全文获取类型
收费全文 | 41490篇 |
免费 | 4574篇 |
国内免费 | 3696篇 |
专业分类
电工技术 | 3447篇 |
技术理论 | 2篇 |
综合类 | 7249篇 |
化学工业 | 1968篇 |
金属工艺 | 950篇 |
机械仪表 | 2827篇 |
建筑科学 | 3154篇 |
矿业工程 | 1059篇 |
能源动力 | 845篇 |
轻工业 | 2550篇 |
水利工程 | 1130篇 |
石油天然气 | 940篇 |
武器工业 | 513篇 |
无线电 | 5363篇 |
一般工业技术 | 3857篇 |
冶金工业 | 1047篇 |
原子能技术 | 491篇 |
自动化技术 | 12368篇 |
出版年
2024年 | 166篇 |
2023年 | 516篇 |
2022年 | 936篇 |
2021年 | 1015篇 |
2020年 | 1068篇 |
2019年 | 987篇 |
2018年 | 1007篇 |
2017年 | 1219篇 |
2016年 | 1347篇 |
2015年 | 1424篇 |
2014年 | 2198篇 |
2013年 | 2422篇 |
2012年 | 2842篇 |
2011年 | 3082篇 |
2010年 | 2464篇 |
2009年 | 2635篇 |
2008年 | 2725篇 |
2007年 | 3181篇 |
2006年 | 2849篇 |
2005年 | 2541篇 |
2004年 | 2125篇 |
2003年 | 1819篇 |
2002年 | 1499篇 |
2001年 | 1246篇 |
2000年 | 1089篇 |
1999年 | 929篇 |
1998年 | 745篇 |
1997年 | 618篇 |
1996年 | 568篇 |
1995年 | 495篇 |
1994年 | 427篇 |
1993年 | 302篇 |
1992年 | 267篇 |
1991年 | 220篇 |
1990年 | 196篇 |
1989年 | 175篇 |
1988年 | 114篇 |
1987年 | 71篇 |
1986年 | 36篇 |
1985年 | 35篇 |
1984年 | 26篇 |
1983年 | 33篇 |
1982年 | 23篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1963年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
山东改造工程旧房质量检测 总被引:5,自引:4,他引:1
结合某成品仓库改作商业用房的工程实例,对该建筑进行了详细的检测与分析,并根据结果提出了针对性的加固方案,并对加固效果进行了探讨,为工程改造提供了依据,可供类似工程借鉴。 相似文献
42.
H9000 V4.0计算机监控系统技术特点概要 总被引:8,自引:3,他引:5
为了满足三峡右岸电站的应用需要,在H9000 V3.0计算机监控系统的基础上研制开发了H9000 V4.0系统,改进和完善了原系统已有功能,开发了新功能,进一步提高了系统的性能指标和可靠性指标。文中主要介绍H9000 V4.0系统的设计原则,以及数据采集、人机联系、报表定制、Web信息发布、历史数据管理等主要新功能。 相似文献
43.
44.
An optimal control problem with nonsmooth performance criterion described by a system of ordinary differential equations is considered. Necessary first-order optimality conditions are obtained. 相似文献
45.
Herbert S. Bennett 《Journal of research of the National Institute of Standards and Technology》2007,112(4):209-221
In this paper, we present the theory for calculating Raman line shapes as functions of the Fermi energy and finite temperatures in zinc blende, n-type GaAs for donor densities between 1016 cm−3 and 1019 cm−3. Compared to other theories, this theory is unique in two respects: 1) the many-body effects are treated self-consistently and 2) the theory is valid at room temperature for arbitrary values of the ratio R = (Q2/α), where Q is the magnitude of the normalized wave vector and α is the normalized frequency used in the Raman measurements. These calculations solve the charge neutrality equation self-consistently for a two-band model of GaAs at 300 K that includes the effects of high carrier concentrations and dopant densities on the perturbed densities of states used to calculate the Fermi energy as a function of temperature. The results are then applied to obtain the carrier concentrations from Fermi energies in the context of line shapes in Raman spectra due to the coupling between longitudinal optical phonons and plasmons. Raman measurements have been proposed as a non-destructive method for wafer acceptance tests of carrier density in semiconductor epilayers. The interpretation of Raman spectra to determine the majority electron density in n-type semiconductors requires an interdisciplinary effort involving experiments, theory, and computer-based simulations and visualizations of the theoretical calculations. 相似文献
46.
The paper considers vulnerable multi-state series-parallel systems operating under influence of external impacts. Both the external impacts and internal failures affect system survivability, which is determined as the probability of meeting a given demand. The external impacts are characterized by several destructive factors affecting the system or its parts simultaneously.In order to increase the system's survivability a multilevel protection against the destructive factors can be applied to its subsystems. In such systems, the protected subsystems can be destroyed only if all of the levels of their protection are destroyed.The paper presents an algorithm for evaluating the survivability of series-parallel systems with arbitrary configuration of multilevel protection against multiple destructive factor impacts. The algorithm is based on a composition of Boolean and the Universal Generating Function techniques.Illustrative examples are presented. 相似文献
47.
Tian-Ge Shao Jian-Guo Wang 《中国电子科技》2007,5(3):255-259
In this paper, the spatial resolutions at different directions of bistatic synthetic aperture radar (BiSAR) have been derived from the ambiguity function. Compared with monostatic signal to noise ratio, BiSAR's resolutions of a fixed point target are varying with slow time since BiSAR system is space-variant. Constraints for the assumption of space-invariant bistatic topology are proposed in the paper. Moreover, under the assumption of invariance, the change of resolutions at different point in the image scene is taken into account, and we have specified two key parameters that affect resolutions directly and analyzed the way how they influence on the resolutions. 相似文献
48.
论社区服务产业化 总被引:2,自引:0,他引:2
刘波 《重庆理工大学学报(自然科学版)》2003,17(1):127-131
社区经济作为一种优化的资源配置方式,利用社区服务为载体,将社区内互不相联的各种经济成份变为利益共同体,建立一种新的经济生产方式,从而带动社区乃至更广区域的经济发展。 相似文献
49.
Magnesiumandmagnesiumalloyshavebeenin vestigatedashydrogenstoragematerialsforseveralde cadesbecausefarmorehydrogenbyweightcanbestoredinthemthaninmostoftheothercurrentlyknownhydrogenstoragealloys .Moreover ,thehighnaturalabundanceofMg ,itslightmassandenviron mentalcompatibilitypotentiallymakemagnesiumoneofthemostprospectivecandidatesforfuturehydrogenstoragematerials .Unfortunately ,thepracticalappli cationofMganditsalloyshasbeenlimitedonlytocertainstoragedevicebecauseoftheirpoorhydriding dehydr… 相似文献
50.
This paper presents an application of digital signal processing to data acquired by the radio imaging method (RIM) that was adopted to measure moisture distribution inside the human body. RIM was originally developed for the mining industry; we are applying the method to a biomedical measurement because of its simplicity, economy, and safety. When a two‐dimensional image was constructed from the measured data, the method provided insufficient resolution because the wavelength of the measurement medium, a weak electromagnetic wave in a VHF band, was longer than human tissues. We built and measured a phantom, a model simulating the human body, consisting of two water tanks representing large internal organs. A digital equalizer was applied to the measured values as a weight function, and images were reconstructed that corresponded to the original shape of the two water tanks. As a result, a two‐dimensional image containing two individual peaks corresponding to the original two small water tanks was constructed. The result suggests the method was applicable to biomedical measurement by the assistance of digital signal processing. This technique may be applicable to home‐based medical care and other situations in which safety, simplicity, and economy are important. 相似文献