全文获取类型
收费全文 | 3027篇 |
免费 | 29篇 |
国内免费 | 35篇 |
专业分类
电工技术 | 42篇 |
综合类 | 74篇 |
化学工业 | 449篇 |
金属工艺 | 227篇 |
机械仪表 | 827篇 |
建筑科学 | 86篇 |
矿业工程 | 42篇 |
能源动力 | 184篇 |
轻工业 | 316篇 |
水利工程 | 12篇 |
石油天然气 | 26篇 |
武器工业 | 5篇 |
无线电 | 177篇 |
一般工业技术 | 385篇 |
冶金工业 | 62篇 |
原子能技术 | 24篇 |
自动化技术 | 153篇 |
出版年
2024年 | 1篇 |
2023年 | 32篇 |
2022年 | 68篇 |
2021年 | 93篇 |
2020年 | 66篇 |
2019年 | 78篇 |
2018年 | 63篇 |
2017年 | 78篇 |
2016年 | 57篇 |
2015年 | 58篇 |
2014年 | 109篇 |
2013年 | 301篇 |
2012年 | 129篇 |
2011年 | 220篇 |
2010年 | 140篇 |
2009年 | 183篇 |
2008年 | 176篇 |
2007年 | 160篇 |
2006年 | 134篇 |
2005年 | 120篇 |
2004年 | 131篇 |
2003年 | 125篇 |
2002年 | 89篇 |
2001年 | 78篇 |
2000年 | 68篇 |
1999年 | 55篇 |
1998年 | 53篇 |
1997年 | 39篇 |
1996年 | 42篇 |
1995年 | 27篇 |
1994年 | 27篇 |
1993年 | 21篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有3091条查询结果,搜索用时 0 毫秒
51.
Contact surfaces do not make contact perfectly because such surfaces have a lot of asperities. The real contact area is much smaller than the nominal contact area, and the real contact areas has a non-uniform distribution because of the waviness in the contact surface. The contact stiffness is influenced not only by the deformation of the asperities, but also by the distribution of the real contact areas. In general, a contact surface with a uniform distribution of the real contact areas has greater contact stiffness. However, this requires a grinding finish and costs more than the cutting finish. In this study, a method for uniformly distributing the real contact areas easily, is proposed to improve the contact stiffness of a contact surface finished by cutting. The method is called the cutter mark cross (CMC) method. The allowable waviness in the CMC method is shown. In addition, the effect of the CMC method is investigated by experimentation. The results show that the real contact areas can be distributed uniformly using the CMC method. The horizontal and vertical contact stiffness can also be improved. 相似文献
52.
针对带式烧结机的星轮与台车辊轮啮合时出现的齿面塑性变形、飞边等损伤,应用赫兹接触理论对齿面接触应力进行了计算。分析了星轮承载能力低的原因,并从辊轮结构的确定、齿形压力角的选择、齿面摩擦的降低等三方面给出了提高星轮齿面承载能力的措施。采用非线性有限元方法对理想接触工况及实际接触工况进行了模拟,进一步揭示了齿面损伤产生的原因,并证明了提高齿面承载能力所采用措施的有效性。 相似文献
53.
发展高电压等级真空断路器的技术问题探讨 总被引:9,自引:1,他引:9
本文对发展高电压等级真空断路器的关键技术问题,如触头材料,灭弧室耐压特性、电弧特性、弧后特性、波纹管设计及触头运动特性等进行了探讨,可为高电压等级真空断路器的设计提供依据。 相似文献
54.
S. Zimmermann N. AhnerF. Blaschta M. SchallerH. Zimmermann H. RülkeN. Lang J. RöpckeS.E. Schulz T. Gessner 《Microelectronic Engineering》2011,88(5):671-676
Reactive ion etch processes for modern interlevel dielectrics become more and more complex, especially for further scaling of interconnect dimensions. The materials will be damaged within such processes with the result of an increase in their dielectric constants. The capability of selected additives to minimize the low-k sidewall damage during reactive ion etching (RIE) of SiCOH materials in fluorocarbon plasmas was shown in different works in the past. Most of the investigated additive gases alter the fluorine to carbon ratio as well as the dissociation of the parent gas inside the etch plasma. The result is a changed etch rate, a modified polymerization behavior and other characteristics of the process induced SiCOH damage. Heavy inert ions like argon will be accelerated to the sample surface in the cathode dark space and enhance therewith the sputter yield on the SiCOH network [1]. In this paper the additives Ar, O2, C4F8, H2, N2 and CO were added to a conventional CF4 etch plasma. We try to provoke different changes in the plasma conditions and therewith in the process results. Contact angle measurements, spectroscopic ellipsometry, Hg-probe analysis, FTIR measurements and SEM cross-sections were used to overview the additive induced modifications. To understand the influences of the additives gases more exactly, changes in the physical and chemical plasma behavior must be analyzed. Therefore quadrupole mass spectrometry (QMS) and quantum cascade laser absorption spectroscopy (QCLAS) were used. 相似文献
55.
