全文获取类型
收费全文 | 950篇 |
免费 | 11篇 |
国内免费 | 31篇 |
专业分类
化学 | 427篇 |
力学 | 10篇 |
综合类 | 4篇 |
数学 | 426篇 |
物理学 | 125篇 |
出版年
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 6篇 |
2020年 | 8篇 |
2019年 | 17篇 |
2018年 | 19篇 |
2017年 | 9篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 22篇 |
2013年 | 119篇 |
2012年 | 23篇 |
2011年 | 29篇 |
2010年 | 22篇 |
2009年 | 33篇 |
2008年 | 36篇 |
2007年 | 27篇 |
2006年 | 30篇 |
2005年 | 19篇 |
2004年 | 18篇 |
2003年 | 17篇 |
2002年 | 13篇 |
2001年 | 14篇 |
2000年 | 22篇 |
1999年 | 12篇 |
1998年 | 84篇 |
1997年 | 44篇 |
1996年 | 13篇 |
1995年 | 31篇 |
1994年 | 30篇 |
1993年 | 23篇 |
1992年 | 46篇 |
1991年 | 66篇 |
1990年 | 40篇 |
1989年 | 35篇 |
1988年 | 19篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有992条查询结果,搜索用时 15 毫秒
21.
Rivard C. J. Himmel M. E. Vinzant T. B. Adney W. S. Wyman C. E. Grohmann K. 《Applied biochemistry and biotechnology》1989,(1):461-478
Economic evaluations of the capital costs for anaerobic digestion systems for gas production show that the reactor is a significant
cost component. The successful application of high solids digestion of processed MSW (e.g., greater than 10% solids within
the digester) would allow a decrease in reactor volume with maintenance of relatively high gas production rates. However,
high solids slurries do not mix well in conventional stirred tank reactors. A horizontal shaft, hydraulically driven reactor
was designed and fabricated to test the anaerobic digestion of high solids concentrations. Digester performance was evaluated
as a function of experimental parameters such as nutrient requirements, feeding rates, pH control, and agitator design/ rotation
speed; horsepower of mixing was also evaluated for the reactor. Several startup protocols were examined to obtain a biologically
stable anaerobic fermentation at high solids levels. 相似文献
22.
Lamb pregastric lipase was purified from a commercial source using delipidation, solubilization with KSCN, acid-precipitation, pepsin-digestion, affinity chromatography with agarose-Cibacron Blue F3GA, gel filtration, and elution from a native 10% (w/v) polyacrylamide gel. The enzyme had a single subunit of 68,000 Da with maximum esterase activity when measured at pH 6.0 and 30 degrees C. The enzyme preferentially hydrolyzed short- and medium-chain (C4, C6, and C8) synthetic esters and short-chain (C4 and C6) monoacid triglycerides. The NH2-terminal sequence demonstrated high homology with gastric and lingual lipases. 相似文献
23.
Converse A. O. Kwarteng I. K. Grethlein H. E. Ooshima H. 《Applied biochemistry and biotechnology》1989,(1):63-78
The results of an experimental study of the acid hydrolysis of hardwood are presented in the form of values for the three
parameters, activation energy, power on the acid concentration, and pre-exponen-tial factor, of the first order kinetic constants
for each of the following reaction participants: xylan remaining, glucan remaining, xylose formed, and xylose decomposed.
These are used as a base for a quantitative theory to predict the temperature, time, and acid concentrations needed for effective
pretreatment of the substrate for subsequent enzymatic hydrolysis of the glucan. This theory is based on the assumption that
successful pretreatment requires >90% removal of the xylan, <10% removal of the glucan, and >80% xylose yield. This theory
is compared with selected published data. 相似文献
24.
25.
Nidetzky Bernd Griessler Richard Weinhausel Andreas Haltrich Dietmar Kulbe Klaus D. 《Applied biochemistry and biotechnology》1997,(1):159-172
Some important process properties of α-l,4-D-ghican phosphorylases isolated from the bacteriumCorynebacterium callunae and potato tubers (Solatium tuberosum) were compared. Apart from minor differences in their stability and specificity (represented by the maximum degree of maltodextrin
conversion) and a 10-fold higher affinity of the plant phosphorylase for maltodextrin (K
M of 1.3 g/L at 300 mM of orthophosphate), the performances of both enzymes in a continuous ultrafiltration membrane reactor
were almost identical. Product synthesis was carried out over a time course of 300–400 h in the presence or absence of auxiliary
pullulanase (increasing the accessibility of the glucan substrate for phosphorolytic attack up to 15–20%). The effect of varied
dilution rate and reaction temperature on the resulting productivities was quantitated, and a maximum operational temperature
of 40°C was identified. 相似文献
26.
