全文获取类型
收费全文 | 519篇 |
免费 | 20篇 |
国内免费 | 14篇 |
专业分类
化学 | 479篇 |
综合类 | 33篇 |
数学 | 12篇 |
物理学 | 29篇 |
出版年
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 44篇 |
2020年 | 16篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 11篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 8篇 |
2012年 | 18篇 |
2011年 | 9篇 |
2010年 | 11篇 |
2009年 | 12篇 |
2008年 | 31篇 |
2007年 | 20篇 |
2006年 | 24篇 |
2005年 | 27篇 |
2004年 | 31篇 |
2003年 | 18篇 |
2002年 | 30篇 |
2001年 | 16篇 |
2000年 | 19篇 |
1999年 | 14篇 |
1998年 | 21篇 |
1997年 | 15篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有553条查询结果,搜索用时 21 毫秒
121.
Experimental results are presented for continuous conversion of pretreated hardwood flour to ethanol. A simultaneous saccharification
and fermentation (SSF) system comprised ofTrichoderma reesei cellulase supplemented with additional β-glucosidase and fermentation bySaccharomyces cerevisiae was used for most experiments, with data also presented for a direct microbial conversion (DMC) system comprised ofClostridium thermocellum. Using a batch SSF system, dilute acid pretreatment of mixed hardwood at short residence time(10 s, 220°C, 1% H2SO4) was compared to poplar wood pretreated at longer residence time (20 min, 160°C, 0.45% H2SO4). The short residence time pretreatment resulted in a somewhat (10–20%) more reactive substrate, with the reactivity difference
particularly notable at low enzyme loadings and/or low agitation. Based on a preliminary screening, inhibition of SSF by byproducts
of short residence time pretreatment was measurable, but minor. Both SSF and DMC were carried out successfully in well-mixed
continuous systems, with steady-state data obtained at residence times of 0.58–3 d for SSF as well as 0.5 and 0.75 d for DMC.
The SSF system achieved substrate conversions varying from 31% at a 0.58-d residence time to 86% at a 2-d residence time.
At comparable substrate concentrations (4–5 g/l) and residence times (0.5–0.58 d), substrate conversion in the DMC system
(77%) was significantly higher than that in the SSF system (31%). Our results suggest that the substrate conversion in SSF
carried out in CSTR is relatively insensitive to enzyme loading in the range 7–25 U/g cellulose and to substrate concentration
in the range of 5–60 g/L cellulose in the feed. 相似文献
122.
Pretreatment of yellow poplar sawdust by pressure cooking in water 总被引:11,自引:0,他引:11
Joe Weil Ayda Sarikaya Shiang-Lan Rau Joan Goetz Christine M. Ladisch Mark Brewer Rick Hendrickson Michael R. Ladisch 《Applied biochemistry and biotechnology》1997,68(1-2):21-40
The pretreatment of yellow poplar wood sawdust using liquid water at temperatures above 220°C enhances enzyme hydrolysis.
This paper reviews our prior research and describes the laboratory reactor system currently in use for cooking wood sawdust
at temperatures ranging from 220 to 260°C. The wood sawdust at a 6–6.6% solid/liquid slurry was treated in a 2 L, 304 SS,
Parr reactor with three turbine propeller agitators and a proportional integral derivative (PID) controller, which controlled
temperature within ±1°C. Heat-up times to the final temperatures of 220, 240, or 260°C were achieved in 60–70 min. Hold time
at the final temperature was less than 1 min. A serpentine cooling coil, through which tap water was circulated at the completion
of the run, cooled the reactor’s contents within 3 min after the maximum temperature was attained. A bottoms port, as well
as ports in the reactor’s head plate, facilitated sampling of the slurry and measuring the pH, which changes from an initial
value of 5 before cooking to a value of approx 3 after cooking. Enzyme hydrolysis gave 80–90% conversion of cellulose in the
pretreated wood to glucose. Simultaneous saccharification and fermentation of washed, pretreated lignocellulose gave an ethanol
yield that was 55% of theoretical. Untreated wood sawdust gave less than 5% hydrolysis under the same conditions. 相似文献
123.
Production of fuel ethanol from rye and triticale by very-high-gravity (VHG) fermentation 总被引:1,自引:0,他引:1
S. Wang K. C. Thomas W. M. Ingledew K. Sosulski F. W. Sosulski 《Applied biochemistry and biotechnology》1998,69(3):157-175
Very-high-gravity (VHG) rye and triticale mashes, containing about 28.5 g dissolved solids/100 mL of mash supernatant, were
prepared by adjusting water:grain ratios to 2:1. Because of high viscosity, which develops during mashing, it was necessary
to pretreat ground rye-water slurries with viscosity-reducing enzymes. There were no viscosity problems during the preparation
of triticale mashes. Fermentations were conducted at 20°C, with and without 16 mM urea as a nitrogenous supplement. All fermentations
were completed within 120–144 h. Supplementation with urea shortened the times required for completion of fermentation by
33% for triticale and by 40% for rye. The fermentation efficiencies for both grains ranged between 90 and 93%. These values
are comparable to those reported for wheat, implying competitiveness of rye and triticale as fermentation feedstocks to replace
wheat. The final ethanol yields were 409 L for rye and 417–435 L for triticale/t (dry basis). For a given size of fermentation
vessel, 33% more grain was used in the VHG fermentation process than in normal gravity fermentation. This resulted in a 35–56%
increase in ethanol concentration in the beer, when fermentors were filled to a constant volume. The corresponding reduction
in water use by about one-third would result in savings in energy consumption in mash heating, mash cooling, and ethanol distillation.
Fermentation efficiencies and final ethanol yields obtained per unit weight of grain fermented were not significantly different
from the normal gravity fermentations. 相似文献
124.
