全文获取类型
收费全文 | 659篇 |
免费 | 74篇 |
国内免费 | 1篇 |
出版年
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 11篇 |
2017年 | 14篇 |
2016年 | 21篇 |
2015年 | 19篇 |
2014年 | 19篇 |
2013年 | 34篇 |
2012年 | 30篇 |
2011年 | 39篇 |
2010年 | 25篇 |
2009年 | 20篇 |
2008年 | 28篇 |
2007年 | 26篇 |
2006年 | 19篇 |
2005年 | 16篇 |
2004年 | 22篇 |
2003年 | 20篇 |
2002年 | 21篇 |
2001年 | 27篇 |
2000年 | 23篇 |
1999年 | 18篇 |
1998年 | 14篇 |
1997年 | 19篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 13篇 |
1991年 | 7篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1977年 | 7篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1972年 | 4篇 |
1970年 | 3篇 |
1968年 | 3篇 |
1966年 | 3篇 |
1961年 | 3篇 |
排序方式: 共有734条查询结果,搜索用时 31 毫秒
1.
Summary The effect of different ethanol concentrations on the growth of Candida shehatae and Pichia stipitis with xylose as substrate was evaluated in a temperature gradient incubator. The upper limit of the temperature profiles of ethanol tolerance of both yeast strains were similar, although P. stipitis appeared to have a slightly higher ethanol tolerance in the higher temperature range. An increase in the ethanol concentration severely depressed the maximum growth temperature, and also increased the minimum growth temperature slightly. The ethanol tolerance limit of 46–48 g·l-1 occurred within a narrow temperature plateau of 11 to 22° C. The low ethanol tolerance of these pentose fermenting yeasts is detrimental for commercial ethanol production from hemicellulose hydrolysates. 相似文献
2.
The effect of hydrogen acceptors on the kinetic parameters of D-xylose fermentation under anaerobic conditions was studied in a transient culture of immobilized Pachysolen tannophilus cells. Addition of oxygen to a steady-state culture resulted in a rapid increase (up to fivefold) in the rates of ethanol production and D-xylose uptake, but the rate of xylitol production was unaffected. Furthermore, the molar ethanol yield increased from 0.97 to 1.43 in the presence of oxygen. The moles of ethanol produced per moles of oxygen utilized were considerably greater than would be predicted from the stoichiometry of D-xylose fermentation, which suggests that the organism required oxygen for other functions in addition to its role as a hydrogen acceptor in D-xylose metabolism. When the artificial hydrogen acceptors acetone, acetaldehyde, and acetoin were added to the culture, the rate of ethanol production increased while the xylitol production rate decreased but the rate of xylose uptake was unaffected. The molar ethanol yields increased from 1.03 to 1.63, 1.43, and 1.24 upon addition of acetaldehyde, acetone, and acetoin, respectively, at the expense of the molar xylitol yields. The hydrogen acceptors sodium acetate, methylene blue, benzyl viologen, phenazine methosulfate, indigo carmine, and tetrazolium chloride had no effect on ethanol production. 相似文献
3.
The pMTL nic- cloning vectors. I. Improved pUC polylinker regions to facilitate the use of sonicated DNA for nucleotide sequencing 总被引:60,自引:0,他引:60
A series of nic- cloning vectors have been constructed analogous to the pUC plasmids but which are smaller in size and carry more extensive polylinker regions within the lacZ' gene. The vectors pMTL20 and pMTL21 carry six additional sites (AatII, MluI, NcoI, BglII, XhoI and StuI) to those present in pUC18 and pUC19, while pMTL22 and -23 possess eleven new cloning sites (ActII, MluI, NcoI, BglII, XhoI, StuI, NaeI, EcoRV, ClaI, NdeI and NruI). More importantly, the relative order of the restriction sites within the polylinker of these latter vectors has been totally rearranged, relative to pUC18 and pUC19, to facilitate the conversion of DNA fragments with incompatible ends to fragments with compatible termini. The availability of such DNA fragments is a crucial requirement when M13 templates are generated for dideoxy sequencing by the sonication procedure. Derivatives of these vectors have also been constructed which demonstrate improved segregational stability by incorporation of the pSC101 par locus. During the construction of these new vectors data were obtained which demonstrated that the pUC and pMTL plasmids contain a previously unreported single base pair difference within the RNA I/RNA II region (compared to pBR322) responsible for a three-fold increase in plasmid copy number. The pUC and pMTL plasmids were also shown to be functionally nic-, thus affording the lowest categorisation in genetic manipulation experiments. 相似文献
4.
