全文获取类型
收费全文 | 103篇 |
免费 | 23篇 |
出版年
2021年 | 1篇 |
2019年 | 1篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 3篇 |
2012年 | 2篇 |
2011年 | 2篇 |
2010年 | 2篇 |
2009年 | 8篇 |
2008年 | 5篇 |
2006年 | 3篇 |
2005年 | 1篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1972年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有126条查询结果,搜索用时 265 毫秒
91.
This paper presents a real-world optimization problem in home health care that is solved on a daily basis. It can be described as follows: care staff members with different qualification levels have to visit certain clients at least once per day. Assignment constraints and hard time windows at the clients have to be observed. The staff members have a maximum working time and their workday can be separated into two shifts. A mandatory break that can also be partitioned needs to be scheduled if the consecutive working time exceeds a certain threshold. The objective is to minimize the total travel- and waiting times of the care staff. Additionally, factors influencing the satisfaction of the clients or the care staff are considered. Most of the care staff members from the Austrian Red Cross (ARC) in Vienna use a combination of public transport modes (bus, tram, train, and metro) and walking. We present a novel model formulation for this problem, followed by an efficient exact solution approach to compute the time-dependent travel times out of the timetables from public transport service providers on a minute-basis. These travel time matrices are then used as input for three Tabu Search based solution methods for the scheduling problem. Extensive numerical studies with real-world data from the ARC show that the current planning can be improved significantly when these methods are applied. 相似文献
92.
Rapid genome‐wide evolution in Brassica rapa populations following drought revealed by sequencing of ancestral and descendant gene pools 下载免费PDF全文
Steven J. Franks Nolan C. Kane Niamh B. O'Hara Silas Tittes Joshua S. Rest 《Molecular ecology》2016,25(15):3622-3631
There is increasing evidence that evolution can occur rapidly in response to selection. Recent advances in sequencing suggest the possibility of documenting genetic changes as they occur in populations, thus uncovering the genetic basis of evolution, particularly if samples are available from both before and after selection. Here, we had a unique opportunity to directly assess genetic changes in natural populations following an evolutionary response to a fluctuation in climate. We analysed genome‐wide differences between ancestors and descendants of natural populations of Brassica rapa plants from two locations that rapidly evolved changes in multiple phenotypic traits, including flowering time, following a multiyear late‐season drought in California. These ancestor‐descendant comparisons revealed evolutionary shifts in allele frequencies in many genes. Some genes showing evolutionary shifts have functions related to drought stress and flowering time, consistent with an adaptive response to selection. Loci differentiated between ancestors and descendants (FST outliers) were generally different from those showing signatures of selection based on site frequency spectrum analysis (Tajima's D), indicating that the loci that evolved in response to the recent drought and those under historical selection were generally distinct. Very few genes showed similar evolutionary responses between two geographically distinct populations, suggesting independent genetic trajectories of evolution yielding parallel phenotypic changes. The results show that selection can result in rapid genome‐wide evolutionary shifts in allele frequencies in natural populations, and highlight the usefulness of combining resurrection experiments in natural populations with genomics for studying the genetic basis of adaptive evolution. 相似文献
93.
Background
Bacillus anthracis has two major virulence factors: a tripartite toxin that produces lethal and edema toxins and a polyglutamic acid capsule. A recent report suggested that a toxin belonging to the cholesterol dependant cytolysin (CDC) family, anthrolysin O (ALO) was a new virulence factor for B. anthracis but subsequent studies have questioned its relevance in pathogenesis. In this study, we examined the immunogenicity of recombinant anthrolysin O (rALO) in mice. 相似文献94.
Bharat Rekhi Sophia George Bhulaxmi Madur RF Chinoy Rajesh Dikshit Amita Maheshwari 《Diagnostic pathology》2008,3(1):1-7
Introduction
Intravascular lesions of the hand comprise reactive and neoplastic entities. The clinical diagnosis of such lesions is often difficult, and usually requires pathologic examination. We present the largest series to date of intravascular lesions affecting the hand.Methods
A retrospective review of intravascular (arterial and venous) lesions involving the hand was conducted. Data regarding clinicopathologic findings were analyzed.Results
We identified 10 patients with intravascular lesions of their hands including thromboemboli (n = 3), reactive intravascular conditions such as papillary endothelial hyperplasia or Masson's tumor (n = 2) and fasciitis (n = 1), as well as vascular neoplasms including pyogenic granuloma (n = 2) and angioleiomyoma (n = 2).Conclusion
Blood vessel injury and/or venous thrombosis may predispose to several intravascular lesions of the hand. Recognition of reactive entities from neoplastic conditions is important. 相似文献95.
