全文获取类型
收费全文 | 5332篇 |
免费 | 128篇 |
国内免费 | 27篇 |
专业分类
电工技术 | 414篇 |
综合类 | 17篇 |
化学工业 | 1516篇 |
金属工艺 | 139篇 |
机械仪表 | 142篇 |
建筑科学 | 192篇 |
矿业工程 | 1篇 |
能源动力 | 251篇 |
轻工业 | 511篇 |
水利工程 | 19篇 |
石油天然气 | 7篇 |
无线电 | 312篇 |
一般工业技术 | 942篇 |
冶金工业 | 216篇 |
原子能技术 | 221篇 |
自动化技术 | 587篇 |
出版年
2023年 | 30篇 |
2022年 | 60篇 |
2021年 | 96篇 |
2020年 | 52篇 |
2019年 | 63篇 |
2018年 | 77篇 |
2017年 | 63篇 |
2016年 | 113篇 |
2015年 | 80篇 |
2014年 | 154篇 |
2013年 | 328篇 |
2012年 | 192篇 |
2011年 | 315篇 |
2010年 | 261篇 |
2009年 | 285篇 |
2008年 | 319篇 |
2007年 | 265篇 |
2006年 | 206篇 |
2005年 | 225篇 |
2004年 | 179篇 |
2003年 | 164篇 |
2002年 | 168篇 |
2001年 | 112篇 |
2000年 | 101篇 |
1999年 | 100篇 |
1998年 | 122篇 |
1997年 | 80篇 |
1996年 | 76篇 |
1995年 | 61篇 |
1994年 | 84篇 |
1993年 | 72篇 |
1992年 | 57篇 |
1991年 | 76篇 |
1990年 | 52篇 |
1989年 | 78篇 |
1988年 | 65篇 |
1987年 | 41篇 |
1986年 | 74篇 |
1985年 | 58篇 |
1984年 | 53篇 |
1983年 | 58篇 |
1982年 | 60篇 |
1981年 | 48篇 |
1980年 | 43篇 |
1979年 | 41篇 |
1978年 | 41篇 |
1977年 | 30篇 |
1976年 | 30篇 |
1975年 | 18篇 |
1973年 | 17篇 |
排序方式: 共有5487条查询结果,搜索用时 0 毫秒
181.
Preparation of sharp-melting hard palm midfraction and its use as hard butter in chocolate 总被引:1,自引:0,他引:1
Satsuki Hashimoto Toru Nezu Hiroshi Arakawa Tomonori Ito Shoji Maruzeni 《Journal of the American Oil Chemists' Society》2001,78(5):455-460
Preparation of hard palm midfractions (PMF) and its use as a cocoa butter equivalent ingredient were studied. Hard PMF is
obtained by multistep fractionation of palm oil involving dry fractionation (DF) and/or solvent fractionation (SF), usually
using hexane or acetone. From our experience, in acetone, a polar solvent, symmetrical 1,3-disaturated triacylglycerols tend
to selectively crystallize more than nonsymmetrical 1,2- or 2,3-disaturated triacylglycerols, making it suitable for obtaining
the solid midfraction. Unfortunately, triacylglycerols are very soluble in hexane, and temperatures at least 15 degrees lower
than those required for acetone must be used for equivalent crystal yields. On the other hand, DF is a less expensive and
safer process. Thus, multistep fractionation combining DF and SF using acetone was developed to achieve sufficient removal
of high-melting components, and further enrichment of 1,3-dipalmitoyl-2-oleoylglycerol and the hard PMF was obtained by triple-step
fractionation of palm olein or double-step fractionation of soft PMF. Compared to conventional hard PMF, this hard PMF had
a steeper melting curve and better snapping and sharp-melting qualities when used in chocolate. Heat resistance of the hard
PMF chocolate was similar to the conventional hard PMF chocolate, and its bloom resistance could be improved by adding polyglycerol
fatty acid esters. 相似文献
182.
Moriwaki H Takagi Y Tanaka M Tsuruho K Okitsu K Maeda Y 《Environmental science & technology》2005,39(9):3388-3392
Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are shown to be globally distributed, environmentally persistent, and bioaccumulative. Although the toxicities of these compounds were reported, the cleanup procedure from the environment is not developed because of their inertness. In this report the sonochemical degradations of PFOS and PFOA to the products through the fission of the perfluorocarbon chains were observed and the half-life times of the PFOS and PFOA degradations under an argon atmosphere determined to be 43 and 22 min, respectively. The shortening of perfluorocarbon chain of PFOS and PFOA leads to the lowering of the toxicity in view of the decrease of the persistence, and the technique would contribute to the remediation of the environmental pollution by these compounds. 相似文献
183.
Catalytic gasification of wood (Cedar) biomass was carried out using a specially designed flow-type double beds micro reactor in a two step process: temperature programmed non-catalytic steam gasification of biomass was performed in the first (top) bed at 200–850 °C followed by catalytic decomposition gasification of volatile matters (including tars) in the second (bottom) bed at a constant temperature, mainly 600 °C. Iron oxide catalysts, which transformed to Fe3O4 after use possessed catalytic activity in biomass tar decomposition. Above 90% of the volatile matters was gasified by the use of iron oxide catalyst (prepared from FeCl3 and NH3aq) at SV of 4.5 × 103 h?1. Tar was decomposed over the iron oxide catalysts followed by water gas shift reaction. Surface area of the iron oxide seemed to be an important factor for the catalytic tar decomposition. The activity of the iron oxide catalysts for tar decomposition seemed stable with cyclic use but the activity of the catalysts for the water gas shift reaction decreased with repeated use. 相似文献
184.
