全文获取类型
收费全文 | 36825篇 |
免费 | 1674篇 |
国内免费 | 1902篇 |
专业分类
电工技术 | 972篇 |
技术理论 | 1篇 |
综合类 | 1766篇 |
化学工业 | 2411篇 |
金属工艺 | 1318篇 |
机械仪表 | 3455篇 |
建筑科学 | 2315篇 |
矿业工程 | 697篇 |
能源动力 | 948篇 |
轻工业 | 855篇 |
水利工程 | 389篇 |
石油天然气 | 837篇 |
武器工业 | 327篇 |
无线电 | 3101篇 |
一般工业技术 | 1818篇 |
冶金工业 | 950篇 |
原子能技术 | 421篇 |
自动化技术 | 17820篇 |
出版年
2024年 | 65篇 |
2023年 | 311篇 |
2022年 | 454篇 |
2021年 | 665篇 |
2020年 | 619篇 |
2019年 | 517篇 |
2018年 | 583篇 |
2017年 | 758篇 |
2016年 | 942篇 |
2015年 | 1003篇 |
2014年 | 1873篇 |
2013年 | 1813篇 |
2012年 | 1940篇 |
2011年 | 2684篇 |
2010年 | 1828篇 |
2009年 | 1903篇 |
2008年 | 2073篇 |
2007年 | 2567篇 |
2006年 | 2498篇 |
2005年 | 2341篇 |
2004年 | 2076篇 |
2003年 | 2064篇 |
2002年 | 1575篇 |
2001年 | 1236篇 |
2000年 | 1001篇 |
1999年 | 919篇 |
1998年 | 772篇 |
1997年 | 596篇 |
1996年 | 519篇 |
1995年 | 474篇 |
1994年 | 331篇 |
1993年 | 249篇 |
1992年 | 193篇 |
1991年 | 131篇 |
1990年 | 114篇 |
1989年 | 128篇 |
1988年 | 92篇 |
1987年 | 54篇 |
1986年 | 57篇 |
1985年 | 64篇 |
1984年 | 54篇 |
1983年 | 42篇 |
1982年 | 38篇 |
1981年 | 38篇 |
1980年 | 25篇 |
1979年 | 22篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1976年 | 38篇 |
1975年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
介绍I/A’S系统在巨化热电厂八号50MW供热机组上应用实例,并从DCS系统的整体设计到实现的功能、控制效果等多方面进行了分折,总结了调试和运行经验。 相似文献
53.
Inaki Arrazola Agn s Plainfoss Henri Prade Claudette Testemale 《Information Systems》1989,14(6):487-492
This paper presents different approaches which enable a data base management system to obtain a plausible fuzzy estimate for an attribute value of an item for which the information is not explicitly stored in the data base. This can be made either by a kind of analogical reasoning from information about particular items or by means of expert rules which specify the (fuzzy) sets of possible values of the attribute under consideration, for various classes of items. Another kind of expert rules enables the system to compute an estimate from the attribute value of another item provided that, in other respects, this latter item sufficiently resembles the item, the value of which we are interested in; then these expert rules are used either for controlling the analogical reasoning process or for enlarging the scope of application of the first kind of expert rules. The different approaches are discussed in the framework of possibility theory. 相似文献
54.
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
55.
H. Luo 《Microsystem Technologies》2006,12(4):324-329
This paper focuses on tracking, reconstruction and motion estimation of a well-defined MEMS optical switch from a microscopic
view. For out-of-view reconstruction, a homography capable of transforming feature points and feature lines between a microscopic
image and a CAD model of the switch is implemented. The homography between two sequential microscopic images is decomposed
and factorized for motion estimation. Optical flow has also been explored to provide rough estimations of rotation centre
and angle. The paper also illustrates motion parameter optimization principles to deal with uncertainty inherent in micro
world. After non-linear optimization, estimation accuracy for rotation angle and rotation centre can reach 0.06° and pixel
level, respectively. 相似文献
56.
57.
Shinsook Yoon Mi-Kyoung Kim In-Young Lee Mikyung Yun Jeong E. Nam Shin 《Journal of Industrial and Engineering Chemistry》2008,14(6):759-764
We have developed a mutant strain derived from Agrobacterium sp. ATCC 31750, which produces a water-soluble polysaccharide having potential utility to the food, feed, pharmaceutical and cosmetic industries. A high concentration of product (15 g/L) is obtained by 48 h cultivation of the mutant strain under optimized fermentation conditions. The water-soluble polysaccharide obtained from cultures of the mutant strain beta82 has Glc:Man:Gal in approximate molar ratios of 5.8:6.7:1.0. The molecular weight of the polysaccharide was determined to be approximately 1000 kDa by HPSEC analysis. Linkage analysis contained 3-Glcp, 3-Manp, terminal Glcp and terminal Manp, as well as a small proportion of 3- and 3,4-Galp, and 4,6-Manp residues. Based on analyses using FT-IR and 13C NMR spectrometers, most glycosidic bonds joining these sugar residues are of the α-type, and acetyl groups are apparently attached to the polymer chain at random. 相似文献
58.
In polyolefin processes the melt index (MI) is the most important control variable indicating product quality. Because of
the difficulty in the on-line measurement of MI, a lot of MI estimation and correlation methods have been proposed. In this
work a new dynamic MI estimation scheme is developed based on system identification techniques. The empirical MI estimation
equation proposed in the present study is derived from the 1
st
-order dynamic models. Effectiveness of the present estimation scheme was illustrated by numerical simulations based on plant
operation data including grade change operations in high density polyethylene (HDPE) processes. From the comparisons with
other estimation methods it was found that the proposed estimation scheme showed better performance in MI predictions. The
virtual sensor model developed based on the estimation scheme was combined with the virtual on-line analyzer (VOA) to give
a quality control system to be implemented in the actual HDPE plant. From the application of the present control system, significant
reduction of transition time and the amount of off-spec during grade changes was achieved 相似文献
59.
J.R. Red-Horse T.L. Paez 《Computer Methods in Applied Mechanics and Engineering》2008,197(29-32):2578
This article specifies a virtual structural dynamic subsystem and some systems, as well as mathematical models that approximately simulate them. The purpose is to define a setting for model validations conceived by participants in the Sandia National Laboratories Validation Workshop. Some broad guidelines for the model validations are set, as well as a regulatory requirement to be satisfied by the target system. Participants are directed to present techniques for subsystem model validation, to analytically predict whether or not the regulatory requirement will be met, and to estimate the likelihood of accuracy of the prediction. 相似文献
60.
Takeshi Kondo Sang Min Lee Michal Malicki Benoit Domercq Seth R. Marder Bernard Kippelen 《Advanced functional materials》2008,18(7):1112-1118
We report on a single‐layer organic memory device made of poly(N‐vinylcarbazole) embedded between an Al electrode and ITO modified with Ag nanodots (Ag‐NDs). Devices exhibit high ON/OFF switching ratios of 104. This level of performance could be achieved by modifying the ITO electrodes with some Ag‐NDs that act as trapping sites, reducing the current in the OFF state. Temperature dependence of the electrical characteristics suggest that the current of the low‐resistance state can be attributed to Schottky charge tunnelling through low‐resistance pathways of Al particles in the polymer layer and that the high‐resistance state can be controlled by charge trapping by the Al particles and Ag‐NDs. 相似文献