全文获取类型
收费全文 | 20464篇 |
免费 | 1890篇 |
国内免费 | 573篇 |
专业分类
电工技术 | 1027篇 |
技术理论 | 3篇 |
综合类 | 824篇 |
化学工业 | 4339篇 |
金属工艺 | 999篇 |
机械仪表 | 1319篇 |
建筑科学 | 893篇 |
矿业工程 | 313篇 |
能源动力 | 744篇 |
轻工业 | 1335篇 |
水利工程 | 261篇 |
石油天然气 | 741篇 |
武器工业 | 107篇 |
无线电 | 2803篇 |
一般工业技术 | 3504篇 |
冶金工业 | 999篇 |
原子能技术 | 277篇 |
自动化技术 | 2439篇 |
出版年
2024年 | 38篇 |
2023年 | 316篇 |
2022年 | 323篇 |
2021年 | 767篇 |
2020年 | 626篇 |
2019年 | 572篇 |
2018年 | 656篇 |
2017年 | 721篇 |
2016年 | 726篇 |
2015年 | 781篇 |
2014年 | 1068篇 |
2013年 | 1256篇 |
2012年 | 1342篇 |
2011年 | 1562篇 |
2010年 | 1207篇 |
2009年 | 1227篇 |
2008年 | 1242篇 |
2007年 | 1053篇 |
2006年 | 979篇 |
2005年 | 872篇 |
2004年 | 684篇 |
2003年 | 673篇 |
2002年 | 682篇 |
2001年 | 551篇 |
2000年 | 424篇 |
1999年 | 400篇 |
1998年 | 366篇 |
1997年 | 311篇 |
1996年 | 300篇 |
1995年 | 212篇 |
1994年 | 217篇 |
1993年 | 127篇 |
1992年 | 122篇 |
1991年 | 94篇 |
1990年 | 60篇 |
1989年 | 65篇 |
1988年 | 44篇 |
1987年 | 33篇 |
1986年 | 21篇 |
1985年 | 40篇 |
1984年 | 27篇 |
1983年 | 15篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1977年 | 8篇 |
1976年 | 14篇 |
1975年 | 8篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
The deactivation characteristics of Pd/SiO2 in the selective hydrogenation of acetylene were correlated with changes in the amount of the C4 species produced. The amounts of butenes produced changed in parallel with the catalyst activity, indicating that the rate limiting step for butene production was the same as that for acetylene hydrogenation. On the other hand, the amount of 1,3-butadiene produced changed, showing a maximum with catalyst deactivation because 1,3-butadiene is an intermediate in the sequential reaction process which involves both the production and consumption of 1,3-butadiene. This was verified by a simultaneous TG/reaction experiment showing that 1,3-butadiene was a precursor of green oil. The catalyst showed a self-regenerative behavior in its activity and the amounts of C4 species produced during the early stage of deactivation because two opposite factors, which contributed to either the lowering or the promotion of activity, were involved in the process. A specific type of polymer species, produced during the initial period of deactivation, is proposed to be responsible for the promotion of catalyst activity. 相似文献
82.
Sang C. Park 《The Visual computer》2003,19(1):38-49
A sweeping operation called polygonal extrusion is defined to improve the modeling power of CSG-based modeling. It is assumed that a 2D cross-sectional polygon (sweeping
polygon) moves in space while its containing plane is kept orthogonal to the tangent direction of the trajectory curve, a planar
polygonal chain having no self-intersections. The objective of the paper is to compute the boundary of the swept volume of
the sweeping polygon as a set of polygons (or triangles). The most significant challenge to accomplishing this objective is
the problem of trimming the swept volume. To solve the trimming problem, 2D-curve offsetting methods are employed. Two algorithms
are presented for polygonal extrusion that are based on different offsetting methods, the Voronoi diagram and PWID offset.
The proposed algorithms have been implemented and tested with various examples.
Published online: 28 January 2003 相似文献
83.
