全文获取类型
收费全文 | 544篇 |
免费 | 47篇 |
国内免费 | 1篇 |
专业分类
592篇 |
出版年
2021年 | 5篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 18篇 |
2014年 | 18篇 |
2013年 | 22篇 |
2012年 | 37篇 |
2011年 | 32篇 |
2010年 | 15篇 |
2009年 | 9篇 |
2008年 | 32篇 |
2007年 | 23篇 |
2006年 | 27篇 |
2005年 | 9篇 |
2004年 | 18篇 |
2003年 | 21篇 |
2002年 | 24篇 |
2001年 | 7篇 |
2000年 | 16篇 |
1999年 | 14篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 11篇 |
1973年 | 10篇 |
1972年 | 4篇 |
1971年 | 8篇 |
1970年 | 4篇 |
1969年 | 5篇 |
1968年 | 4篇 |
1967年 | 5篇 |
1966年 | 5篇 |
排序方式: 共有592条查询结果,搜索用时 15 毫秒
71.
To investigate the encoding of behaviorally relevant stimuli in the rodent whisker-somatosensory system, we recorded responses to moving gratings from trigeminal ganglion neurons. This allowed us to quantify how spike patterns in these neurons encode behaviorally distinguishable tactile stimuli presented with the variability inherent in a freely moving whisker paradigm. Our stimulus set consisted of three grating plates with raised bars of the same thickness (275 microm) having different spatial periods (1.0, 1.1, and 1.5 mm) swept rostro-caudally past the whiskers at velocities ranging from 50 to 330 mm/s. This resulted in 20 presentations each of nine different temporal frequencies (ranging from 50 to 220 Hz) for every grating plate. We found that despite the additional degrees of freedom introduced in this freely moving whisker paradigm, firing patterns from the majority (83%) of trigeminal ganglion neurons were statistically distinguishable, and corresponded to the temporal frequency of stimulation. The range of velocities (100-160 mm/s) that resulted in the most accurate and least variable representation of stimulus temporal frequency by trigeminal firing patterns closely corresponds to the whisking velocities employed by trained rats performing similar discrimination tasks. This suggests that, during naturally occurring whisking, individual primary afferents faithfully encode temporal frequency evoked by whisker contacts. 相似文献
72.
Lamour KH Mudge J Gobena D Hurtado-Gonzales OP Schmutz J Kuo A Miller NA Rice BJ Raffaele S Cano LM Bharti AK Donahoo RS Finley S Huitema E Hulvey J Platt D Salamov A Savidor A Sharma R Stam R Storey D Thines M Win J Haas BJ Dinwiddie DL Jenkins J Knight JR Affourtit JP Han CS Chertkov O Lindquist EA Detter C Grigoriev IV Kamoun S Kingsmore SF 《Molecular plant-microbe interactions : MPMI》2012,25(10):1350-1360
The oomycete vegetable pathogen Phytophthora capsici has shown remarkable adaptation to fungicides and new hosts. Like other members of this destructive genus, P. capsici has an explosive epidemiology, rapidly producing massive numbers of asexual spores on infected hosts. In addition, P. capsici can remain dormant for years as sexually recombined oospores, making it difficult to produce crops at infested sites, and allowing outcrossing populations to maintain significant genetic variation. Genome sequencing, development of a high-density genetic map, and integrative genomic or genetic characterization of P. capsici field isolates and intercross progeny revealed significant mitotic loss of heterozygosity (LOH) in diverse isolates. LOH was detected in clonally propagated field isolates and sexual progeny, cumulatively affecting >30% of the genome. LOH altered genotypes for more than 11,000 single-nucleotide variant sites and showed a strong association with changes in mating type and pathogenicity. Overall, it appears that LOH may provide a rapid mechanism for fixing alleles and may be an important component of adaptability for P. capsici. 相似文献
73.
