全文获取类型
收费全文 | 43203篇 |
免费 | 4267篇 |
国内免费 | 3141篇 |
专业分类
电工技术 | 1272篇 |
综合类 | 4398篇 |
化学工业 | 5878篇 |
金属工艺 | 5386篇 |
机械仪表 | 3575篇 |
建筑科学 | 6049篇 |
矿业工程 | 2668篇 |
能源动力 | 1234篇 |
轻工业 | 2540篇 |
水利工程 | 1977篇 |
石油天然气 | 2397篇 |
武器工业 | 365篇 |
无线电 | 1509篇 |
一般工业技术 | 6945篇 |
冶金工业 | 2821篇 |
原子能技术 | 349篇 |
自动化技术 | 1248篇 |
出版年
2024年 | 175篇 |
2023年 | 583篇 |
2022年 | 1817篇 |
2021年 | 1827篇 |
2020年 | 1357篇 |
2019年 | 1275篇 |
2018年 | 1193篇 |
2017年 | 1479篇 |
2016年 | 1593篇 |
2015年 | 1654篇 |
2014年 | 2338篇 |
2013年 | 2677篇 |
2012年 | 2789篇 |
2011年 | 3075篇 |
2010年 | 2335篇 |
2009年 | 2471篇 |
2008年 | 2331篇 |
2007年 | 2745篇 |
2006年 | 2413篇 |
2005年 | 2097篇 |
2004年 | 1841篇 |
2003年 | 1544篇 |
2002年 | 1403篇 |
2001年 | 1150篇 |
2000年 | 1067篇 |
1999年 | 869篇 |
1998年 | 744篇 |
1997年 | 664篇 |
1996年 | 558篇 |
1995年 | 450篇 |
1994年 | 391篇 |
1993年 | 307篇 |
1992年 | 281篇 |
1991年 | 196篇 |
1990年 | 175篇 |
1989年 | 183篇 |
1988年 | 116篇 |
1987年 | 80篇 |
1986年 | 53篇 |
1985年 | 60篇 |
1984年 | 59篇 |
1983年 | 36篇 |
1982年 | 45篇 |
1981年 | 10篇 |
1980年 | 16篇 |
1979年 | 22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
71.
72.
曲轴激光喷丸强化试验研究 总被引:2,自引:2,他引:0
采用实验的方法,研究了激光冲击强化对175A型柴油机曲轴疲劳寿命的影响,取得了激光冲击强化试验条件下曲轴过渡圆角处残余应力场的数据。并将激光冲击强化工艺效果和曲轴滚压强化效果做了对比性分析,结果表明:虽然激光冲击强化效果不如曲轴滚压强化,但考虑到激光工艺参数精确可控、加工质量好、成本低以及可避免滚压强化所造成的表面疲劳、撕痕等,激光冲击强化工艺可望代替滚压强化成为新型的曲轴强化手段。通过此类激光冲击强化强化实验可优化激光冲击的相关参数,使曲轴过渡圆角产生有利的残余应力场。 相似文献
73.
Isothermal short-term creep of poly (vinylidene fluoride) (PVDF) monofilament sutures was determined at several temperatures between 10 and 90 °C under the stress of 10 MPa. Long term service performance was predicted for 10 decades of time. The compliance master curve as a function of time fits a hyperbolic sine equation. The temperature shift factor as a function of the temperature aT (T) is accurately represented by a general equation based on free volume. A simple relationship between the two parameters of the equation is explored. The viscoelasticity of PVDF is also seen in dynamic mechanical analysis performed at the frequency of 1 Hz. The origin of the viscoelastic character well present in the deformability of the PVDF in service is due to the occurrence of the αc relaxation that is active at ∼50 °C (E″ peak at 1 Hz). 相似文献
74.
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
75.
Stress Heterogeneity Effect on the Strength of Silicon Nitride 总被引:1,自引:0,他引:1
François Hild Elisabeth Amer Didier Marquis 《Journal of the American Ceramic Society》1992,75(3):700-702
The experiments reported in this paper demonstrate the causes of the failure of monolithic ceramics. The specimens are made of silicon nitride and tested at room temperature. The stress field within the specimen is different for each of four series of tests that have been conducted. Fractographic observations have also been made to identify the causes of the failures. A size effect analysis is performed. 相似文献
76.
脆断事故的原因分析和预防措施 总被引:1,自引:0,他引:1
戚国胜 《南方冶金学院学报》2002,23(1):28-33
分析高强度材料和大型工程结构元件发生低应力脆性断裂的原因及条件,指出传统强度设计理论的局限性,从设计和工艺上提出防止发生低应力脆断事故的具体措施,给使用高强度材料和设计大型工程结构元件时提供参考。 相似文献
77.
78.
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
79.
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
80.
Recently, efficient scheduling algorithms based on Lagrangian relaxation have been proposed for scheduling parallel machine
systems and job shops. In this article, we develop real-world extensions to these scheduling methods. In the first part of
the paper, we consider the problem of scheduling single operation jobs on parallel identical machines and extend the methodology
to handle multiple classes of jobs, taking into account setup times and setup costs. The proposed methodology uses Lagrangian
relaxation and simulated annealing in a hybrid framework. In the second part of the paper, we consider a Lagrangian relaxation
based method for scheduling job shops and extend it to obtain a scheduling methodology for a real-world flexible manufacturing
system with centralized material handling.
This research was supported in part by the Office of Naval Research and the Department of Science and Technology grant N00014-93-1017. 相似文献