全文获取类型
收费全文 | 27992篇 |
免费 | 3087篇 |
国内免费 | 1827篇 |
专业分类
电工技术 | 1938篇 |
综合类 | 3536篇 |
化学工业 | 1586篇 |
金属工艺 | 2054篇 |
机械仪表 | 2540篇 |
建筑科学 | 4318篇 |
矿业工程 | 1396篇 |
能源动力 | 774篇 |
轻工业 | 921篇 |
水利工程 | 1426篇 |
石油天然气 | 2008篇 |
武器工业 | 279篇 |
无线电 | 2027篇 |
一般工业技术 | 2149篇 |
冶金工业 | 989篇 |
原子能技术 | 629篇 |
自动化技术 | 4336篇 |
出版年
2024年 | 30篇 |
2023年 | 254篇 |
2022年 | 595篇 |
2021年 | 728篇 |
2020年 | 861篇 |
2019年 | 660篇 |
2018年 | 605篇 |
2017年 | 945篇 |
2016年 | 1013篇 |
2015年 | 1152篇 |
2014年 | 1782篇 |
2013年 | 1654篇 |
2012年 | 2193篇 |
2011年 | 2290篇 |
2010年 | 1758篇 |
2009年 | 1816篇 |
2008年 | 1657篇 |
2007年 | 2007篇 |
2006年 | 1795篇 |
2005年 | 1429篇 |
2004年 | 1222篇 |
2003年 | 1028篇 |
2002年 | 894篇 |
2001年 | 797篇 |
2000年 | 684篇 |
1999年 | 555篇 |
1998年 | 401篇 |
1997年 | 364篇 |
1996年 | 336篇 |
1995年 | 346篇 |
1994年 | 252篇 |
1993年 | 155篇 |
1992年 | 142篇 |
1991年 | 107篇 |
1990年 | 81篇 |
1989年 | 96篇 |
1988年 | 65篇 |
1987年 | 34篇 |
1986年 | 25篇 |
1985年 | 19篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 3篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1959年 | 4篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(19):10747-10761
To obtain the mixing enhancement mechanism of H2–Water combined jets in supersonic crossflows in a combustor with expanded section for rotating detonation ramjet, the flow field shape and spray structure were studied by experimental and numerical methods. The Eulerian–Lagrangian method was used to investigate the diffusion mechanism and H2–Water interaction law of combined jets with different sequences. At the same time, high-speed photography and the schlieren technique were used to capture the flow field. The effects of jet pressure drop, orifice diameter, orifice spacing, incoming Mach number, and other parameters on the penetration depth of water jets were studied. The results of experiment and simulation show that using H2–Water combined jets, the penetration depth of the jet spray can be greatly increased and the jet mixing effect can be significantly improved, which will contribute to the engine's ignition and stable combustion. In the case of pre-water/post-H2, the penetration depth of the hydrogen jet is greater. In the case of pre-H2/post-water, the hydrogen jet raises the water spray mainly by protecting the integrity of the water column. 相似文献
2.
为避免传统均匀采样方法因忽视曲线重要特征而生成不理想的采样结果,获得给定数量且由特征点和辅助点组成的采样点序列,提出基于特征识别的高质量空间曲线非均匀采样方法.首先使用抛物线插值法得到曲线上所有曲率极大值点和挠率极大值点的近似位置,经筛选后产生特征点,以更好地抓住空间曲线的轮廓特征.然后定义基于弧长、曲率和挠率加权组合的特征函数,并以此自适应地选取曲线上的辅助点.与3种主流采样方法比较的实验结果表明,该方法能够获得更高质量的采样结果且具有更好的实用性,从而进一步改善空间曲线的B样条拟合效果. 相似文献
3.
4.
目的 利用产品形态审美基因网络,对台灯外轮廓曲线的相关性进行综合分析,析出产品优化与创新设计的关键要素。方法 以三次贝塞尔曲线对台灯的外轮廓曲线进行基因编码,规律性调整控制点的坐标生成新曲线形态,进行曲线视觉力感知识别,挖掘曲线间的相关性;以曲线基因为节点,相关性为边构建产品形态审美基因网络,并对网络进行拓扑分析,析出关键设计节点辅助设计者进行产品设计。结果 运用产品形态基因网络的理论找到原型设计的关键性节点,并进行设计优化,使产品造型设计更符合消费者的审美习惯和偏好。结论 通过对台灯外轮廓线的案例实践,证实了产品形态基因网络在产品细节优化和造型创新设计方面具有实用性和可靠性,能够辅助设计者找到关键设计节点并协调设计的基因集团。 相似文献
5.
6.
Barak Ratzker Avital Wagner Bar Favelukis Sharone Goldring Sergey Kalabukhov Nachum Frage 《Journal of the European Ceramic Society》2021,41(6):3520-3526
Doped transparent ceramics with high optical quality can serve as materials for photonic applications such as laser gain media. In that regard, transparent polycrystalline alumina has potential for high-power applications due to its excellent physical and chemical properties, combined with unique doping possibilities. However, optical birefringence of Al2O3 crystals make achieving sufficiently high optical transmittance a processing challenge. In the present study, we demonstrated fabrication of highly transparent 0.5 at.% Cr:Al2O3 ceramics by high-pressure spark plasma sintering (HPSPS). The optical properties of these polycrystalline ruby ceramics were analyzed in order to assess possible laser operation (at 694.3 nm). The obtained ceramics exhibit high in-line transmittance (~72.5 % at 700 nm), equivalent to a scattering coefficient of 2.15 cm?1, and characteristic ruby photoluminescence. The theoretically estimated lasing threshold and percentage of absorbed pump power indicate that such ruby ceramic lasers could operate at reasonable thresholds of 80?225 mW with short lengths of 0.5?5 mm. Thus, HPSPS is a promising method for producing laser-quality doped transparent ceramics for compact laser systems. 相似文献
7.