Hellman B Salehi A Grapengiesser E Gylfe E 《Biochemical and biophysical research communications》2012,417(4):1219-1223
Recent studies of isolated human islets have shown that glucose induces hormone release with repetitive pulses of insulin and somatostatin in antisynchrony with those of glucagon. Since the mouse is the most important animal model we studied the temporal relation between hormones released from mouse islets. Batches of 5-10 islets were perifused and the hormones measured with radioimmunoassay in 30s fractions. At 3mM glucose, hormone secretion was stable with no detectable pulses of glucagon, insulin or somatostatin. Increase of glucose to 20mM resulted in an early secretory phase with a glucagon peak followed by peaks of insulin and somatostatin. Subsequent hormone secretion was pulsatile with a periodicity of 5min. Cross-correlation analyses showed that the glucagon pulses were antisynchronous to those of insulin and somatostatin. In contrast to the marked stimulation of insulin and somatostatin secretion, the pulsatility resulted in inhibition of overall glucagon release. The cytoarchitecture of mouse islets differs from that of human islets, which may affect the interactions between the hormone-producing cells. Although indicating that paracrine regulation is important for the characteristic patterns of pulsatile hormone secretion, the mouse data mimic those of human islets with more than 20-fold variations of the insulin/glucagon ratio. The data indicate that the mouse serves as an appropriate animal model for studying the temporal relation between the islet hormones controlling glucose production in the liver. 相似文献
74.
Hendra virus is a highly pathogenic paramyxovirus classified as a biosafety level four agent. The fusion (F) protein of Hendra virus is critical for promoting viral entry and cell-to-cell fusion. To be fusogenically active, Hendra virus F must undergo endocytic recycling and cleavage by the endosomal/lysosomal protease cathepsin L, but the route of Hendra virus F following internalization and the recycling signals involved are poorly understood. We examined the intracellular distribution of Hendra virus F following endocytosis and showed that it is primarily present in Rab5- and Rab4-positive endosomal compartments, suggesting that cathepsin L cleavage occurs in early endosomes. Hendra virus F transmembrane domain (TMD) residues S490 and Y498 were found to be important for correct Hendra virus F recycling, with the hydroxyl group of S490 and the aromatic ring of Y498 important for this process. In addition, changes in association of isolated Hendra virus F TMDs correlated with alterations to Hendra virus F recycling, suggesting that appropriate TMD interactions play an important role in endocytic trafficking. 相似文献
75.
Spiegel R Pines O Ta-Shma A Burak E Shaag A Halvardson J Edvardson S Mahajna M Zenvirt S Saada A Shalev S Feuk L Elpeleg O 《American journal of human genetics》2012,90(3):518-523
Degeneration of the cerebrum, cerebellum, and retina in infancy is part of the clinical spectrum of lysosomal storage disorders, mitochondrial respiratory chain defects, carbohydrate glycosylation defects, and infantile neuroaxonal dystrophy. We studied eight individuals from two unrelated families who presented at 2-6 months of age with truncal hypotonia and athetosis, seizure disorder, and ophthalmologic abnormalities. Their course was characterized by failure to acquire developmental milestones and culminated in profound psychomotor retardation and progressive visual loss, including optic nerve and retinal atrophy. Despite their debilitating state, the disease was compatible with survival of up to 18 years. Laboratory investigations were normal, but the oxidation of glutamate by muscle mitochondria was slightly reduced. Serial brain MRI displayed progressive, prominent cerebellar atrophy accompanied by thinning of the corpus callosum, dysmyelination, and frontal and temporal cortical atrophy. Homozygosity mapping followed by whole-exome sequencing disclosed a Ser112Arg mutation in ACO2, encoding mitochondrial aconitase, a component of the Krebs cycle. Specific aconitase activity in the individuals' lymphoblasts was severely reduced. Under restrictive conditions, the mutant human ACO2 failed to complement a yeast ACO1 deletion strain, whereas the wild-type human ACO2 succeeded, indicating that this mutation is pathogenic. Thus, a defect in mitochondrial aconitase is associated with an infantile neurodegenerative disorder affecting mainly the cerebellum and retina. In the absence of noninvasive biomarkers, determination of the ACO2 sequence or of aconitase activity in lymphoblasts are warranted in similarly affected individuals, based on clinical and neuroradiologic grounds. 相似文献
76.