Candida pseudotropicalis ATCC 8619 was selected among nine strains of lactose fermenting yeast for the production of ethanol from cheese whey. The
effects of three nutrients (ammonium sulfate (NH4)2SO4, dipotassium hydrogen phosphate K2HPO4, yeast extract, and a combination of them) on the ethanol yield from cheese whey were investigated. The results indicated
that no addition of nutrient supplement is necessary to achieve complete lactose utilization during the cheese whey ethanol
fermentation. However, addition of a small concentration (0.005% w/v) of these supplements reduced the lag period and the
total fermentation time and increased the specific growth rate of the yeast. Higher concentrations (0.01 and 0.015% w/v) of
ammonium sulfate and dipotassium hydrogen phosphate inhibited the cell growth and reduced lactose consumption. The highest
ethanol (21.17 g/L) was achieved using yeast extract at a concentration of 0.01% w/v, given a conversion efficiency of 98.3%.
No indication of alcohol inhibition was observed in this study. 相似文献
125.
Fumihisa Kobayashi Tatsuro Sawada Yoshitoshi Nakamura Makoto Ohnaga Mutui Godliving Tomoo Ushiyama 《Applied biochemistry and biotechnology》1998,69(3):177-189
Steam explosion pretreatment of potato for the efficient production of alcohol was experimentally studied. The amount of water-soluble
starch increased with the increase of steam pressure, but the amounts of methanol-soluble material and Klason lignin remained
insignificant, regardless of steam pressure. The potatoes exploded at high pressure were hydrolyzed into a low molecular liquid
starch, and then easily converted into ethanol by simultaneous saccharification and fermentation using mixed microorganisms:
an amylolytic microorganism,Aspergillus awamori, and a fermentation microorganism,Saccharomyces cerevisiae. The maximal ethanol concentration was 4.2 g/L in a batch culture at 15 g/L starch concentration, and 3.6 g/L in a continuous
culture fed the same starch concentration. In the fed-batch culture, the maximal ethanol concentration increased more than
twofold, compared to the batch culture. 相似文献
126.
Vandenberghe LP Soccol CR Prado FC Pandey A 《Applied biochemistry and biotechnology》2004,118(1-3):293-303
Studies were conducted to evaluate citric acid production by solid-state fermentation (SSF) using cassava bagasse as substrate
employing a fungal culture of Aspergillus niger LPB 21 at laboratory and semipilot scale. Optimization of the process parameters temperature, pH, initial humidity, aeration,
and nutritive composition was conducted in flasks and column fermentors. The results showed that thermal treatment of cassava
bagasse enhanced fungal fermentation efficacy, resulting in 220 g of citric acid/kg of dry cassava bagasse with only treated
cassava bagasse as substrate. The results obtained from the factorial experimental design in a column bioreactor showed that
an aeration rate of 60 mL/min (3 mL/[g·min]) and 60% initial humidity were optimum, resulting in 265.7 g/kg of dry cassava
bagasse citric acid production. This was almost 1.6 times higher than the quantities produced under unoptimized conditions
(167.4 g of citric acid/kg of dry cassava bagasse). The defined parameters were transferred to semipilot scale, which showed
high promise for large-scale citric acid production by SSF with cassava bagasse. Respirometry assays were carried out in order
to follow indirectly the biomass evolution of the process. Citric acid production reached 220, 309, 263, and 269 g/kg of dry
cassava bagasse in Erlenmeyer flasks, column fermentors, a tray bioreactor, and a horizontal drum bioreactor, respectively. 相似文献
127.
128.
Cao Ning-Jun Tang Rentian Gong C. S. Chen L. F. 《Applied biochemistry and biotechnology》1994,(1):515-519
The rate of xylitol production from D-xylose increased with increasing yeast cell density. The optimal temperature for xylitol
production is 36‡ C, and the optimal pH range is from 4.0 to 6.0. At high initial yeast cell concentration of 26 mg/mL, 210
g/L of xylitol was produced from 260 g/L of D-xylose after 96 h of incubation with an indicated yield of 81% of the theoretical
value. 相似文献
129.
Arabinose utilization by xylose-fermenting yeasts and fungi 总被引:1,自引:0,他引:1
Various wild-type yeasts and fungi were screened to evaluate their ability to fermentl-arabinose under oxygen-limited conditions when grown in defined minimal media containing mixtures ofl-ara-binose,d-xylose, andd-glucose. Although all of the yeasts and some of the fungi consumed arabinose, arabinose was not fermented to ethanol by any
of the strains tested. Arabitol was the only major product other than cell mass formed froml-arabinose; yeasts converted arabinose to arabitol at high yield. The inability to fermentl-arabinose appears to be a consequence of inefficient or incomplete assimilation pathways for this pentose sugar. 相似文献
130.
Keller Fcred A. Bates Delicia Ruiz Ray Nguyen Quang 《Applied biochemistry and biotechnology》1998,(1):137-148
Several strains and genera of yeast, includingSaccharomyces cerevisiae D5A,Pachysolen tannophilus, S. cerevisiae K-l,Brettanomyces custersii, Candida shehatae, andCandida acidothermophilum, are screened for growth on dilute acid-pretreated softwood prehydrolysate. Selected softwood species found in forest underbrush
of the western United States, which contain predominantly hexosan hemicellulose, were studied. This phase of the work emphasized
debarked Douglas fir. The two best initial isolates were gradually selected for improved growth by adaptation to increasing
prehydrolysate concentrations in batch culture, with due consideration of nutrient requirements. Microaerophilic conditions
were evaluated to encourage tolerance of pretreatment hydrolysate, as well as ethanol product. Adaptation and simultaneous
saccharification and fermentation (SSF) results are used to illustrate improved performance with an adapted strain, compared
to the wild type. 相似文献