全文获取类型
收费全文 | 6531篇 |
免费 | 633篇 |
国内免费 | 80篇 |
专业分类
电工技术 | 13篇 |
综合类 | 226篇 |
化学工业 | 1888篇 |
金属工艺 | 37篇 |
机械仪表 | 65篇 |
建筑科学 | 27篇 |
矿业工程 | 10篇 |
能源动力 | 46篇 |
轻工业 | 4513篇 |
水利工程 | 5篇 |
石油天然气 | 55篇 |
武器工业 | 2篇 |
无线电 | 33篇 |
一般工业技术 | 192篇 |
冶金工业 | 45篇 |
原子能技术 | 13篇 |
自动化技术 | 74篇 |
出版年
2024年 | 67篇 |
2023年 | 147篇 |
2022年 | 282篇 |
2021年 | 354篇 |
2020年 | 271篇 |
2019年 | 278篇 |
2018年 | 248篇 |
2017年 | 262篇 |
2016年 | 284篇 |
2015年 | 299篇 |
2014年 | 345篇 |
2013年 | 374篇 |
2012年 | 475篇 |
2011年 | 432篇 |
2010年 | 279篇 |
2009年 | 246篇 |
2008年 | 242篇 |
2007年 | 313篇 |
2006年 | 282篇 |
2005年 | 225篇 |
2004年 | 220篇 |
2003年 | 176篇 |
2002年 | 169篇 |
2001年 | 153篇 |
2000年 | 148篇 |
1999年 | 117篇 |
1998年 | 88篇 |
1997年 | 61篇 |
1996年 | 57篇 |
1995年 | 44篇 |
1994年 | 49篇 |
1993年 | 40篇 |
1992年 | 43篇 |
1991年 | 29篇 |
1990年 | 20篇 |
1989年 | 20篇 |
1988年 | 20篇 |
1987年 | 20篇 |
1986年 | 13篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有7244条查询结果,搜索用时 15 毫秒
91.
Yinglai Teng Elinor L. Scott Johan P. M. Sanders 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2012,87(10):1458-1465
BACKGROUND: Amino acids are promising feedstocks for the chemical industry due to their chemical functionality. They can be obtained by the hydrolysis of potentially inexpensive protein streams such as the byproduct of biofuel production. However, individual amino acids are required before they can be used for the further production of chemicals. Here, the separation of L‐aspartic acid (Asp) and L‐glutamic acid (Glu) mixture, which can be isolated from protein hydrolysis solutions at low pH or from electrodialysis of complex amino acid mixtures, was studied. RESULTS: Glu was converted into L‐pyroglutamic acid (pGlu) which can be separated from the mixture of Asp and Glu due to its higher solubility in water. The conversion was carried out under aqueous or melt conditions. Under aqueous conditions, the conversion was studied as a factor of time, temperature and the amount of Glu. The conversion was specific with high yield and not effected by Asp. After pGlu was separated from Asp and residual Glu by solubility difference, it can be transferred back to Glu through hydrolysis. CONCLUSION: The conversion of Glu to pGlu is specific and can be applied to separation Asp and Glu for their use in the production of bio‐based chemicals. Copyright © 2012 Society of Chemical Industry 相似文献
92.
Xavier Viader-Godoy Maria Manosas Felix Ritort 《International journal of molecular sciences》2021,22(9)
The accurate knowledge of the elastic properties of single-stranded DNA (ssDNA) is key to characterize the thermodynamics of molecular reactions that are studied by force spectroscopy methods where DNA is mechanically unfolded. Examples range from DNA hybridization, DNA ligand binding, DNA unwinding by helicases, etc. To date, ssDNA elasticity has been studied with different methods in molecules of varying sequence and contour length. A dispersion of results has been reported and the value of the persistence length has been found to be larger for shorter ssDNA molecules. We carried out pulling experiments with optical tweezers to characterize the elastic response of ssDNA over three orders of magnitude in length (60–14 k bases). By fitting the force-extension curves (FECs) to the Worm-Like Chain model we confirmed the above trend:the persistence length nearly doubles for the shortest molecule (60 b) with respect to the longest one (14 kb). We demonstrate that the observed trend is due to the different force regimes fitted for long and short molecules, which translates into two distinct elastic regimes at low and high forces. We interpret this behavior in terms of a force-induced sugar pucker conformational transition (C3′-endo to C2′-endo) upon pulling ssDNA. 相似文献
93.
Jiang Li Fenghui Sun Xiangzhen Li Zhiying Yan Yuexiang Yuan XiaoFeng Liu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2012,87(12):1687-1693
BACKGROUND: This work investigated the monokaryogenesis of dikaryon strains of Trametes hirsuta by protoplasts regeneration for extracellular ligninolytic enzyme production. Saccharification of corn straw was enhanced by alkali pretreatment combining crude ligninolytic enzymes. RESULTS: Effectiveness of alkali pretreatment of corn straw on delignification was evaluated under different concentrations. About 45% lignin loss was achieved at the concentration of 1.5% NaOH. In addition, 79.0% sugar yield was obtained after combined pretreatment with NaOH and crude ligninolytic enzyme produced from monokaryotic strains of Trametes hirsuta. Scanning electron microscopy (SEM) images showed that the porosity and surface area increased significantly after combined pretreatment. The FTIR spectra indicated that great intensity changes occurred at the 890–900 cm?1, 1509–1513 cm?1 and 1595 cm?1 bands. CONCLUSION: The proposed combined pretreatment removes lignin and enhances saccharification of corn straw effectively. Copyright © 2012 Society of Chemical Industry 相似文献
94.
