全文获取类型
收费全文 | 2028篇 |
免费 | 75篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 36篇 |
综合类 | 6篇 |
化学工业 | 626篇 |
金属工艺 | 54篇 |
机械仪表 | 44篇 |
建筑科学 | 125篇 |
矿业工程 | 9篇 |
能源动力 | 47篇 |
轻工业 | 134篇 |
水利工程 | 5篇 |
无线电 | 132篇 |
一般工业技术 | 362篇 |
冶金工业 | 114篇 |
原子能技术 | 28篇 |
自动化技术 | 386篇 |
出版年
2023年 | 20篇 |
2022年 | 35篇 |
2021年 | 66篇 |
2020年 | 34篇 |
2019年 | 35篇 |
2018年 | 37篇 |
2017年 | 38篇 |
2016年 | 72篇 |
2015年 | 53篇 |
2014年 | 63篇 |
2013年 | 93篇 |
2012年 | 112篇 |
2011年 | 145篇 |
2010年 | 113篇 |
2009年 | 95篇 |
2008年 | 111篇 |
2007年 | 94篇 |
2006年 | 109篇 |
2005年 | 75篇 |
2004年 | 76篇 |
2003年 | 49篇 |
2002年 | 42篇 |
2001年 | 40篇 |
2000年 | 33篇 |
1999年 | 37篇 |
1998年 | 38篇 |
1997年 | 33篇 |
1996年 | 24篇 |
1995年 | 22篇 |
1994年 | 24篇 |
1993年 | 20篇 |
1992年 | 22篇 |
1991年 | 21篇 |
1990年 | 16篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 14篇 |
1974年 | 16篇 |
1973年 | 7篇 |
排序方式: 共有2108条查询结果,搜索用时 15 毫秒
931.
Stefan Kupferschmid Matthew Lewis Tobias Schubert Bernd Becker 《Formal Methods in System Design》2011,39(2):185-204
Traditional incremental SAT solvers have achieved great success in the domain of Bounded Model Checking (BMC). Recently, modern
solvers have introduced advanced preprocessing procedures that have allowed them to obtain high levels of performance. Unfortunately,
many preprocessing techniques such as variable and (blocked) clause elimination cannot be directly used in an incremental
manner. This work focuses on extending these techniques and Craig interpolation so that they can be used effectively together
in incremental SAT solving (in the context of BMC). The techniques introduced here doubled the performance of our BMC solver
on both SAT and UNSAT problems. For UNSAT problems, preprocessing had the added advantage that Craig interpolation was able
to find the fixed point sooner, reducing the number of incremental SAT iterations. Furthermore, our ideas seem to perform
better as the benchmarks become larger, and/or deeper, which is exactly when they are needed. Lastly, our methods can be integrated
into other SAT based BMC tools to achieve similar speedups. 相似文献
932.
Anisotropic noise samples 总被引:1,自引:0,他引:1
Feng L Hotz I Hamann B Joy K 《IEEE transactions on visualization and computer graphics》2008,14(2):342-354
We present a practical approach to generate stochastic anisotropic samples with Poisson-disk characteristic over a two-dimensional domain. In contrast to isotropic samples, we understand anisotropic samples as non-overlapping ellipses whose size and density match a given anisotropic metric. Anisotropic noise samples are useful for many visualization and graphics applications. The spot samples can be used as input for texture generation, e.g., line integral convolution (LIC), but can also be used directly for visualization. The definition of the spot samples using a metric tensor makes them especially suitable for the visualization of tensor fields that can be translated into a metric. Our work combines ideas from sampling theory and mesh generation. To generate these samples with the desired properties we construct a first set of non-overlapping ellipses whose distribution closely matches the underlying metric. This set of samples is used as input for a generalized anisotropic Lloyd relaxation to distribute noise samples more evenly. Instead of computing the Voronoi tessellation explicitly, we introduce a discrete approach which combines the Voronoi cell and centroid computation in one step. Our method supports automatic packing of the elliptical samples, resulting in textures similar to those generated by anisotropic reaction-diffusion methods. We use Fourier analysis tools for quality measurement of uniformly distributed samples. The resulting samples have nice sampling properties, for example, they satisfy a blue noise property where low frequencies in the power spectrum are reduced to a minimum. 相似文献
933.
934.
935.
936.
937.
