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101.
Chakrabarti PP Suveyzdis Y Wittinghofer A Gerwert K 《The Journal of biological chemistry》2004,279(44):46226-46233
GTPase activating proteins (GAPs) down-regulate Ras-like proteins by stimulating their GTP hydrolysis, and a malfunction of this reaction leads to disease formation. In most cases, the molecular mechanism of activation involves stabilization of a catalytic Gln and insertion of a catalytic Arg into the active site by GAP. Rap1 neither possesses a Gln nor does its cognate Rap-GAP employ an Arg. Recently it was proposed that RapGAP provides a catalytic Asn, which substitutes for the Gln found in all other Ras-like proteins (Daumke, O., Weyand, M., Chakrabarti, P. P., Vetter, I. R., and Wittinghofer, A. (2004) Nature 429, 197-201). Here, RapGAP-mediated activation has been investigated by time-resolved Fourier transform infrared spectroscopy. Although the intrinsic hydrolysis reactions of Rap and Ras are very similar, the GAP-catalyzed reaction shows unique features. RapGAP binding induces a GTP(*) conformation in which the three phosphate groups are oriented such that they are vibrationally coupled to each other, in contrast to what was seen in the intrinsic and the Ras.RasGAP reactions. However, the charge shift toward beta-phosphate observed with RasGAP was also observed for RapGAP. A GDP.P(i) intermediate accumulates in the GAP-catalyzed reaction, because the release of P(i) is eight times slower than the cleavage reaction, and significant GTP synthesis from GDP.P(i) was observed. Partial steps of the cleavage reaction are correlated with structural changes of protein side groups and backbone. Thus, the Rap.RapGAP catalytic machinery compensates for the absence of a cis-Gln by a trans-Asn and for the catalytic Arg by inducing a different GTP conformation that is more prone to be attacked by a water molecule. 相似文献
102.
Sinha PS Schiöth HB Tatro JB 《American journal of physiology. Regulatory, integrative and comparative physiology》2003,284(6):R1595-R1603
Activation of central melanocortin receptors (MCR) inhibits fever, but the identity of the MCR subtype(s) mediating this antipyretic effect is unknown. To determine whether selective central melanocortin receptor-4 (MC4R) activation produces antipyretic effects, the MC4R selective agonist MRLOB-0001 (CO-His-d-Phe-Arg-Trp-Dab-NH(2)) was administered intracerebroventricularly to rats treated with Escherichia coli lipopolysaccharide (LPS, 30 microg/kg ip). Treatment with MRLOB-0001 (150 ng icv) did not lower core body temperature (T(c)) in afebrile rats but did suppress LPS-induced increases in T(c) and associated decreases in tail skin temperature (T(sk)), an indicator of vasomotor thermoeffector function. In contrast, systemic treatment with MRLOB-0001 (150 ng iv) did not produce similar antipyretic effects. Coadministration of the selective MC4R antagonist HS014 (1 microg icv) blocked the antipyretic effects of MRLOB-0001. HS014 alone (1 microg icv) had no significant effect on LPS-induced increases in T(c) or decreases in T(sk) and in afebrile rats had no significant effects on T(c) or T(sk). We conclude that pharmacological activation of central MC4R suppresses febrile increases in T(c) and that inhibition of heat conservation pathways may contribute to this effect. These findings suggest that the central MC4R may mediate the long-recognized antipyretic effects of centrally administered melanocortins. 相似文献
103.
Structure of the mammalian mitochondrial ribosome reveals an expanded functional role for its component proteins 总被引:12,自引:0,他引:12
The mitochondrial ribosome is responsible for the biosynthesis of protein components crucial to the generation of ATP in the eukaryotic cell. Because the protein:RNA ratio in the mitochondrial ribosome (approximately 69:approximately 31) is the inverse of that of its prokaryotic counterpart (approximately 33:approximately 67), it was thought that the additional and/or larger proteins of the mitochondrial ribosome must compensate for the shortened rRNAs. Here, we present a three-dimensional cryo-electron microscopic map of the mammalian mitochondrial 55S ribosome carrying a tRNA at its P site, and we find that instead, many of the proteins occupy new positions in the ribosome. Furthermore, unlike cytoplasmic ribosomes, the mitochondrial ribosome possesses intersubunit bridges composed largely of proteins; it has a gatelike structure at its mRNA entrance, perhaps involved in recruiting unique mitochondrial mRNAs; and it has a polypeptide exit tunnel that allows access to the solvent before the exit site, suggesting a unique nascent-polypeptide exit mechanism. 相似文献
104.
Chromatin immunoprecipitation assay 总被引:5,自引:0,他引:5
105.