Koreyoshi Imamura Kohshi Kinugawa Ryo Kagotani Mayo Nomura Kazuhiro Nakanishi 《Journal of food engineering》2012
Amorphous matrices made up of sugar molecules, are frequently used in food and pharmaceutical industries. A drawback to their use is that they are susceptible to collapse, as a result of water uptake and an increase in temperature and subsequently crystallize. Herein, the crystallization characteristics of amorphous sugar (sucrose and α-lactose) preparations were analyzed, with the purpose of obtaining knowledge that could lead to the prediction of how long the amorphous state is retained under various conditions. The impact of compression, physical aging and freezing rate on the induction period (tind) for crystallization were examined. Freeze-dried sugar samples were compressed at 74 or 443 MPa (5 min) and then rehumidified at specified RHs. Some freeze-dried sucrose samples were physically aged, and alternatively freeze-drying was conducted under different conditions. The isothermal crystallization of the prepared samples at different temperatures (T), the glass transition and the crystallization temperature (Tcry) were measured, using differential scanning calorimetry. The compression markedly decreased the tind, while significantly lowered the hygroscopicity. Physical aging and slower-freezing also shortened the tind. The tind was found to be correlated exclusively with (Tcry–T), regardless of rehumidification, compression, sugar type, physical aging and freezing rate in the freeze-drying process. 相似文献
95.
Nancy J. McGraw Nida Napawan Mitchell R. Toland John Schulze Barry M. Tulk Elaine S. Krul 《Journal of food science》2014,79(9):H1832-H1840
Consumption of protein hydrolysates has been proposed to stimulate muscle anabolism more than intact (nonhydrolyzed) proteins via accelerated delivery of amino acids for muscle protein synthesis (MPS). We evaluated whether the rate of amino acid uptake and transport across intestinal cells was enhanced for soy protein hydrolysates versus nonhydrolyzed soy protein. Intact and partially hydrolyzed proteins were subject to simulated gut digestion and applied to the apical surface of Caco‐2 monolayers. Basolateral media was harvested after 3 h and quantitatively analyzed for free amino acids using ion‐exchange chromatography and comparison to an included reference standard. Basolateral concentrations of all amino acids were higher (mean 32%) for hydrolyzed versus nonhydrolyzed protein with the greatest differences in histidine, lysine, and valine. Scale‐up production of the soy protein hydrolysate did not diminish its enhanced absorption properties. These data support the hypothesis that hydrolyzed soy protein may provide dietary amino acids that are more rapidly transported across the intestinal epithelium versus intact soy protein. This would be important under conditions where rapid and increased levels of amino acids are needed such as in the stimulation of MPS. 相似文献
96.
《Journal of the Institute of Brewing》2017,123(2):268-276
An infusion of tea leaves was prepared using 4 g tea/100 mL of the apple juice, ameliorated with different sugar sources, supplemented with different nitrogen sources and inoculated with 5% incola (Saccharomyces cerevisiae var. ellipsoideus , consortia 1 and consortia 2). The highest rate of fermentation and ethanol were found in the apple tea wine having sucrose as a sugar source, while apple juice concentrate as a sugar source gave the highest total phenols, caffeine content and overall acceptability. Higher alcohols, volatile acidity and antioxidant activity were the highest in honey as a sugar source. Apple tea wine having DAHP as a nitrogen source documented the highest ethanol, caffeine content and overall acceptability, lowest higher alcohols, whereas peptone as a nitrogen source had the highest total phenols. Among the different types of inocula, for most of the parameters there were non‐significant differences. However, must inoculated with S. cerevisiae var. ellipsoideus for the preparation of apple tea wine resulted in the highest fermentation efficiency, ethanol and overall acceptability but the lowest volatile acidity. Apple tea wine prepared by ameliorating the apple tea must with apple juice concentrate, DAHP and inoculated with S. cerevisiae var. ellipsoideus was rated as the best. Copyright © 2017 The Institute of Brewing & Distilling 相似文献
97.
98.
99.
100.
Vincenza Ferraro Ruben Ferreira Jorge Isabel B. Cruz Filipa Antunes Bruno Sarmento Paula M. L. Castro Manuela E. Pintado 《International Journal of Food Science & Technology》2014,49(1):27-33
This study reports on the intestinal permeability of salt‐containing mixtures of amino acids extracted from codfish salting wastewater. Permeability was evaluated in vitro using the Caco‐2 cell line model; cell integrity during exposure to mixtures of amino acids was estimated by measuring the transepithelial electrical resistance (TEER). The effect of salt (NaCl) on the permeability and on the intestinal cell's integrity was also examined. Permeation rate (i.e. transport) was ≥95% for all amino acids except for creatine, for which it was 6%. Values for apparent permeability coefficients, Papp > 10?5 cm s?1, for mixture with isotonic concentration of NaCl suggest that amino acids are very likely to be absorbed in humans. Mixture with a hypertonic level of NaCl exerts a cytotoxic effect in intestinal cells resulting in a loss of epithelium integrity. Results show that isotonic mixture of amino acids extracted from codfish salting wastewater could be used in food, feed, cosmetic and pharmaceutical formulations. These applications could contribute to the fish industry sustainability. 相似文献