全文获取类型
收费全文 | 33293篇 |
免费 | 2397篇 |
国内免费 | 1205篇 |
专业分类
电工技术 | 1511篇 |
综合类 | 1931篇 |
化学工业 | 5908篇 |
金属工艺 | 1567篇 |
机械仪表 | 1895篇 |
建筑科学 | 3002篇 |
矿业工程 | 610篇 |
能源动力 | 1050篇 |
轻工业 | 2054篇 |
水利工程 | 486篇 |
石油天然气 | 1811篇 |
武器工业 | 210篇 |
无线电 | 4071篇 |
一般工业技术 | 4389篇 |
冶金工业 | 1776篇 |
原子能技术 | 435篇 |
自动化技术 | 4189篇 |
出版年
2024年 | 101篇 |
2023年 | 444篇 |
2022年 | 717篇 |
2021年 | 1090篇 |
2020年 | 842篇 |
2019年 | 723篇 |
2018年 | 794篇 |
2017年 | 933篇 |
2016年 | 855篇 |
2015年 | 1118篇 |
2014年 | 1455篇 |
2013年 | 1869篇 |
2012年 | 1966篇 |
2011年 | 2131篇 |
2010年 | 1785篇 |
2009年 | 1791篇 |
2008年 | 1746篇 |
2007年 | 1727篇 |
2006年 | 1772篇 |
2005年 | 1605篇 |
2004年 | 1102篇 |
2003年 | 991篇 |
2002年 | 983篇 |
2001年 | 834篇 |
2000年 | 909篇 |
1999年 | 980篇 |
1998年 | 965篇 |
1997年 | 783篇 |
1996年 | 780篇 |
1995年 | 639篇 |
1994年 | 501篇 |
1993年 | 455篇 |
1992年 | 312篇 |
1991年 | 228篇 |
1990年 | 230篇 |
1989年 | 161篇 |
1988年 | 130篇 |
1987年 | 92篇 |
1986年 | 73篇 |
1985年 | 52篇 |
1984年 | 45篇 |
1983年 | 31篇 |
1982年 | 32篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1973年 | 8篇 |
1970年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
机动目标跟踪中一种新的自适应滤波算法 总被引:1,自引:0,他引:1
通过分析基于“当前”统计模型的机动目标自适应跟踪算法,指出该算法对目标机动加速度极限值的依赖性,而实际中预先设定加速度的最大值是不可行的。为克服这一缺点,文中给出一种新的自适应滤波算法,该方法无需提前给定加速度最大值,可以直接利用位置估计值和加速度之间的函数关系进行加速度方差自适应调整。仿真结果表明,与标准的自适应滤波相比其跟踪精度有了较大提高。 相似文献
992.
工程总承包公司的合同管理研究 总被引:1,自引:0,他引:1
山东鲁能工程有限责任公司开展电力工程总承包始于上世纪九十年代中期,近五年来总承包事业发展迅速,公司陆续签订了嘉峪关宏晟2×300M W电厂、重庆永川2×125M W电厂、费县2×600M W电厂脱硫、章丘2×300M W电厂脱硫、潍坊2×25M W电厂、单县1×25M W生物发电厂等一批总承包合同,均采用了国际上通行的FID IC合同条款。为规范公司的经营管理,防范合同风险,维护公司合法权益,我们研究摸索了一套适应矩阵管理的总承包公司合同管理体系,在此做简要介绍,与同行交流。一、合同管理中常见问题合同是市场经济下确定不同主体之间经济关系的重… 相似文献
993.
Jianjun Xie Jingying Liao Zhengsong Geng Chongzhi Ye Hui Yuan Wei Xiong Dunhua Cao Zhonggui Zhan Liang Chen Bingfu Shen Zhiwen Yin 《Materials Science and Engineering: B》2006,130(1-3):31-35
The effects of Y3+ doping at different concentration on the luminescnece properties of PbWO4 crystals have been investigated by means of Fourier transform infrared (FT-IR) spectrum, optical transmission, thermoluminescence (TL), X-ray excited luminescence (XEL), photoluminescence (PL) under excitation of UV light and light yield measurements. The series PbWO4:Y crystal samples were grown by modified Bridgman method and the concentration of Y3+ in the melt was in the range of 0–1.0 mol%. The slight blue-shift and evident red-shift of the absorption edge in PbWO4 crystal were observed at low and heavy doping concentration, respectively. TL peaks in the range of from room temperature to 250 °C disappeared after the doping with Y3+. With the increase of doping concentration, the luminescence intensity in the XEL and PL spectra was found to decrease accordingly, especially in the case of heavy doping. The measuring results demonstrate that Y3+ doping concentration below 100 ppm in the crystal seems to be the best for optimizing the optical and scintillation properties of the material. The mechanism of Y3+ doping concentration influence on luminescence was also discussed in this paper. 相似文献
994.
Haixue Yan Hongtao Zhang Rick Ubic Mike Reece Jing Liu Zhijian Shen 《Journal of Materials Science: Materials in Electronics》2006,17(9):657-661
Grain-oriented Aurivillius phase BaBi2Nb2 O9 ceramics were fabricated using Spark Plasma Sintering (SPS). Their relaxor behaviour was confirmed by a strong frequency
dispersion of the dielectric response. The dielectric behaviour has been fitted using different relaxor models. The relaxor
parameters are isotropic, while the dielectric constants are highly anisotropic. The piezoelectric constant d
33 is zero perpendicular and parallel to the hot pressing direction, and the P–E response is dominated by losses. The inability to pole the samples at room temperature is consistent with the T
f temperature (∼
∼115 K) estimated from fitting the experimental data to the Vogel–Fulcher model. This suggests that it may be possible to
observe piezoelectric and ferroelectric properties at very low temperatures. 相似文献
995.
