全文获取类型
收费全文 | 158719篇 |
免费 | 8155篇 |
国内免费 | 4028篇 |
专业分类
电工技术 | 5495篇 |
技术理论 | 7篇 |
综合类 | 7255篇 |
化学工业 | 23797篇 |
金属工艺 | 9227篇 |
机械仪表 | 8118篇 |
建筑科学 | 7953篇 |
矿业工程 | 3181篇 |
能源动力 | 3503篇 |
轻工业 | 8921篇 |
水利工程 | 2855篇 |
石油天然气 | 4523篇 |
武器工业 | 707篇 |
无线电 | 17593篇 |
一般工业技术 | 25225篇 |
冶金工业 | 6404篇 |
原子能技术 | 1269篇 |
自动化技术 | 34869篇 |
出版年
2024年 | 304篇 |
2023年 | 1323篇 |
2022年 | 2307篇 |
2021年 | 3276篇 |
2020年 | 2435篇 |
2019年 | 2146篇 |
2018年 | 16550篇 |
2017年 | 15659篇 |
2016年 | 12143篇 |
2015年 | 3750篇 |
2014年 | 4229篇 |
2013年 | 4968篇 |
2012年 | 8419篇 |
2011年 | 14867篇 |
2010年 | 13066篇 |
2009年 | 10112篇 |
2008年 | 11153篇 |
2007年 | 11884篇 |
2006年 | 4121篇 |
2005年 | 4637篇 |
2004年 | 3628篇 |
2003年 | 3459篇 |
2002年 | 2923篇 |
2001年 | 2157篇 |
2000年 | 1897篇 |
1999年 | 1793篇 |
1998年 | 1308篇 |
1997年 | 1056篇 |
1996年 | 996篇 |
1995年 | 830篇 |
1994年 | 665篇 |
1993年 | 537篇 |
1992年 | 420篇 |
1991年 | 308篇 |
1990年 | 199篇 |
1989年 | 154篇 |
1988年 | 182篇 |
1987年 | 90篇 |
1986年 | 91篇 |
1985年 | 48篇 |
1984年 | 36篇 |
1968年 | 44篇 |
1966年 | 42篇 |
1965年 | 46篇 |
1959年 | 36篇 |
1958年 | 38篇 |
1957年 | 37篇 |
1956年 | 36篇 |
1955年 | 66篇 |
1954年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Journal of Computer Science and Technology - DOACROSS loops are significant parts in many important scientific and engineering applications, which are generally exploited pipeline/wave-front... 相似文献
42.
对赤红球菌的组氨酸激酶基因进行密码子优化,将优化后的组氨酸激酶基因(rhks)构建重组表达质粒pGEX-4T-2-rhks。将此质粒导入到大肠杆菌BL21(DE3)中进行异源表达。在25 ℃和1 mmol/L异丙基-β-D-硫代吡喃半乳糖苷诱导条件下,组氨酸激酶融合蛋白(GST-RHK)获得成功表达,并具有催化活性。经谷胱甘肽琼脂糖亲和层析纯化,获得电泳纯的GST-RHK,其中纯化倍数为3.1,得率为19.5%。该蛋白大小约为72.75 kDa,Km、Vmax和Kcat值分别为20.92 μmol/L、0.17 μmol/(L·min)和1.4 min-1。野生型赤红球菌、组氨酸激酶基因增强株sdrhkE和组氨酸激酶基因敲减株sdrhkD在分别含有苯酚、甲苯、氯苯、异辛烷4 种有机溶剂的培养基中培养,菌株sdrhkD的生长情况都优于野生型赤红球菌,菌株sdrhkE的生长情况都低于野生型赤红球菌。本研究为进一步揭示赤红球菌SD3中组氨酸激酶涉及的信号转导途径与赤红球菌有机溶剂耐受性的关联机制提供一定参考依据。 相似文献
43.
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
44.
Neural Computing and Applications - Traffic identification is currently an important challenge for network management and security. In this paper, we propose a novel application identification... 相似文献
45.
Yue Gao Miao-miao Zhang Xiao-peng Guo Wen-jian Li Dong Lu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2020,95(5):1290-1297
Toxicity caused by the accumulation of butanol in fermentation media is an important factor limiting the concentration of butanol. There is currently no systematic research in place investigating the butanol tolerance mechanism of bacteria such as Clostridium acetobutylicum, which adapts to butanol stress and regulates its growth and metabolism. Here, research results related to the butanol tolerance of C. acetobutylicum are reviewed to understand the molecular basis of changes in butanol-tolerant strains. Organic solvent-tolerant bacteria play an important role in the fields of biofuel production, enzyme preparation and bioremediation. An analysis of limitations of the application of organic solvent-tolerant bacteria has revealed that future research should focus on combining the microbial tolerance phenotype with specific utilization to achieve an optimal balance between organic solvent tolerance and production. This review serves as a reference for the improvement and engineering of strains that tolerate organic solvents. © 2019 Society of Chemical Industry 相似文献
46.
Mobile software applications have to cope with a particular environment that involves small size, limited resources, high autonomy requirements, competitive business models and many other challenges. To provide development guidelines that respond to these needs, several practices have been introduced; however, it is not clear how these guidelines may contribute to solve the issues present in the mobile domain. Furthermore, the rapid evolution of the mobile ecosystem challenges many of the premises upon which the proposed practices were designed. In this paper, we present a survey of the literature on software assurance practices for mobile applications, with the objective of describing them and assessing their contribution and success. We identified, organized and reviewed a body of research that spans in three levels: software development processes, software product assurance practices, and software implementation practices. By carrying out this literature survey, we reviewed the different approaches that researchers on Software Engineering have provided to address the needs that raise in the mobile software development arena. Moreover, we review the evolution of these practices, identifying how the constant changes and modernization of the mobile execution environment has impacted the methods proposed in the literature. Finally, we introduced discussion on the application of these practices in a real productive setting, opening an area for further research that may determine if practitioners have followed the proposed assurance paradigms. 相似文献
47.
48.
49.
Xiao-Guang Yue Guang Zhang Qu Wu Fei Li Xian-Feng Chen Gao-Feng Ren Mei Li 《稀有金属(英文版)》2015,(2):125-132
In order to predict the wearing of stellite alloys,the related methods of rare metals data processing were discussed. The method of opposite degree(OD) algorithm was put forward to predict the wearing of stellite alloys.OD algorithm is based on prior numerical data, posterior numerical data and the opposite degree between numerical forecast data. To compare the performance of predicted results based on different algorithms, the back propagation(BP) and radial basis function(RBF) neural network methods were introduced. Predicted results show that the relative error of OD algorithm is smaller than those of BP and RBF neural network methods. OD algorithm is an effective method to predict the wearing of stellite alloys and it can be applied in practice. 相似文献
50.
This paper presents an integrated passive damping approach in hybrid metal-CFRP parts for structural applications. In this concept a viscoelastic material is embedded in the joint zone of the hybrid component. To examine the connection strength single-lap-joint specimens were produced and tested and the influence of the used material combinations, different surface structures, and different process parameters i.e. the moment of cross-linking were evaluated. Afterwards, the metal-CFRP hybrids were tested in quasi-static tests to assess their connection strength and failure behaviour. Dynamic cyclic tensile tests with step-wise increased loading conditions were performed to determine the specimens damping behaviour and to estimate their fatigue performance. Finally, these results are compared to a state of the art metal-CFRP hybrid with rivets connecting both materials. 相似文献