全文获取类型
收费全文 | 279857篇 |
免费 | 24208篇 |
国内免费 | 16446篇 |
专业分类
电工技术 | 17968篇 |
技术理论 | 51篇 |
综合类 | 38577篇 |
化学工业 | 28910篇 |
金属工艺 | 10236篇 |
机械仪表 | 15984篇 |
建筑科学 | 38902篇 |
矿业工程 | 15339篇 |
能源动力 | 8055篇 |
轻工业 | 14942篇 |
水利工程 | 14132篇 |
石油天然气 | 12045篇 |
武器工业 | 2697篇 |
无线电 | 19564篇 |
一般工业技术 | 19666篇 |
冶金工业 | 15845篇 |
原子能技术 | 2671篇 |
自动化技术 | 44927篇 |
出版年
2024年 | 1083篇 |
2023年 | 3068篇 |
2022年 | 5912篇 |
2021年 | 6813篇 |
2020年 | 7171篇 |
2019年 | 6023篇 |
2018年 | 5546篇 |
2017年 | 6682篇 |
2016年 | 7873篇 |
2015年 | 8764篇 |
2014年 | 15830篇 |
2013年 | 14294篇 |
2012年 | 18832篇 |
2011年 | 19942篇 |
2010年 | 15969篇 |
2009年 | 16491篇 |
2008年 | 15499篇 |
2007年 | 20071篇 |
2006年 | 18893篇 |
2005年 | 16534篇 |
2004年 | 14051篇 |
2003年 | 12615篇 |
2002年 | 10394篇 |
2001年 | 8762篇 |
2000年 | 7433篇 |
1999年 | 6081篇 |
1998年 | 4605篇 |
1997年 | 4022篇 |
1996年 | 3716篇 |
1995年 | 3115篇 |
1994年 | 2774篇 |
1993年 | 2060篇 |
1992年 | 1846篇 |
1991年 | 1355篇 |
1990年 | 1191篇 |
1989年 | 1048篇 |
1988年 | 829篇 |
1987年 | 567篇 |
1986年 | 436篇 |
1985年 | 356篇 |
1984年 | 338篇 |
1983年 | 253篇 |
1982年 | 216篇 |
1981年 | 166篇 |
1980年 | 131篇 |
1979年 | 114篇 |
1978年 | 63篇 |
1977年 | 75篇 |
1976年 | 56篇 |
1975年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
51.
Isolation and preliminary characterization of Pichia pinus mutants insensitive to glucose repression
A new method for the isolation of glucose repression-insensitive mutants in the methylotrophic yeast Pichia pinus was developed. The method is based on screening of small suspension samples derived from 2-deoxyglucose-resistant colonies for alcohol oxidase activity. Alcohol oxidase activity was evaluated by determination of formaldehyde excreted by cells. Mutants with glucose non-repressible alcohol oxidase and catalase synthesis were obtained. All mutants grew poorly on D -xylose compared to the wild type, whereas growth on L -arabinose was similar to the wild type. Changes in the glucose transport system were suggested to be responsible for altered growth characteristics and defective glucose repression. 相似文献
52.
多孔粒状铵油炸药在边坡预裂爆破中的应用 总被引:3,自引:0,他引:3
通过工程实践,介绍了利用多孔粒状铵油炸药进行边坡预裂爆破的设计原理及施工工艺。该技术能确保预裂爆破质量。简化施工工序,大幅度降低爆破成本。技术经济指标优越。 相似文献
53.
Sang Cheol Lee Won Kook Lee 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,55(3):251-261
The extraction of penicillin G from simulated media was performed by water/oil/water (w/o/w) emulsion liquid membranes (ELMs) and studied under various operational conditions in a batch system. The degree of extraction achieved was between 80% and 95% under specific conditions. A concentration of greater than nine times the initial concentration of penicillin G in the external phase was obtained in the internal phase. The pH of the internal aqueous solution, containing a basic salt, was theoretically calculated on the basis of the amount of penicillin G transported into the internal phase. The calculated results agreed with the experimental data well and were used to select a suitable type and concentration of a basic salt in the internal phase to give a pH within the range 5 to 8 where penicillin G was stable after the termination of extraction. The extraction of penicillin G was successfully performed by the ELM process with sodium carbonate in the internal phase. 相似文献
54.
