全文获取类型
收费全文 | 22198篇 |
免费 | 1847篇 |
国内免费 | 1166篇 |
专业分类
电工技术 | 1180篇 |
技术理论 | 4篇 |
综合类 | 1473篇 |
化学工业 | 3813篇 |
金属工艺 | 1569篇 |
机械仪表 | 1400篇 |
建筑科学 | 1720篇 |
矿业工程 | 732篇 |
能源动力 | 602篇 |
轻工业 | 1373篇 |
水利工程 | 392篇 |
石油天然气 | 1511篇 |
武器工业 | 168篇 |
无线电 | 2293篇 |
一般工业技术 | 2834篇 |
冶金工业 | 1151篇 |
原子能技术 | 250篇 |
自动化技术 | 2746篇 |
出版年
2024年 | 100篇 |
2023年 | 400篇 |
2022年 | 644篇 |
2021年 | 897篇 |
2020年 | 732篇 |
2019年 | 614篇 |
2018年 | 687篇 |
2017年 | 693篇 |
2016年 | 637篇 |
2015年 | 836篇 |
2014年 | 1081篇 |
2013年 | 1193篇 |
2012年 | 1349篇 |
2011年 | 1456篇 |
2010年 | 1266篇 |
2009年 | 1250篇 |
2008年 | 1327篇 |
2007年 | 1139篇 |
2006年 | 1195篇 |
2005年 | 978篇 |
2004年 | 802篇 |
2003年 | 763篇 |
2002年 | 851篇 |
2001年 | 702篇 |
2000年 | 610篇 |
1999年 | 583篇 |
1998年 | 429篇 |
1997年 | 374篇 |
1996年 | 340篇 |
1995年 | 298篇 |
1994年 | 227篇 |
1993年 | 158篇 |
1992年 | 143篇 |
1991年 | 92篇 |
1990年 | 89篇 |
1989年 | 78篇 |
1988年 | 51篇 |
1987年 | 30篇 |
1986年 | 25篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1965年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
11.
Wenjia Jing Baoqiang Hou Jinxiao Wang Qiang Zhi Jianfeng Yang Bo Wang 《Journal of the American Ceramic Society》2022,105(5):3141-3146
Photocatalysts often show excellent performances on the basis of their surface state of exposed faces with high reactivity, but unfortunately surfaces of this type are usually concealed into the interior of crystals for their high surface energy. We report here a possibility that for fluorine-terminated surfaces of monoclinic ZrO2, these higher-energy surfaces could be retained and exposed. Urchin-like ZrO2 hollow microspheres (UZHS) composed of nanoribbons with exposed (010) facets are obtained through a fluoride mediately solvothermal method. We prove the stabilization effect of fluorine adsorption on (010) facets by density functional theory calculations. More interestingly, UZHS exhibit tunable photocatalytic selectivity in dye degradation. The fluorinated UZHS exhibit good performances both on decomposing Congo red (CR) and methylene blue, while the surface-modified UZHS by calcination only favor decomposition of CR. 相似文献
12.
Replacement of precious single metal catalysts with cost-effective, highly-dispersed composite catalysts for catalytic hydrothermal conversion of residue holds tremendous promise for the residue upgrading technologies. Organic metals were added to the feed as the oil-soluble precursors, and transformed into the catalytic active phases in this work. Physical properties and structures of the composite catalysts had been investigated by X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope and transmission electron microscopy. The composite catalysts were found to be highly efficient in the catalytic hydrothermal conversion of both model compound and residue. Increased metal dispersion and synergistic effects of two metals played indispensable roles in such catalytic system. Results showed that under the test conditions in the article, the catalyst had the best catalytic performance when the mass ratio of molybdenum to iron was 1.5. 相似文献
13.
