全文获取类型
收费全文 | 75273篇 |
免费 | 7312篇 |
国内免费 | 5515篇 |
专业分类
电工技术 | 2353篇 |
技术理论 | 1篇 |
综合类 | 4915篇 |
化学工业 | 19449篇 |
金属工艺 | 6447篇 |
机械仪表 | 3938篇 |
建筑科学 | 2717篇 |
矿业工程 | 2095篇 |
能源动力 | 1880篇 |
轻工业 | 5024篇 |
水利工程 | 1243篇 |
石油天然气 | 2764篇 |
武器工业 | 616篇 |
无线电 | 9352篇 |
一般工业技术 | 10730篇 |
冶金工业 | 3024篇 |
原子能技术 | 984篇 |
自动化技术 | 10568篇 |
出版年
2024年 | 243篇 |
2023年 | 1357篇 |
2022年 | 2183篇 |
2021年 | 2962篇 |
2020年 | 2418篇 |
2019年 | 2176篇 |
2018年 | 1959篇 |
2017年 | 2433篇 |
2016年 | 2696篇 |
2015年 | 2720篇 |
2014年 | 3957篇 |
2013年 | 4276篇 |
2012年 | 4962篇 |
2011年 | 6337篇 |
2010年 | 4682篇 |
2009年 | 5270篇 |
2008年 | 4632篇 |
2007年 | 5370篇 |
2006年 | 4774篇 |
2005年 | 4044篇 |
2004年 | 3105篇 |
2003年 | 2733篇 |
2002年 | 2184篇 |
2001年 | 1650篇 |
2000年 | 1607篇 |
1999年 | 1312篇 |
1998年 | 1041篇 |
1997年 | 827篇 |
1996年 | 783篇 |
1995年 | 615篇 |
1994年 | 591篇 |
1993年 | 458篇 |
1992年 | 360篇 |
1991年 | 296篇 |
1990年 | 224篇 |
1989年 | 177篇 |
1988年 | 119篇 |
1987年 | 99篇 |
1986年 | 110篇 |
1985年 | 59篇 |
1984年 | 45篇 |
1983年 | 39篇 |
1982年 | 47篇 |
1981年 | 24篇 |
1980年 | 38篇 |
1979年 | 28篇 |
1977年 | 17篇 |
1976年 | 16篇 |
1975年 | 9篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 297 毫秒
181.
182.
183.
Several types of reinforced Nb3Sn wires have been developed to prevent reduction of superconducting properties by applying a strong electromagnetic force. To fabricate a cryocooled magnet using those reinforced wires, we experimentally measured the minimum quench energy (MQE) under cryocooled conditions of some reinforced Nb3Sn wires. As a result, it became clear that thermal stability expressed as MQE was controlled by the temperature margin between the temperature of the operating condition and the transition temperature from superconductivity to normal. Using the FEM analysis, it was realized that the cause of the decline in thermal stability for the reinforced wires was the low thermal conductivity of the reinforced materials. 相似文献
184.
Ferdinando Auricchio Lorenza Petrini 《International journal for numerical methods in engineering》2004,61(6):807-836
An always increasing knowledge on material properties as well as a progressively more sophisticated production technology make shape memory alloys (SMA) extremely interesting for the industrial world. At the same time, SMA devices are typically characterized by complex multi‐axial stress states as well as non‐homogeneous and non‐isothermal conditions both in space and time. This aspect suggests the finite element method as a useful tool to help and improve application design and realization. With this aim, we focus on a three‐dimensional macroscopic thermo‐mechanical model able to reproduce the most significant SMA features (Int. J. Numer. Methods Eng. 2002; 55 : 1255–1264), proposing a simple modification of such a model. However, the suggested modification allows the development of a time‐discrete solution algorithm, which is more effective and robust than the one previously discussed in the literature. We verify the computational tool ability to simulate realistic mechanical boundary value problems with prescribed temperature dependence, studying three SMA applications: a spring actuator, a self‐expanding stent, a coupling device for vacuum tightness. The effectiveness of the model to solve thermo‐mechanical coupled problems will be discussed in a forthcoming work. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
185.
