全文获取类型
收费全文 | 97104篇 |
免费 | 5984篇 |
国内免费 | 3605篇 |
专业分类
电工技术 | 10380篇 |
技术理论 | 21篇 |
综合类 | 10199篇 |
化学工业 | 5111篇 |
金属工艺 | 1362篇 |
机械仪表 | 4708篇 |
建筑科学 | 16145篇 |
矿业工程 | 4159篇 |
能源动力 | 3100篇 |
轻工业 | 3498篇 |
水利工程 | 5458篇 |
石油天然气 | 2325篇 |
武器工业 | 498篇 |
无线电 | 8348篇 |
一般工业技术 | 5752篇 |
冶金工业 | 5729篇 |
原子能技术 | 715篇 |
自动化技术 | 19185篇 |
出版年
2024年 | 194篇 |
2023年 | 772篇 |
2022年 | 1532篇 |
2021年 | 2093篇 |
2020年 | 2359篇 |
2019年 | 1622篇 |
2018年 | 1540篇 |
2017年 | 2037篇 |
2016年 | 2530篇 |
2015年 | 2880篇 |
2014年 | 7741篇 |
2013年 | 6326篇 |
2012年 | 7246篇 |
2011年 | 7489篇 |
2010年 | 5748篇 |
2009年 | 6148篇 |
2008年 | 6083篇 |
2007年 | 7422篇 |
2006年 | 6526篇 |
2005年 | 5518篇 |
2004年 | 4814篇 |
2003年 | 4155篇 |
2002年 | 3221篇 |
2001年 | 2431篇 |
2000年 | 1932篇 |
1999年 | 1443篇 |
1998年 | 1007篇 |
1997年 | 745篇 |
1996年 | 604篇 |
1995年 | 523篇 |
1994年 | 383篇 |
1993年 | 285篇 |
1992年 | 218篇 |
1991年 | 175篇 |
1990年 | 116篇 |
1989年 | 134篇 |
1988年 | 97篇 |
1987年 | 51篇 |
1986年 | 77篇 |
1985年 | 100篇 |
1984年 | 92篇 |
1983年 | 99篇 |
1982年 | 39篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1977年 | 14篇 |
1975年 | 7篇 |
1961年 | 7篇 |
1959年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
34.
Veysel T. Yilmaz Evrim Senel Canan Kazak 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(3):407-413
The reaction of [Cu(sac)2(H2O)4] · 2H2O with 2-methylpyrazine (mpyz) leads two complexes, concomitant crystallization of a mononuclear complex [Cu(sac)2(mpyz)(H2O)2] (1) and a polymeric complex [Cu(sac)2(μ-mpyz)]n (2). Both complexes have been characterized by elemental analyses, magnetic measurements, FT-IR and ESR, TG-DTA and single-crystal
X-ray diffraction analyses. Single-crystal X-ray analyses show that complex 1 consists of discrete molecules in which the copper(II) ions exhibits a square-pyramidal coordination geometry. The individual
molecules of 1 are connected into a hydrogen-bonded chain structure, which is further assembled to form a three-dimensional network by π–π stacking interactions.
Complex 2 is an 1D coordination polymer in which copper(II) centers are bridged by the mpyz ligand. The chains are further assembled
to form two-dimensional frameworks by π–π and C–H···π stacking interactions. 相似文献
35.
In this study, a single unit of planar micro-solid-oxide fuel cell (μSOFC) is investigated numerically to evaluate the influences of flow channel design, oxygen composition, and thermal operating conditions on cell performance. Four flow channel designs are examined under the co-flow configuration: serpentine, double serpentine, rod bundle, and oblique rib. For all designs, the contacts areas of interconnect to electrodes are kept consistent to maintain the ohmic losses at the same level. To characterize the mass transport effects, there are three different compositions, 100% O2, 50% O2/50% N2 and air, fed to the cathode inlet. Different thermal conditions, adiabatic and isothermal, are applied to the outer boundary of the μSOFC and the results are compared. The outcomes suggest that both thermal conditions and oxidant composition show remarkable influences on μSOFC performance. Under adiabatic conditions, the rise of cell temperature causes a decrease in reversible voltage, deteriorating the overall cell competence. When oxygen is diluted with nitrogen, local gas diffusion becomes dominant to the cathode reaction. Bulk flow, on the other hand, plays a minor role in cell performance since there is little deviation in the polarization curves for all flow channel designs, even at high current densities. For comparison, the flow visualization technique is employed to observe the transport phenomena in various flow channel designs. The flow patterns are found to resemble the concentration distribution, providing a useful tool to design μSOFCs. 相似文献
36.
高职高专现代教育技术管理体制之我见 总被引:3,自引:1,他引:2
吴玉霞 《宁波工程学院学报》2004,16(2):99-102
本文从教育技术的含义和发展的历史出发,分析目前高职高专院校的教育技术管理体制现状,提出应建立完善的教育技术管理体制,以推进教育技术工作的协调发展。 相似文献
37.
In this paper we present the results of a simulation study to explore the ability of Bayesian parametric and nonparametric models to provide an adequate fit to count data of the type that would routinely be analyzed parametrically either through fixed-effects or random-effects Poisson models. The context of the study is a randomized controlled trial with two groups (treatment and control). Our nonparametric approach uses several modeling formulations based on Dirichlet process priors. We find that the nonparametric models are able to flexibly adapt to the data, to offer rich posterior inference, and to provide, in a variety of settings, more accurate predictive inference than parametric models. 相似文献
38.
电信管理及运营支撑是爱立信公司为公用电信网提供的有关管理及运营支撑功能的综合方案,本文介绍了其中的公网管理系统和蜂窝移动网络管理系统。 相似文献
39.
隆德县在大水沟农村饮水工程建设管理中,科学规划,优化设计方案,完善政策措施,创新管理体制和运行机制,尤其是用水户全过程参与工程建设管理、实行“两部制”水价、实施工程定期检查养护制度、建立工程管理单位目标责任考核制度、执行水费统一管理和提留统筹费等一系列做法.确保了国家投资效益的充分发挥和工程的可持续利用. 相似文献
40.
Manabu Ishitobi Takeshi Myoi Koji Soshin Eiji Hiraki Mutsuo Nakaoka 《Electrical Engineering in Japan》2005,153(3):79-87
This paper presents a single lossless inductive snubber‐assisted ZCS‐PFM series resonant DC‐DC power converter with a high‐frequency high‐voltage transformer link for industrial‐use high‐power magnetron drive. The current flowing through the active power switches rises gradually at a turned‐on transient state with the aid of a single lossless snubber inductor, and ZCS turn‐on commutation based on overlapping current can be achieved via the wide range pulse frequency modulation control scheme. The high‐frequency high‐voltage transformer primary side resonant current always becomes continuous operation mode, by electromagnetic loose coupling design of the high‐frequency high‐voltage transformer and the magnetizing inductance of the high‐frequency high‐voltage transformer. As a result, this high‐voltage power converter circuit for the magnetron can achieve a complete zero current soft switching under the condition of broad width gate voltage signals. Furthermore, this high‐voltage DC‐DC power converter circuit can regulate the output power from zero to full over audible frequency range via the two resonant frequency circuit design. Its operating performances are evaluated and discussed on the basis of the power loss analysis simulation and the experimental results from a practical point of view. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(3): 79–87, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20126 相似文献