全文获取类型
收费全文 | 373254篇 |
免费 | 30906篇 |
国内免费 | 17632篇 |
专业分类
电工技术 | 22872篇 |
技术理论 | 69篇 |
综合类 | 45913篇 |
化学工业 | 44423篇 |
金属工艺 | 11502篇 |
机械仪表 | 17230篇 |
建筑科学 | 56237篇 |
矿业工程 | 21473篇 |
能源动力 | 14011篇 |
轻工业 | 23609篇 |
水利工程 | 33711篇 |
石油天然气 | 19654篇 |
武器工业 | 3261篇 |
无线电 | 19138篇 |
一般工业技术 | 24585篇 |
冶金工业 | 19563篇 |
原子能技术 | 4560篇 |
自动化技术 | 39981篇 |
出版年
2024年 | 616篇 |
2023年 | 3712篇 |
2022年 | 7140篇 |
2021年 | 9132篇 |
2020年 | 9550篇 |
2019年 | 7912篇 |
2018年 | 7551篇 |
2017年 | 9076篇 |
2016年 | 11001篇 |
2015年 | 11801篇 |
2014年 | 22295篇 |
2013年 | 20778篇 |
2012年 | 26332篇 |
2011年 | 27488篇 |
2010年 | 21442篇 |
2009年 | 21997篇 |
2008年 | 20352篇 |
2007年 | 26284篇 |
2006年 | 24748篇 |
2005年 | 21632篇 |
2004年 | 18010篇 |
2003年 | 16261篇 |
2002年 | 13530篇 |
2001年 | 11220篇 |
2000年 | 9437篇 |
1999年 | 7376篇 |
1998年 | 5478篇 |
1997年 | 4731篇 |
1996年 | 4287篇 |
1995年 | 3752篇 |
1994年 | 3221篇 |
1993年 | 2432篇 |
1992年 | 2102篇 |
1991年 | 1579篇 |
1990年 | 1357篇 |
1989年 | 1224篇 |
1988年 | 972篇 |
1987年 | 693篇 |
1986年 | 524篇 |
1985年 | 469篇 |
1984年 | 434篇 |
1983年 | 306篇 |
1982年 | 250篇 |
1981年 | 182篇 |
1980年 | 155篇 |
1979年 | 131篇 |
1978年 | 67篇 |
1977年 | 83篇 |
1976年 | 62篇 |
1975年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
71.
72.
73.
Natalia Kaczynska Ewa Lojkowska Magdalena Narajczyk Robert Czajkowski 《International journal of molecular sciences》2021,22(9)
Temperature is one of the critical factors affecting gene expression in bacteria. Despite the general interest in the link between bacterial phenotypes and environmental temperature, little is known about temperature-dependent gene expression in plant pathogenic Pectobacterium atrosepticum, a causative agent of potato blackleg and tuber soft rot worldwide. In this study, twenty-nine P. atrosepticum SCRI1043 thermoregulated genes were identified using Tn5-based transposon mutagenesis coupled with an inducible promotorless gusA gene as a reporter. From the pool of 29 genes, 14 were up-regulated at 18 °C, whereas 15 other genes were up-regulated at 28 °C. Among the thermoregulated loci, genes involved in primary bacterial metabolism, membrane-related proteins, fitness-corresponding factors, and several hypothetical proteins were found. The Tn5 mutants were tested for their pathogenicity in planta and for features that are likely to remain important for the pathogen to succeed in the (plant) environment. Five Tn5 mutants expressed visible phenotypes differentiating these mutants from the phenotype of the SCRI1043 wild-type strain. The gene disruptions in the Tn5 transposon mutants caused alterations in bacterial generation time, ability to form a biofilm, production of lipopolysaccharides, and virulence on potato tuber slices. The consequences of environmental temperature on the ability of P. atrosepticum to cause disease symptoms in potato are discussed. 相似文献
74.
