全文获取类型
收费全文 | 131684篇 |
免费 | 11797篇 |
国内免费 | 6723篇 |
专业分类
电工技术 | 8558篇 |
技术理论 | 9篇 |
综合类 | 9360篇 |
化学工业 | 21053篇 |
金属工艺 | 7855篇 |
机械仪表 | 8858篇 |
建筑科学 | 10465篇 |
矿业工程 | 4553篇 |
能源动力 | 3603篇 |
轻工业 | 8136篇 |
水利工程 | 2562篇 |
石油天然气 | 8100篇 |
武器工业 | 1301篇 |
无线电 | 15177篇 |
一般工业技术 | 14776篇 |
冶金工业 | 6016篇 |
原子能技术 | 1460篇 |
自动化技术 | 18362篇 |
出版年
2024年 | 608篇 |
2023年 | 2041篇 |
2022年 | 3956篇 |
2021年 | 5374篇 |
2020年 | 4086篇 |
2019年 | 3376篇 |
2018年 | 3754篇 |
2017年 | 4228篇 |
2016年 | 3834篇 |
2015年 | 5572篇 |
2014年 | 6727篇 |
2013年 | 8099篇 |
2012年 | 8894篇 |
2011年 | 9676篇 |
2010年 | 8667篇 |
2009年 | 8522篇 |
2008年 | 8336篇 |
2007年 | 7959篇 |
2006年 | 7571篇 |
2005年 | 6547篇 |
2004年 | 4294篇 |
2003年 | 3722篇 |
2002年 | 3429篇 |
2001年 | 3047篇 |
2000年 | 2847篇 |
1999年 | 2993篇 |
1998年 | 2181篇 |
1997年 | 1892篇 |
1996年 | 1662篇 |
1995年 | 1429篇 |
1994年 | 1177篇 |
1993年 | 866篇 |
1992年 | 668篇 |
1991年 | 508篇 |
1990年 | 422篇 |
1989年 | 322篇 |
1988年 | 267篇 |
1987年 | 168篇 |
1986年 | 136篇 |
1985年 | 69篇 |
1984年 | 62篇 |
1983年 | 44篇 |
1982年 | 46篇 |
1981年 | 29篇 |
1980年 | 31篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1976年 | 7篇 |
1959年 | 5篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
本文以CAI课件的开发制作过程遇到的一些关键的技术问题加以探讨.并结合实际制作介绍了一些技艺方法、 相似文献
22.
23.
Chen J.J. Gao G.-B. Chyi J.-I. Morkoc H. 《Electron Devices, IEEE Transactions on》1989,36(10):2165-2172
Avalanche breakdown behavior at the collector junction of the GaAs/AlGaAs HBT (heterojunction bipolar transistor) has been studied. Junction breakdown characteristics displaying hard breakdown, soft breakdown, and negative resistance breakdown behavior were observed and are interpreted by analysis of localized microplasma effects, uniform microplasma-free behavior, and associated current gain measurements. Light emission from the collector-base junction of the GaAs/AlGaAs HBT was observed and used to investigate breakdown uniformity. Using a simple punchthrough breakdown model, the theoretical breakdown curves at different collector doping concentrations and thicknesses were computed and found to be in agreement with maximum breakdown voltages measured from devices displaying the most uniform junction breakdown. The serious current gain degradation of GaAs/AlGaAs HBTs at low current densities was analyzed in connection with the measurement of a large collector-emitter breakdown voltage. The unexpected functional relationship between the collector-emitter breakdown voltage and collector-base breakdown voltage is explained by the absence of a hole-feedback effect for devices not exhibiting transistor action 相似文献
24.
25.
目的探讨膝下动脉的球囊成形术在治疗糖尿病缺血性下肢病变中的价值。方法对53例糖尿病合并缺血性下肢病变患者64侧缺血性下肢进行膝下动脉Deep球囊扩张成形术。对比患者手术前后临床症状的改变及足部溃疡的变化。结果53例患者共119支动脉分支接受PTA治疗,50例患者的101个分支成功地开通,技术成功率为84.9%,所有50例患者的临床症状均明显缓解,足部溃疡均变小,无需截肢。结论膝下动脉的球囊成形术是治疗缺血性糖尿病下肢病变安全有效的微创手段 相似文献
26.
Squeeze-film effects of perforated plates for small amplitude vibration are analyzed through modified Reynolds equation (MRE).
The analytical analysis reckons in most important influential factors: compressibility of the air, border effects, and the
resistance caused by vertical air flow passing through perforated holes. It is found that consideration of air compressibility
is necessary for high operating frequency and small ratio of the plate width to the attenuation length. The analytical results
presented in this paper agree with ANSYS simulation results better than that under the air incompressibility assumption. The
analytical analysis can be used to estimate the squeeze-film effects causing damping and stiffness added to the system. Since
the value of Reynolds number involved in this paper is low (< 1), inertial effects are neglected. 相似文献
27.
Ultraviolet (UV) disinfection is becoming increasingly popular as an alternative disinfection technology to chlorination in recent years. In this study, we investigated the photoreactivation of Escherichia coli following medium-pressure (MP) UV disinfection of synthetic water by a bench-scale collimated beam apparatus. The UV doses ranged from 1.6 -19.7 mWs/cm2 and photoreactivation was investigated for 6 hours under fluorescent light. In addition, chloramination was applied after UV disinfection to investigate its ability to control photoreactivation. It was found that photoreactivation occurred for all UV doses tested and the increase in bacteria numbers ranged from 0.04 to 1.35 log10. However, the degree of photoreactivation decreased with increased UV doses. Chloramination experiments revealed that the addition of 0.5 mg/l of monochloramine resulted in suppression of photoreactivation for 1 hour only. An increased monochloramine dose of 1 mg/l was found to prevent photoreactivation for the entire duration of the experiment. The results of this study have shown that photoreactivation occurs even after MP UV disinfection, although it is of a lesser extent at higher UV doses. This study has also established that secondary chloramination can effectively suppress and eliminate photoreactivation with a chloramine dose of 1 mg/l. 相似文献
28.
29.
小秦岭地区金矿床严格受构造控制,各成矿阶段及矿物学特征明显,通过对矿物学特征的研究找出矿物学标志,认为今后找矿要注意各阶段石英的颜色、黄铁矿中金的含量以及矿石中银的含量,这些与金有密切关系. 相似文献
30.
粘土作为高放废物处置回填材料的可行性研究 总被引:5,自引:0,他引:5
本文以西北粘土为对象,对其压实行为、热传导、膨胀特性,以及吸附和渗透性能进行了初步研究,借以探讨西北粘土在高放废物处置中用作回填材料的可行性。试验表明,以西北粘土为基材,经过适当的热改性和吸附改性,在初始含水量约为9%,于70MPa 下成型,用作高放废物处置中的回填材料是可行的。 相似文献