56.
为了定量分析碳酸盐岩接触变质作用形成的CO2,研究了松辽盆地东北缘碳酸盐岩接触变质带常量元素和稀土元素的元素分配关系。认为碳酸盐岩接触变质过程中主要体现为硅的富集和钙、碳的亏损,并且CaO、SiO2与ΣREE呈线性关系;随着变质程度增高,元素的含量、稀土元素的分布型式和分馏程度越趋向花岗岩,其主要原因是碳酸盐岩与侵入流体的混染作用、碳酸盐岩硅化及矿化过程引起的稀土变化、碳酸盐岩重结晶对轻稀土元素的富集。计算得出了CO2释放量与岩石体积比(2.7~256.7)。证明了碳酸盐岩接触变质作用是无机成因CO2形成的机制。 相似文献
57.
Inserting a Mn-doped TiO2 layer for improving performance of pentacene organic thin-film transistors
Device performance of pentacene organic thin-film transistors (OTFTs) was significantly improved via inserting a Mn-doped TiO2 layer between pentacene semiconductor and the source–drain electrodes. In comparison with the OTFTs with only-Au electrodes, the introduction of a thin Mn-doped TiO2 layer leads to saturation current increasing from 31.9 μA to 0.22 mA, effective field-effect mobility improving from 0.24 to 1.13 cm2/V s, and threshold voltage downshifting from −11 to −2 V. These performance enhancements are ascribed to the significant reduction of contact resistance and smoothed surface of pentacene layer. This work may provide an effective approach to improve the performance of the pentacene based OTFTs by inserting a Mn-doped TiO2 layer. 相似文献
58.
Zhang Ji-song Yan Lei Yang Lu 《建筑技术开发》2007,34(1)
采用动力有限元时程分析方法,利用大型通用有限元软件MARC,对土-桩基础-框架结构相互作用的接触效应问题进行了数值研究,以野外大比例桩基础框架模型为算例,探讨了在地震荷载作用下土-桩基础-框架结构三维接触效应。结果表明考虑接触效应后,结构柱子上的弯矩、剪力、内力明显减小。对结构附近的土体作用也有一定的影响,影响很小,可以忽略不计。计算表明强震作用下动力时程分析计算时应考虑接触效应。 相似文献
59.
The quantitative theory of image contrast in an electron microscope in the mirror operation mode is given in this paper. This theory permits us to calculate the potential distribution on the object surface from the current density distribution on the microscope screen. The potential distribution results in image formation on the screen. Local electric fields existing on the object surface lead to a perturbation of electron trajectories above the object and to a redistribution of the current density on the screen, causing image contrast. Using the quantitative correlation between these fields and the function of current density distribution on the screen, it is possible to calculate the magnitude of these microfields as well. As illustration, a measured potential distribution on an object surface with spiral structures of adsorbates was analysed. These structures are formed during reaction of CO oxidation on Pt(110). The value of the measured contact potential difference comprised a few hundredths of volt. 相似文献
60.
《Fusion Engineering and Design》2014,89(7-8):1299-1303
Experimental investigations for magnetohydrodynamic flows in rectangular ducts are performed using GaInSn as model fluid. Measurements of electric potential on channel walls and inside the flow show reproducible discrepancies compared to analytical results. These discrepancies can be ascribed to the formation of oxide layers causing a contact resistance between the electrically conducting duct walls and the liquid metal. An exact analytical solution for pressure drop, velocity and potential distributions has been derived taking into account the presence of a contact resistance. Analytical results for velocity and potential profiles and for pressure drop are discussed for different values of contact resistance and strength of the applied magnetic field. A comparison of measured potential with data from the analytical solution allows estimating the order of magnitude of the contact resistance in the present experiments. 相似文献