Alcohol fuels produced from biomass can improve air quality, enhance energy security, create employment opportunities, and
reduce waste disposal problems. Opportunities in California exist to produce alcohols from waste streams from various sectors
of the economy. Government agencies have promoted waste-to-alcohol activities, but efforts have been inconsistent and intermittent.
Often these efforts have been hindered by contradictory but mandate-driven policies.
A prudent approach to coordinate statewide efforts includes the development of an integrated statewide policy to examine barriers
that impede private sector business efforts to produce alcohols from biomass. A multi-agency task force to promote research,
development, commercialization, and marketing efforts for biomass-produced alcohols is desirable.
The views and opinions contained in this document do not necessarily reflect those of the California Energy Commission, its
staff, management, or the State of California. 相似文献
27.
The production cost of cellulolytic enzymes is a major contributor to the high cost of ethanol production from lignocellulosics
using enzymatic hydrolysis. The aim of the present study was to investigate the cellulolytic enzyme production ofTrichoderma reesei Rut C 30, which is known as a good cellulase secreting micro-organism, using willow as the carbon source. The willow, which
is a fast-growing energy crop in Sweden, was impregnated with 1–4% SO2 and steam-pretreated for 5 min at 206°C. The pretreated willow was washed and the wash water, which contains several soluble
sugars from the hemicellulose, was supplemented with fibrous pretreated willow and used for enzyme production. In addition
to sugars, the liquid contains degradation products such as acetic acid, furfural, and 5-hydroxy-methylfurfural, which are
inhibitory for microorganisms. The results showed that 50% of the cellulose can be replaced with sugars from the wash water.
The highest enzyme activity, 1.79 FPU/mL and yield, 133 FPU/g carbohydrate, was obtained at pH 6.0 using 20 g/L carbon source
concentration. At lower pHs, a total lack of growth and enzyme production was observed, which probably could be explained
by furfural inhibition. 相似文献
28.
T. Argiriou A. Kalliafas C. Psarianos K. Kana M. Kanellaki A. A. Koutinas 《Applied biochemistry and biotechnology》1992,36(3):153-161
Two alcohol resistant strains of Saccharomyces cerevisiae species were isolated from a Greek vineyard plantation. The strain AXAZ-1 gave a concentration of 17.6% v/v alcohol and AXAZ-2 16.5%, when musts from raisin and sultana grapes, respectively, were employed in alcoholic fermentations. They were found to be more alcohol tolerant and fermentative in the fermentation of molasse than the traditional baker's yeast. Specifically, using an initial [symbol: see text] Be density of 16 [symbol: see text] Be at the repeated batch fermentation process, in the first as well as fourth batch, the better AXAZ-1 gave final [symbol: see text] Be densities of 6.0 and 10.5 respectively, and the baker's yeast 11.6 and 14.5. 相似文献
29.
Amyloglucosidase from Novo (Copenhagen, Denmark) was immobilized in controlled pore silica particles with the silane-glutaraldehyde
covalent method. Thermal stability of the free and immobilized enzyme (IE) was determined with 30% (w/v) α-amylase liquefied
cassava starch, pH 4.5, temperatures from 35 to 75°C. Free amyloglucosidase maintained its activity practically constant for
240 min and temperatures up to 50°C. The IE has shown higher stability retaining its activity for the same period up to 60°C.
Half-life for free enzyme was 20.6, 6.44, 2.07, 0.69, and 0.24 h for 55, 60, 65, 70, and 75°C, respectively, whereas the IE
at the same temperatures had half-lives of 116.4, 30.88, 8.52, 2.44, and 0.73 h. The energy of thermal deactivation was thus
50.6 and 57.6 kcal/mol, respectively for the free and IE, confirming stabilization by immobilization. 相似文献
30.
C-peptide radioimmunoassay (C-peptide RIA) is widely used in determination of pancreatic B-cell secretion activity.125I labeled TyrC-peptide is indispensable in C-peptide RIA kit. Herein we discuss a way of obtaining recombinant Tyr-C-peptide.
Arg32Tyr human proinsulin mutant (R32Y-proinsulin) gene was constructed by site-directed mutagenesis and overexpressed inEscherichia coli. Purified R32Y-proinsulin was converted to insulin and Tyr-C-peptide by trypsin and carboxypeptidase B codigestion. Tyr-C-peptide
was isolated through reverse-phase HPLC (RP-HPLC) and identified by C-peptide RIA and amino acid analysis. 相似文献