Jong Min Kim Donghee Lee Sang Lyul Min Chong Sang Kim 《Information Processing Letters》2003,85(2):93-97
A new dynamic buffer allocation strategy based on the notion of marginal gains is presented for the buffer cache that is used by the operating system to store frequently accessed disk blocks in main memory, and the performance of the proposed strategy is compared with those of previous allocation strategies. In the proposed strategy, marginal gain values are predicted by exploiting functions that approximate the expected number of buffer hits per unit time. Experimental results from both trace-driven simulation and an actual implementation in the FreeBSD operating system show that the proposed strategy accurately predicts the marginal gain values for various workloads resulting in significantly improved buffer hit ratios. 相似文献
84.
Yi Kai Zhou Sung Woo Choi Shigeya Kimura Shuichi Emura Shigehiko Hasegawa Hajime Asahi 《Journal of Superconductivity and Novel Magnetism》2007,20(6):429-432
GaGdN layers were grown at temperatures below 300°C by radio-frequency plasma-assisted molecular beam epitaxy on sapphire
substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained by lowering the growth temperature. X-ray
diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth
at low temperatures. All samples, including those grown at room temperature, showed ferromagnetic characteristics. Photoluminescence
emission was observed, though spectra exhibit broad and sharp luminescence bands related to many kinds of defects. It is suggested
that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism
occurs in the low-temperature-growth GaGdN. 相似文献
85.
References: 《计算技术与自动化》2003,22(Z1):54-57
In order to avoid unnecessary damage of electrical equipments and installations,high quality power should be delivered to the end user and strict control on frequency should be made, Therefore, it is important to estimate the power system's harmonic components with higher accuracy. This paper presents a new approach for estimating harmonic component in a power system using secant - fuzzy linear regression method. In this approach the non - sinusoidal voltage or current waveform is written as I linear function. The coefficient of this function is assumed to be fuzzy number with a membership function that has center and spread value. The time dependent quantity is written as Taylor series with two different time dependent quantities. The objective is to use the sample obtained from the transmission line to find the power system harmonic components and frequencies. We used an experimental voltage signal from a sub power station as a numerical test. 相似文献
86.
电子诱导脱附是近年来在真空科学与表面科学领域内的热门研究课题。它不仅作为研究和探讨原子激发过程以及电子能量传输机制的有效手段,而且已经逐渐成为获取表面和界面结构、状态等信息的有效方法。“信号调制法”是利用脉冲电流能量调制的电子探束取代传统的直流电子探束,并通过测量电子诱导脱附产物引起的压强变化量,来研究电子诱导脱附的新方法。本文系统地介绍了该方法的基本原理,并从理论上对该方法带来的测量误差进行了分析。 相似文献
87.
In this paper, we propose an efficient design method for area optimization in a digital filter. The conventional methods to reduce the number of adders in a filter have the problem of a long critical path delay caused by the deep logic depth of the filter due to adder sharing. Furthermore, there is such a disadvantage that they use the transposed direct form (TDF) filter which needs more registers than those of the direct form (DF) filter. In this paper, we present a hybrid structure of a TDF and DF based on the flattened coefficients method so that it can reduce the number of flip‐flops and full‐adders without additional critical path delay. We also propose a resource sharing method and sharing‐pattern searching algorithm to reduce the number of adders without deepening the logic depth. Simulation results show that the proposed structure can save the number of adders and registers by 22 and 26%, respectively, compared to the best one used in the past. 相似文献
88.
A ternary blend system comprising poly(cyclohexyl methacrylate) (PCHMA), poly(α‐methyl styrene) (PαMS) and poly(4‐methyl styrene) (P4MS) was investigated by thermal analysis, optical and scanning electron microscopy. Ternary phase behaviour was compared with the behaviour for the three constituent binary pairs. This study showed that the ternary blends of PCHMA/PαMS/P4MS in most compositions were miscible, with an apparent glass transition temperature (Tg) and distinct cloud‐point transitions, which were located at lower temperatures than their binary counterparts. However, in a closed‐loop range of compositions roughly near the centre of the triangular phase diagram, some ternary blends displayed phase separation with heterogeneity domains of about 1 µm. Therefore, it is properly concluded that ternary PCHMA/PαMS/P4M is partially miscible with a small closed‐loop immisciblity range, even though all the constituent binary pairs are fully miscible. Thermodynamic backgrounds leading to decreased miscibility and greater heterogeneity in a ternary polymer system in comparison with the binary counterparts are discussed. © 2003 Society of Chemical Industry 相似文献
89.
90.