全文获取类型
收费全文 | 579608篇 |
免费 | 59349篇 |
国内免费 | 27332篇 |
专业分类
电工技术 | 37436篇 |
技术理论 | 52篇 |
综合类 | 41525篇 |
化学工业 | 99805篇 |
金属工艺 | 32596篇 |
机械仪表 | 36414篇 |
建筑科学 | 45697篇 |
矿业工程 | 18210篇 |
能源动力 | 16098篇 |
轻工业 | 45005篇 |
水利工程 | 11972篇 |
石油天然气 | 32403篇 |
武器工业 | 5119篇 |
无线电 | 66748篇 |
一般工业技术 | 66754篇 |
冶金工业 | 26887篇 |
原子能技术 | 5917篇 |
自动化技术 | 77651篇 |
出版年
2024年 | 2384篇 |
2023年 | 8394篇 |
2022年 | 15939篇 |
2021年 | 22059篇 |
2020年 | 17653篇 |
2019年 | 15572篇 |
2018年 | 17488篇 |
2017年 | 20023篇 |
2016年 | 18722篇 |
2015年 | 25483篇 |
2014年 | 31327篇 |
2013年 | 37734篇 |
2012年 | 39753篇 |
2011年 | 42628篇 |
2010年 | 38894篇 |
2009年 | 36749篇 |
2008年 | 35775篇 |
2007年 | 33944篇 |
2006年 | 32931篇 |
2005年 | 28049篇 |
2004年 | 19662篇 |
2003年 | 17408篇 |
2002年 | 16519篇 |
2001年 | 14680篇 |
2000年 | 13545篇 |
1999年 | 12908篇 |
1998年 | 9198篇 |
1997年 | 7805篇 |
1996年 | 7327篇 |
1995年 | 6119篇 |
1994年 | 4932篇 |
1993年 | 3349篇 |
1992年 | 2657篇 |
1991年 | 1985篇 |
1990年 | 1582篇 |
1989年 | 1263篇 |
1988年 | 1046篇 |
1987年 | 661篇 |
1986年 | 539篇 |
1985年 | 321篇 |
1984年 | 261篇 |
1983年 | 201篇 |
1982年 | 168篇 |
1981年 | 124篇 |
1980年 | 141篇 |
1979年 | 76篇 |
1978年 | 29篇 |
1977年 | 40篇 |
1976年 | 41篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Tunable blazed gratings 总被引:2,自引:0,他引:2
Xiang Li Antoine C. Daesung Lee Jen-Shiang Wang Solgaard O. 《Journal of microelectromechanical systems》2006,15(3):597-604
In this paper, we report on the design, fabrication, and characterization of blazed gratings made tunable by electrostatic actuation. We combine KOH etching and deep-reactive ion etching (DRIE) to fabricate tunable blazed gratings (TBGs) on silicon-on-insulator wafers with optical-quality mirror surfaces on {111} crystalline planes. The actuators that are used to position the individual grating elements are designed to reduce rotation to levels acceptable for spectroscopic applications. We characterize the fabricated devices mechanically, verify the rotation-reduction design, and demonstrate the functionality of TBGs as tunable filters. 相似文献
992.
Emulsification is an undesired phenomenon in the refining of highly acidic oil by alkali-washing electro-refining. In this article, a novel microwave method is applied for demulsification in the removing of naphthenic acid from diesel oil. The internal heating is attributed to molecular rotation and ionic conduction. The decrease of interface zeta-potential and the viscosity of diesel oil are responsible for the demulsification with microwave irradiation. The results exhibited that the demulsification rate is maximized when the optimum microwave irradiation power, exposure time, and irradiation pressure for Anshan and Liaohe diesel oil are deemed to be 375 W, 5/6 min and 0.05 MPa, respectively. 相似文献
993.
改进的第三代相干算法及应用 总被引:1,自引:0,他引:1
在讨论相干技术发展及三代相干算法优缺点的基础上,介绍了改进的第三代相干算法。应用自行开发的相干软件对多个油气勘探和开发区块的三维地震资料进行处理、分析,对相干时窗长度、相关道数等参数对算法效果的影响及相干体对断层、异常地质体的识别,以及解释方法进行了探讨。应用实例证明,改进的第三代相干算法抗干扰能力强,横向分辨率高,不仅适用于倾斜地层,而且对断层尤其对小断层、异常地质体具有较高的检测能力,是油气勘探和开发的一项有效和实用的技术。 相似文献
994.
