全文获取类型
收费全文 | 51308篇 |
免费 | 3302篇 |
国内免费 | 1434篇 |
专业分类
电工技术 | 2048篇 |
技术理论 | 1篇 |
综合类 | 1970篇 |
化学工业 | 9792篇 |
金属工艺 | 2195篇 |
机械仪表 | 2747篇 |
建筑科学 | 2926篇 |
矿业工程 | 1058篇 |
能源动力 | 2197篇 |
轻工业 | 3168篇 |
水利工程 | 698篇 |
石油天然气 | 2156篇 |
武器工业 | 213篇 |
无线电 | 6128篇 |
一般工业技术 | 8249篇 |
冶金工业 | 3039篇 |
原子能技术 | 552篇 |
自动化技术 | 6907篇 |
出版年
2024年 | 277篇 |
2023年 | 1011篇 |
2022年 | 1881篇 |
2021年 | 2426篇 |
2020年 | 1839篇 |
2019年 | 1782篇 |
2018年 | 2143篇 |
2017年 | 1945篇 |
2016年 | 1796篇 |
2015年 | 1759篇 |
2014年 | 2380篇 |
2013年 | 3327篇 |
2012年 | 2834篇 |
2011年 | 3108篇 |
2010年 | 2646篇 |
2009年 | 2566篇 |
2008年 | 2322篇 |
2007年 | 2202篇 |
2006年 | 2244篇 |
2005年 | 1950篇 |
2004年 | 1289篇 |
2003年 | 1171篇 |
2002年 | 1080篇 |
2001年 | 955篇 |
2000年 | 1060篇 |
1999年 | 1120篇 |
1998年 | 1075篇 |
1997年 | 928篇 |
1996年 | 885篇 |
1995年 | 695篇 |
1994年 | 591篇 |
1993年 | 473篇 |
1992年 | 358篇 |
1991年 | 331篇 |
1990年 | 249篇 |
1989年 | 212篇 |
1988年 | 174篇 |
1987年 | 138篇 |
1986年 | 110篇 |
1985年 | 113篇 |
1984年 | 90篇 |
1983年 | 88篇 |
1982年 | 82篇 |
1981年 | 83篇 |
1980年 | 51篇 |
1979年 | 33篇 |
1978年 | 27篇 |
1977年 | 26篇 |
1976年 | 35篇 |
1971年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 26 毫秒
1.
2.
The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and network ferrite are eliminated, the dislocation density and the quantity of dislocated martensite are increased remarkably, and the shape and distribution of inclusions are improved by the addition of RE. Therefore, the mechanical properties of the modified steel can be greatly increased, especially the toughness (αK) by 44%, yield strength (σs) by 10%, and elongation (δ5) by 42%. 相似文献
3.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method
in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer.
But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results
showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that,
the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic
whereas chloride doped polyaniline films were found to be highly hygroscopic. 相似文献
4.
P(DBF-VA)型柴油低温流动性改进剂的研制 总被引:1,自引:1,他引:0
针对新疆地产柴油蜡含量较高的特点,以游离基聚合法合成了富马酸双链混合酯和醋酸乙烯酯共聚物型[P(DBF-VA)]柴油低温流动改进剂,利用正交实验研究了单体配比,引发剂用量,溶剂用量,聚合温度对聚合物降冷滤效果的影响。共聚物用IR进行表征,利用XRD初步探讨了该降凝剂的降凝机理。结果表明:该剂能使吐哈—10~#、0~#柴油冷滤点降低10℃和7℃;使独山子0~#柴油冷滤点下降12℃;使石化0~#柴油冷滤点下降8℃;使克拉玛依0~#柴油的冷滤点下降8℃。 相似文献
5.
6.
7.
8.
Mobile wireless sensor networks (MWSNs) will enable information systems to gather detailed information about the environment on an unprecedented scale. These self‐organizing, distributed networks of sensors, processors, and actuators that are capable of movement have a broad range of potential applications, including military reconnaissance, surveillance, planetary exploration, and geophysical mapping. In many of the foreseen applications, the MWSN will need to form a geometric pattern without assistance from the user. In military reconnaissance, for example, the nodes will be dropped onto the battlefield from a plane and land at random positions. The nodes will be expected to arrange themselves into a predetermined formation in order to perform a specific task. Thus, we present algorithms for forming a line, circle, and regular polygon from a given set of random positions. The algorithms are distributed and use no communication between the nodes to minimize energy consumption. Unlike past studies of geometric problems where algorithms are either tested in simulations where each node has global knowledge of all the other nodes or implemented on a small number of robots, the robustness of our algorithms has been studied with simulations that model the sensor system in detail. The simulations demonstrate that the algorithms are robust against random errors in the sensors and actuators. © 2004 Wiley Periodicals, Inc. 相似文献
9.
10.
对上海高桥分公司2×10~4m~3/h(标准状态)制氢装置原设计的预转化催化剂还原流程进行了改进。先跳开预转化反应器,利用转化炉制取氢气,再用自产的高纯氢气代替重整氢,对预转化催化剂进行单独升温还原,避免了催化剂在还原初期因发生甲烷化反应而超温失活的问题,使催化剂具有更好的活性和稳定性。 相似文献