全文获取类型
收费全文 | 58294篇 |
免费 | 4019篇 |
国内免费 | 2567篇 |
专业分类
电工技术 | 1792篇 |
综合类 | 3653篇 |
化学工业 | 15129篇 |
金属工艺 | 4438篇 |
机械仪表 | 2185篇 |
建筑科学 | 4088篇 |
矿业工程 | 894篇 |
能源动力 | 1981篇 |
轻工业 | 2706篇 |
水利工程 | 217篇 |
石油天然气 | 1968篇 |
武器工业 | 398篇 |
无线电 | 5365篇 |
一般工业技术 | 8846篇 |
冶金工业 | 1876篇 |
原子能技术 | 798篇 |
自动化技术 | 8546篇 |
出版年
2024年 | 131篇 |
2023年 | 759篇 |
2022年 | 1423篇 |
2021年 | 1498篇 |
2020年 | 1309篇 |
2019年 | 1382篇 |
2018年 | 1136篇 |
2017年 | 1585篇 |
2016年 | 1904篇 |
2015年 | 1805篇 |
2014年 | 2320篇 |
2013年 | 2590篇 |
2012年 | 3129篇 |
2011年 | 3771篇 |
2010年 | 2613篇 |
2009年 | 3320篇 |
2008年 | 2681篇 |
2007年 | 3047篇 |
2006年 | 2806篇 |
2005年 | 2319篇 |
2004年 | 2721篇 |
2003年 | 2420篇 |
2002年 | 2798篇 |
2001年 | 2258篇 |
2000年 | 2058篇 |
1999年 | 1712篇 |
1998年 | 1133篇 |
1997年 | 1040篇 |
1996年 | 1892篇 |
1995年 | 1150篇 |
1994年 | 874篇 |
1993年 | 395篇 |
1992年 | 347篇 |
1991年 | 338篇 |
1990年 | 295篇 |
1989年 | 189篇 |
1988年 | 157篇 |
1987年 | 139篇 |
1986年 | 170篇 |
1985年 | 176篇 |
1984年 | 137篇 |
1983年 | 111篇 |
1982年 | 110篇 |
1981年 | 117篇 |
1980年 | 91篇 |
1979年 | 82篇 |
1978年 | 82篇 |
1977年 | 81篇 |
1976年 | 94篇 |
1975年 | 91篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
固相缩聚共聚酯的熔融行为和结晶速率研究 总被引:1,自引:0,他引:1
通过固相缩聚合成了两种不同结构的高分子量共聚酯,研究了样品的熔融行为和结晶速率。研究发现,共聚酯的熔融峰随着固相聚合温度和时间的变化而与纯PET有明显的差别,共聚酯泊结晶速率与慢于纯PET的结晶速率。 相似文献
104.
A Linear Cross-Coupled Control System for High-Speed Machining 总被引:4,自引:0,他引:4
Q. Zhong Y. Shi J. Mo S. Huang 《The International Journal of Advanced Manufacturing Technology》2002,19(8):558-563
We present a linear cross-coupled controller to improve highspeed contouring accuracy independently of tracking accuracy in
a biaxial machine tool feed drive servomechanism. Unlike conventional cross-coupled controllers, the cross-coupled controller
presented here is a linear system, so it is very easy to perform the stability and steady-state error analysis, and to optimise
the controller parameters. The proposed controller is evaluated experimentally on a CNC LOM machine and compared to an uncoupled
controller and a conventional cross-coupled controller. Controller performance is evaluated for a circular contour at a feedrate
of 30 m min _1 . The experimental results show that the proposed controller can greatly reduce the contour error at large feedrates. The
linear cross-coupled controller is simple to implement and is practical. 相似文献
105.
106.
Shizuo Arichi Noriyuki Sakamoto Shozo Himuro Mayumi Miki Masafumi Yoshida 《Polymer》1985,26(8):1175-1180
In order to obtain the additional data concerning the unperturbed dimension of poly-4-substituted styrene, light scattering measurements are performed on the twenty-two fractions with molecular weight of (0.91–352)·104 of poly(4-acetoxystyrene) in dioxan at 25°C, from which the molecular weight obtained was found easily to be evaluated with the gel permeation chromatography using THF. Phase separation experiments for this polymer indicate that the theta state is attained in isopropyl acetate at 19.7°C and butyl acetate at 26.8°C. By making viscosity measurements at that state, the value of KΘ is directly evaluated as 5.4·10?4 dl g?1. The limiting viscosity number is also obtained in good solvents, THF and dioxan, at 25°C and constants of the Mark-Houwink-Sakurada equation in each solvent are determined. Further, approximately the same KΘ as above is obtained from these data with the Stockmayer-Fixman plot. The calculated value of steric factor, 2.37, on this polymer may be plausible, compared with those of polyvinylaromatic derivatives. 相似文献
107.
M. Liess R. Hua K. Elsenaar 《The International Journal of Advanced Manufacturing Technology》2002,20(1):58-62
Cables to moving parts on a linear actuator in production machines, such as pick-and-place machines, are a source of unreliability
owing to the possible breaking of a cable. They further reduce the positioning precision of the actuator owing to additional
forces. Slotted waveguide systems for rail vehicles based on 2.4 GHz transmission frequency are well known, but transmitters/receivers
and waveguides are bulky. The paper reports on the reduction in size of the equipment, adapted to 5.8 GHz using a commercial
off-the-shelf RadioLan communication module. Further, the efficient termination of the wave-guide and a new way to reduce
standing-wave effects is also discussed. 相似文献
108.
报导了新型鞣剂 7-羟基全氢化唑并嗪 (以下简称 OX- Z)的合成方法。试验确定合成的最佳条件为 :在氮气保护下 ,将等摩尔量的二乙醇胺在 10℃水浴中缓慢滴入乙二醛中 ,滴加时间 0 .5 h,在 2 0℃水浴中继续反应 1.5 h,产率为 6 2 .9%。 OX- Z对浸酸绵羊皮单独鞣制 ,可使收缩温度升高到 87℃。最佳鞣制条件为 :p H10 .0 ,OX- Z用量 5 % ,鞣制时间 8h。在对 OX- Z与皮胶原的结合类型的研究中证明它们之间是以化学键结合的。 相似文献
109.
Two commercial Pt modified aluminide coatings (RT22 and MDC150L) on the same single crystal Ni-based superalloy (CMSX-4) were studied by: scanning electron microscopy; transmission electron microscopy; energy dispersive X-ray spectrometry; and gravimetry. The RT22 coating is an inward grown coating (high activity), while MDC150L is produced by outward growth (low activity). Samples were oxidised in still laboratory air at 1050 °C for various times up to 2000 h. It was found that the outward grown coating produced a slower growing oxide that was more spallation resistant. Several possible reasons for this were identified including: coating purity; coating surface topography; and ductile to brittle transition temperature. The microstructural differences between the two coatings in the as-coated condition were investigated and the development of their microstructure during heat treatment was described. A model for coating growth during heat treatment was proposed. 相似文献
110.
大庆长垣外围油田的开发问题 总被引:1,自引:0,他引:1
方凌云 《大庆石油地质与开发》1989,(3)
本文在对大庆长垣外围油田的地质情况、油藏类型综合分析评价的基础上,论述了开发这些油田的一系列有关问题。 相似文献