给水管道在使用过程中很容易受到人为外力、管道材质、地下水、周围空气、土壤等因素的影响而腐蚀,影响了管道的使用质量和寿命,也带来较大的安全隐患。本文主要是从给水管道腐蚀原因出发,并探讨防护措施。 相似文献
75.
Erik Zipperling Benedikt Dahlmann Markus Zdrallek Christian Derksen Stefan Eicker Heiko Serafin 《化学,工程师,技术》2021,93(4):624-631
Demands on production, distribution and consumption of electrical energy change fundamentally with the energy revolution. Energy purchasing costs for inflexible consumers are rising and proceeds of inflexible producers are sinking. Companies are able to reduce costs by marketing operational flexibility options. This article sets out the need of flexibility in the energy system and the new marketing options. Flexibility potentials within infrastructure plants of a chemical park are analyzed, evaluated regarding marketing and activated in the presented research project FlexChemistry. 相似文献
76.
针对热液白云岩展布非均质性强的问题,开展基底断裂与茅三段沉积演化关系研究,分析断裂样式与白云岩分布关系,建立沉积演化模式,预测白云岩的分布。研究结果表明:茅三段可划分为5个小层,1~3小层为白云岩发育主要时期,4~5小层为台地均一化时期,不发育白云岩;15-1、15-2和16号基底断裂控制了早期“台-洼”相间的沉积地貌,断裂附近的地貌高部位为生屑滩发育有利部位,为白云岩的发育提供物质基础;15-1、15-2号基底断裂样式为花状,周边生屑滩白云石化程度高,为白云岩发育最有利区;16号基底断裂为直立状,附近白云石化发育程度较低,为白云岩发育较有利区。研究成果可为热液白云岩领域的进一步勘探提供指导依据。 相似文献
77.
《Journal of Great Lakes research》2022,48(3):659-668
Previous studies reported coastal trapped waves (CTWs) in the Caspian Sea (CS). This study deals with the generation mechanisms, the temporal and spatial variability of CTWs in this area, and their transformations during propagation from the origin to the destination using recent measurements and high-resolution numerical simulations. CTWs are observed at all stations with periods of 2–6 days after northerly storms. The Absheron Peninsula, old Sefidrud delta, and Nur coasts were identified as the CTWs prone regions. The generation of CTWs in these locations was confirmed using numerical experiments. The propagation away from the generating location of CTWs was analyzed using a representative real wind storm. In the west part of the CS, the generation mechanism of CTWs is mainly similar to the barotropic Kelvin waves; in contrast, it is similar to the continental shelf waves in the southern shelves. The results can be used to study the contribution of generated CTWs to the transport of sediment and biological materials in all large lakes. 相似文献
78.
79.
80.
Grace Lara Chieko Takahashi Miku Nagaya Kunihiko Uemura 《International Journal of Food Science & Technology》2022,57(6):3251-3262
The present study aimed to investigate the influence of radio frequency (RF) heating at 70 and 80 °C, in comparison with the traditional conventional heating. The RF heating technology was applied for maintaining the colour and textural quality as well as inactivating the enzymatic activity of polyphenol oxidase (PPO) and reducing the Escherichia coli growth in packaged fresh-cut peach samples. To evaluate this, 120 g of freshly cut peach fruit was placed in heat-resistant plastic bags, and 50 mL of sugar solution (12°Brix) was added to each bag and vacuum-packed for conventional heating and radio frequency (RF) heating. Our results demonstrated that the RF heating process could reduce the heating time by up to 83% at 70 and 80 °C as compared to conventional heating. Moreover, RF heating at 70 and 80 °C reduced the PPO enzymatic activity, which caused enzymatic browning, up to 85.46% and 93.5%, respectively, as compared to 40.86% reduction only for conventional heating. Furthermore, RF heating completely inhibited E. coli growth. Collectively, we demonstrated that RF heating is an emerging and promising technology for improving the quality of fresh-cut fruits such as peach during various storage conditions. The present study provides relatively novel information on the effectiveness of RF heating in maintaining the quality of fresh-cut peaches. In the future, we would like to investigate the effectiveness of RF heating on other agricultural products. 相似文献