一般工业技术 | 740篇 |
冶金工业 | 478篇 |
原子能技术 | 55篇 |
自动化技术 | 373篇 |
出版年
2022年 | 33篇 |
2021年 | 48篇 |
2020年 | 35篇 |
2019年 | 51篇 |
2018年 | 51篇 |
2017年 | 55篇 |
2016年 | 86篇 |
2015年 | 91篇 |
2014年 | 97篇 |
2013年 | 155篇 |
2012年 | 191篇 |
2011年 | 176篇 |
2010年 | 129篇 |
2009年 | 163篇 |
2008年 | 135篇 |
2007年 | 150篇 |
2006年 | 156篇 |
2005年 | 125篇 |
2004年 | 111篇 |
2003年 | 95篇 |
2002年 | 97篇 |
2001年 | 73篇 |
2000年 | 57篇 |
1999年 | 68篇 |
1998年 | 129篇 |
1997年 | 106篇 |
1996年 | 69篇 |
1995年 | 71篇 |
1994年 | 65篇 |
1993年 | 55篇 |
1992年 | 64篇 |
1991年 | 52篇 |
1990年 | 45篇 |
1989年 | 53篇 |
1988年 | 55篇 |
1987年 | 64篇 |
1986年 | 53篇 |
1985年 | 46篇 |
1984年 | 58篇 |
1983年 | 53篇 |
1982年 | 46篇 |
1981年 | 54篇 |
1980年 | 44篇 |
1979年 | 44篇 |
1978年 | 45篇 |
1977年 | 48篇 |
1976年 | 59篇 |
1974年 | 32篇 |
1973年 | 35篇 |
1971年 | 33篇 |
排序方式: 共有4225条查询结果,搜索用时 15 毫秒
81.
82.
László Neumann Kreimir Matkovi Attila Neumann & Werner Purgathofer 《Computer Graphics Forum》1998,17(4):235-247
Every rendering process consists of two steps. The first is the computing of luminance values by methods like ray tracing or radiosity, and the second step is the mapping of the computed values to values appropriate for displaying. In the last years, as alternative to simple linear scaling which maps the average value to the medium luminance, some new ways of mapping were introduced. These new methods are based on photography analogies and on human vision models. All existing methods follow, implicitly or explicitly, the reflected light metering principle. The method introduced in this paper is the first that follows the incident light metering used in professional photography and in the movie industry. Actually the irradiances are measured using a set of diffusors, which are placed automatically in the scene, and a linear scale factor based on these measurements is used to map the computed radiances to the display device. The diffusors act as half space integrators, they collect the light energy from all half space directions. The light comes from the primary light sources, or it is the result of various interreflections. The newly introduced method reproduces original colors faithfully even for scenes with very low or very high average reflectivity. 相似文献
83.
Hardy JL Delahunt PB Okajima K Werner JS 《Journal of the Optical Society of America. A, Optics, image science, and vision》2005,22(1):49-59
Chromatic contrast thresholds for spatially varying patterns of various spatial frequencies (0.5, 1, 2, and 4 cycles per degree) were measured for ten older (65-77 yr of age) and ten younger (18-30 yr of age) observers. The stimuli were Gabor patches modulated along S-varying or (L - M)-varying chromatic axes. Thresholds were determined for two sets of stimuli. For one set of stimuli, the mean chromaticity and luminance were equated at the cornea for all observers. The second set of stimuli was corrected for ocular media density differences to equate stimulation of each of the three cone types at the retina for each individual. Chromatic contrast thresholds were higher for older observers for all stimuli tested. The magnitude of this difference showed little dependence on spatial frequency. When stimuli were equated at the cornea, this difference was greater for S-varying stimuli. When stimuli were equated at the retina, the age-related difference in thresholds for S-varying stimuli was reduced. Both optical and neural factors contribute to these age-related losses in spatial chromatic contrast sensitivity. 相似文献
84.
85.
86.
Microcavity-integrated graphene photodetector 总被引:2,自引:0,他引:2
Furchi M Urich A Pospischil A Lilley G Unterrainer K Detz H Klang P Andrews AM Schrenk W Strasser G Mueller T 《Nano letters》2012,12(6):2773-2777
There is an increasing interest in using graphene (1, 2) for optoelectronic applications. (3-19) However, because graphene is an inherently weak optical absorber (only ≈2.3% absorption), novel concepts need to be developed to increase the absorption and take full advantage of its unique optical properties. We demonstrate that by monolithically integrating graphene with a Fabry-Pérot microcavity, the optical absorption is 26-fold enhanced, reaching values >60%. We present a graphene-based microcavity photodetector with responsivity of 21 mA/W. Our approach can be applied to a variety of other graphene devices, such as electro-absorption modulators, variable optical attenuators, or light emitters, and provides a new route to graphene photonics with the potential for applications in communications, security, sensing and spectroscopy. 相似文献
87.
In 2020, gastric cancer was the fourth leading cause of cancer deaths globally. About 90% of gastric cancers are sporadic and the vast majority are correlated with Helicobacter pylori infection; whereas familial clustering is observed in about 10% of cases. Gastric cancer is now considered to be a disease originating from dysregulated self-renewal of the gastric glands in the setting of an inflammatory environment. The human stomach contains two types of gastric units, which show bi-directional self-renewal from a complex variety of stem cells. This review focuses on recent progress concerning the characterization of the different stem cell populations and the mainly mesenchymal signals triggering their stepwise differentiation as well as the genesis of pre-cancerous lesions and carcinogenesis. Furthermore, a model is presented (Lectin-triggered Receptor Blocking Hypothesis) explaining the role of the lectin TFF1 as an antral tumor suppressor possibly regulating Lgr5+ antral stem cells in a paracrine or maybe autocrine fashion, with neighboring antral gland cells having a role as niche cells. 相似文献
88.
The potential of statistical analyses of functional magnetic resonance images using various threshold strategies in combination with correlation analysis was studied by simulating brain activation. Differences in statistical Type I () and II () errors are substantial for the various thresholds. Absolute thresholds and individualized thresholds based on the assumption of a gaussian noise distribution are producing constant -errors and thus do not sufficiently improve discrimination of truly activated pixels even for very high contrast-to-noise ratios (CNR). Only relative threshold strategies related to the maximum correlation coefficient and thus the individual data quality and activation level, i.e., a data-driven approach, can perfectly discriminate true positives, at least for CNR>2.5. To further improve discrimination of activated and non-activated pixel in studies with lower CNR, additional prior knowledge would be necessary. From the data presented, one would also expect that the best performing threshold strategy in this simulation study would perform best underin vivo conditions.Preliminary results presented in abstract form at the 13th Annual ESMRMB Meeting, Prague, Czech Republic, September 12–15, 1996. 相似文献
89.
Karl Sauer Diemair E. Dinslage Kanitz Schwaibold Willy Lindner Haevecker Lehnartz E. Becker W. Schreiber Werner Hofmann Eduard Hofmann Steinbeck H. Süllmann Griebel Rudolf Abderhalden Lars Erlandsen Heyns O. v. Soden C. Steinhoff J. Großfeld Frey-Wyssling W. Sutthoff Bäurle Willy Lindner Ed. Rentz Bandow Gerards K. N. v. Kaulla O. v. Soden Maria Cicconi Pawletta Baars R. Grau Lerche Beckel O. Windhausen Felicitas Rolleri Jesser Karl Boresch R. W. Seuffert K. Müller Schloemer K. Höll Johannes Wolf Brüning Patzsch W. Ludorff 《European Food Research and Technology》1941,81(3):223-288
90.