Safe and Economic Operation of Power Plants – Research Results in the Field of Materials, Design and Maintenance Components of power plants which undergo high temperatures are subjected to complex loading situations. The requirements on the used materials result from the special operation conditions of the plants and have to be adjusted to the steadily growing requirements on higher efficiency of the complete power plant as well as to those of safe and economic operation. The expenses for control and downtimes are directly connected with economic efficiency and availability. However, in case of new procedures or components it is not possible to revert to the existing know‐how. Different failure mechanisms than known before can occur. The same goes for the load situation. Therefore the knowledge base has to be extended to in‐advance or even parallely running scientific examinations that life assessment and maintenance strategies can be applied which guarantee the operational reliability and the efficiency of the plant. The main emphasis of these F&E works has to be put on condition monitoring based on actual operational data, the standard materials’ and component’s behaviour (deformation, damage and failure behaviour) in connection with design of components and the related material laws. In the framework of applied AVIF projects, following problems are handled:. – qualification of materials by determinating parameters related to practise. – optimal design of components by making available material laws and numerical tools. – economic manufacturing of components by qualifying processing methods such as welding. – The results can be transferred to concepts for safe and economic operation of power plants, especially for newly introduced materials for which there is no operational experience available. 相似文献
55.
总结了实际工作中防突管理的经验和问题 ,探讨了科学理论与具体实际的有机结合与统一 ,采取针对性强的有效措施 ,确保突出矿井的安全生产 相似文献
56.
E.I.P. Volcke M. Loccufier P.A. Vanrolleghem E.J.L. Noldus 《Journal of Process Control》2006,16(10):1003-1012
This paper addresses the dynamics of a SHARON reactor, a promising technology for ammonium removal from concentrated wastewater streams. The contraction mapping theorem is used to determine which operating conditions of a SHARON reactor with pH-control result in a unique equilibrium state. However, this approach only identifies the case of very large dilution rates, in practice corresponding with complete biomass wash-out, i.e. with complete loss of biological activity. Practical operation of a SHARON reactor aims at reaching ammonium conversion to nitrite. To identify such interesting operating points, the equilibrium points are subsequently calculated directly in terms of input variables for a simplified SHARON reactor model. The stability of the obtained equilibrium points is assessed and the corresponding phase portraits are analyzed. The influence of slightly varying parameter and input values is investigated as well. 相似文献
57.
In a series of experiments, participants were required to keep track of 1 or 2 working memory (WM) objects, having to update their values in 80% of the trials. Updating cost, defined as the difference between update and non-update trials, was larger when 2 objects were involved compared with when there was only 1 object was involved. This finding was interpreted as evidence that the updating process encompasses both objects in WM, even though only 1 of them is actually updated. This feature of WM updating is limited to objects defined as "updateable," throughout the trial sequence. The results are explained by the need to reprogram the phonological loop when updating or the need for desynchronization followed by resynchronization of WM contents. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
58.
59.
全文围绕树立和落实科学发展观这一主题 ,研究和探索如何在新时期、新阶段进一步做好国土资源管理工作的新思路、新途径和新方法。提出要进一步加强国土资源宏观管理 ,更好地为甘肃省经济社会的协调、可持续发展提供保障服务。 相似文献
60.
人类聚居环境学对于居住区规划设计的启示 总被引:1,自引:0,他引:1
以人类聚居环境学的研究方法从若干方面对目前的居住区规划设计进行了一定的探讨,分析规划设计及建设方面目前存在的主要问题,提出以人类聚居环境学为指导的居住区规划设计理念。 相似文献