T Akerström J Crona A Delgado Verdugo LF Starker K Cupisti HS Willenberg WT Knoefel W Saeger A Feller J Ip P Soon M Anlauf PF Alesina KW Schmid M Decaussin P Levillain B Wängberg JL Peix B Robinson J Zedenius M Bäckdahl S Caramuta KA Iwen J Botling P Stålberg JL Kraimps H Dralle P Hellman S Sidhu G Westin H Lehnert MK Walz G Akerström T Carling M Choi RP Lifton P Björklund 《PloS one》2012,7(7):e41926
Background
Aldosterone producing lesions are a common cause of hypertension, but genetic alterations for tumorigenesis have been unclear. Recently, either of two recurrent somatic missense mutations (G151R or L168R) was found in the potassium channel KCNJ5 gene in aldosterone producing adenomas. These mutations alter the channel selectivity filter and result in Na+ conductance and cell depolarization, stimulating aldosterone production and cell proliferation. Because a similar mutation occurs in a Mendelian form of primary aldosteronism, these mutations appear to be sufficient for cell proliferation and aldosterone production. The prevalence and spectrum of KCNJ5 mutations in different entities of adrenocortical lesions remain to be defined.Materials and Methods
The coding region and flanking intronic segments of KCNJ5 were subjected to Sanger DNA sequencing in 351 aldosterone producing lesions, from patients with primary aldosteronism and 130 other adrenocortical lesions. The specimens had been collected from 10 different worldwide referral centers.Results
G151R or L168R somatic mutations were identified in 47% of aldosterone producing adenomas, each with similar frequency. A previously unreported somatic mutation near the selectivity filter, E145Q, was observed twice. Somatic G151R or L168R mutations were also found in 40% of aldosterone producing adenomas associated with marked hyperplasia, but not in specimens with merely unilateral hyperplasia. Mutations were absent in 130 non-aldosterone secreting lesions. KCNJ5 mutations were overrepresented in aldosterone producing adenomas from female compared to male patients (63 vs. 24%). Males with KCNJ5 mutations were significantly younger than those without (45 vs. 54, respectively; p<0.005) and their APAs with KCNJ5 mutations were larger than those without (27.1 mm vs. 17.1 mm; p<0.005).Discussion
Either of two somatic KCNJ5 mutations are highly prevalent and specific for aldosterone producing lesions. These findings provide new insight into the pathogenesis of primary aldosteronism. 相似文献77.
Actin exists as a monomer (G-actin) which can be polymerized to filaments) F-actin) that under the influence of actin-binding proteins and polycations bundle and contribute to the formation of the cytoskeleton. Bundled actin from lysed cells increases the viscosity of sputum in lungs of cystic fibrosis patients. The human host defense peptide LL-37 was previously shown to induce actin bundling and was thus hypothesized to contribute to the pathogenicity of this disease. In this work, interactions between actin and the cationic LL-37 were studied by optical, proteolytic and surface plasmon resonance methods and compared to those obtained with scrambled LL-37 and with the cationic protein lysozyme. We show that LL-37 binds strongly to CaATP-G-actin while scrambled LL-37 does not. While LL-37, at superstoichiometric LL-37/actin concentrations polymerizes MgATP-G-actin, at lower non-polymerizing concentrations LL-37 inhibits actin polymerization by MgCl2 or NaCl. LL-37 bundles Mg-F-actin filaments both at low and physiological ionic strength when in equimolar or higher concentrations than those of actin. The LL-37 induced bundles are significantly less sensitive to increase in ionic strength than those induced by scrambled LL-37 and lysozyme. LL-37 in concentrations lower than those needed for actin polymerization or bundling, accelerates cleavage of both monomer and polymer actin by subtilisin. Our results indicate that the LL-37-actin interaction is partially electrostatic and partially hydrophobic and that a specific actin binding sequence in the peptide is responsible for the hydrophobic interaction. LL-37-induced bundles, which may contribute to the accumulation of sputum in cystic fibrosis, are dissociated very efficiently by DNase-1 and also by cofilin. 相似文献
78.
