全文获取类型
收费全文 | 23197篇 |
免费 | 785篇 |
国内免费 | 612篇 |
专业分类
电工技术 | 478篇 |
技术理论 | 1篇 |
综合类 | 878篇 |
化学工业 | 4668篇 |
金属工艺 | 3949篇 |
机械仪表 | 662篇 |
建筑科学 | 259篇 |
矿业工程 | 208篇 |
能源动力 | 274篇 |
轻工业 | 1410篇 |
水利工程 | 101篇 |
石油天然气 | 165篇 |
武器工业 | 141篇 |
无线电 | 1439篇 |
一般工业技术 | 5850篇 |
冶金工业 | 664篇 |
原子能技术 | 154篇 |
自动化技术 | 3293篇 |
出版年
2024年 | 30篇 |
2023年 | 188篇 |
2022年 | 472篇 |
2021年 | 558篇 |
2020年 | 341篇 |
2019年 | 321篇 |
2018年 | 331篇 |
2017年 | 446篇 |
2016年 | 777篇 |
2015年 | 1450篇 |
2014年 | 1495篇 |
2013年 | 1310篇 |
2012年 | 1284篇 |
2011年 | 2238篇 |
2010年 | 1944篇 |
2009年 | 1853篇 |
2008年 | 1633篇 |
2007年 | 1587篇 |
2006年 | 1070篇 |
2005年 | 1035篇 |
2004年 | 921篇 |
2003年 | 905篇 |
2002年 | 809篇 |
2001年 | 330篇 |
2000年 | 251篇 |
1999年 | 233篇 |
1998年 | 184篇 |
1997年 | 137篇 |
1996年 | 111篇 |
1995年 | 62篇 |
1994年 | 66篇 |
1993年 | 33篇 |
1992年 | 34篇 |
1991年 | 15篇 |
1990年 | 24篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1974年 | 5篇 |
1964年 | 1篇 |
1959年 | 1篇 |
1958年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Xue Ren Tiantian Tang Xinfang Xie Wenjun Wang Xuanming Tang Charles S. Brennan Jie Zhang Zhidong Wang 《International Journal of Food Science & Technology》2020,55(11):3475-3483
The effect of a traditional dish sour and spicy potato silk preparation and cooking process on B vitamins, phenolic profiles and antioxidant activities was investigated. Results showed that cutting of potato caused an increase in VB1, VB2, nicotinic acid, nicotinamide, VB7 and VB9. Soaking decreased the content of B vitamins and vitamin C. Blanching and rinsing caused the contents of B vitamins and vitamin C decrease compared to the control. The content of VB1, VB5 and VB6 after rinsing increased compared to soaking and blanching processes. However, VB1, nicotinamide, VB5, VB6 and VC decreased sharply after the stir-frying process. The content of VB1, nicotinic acid, nicotinamide, VB7 and VC retained the most after five steps compared to the control. In addition, there was no difference in VB9 contents among different cooking processes compared to the control. Superoxide dismutase (SOD) exhibited a reduction rate of 95.32% and peroxidase (POD) 97.13% after the stir-frying process. 相似文献
982.
《International Journal of Hydrogen Energy》2019,44(34):18866-18874
A new Cu(I)-exchange method for zeolites in liquid media (acetonitrile) was developed with Cu/Al ratios surpassing 0.5 with ZSM-5 crystals containing pure Cu(I) cations without impurities such as Cl ions. The method resulted in a higher Cu/Al ratio (0.78) for mesoporous [B]-ZSM-5 when compared to microporous [Al]-ZSM-5 and [B]-ZSM-5 (0.55 and 0.66 respectively). H2 storage capacities of these Cu(I)-exchanged zeolites were investigated at 323 K along with their differential heat of H2 adsorption using adsorption calorimetry. H2 storage capacities as high as 0.03 wt. % at 323 K and 40 kPa were achieved on [Al] and [B]-ZSM-5 and mesoporous [B]-ZSM-5 showed an outstanding H2/Cu ratio of 1.03 at 323 K and below 100 kPa. Coverage-dependent differential adsorption heats were found to be ranging from 95 kJ/mol to 5 kJ/mol with observed values of 30–10 kJ/mol for H2/Cu ratios between 0.05 and 0.15. 相似文献
983.
《International Journal of Hydrogen Energy》2019,44(50):27421-27428
Electrochemical water splitting to hydrogen is considered as a promising approach for clean H2 production. However, developing highly active and inexpensive electrocatalysts is an important part of the hydrogen evolution reaction (HER). Herein, we present a multifaceted atom (sp2-and sp-hybridized boron) doping strategy to directly fine-modify the electronic structures of the active site and the HER performance by the density functional theory calculations. It is found that the binding strength between the Co atom and the B doped graphyne nanosheets can be enhanced by doping B atoms. Meanwhile, the Co@B1-GY and Co@B2-GY catalysts exhibit good thermodynamic stability and high HER catalytic activity. Interestingly, the Co@B2-GY catalyst has an ideal HER performance with the ΔGH* value of −0.004 eV. Moreover, the d-band center of the Co atoms is upshifted by the sp2-or sp-hybridized B dopants. The concentrations of the sp-hybridized B atoms have a positive effect on the electrons transformation of the Co atoms. The interaction between the H and Co atoms becomes strong with the increase of the concentrations of the sp-hybridized B atoms and thus the corresponding catalysts show sluggish HER kinetics. This investigation could provide useful guidance for the experimental groups to directly and continuously control the catalytic activity towards HER by precisely doping multifaceted atoms. 相似文献
984.