We investigated the flame-spread characteristics of randomly arranged fuel-droplet arrays in microgravity. Flame-spread probability was calculated based on a percolation model with the flame-spread-limit distance of evenly-spaced n-decane droplet arrays in microgravity. Flame-spread probability depends on the occupation fraction of droplets in a lattice and rapidly increases with the occupation fraction. The local flame-spread-limit distance of unevenly-spaced n-decane droplet arrays was experimentally investigated in microgravity. The droplets were arranged in a straight line at uneven intervals. The local flame-spread-limit distance of the unevenly-spaced droplet arrays depended on the droplet arrangement and increased from the flame-spread-limit distance of the evenly-spaced droplet arrays due to interactive effects. The flame-spread probability considering the increase in local flame-spread-limit distance is larger than that without it. 相似文献
185.
Lawanwong Komgrit Hamasaki Hiroshi Hino Ryutaro Yoshida Fusahito 《The International Journal of Advanced Manufacturing Technology》2020,106(5):1855-1867
The International Journal of Advanced Manufacturing Technology - This paper presents a novel technology called ‘double-action bending (DAB)’ to eliminate springback in hat-shape forming... 相似文献
186.
The rapid growth and innovation of the various mobile communication technologies have caused a change in the paradigm of internet access. Wireless technologies such as WiMAX, WiFi and UMTS/LTE networks have shown great potential in dominating the wireless access markets. The existence of various access technologies requires a means for seamless internetworking to provide anywhere, anytime services without interruption in the ongoing session, especially in multimedia applications with rigid Quality of Services (QoS) requirements. The IEEE 802.21 Media Independent Handover (MIH) working group was formed to develop a set of mechanisms under a standard framework with the capability to support migration of mobile users across heterogeneous networks. Therefore, the implementation of handover is extremely important in the heterogeneous network environment. In order to guarantee various QoS requirements during handover execution especially in multimedia applications, in this paper we propose a novel MIH-based capacity estimation algorithm to execute handover with QoS provision supporting both horizontal and vertical handovers across UMTS and WiMAX networks. Simulation shows that the proposed mechanism achieves lower call dropping rate (highest approximate 3% ) and higher system throughput (average 92% ) than the basic handover method does. 相似文献
187.
This paper presents a novel built-in current sensor that uses two additional power supply voltages besides the system power supply voltage, and that is constructed by using a current mirror circuit to pick up an abnormal IDDQ. It is activated only by an abnormal quiescent power supply current and minimizes the voltage drop at the terminal of the circuit under test. Simulation results showed that it could detect 16-A IDDQ against 0.03-V voltage drop at 3.3-V VDD and that it reduced performance degradation in the circuit under test. It is therefore suitable for testing low-voltage integrated circuits. Moreover, we verified the behavior of the sensor circuit implemented on the board by using discrete devices. Experimental results showed that the real circuit of the sensor functioned properly. 相似文献
188.
Ziqing Zhai Yuichi Miyahara Hiroshi Abe Yutaka Watanabe 《Metallurgical and Materials Transactions A》2014,45(13):6163-6172
The grain boundary segregation of phosphorus and alloying elements in the heat-affected zone (HAZ) of a low alloy steel was studied quantitatively with atom probe tomography. Non-equilibrium segregation mainly occurred during welding and subsequent fast cooling, leading to remarkable segregation of P, C, Mn, and Mo. The segregation of these four types of solutes showed similar microstructure-dependence at this stage, in which the segregation levels are higher in coarse-grained HAZ and intercritically reheated coarse-grained HAZ than in fine-grained HAZ. After simulated aging, P and Mn showed further enrichment at grain boundaries through equilibrium segregation, while desegregation was observed for C and Mo. In addition, it seems that precipitation of Mo at dislocations was greatly promoted during aging, which probably also contributed to the increase of P and Mn at grain boundaries. 相似文献
189.
This paper proposes a method for automatic design of the sensory morphology of a mobile robot. The proposed method employs two types of adaptations, ontogenetic and phylogenetic, to optimize the sensory morphology of the robot. In ontogenetic adaptation, reinforcement learning searches for the optimal policy, which is highly dependent on the sensory morphology. In phylogenetic adaptation, a genetic algorithm is used to select morphologies with which the robot can learn tasks faster. Our proposed method was applied to the design of the sensory morphology of a line‐following robot. We performed simulation experiments to compare the design solution with a hand‐coded robot. The results of the experiments revealed that our robot outperformed the hand‐coded robot in terms of the following accuracy and learning speed, although our robot had fewer sensors than the hand‐coded one. We also built a physical robot using the design solution. The experimental results revealed that this physical robot used its morphology effectively and outperformed the hand‐coded robot. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 172(1): 48–57, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20965 相似文献
190.
A radioactive tracer technique was used to investigate a tribo-chemical surface reaction obtained by a thrust collar type friction Machine. Radioactive dibenzyl disulfide labeled with sulfur-35 was used as an additive. Steel and copper disks were used as friction specimens. Radioactive copper sulfide on the friction surface was quantitatively measured with a G-M tube, and a kinetical analysis of the reaction was carried out. The friction coefficient decreased linearly depending on the amount of surface produced on the friction surface. This dependency was accompanied by adsorption of dibenzyl disulfide, which made a more effective lubricating oil film and was enhanced by the sulfide on the friction surface. The results of kinetical analysis were explained effectively by considering the oil film behavior related to the adsorptive action of the surface sulfide. 相似文献