全文获取类型
收费全文 | 529314篇 |
免费 | 45365篇 |
国内免费 | 26509篇 |
专业分类
电工技术 | 34407篇 |
技术理论 | 53篇 |
综合类 | 41317篇 |
化学工业 | 83330篇 |
金属工艺 | 31422篇 |
机械仪表 | 34585篇 |
建筑科学 | 42009篇 |
矿业工程 | 17016篇 |
能源动力 | 14707篇 |
轻工业 | 38914篇 |
水利工程 | 11006篇 |
石油天然气 | 31149篇 |
武器工业 | 4921篇 |
无线电 | 58341篇 |
一般工业技术 | 56066篇 |
冶金工业 | 24423篇 |
原子能技术 | 5985篇 |
自动化技术 | 71537篇 |
出版年
2024年 | 1626篇 |
2023年 | 7451篇 |
2022年 | 13554篇 |
2021年 | 20283篇 |
2020年 | 15298篇 |
2019年 | 12338篇 |
2018年 | 14015篇 |
2017年 | 15957篇 |
2016年 | 14641篇 |
2015年 | 20961篇 |
2014年 | 26846篇 |
2013年 | 31841篇 |
2012年 | 35949篇 |
2011年 | 39855篇 |
2010年 | 35710篇 |
2009年 | 33967篇 |
2008年 | 33705篇 |
2007年 | 32213篇 |
2006年 | 31733篇 |
2005年 | 26942篇 |
2004年 | 18745篇 |
2003年 | 16237篇 |
2002年 | 15375篇 |
2001年 | 13499篇 |
2000年 | 12521篇 |
1999年 | 12204篇 |
1998年 | 9031篇 |
1997年 | 7578篇 |
1996年 | 7067篇 |
1995年 | 5769篇 |
1994年 | 4648篇 |
1993年 | 3188篇 |
1992年 | 2515篇 |
1991年 | 1893篇 |
1990年 | 1460篇 |
1989年 | 1209篇 |
1988年 | 943篇 |
1987年 | 591篇 |
1986年 | 473篇 |
1985年 | 281篇 |
1984年 | 216篇 |
1983年 | 183篇 |
1982年 | 159篇 |
1981年 | 111篇 |
1980年 | 136篇 |
1979年 | 59篇 |
1978年 | 22篇 |
1977年 | 32篇 |
1976年 | 33篇 |
1959年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
On the basis of the compensation of errors it is postulated that the most accurate correction may not always give the most accurate result for calorific value, and experimental evidence for this is presented. A new criterion is therefore suggested for judging the best (not necessarily the most accurate) cooling correction. Using this principle the cooling correction formula previously proposed is improved which results in higher accuracy whilst retaining the original simplicity. 相似文献
992.
钟控生成器与布尔函数 总被引:3,自引:0,他引:3
引言国外学者Beth.T和Piper F.C于1984年在欧洲密码学会议上首次提出了2值密钥流“停走生成器”(即stop-and-go generator),它是一种以域F,上的线性移位寄存器为基础,通过对移位寄存器的时钟脉冲进行控制来产生伪随机序列的一种钟控生成器,分析表明用这种生成器产生的伪随机序列在一定程度上具有m序列和M序列的良好的伪随机性,同时又克服了m序列具有线性平移相异性的序列数量很小和M序列在硬件上不易实现的缺陷。因而一经出现就受到了相关领域学者们的普遍重视。后来学者又以“停走生成器”为基本构 相似文献
993.
基于双因子认证技术的网络身份识别 总被引:5,自引:0,他引:5
本文提出了一种基于动态双因子认证技术的网络身份识别方法,用户每次登录的口令是利用系统时间和用户ID通过MD5加密算法计算得到,其通过MD5加密后生成的登录口令是随机的,这将进一步提高开放网络环境下身份识别的可靠性和安全性。同时,本文还提出网络身份识别技术可以应用到各类网站的服务器上,用来完成对用户身份的识别,以提高网络系统的安全性。 相似文献
994.
Colour Centres and Energy Transfer in BaF2-xClx:Eu2+ Phosphors 总被引:1,自引:1,他引:0
The optical absorption spectra of BaF2-xClx:Eu2 after ultraviolet (UV) light excitation were investigated.The differences between the absorption spectra after and before excitation (DAS) were observed.The DAS increase at both the high and the low energy side of F band in BaF2-xClx:Eu2 after 245 nm UV light excitation.The bleach effect of UV light and the absorption of electrons in the valence band may account for the former and the formation of Fa centres (association of F(Cl-) centres), whose absorption band matches the HeNe laser better, may explain the latter.In the write-in process, the transfer of electrons is via tunneling.In the readout process, the transfer of electrons captured in F(F-) and Fa centres is more likely via tunneling, and that of F(Cl-) centres is more likely via conduction band. 相似文献
995.
本文介绍了一个用户接口管理系统NUUIMS的设计和实现.重点叙述了该系统基于规范化目标用户接口模型的设计思想,系统组成及描述方法.文章也讨论了使用NUUIMS设计而成的用户接口的特点. 相似文献
996.
As a major pollutant source to urban receiving waters, the non-point source pollution from urban runoff needs to be well studied and effectively controlled. Based on monitoring data from urban runoff pollutant sources, this article describes a systematic estimation of total pollutant loads from the urban areas of Beijing. A numerical model was developed to quantify main pollutant loads of urban runoff in Beijing. A sub-procedure is involved in this method, in which the flush process influences both the quantity and quality of stormwater runoff. A statistics-based method was applied in computing the annual pollutant load as an output of the runoff. The proportions of pollutant from point-source and non-point sources were compared. This provides a scientific basis for proper environmental input assessment of urban stormwater pollution to receiving waters, improvement of infrastructure performance, implementation of urban stormwater management, and utilization of stormwater. 相似文献
997.
998.
999.
Charge in metal-organic chemical vapor deposition-grown HfO/sub 2/ gate stacks has been systematically studied using nMOS capacitors. It is found that, for these films, the charge in the stack is mainly concentrated at the interfaces between the layers and is negative at the HfO/sub 2//interfacial layer (IL) interface and positive at the Si/IL interface. In general, the calculated charge densities at both interfaces are of order 10/sup 12/ cm/sup -2/. A forming gas anneal (FGA) reduces both interface charge greatly. The FGA can also significantly reduce the hysteresis and interface state density. The effects of post deposition anneal at various temperatures and under various ambients have also been studied. It is found that a high-temperature dilute oxidizing ambient anneal followed by an FGA reduces the charge at both interfaces. 相似文献
1000.
Lifang Li Jindal N. Goldsmith A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2005,51(4):1326-1347
We derive the outage capacity region of an M-user fading multiple-access channel (MAC) under the assumption that both the transmitters and the receiver have perfect channel side information (CSI). The outage capacity region is implicitly obtained by deriving the outage probability region for a given rate vector. Given a required rate and average power constraint for each user, we find a successive decoding strategy and a power allocation policy that achieves points on the boundary of the outage probability region. We discuss the scenario where an outage must be declared simultaneously for all users (common outage) and when outages can be declared individually (individual outage) for each user. 相似文献