全文获取类型
收费全文 | 86828篇 |
免费 | 9063篇 |
国内免费 | 5429篇 |
专业分类
电工技术 | 6811篇 |
技术理论 | 3篇 |
综合类 | 6895篇 |
化学工业 | 13075篇 |
金属工艺 | 4891篇 |
机械仪表 | 5771篇 |
建筑科学 | 6756篇 |
矿业工程 | 2488篇 |
能源动力 | 2619篇 |
轻工业 | 5752篇 |
水利工程 | 1853篇 |
石油天然气 | 4461篇 |
武器工业 | 1148篇 |
无线电 | 10873篇 |
一般工业技术 | 9597篇 |
冶金工业 | 3437篇 |
原子能技术 | 1096篇 |
自动化技术 | 13794篇 |
出版年
2024年 | 449篇 |
2023年 | 1453篇 |
2022年 | 2745篇 |
2021年 | 3909篇 |
2020年 | 2950篇 |
2019年 | 2288篇 |
2018年 | 2615篇 |
2017年 | 2891篇 |
2016年 | 2506篇 |
2015年 | 3727篇 |
2014年 | 4676篇 |
2013年 | 5524篇 |
2012年 | 6146篇 |
2011年 | 6592篇 |
2010年 | 6172篇 |
2009年 | 5656篇 |
2008年 | 5682篇 |
2007年 | 5277篇 |
2006年 | 4987篇 |
2005年 | 4174篇 |
2004年 | 3023篇 |
2003年 | 2665篇 |
2002年 | 2688篇 |
2001年 | 2380篇 |
2000年 | 1921篇 |
1999年 | 1723篇 |
1998年 | 1217篇 |
1997年 | 952篇 |
1996年 | 902篇 |
1995年 | 731篇 |
1994年 | 586篇 |
1993年 | 446篇 |
1992年 | 389篇 |
1991年 | 264篇 |
1990年 | 216篇 |
1989年 | 160篇 |
1988年 | 136篇 |
1987年 | 75篇 |
1986年 | 76篇 |
1985年 | 58篇 |
1984年 | 37篇 |
1983年 | 37篇 |
1982年 | 38篇 |
1981年 | 32篇 |
1980年 | 29篇 |
1979年 | 16篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Initialization speed is one of the most important factors in network real time kinematic (NRTK) performance. Owing to the low correlation among the error s 相似文献
32.
34.
Xiaohu Ren Xilou Pu Hongfeng Yin Yun Tang Hudie Yuan Huiqing Fan 《Ceramics International》2021,47(9):12122-12129
Hexagonal barium ferries is a promising and efficient microwave (MW) absorbing material, but the low dielectric loss and poor conductivity have limited their extensive applications. In this work, a simple tactic of coating conductive polymer PANI on hexaferrite BaCo2Fe16O27 is presented, wherein the dielectric properties are customized, and more significantly, the electromagnetic loss is greatly enhanced. As displayed from structural characterizations, PANI were coated equably on the surface of hexaferrite grains by an in-situ polymerization process. The outcomes exhibit the as-prepared PANI@hexaferrite composite has remarkable electromagnetic wave absorption capacity. When the thickness is 6.0 mm, the minimal RL of ?40.4 dB was achieved at 2.9 GHz. The effective absorption bandwidth (RL < ?20 dB) of 0.65 GHz, 0.53 GHz, 0.65 GHz, 0.52 GHz, 0.46 GHz and 0.39 GHz was achieved separately when the thickness ranges from 4 to 9 mm. The highly efficient MW absorbing performance of PANI@hexaferrite composite were the consequence of multiple loss mechanisms and perfect impedance matching. It is demonstrated that the PANI@hexaferrite composite with excellent MW absorption performance is expected to be potential MW absorbers for extensive applications. 相似文献
35.
针对新闻文本领域,该文提出一种基于查询的自动文本摘要技术,更加有针对性地满足用户信息需求。根据句子的TF-IDF、与查询句的相似度等要素,计算句子权重,并根据句子指示的时间给定不同的时序权重系数,使得最近发生的新闻内容具有更高的权重,最后使用最大边界相关的方法选择摘要句。通过与基于TF-IDF、Text-Rank、LDA等六种方法的对比,该摘要方法ROUGE评测指标上优于其他方法。从结合评测结果及摘要示例可以看出,该文提出的方法可以有效地从新闻文档集中摘取核心信息,满足用户查询内容的信息需求。 相似文献
36.
For rechargeable wireless sensor networks, limited energy storage capacity, dynamic energy supply, low and dynamic duty cycles cause that it is unpractical to maintain a fixed routing path for packets delivery permanently from a source to destination in a distributed scenario. Therefore, before data delivery, a sensor has to update its waking schedule continuously and share them to its neighbors, which lead to high energy expenditure for reestablishing path links frequently and low efficiency of energy utilization for collecting packets. In this work, we propose the maximum data generation rate routing protocol based on data flow controlling technology. For a sensor, it does not share its waking schedule to its neighbors and cache any waking schedules of other sensors. Hence, the energy consumption for time synchronization, location information and waking schedule shared will be reduced significantly. The saving energy can be used for improving data collection rate. Simulation shows our scheme is efficient to improve packets generation rate in rechargeable wireless sensor networks. 相似文献
37.
Replacement of precious single metal catalysts with cost-effective, highly-dispersed composite catalysts for catalytic hydrothermal conversion of residue holds tremendous promise for the residue upgrading technologies. Organic metals were added to the feed as the oil-soluble precursors, and transformed into the catalytic active phases in this work. Physical properties and structures of the composite catalysts had been investigated by X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope and transmission electron microscopy. The composite catalysts were found to be highly efficient in the catalytic hydrothermal conversion of both model compound and residue. Increased metal dispersion and synergistic effects of two metals played indispensable roles in such catalytic system. Results showed that under the test conditions in the article, the catalyst had the best catalytic performance when the mass ratio of molybdenum to iron was 1.5. 相似文献
38.
Tong Le Fan Ronggui Yang Shuangchun Zhang Qiushi Pan Yi 《Chemistry and Technology of Fuels and Oils》2022,57(6):991-999
Chemistry and Technology of Fuels and Oils - Application of water flooding technologies in the oilfield causes intensive heterogeneity of the oil reservoir and improper circulation of the injected... 相似文献
39.
以转基因水稻中最常用的CaMV35S启动子、NOS终止子、Cry1Ab/Ac基因、HPT基因及SPS水稻内标基因为研究对象,利用5 种不同的荧光信号(FAM、HEX、Taxas Red、Cy5、Cy5.5)进行多重实时聚合酶链式反应(real-time polymerase chain reaction,real-time PCR)检测方法的研究。通过引物组合筛选、反应体系优化、特异性测试、灵敏度测试、适用性测试等一系列实验,建立了5 重real-time PCR方法,灵敏度可达0.032%。此方法具有灵敏度高、结果准确、通量大等优点,可实现水稻中转基因成分的快速、高效检测。 相似文献
40.