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71.
Natalie Zeytuni Samuel Cronin Christopher T. Lefèvre Pascal Arnoux Dror Baran Zvi Shtein Geula Davidov Raz Zarivach 《PloS one》2015,10(6)
MamA is a highly conserved protein found in magnetotactic bacteria (MTB), a diverse group of prokaryotes capable of navigating according to magnetic fields – an ability known as magnetotaxis. Questions surround the acquisition of this magnetic navigation ability; namely, whether it arose through horizontal or vertical gene transfer. Though its exact function is unknown, MamA surrounds the magnetosome, the magnetic organelle embedding a biomineralised nanoparticle and responsible for magnetotaxis. Several structures for MamA from a variety of species have been determined and show a high degree of structural similarity. By determining the structure of MamA from Desulfovibrio magneticus RS-1 using X-ray crystallography, we have opened up the structure-sequence landscape. As such, this allows us to perform structural- and phylogenetic-based analyses using a variety of previously determined MamA from a diverse range of MTB species across various phylogenetic groups. We found that MamA has remained remarkably constant throughout evolution with minimal change between different taxa despite sequence variations. These findings, coupled with the generation of phylogenetic trees using both amino acid sequences and 16S rRNA, indicate that magnetotaxis likely did not spread via horizontal gene transfer and instead has a significantly earlier, primordial origin. 相似文献
72.
Baran I 《Biophysical journal》2003,84(3):1470-1485
We propose here a unitary approach to the luminal and cytosolic control of calcium release. A minimal number of model elements that realistically describe different data sets are combined and adapted to correctly respond to various physiological constraints. We couple the kinetic properties of the inositol 1,4,5 trisphosphate receptor/calcium channel with the dynamics of Ca(2+) and K(+) in both the lumen and cytosol, and by using a detailed simulation approach, we propose that local (on a radial distance approximately 2 micro m) calcium oscillations in permeabilized cells are driven by the slow inactivation of channels organized in discrete clusters composed of between six and 15 channels. Moreover, the character of these oscillations is found to be extremely sensitive to K(+), so that the cytosolic and luminal calcium variations are in or out of phase if the store at equilibrium has tens or hundreds micro M Ca(2+), respectively, depending on the K(+) gradient across the reticulum membrane. Different patterns of calcium signals can be reproduced through variation of only a few parameters. 相似文献
73.
Maria C. Apella Roxana Totaro Enrique J. Baran 《Biological trace element research》1993,37(2-3):293-299
The superoxide-dismutase-like activity of a series of divalent metal saccharinates of general stoichiometry [MII(Sac)2(H2O)4]·2H2O (with MII=Mn,Fe,Co,Ni,Cu,Zn) has been investigated using the nitroblue tetrazolium O
2
−
reduction assay. The results show that all these complexes possess the capability to dismutate the superoxide anion generated
in the xanthine/xanthine oxidase system. Interestingly, the greatest activity is shown by the corresponding copper complex.
The results are discussed and compared with those obtained for native superoxide dismutase, which was tested under the same
experimental conditions.
Dedicated to Prof. Pedro J. Aymonino on the occasion of his 65th birthday. 相似文献
74.
End product inhibition of hepatic 25-hydroxyvitamin D production in the rat: specificity and kinetics 总被引:3,自引:0,他引:3
The role of vitamin D metabolites in the regulation of hepatic 25-hydroxyvitamin D production was investigated by examining the effects of 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and 24,25-dihydroxyvitamin D on the synthesis of [25-3H]hydroxyvitamin D by rachitic rat liver homogenates. Production of [25-3H]hydroxyvitamin D was inhibited by 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, but not by 24,25-dihydroxyvitamin D. 25-Hydroxyvitamin D increased the Km of the vitamin D-25-hydroxylase enzyme(s), while 1,25-dihydroxyvitamin D decreased the Vmax with a Ki of 88.7 ng/ml. Inhibition of hepatic 25-hydroxyvitamin D production by 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D may be another control mechanism to regulate circulating vitamin D levels. 相似文献
75.
