全文获取类型
收费全文 | 22008篇 |
免费 | 1820篇 |
国内免费 | 842篇 |
专业分类
电工技术 | 5623篇 |
技术理论 | 4篇 |
综合类 | 2416篇 |
化学工业 | 2928篇 |
金属工艺 | 406篇 |
机械仪表 | 636篇 |
建筑科学 | 2459篇 |
矿业工程 | 1070篇 |
能源动力 | 1373篇 |
轻工业 | 963篇 |
水利工程 | 779篇 |
石油天然气 | 806篇 |
武器工业 | 54篇 |
无线电 | 1203篇 |
一般工业技术 | 834篇 |
冶金工业 | 1090篇 |
原子能技术 | 47篇 |
自动化技术 | 1979篇 |
出版年
2024年 | 40篇 |
2023年 | 211篇 |
2022年 | 432篇 |
2021年 | 575篇 |
2020年 | 658篇 |
2019年 | 488篇 |
2018年 | 443篇 |
2017年 | 508篇 |
2016年 | 620篇 |
2015年 | 546篇 |
2014年 | 1202篇 |
2013年 | 942篇 |
2012年 | 1313篇 |
2011年 | 1378篇 |
2010年 | 1201篇 |
2009年 | 1351篇 |
2008年 | 1272篇 |
2007年 | 1710篇 |
2006年 | 1532篇 |
2005年 | 1383篇 |
2004年 | 1321篇 |
2003年 | 1304篇 |
2002年 | 1020篇 |
2001年 | 840篇 |
2000年 | 669篇 |
1999年 | 428篇 |
1998年 | 301篇 |
1997年 | 252篇 |
1996年 | 168篇 |
1995年 | 148篇 |
1994年 | 141篇 |
1993年 | 82篇 |
1992年 | 53篇 |
1991年 | 36篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1976年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
1.
2.
Clive Bell 《Papers in Regional Science》2022,101(2):373-397
The effects of a rural roads programme depend on labour mobility, how the programme is financed, and agglomeration economies. If financed by a rural poll tax and cross-price effects and agglomeration economies are sufficiently small, the wage will rise, with some return migration. Taxes on trade act as countervailing distortions, yielding urban households some relief. Rural-urban commuting promotes the exploitation of agglomeration economies; taxes on international trade are then inferior to a poll tax. The change in the value, at producer prices, of the rural sector's net supply vector can be a poor measure of the programme's social profitability. 相似文献
3.
Khaled Al-Farhany Mohammed A. Alomari Ahmed Al-Saadi Ali Chamkha Hakan F. Öztop Wael Al-Kouz 《亚洲传热研究》2022,51(2):1691-1710
In the current work, numerical simulations are achieved to study the properties and the characteristics of fluid flow and heat transfer of (Cu–water) nanofluid under the magnetohydrodynamic effects in a horizontal rectangular canal with an open trapezoidal enclosure and an elliptical obstacle. The cavity lower wall is grooved and represents the heat source while the obstacle represents a stationary cold wall. On the other hand, the rest of the walls are considered adiabatic. The governing equations for this investigation are formulated, nondimensionalized, and then solved by Galerkin finite element approach. The numerical findings were examined across a wide range of Richardson number (0.1 ≤ Ri ≤ 10), Reynolds number (1 ≤ Re ≤ 125), Hartmann number (0 ≤ Ha ≤ 100), and volume fraction of nanofluid (0 ≤ φ ≤ 0.05). The current study's findings demonstrate that the flow strength increases inversely as the Reynolds number rises, which pushes the isotherms down to the lower part of the trapezoidal cavity. The Nuavg rises as the Ri rise, the maximum Nuavg = 10.345 at Ri = 10, Re = 50, ϕ = 0.05, and Ha = 0; however, it reduces with increasing Hartmann number. Also, it increase by increasing ϕ, at Ri = 10, the Nuavg increased by 8.44% when the volume fraction of nanofluid increased from (ϕ = 0–0.05). 相似文献
4.
