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81.
L1 is a multidomain transmembrane neural recognition molecule essential for neurohistogenesis. While moieties in the immunoglobulin-like domains of L1 have been implicated in both heterophilic and homophilic binding, the function of the fibronectin (FN)-like repeats remains largely unresolved. Here, we demonstrate that the third FN-like repeat of L1 (FN3) spontaneously homomultimerizes to form trimeric and higher order complexes. Remarkably, these complexes support direct RGD-independent interactions with several integrins, including alpha(v)beta(3) and alpha(5)beta(1). A pep- tide derived from the putative C-C' loop of FN3 (GSQRKHSKRHIHKDHV(852)) also forms trimeric complexes and supports alpha(v)beta(3) and alpha(5)beta(1) binding. Substitution of the dibasic RK(841) and KR(845) sequences within this peptide or the FN3 domain limited multimerization and abrogated integrin binding. Evidence is presented that the multimerization of, and integrin binding to, the FN3 domain is regulated both by conformational constraints imposed by other domains and by plasmin- mediated cleavage within the sequence RK( downward arrow)HSK( downward arrow)RH(846). The integrin alpha(9)beta(1), which also recognizes the FN3 domain, colocalizes with L1 in a manner restricted to sites of cell-cell contact. We propose that distal receptor ligation events at the cell-cell interface may induce a conformational change within the L1 ectodomain that culminates in receptor multimerization and integrin recruitment via interaction with the FN3 domain. 相似文献
82.
This study examines the oviposition response of a specialist weevil (Mogulones larvatus) to patches of its host, the noxious weed Paterson"s curse/salvation Jane (Echium plantagineum). We simultaneously examined the effect of patch size and plant density (and their interaction), on the recorded oviposition
patterns. Our results show that oviposition first occurred on the largest patches with the highest number of plants. However,
there was no significant effect of patch size or number of plants per patch at the end of the experiment. At this time the
level of attack per plant was negatively correlated with plant density. This negative effect of density on the level of oviposition
was not mediated by a reduction in plant size at higher densities. The pattern observed may indicate a risk-spreading strategy
by females.
Received: 15 July 1999 / Accepted: 14 April 2000 相似文献
83.
Identification of a novel gene involved in pilin glycosylation in Neisseria meningitidis 总被引:8,自引:8,他引:0
Michael P. Jennings Mumtaz Virji Debbie Evans Virginia Foster Yogitha N. Srikhanta Liana Steeghs Peter van der Ley & E. Richard Moxon 《Molecular microbiology》1998,29(4):975-984
The pili of Neisseria meningitidis are a key virulence factor, being major adhesins of this capsulate organism that contribute to specificity for the human host. Recently it has been reported that meningococcal pili are post-translationally modified by the addition of an O-linked trisaccharide, Gal (β1–4) Gal (α1–3) 2,4-diacetimido-2,4,6-trideoxyhexose. Using a set of random genomic sequences from N. meningitidis strain MC58, we have identified a novel gene homologous to a family of glycosyltransferases. A plasmid clone containing the gene was isolated from a genomic library of N. meningitidis strain MC58 and its nucleotide sequence determined. The clone contained a complete copy of the gene, here designated pglA (pilin glycosylation). Insertional mutations were constructed in pglA in a range of meningococcal strains with well-defined lipopolysaccharide (LPS) or pilin-linked glycan structures to determine whether pglA had a role in the biosynthesis of these molecules. There was no alteration in the phenotype of LPS from pglA mutant strains as judged by gel migration and the binding of monoclonal antibodies. In contrast, decreased gel migration of the pilin subunit molecules of pglA mutants was observed, which was similar to the migration of pilins of galE mutants of same strains, supporting the notion that pglA is a glycosyltransferase involved in the biosynthesis of the pilin-linked trisaccharide structure. The pglA mutation, like the galE mutation reported previously, had no effect on pilus-mediated adhesion to human epithelial or endothelial cells. Pilin from pglA mutants were unable to bind to monospecific antisera recognizing the Gal (β1–4) Gal structure, suggesting that PglA is a glycosyltransferase involved in the addition of galactose of the trisaccharide substituent of pilin. 相似文献
84.
Charles R. C. Sheppard 《Biodiversity and Conservation》1998,7(7):847-868
Corals from 26 sites in the Indian Ocean, from numerous taxonomic sources, are analysed for distribution patterns after applying a consistent synonymy. The data set contains double the amount of distribution information used previously. Cluster analysis shows several contiguous regional groupings within this ocean, and no geographically dispersed groupings exist. Between-site species similarity correlates negatively with distance between sites. Coral species diversity and genus diversity plotted with latitude and longitude confirm that a band of high diversity stretches across the entire Indian Ocean, but that in this Ocean, unlike the Pacific and greater Caribbean area, there is no clear gradient with latitude at least up to the latitudinal limits of coral growth. About half the species are widespread throughout the Indian Ocean. Species frequency/distribution curves and cumulative frequency curves show that 150 species occur at only 2–4 sites. Multi-dimensional scaling (MDS) analysis using only these species confirms that they are important in forming sub-regional groupings which are superimposed on a general Indian Ocean homogeneity.The perennial problem of error in taxonomic data sets is examined. Increasing taxonomic error is introduced into the data using random methods. It is found that about 25% more error can be added to this data set before the relationship between similarity coefficient and geographical distance between pairs of sites is lost. Measures extracted from the clustering procedure using the original data and the data sets with added taxonomic error, show a sharp loss in cluster formation after addition of about 10 or 20% more error. 相似文献
85.
