全文获取类型
收费全文 | 30493篇 |
免费 | 2789篇 |
国内免费 | 1527篇 |
专业分类
电工技术 | 2026篇 |
技术理论 | 2篇 |
综合类 | 2092篇 |
化学工业 | 4944篇 |
金属工艺 | 1508篇 |
机械仪表 | 2004篇 |
建筑科学 | 3031篇 |
矿业工程 | 825篇 |
能源动力 | 831篇 |
轻工业 | 2500篇 |
水利工程 | 539篇 |
石油天然气 | 1361篇 |
武器工业 | 234篇 |
无线电 | 3712篇 |
一般工业技术 | 3549篇 |
冶金工业 | 1208篇 |
原子能技术 | 411篇 |
自动化技术 | 4032篇 |
出版年
2024年 | 149篇 |
2023年 | 572篇 |
2022年 | 1057篇 |
2021年 | 1446篇 |
2020年 | 1039篇 |
2019年 | 859篇 |
2018年 | 923篇 |
2017年 | 1038篇 |
2016年 | 969篇 |
2015年 | 1209篇 |
2014年 | 1558篇 |
2013年 | 1800篇 |
2012年 | 2023篇 |
2011年 | 2151篇 |
2010年 | 2006篇 |
2009年 | 1885篇 |
2008年 | 1741篇 |
2007年 | 1640篇 |
2006年 | 1576篇 |
2005年 | 1346篇 |
2004年 | 899篇 |
2003年 | 840篇 |
2002年 | 823篇 |
2001年 | 743篇 |
2000年 | 672篇 |
1999年 | 702篇 |
1998年 | 500篇 |
1997年 | 477篇 |
1996年 | 470篇 |
1995年 | 385篇 |
1994年 | 313篇 |
1993年 | 209篇 |
1992年 | 164篇 |
1991年 | 115篇 |
1990年 | 83篇 |
1989年 | 84篇 |
1988年 | 63篇 |
1987年 | 45篇 |
1986年 | 36篇 |
1985年 | 24篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1977年 | 4篇 |
1962年 | 42篇 |
1961年 | 39篇 |
1960年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
53.
Zhihong Ye Boroyevich D. Jae-Young Choi Lee F.C. 《Power Electronics, IEEE Transactions on》2002,17(5):609-615
One unique feature in parallel three-phase converters is a potential zero-sequence circulating current. To avoid the circulating current, most present technology uses an isolation approach, such as transformers or separate power supplies. This paper proposes a parallel system where individual converters connect both AC and DC sides directly without additional passive components to reduce size and cost of the overall parallel system. In this case, the control of the circulating current becomes an important objective in the converter design. This paper: (1) develops an averaged model of the parallel converters based on a phase-leg averaging technique; (2) a zero-sequence model is then developed to predict the dynamics of the zero-sequence current; (3) based on the zero-sequence model, this paper introduces a new control variable, which is associated with space-vector modulation; (4) a strong zero-sequence current control loop is designed to suppress the circulating current; and (5) simulation and experimental results validate the developed model and the proposed control scheme. 相似文献
54.
振动采油工艺在稠油区的实验研究与应用 总被引:5,自引:2,他引:3
在天然地震的影响下,油井产量发生波动,使人们受到启示,从而引进了振动采油工艺技术。本文对振动增产的机理进行了探讨,指出振动增油机理在于加快地层中流体的流速;改变储集层内油、气、水的重新分布;改变岩石表面润湿性,有利于清除油层堵塞,提高渗透率。通过分析两个试验区的振动采油效果,总结出在不同扰动力、不同激振频率、不同振动周期下的增产效果和规律,对振动采油的实施具有一定的指导意义。 相似文献
55.
The main objective of this fundamental study was to investigate effects of processing conditions and resulting matrix morphology on interfacial bond strength of fibre reinforced thermoplastic composites. Using a hot stage microscope, single fibre pull-out samples were produced with T700S high strength carbon fibre and two semicrystalline thermoplastic matrices, polyphenylene sulphide (PPS) and polyethylene terephthalate (PET), respectively. Processing temperatures and cooling histories were the major variables in sample preparation. The T700S fibre had no clear effect on the surrounding PPS and PET matrix morphology, as long as direct cooling at constant rates was selected. A transcrystalline phase around the fibres could be induced in the T700S/PPS system, if isothermal crystallization was carried out at 227°C. Fibre pull-out tests were conducted at room temperature and two basic failure paths were observed, i.e. debonding at the fibre-matrix interface and cohesive failure of the matrix close to the fibre surface. The results indicate that slow cooling rate and a resulting coarse spherulitic morphology around the fibres correlate with high interfacial shear strength. In fact somewhat higher strength values were obtained for samples with transcrystalline layers around the fibres. 相似文献
56.
A semi-Markov model is constructed that describes an arbitrarily structured multicomponent technological system and takes
into account its calendar maintenance. Using an aggregation algorithm, approximate values of stationary reliability characteristics
and an optimal term of maintenance work are determined for the system.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 69–86, March–April 2006. 相似文献
57.
58.
Ye Yuan Yanfang Li Cameron B.D. Relue P. 《IEEE journal of selected topics in quantum electronics》2007,13(6):1671-1679
In this study, we wanted to see if fluorescence anisotropy could be used to detect changes in metabolism in cells with significant light scattering and absorption properties. Fluorescence anisotropy measurements of nicotinamide adenine dinucleotide (NADH) were performed with human melanocytes and melanoma cell lines. To demonstrate the feasibility of using fluorescence anisotropy for detecting metabolic changes, the electron transport chain was blocked using rotenone, inducing an accumulation of intracellular NADH. Total fluorescence increased in all cells as a result of rotenone treatment. Fluorescence anisotropy decreased in the rotenone-treated cells relative to the controls, suggesting an increased ratio of free to protein-bound NADH in the treated cells. In general, the fluorescence anisotropy of the melanocytes was significantly higher than that of the melanoma cell lines. Reflectance spectroscopy showed that the differences in fluorescence anisotropy between the cell types were not due to differences in scattering and absorption properties. Intrinsic cellular NADH fluorescence was experimentally extracted by ratioing polarized fluorescence to polarized reflectance. NADH binding, measured as the ratio of fluorescence intensity at 430 and 465 nm, showed more protein-bound NADH in the melanocytes than in the melanoma cells, consistent with the fluorescence anisotropy measurements. 相似文献
59.
60.
Understanding how the structure of the unit-cell affects the cryogenic performance of a Si power Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is an important step toward optimizing of the device for cryogenic operations. In this paper, numerical simulations of the Si power Double Diffused MOSFET’ (DMOS) are performed at room temperature and cryogenic temperatures. Physically based models for temperature dependent silicon properties are employed in the simulations. The performances of power DMOS’ with various unit-cell structures are compared at both room temperature and low temperatures. The effect of the cell structure on the on-resistance and breakdown voltage of the device are analyzed. The simulation results suggest that the device optimized for room temperature operation can be further optimized at cryogenic temperatures. 相似文献