Saray Tabak Sofia Schreiber-Avissar Elie Beit-Yannai 《International journal of molecular sciences》2021,22(5)
Reactive oxygen species (ROS) plays a key role in the pathogenesis of primary open-angle glaucoma (POAG), a chronic neurodegenerative disease that damages the trabecular meshwork (TM) cells, inducing apoptosis of the retinal ganglion cells (RGC), deteriorating the optic nerve head, and leading to blindness. Aqueous humor (AH) outflow resistance and intraocular pressure (IOP) elevation contribute to disease progression. Nevertheless, despite the existence of pharmacological and surgical treatments, there is room for the development of additional treatment approaches. The following review is aimed at investigating the role of different microRNAs (miRNAs) in the expression of genes and proteins involved in the regulation of inflammatory and degenerative processes, focusing on the delicate balance of synthesis and deposition of extracellular matrix (ECM) regulated by chronic oxidative stress in POAG related tissues. The neutralizing activity of a couple of miRNAs was described, suggesting effective downregulation of pro-inflammatory and pro-fibrotic signaling pathways, including nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB), transforming growth factor-beta 2 (TGF-β2), Wnt/β-Catenin, and PI3K/AKT. In addition, with regards to the elevated IOP in many POAG patients due to increased outflow resistance, Collagen type I degradation was stimulated by some miRNAs and prevented ECM deposition in TM cells. Mitochondrial dysfunction as a consequence of oxidative stress was suppressed following exposure to different miRNAs. In contrast, increased oxidative damage by inhibiting the mTOR signaling pathway was described as part of the action of selected miRNAs. Summarizing, specific miRNAs may be promising therapeutic targets for lowering or preventing oxidative stress injury in POAG patients. 相似文献
5.
Dr. Ying Wang Prof. Dr. Andrew Ewing 《Chembiochem : a European journal of chemical biology》2021,22(5):807-813
Exocytosis plays an essential role in the communication between cells in the nervous system. Understanding the regulation of neurotransmitter release during exocytosis and the amount of neurotransmitter content that is stored in vesicles is of importance, as it provides fundamental insights to understand how the brain works and how neurons elicit a certain behavior. In this minireview, we summarize recent progress in amperometric measurements for monitoring exocytosis in single cells and electrochemical cytometry measurements of vesicular neurotransmitter content in individual vesicles. Important steps have increased our understanding of the different mechanisms of exocytosis. Increasing evidence is firmly establishing that partial release is the primary mechanism of release in multiple cell types. 相似文献
6.
In collaborative crowdsourcing communities for open innovation, users generate and submit ideas as idea co‐creators. Firms then select and implement valuable ideas for new product development. Despite the popularity and success of these open innovation communities, relatively little is known about the factors that determine the implementation of the user‐generated ideas. Based on research on individual creativity, we propose a conceptual model integrating users' previous experience, idea presentation characteristics and feedback valence to explain the likelihood of idea implementation. We validate our research model with a panel data analysis of 43 550 ideas submitted by 16 360 users in the MIUI new product development community hosted by Xiaomi, a large electronics manufacturing company in China. We find an inverted U‐shaped relationship between users' past successful experience and idea implementation. Furthermore, the length of ideas is positively associated with the likelihood of idea implementation. There is also an inverted U‐shaped relationship between supporting evidence and idea implementation. Finally, we demonstrate the negative effect of positive feedback and the positive effect of negative feedback on idea implementation. These findings offer rich insights to understand the phenomenon of open innovation better. Theoretical and practical implications are discussed. 相似文献
7.
《Oil and Energy Trends》2020,45(6):23-24
Current data on net electricity production, as well as a breakdown of production by country. Updated on a monthly basis. 相似文献
8.
2019年天然橡胶期货市场起起落落,沪胶价格继续低位震荡。2020年天然橡胶供大于求的局面仍不会发生根本性改变,由极端天气引发的天然橡胶市场行情变动可能会减小,汽车行业可能会在政策支持下再次振兴,尤其重型卡车市场会成为亮点,轮胎企业继续寻求扩大出口。2020年上半年,天然橡胶期货市场可能还会受到2019年异常天气和病害等的余波作用,胶价会达到一个相对的高点,价格底部抬升,但很难出现持续性上涨的市场行情。2020年下半年,随着天然橡胶产量的季节性增长,胶价可能会再次回落。 相似文献
9.
《Oil and Energy Trends》2020,45(12):23-24
Current data on net electricity production, as well as a breakdown of production by country. Updated on a monthly basis. 相似文献
10.