Dietmar Baither Martin Bartsch Bernd Baufeld Aleksander Tikhonovsky reas Foitzik Manfred Rühle Ulrich Messerschmidt 《Journal of the American Ceramic Society》2001,84(8):1755-1762
Polydomain tetragonal ( t' ) zirconia was deformed in compression along a 〈100〉 orientation at various temperatures between 500° and 1400°C. The stress-strain curves showed a plateau corresponding to ferroelastic deformation, followed by plastic deformation at a higher yield stress level. In both ranges, the strain-rate sensitivity of the stress was measured by stress-relaxation tests. The microstructure of the tetragonal domains after ferroelastic deformation and the dislocation substructure were studied by transmission electron microscopy in a high-voltage electron microscope. As expected, ferroelastic deformation suppressed the tetragonal variant with its c -axis parallel to the loading direction. The dislocation structure consisted of intersecting dislocations on different slip systems with strongly bowed-out segments. The microprocesses of deformation are discussed here by comparing the deformation data with those of cubic zirconia deformed in the same orientation and based on the observed microstructure. The particular microstructure of t' zirconia seems to prevent recovery, so that the high flow stress of ∼700 MPa is preserved up to 1400°C. 相似文献
938.
Ricardo Cabeza Bernd Steingrobe Wilhelm R?mer Norbert Claassen 《Nutrient Cycling in Agroecosystems》2011,91(2):173-184
World phosphorus (P) resources are limited and may be exhausted within 70?C175 years. Therefore recycling of P from waste materials by chemical or thermal processes is important. This study evaluated the effectiveness of recycled P products from sewage sludge and animal wastes as P fertilizer. Four products were obtained from chemical processes, three magnesium-ammonium-phosphates (MAP) of different sewage treatment plants and a Ca phosphate precipitated from wastewater (Ca-P) and four from thermal processes, an alkali sinter phosphate (Sinter-P), a heavy metal depleted sewage sludge ash (Sl-ash), a cupola furnace slag made from sewage sludge (Cupola slag) and a meat-and-bone meal ash (MB meal ash). The effectiveness of these products as P fertilizers compared with triple superphosphate (TSP) and phosphate rock (PR) was determined in a 2-year pot experiment with maize (Zea mays L., cv. Atletico) in two soils with contrasting pH (pH(CaCl2) 4.7 and 6.6). The parameters used to evaluate the effectiveness were P uptake, P concentration in soil solution (CLi) and isotopically exchangeable P (IEP). MAP products were as effective as TSP in both soils, while Ca-P was only effective in the acid soil. Sinter-P was as effective as TSP in the acid soil, while Cupola slag was in the neutral soil. The products Sl-ash and MB meal ash were of low effectiveness and were comparable to PR. The effect of the fertilizers on IEP, but not on CLi, described their effectiveness. Recycled P products obtained by chemical processes, especially MAP, could be directly applied as P fertilizers, while products such as Sl-ash and MB meal ash are potential raw materials for P fertilizer production. 相似文献
939.
Dr. Jihye Jung Jan Braun Dr. Tibor Czabany Prof. Dr. Bernd Nidetzky 《Chembiochem : a European journal of chemical biology》2020,21(10):1534-1543
The nitrile reductase QueF catalyzes NADPH-dependent reduction of the nitrile group of preQ0 (7-cyano-7-deazaguanine) into the primary amine of preQ1 (7-aminomethyl-7-deazaguanine), a biologically unique reaction important in bacterial nucleoside biosynthesis. Here we have discovered that the QueF from Escherichia coli—its D197A and E89L variants in particular (apparent kcat≈10−2 min−1)—also catalyze the slow hydration of the C5=C6 double bond of the dihydronicotinamide moiety of NADPH. The enzymatically C6-hydrated NADPH is a 3.5:1 mixture of R and S forms and rearranges spontaneously through anomeric epimerization (β→α) and cyclization at the tetrahydronicotinamide C6 and the ribosyl O2. NADH and 1-methyl- or 1-benzyl-1,4-dihydronicotinamide are not substrates of the enzymatic hydration. Mutagenesis results support a QueF hydratase mechanism, in which Cys190—the essential catalytic nucleophile for nitrile reduction—acts as the general acid for protonation at the dihydronicotinamide C5 of NADPH. Thus, the NADPH hydration in the presence of QueF bears mechanistic resemblance to the C=C double bond hydration in natural hydratases. 相似文献
940.
Harald Klein Philipp Fritsch Patrick Haider Robert Kender Felix Rößler Sebastian Rehfeldt Pascal Freko Rainer Hoffmann Ingo Thomas Bernd Wunderlich 《化学,工程师,技术》2020,92(12):1921-1940
As part of the Energiewende, the current research on energy-optimized, flexible operation of air separation units is described. A realistic, pressure-driven approach for dynamic simulation is presented, which is used to provide a detailed, transient simulation model, a digital twin, of an air separation unit. Extreme operation scenarios, such as start-up and shutdown of the main heat exchanger, the distillation columns or the entire air separation unit, are described. Since the main heat exchanger experiences repeated temperature changes, its lifetime is investigated in a test rig. The gathered data is used to derive and validate three dimensional simulation models. 相似文献