In vitro anti-herpetic activity of sulfated polysaccharide fractions from Caulerpa racemosa 总被引:5,自引:0,他引:5
Ghosh P Adhikari U Ghosal PK Pujol CA Carlucci MJ Damonte EB Ray B 《Phytochemistry》2004,65(23):3151-3157
A sulfated polysaccharide fraction was isolated from the hot water extract of the green alga Caulerpa racemosa and designated HWE. This polymer, which contained galactose, glucose, arabinose and xylose as the major component sugars, had [alpha](D)(30) + 46.2 degrees in water and contained 9% sulfate hemiester groups. Sugar linkage analysis indicates that HWE was branched and mainly contained 1,3- and 1,3,6-linked galactose, 1,3,4-linked arabinose, 1,4-linked glucose and terminal- and 1,4-linked xylose residues. Sulfation was deduced from infrared spectroscopy and methylation analysis to occur on O-6 of galactose and O-3 of arabinose. The native polysaccharide could be fractionated by size exclusion chromatography into two overlapping fractions and the major fraction has a hydrodynamic volume similar to that of 70 kDa dextran. HWE was a selective inhibitor of reference strains and TK(-) acyclovir-resistant strains of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) in Vero cells, with antiviral effective concentration 50% (EC(50)) values in the range of 2.2-4.2 microg/ml and lacking cytotoxic effects. Furthermore, HWE did not exhibit anticoagulant properties at concentrations near the EC(50). 相似文献
106.
Ravi Pathiyil Shankar Praveen Partha Nagesh Kumar Shenoy Maducolil Joshy Easow Kottallur Narayanan Brahmadathan 《Annals of clinical microbiology and antimicrobials》2003,2(1):1-9
Background
Information about antibiotic use and resistance patterns of common microorganisms are lacking in hospitals in Western Nepal. Excessive and inappropriate use of antibiotics contributes to the development of bacterial resistance. The parameter: Defined daily dose/100 bed-days, provides an estimate of consumption of drugs among hospital in-patients. This study was carried out to collect relevant demographic information, antibiotic prescribing patterns and the common organisms isolated including their antibiotic sensitivity patterns.Methods
The study was carried out over a 3-month period (01.04.2002 to 30.06.2002) at the Manipal Teaching Hospital, Western Nepal. The median number of days of hospitalization and mean ± SD cost of antibiotics prescribed during hospital stay were calculated. The use of antibiotics was classified for prophylaxis, bacteriologically proven infection or non-bacteriologically proven infection. Sensitivity patterns of the common organisms were determined. Defined daily dose/100 bed-days of the ten most commonly prescribed antibiotics were calculated.Results
203 patients were prescribed antibiotics; 112 were male. Median duration of hospitalization was 5 days. 347 antibiotics were prescribed. The most common were ampicillin, amoxicillin, metronidazole, ciprofloxacin and benzylpenicillin. Mean ± SD cost of antibiotics was 16.5 ± 13.4 US$. Culture and sensitivity testing was carried out in 141 patients. The common organisms isolated were H. influenzae, E. coli, K. pneumoniae and S. aureus.Conclusions
Antibiotic resistance is becoming a problem in the Internal Medicine ward. Formulation of a policy for hospital antibiotic use and an educational programme especially for junior doctors is required. 相似文献107.
108.
Partha P. Majumder 《Evolutionary anthropology》1998,6(3):100-110
The Indian subcontinent comprises a vast collection of peoples with different morphological, genetic, cultural, and linguistic characteristics. While much of this variability is indigenous, a considerable fraction of it has been introduced through large-scale immigrations into India in historical times. From an evolutionary standpoint, it is of immense interest to quantify biological diversity in contemporary human populations, to study biological affinities and to relate observed patterns of affinities with cultural, linguistic and demographic histories of populations. Such efforts are intended to shed light on the peopling of India. The purpose of this paper is to present a broad overview of the physical (anthropometric) and genetic diversities and affinities of the peoples of India. I shall also attempt to examine how well biological, particularly genetic, diversities and affinities correlate with geographical, socio-cultural, and linguistic diversities and affinities. © 1998 Wiley-Liss, Inc. 相似文献
109.
In wild-type proteorhodopsin (pR), titration of the chromophore's counterion Asp(97) occurs with a pK(a) of 8.2+/-0.1. R94C mutation reduces this slightly to 7.0+/-0.2, irrespective of treatment with ethylguanidinium. This contrasts with the homologous archaeal protein bacteriorhodopsin (bR), where R82C mutation was previously shown to elevate the pK(a) of Asp(85) by approximately 5 units, while reconstitution with ethylguanidinium restores it nearly to the wild-type value of 2.5. We conclude there is much weaker electrostatic coupling between Arg(94) and Asp(97) in the unphotolyzed state of pR, in comparison to Arg(82) and Asp(85) in bR. Therefore, while fast light-driven H(+) release may depend on these two residues in pR as in bR, no tightly conserved pre-photolysis configuration of them is required. 相似文献
110.
Tailor-made antibody therapeutics 总被引:1,自引:0,他引:1
Therapeutic antibodies represent one of the fastest growing areas of the pharmaceutical industry. There are currently 18 monoclonal antibodies in the market that have been approved by the FDA and over 150 in clinical developments. Driven by innovation and technological developments, scientists have gone beyond the traditional antibody molecules. Antibodies have been engineered in a variety of ways to meet the challenges posed by different biological settings. Described in this review is an abridged account of the different ways antibodies have been tailored to make them efficient drug molecules. 相似文献