We fulfill a comprehensive study based on density functional theory (DFT) computations to cast insight into the dissociation mechanism of hydrogen molecule on pristine, B‐, and N‐doped penta‐graphene. The doping effect has been also illustrated by varying the concentration of dopant from 4.2 at% (one doping atom in 24 host atoms) to 8.3 at% (two doping atoms in 24 host atoms) and by contemplating different doping sites. Our theoretical investigation shows that the adsorption energy of H2 molecule and H atom on the substrate can be substantially enhanced by incorporating boron or nitrogen into penta‐graphene sheet. The B‐ and N‐doped penta‐graphene can effectively decompose H2 molecule into two H atoms. Our results demonstrate that activation energies for H2 dissociation and H diffusion on the B‐ and N‐doped penta‐graphene are much smaller than the pristine penta‐graphene. Further investigation of increasing concentration dopants of the penta‐graphene sheet gives sufficiently low activation barrier for H2 dissociation process. This investigation reveals that the boron and nitrogen dopants can act as effective active site for H2 dissociation and storage. 相似文献
985.
986.
987.
Polyacrylonitrile (PAN) nanofiber and silica aerogel (SAG) laminated composites were prepared via electrospinning for thermal insulation. Conventional single nozzle and co-axial electrospinning were used to increase the fraction of aerogel particles in the composite sheets while maintaining the mechanical strength of the sheet. When the core-shell electrospinning technique with co-axial nozzle was applied, the proportion of aerogel particles increased two fold without a deterioration of the mechanical properties. The average thermal conductivity of the laminated composite sheet was reduced by approximately 12.5% as compared to the nanofiber composite prepared using the single-nozzle electrospinning technique. For additional reduction in thermal conductivity, hollow glass microspheres (HGM) was inserted between the interlayer spacing of the electrospun sheets to increase the interlayer spacing. When HGM particles were inserted, it was observed that the thermal conductivity decreased by approximately 20% compared to that of the specimen without particles. 相似文献
988.
989.
Toby J. Holda Lars G. Rudstam Kelly L. Bowen Brian C. Weidel James M. Watkins Patrick J. Sullivan Jeremy P. Holden Michael J. Connerton 《Journal of Great Lakes research》2019,45(2):307-316
Mysis diluviana is a major component of prey fish diets in the Great Lakes, so annual production of M. diluviana is important for understanding and modeling energy flow through Great Lakes food webs. However, only three lake-wide measurements of M. diluviana annual production in Lake Ontario are currently available (1971, 1990, 1995). During 2013, lake-wide coverage of Lake Ontario was achieved during four periods from April to November. Annual mean density and biomass of M. diluviana in 2013 were 99?#/m2 (SE: 8) and 318?mg?dw/m2 (SE: 28) – approximately half of values observed in 1990s. M. diluviana comprised 13–30% of offshore zooplankton biomass in each period. Reproduction peaked in fall, with mean brood size of 32 embryos (range: 11–49), at least 10% larger than in 1990s. Generation time was two years from embryo to initial reproduction. Growth rates were 0.052?mm/d for the age-0 cohort and 0.027?mm/d for the age-1 cohort. Age-0 growth rate was significantly higher than in 1980s–90s (0.035?mm/d). Annual production in 2013 was 0.85?g?dw/m2/yr (SE: 0.03) which was 30–40% of values observed in 1990 and 1995 (2.23 and 2.53?g/m2/yr). Annual production to biomass ratio (P/B) in 2013 was 2.65?/yr which was 80–85% of values observed in 1990 and 1995 (3.24 and 3.11?/yr), but this difference was not statistically significant. Our results suggest that changes in annual production over time can be estimated using changes in biomass over time and a mean P/B ratio. 相似文献
990.
Physicochemical Properties,Fatty Acid Profiles,and Sensory Characteristics of Fermented Beef Sausage by Probiotics Lactobacillus plantarum IIA‐2C12 or Lactobacillus acidophilus IIA‐2B4 下载免费PDF全文
Irma Isnafia Arief Dyah Nurul Afiyah Zakiah Wulandari Cahyo Budiman 《Journal of food science》2016,81(11):M2761-M2769
Probiotics may be used to enhance the functionality and nutritional values of fermented sausages. This study aims to evaluate the physicochemical and sensory properties of beef sausages fermented by lactic acid bacteria of Lactobacillus plantarum IIA‐2C12 and L. acidophilus IIA‐2B4. These strains were isolated from beef cattle and have shown to display probiotic features. While the nutrient contents were not affected by the probiotics, the pH, texture, and color varied among the sausages. Further analysis on fatty acids showed different profiles of saturated (C14:0, C17:0, and C20:0) and unsaturated (C14:1, C18:1n9c, C18:2n6c, and C22:6n3) fatty acids in sausages with probiotics. Gas chromatography–mass spectrometry further revealed some flavor development compounds including acid, alcohols, aldehydes, aromatic, ketones, sulfur, hydrocarbons and terpenes, varied among the sausages. Hedonic test showed no difference in the preference toward aroma, texture, and color for untrained panelists. 相似文献