全文获取类型
收费全文 | 113篇 |
免费 | 6篇 |
专业分类
119篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 8篇 |
2012年 | 8篇 |
2011年 | 8篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 11篇 |
2006年 | 6篇 |
2005年 | 14篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1988年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
排序方式: 共有119条查询结果,搜索用时 15 毫秒
21.
Background
Molecular hydrogen is an environmentally-clean fuel and the reversible (bi-directional) hydrogenase of the cyanobacterium Synechocystis sp. PCC 6803 as well as the native Escherichia coli hydrogenase 3 hold great promise for hydrogen generation. These enzymes perform the simple reaction 2H+ + 2e- ↔ H2 (g). 相似文献22.
The large subunit (HycE, 569 amino acids) of Escherichia coli hydrogenase 3 produces hydrogen from formate via its Ni–Fe-binding site. In this paper, we engineered HycE for enhanced hydrogen
production by an error-prone polymerase chain reaction (epPCR) using a host that lacked hydrogenase activity via the hyaB hybC hycE mutations. Seven enhanced HycE variants were obtained with a novel chemochromic membrane screen that directly detected hydrogen
from individual colonies. The best epPCR variant contained eight mutations (S2T, Y50F, I171T, A291V, T366S, V433L, M444I,
and L523Q) and had 17-fold higher hydrogen-producing activity than wild-type HycE. In addition, this variant had eightfold
higher hydrogen yield from formate compared to wild-type HycE. Deoxyribonucleic acid shuffling using the three most-active
HycE variants created a variant that has 23-fold higher hydrogen production and ninefold higher yield on formate due to a
74-amino acid carboxy-terminal truncation. Saturation mutagenesis at T366 of HycE also led to increased hydrogen production
via a truncation at this position; hence, 204 amino acids at the carboxy terminus may be deleted to increase hydrogen production
by 30-fold. This is the first random protein engineering of a hydrogenase. 相似文献
23.
24.
Hiroshi Kamiya Hitoshi Ohshiro Yu Tabayashi Yoshihiro Kano Koji Mishima Toshiyuki Godo Masumi Yamamuro Osamu Mitamura Yu Ishitobi 《Landscape and Ecological Engineering》2011,7(1):53-64
In situ phosphorus release rates in three contiguous shallow brackish lakes were calculated by considering the amount of water
inflow, changes in salinity and phosphorus stock, and loading from phosphorus inflow based on monthly data. The annual amount
of sedimental phosphorus relative to that of phosphorus inflow was different for each of the three water bodies: 16% for Lake
Shinji, 3% for the Honjo area, and −8% for Lake Nakaumi, as estimated in a 10-year period from January 1993 to December 2002.
During the warm season, the quantity of phosphorus released surpassed sedimentation in these three water bodies. The low annual
sedimentation ratio in Lake Nakaumi is related to a large seawater backflow resulting in phosphorus removal, in addition to
a stable stratified structure promoting phosphorus release from sediment due to oxygen depletion in the lower layer. In Lake
Nakaumi, field data shows that if dissolved oxygen at the sediment surface falls below 2.54 mg L−1, phosphorus release from the sediment begins to be accelerated. 相似文献
25.
We designed a novel type of cationic lipid, lipids with a cationic polar group in the polyamidoamine dendron, because these dendron-bearing lipids are expected to form complexes with plasmid DNA and achieve efficient transfection of cells by synergy of endosome buffering and membrane fusion with the endosome, both of which are useful for the promotion of the transfer of plasmid DNA from endosome to cytosol. Four kinds of lipids with polyamidoamine dendrons of first to fourth generations, DL-G1, DL-G2, DL-G3, and DL-G4, were synthesized. The lipid with a dendron of a higher generation exhibited greater ability to form lipoplexes with plasmid DNA, as estimated by agarose gel electrophoresis. While the DL-G1 lipoplex did not transfect CV1 cells, the lipoplexes containing the DL-G2, DL-G3, or DL-G4 could induce transfection of the cells, and their activity was elevated with increasing generation of the dendron. Addition of dioleoylphosphatidylethanolamine (DOPE), which is known to increase fusion ability of a lipid membrane, into the lipoplexes greatly enhanced their transfection activity. In addition, the comparison with DC-Chol-containing lipoplex, which is widely used as a nonviral vector, showed that the DL-G3-DOPE lipoplex exhibits more efficient transfections. These findings imply that these dendron-bearing lipids may form the basis for a novel family of cationic lipids for efficient gene delivery. 相似文献
26.
We have evaluated the role of monofunctional heme-containing catalase encoded by cat-1 gene from the soil bacterium Comamonas terrigena N3H in the response to various forms of oxidative stress. Our results indicate that this constitutively expressed catalase
represents the major source for the defence of Comamonas terrigena cells against toxic peroxides but the cells can express also a second form of catalase that is bigger and its regulation
is probably more complicated. The sequence analysis confirmed the presence of highly conserved catalase sequence motifs in
two environmental strains of Comamonas terrigena but in those strains that were not exposed to oxidative stress, no such sequence motif could be detected. The results obtained
underline the importance of catalase expression in the defence mechanism against oxidative stress in bacterial cells. 相似文献
27.
28.
