全文获取类型
收费全文 | 264071篇 |
免费 | 3462篇 |
国内免费 | 902篇 |
专业分类
电工技术 | 4969篇 |
综合类 | 210篇 |
化学工业 | 37842篇 |
金属工艺 | 9746篇 |
机械仪表 | 7815篇 |
建筑科学 | 6502篇 |
矿业工程 | 903篇 |
能源动力 | 7451篇 |
轻工业 | 22509篇 |
水利工程 | 2297篇 |
石油天然气 | 3255篇 |
武器工业 | 15篇 |
无线电 | 35492篇 |
一般工业技术 | 51611篇 |
冶金工业 | 51358篇 |
原子能技术 | 5219篇 |
自动化技术 | 21241篇 |
出版年
2022年 | 1545篇 |
2021年 | 2347篇 |
2020年 | 1669篇 |
2019年 | 2074篇 |
2018年 | 3464篇 |
2017年 | 3492篇 |
2016年 | 3626篇 |
2015年 | 2348篇 |
2014年 | 4200篇 |
2013年 | 12021篇 |
2012年 | 6649篇 |
2011年 | 9077篇 |
2010年 | 7304篇 |
2009年 | 8281篇 |
2008年 | 8848篇 |
2007年 | 8713篇 |
2006年 | 7730篇 |
2005年 | 6848篇 |
2004年 | 6560篇 |
2003年 | 6818篇 |
2002年 | 6300篇 |
2001年 | 6763篇 |
2000年 | 6216篇 |
1999年 | 6675篇 |
1998年 | 17378篇 |
1997年 | 11956篇 |
1996年 | 9211篇 |
1995年 | 6923篇 |
1994年 | 6146篇 |
1993年 | 6110篇 |
1992年 | 4278篇 |
1991年 | 4151篇 |
1990年 | 3985篇 |
1989年 | 3785篇 |
1988年 | 3690篇 |
1987年 | 3115篇 |
1986年 | 3046篇 |
1985年 | 3348篇 |
1984年 | 3025篇 |
1983年 | 2917篇 |
1982年 | 2702篇 |
1981年 | 2632篇 |
1980年 | 2551篇 |
1979年 | 2389篇 |
1978年 | 2153篇 |
1977年 | 2710篇 |
1976年 | 3718篇 |
1975年 | 1814篇 |
1974年 | 1769篇 |
1973年 | 1722篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
41.
Diffusional limitations (the gel, glass, and cage effects) are manifested in several bulk free radical homopolymerizations as well as in random copolymerizations. These are associated with decreases of several orders of magnitude of the rate constants of termination, propagation, and initiation (the initiator efficiency), respectively. These phenomena have been modeled earlier using the free volume theory for the diffusivities of primary radicals, macro‐radicals, and monomer molecules, and have been applied to homopolymerizations. In this study, a similar model is developed for random bulk copolymerizations. The parameters of the model are fitted using isothermal data on styrene acrylonitrile random copolymerization carried out in small ampoules. Thereafter, best‐fit global correlations have been developed for this system. This enables the model to be used for studying non‐isothermal copolymerizations, as well as for carrying out optimization of industrial reactors, where non‐isothermal conditions are a norm. POLYM. ENG. SCI., 55:2098–2110, 2015. © 2014 Society of Plastics Engineers 相似文献
42.
Klaus Reinhardt Hans Georg Breunig Aisada Uchugonova Karsten K?nig 《Journal of the Royal Society Interface》2015,12(110)
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype. 相似文献
43.
44.
45.
46.
47.
48.
This work investigates the performance of the inverted-T (IT) junctionless (JL) FinFET with selective buried oxide (SELBOX) topology. The electrical charac 相似文献
49.
50.