全文获取类型
收费全文 | 3503篇 |
免费 | 35篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 15篇 |
化学工业 | 228篇 |
金属工艺 | 14篇 |
机械仪表 | 11篇 |
建筑科学 | 16篇 |
能源动力 | 14篇 |
轻工业 | 132篇 |
水利工程 | 3篇 |
石油天然气 | 7篇 |
无线电 | 49篇 |
一般工业技术 | 92篇 |
冶金工业 | 2877篇 |
原子能技术 | 13篇 |
自动化技术 | 70篇 |
出版年
2022年 | 17篇 |
2021年 | 21篇 |
2020年 | 14篇 |
2019年 | 15篇 |
2018年 | 29篇 |
2017年 | 26篇 |
2016年 | 25篇 |
2015年 | 26篇 |
2014年 | 24篇 |
2013年 | 57篇 |
2012年 | 38篇 |
2011年 | 34篇 |
2010年 | 30篇 |
2009年 | 30篇 |
2008年 | 33篇 |
2007年 | 31篇 |
2006年 | 22篇 |
2005年 | 19篇 |
2004年 | 20篇 |
2003年 | 22篇 |
2002年 | 19篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 89篇 |
1998年 | 849篇 |
1997年 | 465篇 |
1996年 | 328篇 |
1995年 | 175篇 |
1994年 | 163篇 |
1993年 | 178篇 |
1992年 | 19篇 |
1991年 | 40篇 |
1990年 | 41篇 |
1989年 | 43篇 |
1988年 | 43篇 |
1987年 | 42篇 |
1986年 | 28篇 |
1985年 | 32篇 |
1983年 | 6篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1980年 | 34篇 |
1978年 | 11篇 |
1977年 | 98篇 |
1976年 | 219篇 |
1975年 | 5篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1955年 | 4篇 |
排序方式: 共有3541条查询结果,搜索用时 31 毫秒
1.
Ricardo Beristain‐Cardoso Anne‐Claire Texier Reyes Sierra‐Álvarez Jim A Field Elías Razo‐Flores Jorge Gómez 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(9):1197-1203
BACKGROUND: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH3COO?/NO3? molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). RESULTS: Three molar ratios of CH3COO?/NO3? (0.85, 0.72 and 0.62) with a constant S2?/NO3? molar ratio of 0.13 were evaluated. At a CH3COO?/NO3? molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N2 yield (g N2 g?1 NO3?‐N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic‐C g?1 CH3COO?‐C consumed. Sulfide was partially oxidized to S0, and 71% of the S2? consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH3COO?/NO3? molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N2 and inorganic‐C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S0, with a yield of 0.92 g SO42?‐S g?1 S2? consumed. CONCLUSIONS: The CH3COO?/NO3? molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S0 or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO2, S0 and N2 as the major end products. Copyright © 2008 Society of Chemical Industry 相似文献
2.
The impact of VBR video traffic characteristics on broadband network performance is analysed. In particular, the authors compare in a queue the behaviour of several models that adjust different statistical parameters of actual MPEG traces. It is proved that a good fit of the probability density function (PDF) is essential to approximate queuing behaviour while the effects of short range dependence (SRD) are of secondary importance and those of long range dependence (LRD) could be neglected for practical purposes if realistic scenarios, with strict QoS requirements, are considered 相似文献
3.
Optical absorption and photoluminescence of Ca3(VO4)2 single crystal grown by a floating-zone technique and containing Nd3+ ions were investigated. High absorption coefficients and broadening of most absorption bands are present at 300 K, while substructures in some of the same bands can be evidenced at 12 K. Most features of measured spectra are characteristic of random occupation of more than a single Ca2+ site by the Nd3+ ion and of distortions provoked by different charge compensation mechanisms involving oxygen vacancies promotion in the crystal lattice. Nd3+ optical properties were studied by using the Judd-Ofelt theory to calculate the spectral parameters relevant for laser applications. 相似文献
4.
5.
6.
7.
8.
9.
The transitions and reactions involved in the thermal treatment of several commercial azodicarbonamides (ADC) in an inert atmosphere have been studied by dynamic thermogravimetry analysis (TGA), mass spectrometry and Fourier transform infrared (FTIR) spectroscopy. A pseudo‐mechanistic model, involving several competitive and non‐competitive reactions, has been suggested and applied to the correlation of the weight loss data. The model applied is capable of accurately representing the different processes involved, and can be of great interest in the understanding and quantification of such phenomena, including the simulation of the instantaneous amount of gases evolved in a foaming process. In addition, a brief discussion on the methodology related to the mathematical modeling of TGA data is presented, taking into account the complex thermal behaviour of the ADC. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
10.
The effects of 10 day clenbuterol administration on cardiac and skeletal muscle capillarities were studied, particularly in terms of the distribution of arteriolar and venular capillaries and their capillary density, in young (10-week-old) and middle-aged (37-week-old) male Wistar rats. Rats of the treated groups were fed a diet containing 2 mg kg-1 clenbuterol hydrochloride. In both young and middle aged rats, clenbuterol treatment increased the body wt and the weights of the heart and hindlimb muscles. The mean fibre cross-sectional area was significantly increased after the treatment in the left ventricle, soleus, plantaris and both deep and superficial portions of gastrocnemius (P < 0.01). In the left ventricle, the total capillary density and the density of venular capillaries were decreased after the treatment in both young (9 and 13%, respectively) and middle-aged rats (10 and 11%, respectively). A decrease in total capillary density was also observed in all skeletal muscles examined. In both young and middle-aged rats, the capillary-to-fibre (C:F) ratio and the proportion of each capillary did not change after the treatment in both the left ventricle and skeletal muscles. Clenbuterol significantly decreased the activity of succinate dehydrogenase in all skeletal muscles examined (P < 0.01). These results suggest that clenbuterol increased the diffusion distance for oxygen in the left ventricle and skeletal muscles. These changes may reduce the oxygen supply to tissues and increase muscle fatigability. 相似文献