全文获取类型
收费全文 | 61762篇 |
免费 | 6818篇 |
国内免费 | 4018篇 |
专业分类
电工技术 | 4642篇 |
综合类 | 5963篇 |
化学工业 | 8628篇 |
金属工艺 | 3484篇 |
机械仪表 | 4054篇 |
建筑科学 | 4735篇 |
矿业工程 | 2189篇 |
能源动力 | 1616篇 |
轻工业 | 6754篇 |
水利工程 | 1981篇 |
石油天然气 | 2912篇 |
武器工业 | 578篇 |
无线电 | 6710篇 |
一般工业技术 | 6035篇 |
冶金工业 | 2586篇 |
原子能技术 | 984篇 |
自动化技术 | 8747篇 |
出版年
2024年 | 321篇 |
2023年 | 1095篇 |
2022年 | 2145篇 |
2021年 | 2840篇 |
2020年 | 2111篇 |
2019年 | 1556篇 |
2018年 | 1719篇 |
2017年 | 1998篇 |
2016年 | 1787篇 |
2015年 | 2683篇 |
2014年 | 3417篇 |
2013年 | 4090篇 |
2012年 | 4851篇 |
2011年 | 5150篇 |
2010年 | 4748篇 |
2009年 | 4495篇 |
2008年 | 4605篇 |
2007年 | 4470篇 |
2006年 | 3920篇 |
2005年 | 3221篇 |
2004年 | 2243篇 |
2003年 | 1588篇 |
2002年 | 1458篇 |
2001年 | 1339篇 |
2000年 | 1124篇 |
1999年 | 772篇 |
1998年 | 507篇 |
1997年 | 431篇 |
1996年 | 413篇 |
1995年 | 324篇 |
1994年 | 262篇 |
1993年 | 205篇 |
1992年 | 163篇 |
1991年 | 126篇 |
1990年 | 72篇 |
1989年 | 81篇 |
1988年 | 70篇 |
1987年 | 31篇 |
1986年 | 28篇 |
1985年 | 21篇 |
1984年 | 13篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 23篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1959年 | 10篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
93.
催化裂化汽油选择性加氢脱硫催化剂RSDS-1的开发 总被引:24,自引:4,他引:20
介绍了用于催化裂化汽油选择性加氢脱硫催化剂RSDS-1的研究开发,考察了载体、活性组元、金属原子比以及助剂对催化剂选择性的影响。研究结果表明,催化裂化汽油中烯烃的加氢饱和受扩散限制;Co—Mo组合对烯烃饱和的能力相对较弱;较高的Co/Mo原子比有利于提高催化剂选择性;助剂的加入对催化剂选择性有明显的影响;RSDS—1催化剂用于催化裂化汽油选择性脱硫,对不同原料油适应性好,脱硫率可达80%,RON损失小于2个单位,且可长周期稳定运转。 相似文献
94.
Toughness variation of non-notched poly(acrylonitrile-butadiene-styrene) (ABS) subjected to uniaxial fatigue loading was investigated. The experiments were conducted by applying fatigue loading to strip specimens first, from which dog-bone specimens were machined. The dog-bone specimens were tested to measure the strain for the on-set of fracture, named cracking strain here, thus to monitor the toughness change due to the fatigue loading.The test results showed that the fatigue loading caused the toughness drop in ABS, even before any visible crack was developed. Damage development and fracture behavior were then analyzed using scanning electron microscopy (SEM). The SEM analysis revealed that damage zones, not cracks, were initiated during the fatigue loading, and were the main cause of the toughness drop. Mechanisms for the damage initiation include matrix crazing and debonding of small rubber particles; however, large rubber particles remained intact. Based on the results, a deformation model is proposed for the damage zone initiation, which provides an explanation for the toughness change under the fatigue loading. 相似文献
95.
Yong Xia Rongming Lin 《International journal for numerical methods in engineering》2004,59(1):153-172
Order reduction is a computationally efficient method to estimate some lowest eigenvalues and the corresponding eigenvectors of large structural systems by reducing the order of the original model to a smaller one. But its accuracy is limited to a small range of frequencies that depends on the selection of the retained degrees of freedom. This paper proposes a new iterative order reduction (IOR) technique to obtain accurately the eigensolutions of large structural systems. The technique retains all the inertia terms associated with the removed degrees of freedom. This hence leads to the reduced mass matrix being in an iterated form and the reduced stiffness matrix constant. From these mass and stiffness matrices, the eigensolutions of the reduced system can be obtained iteratively. On convergence the reduced system reproduces the eigensolutions of the original structure. A proof of the convergence property is also presented. Applications of the method to a practical GARTEUR structure as well as a plate have demonstrated that the proposed method is comparable to the commonly used Subspace Iteration method in terms of numerical accuracy. Moreover, it has been found that the proposed method is computationally more efficient than the Subspace Iteration method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
96.
随着电容测量技术的迅速发展,电容传感器在非电量测量和自动检测中得到广泛应用,但它在使用过程中也存在一些问题,针对在使用电容传感器过程中存在的几个问题,从电容传感器的原理和工作过程两个方面进行了讨论,并提出行之有效的处理方法。 相似文献
97.
J. Chen J. B. Xu K. Xue J. An N. Ke W. Cao H. B. Xia J. Shi D. C. Tian 《Microelectronics Reliability》2005,45(1):137-142
Transition-metal compound TiC60 thin films were grown by co-deposition from two separated sources of fullerene C60 powder and titanium. Study of structural properties of the films, by Raman spectroscopy, atomic force microscopy, and scanning tunneling spectroscopy reveals that the films have a deformed C60 structure with certain amount of sp3 bonds and a rough surface with a large number of nanoclusters. z–V tunnelling spectroscopic measurements suggest that several charge transport mechanisms are involved in as the tip penetrates into the thin film. Conventional field electron emission (FEE) measurements show a high emission current density of 10 mA/cm2 and a low turn-on field less than 8 V/μm, with the field enhancement factors being 659 and 1947 for low-field region and high-field region, respectively. By exploiting STM tunneling spectroscopy, local FEE on nanometer scale has also been characterized in comparison with the conventional FEE. The respective field enhancement factors are estimated to be 99–355 for a gap varying from 36 to 6 nm. The enhanced FEE of TiC60 thin films can be ascribed to structural variation of C60 in the films and the electrical conducting paths formed by titanium nanocrystallites embedded in C60 matrix. 相似文献
99.
天然气长输管道泄漏检测方案对比 总被引:7,自引:1,他引:6
大口径、长距离天然气输送管道的泄漏检测和定位技术日益受到人们的重视。总结评价了用于天然气长输管道泄漏检测和安全预警的各种技术方案,讨论了其基本原理、适用范围、技术成熟度、优点和缺点以及工程应用情况;采用灵敏度、定位精度等7项技术指标对各种泄漏检测方法进行了评价和对比。目前,音波泄漏检测技术和分布式光纤泄漏检测技术由于具有诸多方面的优点,是近年来国内外泄漏检测技术研究的重点和热点,这两种技术已初步应用于实际,并取得了良好的效果。重点对这两种泄漏检测技术的原理、适用范围、所能达到的技术指标、优、缺点以及工程案例进行了详细讨论、分析和对比,可为我国天然气长输管道泄漏检测和安全预警系统的开发和研究提供技术依据。 相似文献
100.