全文获取类型
收费全文 | 7204篇 |
免费 | 413篇 |
国内免费 | 3篇 |
出版年
2023年 | 17篇 |
2022年 | 56篇 |
2021年 | 104篇 |
2020年 | 53篇 |
2019年 | 85篇 |
2018年 | 96篇 |
2017年 | 107篇 |
2016年 | 138篇 |
2015年 | 252篇 |
2014年 | 289篇 |
2013年 | 484篇 |
2012年 | 463篇 |
2011年 | 463篇 |
2010年 | 341篇 |
2009年 | 299篇 |
2008年 | 502篇 |
2007年 | 483篇 |
2006年 | 500篇 |
2005年 | 473篇 |
2004年 | 471篇 |
2003年 | 457篇 |
2002年 | 451篇 |
2001年 | 56篇 |
2000年 | 45篇 |
1999年 | 93篇 |
1998年 | 100篇 |
1997年 | 77篇 |
1996年 | 72篇 |
1995年 | 59篇 |
1994年 | 71篇 |
1993年 | 62篇 |
1992年 | 43篇 |
1991年 | 37篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 33篇 |
1987年 | 20篇 |
1986年 | 21篇 |
1985年 | 17篇 |
1984年 | 28篇 |
1983年 | 12篇 |
1982年 | 28篇 |
1981年 | 25篇 |
1980年 | 14篇 |
1979年 | 20篇 |
1978年 | 7篇 |
1977年 | 14篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1970年 | 5篇 |
排序方式: 共有7620条查询结果,搜索用时 15 毫秒
991.
We investigated the intermolecular mechanism and kinetics of the synthesis of a novel biodegradable protein-based plastic from bovine serum albumin under subcritical water conditions using batch reactors. The reaction mechanism could be viewed as a chain reaction stabilized by the formation of intermolecular disulfide bonds. The kinetic analysis was based on non-steady-state kinetics using a theoretical model developed in one of our previous works. The activation energy and pre-exponential factor were found to be 7.2 kJ/mol and 0.9 s-1, respectively. These low values signify that the reaction is relatively temperature-insensitive with some diffusion limitation. 相似文献
992.
Sakiyama H Wynn RM Lee WR Fukasawa M Mizuguchi H Gardner KH Repa JJ Uyeda K 《The Journal of biological chemistry》2008,283(36):24899-24908
993.
Saito S Matsui H Kawano M Kumagai K Tomishige N Hanada K Echigo S Tamura S Kobayashi T 《The Journal of biological chemistry》2008,283(10):6584-6593
Protein phosphatase 2Cepsilon (PP2Cepsilon), a mammalian PP2C family member, is expressed in various tissues and is implicated in the negative regulation of stress-activated protein kinase pathways. We show that PP2Cepsilon is an endoplasmic reticulum (ER) transmembrane protein with a transmembrane domain at the amino terminus and the catalytic domain facing the cytoplasm. Yeast two-hybrid screening of a human brain library using PP2Cepsilon as bait resulted in the isolation of a cDNA that encoded vesicle-associated membrane protein-associated protein A (VAPA). VAPA is an ER resident integral membrane protein involved in recruiting lipid-binding proteins such as the ceramide transport protein CERT to the ER membrane. Expression of PP2Cepsilon resulted in dephosphorylation of CERT in a VAPA expression-dependent manner, which was accompanied by redistribution of CERT from the cytoplasm to the Golgi apparatus. The expression of PP2Cepsilon also enhanced the association between CERT and VAPA. In addition, knockdown of PP2Cepsilon expression by short interference RNA attenuated the interaction between CERT and VAPA and the sphingomyelin synthesis. These results suggest that CERT is a physiological substrate of PP2Cepsilon and that dephosphorylation of CERT by PP2Cepsilon may play an important role in the regulation of ceramide trafficking from the ER to the Golgi apparatus. 相似文献
994.
In addition to its role as a neurotransmitter, dopamine can stimulate neurite outgrowth and morphological effects upon primary neurons. To investigate the signal transduction mechanisms used by dopamine in developing striatal neurons, we focused upon the effects of activating the dopamine D1 receptor. Using the D1 receptor agonist SKF38393, we found that Trk neurotrophin receptors were activated in embryonic day 18 striatal neurons. K-252a, a Trk tyrosine kinase inhibitor, and a dopamine D1 receptor antagonist could block the effects of SKF38393. The increase in TrkB phosphorylation was not the result of increased neurotrophin production. Induction of TrkB activity by SKF38393 was accompanied by the phosphorylation of several Trk signaling proteins, including phospholipase Cgamma, Akt, and MAPK. Biotinylation experiments followed by immunostaining by phospho-TrkB-specific antibodies indicated that the mechanism involved increased TrkB surface expression by dopamine D1 receptor activation. This increase in cell surface TrkB expression was dependent upon an increase in intracellular Ca(2+). These results indicate that stimulation of dopamine D1 receptors can be coupled to the neurotrophin receptor signaling to mediate the effects of dopamine upon striatal neurons. 相似文献
995.