86.
87.
While recent imaging techniques provide insights into biological processes from the molecular to the cellular scale, phenotypes at larger scales remain poorly amenable to quantitative analyses. For example, investigations of the biophysical mechanisms generating skin morphological complexity and diversity would greatly benefit from 3D geometry and colour-texture reconstructions. Here, we report on R2OBBIE-3D, an integrated system that combines a robotic arm, a high-resolution digital colour camera, an illumination basket of high-intensity light-emitting diodes and state-of-the-art 3D-reconstruction approaches. We demonstrate that R2OBBIE generates accurate 3D models of biological objects between 1 and 100 cm, makes multiview photometric stereo scanning possible in practical processing times, and enables the capture of colour-texture and geometric resolutions better than 15 μm without the use of magnifying lenses. R2OBBIE has the potential to greatly improve quantitative analyses of phenotypes in addition to providing multiple new applications in, e.g., biomedical science. 相似文献
88.
Osamu Nureki Patrick O’Donoghue Nobuhisa Watanabe Atsuhiko Ohmori Hiroyuki Oshikane Yuhei Araiso Kelly Sheppard Dieter S?ll Ryuichiro Ishitani 《Nucleic acids research》2010,38(20):7286-7297
The molecular basis of the genetic code relies on the specific ligation of amino acids to their cognate tRNA molecules. However, two pathways exist for the formation of Gln-tRNAGln. The evolutionarily older indirect route utilizes a non-discriminating glutamyl-tRNA synthetase (ND-GluRS) that can form both Glu-tRNAGlu and Glu-tRNAGln. The Glu-tRNAGln is then converted to Gln-tRNAGln by an amidotransferase. Since the well-characterized bacterial ND-GluRS enzymes recognize tRNAGlu and tRNAGln with an unrelated α-helical cage domain in contrast to the β-barrel anticodon-binding domain in archaeal and eukaryotic GluRSs, the mode of tRNAGlu/tRNAGln discrimination in archaea and eukaryotes was unknown. Here, we present the crystal structure of the Methanothermobacter thermautotrophicus ND-GluRS, which is the evolutionary predecessor of both the glutaminyl-tRNA synthetase (GlnRS) and the eukaryotic discriminating GluRS. Comparison with the previously solved structure of the Escherichia coli GlnRS-tRNAGln complex reveals the structural determinants responsible for specific tRNAGln recognition by GlnRS compared to promiscuous recognition of both tRNAs by the ND-GluRS. The structure also shows the amino acid recognition pocket of GluRS is more variable than that found in GlnRS. Phylogenetic analysis is used to reconstruct the key events in the evolution from indirect to direct genetic encoding of glutamine. 相似文献
89.
Henri D. Grissino-Mayer Paul R. Sheppard Malcolm K. Cleaveland Paolo Cherubini Peter Ratcliff John Topham 《Dendrochronologia》2010,28(3):149-159
A recent report by Mondino and Avalle (2009) was widely distributed that demonstrated a re-dating of the famous “Messiah” violin, a violin attributed to Antonio Stradivari with a label date of 1716. An outermost ring date of 1844 is instead suggested rather than dates in the 1680s reported in previous studies. Mondino and Avalle suggest that this outermost ring date supports the attribution of the violin to Jean-Baptiste Vuillaume, a prolific French instrument maker who was well known for his copies of famous instruments. The statistical techniques and exercises used by Mondino and Avalle, however, are problematic and do not support this revised outermost date for the “Messiah” violin. Raw measurement data with original trends are used in their statistical crossdating, properties previously shown to hinder precise crossdating. They then substantiate their re-dating with polynomial trend curves, which has ever been accepted practice in dendrochronology. Furthermore, the authors use re-scaled correlation coefficients and t-values which artificially inflate the strength of the relationship between tree-ring series that are being statistically crossdated. Using the exact same tree-ring data, but using accepted techniques in statistical crossdating (e.g., the removal of all low-frequency trends and autocorrelation), we could not verify the revised dating of the “Messiah” violin. We urge caution for those who intend to use the SynchroSearch software, book, and lesson plans developed and distributed by Mondino and Avalle. This study illustrates the adverse effects possible in dendrochronology when investigators do not adhere to accepted and time-tested techniques, and are not versed in the extensive literature that highlights issues commonly encountered in statistical crossdating. 相似文献
90.
Eliso Kvavadze Goderdzi Narimanishvili Liana Bitadze 《Vegetation History and Archaeobotany》2010,19(5-6):479-494
Pollen analyses were performed on sediment samples from ten different Saphar-Kharaba burials dating to the 15th–14th centuries b.c. Along with pollen and spores, a large amount of micro-remains of textile fibres was found near skeleton bones and especially under big bones. It was established that in all the studied samples 95% of the remains of the clothing and shroud of the deceased was made of Linum (flax) and Gossypium (cotton). Wool fibres were found in very small quantities. Based on pollen spectra and the number of the fibres found in the samples taken from under the skull it became possible to identify the sex of the deceased and especially that of children, which is rather difficult to do using palaeoanthropological methods alone. The discovery of cotton fibres in the burials of the early late Bronze Age is new not only for the Georgian region under consideration, but also for the whole Caucasus. This might indicate trade relations of the peoples of the southern Caucasus with India, where at that time cotton textiles were manufactured. 相似文献