The genome of the polar eukaryotic microalga Coccomyxa subellipsoidea reveals traits of cold adaptation 总被引:2,自引:0,他引:2
Blanc G Agarkova I Grimwood J Kuo A Brueggeman A Dunigan DD Gurnon J Ladunga I Lindquist E Lucas S Pangilinan J Pröschold T Salamov A Schmutz J Weeks D Yamada T Lomsadze A Borodovsky M Claverie JM Grigoriev IV Van Etten JL 《Genome biology》2012,13(5):R39-12
Background
Little is known about the mechanisms of adaptation of life to the extreme environmental conditions encountered in polar regions. Here we present the genome sequence of a unicellular green alga from the division chlorophyta, Coccomyxa subellipsoidea C-169, which we will hereafter refer to as C-169. This is the first eukaryotic microorganism from a polar environment to have its genome sequenced.Results
The 48.8 Mb genome contained in 20 chromosomes exhibits significant synteny conservation with the chromosomes of its relatives Chlorella variabilis and Chlamydomonas reinhardtii. The order of the genes is highly reshuffled within synteny blocks, suggesting that intra-chromosomal rearrangements were more prevalent than inter-chromosomal rearrangements. Remarkably, Zepp retrotransposons occur in clusters of nested elements with strictly one cluster per chromosome probably residing at the centromere. Several protein families overrepresented in C. subellipsoidae include proteins involved in lipid metabolism, transporters, cellulose synthases and short alcohol dehydrogenases. Conversely, C-169 lacks proteins that exist in all other sequenced chlorophytes, including components of the glycosyl phosphatidyl inositol anchoring system, pyruvate phosphate dikinase and the photosystem 1 reaction center subunit N (PsaN).Conclusions
We suggest that some of these gene losses and gains could have contributed to adaptation to low temperatures. Comparison of these genomic features with the adaptive strategies of psychrophilic microbes suggests that prokaryotes and eukaryotes followed comparable evolutionary routes to adapt to cold environments. 相似文献79.
Robin A. Ohm Nicolas Feau Bernard Henrissat Conrad L. Schoch Benjamin A. Horwitz Kerrie W. Barry Bradford J. Condon Alex C. Copeland Braham Dhillon Fabian Glaser Cedar N. Hesse Idit Kosti Kurt LaButti Erika A. Lindquist Susan Lucas Asaf A. Salamov Rosie E. Bradshaw Lynda Ciuffetti Richard C. Hamelin Gert H. J. Kema Christopher Lawrence James A. Scott Joseph W. Spatafora B. Gillian Turgeon Pierre J. G. M. de Wit Shaobin Zhong Stephen B. Goodwin Igor V. Grigoriev 《PLoS pathogens》2012,8(12)
The class Dothideomycetes is one of the largest groups of fungi with a high level of ecological diversity including many plant pathogens infecting a broad range of hosts. Here, we compare genome features of 18 members of this class, including 6 necrotrophs, 9 (hemi)biotrophs and 3 saprotrophs, to analyze genome structure, evolution, and the diverse strategies of pathogenesis. The Dothideomycetes most likely evolved from a common ancestor more than 280 million years ago. The 18 genome sequences differ dramatically in size due to variation in repetitive content, but show much less variation in number of (core) genes. Gene order appears to have been rearranged mostly within chromosomal boundaries by multiple inversions, in extant genomes frequently demarcated by adjacent simple repeats. Several Dothideomycetes contain one or more gene-poor, transposable element (TE)-rich putatively dispensable chromosomes of unknown function. The 18 Dothideomycetes offer an extensive catalogue of genes involved in cellulose degradation, proteolysis, secondary metabolism, and cysteine-rich small secreted proteins. Ancestors of the two major orders of plant pathogens in the Dothideomycetes, the Capnodiales and Pleosporales, may have had different modes of pathogenesis, with the former having fewer of these genes than the latter. Many of these genes are enriched in proximity to transposable elements, suggesting faster evolution because of the effects of repeat induced point (RIP) mutations. A syntenic block of genes, including oxidoreductases, is conserved in most Dothideomycetes and upregulated during infection in L. maculans, suggesting a possible function in response to oxidative stress. 相似文献
80.
Peptide mass fingerprinting (PMF) has over the years become one of the most commonly used tools for high-throughput analysis and identification of proteins. This method is applicable when relatively simple samples have to be analysed and it is commonly used for analysing proteins previously separated by 2-DE. The most common type of instrument used for this approach is the MALDI-TOF that has proved to be particularly suitable for the PMF analysis because of its characteristics of speed, robustness, sensitivity and automation. We have used a MALDI-TOF equipped with a novel parallel PSD capability (MALDI micro MX), to perform the analysis of two sets of different biological samples isolated by 2-DE. By using a method that integrates the data obtained by PMF analysis with the PSD data obtained in the same experiment, we show that the new multiplexed PSD solution increases the protein identification rate compared to the normal PMF approach. We also investigated the use of a charge-directed fragmentation modification reagent to improve the identification rate and confidence levels. 相似文献