Taketa K Matsumura T Yano M Ishii N Senokuchi T Motoshima H Murata Y Kim-Mitsuyama S Kawada T Itabe H Takeya M Nishikawa T Tsuruzoe K Araki E 《The Journal of biological chemistry》2008,283(15):9852-9862
It has been reported that oxidized low density lipoprotein (Ox-LDL) can activate both peroxisome proliferator-activated receptor-alpha (PPARalpha) and PPARgamma. However, the detailed mechanisms of Ox-LDL-induced PPARalpha and PPARgamma activation are not fully understood. In the present study, we investigated the effect of Ox-LDL on PPARalpha and PPARgamma activation in macrophages. Ox-LDL, but not LDL, induced PPARalpha and PPARgamma activation in a dose-dependent manner. Ox-LDL transiently induced cyclooxygenase-2 (COX-2) mRNA and protein expression, and COX-2 specific inhibition by NS-398 or meloxicam or small interference RNA of COX-2 suppressed Ox-LDL-induced PPARalpha and PPARgamma activation. Ox-LDL induced phosphorylation of ERK1/2 and p38 MAPK, and ERK1/2 specific inhibition abrogated Ox-LDL-induced COX-2 expression and PPARalpha and PPARgamma activation, whereas p38 MAPK-specific inhibition had no effect. Ox-LDL decreased the amounts of intracellular long chain fatty acids, such as arachidonic, linoleic, oleic, and docosahexaenoic acids. On the other hand, Ox-LDL increased intracellular 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) level through ERK1/2-dependent overexpression of COX-2. Moreover, 15d-PGJ(2) induced both PPARalpha and PPARgamma activation. Furthermore, COX-2 and 15d-PGJ(2) expression and PPAR activity were increased in atherosclerotic lesions of apoE-deficient mice. Finally, we investigated the involvement of PPARalpha and PPARgamma on Ox-LDL-induced mRNA expression of ATP-binding cassette transporter A1 and monocyte chemoattractant protein-1. Interestingly, specific inhibition of PPARalpha and PPARgamma suppressed Ox-LDL-induced ATP-binding cassette transporter A1 mRNA expression and enhanced Ox-LDL-induced monocyte chemoattractant protein-1 mRNA expression. In conclusion, Ox-LDL-induced increase in 15d-PGJ(2) level through ERK1/2-dependent COX-2 expression is one of the mechanisms of PPARalpha and PPARgamma activation in macrophages. These effects of Ox-LDL may control excess atherosclerotic progression. 相似文献
996.
Functional differences of the catalytic and non-catalytic domains in human ADAMTS-4 and ADAMTS-5 in aggrecanolytic activity 总被引:2,自引:0,他引:2
Fushimi K Troeberg L Nakamura H Lim NH Nagase H 《The Journal of biological chemistry》2008,283(11):6706-6716
ADAMTS-4 (aggrecanase-1) and ADAMTS-5 (aggrecanase-2) are multidomain metalloproteinases belonging to the ADAMTS family. We have previously reported that human ADAMTS-5 has much higher aggrecanolytic activity than human ADAMTS-4. To investigate the different proteolytic activity of the two enzymes, we generated a series of chimeras by exchanging various non-catalytic domains of the two proteinases. We found that the catalytic domain of ADAMTS-5 has higher intrinsic catalytic ability than that of ADAMTS-4. The studies also demonstrated that the non-catalytic domains of ADAMTS-5 are more effective modifiers than those of ADAMTS-4, making both catalytic domains more active against aggrecan, an Escherichia coli-expressed interglobular domain of aggrecan and fibromodulin. Addition of the C-terminal thrombospondin type I motif of ADAMTS-5 to the C terminus of ADAMTS-4 increased the activity of ADAMTS-4 against aggrecan and fibromodulin severalfold. In contrast to previous reports (Kashiwagi, M., Enghild, J. J., Gendron, C., Hughes, C., Caterson, B., Itoh, Y., and Nagase, H. (2004) J. Biol. Chem. 279, 10109-10119 and Gao, G., Plaas, A., Thompson, V. P., Jin, S., Zuo, F., and Sandy, J. D. (2004) J. Biol. Chem. 279, 10042-10051), our detailed investigation of the role of the C-terminal spacer domain of ADAMTS-4 indicated that full-length ADAMTS-4 is approximately 20-times more active against aggrecan than its spacer domain deletion mutant, even at the Glu373-Ala374 site of the interglobular domain. This discrepancy is most likely due to selective inhibition of full-length ADAMTS-4 by heparin, particularly for cleavage at the Glu373-Ala374 bond. However, removal of the spacer domain from ADAMTS-4 greatly enhanced more general proteolytic activity against non-aggrecan substrates, e.g. E. coli-expressed interglobular domain, fibromodulin, and carboxymethylated transferrin. 相似文献
997.
