全文获取类型
收费全文 | 21848篇 |
免费 | 1926篇 |
国内免费 | 1256篇 |
专业分类
电工技术 | 331篇 |
技术理论 | 1篇 |
综合类 | 2500篇 |
化学工业 | 855篇 |
金属工艺 | 1534篇 |
机械仪表 | 1925篇 |
建筑科学 | 6041篇 |
矿业工程 | 520篇 |
能源动力 | 253篇 |
轻工业 | 246篇 |
水利工程 | 349篇 |
石油天然气 | 458篇 |
武器工业 | 214篇 |
无线电 | 4077篇 |
一般工业技术 | 3128篇 |
冶金工业 | 565篇 |
原子能技术 | 1097篇 |
自动化技术 | 936篇 |
出版年
2024年 | 55篇 |
2023年 | 183篇 |
2022年 | 332篇 |
2021年 | 440篇 |
2020年 | 532篇 |
2019年 | 478篇 |
2018年 | 450篇 |
2017年 | 574篇 |
2016年 | 603篇 |
2015年 | 698篇 |
2014年 | 1231篇 |
2013年 | 1210篇 |
2012年 | 1570篇 |
2011年 | 1792篇 |
2010年 | 1323篇 |
2009年 | 1488篇 |
2008年 | 1372篇 |
2007年 | 1581篇 |
2006年 | 1406篇 |
2005年 | 1183篇 |
2004年 | 979篇 |
2003年 | 864篇 |
2002年 | 739篇 |
2001年 | 641篇 |
2000年 | 558篇 |
1999年 | 472篇 |
1998年 | 407篇 |
1997年 | 336篇 |
1996年 | 296篇 |
1995年 | 241篇 |
1994年 | 224篇 |
1993年 | 147篇 |
1992年 | 120篇 |
1991年 | 104篇 |
1990年 | 90篇 |
1989年 | 64篇 |
1988年 | 63篇 |
1987年 | 46篇 |
1986年 | 44篇 |
1985年 | 16篇 |
1984年 | 23篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 3篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
激光光束质量诊断技术的进展 总被引:1,自引:0,他引:1
本文介绍了激光光束质量诊断技术近年来的进展,以及国际标准化组织推荐的聚集光束测量法,指出了该技术的发展方向。 相似文献
82.
The pyrolysis of tertiarybutylphosphine (TBP) has been studied in the low pressure conditions used for chemical beam epitaxy
(CBE). The pyrolysis studies were carried out in low pressure reactors of two different configurations, one of which is a
cracker cell designed for use in a CBE system. The reaction products were studied using a quadrupole mass spectrometer. The
products observed are accounted for by a reaction mechanism involving homolysis of the parent TBP molecule to produce PH2 and C4H9 radicals. These undergo subsequent reactions to form the stable products C4H8, PH3 and H2, with smaller amounts of P and P2 being produced. The production of the sub-hydride PH2 using this cracker cell design indicates that the use of partially cracked TBP may be a promising technique for reducing
the amount of carbon incorporated into the growing epitaxial layer. 相似文献
83.
步进式加热炉炉温优化设定模型及软件开发 总被引:1,自引:0,他引:1
针对线材厂步进式加热炉实际工况,提出了基于经验规则的炉温优化设定模型和在线自学习获取知识的思想,并以炉温优化设定模型为核心,开发出加热炉计算机控制系统的优化运行软件。 相似文献
84.
讲述了参观Semicon/west94′展览会及考察美国和西德的5个公司、1所大学所了解到的投影光刻技术、电子束曝光技术、透镜面形测试技术的发展。 相似文献
85.
采用锁相技术,对电子束曝光机工件台运动实现速度环的全数字控制。设计了数字差频积分回路和数字差频比例控制器,能有效消除速度的静态误差和改善系统的动态特性。 相似文献
86.
We have performed selective area epitaxy (SAE) of CdTe layers grown by molecular beam epitaxy using a shadow mask technique.