Dominik KUERES Dritan TOPUZI Maria Anna POLAK 《Frontiers of Structural and Civil Engineering》2022,16(5):624
In the past, glass fiber-reinforced polymer (GFRP)-reinforcement has been successfully applied in reinforced concrete (RC) structures where corrosion resistance, electromagnetic neutrality, or cuttability were required. Previous investigations suggest that the application of GFRP in RC structures could be advantageous in areas with seismic activity due to their high deformability and strength. However, especially the low modulus of elasticity of GFRP limited its wide application as GFRP-reinforced members usually exhibit considerably larger deformations under service loads than comparable steel-reinforced elements. To overcome the aforementioned issues, the combination of steel and GFRP reinforcement in hybrid RC sections has been investigated in the past. Based on this idea, this paper presents a novel concept for the predetermination of potential plastic hinges in RC frames using GFRP reinforcement. To analyze the efficiency of the concept, nonlinear finite element simulations were performed. The results underscore the high efficiency of hybrid steel-GFRP RC sections for predetermining potential plastic hinges on RC frames. The results also indicate that the overall seismic behavior of RC structures could be improved by means of GFRP as both the column base shear force during the seismic activity as well as the plastic deformations after the earthquake were considerably less pronounced than in the steel-reinforced reference structure. 相似文献
8.
Atsuki Yamaguchi Kazuki Fukui Yuki Fujiwara Shingo Tamaki Sachie Kusaka Fuminobu Sato 《Journal of Nuclear Science and Technology》2021,58(1):80-86
ABSTRACT It is important to perform neutron transport simulations with accurate nuclear data in the neutronics design of a fusion reactor. However, absolute values of large-angle scattering cross sections vary among nuclear data libraries even for well-examined nuclide of iron. Benchmark experiments focusing on large-angle scattering cross sections were thus performed to confirm the correctness of nuclear data libraries. The series benchmark experiments were performed at a DT neutron source facility, OKTAVIAN of Osaka University, Japan, by the unique experimental system established by the authors’ group, which can extract only the contribution of large-angle scattering reactions. This system consists of two shadow bars, target plate (iron), and neutron detector (niobium). Two types of shadow bars were used and four irradiations were conducted for one experiment, so that contribution of room-return neutrons was effectively removed and only large-angle scattering neutrons were extracted from the measured four Nb reaction rates. The obtained experimental results were compared with calculations for five nuclear data libraries including JENDL-4.0, JEFF.-3.3, FENDL-3.1, ENDF/B- VII, and recently released ENDF/B-VIII. It was found from the comparison that ENDF/B-VIII showed the best result, though ENDF/B-VII showed overestimation and others are in large underestimation at 14 MeV. 相似文献
9.
Woong-Kee Loh 《计算机、材料和连续体(英文)》2021,66(2):1251-1267
Many database applications currently deal with objects in a metric space. Examples of such objects include unstructured multimedia objects and points of interest (POIs) in a road network. The M-tree is a dynamic index structure that facilitates an efficient search for objects in a metric space. Studies have been conducted on the bulk loading of large datasets in an M-tree. However, because previous algorithms involve excessive distance computations and disk accesses, they perform poorly in terms of their index construction and search capability. This study proposes two efficient M-tree bulk loading algorithms. Our algorithms minimize the number of distance computations and disk accesses using FastMap and a space-filling curve, thereby significantly improving the index construction and search performance. Our second algorithm is an extension of the first, and it incorporates a partitioning clustering technique and flexible node architecture to further improve the search performance. Through the use of various synthetic and real-world datasets, the experimental results demonstrated that our algorithms improved the index construction performance by up to three orders of magnitude and the search performance by up to 20.3 times over the previous algorithm. 相似文献
10.
《Geotextiles and Geomembranes》2021,49(5):1085-1094
Several studies have confirmed the geocell reinforcement system as potential road material. However, there is a wide gap between the number of research studies evaluating the geocell in the laboratory and those dealing with road design methods using the geocell. Due to this gap, the geocell system has not reached its full potential in highways. The present study proposes fragility modeling to design low volume roads by considering the geocell reinforced layer's modulus. A predictive model was developed to estimate the geocell layer's modulus using laboratory and finite element analysis results. The results indicate that geocell reinforcement reduces the stresses on the underlying road layers. The developed fragility approach is then used to examine three road designs for Texas's low volume road involving different geocell reinforced layers. The obtained fragility curves indicate the reliability of each of the three road designs against the traffic load and can thereby assist decision-makers in selecting the optimum design. By designing geocell reinforced roads via fragility modeling, highway officials will be able to integrate any uncertainties in the design inputs and check designs against road performance criteria such as rutting and fatigue cracking, and against decision criteria such as cost, emissions, etc. 相似文献