全文获取类型
收费全文 | 37819篇 |
免费 | 6274篇 |
国内免费 | 2797篇 |
专业分类
电工技术 | 10923篇 |
技术理论 | 1篇 |
综合类 | 3501篇 |
化学工业 | 1608篇 |
金属工艺 | 1359篇 |
机械仪表 | 3826篇 |
建筑科学 | 2423篇 |
矿业工程 | 3068篇 |
能源动力 | 1246篇 |
轻工业 | 369篇 |
水利工程 | 1269篇 |
石油天然气 | 3892篇 |
武器工业 | 574篇 |
无线电 | 2329篇 |
一般工业技术 | 2504篇 |
冶金工业 | 1224篇 |
原子能技术 | 251篇 |
自动化技术 | 6523篇 |
出版年
2024年 | 308篇 |
2023年 | 659篇 |
2022年 | 1248篇 |
2021年 | 1537篇 |
2020年 | 1652篇 |
2019年 | 1251篇 |
2018年 | 1145篇 |
2017年 | 1428篇 |
2016年 | 1597篇 |
2015年 | 1817篇 |
2014年 | 2680篇 |
2013年 | 2258篇 |
2012年 | 3046篇 |
2011年 | 3017篇 |
2010年 | 2260篇 |
2009年 | 2428篇 |
2008年 | 2293篇 |
2007年 | 2673篇 |
2006年 | 2380篇 |
2005年 | 1950篇 |
2004年 | 1679篇 |
2003年 | 1472篇 |
2002年 | 1131篇 |
2001年 | 1027篇 |
2000年 | 845篇 |
1999年 | 716篇 |
1998年 | 480篇 |
1997年 | 375篇 |
1996年 | 342篇 |
1995年 | 315篇 |
1994年 | 205篇 |
1993年 | 139篇 |
1992年 | 143篇 |
1991年 | 108篇 |
1990年 | 88篇 |
1989年 | 58篇 |
1988年 | 32篇 |
1987年 | 27篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1959年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
In this article, two novel kinds of focusing elements as reflectors are analyzed and compared. One is the grooved Fresnel zone plate reflector with continuous phase‐correcting. The other called subzone paraboloid reflector, has the profile that consists of a series of paraboloids. Their diffraction efficiencies and bandwidths are described. The two elements still preserve the advantages of Fresnel zone plates, namely, low profile, high efficiency, and simple fabrication. Two dual‐reflector antennas using the proposed focusing elements as the main reflectors are simulated and the results show that these antennas have good radiation performances. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:101–108, 2015. 相似文献
2.
3.
Industrialized white organic light-emitting diodes (OLEDs) currently require host-guest doping, a complicated process necessitating precise control of the guest concentration to get high efficiency and stability. Two doping-free, hybrid white OLEDs with fluorescent blue, and phosphorescent green and red emissive layers (EMLs) are reported in this work. An ultra-thin red phosphorescent EML was situated in a blue-emitting electron transport layer (ETL), while the ultra-thin green phosphorescent EML was placed either in the ETL (Device 1), or the hole transport layer (HTL) (Device 2). Device 2 exhibits higher efficiency and more stable spectrum due to the enhanced utilization of excitons by ultra-thin green EML at the exciton generation zone within the HTL. Values of current efficiency (CE), power efficiency (PE), and CRI obtained for the optimized hybrid white OLEDs fabricated through a doping-free process were of 23.2 cd/A, 20.5 lm/W and 82 at 1000 cd/m2, respectively. 相似文献
4.
5.
6.
SUNShou-qun ZHAOSan-xing ZHANGWei CHANGXin-long 《国际设备工程与管理》2003,8(2):80-87
The multi-fault phenomena are common in the turbo-rotor system of a liquid rocket engine.As it has many excellent qualities,the neural network might be used to solve the problems of multi-fault diagnasis of a turbo-rotor system.First,the feature expression of a common turbo-rotor fault was studied in order to build up the standard fault pattern and satisfy the need of neural network studying and diagnosing.Then.the turbo-rotor fault identification and diagnosis problems were investigated by using a BP(back-propaga-tion)neural network.According to the BP neural network problems,the parallel BP neural network method of multi-fault diagnosis and classification was presented and investigated.The results indicated that the parallel Bp neural network method could solve the turbo-rotor multi-fault diagnosis problems. 相似文献
7.
8.
砂砾岩储集层含油性解释方法 总被引:15,自引:4,他引:11
LJ地区砂砾岩地层具有岩石结构复杂,储集层非均质性强,稠油和稀油并存的特点,利用测井资料解释含油性难度很大,以地层测试资料为依据,综合利用多种测井信息,提取反映含油性变化的测井特征参数;应用测井参数交会法和测井相分析法建立有效,快速识别稠油,油层和水层的标准,测井相分析法消除了用测井单参数和两参数交会解释含油性存在的多解性,提高子解释结果的成功率,用编制的解释软件处理了LJ地区58口井的资料,解释结果与试油资料对比吻合程度较高,为砂岩储层含油性解释提供了一种有效,快速的方法,为该区先导性试验提供了可靠的依据。 相似文献
9.
10.
Modeling and assimilation of root zone soil moisture using remote sensing observations in Walnut Gulch Watershed during SMEX04 总被引:1,自引:0,他引:1
Soil moisture status in the root zone is an important component of the water cycle at all spatial scales (e.g., point, field, catchment, watershed, and region). In this study, the spatio-temporal evolution of root zone soil moisture of the Walnut Gulch Experimental Watershed (WGEW) in Arizona was investigated during the Soil Moisture Experiment 2004 (SMEX04). Root zone soil moisture was estimated via assimilation of aircraft-based remotely sensed surface soil moisture into a distributed Soil-Water-Atmosphere-Plant (SWAP) model. An ensemble square root filter (EnSRF) based on a Kalman filtering scheme was used for assimilating the aircraft-based soil moisture observations at a spatial resolution of 800 m × 800 m. The SWAP model inputs were derived from the SSURGO soil database, LAI (Leaf Area Index) data from SMEX04 database, and data from meteorological stations/rain gauges at the WGEW. Model predictions are presented in terms of temporal evolution of soil moisture probability density function at various depths across the WGEW. The assimilation of the remotely sensed surface soil moisture observations had limited influence on the profile soil moisture. More specifically, root zone soil moisture depended mostly on the soil type. Modeled soil moisture profile estimates were compared to field measurements made periodically during the experiment at the ground based soil moisture stations in the watershed. Comparisons showed that the ground-based soil moisture observations at various depths were within ± 1 standard deviation of the modeled profile soil moisture. Density plots of root zone soil moisture at various depths in the WGEW exhibited multi-modal variations due to the uneven distribution of precipitation and the heterogeneity of soil types and soil layers across the watershed. 相似文献