This technique was chosen over other SAE techniques due to its simplicity and its compatibility with multiple SAE patterning
steps. Features as small as 50 microns × 50 microns were obtained with sharp, abrupt side walls and flat mesa tops. Separations
between mesas as small as 20 microns were also obtained. Shadowing effects due to the finite thickness of the mask were reduced
by placing the CdTe source in a near normal incidence position. Intimate contact between the mask and the substrate was essential
in order to achieve good pattern definition. 相似文献
87.
微型电磁继电器的制作和仿真分析 总被引:4,自引:0,他引:4
介绍了一种基于MEMS技术的微型电磁继电器的制作过程和仿真分析.这种微继电器的大小约是4mm×4mm×0.5mm,主要采用普通的微加工技术来完成全部制作工艺.与传统继电器相比,这种继电器采用平面线圈来代替螺线管线圈,有利于MEMS工艺,并且提出了一种双支撑的悬臂梁结构做为活动电极,具有较高的灵敏性和稳定性.另外,还进行了一些有关线圈通过激励电流后对活动电极产生电磁力的理论计算和仿真分析,利用这些结果可以对这种电磁继电器的结构和参数进一步优化. 相似文献
88.
The motion equations governing the dynamical behavior of a viscoelasticTimoshenko beam with finite deformation are derived and simplified byGalerkin method. The viscoelastic material is assumed to obey thethree-dimensional fractional derivative constitutive relation. Thedynamical behaviors of the simplified systems with order 1 and order 2are numerically computed and compared by using the computational methodpresented by the authors. The dynamical behaviors of the systems areuniform qualitatively, but there is a little deviation quantitatively.And the truncated system with order 1 is safer than the one of order 2.It is also shown that the lower order system is reasonable. Theinfluences of the load parameter and the fractional derivative parameter(material parameter) on the deflection of the beam are consideredrespectively. The numerical methods in nonlinear dynamics, such as phasediagram, and Poincaré section, are applied to reveal dynamical behaviorsof the nonlinear viscoelastic Timoshenko beam. There are plenty ofdynamical behaviors, such as periodicity, bifurcation, quasi-periodicityand chaos in the dynamical system. 相似文献
89.
D. Spemann T. Reinert J. Vogt D. Dobrev T. Butz 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2002,190(1-4):312-317
For the precise determination of the sizes of submicron beam spots test structures with an excellent edge definition are required. For this purpose a semiconductor heterostructure consisting of an 1.62 μm GaInP epi-layer grown on (0 0 1) GaAs has been made, which provides atomically sharp edges for beam spot size measurements. Since the sample has been thinned down by standard transmission electron microscope (TEM) preparation techniques, it can be used for both PIXE and STIM. The sample has been investigated with a TEM and the ion nanoprobe LIPSION. A one-dimensional beam profile in the low current mode was determined by a STIM measurement using 2 MeV protons and yielded a FWHM of (41±4) nm, which is the smallest value reported so far for high energy nuclear micro- and nanoprobes. Furthermore we present nickel nanowhiskers produced at the GSI Darmstadt by electrochemical preparation of etched ion track membranes that have been used to obtain two-dimensional images of the shapes of submicron beam spots. For these measurements a scan over a single nickel nanowhisker having a diameter of 220 nm and a height of about 6 μm was performed. 相似文献
90.
Peter Rez 《Journal of research of the National Institute of Standards and Technology》2002,107(6):487-495
To calculate the intensity of x-ray emission in electron beam microanalysis requires a knowledge of the energy distribution of the electrons in the solid, the energy variation of the ionization cross section of the relevant subshell, the fraction of ionizations events producing x rays of interest and the absorption coefficient of the x rays on the path to the detector. The theoretical predictions and experimental data available for ionization cross sections are limited mainly to K shells of a few elements. Results of systematic plane wave Born approximation calculations with exchange for K, L, and M shell ionization cross sections over the range of electron energies used in microanalysis are presented. Comparisons are made with experimental measurement for selected K shells and it is shown that the plane wave theory is not appropriate for overvoltages less than 2.5 V. 相似文献