Hiroto Imai Toshiyuki Ogawa Kazuo Sugimoto Masakazu Kataoka Yumo Tanaka Takehiko Ono 《Applied catalysis. B, Environmental》2005,55(4):259-265
The Co/MFI(SiO2/Al2O3 = 30) were prepared by a precipitation method with NaOCl in alkali solutions exhibited high activities to N2 at 250 °C for the selective catalytic reduction (SCR) of NOx. These catalysts showed two UV–vis bands at 700 and 400 nm, indicating the presence of octahedral Co(III) as well as tetrahedral Co(II). The high SCR activity over such Co(III, II)/MFI(30) seems to come from Co(III)---O moieties. The Co(II)MFI(30) catalysts prepared from Co(II)Cl2 exhibited low SCR activities due to the presence of tetrahedral Co(II) ions in MFI. Less CO formation occurred over Co/MFI catalysts. The Fe/MFI(30) catalyst exhibited high activity due to the presence of some Fe---O species in MFI but more amount of CO were produced during SCR. H/MFI(30) catalyst exhibited a good SCR activity. However, more amount of carbonaceous deposits were produced on it. The correlation between acid concentration and SCR activity was discussed over H/MFIs. 相似文献
186.
T. YAMAMOTO M. IWATA M. SAKANE Y. TSUKADA H. NISHIMURA 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(5):376-386
This paper describes the creep‐fatigue life of Sn–8Zn–3Bi under push–pull loading. Creep‐fatigue tests were carried out using Sn–8Zn–3Bi specimens in fast–fast, fast–slow, slow–fast, slow–slow and hold–time strain waveforms. Creep‐fatigue lives in the slow–slow and hold‐time waveforms showed a small reduction from the fast–fast lives but those in the slow–fast and fast–slow waveforms showed a significant reduction from the fast–fast lives. Conventional creep‐fatigue life prediction methods were applied to the experimental data and the applicability of the methods was discussed. Creep‐fatigue characteristics of Sn–8Zn–3Bi were compared with those of Sn–3.5Ag and Sn–37Pb. 相似文献
187.
ISIS全局优化多道反演技术在墩2块岩性油藏描述中的应用 总被引:2,自引:0,他引:2
为进一步落实墩2块戴一段岩性油藏成藏规模及分布规律,针对该储层薄、横向变化快的特点,利用ISIS全局优化多道反演技术,对该构造区岩性储层进行了精细描述,较好的预测出戴一段储层平面分布规律。 相似文献
188.
25Cr3Mo3NiNb二次硬化钢中的碳化物 总被引:1,自引:0,他引:1
利用TEM和萃取相分析方法,研究了25Cr3Mo3NiNb二次硬化钢淬火回火组织中的碳化物。结果表明,随淬火奥氏体化温度的升高,M6C型碳化物逐渐溶解。于1050℃奥氏体化时M6C型碳化物全部溶解,淬火态试样中只有少量的Nb(C,N)颗粒和自回火M3C型碳化物。随回火温度的升高,先后析出ε、M3C、M2C和M7C3等类型的碳化物。Nb(C,N)颗粒可以阻止淬火奥氏体晶粒的异常长大,而高温回火析出的M2C碳化物有二次硬化作用,从而提高回火稳定性和高温强韧性。 相似文献
189.
The effect of rare earth oxides Y203 or Ce02 on sintering properties of Si3N4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results in dicate that the best sintering properties appear in Si3N4 ceramics with 5% Y203 or 8% CeO2. Secondary crystallites are formed at grain boundaries after heat treatment,which decreases the amount of glass phase and contributes to the improvement of high-temperature mechanical properties of silicon nitride. 相似文献
190.