全文获取类型
收费全文 | 381719篇 |
免费 | 6122篇 |
国内免费 | 1376篇 |
专业分类
电工技术 | 7488篇 |
综合类 | 393篇 |
化学工业 | 58327篇 |
金属工艺 | 14314篇 |
机械仪表 | 12538篇 |
建筑科学 | 9084篇 |
矿业工程 | 1148篇 |
能源动力 | 10059篇 |
轻工业 | 33451篇 |
水利工程 | 2853篇 |
石油天然气 | 3609篇 |
武器工业 | 13篇 |
无线电 | 53151篇 |
一般工业技术 | 71905篇 |
冶金工业 | 72075篇 |
原子能技术 | 6054篇 |
自动化技术 | 32755篇 |
出版年
2021年 | 3310篇 |
2020年 | 2357篇 |
2019年 | 2969篇 |
2018年 | 4323篇 |
2017年 | 4389篇 |
2016年 | 4836篇 |
2015年 | 3681篇 |
2014年 | 6096篇 |
2013年 | 16991篇 |
2012年 | 10144篇 |
2011年 | 13687篇 |
2010年 | 10781篇 |
2009年 | 12237篇 |
2008年 | 12723篇 |
2007年 | 12504篇 |
2006年 | 11263篇 |
2005年 | 10458篇 |
2004年 | 10195篇 |
2003年 | 9902篇 |
2002年 | 9658篇 |
2001年 | 9708篇 |
2000年 | 9049篇 |
1999年 | 9589篇 |
1998年 | 23321篇 |
1997年 | 16131篇 |
1996年 | 12859篇 |
1995年 | 9777篇 |
1994年 | 8553篇 |
1993年 | 8386篇 |
1992年 | 6184篇 |
1991年 | 5999篇 |
1990年 | 5797篇 |
1989年 | 5668篇 |
1988年 | 5214篇 |
1987年 | 4405篇 |
1986年 | 4409篇 |
1985年 | 5072篇 |
1984年 | 4538篇 |
1983年 | 4171篇 |
1982年 | 3910篇 |
1981年 | 3960篇 |
1980年 | 3570篇 |
1979年 | 3459篇 |
1978年 | 3369篇 |
1977年 | 4043篇 |
1976年 | 5250篇 |
1975年 | 2934篇 |
1974年 | 2732篇 |
1973年 | 2714篇 |
1972年 | 2251篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
22.
Honour Index (HoI), a method to evaluate research performance within different research fields, was derived from the impact
factor (IF). It can be used to rate and compare different categories of journals. HoI was used in this study to determine
the scientific productivity of stem cell research in the Asian Four Dragons (Hong Kong, Singapore, South Korea and Taiwan)
from 1981 to 2001. The methodology applied in this study represents a synthesis of universal indicator studies and bibliometric
analyses of subfields at the micro-level. We discuss several comparisons, and conclude the developmental trend in stem cell
research for two decades.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
23.
The objective of this study was to compare methane production and characteristics of digested material in anaerobic digestion concepts according to the Animal By-Products Regulation (ABP-Regulation) of the EC (hygienisation of biowaste for 1 hour at 70 degrees C, particle size < 12 mm) and Finnish national regulations (treatment temperature 55 degrees C, feeding interval 24 h, hydraulic retention time (HRT) 20 d, particle size < 40 mm) and with small variations in treatment methods for treating manure and biowaste. Moreover, the survival of three different salmonella bacteria in these processes was studied. Hygienisation of biowaste prior to digestion at 35 degrees C enhanced methane production by 14-18% compared to similar treatment without hygienisation. The differences in treatment temperature, HRT and hygienisation of biowaste prior to digestion did not significantly affect the characteristics of digested material. The concepts according to the ABP-Regulation and Finnish national regulations were effective in destroying salmonella bacteria to an undetectable level. 相似文献
24.
Y Terashima H Ozaki R R Giri T Tano S Nakatsuji R Takanami S Taniguchi 《Water science and technology》2006,54(8):55-63
Environmental pollution by low concentrations of 2,4-Dichlorophenoxyacetic acid (2,4-D) is a concern these days due to ever increasingly stringent regulations. Photocatalysis with immobilized TiO2 fiber is a promising oxidation method. Laboratory experiments on photocatalytic degradation of 0.045 mmol l(-1) 2,4-D with the world's first high-strength TiO2 fiber catalyst were carried out in a continuous flow reactor in which the degradations were, in general, similar to those with high 2,4-D concentrations investigated elsewhere. Degradation and mineralization of 2,4-D were significantly enhanced with no initial pH adjustments. The rate constants for total organic carbon (TOC) without pH adjustment were about two-fold bigger than the pH adjustment cases. CO2 gas measurement and carbon mass-balance were carried out for the first time, where about 34% organic carbon converted into CO2 gas during four-hour oxidation. 2,4-Dichlorophenol (2,4-DCP), phenol, benzyl alcohol and two unknowns (RT = 2.65 and 3.78 min.) were detected as aromatic intermediates while Phenol was the new aromatic in HPLC analysis. Dechlorination efficiencies were high (> 70%) in all the cases, and more than 90% efficiencies were observed in chloride mass balance. Bigger flow rates and solution temperature fixed at 20 degrees C without pH adjustment greatly enhanced 2,4-D mineralization. These results can be an important basis in applying the treatment method for dioxin-contaminated water and wastewater. 相似文献
25.
26.
27.
28.
Jaehoon Lee Seongha Kim Yonghoon Kim Yunje Oh Seongtaek Hwang Jichai Jeong 《Lightwave Technology, Journal of》2003,21(2):521-527
Optically preamplified receiver performance according to the vestigial sideband (VSB) filtering has been numerically investigated for 40-Gb/s optical signals modulated with nonreturn-to-zero, duobinary nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed RZ, and duobinary carrier-suppressed RZ formats. The VSB filtering enables the spectral widths of NRZ, duobinary NRZ, and RZ signals to be reduced without severe power penalties at the receiver. On the other hand, carrier-suppressed RZ and duobinary carrier-suppressed RZ signals have no large advantages over VSB filtering because of the characteristics of their signals. Our results suggest that RZ signals are the most suitable modulation format for VSB filtering, without considering the filter loss, because of the tolerance of the intersymbol interference and a large spectral width. However, duobinary NRZ signals are the most suitable modulation format for VSB filtering, considering the filter loss, because of their narrow spectral width. 相似文献
29.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture. 相似文献
30.