全文获取类型
收费全文 | 357820篇 |
免费 | 28799篇 |
国内免费 | 15951篇 |
专业分类
电工技术 | 21715篇 |
技术理论 | 33篇 |
综合类 | 23962篇 |
化学工业 | 58755篇 |
金属工艺 | 21014篇 |
机械仪表 | 23406篇 |
建筑科学 | 29081篇 |
矿业工程 | 11707篇 |
能源动力 | 10037篇 |
轻工业 | 22655篇 |
水利工程 | 6675篇 |
石油天然气 | 23004篇 |
武器工业 | 3127篇 |
无线电 | 39445篇 |
一般工业技术 | 40344篇 |
冶金工业 | 17725篇 |
原子能技术 | 3751篇 |
自动化技术 | 46134篇 |
出版年
2024年 | 1544篇 |
2023年 | 5618篇 |
2022年 | 9959篇 |
2021年 | 14065篇 |
2020年 | 10602篇 |
2019年 | 8805篇 |
2018年 | 9961篇 |
2017年 | 11241篇 |
2016年 | 9899篇 |
2015年 | 13942篇 |
2014年 | 17477篇 |
2013年 | 20524篇 |
2012年 | 22720篇 |
2011年 | 24564篇 |
2010年 | 21701篇 |
2009年 | 20756篇 |
2008年 | 20430篇 |
2007年 | 19621篇 |
2006年 | 20279篇 |
2005年 | 17634篇 |
2004年 | 11902篇 |
2003年 | 10686篇 |
2002年 | 10788篇 |
2001年 | 9404篇 |
2000年 | 8792篇 |
1999年 | 9549篇 |
1998年 | 7393篇 |
1997年 | 6258篇 |
1996年 | 5821篇 |
1995年 | 4824篇 |
1994年 | 4011篇 |
1993年 | 2796篇 |
1992年 | 2282篇 |
1991年 | 1715篇 |
1990年 | 1247篇 |
1989年 | 999篇 |
1988年 | 797篇 |
1987年 | 557篇 |
1986年 | 418篇 |
1985年 | 272篇 |
1984年 | 192篇 |
1983年 | 124篇 |
1982年 | 142篇 |
1981年 | 102篇 |
1980年 | 80篇 |
1979年 | 37篇 |
1978年 | 4篇 |
1965年 | 2篇 |
1959年 | 17篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Environmental factors such as oxygen, temperature, and microbial species may have significant effects on decomposition of biodegradable polymers. A representative biodegradable, thermoplastic polymer, poly(3‐hydroxybutyrate‐co‐hydroxyvalerate) (PHBV), was decomposed in an aqueous medium under controlled laboratory conditions by soil microbes for the intrinsic degradation kinetics and the effects of the environmental factors on polymer biodegradation. The amount of proteins, including the PHBV depolymerases, that attached to the polymer surfaces was quite constant during the period of significant mass loss of the polymer specimens. The microbial polymer degradation followed a zero‐order rate model, so the residual mass fraction of PHBV films declined linearly with time. The mixed aerobic microbial organisms from fertile soil showed a higher activity of polymer degradation than an aerobic PHBV‐producing bacterium and the mixed anaerobes in the same soil. The mixed anaerobic microorganisms from barren soil decomposed the polymer at a slower rate than the anaerobes from fertile soil, and this was attributed to fewer microbial cells in the barren soil instead of the difference in the microbial species. The temperature effect on PHBV degradation can be described with an Arrhenius equation, and the activation energy is around 16 kcal/mol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 205–213, 2003 相似文献
32.
Stewart C. Kai Shen Dwarkadas S. Scott M.L. Jian Yin 《Distributed Systems Online, IEEE》2004,5(10):1-1
The growth of the Internet and of various intranets has spawned a wealth of online services, most of which are implemented on local-area clusters using remote invocation (for example, remote procedure call/remote method invocation) among manually placed application components. Component placement can be a significant challenge for large-scale services, particularly when application resource needs are workload dependent. Automatic component placement has the potential to maximize overall system throughput. The key idea is to construct (offline) a mapping between input workload and individual-component resource consumption. Such mappings, called component profiles, then support high-performance placement. Preliminary results on an online auction benchmark based on J2EE (Java 2 Platform, Enterprise Edition) suggest that profile-driven tools can identify placements that achieve near-optimal overall throughput. 相似文献
33.
Hogari K. Tetsutani S. Jian Zhou Yamamoto F. Sato K. 《Lightwave Technology, Journal of》2003,21(2):540-545
Many cables containing 1.3-/spl mu/m zero-dispersion single-mode (SM) optical fibers are installed in trunk and access networks. Recently, there have been a number of studies on wavelength-division-multiplexing (WDM) systems designed to increase transmission capacity and flexibility. If we can construct WDM systems using SM optical-fiber cable networks designed to transmit using wavelengths in the 1.3-/spl mu/m window (O-band), this will prove very effective in reducing construction costs. It is therefore important to examine the wavelength dependence of the transmission characteristics of SM optical-fiber cables and networks that have already been installed and in which several optical fibers are joined. In this paper, we describe the measured optical characteristics of SM optical-fiber cables and installed optical-fiber cable networks at various wavelengths. The optical characteristics were stable in the 1.46 to 1.625-/spl mu/m wavelength range and we confirmed that the installed SM optical-fiber cable networks could be used for WDM system applications. 相似文献
34.
Studies on the deactivations and initiations of gas phase polymerizations of 1,3‐butadiene have been achieved by Monte Carlo simulation. Initiation and deactivation control the reaction before and after the peak of the polymerization rate, respectively. The influence of polymerization temperature has been studied. Monte Carlo modeling of polymerization kinetics and mechanism was confirmed by the agreement of experimental data and simulation results of polymerizations run with a temporary evacuation of monomer. The balance of catalysts and active chains is established by both initiation and chain transfer reactions with cocatalyst, which causes a ‘pseudo‐stability’ stage. © 2003 Society of Chemical Industry 相似文献
35.
36.
根据IETF SIPPING工作组提出的集中式会议模型,设计并实现了基于SIP的视频会议系统。该系统各部分可分别设计,具有良好的可扩展性。详细介绍了此系统的结构和工作原理。 相似文献
37.
在全IP体系下,无缝连接将保证用户在跨越同构和异构网络时业务体验的连续性和一致性.无缝连接包括无缝切换和协同两方面内容,需要情景管理、公共无线资源管理、媒体转换以及网络协同等功能实体,从终端的角度看,无缝连接需要基于配置文件、情景和应用自动完成连接的建立、更新和修改.以UMA为例说明了无缝连接的应用和价值. 相似文献
38.
1987年前,除个别成员国在推动电信改革外。欧盟没有共同的电信政策,更没有形成统一的电信市场。欧盟的电信改革始于1987年。先后经历了三个阶段,第一阶段:公布《开发电信服务和设备的共同市场》绿皮书,开放终端设备和增值服务市场。实行电信业的管理与经营分离。保留对语音电话服务 相似文献
39.
张媛媛 《安徽电子信息职业技术学院学报》2003,2(6):3-4
简要介绍了通用串行总线USB的特点,对USB接口芯片USBN9602的内部结构、引脚、寄存器组作了详细的论述,并介绍了其应用。 相似文献
40.