全文获取类型
收费全文 | 164253篇 |
免费 | 20066篇 |
国内免费 | 15592篇 |
专业分类
电工技术 | 12850篇 |
技术理论 | 9篇 |
综合类 | 18864篇 |
化学工业 | 23284篇 |
金属工艺 | 5989篇 |
机械仪表 | 10477篇 |
建筑科学 | 13703篇 |
矿业工程 | 4822篇 |
能源动力 | 6702篇 |
轻工业 | 8978篇 |
水利工程 | 8772篇 |
石油天然气 | 9181篇 |
武器工业 | 2211篇 |
无线电 | 13347篇 |
一般工业技术 | 14130篇 |
冶金工业 | 5500篇 |
原子能技术 | 1778篇 |
自动化技术 | 39314篇 |
出版年
2024年 | 821篇 |
2023年 | 2574篇 |
2022年 | 6213篇 |
2021年 | 6814篇 |
2020年 | 5792篇 |
2019年 | 5102篇 |
2018年 | 4864篇 |
2017年 | 6007篇 |
2016年 | 6978篇 |
2015年 | 7300篇 |
2014年 | 9686篇 |
2013年 | 10430篇 |
2012年 | 11614篇 |
2011年 | 12717篇 |
2010年 | 9846篇 |
2009年 | 10365篇 |
2008年 | 10251篇 |
2007年 | 11442篇 |
2006年 | 10036篇 |
2005年 | 8688篇 |
2004年 | 7068篇 |
2003年 | 6181篇 |
2002年 | 4940篇 |
2001年 | 4059篇 |
2000年 | 3523篇 |
1999年 | 2782篇 |
1998年 | 2309篇 |
1997年 | 1953篇 |
1996年 | 1823篇 |
1995年 | 1621篇 |
1994年 | 1344篇 |
1993年 | 944篇 |
1992年 | 780篇 |
1991年 | 627篇 |
1990年 | 512篇 |
1989年 | 422篇 |
1988年 | 276篇 |
1987年 | 176篇 |
1986年 | 169篇 |
1985年 | 144篇 |
1984年 | 151篇 |
1983年 | 78篇 |
1982年 | 102篇 |
1981年 | 65篇 |
1980年 | 79篇 |
1979年 | 81篇 |
1978年 | 29篇 |
1977年 | 18篇 |
1974年 | 18篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
William Kent 《Computer Standards & Interfaces》1991,13(1-3):201-206
OSQL is the object-oriented database language developed for the Iris object-oriented database management system at Hewlett-Packard Laboratories. Its three fundamental constructs are objects, types, and functions. This paper provides an overview of the underlying concepts and some important features of OSQL. 相似文献
62.
环境友好包装材料是一类具有环境意识特征的概念.环境友好包装材料依据“4R 1D“原则,注重包装材料与环境的协调性,指导包装材料的研发,一是有利于保护自然资源;二是对生态环境损害最少化.运用环境友好包装材料的概念,实现包装的可持续发展. 相似文献
63.
64.
Quenching with gases rather than oil or other liquid media has the advantages of reducing the risks concerning health and environment, while simultaneously homogenizing the quenching results and minimizing distortion due to a wide range of possible process parameter variations and the pure convective heat transfer. In this contribution, a coupled solution for increasing homogenization of quenching results within high pressure gas quenching will be presented. In the first stage, an experimental test facility was set up for flow investigations and in the second stage a numerical simulation model was generated. The numerical and experimental results of the flow through the chamber were compared for several boundary conditions. Finally, after complete verification of the simulation, the model may be used to assist in parameter variation for optimization of homogeneous high pressure gas quenching. 相似文献
65.
Anacardic acids, 6-pentadec(en)ylsalicylic acids isolated from the cashew Anacardium occidentale L. (Anacardiaceae) nut and apple, were found to possess preventive antioxidant activity while salicylic acid did not show this activity. These anacardic acids prevent generation of superoxide radicals by inhibiting xanthine oxidase (EC 1.1.3.22, Grade IV) without radical-scavenging activity. Notably, the inhibition kinetics of anacardic acids do not follow hyperbolic dependence of enzyme inhibition on inhibitor contents (Michaelis–Menten equation) but follow the Hill equation instead. Anacardic acid (C15:1) inhibited the soybean lipoxygenase-1 (EC 1.13.11.12, Type 1) catalyzed oxidation of linoleic acid with an IC50 of 6.8 μM. The inhibition is a slow and reversible reaction without residual enzyme activity. The inhibition kinetics indicate that anacardic acid (C15:1) is a competitive inhibitor and the inhibition constant, KI, was 2.8 μM. Anacardic acids act as antioxidants in a variety ways, including inhibition of various prooxidant enzymes involved in the production of the reactive oxygen species and chelate divalent metal ions such as Fe2+ or Cu2+, but do not quench reactive oxygen species. The C15-alkenyl side chain is largely associated with the activity. 相似文献
66.
