全文获取类型
收费全文 | 20151篇 |
免费 | 1967篇 |
国内免费 | 1221篇 |
专业分类
电工技术 | 1546篇 |
综合类 | 1741篇 |
化学工业 | 2676篇 |
金属工艺 | 892篇 |
机械仪表 | 1220篇 |
建筑科学 | 1187篇 |
矿业工程 | 525篇 |
能源动力 | 547篇 |
轻工业 | 1886篇 |
水利工程 | 453篇 |
石油天然气 | 381篇 |
武器工业 | 248篇 |
无线电 | 1961篇 |
一般工业技术 | 1953篇 |
冶金工业 | 2858篇 |
原子能技术 | 309篇 |
自动化技术 | 2956篇 |
出版年
2024年 | 69篇 |
2023年 | 261篇 |
2022年 | 565篇 |
2021年 | 771篇 |
2020年 | 555篇 |
2019年 | 435篇 |
2018年 | 441篇 |
2017年 | 490篇 |
2016年 | 477篇 |
2015年 | 728篇 |
2014年 | 905篇 |
2013年 | 1199篇 |
2012年 | 1458篇 |
2011年 | 1579篇 |
2010年 | 1472篇 |
2009年 | 1414篇 |
2008年 | 1457篇 |
2007年 | 1453篇 |
2006年 | 1197篇 |
2005年 | 1032篇 |
2004年 | 765篇 |
2003年 | 562篇 |
2002年 | 516篇 |
2001年 | 439篇 |
2000年 | 390篇 |
1999年 | 203篇 |
1998年 | 470篇 |
1997年 | 293篇 |
1996年 | 230篇 |
1995年 | 163篇 |
1994年 | 151篇 |
1993年 | 161篇 |
1992年 | 69篇 |
1991年 | 62篇 |
1990年 | 75篇 |
1989年 | 87篇 |
1988年 | 76篇 |
1987年 | 56篇 |
1986年 | 46篇 |
1985年 | 56篇 |
1984年 | 51篇 |
1983年 | 35篇 |
1982年 | 36篇 |
1981年 | 50篇 |
1980年 | 36篇 |
1979年 | 21篇 |
1978年 | 40篇 |
1977年 | 56篇 |
1976年 | 113篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
实施独立计量分区(district metered area,DMA)是辅助供水管网管理和漏损识别的重要手段.图划分算法是进行DMA分区的方法之一,常规图划分算法应用中,存在解空间受限、分区后原水流状态易发生较大改变、形成较多串联分区(对流量计算不利)的缺点.在常规图划分算法基础上进行了改进:粗化阶段按照特定规则匹配、合并非输水干管两端的节点,形成简化的管网拓扑结构;分区阶段得到管网初步分区方案;细化阶段提出基于贪心算法、枚举算法、蒙特卡洛算法的分区调整方法,结合改进的仪表安置方法、水力模拟、优劣解距离法(technique for order preference by similarity to an ideal solution,TOPSIS),对分区方案进行调整.将该方法应用于YX市供水管网,成功进行了分区. 相似文献
3.
High-efficiency filtration in residential forced-air heating, ventilation, and air conditioning (HVAC) systems protects equipment and can reduce exposure to particulate matter. Laboratory tests provide a measure of the nominal efficiency, but they may not accurately reflect the in situ efficiency of the filters because of variations in system conditions and changes in filter performance over time. The primary focus of this paper is to evaluate the effective filtration efficiency, which is inclusive of any loading and system impacts, in 21 occupied residential homes through in-duct concentration measurements. We considered the role of filter media by testing both electret and non-electret media, as well as the role of loading by considering new and used filters. The results show that filters with higher nominal efficiency generally had higher effective filtration efficiency in the same home. In terms of performance change, there is no significant difference in efficiency between initial and 3-month non-electret filters, but the efficiency of electret filters generally decreased over time. However, both nominal efficiency and performance change were vastly overshadowed by the wide variety in loading and system conditions across homes, making it hard to predict filter efficiency in a given home without in situ measurements. 相似文献
4.
5.
Dr. Emilianne M. Limbrick Audrey E. Yñigez-Gutierrez Callie C. Dulin Dagmara K. Derewacz Dr. Jeffrey M. Spraggins Dr. Kathryn M. McCulloch Prof. T. M. Iverson Prof. Brian O. Bachmann 《Chembiochem : a European journal of chemical biology》2020,21(23):3349-3358
Everninomicins are orthoester oligosaccharide antibiotics with potent activity against multidrug-resistant bacterial pathogens. Everninomicins act by disrupting ribosomal assembly in a distinct region in comparison to clinically prescribed drugs. We employed microporous intergeneric conjugation with Escherichia coli to manipulate Micromonospora for targeted gene-replacement studies of multiple putative methyltransferases across the octasaccharide scaffold of everninomicin effecting the A1, C, F, and H rings. Analyses of gene-replacement and genetic complementation mutants established the mutability of the everninomicin scaffold through the generation of 12 previously unreported analogues and, together with previous results, permitted assignment of the ten methyltransferases required for everninomicin biosynthesis. The in vitro activity of A1- and H-ring-modifying methyltransferases demonstrated the ability to catalyze late-stage modification of the scaffold on an A1-ring phenol and H-ring C-4’ hydroxy moiety. Together these results establish the potential of the everninomicin scaffold for modification through mutagenesis and in vitro modification of advanced biosynthetic intermediates. 相似文献
6.
7.
David L. Wood Jeffrey D. Quass Jianlin Li Shabbir Ahmed David Ventola Claus Daniel 《Drying Technology》2018,36(2):234-244
Processing lithium-ion battery (LIB) electrode dispersions with water as the solvent during primary drying offers many advantages over N-methylpyrrolidone (NMP). An in-depth analysis of the comparative drying costs of LIB electrodes is discussed for both NMP- and water-based dispersion processing in terms of battery pack $/kWh. Electrode coating manufacturing and capital equipment cost savings are compared for water vs. conventional NMP organic solvent processing. A major finding of this work is that the total electrode manufacturing costs, whether water- or NMP-based, contribute about 8–9% of the total pack cost. However, it was found that up to a 2?×?reduction in electrode processing (drying and solvent recovery) cost can be expected along with a $3–6?M savings in associated plant capital equipment (for a plant producing 100,000 10-kWh Plug-in Hybrid Electric Vehicle (PHEV) batteries) using water as the electrode solvent. This paper shows a different perspective in that the most important benefits of aqueous electrode processing actually revolve around capital equipment savings and environmental stewardship and not processing cost savings. 相似文献
8.
9.
10.