S B Sheren E F Eikenberry D L Broek M van der Rest T Doering J Kelly T Hardt B Brodsky 《Comparative biochemistry and physiology. B, Comparative biochemistry》1986,85(1):5-14
The major collagen in lamprey notochord is type II, as determined by its amino acid composition and solubility properties. This collagen has a distribution of charged residues indistinguishable from higher vertebrate Type II collagens as judged by its SLS banding pattern. Lamprey type II collagen has a higher thermal stability than lamprey skin collagen, in contrast to the identical melting temperatures for these types in mammals. A minor collagen in lamprey notochord has solubility properties, amino acid composition, and electrophoretic mobility similar to that of 1 alpha, 2 alpha, 3 alpha collagen in human cartilage. 相似文献
96.
Joseph W Brown Joshua S Rest Jaime García-Moreno Michael D Sorenson David P Mindell 《BMC biology》2008,6(1):6
Background
Determining an absolute timescale for avian evolutionary history has proven contentious. The two sources of information available, paleontological data and inference from extant molecular genetic sequences (colloquially, 'rocks' and 'clocks'), have appeared irreconcilable; the fossil record supports a Cenozoic origin for most modern lineages, whereas molecular genetic estimates suggest that these same lineages originated deep within the Cretaceous and survived the K-Pg (Cretaceous-Paleogene; formerly Cretaceous-Tertiary or K-T) mass-extinction event. These two sources of data therefore appear to support fundamentally different models of avian evolution. The paradox has been speculated to reflect deficiencies in the fossil record, unrecognized biases in the treatment of genetic data or both. Here we attempt to explore uncertainty and limit bias entering into molecular divergence time estimates through: (i) improved taxon (n = 135) and character (n = 4594 bp mtDNA) sampling; (ii) inclusion of multiple cladistically tested internal fossil calibration points (n = 18); (iii) correction for lineage-specific rate heterogeneity using a variety of methods (n = 5); (iv) accommodation of uncertainty in tree topology; and (v) testing for possible effects of episodic evolution. 相似文献97.
98.
Cartilage type IX collagen-proteoglycan contains a large amino-terminal globular domain encoded by multiple exons 总被引:7,自引:0,他引:7
G Vasios I Nishimura H Konomi M van der Rest Y Ninomiya B R Olsen 《The Journal of biological chemistry》1988,263(5):2324-2329
Type IX collagen in cartilage consists of molecules composed of three genetically distinct polypeptide subunits. One of the subunits, alpha 2(IX), contains a covalently attached glycosaminoglycan side chain whereas a second subunit, alpha 1(IX), contains a large noncollagenous, amino-terminal domain called NC4. In this report, we describe for the first time the complete primary structure of this noncollagenous domain, based on cloning and sequencing of cDNA and genomic DNA as well as amino acid sequencing of tryptic peptides. Analysis of genomic clones has also allowed determination of the exon structure of NC4. Our results demonstrate that the noncollagenous, amino-terminal domain of alpha 1(IX) chains contains 266 amino acid residues (including the signal peptide) with 5 cysteinyl residues forming two disulfide bridges. The domain is basic with an estimated pI of 9.7, thus supporting the idea that it may participate in ionic interactions with polyanionic glycosaminoglycans in cartilage. Both the sequence and exon structure of the NC4 domain is unique among collagens and there is no obvious homology with the noncollagenous domains of other types of collagen, including the propeptides of fibrillar collagens. 相似文献
99.
100.
Sandra Wydau Guillaume van der Rest Caroline Aubard Pierre Plateau Sylvain Blanquet 《The Journal of biological chemistry》2009,284(21):14096-14104
Several l-aminoacyl-tRNA synthetases can transfer a
d-amino acid onto their cognate tRNA(s). This harmful reaction is
counteracted by the enzyme d-aminoacyl-tRNA deacylase. Two distinct
deacylases were already identified in bacteria (DTD1) and in archaea (DTD2),
respectively. Evidence was given that DTD1 homologs also exist in nearly all
eukaryotes, whereas DTD2 homologs occur in plants. On the other hand, several
bacteria, including most cyanobacteria, lack genes encoding a DTD1 homolog.
Here we show that Synechocystis sp. PCC6803 produces a third type of
deacylase (DTD3). Inactivation of the corresponding gene (dtd3)
renders the growth of Synechocystis sp. hypersensitive to the
presence of d-tyrosine. Based on the available genomes, DTD3-like
proteins are predicted to occur in all cyanobacteria. Moreover, one or several
dtd3-like genes can be recognized in all cellular types, arguing in
favor of the nearubiquity of an enzymatic function involved in the defense of
translational systems against invasion by d-amino acids.Although they are detected in various living organisms (reviewed in Ref.
1), d-amino acids
are thought not to be incorporated into proteins, because of the
stereospecificity of aminoacyl-tRNA synthetases and of the translational
machinery, including EF-Tu and the ribosome
(2). However, the
discrimination between l- and d-amino acids by
aminoacyl-tRNA synthetases is not equal to 100%. Significant
d-aminoacylation of their cognate tRNAs by Escherichia
coli tyrosyl-, tryptophanyl-, aspartyl-, lysyl-, and histidyl-tRNA
synthetases has been characterized in vitro
(3–9).
