全文获取类型
收费全文 | 105550篇 |
免费 | 11759篇 |
国内免费 | 8002篇 |
专业分类
电工技术 | 9631篇 |
技术理论 | 2篇 |
综合类 | 10239篇 |
化学工业 | 13744篇 |
金属工艺 | 6971篇 |
机械仪表 | 7845篇 |
建筑科学 | 9141篇 |
矿业工程 | 3650篇 |
能源动力 | 3149篇 |
轻工业 | 9300篇 |
水利工程 | 3017篇 |
石油天然气 | 4183篇 |
武器工业 | 1366篇 |
无线电 | 12073篇 |
一般工业技术 | 9415篇 |
冶金工业 | 4021篇 |
原子能技术 | 1610篇 |
自动化技术 | 15954篇 |
出版年
2024年 | 471篇 |
2023年 | 1536篇 |
2022年 | 3425篇 |
2021年 | 4497篇 |
2020年 | 3296篇 |
2019年 | 2532篇 |
2018年 | 2864篇 |
2017年 | 3094篇 |
2016年 | 2839篇 |
2015年 | 4319篇 |
2014年 | 5670篇 |
2013年 | 6426篇 |
2012年 | 7878篇 |
2011年 | 8223篇 |
2010年 | 7774篇 |
2009年 | 7607篇 |
2008年 | 7989篇 |
2007年 | 7381篇 |
2006年 | 7050篇 |
2005年 | 5526篇 |
2004年 | 4469篇 |
2003年 | 3971篇 |
2002年 | 4877篇 |
2001年 | 4092篇 |
2000年 | 2558篇 |
1999年 | 1454篇 |
1998年 | 702篇 |
1997年 | 576篇 |
1996年 | 476篇 |
1995年 | 402篇 |
1994年 | 329篇 |
1993年 | 217篇 |
1992年 | 170篇 |
1991年 | 139篇 |
1990年 | 98篇 |
1989年 | 93篇 |
1988年 | 56篇 |
1987年 | 47篇 |
1986年 | 34篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 19篇 |
1978年 | 2篇 |
1966年 | 2篇 |
1959年 | 19篇 |
1951年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
龙口水利枢纽坝基岩体主要由奥陶系中统马家沟组(O2m2)灰岩组成,其中发育有多层软弱夹层。作为其中之一的钙质充填夹层,强度虽不很低,但由于处于坝基下的持力层内,间距不大,发育密集,产状平缓,是坝基浅层抗滑稳定的主要控制因素,因此,在大坝抗滑稳定分析时,应进行分析和研究。 相似文献
72.
结合工程实例,介绍了我国第一座可拆装高架火炬的基本原理及组成,并对可拆装高架火炬与普通高架火炬在安全、技术、安装、维修、占地面积、投资等方面进行了比较,还分析了高架火炬未来的发展趋势. 相似文献
73.
74.
分析了新乡观测到的VLF相位周期滑移现象,研究了产生相位周期滑移的原因,揭示了相位周期滑移的实质:VLF传播相位周期滑移是发生在日出或日落过渡期间一种特殊的多模干涉现象,它是由传播路径昼夜分界处的低电离层不连续性所引起的模转换干涉所造成的. 相似文献
75.
Jianhua Liu Jian Li 《Mobile Computing, IEEE Transactions on》2006,5(9):1133-1142
We consider improving the performance of orthogonal frequency-division multiplexing (OFDM)-based mobile broadband wireless communication (MBWC) systems. We show that a recently approved packet-based MBWC standard can cause the resulting systems to suffer from severe performance degradations for time-varying channels due to the lack of a mechanism for tracking the time-varying channels needed for coherent detection. We consider both packet design and signal processing to deal with time-varying channels. For the packet design, we segment an entire packet into multiple subpackets—with each subpacket having zero tail bits to reset the convolutional channel encoder—so that the detection/decoding result of each subpacket can be used to update the channel response for this subpacket. For signal processing, we use weighted polynomial fitting and prediction at the receiver to improve the channel tracking accuracy. Simulation results show that the coherent detection based on our new scheme can significantly outperform the commonly suggested differential modulation/detection methods. 相似文献
76.
77.
提出了用于水利项目方案评价的方法——基于相对最优方案的指标赋权模型,介绍了该方法的基本原理,建立了综合考虑保证出力、年发电量、单位千瓦投资等因素的基于相对最佳方案的指标赋权模型,并用实例加以说明,与模糊优选神经网络模型的评价结果相对比,研究表明该模型适合于水利项目方案的评价和优选。 相似文献
78.
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
79.
80.
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