Penicillium citrinum β-keto ester reductase (KER) can catalyze the reduction of methyl 4-bromo-3-oxobutyrate (BAM) to methyl (S)-4-bromo-3-hydroxybutyrate with high optical purity. To improve the thermostability of KER, protein engineering was performed
using error-prone polymerase chain reaction-based random mutagenesis. Variants with the highest levels of thermostability
contained the single amino acid substitutions L54Q, K245R, and N271D. The engineered L54Q variant of KER retained 62% of its
initial activity after heat treatment at 30°C for 6 h, whereas wild-type KER showed only 15% activity. The L54Q substitution
also conferred improved enantioselectivity by KER. An Escherichia coli cell biocatalyst that overproduced the L54Q mutant of KER and glucose dehydrogenase as a cofactor regeneration enzyme showed
the highest level of BAM reduction in a water/butyl acetate two-phase system. 相似文献
998.
Okochi M Kanie K Kurimoto M Yohda M Honda H 《Applied microbiology and biotechnology》2008,79(3):443-449
Prefoldin is a jellyfish-shaped hexameric chaperone that captures a protein-folding intermediate and transfers it to the group II chaperonin for correct folding. In this work, we characterized the organic solvent tolerance of Escherichia coli cells that overexpress prefoldin and group II chaperonin from a hyperthermophilic archeaum, Pyrococcus horikoshii OT3. The colony-forming efficiency of E. coli cells overexpressing prefoldin increased by 1,000-fold and decreased the accumulation of intracellular organic solvent. The effect was impaired by deletions of the region responsible for the chaperone function of prefoldin. Therefore, we concluded that prefoldin endows E. coli cells by preventing accumulation of intracellular organic solvent through its molecular chaperone activity. 相似文献
999.
Honda K Yamashita S Nakagawa H Sameshima Y Omasa T Kato J Ohtake H 《Applied microbiology and biotechnology》2008,78(5):767-773
Rhodococcus opacus B-4, which has recently been isolated as an organic solvent-tolerant bacterium, stabilized water-in-oil (w/o) emulsions by
inhibition of droplet coalescence when the cells were dispersed in 90% (v/v) organic solvents. Confocal microscopy revealed that many bacterial cells assembled at the interface between oil and water
droplets, though free cells were also detectable at the inside of water droplets. Bacterial cells in the w/o emulsion were
capable of utilizing both a water-soluble (glucose) and an oil-soluble substrate (oleic acid) as an energy source. Availability
of the w/o emulsion as an immobilized cell system in organic solvents was demonstrated using production of indigo from indole
and production of o-cresol from toluene as model conversions. When glucose and oleic acid were simultaneously supplied as energy sources, the
w/o emulsion culture of R. opacus B-4 produced indigo and o-cresol at levels of 0.217 and 2.12 mg ml−1, respectively, by 12 h. 相似文献
1000.
Ito S Taguchi H Hamada S Kawauchi S Ito H Senoura T Watanabe J Nishimukai M Ito S Matsui H 《Applied microbiology and biotechnology》2008,79(3):433-441
The gene for cellobiose 2-epimerase (CE) from Ruminococcus albus NE1 was overexpressed in Escherichia coli cells. The recombinant CE was purified to homogeneity by a simple purification procedure with a high yield of 88%, and the molecular mass was 43.1 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis and 44.0 kDa on gel chromatography. It exhibited optimal activity around at 30 degrees C and pH 7.5, and the enzyme activity was inhibited by Al3+, Fe3+, Co2+, Cu2+, Zn2+, Pb2+, Ag+, N-bromosuccinimide, iodoacetate, and 4-chloromercuribenzoate. In addition to cello-oligosaccharides, the enzyme was found to effectively 2-epimerize lactose to yield 4-O-beta-D-galactopyranosyl-D-mannose (epilactose), which occurs in cow milk as a rare oligosaccharide. The Km and kcat/Km values toward lactose were 33 mM and 1.6 s(-1) mM(-1), and those toward cellobiose were 13.8 mM and 4.6 s(-1) mM(-1), respectively. N-Acetyl-D-glucosamine, uridine 5'-diphosphate-glucose, D-glucose 6-phosphate, maltose, sophorose, laminaribiose, and gentiobiose were inert as substrates for the recombinant CE. We demonstrated that epilactose was resistant to rat intestinal enzymes, utilized by human adult bifidobacteria, and stimulated the tight junction permeability in Caco-2 cells. These results strongly suggest that this rare disaccharide is promising for use as a prebiotic. 相似文献