5.
B. A. Prior C. P. Kenyon ‡ Michelle van der Veen J. P. Mildenhall 《Journal of applied microbiology》1987,62(2):119-128
When Pseudomonas fluorescens was grown in a glucose salts medium adjusted with NaCl to a water activity (aw ) value of 0.980, the intracellular glutamic acid concentration increased 23-fold and comprised 90% of the total amino acid pool. This increase was not observed when the aw of the medium was reduced to 0.980 with sorbitol. Sorbitol was taken up rapidly over a 30 min period and accumulated intracellularly to a level approximately two-fold greater than the concentration in the growth medium. In continuous culture, the specific rate of glutamic acid production and glucose uptake was greater at 0.980 (NaCl) than at 0.997 aw . The maintenance coefficients for glucose uptake were similar at both aw values but were 2.4-fold greater for glutamic acid production at 0.980 (NaCl) than at 0.997 aw . 相似文献
6.
7.
Petrus Jakobus van Zyl Bernard Alexander Prior 《Applied microbiology and biotechnology》1990,33(1):12-17
Summary Glycerol and arabitol were the main polyols accumulated by Zygosaccharomyces rouxii in continuous culture but the intracellular and extracellular concentrations of the polyols varied with the dilution rate and osmoticum used to adjust the water activity (aw) to 0.960. When the aw was adjusted with NaCl, glycerol was the main polyol accumulated intracellularly whereas glycerol and arabitol were accumulated when polyethylene glycol (PEG) 400 was used. The extracellular glycerol and arabitol concentrations at 0.960 aw (NaCl or PEG 400) were similar or decreased relative to cultures at 0.998 aw. Compared to steady-state cultivation at 0.998 aw, the yeast retained at 0.960 aw (NaCl or PEG 400) a greater proportion of the total glycerol intracellularly against an increased concentration ratio without significantly greater production of glycerol. Arabitol was only significant in osmoregulation when cultivated at 0.960 aw (PEG 400). The intracellular glycerol concentration was insufficient to balance the aw across the membrane, but an equilibrium could be achieved under certain conditions if arabitol was also osmotically active.
Offprint requests to: P. J. van Zyl 相似文献
8.
Petrus Jakobus van Zyl Stephanus Gouws Kilian Bernard Alexander Prior 《Applied microbiology and biotechnology》1990,34(2):231-235
Summary At water activities (a
w) of 0.998 (no osmoticum) and 0.960 a
w(NaCl), the affinity (K
m) of glycerol transport by Zygosaccharomyces rouxii was 25.6 and 6.4 mmol/l respectively. The maximum uptake rate (V
max) was ca. 2.3 mol/g/min at both a
w's. However, at an a
wof 0.960 using polyethylene glycol (PEG) 400 the K
mand V
max for glycerol transport increased to 61.1 mmol/l and 32.2 mol/g per minute respectively. This suggests that different glycerol transport mechanisms operate during stress by the two osmotica. The addition of uncouplers (2,4-dinitrophenol or carbonylcyanide-m-chlorophenylhydrazine) resulted in the outflow of accumulated [14C]glycerol from Z. rouxii after on osmotic upshock indicating that an active transport mechanism was operative. The transport mechanism was specific for glycerol since other polyols (mannitol, meso-erythritol and arabitol) had no effect on the uptake rate. During upshock from 0.998 to 0.960 a
w(NaCl), a transient increases in the rate of [14C]glycerol uptake was observed. However, if PEG 400 was used as osmoticum, the rate of glycerol uptake failed to increase.Offprint requests to: P. J. van Zyl 相似文献
9.
We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
10.
Grafting Tomato Cultivars Resistant or Susceptible to Bacterial Wilt: Analysis of Resistance Mechanisms 总被引:2,自引:0,他引:2
Grafting experiments were carried out in order to understand tomato resistance mechanisms to Pseudomonas solanacearum . Resistant scions grafted on susceptible root-stocks wilted, indicating that vascular tissues of resistant cultivars were not tolerant to higher bacterial populations than susceptible ones. Colonization frequencies and bacterial densities observed in plant grafted on resistant or susceptiblle root-stocks showed that resistance was correlated to the limitation of bacterial spread in the lower part of the stem. 相似文献