995.
Different qualities of concrete have been fire tested using different geometries of the specimens as well as different load levels and load configurations. The main objective with the study was to examine a test methodology consisting of a full‐scale test and different small scale‐tests for determining the probability of spalling and the amount of spalling of fire exposed concrete structures. A reference specimen was defined as a one‐sided fire exposed slab with the dimensions 1800 × 1200 mm2 giving an exposed area of 1500 × 1200 mm2. A number of concrete qualities with different probabilities for spalling, were tested using the reference specimen. These tests showed that the reference specimens worked well giving the expected test results. Small specimens were manufactured in different shapes with the same concrete as the one used in the reference tests. These small specimens were tested either at the same time as the reference specimens in the large furnace or afterwards on a small‐scale furnace where the fire exposed surface was 450 × 360 mm2. The test results clearly show the increased probability and the increased amount of spalling by using external compressive loading. The results also show that by using pre‐stress through bars or wires the load can be lost due to heating of the bars/wires which results in a decreased amount of spalling. The boundary of the specimen also affects the amount of spalling. The spalling around the edges was in all tests less than the spalling on the central parts of the exposed area. It could also be noted that the spalling did not pass completely through any of the specimens. The reason for this is probably that the water/vapour could migrate out from the unexposed surface of the specimen. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
996.
介绍了夹杂物的来源,包括内生夹杂和外来夹杂,着重于二次氧化产物、卷渣、内衬侵蚀.同时介绍了鄂钢电炉厂在冶炼和连铸过程中控制夹杂物的操作实践. 相似文献
997.
Exchanges of total N and C between a river and its floodplain forest have been enhanced by sedimentation processes during flood pulses at a 5‐ha bottomland hardwood forest located at the Olentangy River Wetland Research Park in central Ohio. In the spring of 2000, the forest was hydrologically restored by notching an artificial levee that had separated the Olentangy River and its floodplain forest for 100 years. One‐hundred flat sediment traps (30 cm × 30 cm) were used to collect sediment samples during spring/summer flooding events from 2003 to 2005. Results showed that sediment deposition is determined by the landscape variability during flooding events, Net sediment deposit in the wettest area averaged 134 ± 12 g‐dry wt m?2 in 2003, 127 ± 17 g‐dry wt m?2 in 2004 and 149 ± 23 g‐dry wt m?2 in 2005. Total N and C sedimentation ranged from 0.49 to 0.92 g‐N m?2 and 5.2 to 19.9 g‐C m?2. Fe dominates the sediment chemistry and results show the elemental abundance in the order of Al > Fe > Ca > K > Mg > S > P > Na > Mn > Zn > B > Cu > Mo. A hydrologic pulsing index (HPI) could be used as an indicator for mass changes of energies with hydrologic pulsing events. Restoration of seasonally flooded bottomland forests could stimulate potentially large nutrient and Fe releases, which would eventually lead to an enhanced forest productivity and biodiversity. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
998.
Jin Wang Marculescu A. Jingshi Li Vorreau P. Tzadok S. Ben Ezra S. Tsadka S. Freude W. Leuthold J. 《Photonics Technology Letters, IEEE》2007,19(24):1955-1957
A technique to overcome pattern dependence in semiconductor-optical-amplifier-based wavelength converters is presented. The technique is based on a careful selection of red- and blue-shifted spectral components having complementary pattern effects in the output spectrum of a wavelength-converted signal. Significant signal quality improvements are reported at a bit rate of 40 Gb/s. 相似文献
999.
1000.
输气干线分输站站址规划设计合理与否,直接影响到分输站至各城市门站之间输气管线总投资和未来管网系统的发展。为此,着重讨论并建立了以分输站站址、各城市门站与分输站之间管道直径、壁厚、分输站压力为设计变量,以各城市门站与分输站之间管道投资最小为目标函数的分输站站址优化数学模型。根据模型特点,采用混合离散变量复合形法与数据库技术相结合来求解分输站站址。以此站址为参考点,结合现场勘察,在参考点附近沿输气干线预选多个分输站站址,并对影响分输站建设和管理的环境因素用多目标模糊评价方法进行综合评价,以评价效果好的站址为最优分输站站址。用算例说明了分输站站址优化结果不仅与工艺参数变化有关,且与分输站所处环境因素有关。提出还应深入研究输气干线中具有多个分输站的站址优化问题。 相似文献