Recently, using a bacterium, transfer of d-tyrosine onto
tRNATyr was shown to occur in vivo
(10).With such misacylation reactions, the resulting
d-aminoacyl-tRNAs form a pool of metabolically inactive molecules,
at best. At worst, d-aminoacylated tRNAs infiltrate the protein
synthesis machinery. Although the latter harmful possibility has not yet been
firmly established, several cells were shown to possess a
d-tyrosyl-tRNA deacylase, or DTD, that should help them counteract
the accumulation of d-aminoacyl-tRNAs. This enzyme shows a broad
specificity, being able to remove various d-aminoacyl moieties from
the 3′-end of a tRNA
(4–6,
11). Such a function makes the
deacylase a member of the family of enzymes capable of editing in
trans mis-aminoacylated tRNAs. This family includes several homologs
of aminoacyl-tRNA synthetase editing domains
(12), as well as peptidyl-tRNA
hydrolase (13,
14).Two distinct deacylases have already been discovered. The first one, called
DTD1, is predicted to occur in most bacteria and eukaryotes (see
d-amino acids, including
d-tyrosine (6). In
fact, in an E. coli Δdtd strain grown in the presence
of 2.4 mm d-tyrosine, as much as 40% of the cellular
tRNATyr pool becomes esterified with d-tyrosine
(10).
Open in a separate windowHomologs of dtd/DTD1 are not found in the available archaeal
genomes except that of Methanosphaera stadtmanae. A search for
deacylase activity in Sulfolobus solfataricus and Pyrococcus
abyssi led to the detection of another enzyme (DTD2), completely
different from the DTD1 protein
(15). Importing dtd2
into E. coli functionally compensates for dtd deprivation.
As shown in 16).Several cells contain neither dtd nor dtd2 homologs
(d-tyrosyl-tRNA deacylase
(DTD3). This protein, encoded by dtd3, behaves as a metalloenzyme.
Sensitivity of the growth of Synechocystis to external
d-tyrosine is strongly exacerbated by the disruption of
dtd3. Moreover, expression of the Synechocystis DTD3 in a
Δdtd E. coli strain, from a plasmid, restores the resistance of
the bacterium to d-tyrosine. Finally, using the available genomes,
we examined the occurrence of DTD3 in the living world. The prevalence of
DTD3-like proteins is surprisingly high. It suggests that the defense of
protein synthesis against d-amino acids is universal. 相似文献
TABLE 1
Distribution of DTD1 and DTD2 homologs in various phylogenetic groupsHomologs of DTD1 and DTD2 were searched for using a genomic Blast analysis against complete genomes in the NCBI Database (www.ncbi.nlm.nih.gov). Values in the table are number of species. For instance, E. coli is counted only once in γ-proteobacteria despite the fact that several E. coli strains have been sequenced.DTD1 | DTD2 | DTD1 + DTD2 | None | |
---|---|---|---|---|
Bacteria | ||||
Acidobacteria | 2 | 0 | 0 | 0 |
Actinobacteria | 27 | 0 | 0 | 8 |
Aquificae | 1 | 0 | 0 | 0 |
Bacteroidetes/Chlorobi | 12 | 0 | 0 | 5 |
Chlamydiae | 1 | 0 | 0 | 6 |
Chloroflexi | 4 | 0 | 0 | 0 |
Cyanobacteria | 5 | 0 | 0 | 16 |
Deinococcus/Thermus | 4 | 0 | 0 | 0 |
Firmicutes | ||||
Bacillales | 19 | 0 | 0 | 0 |
Clostridia | 19 | 0 | 0 | 0 |
Lactobacillales | 23 | 0 | 0 | 0 |
Mollicutes | 0 | 0 | 0 | 15 |
Fusobacteria/Planctomycetes | 2 | 0 | 0 | 0 |
Proteobacteria | ||||
α | 6 | 0 | 0 | 55 |
β | 24 | 0 | 0 | 11 |
γ | 80 | 0 | 0 | 8 |
δ | 15 | 0 | 0 | 0 |
ε | 1 | 0 | 0 | 12 |
Spirochaetes | 0 | 0 | 0 | 7 |
Thermotogae | 5 | 0 | 0 | 0 |
Archaea | ||||
Crenarchaeota | 0 | 13 | 0 | 0 |
Euryarchaeota | 1 | 26 | 0 | 2 |
Nanoarchaeota | 0 | 0 | 0 | 1 |
Eukaryota | ||||
Dictyosteliida | 1 | 0 | 0 | 0 |
Fungi/Metazoa | ||||
Fungi | 13 | 0 | 0 | 1 |
Metazoa | 19 | 0 | 0 | 0 |
Kinetoplastida | 3 | 0 | 0 | 0 |
Viridiplantae | 4 | 4 | 4 | 0 |