Abstract: Two kynurenine aminotransferases (KATs), arbitrarily termed KAT I and KAT II, are capable of producing the neuroinhibitory brain metabolite kynurenic acid from l -kynurenine in human brain tissue. Here we describe the purification of KAT I to homogeneity and the subsequent characterization of the enzyme using physicochemical, biochemical, and immunological methods. KAT I was purified from human brain ∼2,000-fold with a yield of 2%. Assessed by polyacrylamide gel electrophoresis, KAT I migrated toward the anode as a single protein with a mobility of 0.5. The pure enzyme was found to be a dimer consisting of two identical subunits of ∼60 kDa. Among several oxo acids tested, KAT I showed highest activity with 2-oxoisocaproate. Kinetic analyses of the pure enzyme revealed an absolute K m of 2.0 m M and 10.0 m M for l -kynurenine and pyruvate, respectively. KAT I activity was substantially inhibited by l -glutamine, l -phenylalanine, and l -tryptophan, using either pyruvate (1 m M ) or 2-oxoisocaproate (1 m M ) as a cosubstrate. l -Tryptophan inhibited enzyme activity noncompetitively with regard to pyruvate ( K i = 480 µ M ) and competitively with regard to l -kynurenine ( K i = 200 µ M ). Anti-KAT I antibodies were produced against pure KAT I and were partially purified by conventional techniques. Immunotitration and immunoblotting analyses confirmed that KAT I is clearly distinct from both human KAT II and rat kynurenine-pyruvate aminotransferase. Pure human KAT I and its antibody will serve as valuable tools in future studies of kynurenic acid production in the human brain under physiological and pathological conditions. 相似文献
76.
Summary A sample of 107 Belgian cystic fibrosis patients has been tested for the presence of the ΔF508 deletion. We have shown that
166 (78%) of the CF chromosomes presented the deletion, and that 97% of the deleted chromosomes and 50% of the non-deleted
chromosomes presented the haplotype B (KM19-2/XV2c-1). 相似文献
77.
Didem Şöhretoğlu Merve Yüzbaşıoğlu Baran Randolph Arroo Ayşe Kuruüzüm-Uz 《Phytochemistry Reviews》2018,17(5):973-1005
Polydatin (PLD), the 3-O-β-glucopyranoside of the well-known stilbenoid compound resveratrol, is a major compound of Fallopia japonica (Houtt.) R. Decr. (Japanese knotweed), which is widely used in traditional Chinese medicine to treat infection, inflammatory diseases and circulatory problems. It has shown a wide range of biological activities including anti-inflammatory, anti-oxidant, anti-cancer, neuroprotective, hepatoprotective, nephroprotective and immunostimulatory effects. Although resveratrol has similar beneficial effects, its low bioavailability has remained a problem. Glycosylation increases solubility of resveratrol in an aqueous environment, thus improving its bioavailability. This has led to a growing interest in PLD. Promising results obtained from bioactivity studies have boosted an intense research on this compound. The aim of this review is to give a comprehensive overview of the botanical sources, pharmacology, biosynthesis, biotechnological production, and bioactivities of PLD, and to discuss clinical studies on this compound. 相似文献
78.
Gokay Aydin Tahir Savran Şule Baran Arif Baran 《Bioorganic & medicinal chemistry letters》2018,28(14):2555-2560
Stereoselective and efficient synthesis of hydroxymethyl-substituted rac-quercitols (13–15) was achieved, starting from cis-furan (Kobayashi, 2008) with photooxygenation reaction, which is readily available by the reduction of cis-phtalic anhydride. α- and β-Glucosidase enzyme activity of the target molecules was evaluated and good inhibitor activity was seen. One- and two-dimensional NMR spectroscopy, IR spectroscopy and X-ray crystallography were utilized in the structure characterization of products. 相似文献
79.
80.
Physical study of prophage excision and curing of lambda prophage from lysogenic Escherichia coli 总被引:4,自引:0,他引:4
A sex factor, F′450(λ), which can be isolated as a covalent circle of DNA, has been examined by alkaline sucrose gradient centrifugation of lysates of induced cells in order to study λ prophage excision. Thermal derepression of the prophage results in loss of F′450(λ) covalent circles, which is mediated by systems involved in excision and initiation of replication. When protocols known to result in prophage curing are used, the F′450(λ) is converted to an F′450 and a λ covalent circle; in normal excision leading to phage development, F′450 covalent circles are not found. We have shown that: (1) excision usually occurs later than initiation of DNA replication of the prophage so that the excised prophage is usually already replicated or in the act of replication; (2) the DNA growing points of the prophage leave the prophage and enter the bacterial DNA; (3) the int and xis genes are involved in the earliest detectable stage of the excision process, i.e. breakage of the DNA at the attachment region; (4) the xis gene product is involved in a weak non-specific nuclease activity in addition to its highly specific activity in excision; and (5) the excision system fails to attack a single attachment site. 相似文献