For the survival of individual isolates of gram-negative bacteria Pseudomonas putida, Achromobacter xylosoxidans, and the gram-positive bacterium Bacillus megaterium, in an environment polluted with crude oil products, the production of catalases exhibiting both catalase and dianisidine-peroxidase
activity is important. Electrophoretic resolution of cell-free extracts of aerobically grown strains in Luria–Bertani medium
during exponential phase revealed distinctive expression of catalatic and peroxidatic activities detected with 3,3′-diaminobenzidine
tetrahydrochloride. A considerable diversity in microbial catalase and peroxidase responses to 20 or 40 mM H2O2 stress, resulted from hydroperoxidase’s variant of original isolates, indicating an environmental selective pressure. However,
catalase was important for the adaptation of cultures to high concentration of 60 mM H2O2. Appreciable differences in the sensitivity to toxic effect of H2O2 (20 or 40 mM) treatment between individual isolates and their adapted variants during growth were observed until the middle
of exponential phase, but they were insignificant at the entry to stationary phase. Isolates also exhibited a considerable
diversity in catalases responses to phenolic contaminants 1 and 2 mM o- or p-phenylenediamine. Catalase activity of bacterium P. putida was visibly stimulated only by p-phenylenediamine and not by its positional isomer o-PDA. This study contributes to a better understanding of the role catalases play in bacterial responses to a polluted environment. 相似文献
29.
Seiji Nakamura Toshinari Takamura Naoto Matsuzawa-Nagata Hiroaki Takayama Hirofumi Misu Hiroyo Noda Satoko Nabemoto Seiichiro Kurita Tsuguhito Ota Hitoshi Ando Ken-ichi Miyamoto Shuichi Kaneko 《The Journal of biological chemistry》2009,284(22):14809-14818
Visceral adiposity in obesity causes excessive free fatty acid (FFA) flux
into the liver via the portal vein and may cause fatty liver disease and
hepatic insulin resistance. However, because animal models of insulin
resistance induced by lipid infusion or a high fat diet are complex and may be
accompanied by alterations not restricted to the liver, it is difficult to
determine the contribution of FFAs to hepatic insulin resistance. Therefore,
we treated H4IIEC3 cells, a rat hepatocyte cell line, with a monounsaturated
fatty acid (oleate) and a saturated fatty acid (palmitate) to investigate the
direct and initial effects of FFAs on hepatocytes. We show that palmitate, but
not oleate, inhibited insulin-stimulated tyrosine phosphorylation of insulin
receptor substrate 2 and serine phosphorylation of Akt, through c-Jun
NH2-terminal kinase (JNK) activation. Among the well established
stimuli for JNK activation, reactive oxygen species (ROS) played a causal role
in palmitate-induced JNK activation. In addition, etomoxir, an inhibitor of
carnitine palmitoyltransferase-1, which is the rate-limiting enzyme in
mitochondrial fatty acid β-oxidation, as well as inhibitors of the
mitochondrial respiratory chain complex (thenoyltrifluoroacetone and carbonyl
cyanide m-chlorophenylhydrazone) decreased palmitate-induced ROS
production. Together, our findings in hepatocytes indicate that palmitate
inhibited insulin signal transduction through JNK activation and that
accelerated β-oxidation of palmitate caused excess electron flux in the
mitochondrial respiratory chain, resulting in increased ROS generation. Thus,
mitochondria-derived ROS induced by palmitate may be major contributors to JNK
activation and cellular insulin resistance.Insulin is the major hormone that inhibits gluconeogenesis in the liver.
Visceral adiposity in obesity causes hepatic steatosis and insulin resistance.
In an insulin-resistant state, impaired insulin action allows enhancement of
glucose production in the liver, resulting in systemic hyperglycemia
(1) and contributing to the
development of type 2 diabetes. In addition, we have demonstrated
experimentally that insulin resistance accelerated the pathology of
steatohepatitis in genetically obese diabetic OLETF rats
(2). In contrast, lipid-induced
oxidative stress caused steatohepatitis and hepatic insulin resistance in mice
(3). In fact, steatosis of the
liver is an independent predictor of insulin resistance in patients with
nonalcoholic fatty liver disease
(4).It remains unclear whether hepatic steatosis causally contributes to
insulin resistance or whether it is merely a resulting pathology. Excessive
dietary free fatty acid
(FFA)2 flux into the
liver via the portal vein may cause fatty liver disease and hepatic insulin
resistance. Indeed, elevated plasma FFA concentrations correlate with obesity
and decreased target tissue insulin sensitivity
(5).Experimentally, lipid infusion or a high fat diet that increases
circulating FFA levels promotes insulin resistance in the liver. Candidate
events linking FFA to insulin resistance in vivo are the
up-regulation of SREBP-1c (6),
inflammation caused by activation of c-Jun amino-terminal kinase (JNK)
(7) or IKKβ
(8), endoplasmic reticulum (ER)
stress (9), ceramide
(10,
11), and TRB3
(12).However, which event is the direct and initial target of FFA in the liver
is unclear. Insulin resistance induced by lipid infusion or a high fat diet is
complex and may be accompanied by alterations not restricted to the liver,
making it difficult to determine the contribution of FFAs to hepatic insulin
resistance. For example, hyperinsulinemia and hyperglycemia secondary to the
initial event also may contribute to the development of diet-induced insulin
resistance in vivo
(6).To address the early event(s) triggering the development of high fat diet-
or obesity-induced insulin resistance, we investigated the molecular
mechanism(s) underlying the direct action of FFA on hepatocytes to cause
insulin resistance in vitro, using the rat hepatocyte cell line
H4IIEC3. We found that mitochondria-derived reactive oxygen species (ROS) were
a cause of palmitate-induced insulin resistance in hepatocytes. 相似文献
30.
Current state and perspectives in hydrogen production by Escherichia coli: roles of hydrogenases in glucose or glycerol metabolism 总被引:1,自引:0,他引:1
Maeda Toshinari Tran Kien Trung Yamasaki Ryota Wood Thomas K. 《Applied microbiology and biotechnology》2018,102(5):2041-2050
Applied Microbiology and Biotechnology - Escherichia coli has been a robust host strain for much biological research, in particular, research in metabolic engineering, protein engineering, and... 相似文献