全文获取类型
收费全文 | 2073篇 |
免费 | 179篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 36篇 |
综合类 | 9篇 |
化学工业 | 644篇 |
金属工艺 | 111篇 |
机械仪表 | 81篇 |
建筑科学 | 46篇 |
矿业工程 | 1篇 |
能源动力 | 78篇 |
轻工业 | 131篇 |
水利工程 | 6篇 |
石油天然气 | 4篇 |
无线电 | 352篇 |
一般工业技术 | 411篇 |
冶金工业 | 110篇 |
原子能技术 | 28篇 |
自动化技术 | 210篇 |
出版年
2024年 | 2篇 |
2023年 | 27篇 |
2022年 | 52篇 |
2021年 | 62篇 |
2020年 | 51篇 |
2019年 | 71篇 |
2018年 | 74篇 |
2017年 | 96篇 |
2016年 | 117篇 |
2015年 | 63篇 |
2014年 | 87篇 |
2013年 | 131篇 |
2012年 | 158篇 |
2011年 | 175篇 |
2010年 | 116篇 |
2009年 | 115篇 |
2008年 | 104篇 |
2007年 | 92篇 |
2006年 | 83篇 |
2005年 | 62篇 |
2004年 | 45篇 |
2003年 | 51篇 |
2002年 | 54篇 |
2001年 | 37篇 |
2000年 | 44篇 |
1999年 | 23篇 |
1998年 | 51篇 |
1997年 | 25篇 |
1996年 | 36篇 |
1995年 | 23篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有2258条查询结果,搜索用时 15 毫秒
101.
Different structured activated carbons were prepared from macadamia nutshell by chemical activation with potassium hydroxide and zinc chloride. The influence of process variables on the carbons' pore structure was studied in order to optimise these parameters. The results were also compared with those previously obtained on the chemical activation of coal. The most important parameter in chemical activation with both chemical agents was found to be the impregnation ratio. Carbonization temperature is the second important variable which had significant effect on pore volume evolution. Under the experimental circumstances studied, the optimum conditions in preparation of carbons with high surface area and pore volumes with both chemical agents are identified. 相似文献
102.
The subfamily Geometrinae (Lepidoptera: Geometridae) includes many species called emerald moths. Based on our recent finding
of novel polyenyl compounds, including a double bond at the 12-position from two geometrine species, Hemithea tritonaria and Thalassodes immissaria intaminata, (6Z,9Z,12Z)-6,9,12-trienes and (3Z,6Z,9Z,12Z)-3,6,9,12-tetraenes with a C17–C20 straight chain were synthesized and analyzed by GC-MS. The 6,9,12-trienes, which were prepared by a double Wittig reaction
between two alkanals and an ylide derived from (Z)-1,6-diiodo-3-hexene, characteristically produced fragment ions at m/z 79, 150, and M–98. The 3,6,9,12-tetraenes, which were prepared by a coupling between (Z)-3-alkenal and an ylide derived from (3Z,6Z)-1-iodo-3,6-nonadiene, showed fragment ions at m/z 79, 148, and M–96. These diagnostic ions were useful to distinguish these compounds from other known polyenyl pheromones,
such as 4,6,9- and 6,9,11-trienes and 1,3,6,9-tetraenes. With reference to the GC-MS data, pheromone extracts of other species
in Geometrinae inhabiting the Iriomote Islands were analyzed, and the 6,9,12-trienes were identified in the pheromone gland
extracts of Pamphlebia rubrolimbraria rubrolimbraria and Maxates versicauda microptera. Furthermore, a field evaluation of the synthetic polyenes in a mixed forest of Tokyo revealed the following new male attractants
for emerald moths: Idiochlora ussuriaria by a C17 6,9,12-triene and Jodis lactearia by a C20 3,6,9,12-tetraene, indicating the characteristic chemical structures of Geometrinae pheromones. On the other hand, through
reexamination of the pheromone extract of H. tritonaria, (3E,6E)-α-farnesene was identified as an electrophysiologically active component in addition to the C17 6,9,12-triene. The binary mixture attracted more males than the single component lure baited with the triene in the Iriomote
Islands. 相似文献
103.
Jae‐Won Yang Hyun‐Lark Do 《International Journal of Circuit Theory and Applications》2014,42(6):620-631
A soft‐switching high step‐up DC‐DC converter with a single magnetic component is presented in this paper. The proposed converter can provide high voltage gain with a relatively low turn ratio of a transformer. Voltage doubler structure is selected for the output stage. Due to this structure, the voltage gain can be increased, and the voltage stresses of output diodes are clamped as the output voltage. Moreover, the output diode currents are controlled by a leakage inductance of a transformer, and the reverse‐recovery loss of the output diodes is significantly reduced. Two power switches in the proposed converter can operate with soft‐switching due to the reflected secondary current. The voltages across the power switches are confined to the clamping capacitor voltage. Steady‐state analysis, simulation, and experimental results for the proposed converter are presented to validate the feasibility and the performance of the proposed converter. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
104.