The lead-free piezoelectric ceramics (Na.47Bi.47Ba.06)1-xCaxTiO3 (x?=?0, 0.01, 0.02, 0.03, 0.05, and 0.08, abbreviated as BNBTC/0, BNBTC/1, BNBTC/2, BNBTC/3, BNBTC/5, and BNBTC/8, respectively) were obtained using the solid-state reaction method. The structure, electric conductivity, and dielectric, ferroelectric, and piezoelectric properties of the Ca2+-doped (Na.47Bi.47Ba.06)TiO3 ceramics were thoroughly investigated. The ceramics sintered at 1200?°C exhibit dense microstructures, having relative densities higher than 96%. The X-ray diffraction results demonstrate that all ceramics have a pure perovskite structure. The mean grain sizes of the ceramics are related to the Ca2+ quantity. A small quantity of Ca2+ ions (x?≤?0.03) improves the piezoelectric and ferroelectric properties of the samples. The dielectric behavior of the samples is sensitive to the Ca2+ content and electric poling. The results demonstrate that the electrical properties of the (Na.47Bi.47Ba.06)TiO3 lead-free ceramics can be well tuned by varying the Ca2+ quantity. 相似文献
14.
Yejun Wu Bowen Yan Juan Zhou Huizhang Lian Xiaojun Yu Jianxin Zhao Hao Zhang Wei Chen Daming Fan 《Journal of food science》2020,85(10):3282-3292
15.
Haibo Zhang Guohua Geng Kang Li Cheng Liu Yuqing Hou 《Journal of Modern Optics》2018,65(20):2278-2289
Cone-beam X-ray luminescence computed tomography (CB-XLCT) is an attractive hybrid imaging modality, and it has the potential of monitoring the metabolic processes of nanophosphors-based drugs in vivo. However, the XLCT imaging suffers from a severe ill-posed problem. In this work, a sparse nonconvex Lp (0?p?1) regularization was utilized for the efficient reconstruction for early detection of small tumour in CB-XLCT imaging. Specifically, we transformed the non-convex optimization problem into an iteratively reweighted scheme based on the L1 regularization. Further, an iteratively reweighted split augmented lagrangian shrinkage algorithm (IRW_SALSA-Lp) was proposed to efficiently solve the non-convex Lp (0?p?1) model. We studied eight different non-convex p-values (1/16, 1/8, 1/4, 3/8, 1/2, 5/8, 3/4, 7/8) in both 3D digital mouse experiments and in vivo experiments. The results demonstrate that the proposed non-convex methods outperform L2 and L1 regularization in accurately recovering sparse targets in CB-XLCT. And among all the non-convex p-values, our Lp(1/4?p?1/2) methods give the best performance. 相似文献
17.
GIS在深圳市三防指挥信息系统中的应用 总被引:1,自引:0,他引:1
深圳市三防指挥信息系统利用GIS技术,结合水利(水务)、防汛、抗旱的具体业务,建立了水情遥测数据处 理分系统、工况监测数据处理分系统、水务行业三防信息管理分系统、决策支持分系统、水源优化调度分 系统,提高了现代化管理水平。 相似文献
18.
腐蚀引起钻柱刺漏的机理分析及预防措施 总被引:7,自引:7,他引:0
详细分析了腐蚀引起钻柱刺漏的机理,得知:造成钻柱刺漏的主要原因是空气中的O2、地层中的硫化氢和二氧化碳、钻井液残液、钻井液中的盐类对钻柱的腐蚀和钻井液对钻柱的冲蚀。针对引起钻柱刺漏的原因,制定了去除钻井液中的O2、监测钻井液腐蚀性并加入相应的添加剂去除CO2和H2S、定期对钻杆进行检测、对存放的钻杆进行防腐处理、使用厚过渡区改进型钻杆等措施。在苏丹某区块现场实践证明,采取这些措施,由腐蚀引起的钻柱刺漏事故大大减少,在该区块的T-1井和D-1井钻进的3个月中,仅发生一次钻柱刺漏事故。 相似文献
19.
In this paper, we consider the problem of designing optimal asynchronous wake-up schedules to facilitate distributed power management and neighbor discovery in multihop wireless networks. We first formulate it as a block design problem and derive the fundamental trade-offs between wake-up latency and the average duty cycle of a node. After the theoretical foundation is laid, we then devise a neighbor discovery and schedule bookkeeping protocol that can operate on the optimal wake-up schedule derived. To demonstrate the usefulness of asynchronous wake-up, we investigate the efficiency of neighbor discovery and the application of on-demand power management, which overlays a desirable communication schedule over the wake-up schedule mandated by the asynchronous wake-up mechanism. Simulation studies demonstrate that the proposed asynchronous wake-up protocol has short discovery time which scales with the density of the network; it can accommodate various traffic characteristics and loads to achieve an energy savings that can be as high as 70 percent, while the packet delivery ratio is comparable to that without power management. 相似文献
20.