In this paper, we employ a nonlinear adaptive mechanism to globally stabilize nth-order reactions. 相似文献
67.
68.
Yu Zheng Haiyi Zhang Li Zhao Liujing Wei Xingyuan Ma Dongzhi Wei 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(10):1409-1412
BACKGROUND: 2,3‐Butanediol (2,3‐BD) is a valuable chemical that can be biosynthesized from many kinds of substrates. For commercial biological production of 2,3‐BD, it is desirable to use cheap substrate without pretreatment, such as starch. However, there have been few reports on the production of 2,3‐BD directly from starch. RESULTS: In this work, gene malS coding for α‐amylase (EC 3.2.1.1) precursor was inserted into plasmid pUC18K, and secretory over‐expression of α‐amylase was achieved by engineered Klebsiella pneumoniae. The extracellular recombinant amylase accelerated the hydrolyzation of starch, and one‐step production of 2,3‐BD from starch was carried out by engineered K. pneumoniae. A 2,3‐BD concentration of 3.8 g L?1 and yield of 0.19 g 2,3‐BD g?1 starch were obtained after 24 h fermentation. CONCLUSION: The one‐step production of 2,3‐BD from starch was achieved by secretory over‐expression of amylase in K. pneumoniae. This would simplify the process and reduce the production cost considerably by enabling use of starch with minimal pretreatment. Copyright © 2008 Society of Chemical Industry 相似文献
69.
HLA-DRB1等位基因主要参与人类的抗原免疫功能,对其进行比较研究,有助于追溯人类的进化迁移史,开发类群特异性药物.本研究以Matlab为平台,用自组织竞争网络(Self-Organizing Competitive Neural Network),对世界54个民族和人群、14个HLA-DRB1等位基因,进行了无监督模式分类.结果表明,各民族之间存在差异性,同民族的各人群之间有相似性.西伯利亚各人群,澳洲各土著人群,黑人各人群,南美印第安各人群,犹太族各人群,日本各人群,及欧美白人各人群有相对独立性:南美印第安人与西伯利亚人有高度相似性;中国民族在南方人群和北方人群间存在较大差异;中国汉族中,广东汉族地位特殊,与少数民族如拉祜族、瑶族关系密切. 相似文献
70.
Guiying Li Ze He Taicheng An Xiangying Zeng Guoying Sheng Jiamo Fu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(7):1019-1026
BACKGROUND: To investigate the microbial degradation performance of organic pollutants in the atmosphere using a biotrickling filter, two microorganism strains, Bacillus cereus S1 and Bacillus cereus S2, were selected, identified and inoculated into a twin biotrickling filter for comparison. RESULTS: Both strains showed good performance towards the degradation of model organic pollutants when gas flow rates ranged from 100 to 600 L h−1. For S1, the total maximum removal efficiency (RE) of toluene was maintained nearly 100% not only at gas flow rates of 100 L h−1 corresponding to empty bed residence time (EBRT) 199.44 s, but also at gas flow rates of 200 L h−1 (EBRT = 99.72 s) and 300 L h−1 (EBRT = 66.48 s). However, S2 had a much lower degradation capability; near 100% removal efficiency was obtained only at the gas flow rate of 100 L h−1 although both bacteria belong to the same Bacillus cereus. With further increase in gas flow rate, the total REs for both S1 and S2 decreased slightly at first and then dropped sharply to 46% and 35%, respectively, at an EBRT of 33.24 s, corresponding to a gas flow rate of 600 L h−1. Starvation for between 2 and 10 days resulted in the re‐acclimation times of both strains ranging between 1.0 and 15.5 h. CONCLUSION: Strain S1 would be a better choice for inoculation into a biotrickling filter than strain S2, because of its much higher toluene removal capacity and rapid recovery to full performance. Copyright © 2008 Society of Chemical Industry 相似文献