全文获取类型
收费全文 | 74716篇 |
免费 | 6115篇 |
国内免费 | 5983篇 |
专业分类
电工技术 | 1987篇 |
综合类 | 5987篇 |
化学工业 | 11732篇 |
金属工艺 | 17112篇 |
机械仪表 | 4368篇 |
建筑科学 | 8236篇 |
矿业工程 | 3578篇 |
能源动力 | 2076篇 |
轻工业 | 2589篇 |
水利工程 | 2296篇 |
石油天然气 | 8310篇 |
武器工业 | 490篇 |
无线电 | 1674篇 |
一般工业技术 | 10319篇 |
冶金工业 | 4463篇 |
原子能技术 | 631篇 |
自动化技术 | 966篇 |
出版年
2024年 | 197篇 |
2023年 | 966篇 |
2022年 | 1820篇 |
2021年 | 2902篇 |
2020年 | 2472篇 |
2019年 | 2291篇 |
2018年 | 2020篇 |
2017年 | 2680篇 |
2016年 | 2759篇 |
2015年 | 2822篇 |
2014年 | 4188篇 |
2013年 | 4555篇 |
2012年 | 4905篇 |
2011年 | 5584篇 |
2010年 | 4328篇 |
2009年 | 4495篇 |
2008年 | 3842篇 |
2007年 | 4717篇 |
2006年 | 4422篇 |
2005年 | 3761篇 |
2004年 | 3381篇 |
2003年 | 2969篇 |
2002年 | 2527篇 |
2001年 | 2122篇 |
2000年 | 1858篇 |
1999年 | 1525篇 |
1998年 | 1222篇 |
1997年 | 1080篇 |
1996年 | 858篇 |
1995年 | 738篇 |
1994年 | 598篇 |
1993年 | 455篇 |
1992年 | 393篇 |
1991年 | 258篇 |
1990年 | 252篇 |
1989年 | 226篇 |
1988年 | 134篇 |
1987年 | 88篇 |
1986年 | 56篇 |
1985年 | 52篇 |
1984年 | 53篇 |
1983年 | 24篇 |
1982年 | 39篇 |
1981年 | 20篇 |
1980年 | 35篇 |
1979年 | 28篇 |
1978年 | 12篇 |
1959年 | 12篇 |
1955年 | 11篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 29 毫秒
91.
The corrosion behavior of synthetic Cu–Sn bronze alloys with six different Sn contents was examined through an electrochemical test and a synthetic test in a simulated corrosive medium. The mechanism of corrosion and the morphology of the corroded surfaces were characterized through field emission scanning electron microscopy equipped with energy-dispersive spectroscopy. At the corrosion potential, the corrosion behavior appears to be determined by the charge transfer step and the diffusion process. It was found that the bronze-IV (Cu–26.8Sn) specimen exhibited the best corrosion resistance, as evidenced by a low corrosion current density and a high impedance. This improvement resulted from an increase in the content of the Cu–Sn solid solution in the alloy, which was conducive to forming a relatively more protective passive film on the surface of the bronze alloy. This finding would be valuable in the anticorrosion protection of archeological artefacts after their excavation. 相似文献
92.
The paper analyses the corrosion behaviour of naturally and artificially aged AA2024 alloy in NaCl solution and in the presence of an environment-friendly corrosion inhibitor, CeCl3. On the basis of the values of polarisation resistance and corrosion current density, the corrosion resistance of the protective inhibitor film is established as well as the general corrosion resistance of this aluminium alloy. Resistance to pit formation is determined based on the difference in pitting and corrosion potentials while resistance to pit growth is determined based on the amount of charge consumed during pit growth. A scanning electron microscope is used to examine the morphology of the pits formed during the pitting corrosion testing, as well as to determine the cerium content on intermetallic particles and the matrix AA2024 alloy. The corrosion behaviour of AA2024 alloy is investigated after different test periods in NaCl solution and in the same solution with the CeCl3 inhibitor. The corrosion resistance of both tempers of AA2024 alloy is more than one order of magnitude higher in the presence of CeCl3. An explanation of the observed differences in the corrosion behaviour of the naturally and artificially aged AA2024 alloy is proposed. Different corrosion behaviour of the alloy after different test periods is also explained. 相似文献
93.
94.
95.
系统地论述了氧气底吹熔炼氧枪的结构、工作原理、设计计算方法、材质及蚀损机理.指出了延长氧枪使用寿命的措施。 相似文献
96.
Role stress has received a lot of research attention in psychological, sociological, and organizational studies over the last several decades. Based on a literature review of about 300 journal articles, this article examines prominent consequences of role stress. Specific focus is on researching differences in relationships between facets of role stress (i.e., role ambiguity, role conflict, and role overload) and frequently cited consequences using techniques of meta-analysis. Findings indicate that each role stress facet has a different relationship with the eight consequences studied. Role stress research can benefit from looking at each facet individually in addition to role stress generally. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
97.
98.
油藏演化的两个极端过程 总被引:25,自引:3,他引:22
油气藏形成之后,在地质务件变化不大的情况下,储集层中的油气一般保持相对的稳定。但当地质条件变化较大时,油气藏中则发生明显的蚀变。其中两个极端的演化过程,一是抬升破坏形成生物降解沥青,一是深埋发生原油裂解转化成焦沥青和天然气。生物降解沥青没有一定的形态.在显微镜下呈席状分布,沥青反射率低,抽提物具有明显的生物降解特征。原油裂解形成的焦沥青具有一定的几何形态,沥青反射率很高而无常规抽提物。原油裂解生成的天然气在组分和碳同位素特征上与干酪根裂解生成的天然气有别。图6参15 相似文献
99.
Behavior of Magnesium‐Alloys for Automotive Applications under Mechanical and Environmental Loading: Influence of Passivating Films and Mechanisms of Local Breakdown To assure an efficient design of components under cyclic loading, all available data concerning fatigue have to be observed. Therefore the influences of manufacturing on the material condition, the mechanical loads and environmental effects have to be analysed. Magnesium‐alloys are of special interest for lightweight applications because of their excellent strength‐density ratio. The corrosion resistance of magnesium‐alloys depends on the same factors that are critical to other metals. The alloys have a good stability to atmospheric exposure and a good resistance to attack by alkali, chromic and hydrofluoric acids. However, because of the electrochemical activity of magnesium, the relative importance of some factors is greatly amplified. The nature and composition of passive films formed on magnesium‐alloys depend on the prevailing conditions, viz. alloy‐composition, passivation potential, pH, electrolyte composition and temperature. Passive films may be damaged by local breakdown. Because of this, magnesium‐alloys suffer a degradation of their properties when exposed to an aqueous environment. The main topic of the present investigations is the verification of mechanisms of the local breakdown of the protecting film. At least two mechanisms are possible for this localization: mechanical breakdown by slip steps and electrochemical breakdown (for e.g. by the effects of chloride ions). Corrosion and passivation of different high purity alloys have been studied in different solutions (neutral, alkaline with specific anions and cations) using electrochemical techniques. The diecasted alloys were tested as produced and machined. The results clarified that depending on alloy/material and surface condition/corrosion environment different mechanisms for electrochemical breakdown of the protecting films are possible. Hence fatigue life under environmental loading is influenced by surface and testing conditions. 相似文献
100.
为了满足市场的需要,中石化天津分公司炼油厂根据FCCU自身特点采取了一系列提高柴汽比的措施,包括:调节反应系统和分馏的操作条件及采用MGD技术,以提高柴油产率。实施后,FCCU的柴汽比从0.5提高到0.9,创造了良好的经济效益。 相似文献