全文获取类型
收费全文 | 264681篇 |
免费 | 22641篇 |
国内免费 | 11934篇 |
专业分类
电工技术 | 16279篇 |
技术理论 | 18篇 |
综合类 | 17374篇 |
化学工业 | 42762篇 |
金属工艺 | 15225篇 |
机械仪表 | 17629篇 |
建筑科学 | 20920篇 |
矿业工程 | 8414篇 |
能源动力 | 7824篇 |
轻工业 | 17655篇 |
水利工程 | 4796篇 |
石油天然气 | 17066篇 |
武器工业 | 2153篇 |
无线电 | 30596篇 |
一般工业技术 | 31004篇 |
冶金工业 | 12694篇 |
原子能技术 | 2786篇 |
自动化技术 | 34061篇 |
出版年
2024年 | 813篇 |
2023年 | 4556篇 |
2022年 | 7580篇 |
2021年 | 11577篇 |
2020年 | 8946篇 |
2019年 | 7090篇 |
2018年 | 8022篇 |
2017年 | 8986篇 |
2016年 | 8134篇 |
2015年 | 11049篇 |
2014年 | 13710篇 |
2013年 | 16348篇 |
2012年 | 17843篇 |
2011年 | 18862篇 |
2010年 | 16203篇 |
2009年 | 15371篇 |
2008年 | 14806篇 |
2007年 | 13819篇 |
2006年 | 14255篇 |
2005年 | 12305篇 |
2004年 | 8076篇 |
2003年 | 7098篇 |
2002年 | 6501篇 |
2001年 | 5904篇 |
2000年 | 5734篇 |
1999年 | 6592篇 |
1998年 | 5350篇 |
1997年 | 4529篇 |
1996年 | 4296篇 |
1995年 | 3484篇 |
1994年 | 2853篇 |
1993年 | 1977篇 |
1992年 | 1636篇 |
1991年 | 1180篇 |
1990年 | 884篇 |
1989年 | 735篇 |
1988年 | 564篇 |
1987年 | 370篇 |
1986年 | 300篇 |
1985年 | 186篇 |
1984年 | 149篇 |
1983年 | 114篇 |
1982年 | 116篇 |
1981年 | 91篇 |
1980年 | 83篇 |
1979年 | 42篇 |
1978年 | 26篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
Katja F. Hellendahl Felix Kaspar Dr. Xinrui Zhou Zhaoyi Yang Prof. Dr. Zhen Huang Prof. Dr. Peter Neubauer Dr. Anke Kurreck 《Chembiochem : a European journal of chemical biology》2021,22(11):2002-2009
Selenium-modified nucleosides are powerful tools to study the structure and function of nucleic acids and their protein interactions. The widespread application of 2-selenopyrimidine nucleosides is currently limited by low yields in established synthetic routes. Herein, we describe the optimization of the synthesis of 2-Se-uridine and 2-Se-thymidine derivatives by thermostable nucleoside phosphorylases in transglycosylation reactions using natural uridine or thymidine as sugar donors. Reactions were performed at 60 or 80 °C and at pH 9 under hypoxic conditions to improve the solubility and stability of the 2-Se-nucleobases in aqueous media. To optimize the conversion, the reaction equilibria in analytical transglycosylation reactions were studied. The equilibrium constants of phosphorolysis of the 2-Se-pyrimidines were between 5 and 10, and therefore differ by an order of magnitude from the equilibrium constants of any other known case. Hence, the thermodynamic properties of the target nucleosides are inherently unfavorable, and this complicates their synthesis significantly. A tenfold excess of sugar donor was needed to achieve 40−48 % conversion to the target nucleoside. Scale-up of the optimized conditions provided four Se-containing nucleosides in 6–40 % isolated yield, which compares favorably to established chemical routes. 相似文献
73.
With the emergence of large-scale knowledge base, how to use triple information to generate natural questions is a key technology in question answering systems. The traditional way of generating questions require a lot of manual intervention and produce lots of noise. To solve these problems, we propose a joint model based on semi-automated model and End-to-End neural network to automatically generate questions. The semi-automated model can generate question templates and real questions combining the knowledge base and center graph. The End-to-End neural network directly sends the knowledge base and real questions to BiLSTM network. Meanwhile, the attention mechanism is utilized in the decoding layer, which makes the triples and generated questions more relevant. Finally, the experimental results on SimpleQuestions demonstrate the effectiveness of the proposed approach. 相似文献
74.
75.
76.
77.
Fluorescence‐Activated Cell Sorters: Standing Surface Acoustic Wave (SSAW)‐Based Fluorescence‐Activated Cell Sorter (Small 40/2018) 下载免费PDF全文
78.
隐患采空区是目前影响露天开采矿山安全生产的主要危害源之一。随着台阶开采的不断剥离,露天开采境界内各台阶与地下空区群的隔离层厚度越来越薄,随时有可能发生采空区顶板坍塌事故。考虑到露天矿采空区地质赋存条件和围岩稳固性等特征,以弓长岭露天铁矿浅层采空区为工程背景,运用现场监测和数值模拟相结合的手段综合分析了浅层采空区的稳定性。将液体静力水准地表沉降监测系统的监测数据与FLAC数值模拟结果对比,调整蠕变参数使得数值模拟的蠕变速率与现场监测结果一致,而后据此进行未来结果的预测。最终根据地表沉降数据确定的蠕变参数取值为A=1.0×10^-12、m=1.75、n=0.35。研究表明:静力水准测点地表最大沉降位移为-9.8 mm,蠕变计算结果顶板最大垂直位移约20.4 mm,应力最大值约25 MPa,综合分析显示该采空区较稳定。上述研究提供了一种基于采空区现场监测数据的数值模拟蠕变分析方法,可为类似矿山采空区稳定性分析提供借鉴。 相似文献
79.
Anaerobic co-digestion of food waste and FOG with sewage sludge – realising its potential in Ireland
Olumide Wesley Awe Yaqian Zhao Ange Nzihou Doan Pham Minh Nathalie Lyczko 《The International journal of environmental studies》2018,75(3):496-517
The severe environmental pollution in many countries is caused by indiscriminate discharge of large quantities of food waste (FW), fat oil and grease (FOG) and sewage sludge (SS) to the environment. There are many possible treatment routes, but anaerobic digestion (AD) is now well accepted for treating several kinds of organic wastes. But AD of FW alone presents some operational challenges because of substrates and variability. Anaerobic co-digestion of two or more substrates is better than single substrate digestion. This can use a plant’s unused capacity, in line with the trend to renewable energy. Co-digestion technology, although well established in many European countries, is still in its infancy in Ireland. There are problems with different regulatory arrangements. They should be resolved. The paper reviews anaerobic co-digestion technology is reviewed, with special focus on possible application in Ireland. 相似文献
80.
To overcome the drawbacks of solid microporous materials for CO2 capture, this proof‐of‐concept study demonstrates a low‐cost and rapid method for producing composites consisting of hypercrosslinked polymers (HCP) with a polyethyleneimine (PEI) binder. The resulting materials capture CO2 through physical and chemical absorption simultaneously. Compared with HCP, the composites exhibit higher CO2 uptake, higher volumetric density, and improved tolerance to water which is attributed to the PEI binder. 相似文献