Kee Do Woo Jae Hwang Kim Eui Pyo Kwon Min Seok Moon Hyun Bom Lee Tatsuo Sato Zhiguang Liu 《Metals and Materials International》2010,16(2):213-218
To fabricate an Al-V matrix composite reinforced with submicron-sized Al2O3 and AlxVy (Al3V, Al10V) phases, high energy mechanical milling (HEMM) and sintering were employed. By increasing the milling time, the size of
mechanically milled powder was significantly reduced. In this study, the average powder size of 59 μm for Al, and 178 μm for
V2O5 decreased with the formation of a new product, Al-Al2O3-AlxVy, with a size range from 1.3 μm to 2.6 μm formed by the in-situ combustion reaction during sintering of HEM milled Al and
V2O5 composite powders. The in-situ reaction between Al and V2O5 during the HEMM and sintering transformed the Al2O3 and AlxVy (Al3V, Al10V) phases. Most of the reduced V reacted with excess the Al to form AlxVy (Al3V, Al10V) with very little V dissolved into Al matrix. By increasing the milling time and weight percentage of V2O5, the hardness of the Al-Al2O3-AlxVy composite sintered at 1173 K increased. The composite fabricated with the HEMM Al-20wt.%V2O5 composite powder and sintering at 1173 K for 2 h had the highest hardness. 相似文献
105.
106.
Earthquake time-history analyses have been performed for a buried gas pipeline of API 5L Grade X65, which is popularly used in Korea. For this purpose, various parameters such as the type of buried gas pipeline, end-restraint conditions, soil characteristics, single and multiple earthquake input ground motions, and burial depths are selected. A comparative study has been performed to obtain the response characteristics of strains in a buried pipeline section, axial relative displacement, and transverse relative displacement. The capacity evaluation of the pipeline with respect to the response characteristics has been performed in comparison with the allowable strain and displacement capacity in axial and transverse directions, as suggested by the Guidelines for the Seismic Design of Buried Gas Pipelines, KOGAS. The present study is expected to provide useful information for an effective seismic evaluation of a buried gas pipeline. 相似文献
107.
Do‐Young Park Seong‐Eui Lee Young‐Mo Kim Jin‐Seok Kim Yong‐Seog Kim 《Journal of the Society for Information Display》2006,14(1):87-92
Abstract— In this study, the effects of diamond and AlN layers inserted beneath the phosphor layer of the rear plate of a PDP were investigated. The layers were formed via an osmotic‐pressure coating process. Macrocells and test panels were prepared to examine their effects on luminance and luminous efficacy. The results indicate that the layers primarily affect the glow‐discharge behavior and eventually enhance the luminous efficacy of the PDP, suggesting the possibile improvement in the performance of PDPs. 相似文献
108.
109.
Test case prioritization provides a way to run test cases with the highest priority earliest. Numerous empirical studies have
shown that prioritization can improve a test suite's rate of fault detection, but the extent to which these results generalize
is an open question because the studies have all focused on a single procedural language, C, and a few specific types of test
suites. In particular, Java and the JUnit testing framework are being used extensively to build software systems in practice,
and the effectiveness of prioritization techniques on Java systems tested under JUnit has not been investigated. We have therefore
designed and performed a controlled experiment examining whether test case prioritization can be effective on Java programs
tested under JUnit, and comparing the results to those achieved in earlier studies. Our analyses show that test case prioritization
can significantly improve the rate of fault detection of JUnit test suites, but also reveal differences with respect to previous
studies that can be related to the language and testing paradigm. To investigate the practical implications of these results,
we present a set of cost-benefits models for test case prioritization, and show how the effectiveness differences observed
can result in savings in practice, but vary substantially with the cost factors associated with particular testing processes. 相似文献
110.
The temperature and pressure dependence of the thermal pressure coefficient and internal pressure for eight polymer solids are calculated. The principal results are as follows: (1) The pressure dependence of the thermal pressure coefficient at constant temperature is relatively small. (2) For some solid polymers, as a function of temperature, a maximum in the thermal pressure coefficient is predicted in the solid region, and the temperatures corresponding to the maximum values are estimated. (3) For most solid polymers, the zeropressure internal pressure increases with increasing temperature over the entire temperature range to the glass transition temperature or the melting point. © 1995 John Wiley & Sons, Inc. 相似文献