全文获取类型
收费全文 | 50815篇 |
免费 | 4600篇 |
国内免费 | 3169篇 |
专业分类
电工技术 | 1411篇 |
综合类 | 5402篇 |
化学工业 | 5630篇 |
金属工艺 | 6435篇 |
机械仪表 | 7460篇 |
建筑科学 | 6162篇 |
矿业工程 | 3427篇 |
能源动力 | 1349篇 |
轻工业 | 3014篇 |
水利工程 | 2067篇 |
石油天然气 | 2584篇 |
武器工业 | 442篇 |
无线电 | 1399篇 |
一般工业技术 | 6912篇 |
冶金工业 | 3201篇 |
原子能技术 | 344篇 |
自动化技术 | 1345篇 |
出版年
2024年 | 194篇 |
2023年 | 640篇 |
2022年 | 2021篇 |
2021年 | 2010篇 |
2020年 | 1498篇 |
2019年 | 1363篇 |
2018年 | 1294篇 |
2017年 | 1571篇 |
2016年 | 1799篇 |
2015年 | 1872篇 |
2014年 | 2761篇 |
2013年 | 2917篇 |
2012年 | 3381篇 |
2011年 | 3729篇 |
2010年 | 2819篇 |
2009年 | 2859篇 |
2008年 | 2613篇 |
2007年 | 3291篇 |
2006年 | 2923篇 |
2005年 | 2577篇 |
2004年 | 2164篇 |
2003年 | 1905篇 |
2002年 | 1668篇 |
2001年 | 1378篇 |
2000年 | 1258篇 |
1999年 | 1012篇 |
1998年 | 853篇 |
1997年 | 775篇 |
1996年 | 653篇 |
1995年 | 543篇 |
1994年 | 464篇 |
1993年 | 335篇 |
1992年 | 316篇 |
1991年 | 215篇 |
1990年 | 209篇 |
1989年 | 191篇 |
1988年 | 129篇 |
1987年 | 81篇 |
1986年 | 52篇 |
1985年 | 38篇 |
1984年 | 44篇 |
1983年 | 19篇 |
1982年 | 32篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 23篇 |
1964年 | 10篇 |
1961年 | 6篇 |
1959年 | 8篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Alleviation Effect of Lanthanum on Cadmium Stress in Seedling Hydroponic Culture of Kidney Bean and Corn 总被引:4,自引:0,他引:4
Since1970s,rare earths(RE)have been exten-sively used as micro-fertilizers for crops in China.Ithas already been proved that REcani mprove the pro-duction and quality of crops.However,there havebeen a fewinvestigations about using RE as regulatorin pollution ecology.For example,An et al[1]studiedthe effects of O3on wheat growth and the protectiveeffect of RE.Yan and Zhou et al[2,3]discussed theprotective effect of RE on plants under acid rainstress.Jia et al[4]and Hu et al[5]reported th… 相似文献
32.
J. Gegner Priv.‐Doz. Dr. W. Nierlich M. Brückner 《Materialwissenschaft und Werkstofftechnik》2007,38(8):613-623
Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology. 相似文献
33.
G. Lange 《Materialwissenschaft und Werkstofftechnik》2003,34(1):80-85
Failures by notch induced fatigue fractures Notches produce local stress concentrations and promote the formation of fatigue cracks. Characteristic types of notches as a result of design, manufacturing and operation are presented and remedial measures are discussed. Examples demonstrate the effect of different kinds of notches on various components. 相似文献
34.
This two-part paper presents a closed-form procedure for evaluation of estimates of local thermomechanical stress fields in two-phase fibrous composites and laminates. The first part is concerned with a unidirectional elastic laminate subjected to uniform mechanical loads and to uniform changes in temperature. Both phases are assumed to be elastic, with temperature-dependent moduli and expansion coefficients; the solution reflects the influence of thermomechanical interactions. Exact solutions are not possible for any real system, because the local geometry is not known in detail. Instead, estimates of the fields are found from a modified Mori-Tanaka approximation. Examples are presented for two SiC/Ti---Al---Nb composites. Local stresses of interest are found after cooling from fabrication to room temperature. The presence of local yielding, and the influence of coupling terms on the local stress magnitudes are examined. Extension of the results to laminated plates is presented in Part II (Dvorak, G.J., Chen, T. & Teply, J., Composites Science and Technology, 43 (1992) 359–368, this issue). 相似文献
35.
36.
垂直平行密集束状孔落矿有底柱崩落法是一种新的采矿方法。通过爆破模型试验,测试爆破应力,观察分析爆破效果,探求最佳布孔形式,选择最优爆破孔网参数。试验结果表明:用平行束状孔取代扇形落矿,改善了爆破效果,简化了采场结构,减少了采切工程量。 相似文献
37.
采用独特的分离方法和途径,综合使用多种质谱分析技术,如电子轰击谱(EI/MS)、场解吸谱(FD/MS)、快速原子轰击谱(FAB/MS)、色/质联用等,对高档齿轮油的主剂-含磷极压剂的结构组成进行了较为详尽的分析研究,提出了复酯胺盐的结构组成。 相似文献
38.
In this work we investigated the mechanism of the electrochemical intercalation reactions in rf sputtered nickel oxide thin films electrodes by two techniques: mechanical stress change measurements by means of an optical technique and mass changes using an electrochemical quartz microbalance (EQCM). The experiments were performed in alkaline electrolytes containing cations of the first column of the periodic table. Reversible mass and volume changes were observed. In order to explain these experimental results, an exchange reaction is proposed, in which the oxidation process is accompanied by the deinteractional of a relative large number of “light” cations, simultaneously with the intercalation of a smaller number of heaviest cations. 相似文献
39.
Taijiro Nonaka Rodney J. Clifton Taichiro Okazaki 《International Journal of Impact Engineering》1996,18(7-8):889-898
An analysis is presented of longitudinal waves in a thin elastic column. Velocity is specified at one end, and the boundary condition at the other end is expressed in terms of a range of effective impedances of an attached structure. Propagation, reflection and interference of the waves are followed by the method of characteristics. Integration of differential equations along characteristics yields the wave-induced stress, which is then applied to problems of earthquake excitation. Numerical examples are given for recorded updown ground motion of the Kobe Earthquake. 相似文献
40.
凌树森 《理化检验(物理分册)》1998,34(3):15-18,36
对圆杆在线弹性阶段,弹-塑性阶段和全塑性阶段的扭转剪应力的计算公式作了分析,并推导了在材料的应力-应变关系(τ-γ关系)不服从虎克定律时,扭转真实剪应力的计算公式。文中对扭转强度计算公式的来源,物理含义及其都作了详细的说明。这对执行和理解国家GB10128-88《金属室温扭转试验方法》是有益的,而且对高校中材料力学的教学具有一定的参考价值。 相似文献