Recurrent Radial Basis Function Network-Based Fuzzy Neural Network Control for Permanent-Magnet Linear Synchronous Motor Servo Drive 总被引:1,自引:0,他引:1
We propose a recurrent radial basis function network-based (RBFN-based) fuzzy neural network (FNN) to control the position of the mover of a field-oriented control permanent-magnet linear synchronous motor (PMLSM) to track periodic reference trajectories. The proposed recurrent RBFN-based FNN combines the merits of self-constructing fuzzy neural network (SCFNN), recurrent neural network (RNN), and RBFN. Moreover, it performs the structureand parameter-learning phases concurrently. The structure learning is based on the partition of input space, and the parameter learning is based on the supervised gradient descent method, using a delta adaptation law. Furthermore, all the control algorithms are implemented in a TMS320C32 DSP-based control computer. The simulated and experimental results due to periodic reference trajectories show that the dynamic behaviors of the proposed recurrent RBFN-based FNN control system are robust with regard to uncertainties 相似文献
996.
The effect of carbon precursor on the pore size distribution of mesoporous carbon during templating synthesis process 总被引:1,自引:0,他引:1
Wenzhong Shen Xiangping Yang Qingjie Guo Yihong Liu Yanru Song Zhongxiang Han Qinglei Sun Jian Cheng 《Materials Letters》2006,60(29-30):3517-3521
The starch and cyclodextrin were selected as the precursors and the mixture of surfactant and tetraethyl orthosilicate (TEOS) as template to prepare mesoporous carbon. The result showed that a bimodal pore size distribution in mesoporous carbon derived from starch appeared; one was around 3.4 nm and the other ranged from 3.8 to 16.2 nm. However, there existed a concentrated pore size distribution from 3.2 to 4.2 nm in mesoporous carbon derived from cyclodextrin. The different molecular structure of starch and cyclodextrin and their polymerization process in the presence of sulfur acid were responsible for the resulted mesoporous carbon structure; the starch could polymerize by head to head or side by side, but the cycleodextrin was only polymerized by head to head. 相似文献
997.
A detailed transmission electron microscope (TEM) study has been conducted to investigate the microstructures of the Zr51Cu20.7Ni12Al16.3 metallic glass formed at different cooling rates. It has been found that the most competitive crystalline phase to the amorphous structure is an oxygen-stabilized FCC NiZr2-type phase, which in turn acts as the leading phase to trigger the formation of other crystalline phases in the slow-cooled alloy. 相似文献
998.
Iridium oxide (IrO2) thin films were deposited on Si (100) substrates by means of pulsed laser deposition technique at various substrate (deposition) temperatures ranging from 250 to 500 °C. Effects of substrate temperature on the crystalline nature, morphology and electrical properties of the deposited films were analyzed by using X-ray diffraction, Raman spectroscopy, Scanning electron microscopy and four-point probe method. It was found that the above properties were strongly dependent on the substrate temperature. The as-deposited films at all substrate temperatures were polycrystalline tetragonal IrO2 and the preferential growth orientation changed with the substrate temperature. IrO2 films exhibited fairly homogeneous thickness and good adhesion with the substrate, the average feature size increases with the substrate temperature. The room-temperature resistivity of IrO2 films decreased with the increase of substrate temperature and the minimum resistivity of (42 ± 6) μΩ cm was obtained at 500 °C. The resistivity of IrO2 films correlated well with the corresponding film morphology changes. 相似文献
999.
Lanthanum oxide films were fabricated using dual plasma deposition. X-ray photoelectron spectroscopy (XPS) showed that La existed in the + 3 oxidation state. X-ray diffraction (XRD) revealed a (101) oriented hexagonal structure. Blood platelet adhesion tests and endothelial cell cultures were used to evaluate the hemocompatibility of the as-deposited films. Scanning electron microscopy (SEM) and optical microscopy were employed to evaluate the surface morphology of the blood platelets and endothelial cells on the films. The results showed that the number of adhered, aggregated and morphologically changed platelets was reduced compared to that observed on low-temperature isotropic carbon (LTIC). Endothelial cells culture tests indicated good adhesion and proliferation of human umbilical vein endothelial (HUVE) cells in vitro. Our study suggests that lanthanum oxide films are potential blood-contacting biomedical materials. 相似文献
1000.
In order to research thoroughly the mechanism of the solid-state interfacial reactions and the induced compound morphology of cubic boron nitride (cBN) abrasive grains and the surface Ti-coating layer, annealing experiments of Ti-coated cBN grains were conducted at different temperatures of 550-950 °C for dwell times of 60 min under high-vacuum conditions. The corresponding interfacial characteristics were investigated by differential thermal analysis, X-ray diffraction and scanning electron microscopy. The results show that the relevant interfacial reactions and compound morphology between cBN and Ti are significantly influenced by the heat-treatment temperature. No reaction occurs below 550 °C, and TiN is the sole reaction product during heating from 650-750 °C. Three kinds of compounds, TiN, TiB2 and TiB, can exist in the interfacial region at 950 °C. Here, the favorable interfacial structures, cBN/TiB2/TiB/(TiB+TiN)/TiN/Ti, are developed for the excellent mechanical and chemical transition effects between cBN grains and Ti coating. The thermodynamic analysis finally predicts that there is a reasonable probability for the formation of such a special interfacial transition layer. 相似文献