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41.
Identification of a tight junction-associated guanine nucleotide exchange factor that activates Rho and regulates paracellular permeability 总被引:14,自引:0,他引:14
Benais-Pont G Punn A Flores-Maldonado C Eckert J Raposo G Fleming TP Cereijido M Balda MS Matter K 《The Journal of cell biology》2003,160(5):729-740
Rho family GTPases are important regulators of epithelial tight junctions (TJs); however, little is known about how the GTPases themselves are controlled during TJ assembly and function. We have identified and cloned a canine guanine nucleotide exchange factor (GEF) of the Dbl family of proto-oncogenes that activates Rho and associates with TJs. Based on sequence similarity searches and immunological and functional data, this protein is the canine homologue of human GEF-H1 and mouse Lfc, two previously identified Rho-specific exchange factors known to associate with microtubules in nonpolarized cells. In agreement with these observations, immunofluorescence of proliferating MDCK cells revealed that the endogenous canine GEF-H1/Lfc associates with mitotic spindles. Functional analysis based on overexpression and RNA interference in polarized MDCK cells revealed that this exchange factor for Rho regulates paracellular permeability of small hydrophilic tracers. Although overexpression resulted in increased size-selective paracellular permeability, such cell lines exhibited a normal overall morphology and formed fully assembled TJs as determined by measuring transepithelial resistance and by immunofluorescence and freeze-fracture analysis. These data indicate that GEF-H1/Lfc is a component of TJs and functions in the regulation of epithelial permeability. 相似文献
42.
Abstract.— Localized dispersal and mating may genetically structure plant populations, resulting in matings among related individuals. This biparental inbreeding has significant consequences for the evolution of mating systems, yet is difficult to estimate in natural populations. We estimated biparental inbreeding in two populations of the largely self-fertilizing plant Aquilegia canadensis using standard inference as well as a novel experiment comparing apparent selfing between plants that were randomly relocated within populations to experimental control plants. Using two allozyme markers, biparental inbreeding ( b ) inferred from the difference between single-locus and multilocus estimates of selfing ( b = ss – sm ) was low. Less than 3% of matings involved close relatives (mean b = 0.029). In contrast, randomly relocating plants greatly reduced apparent selfing (mean ss = 0.674) compared to control plants that had been dug up and replanted in their original locations ( ss = 0.953, P = 0.002). Based on this difference in ss , we estimated that approximately 30% of all matings involved close relatives (mean b = 0.279, 95% CL = 0.072–0.428). Inference from ss – sm underestimated b in these populations by more than an order of magnitude. Biparental inbreeding is thought to influence the evolution of self-fertilization primarily through reducing the genetic cost of outcrossing. This is unlikely to be of much significance in A. canadensis because inbreeding depression (a major cost of selfing) is much stronger than the cost of outcrossing. However, biparental inbreeding combined with strong inbreeding depression may influence selection on dispersal. 相似文献
43.
44.
Eckert K Zielinski F Lo Leggio L Schneider E 《Applied microbiology and biotechnology》2002,60(4):428-436
A gene encoding a beta-1,4-glucanase (CelA) belonging to subfamily E1 of family 9 of glycoside hydrolases was cloned and sequenced from the gram-positive thermoacidophile Alicyclobacillus acidocaldarius strain ATCC27009. The translated protein contains an immunoglobulin-like domain but lacks a cellulose-binding domain. The enzyme, when overproduced in Escherichia coli and purified, displayed a temperature optimum of 70 degrees C and a pH optimum of 5.5. CelA contained one zinc and two calcium atoms. Calcium and zinc are likely to be important for temperature stability. The enzyme was most active against substrates containing beta-1,4-linked glucans (lichenan and carboxy methyl cellulose), but also exhibited activity against oat spelt xylan. A striking pattern of hydrolysis on p-nitrophenyl-glycosides was observed, with highest activity on the cellobioside derivative, some on the cellotetraoside derivative, and none on the glucoside and cellotrioside derivatives. Unmodified cellooligosaccharides were also hydrolyzed by CelA. No signal peptide for transport across the cytoplasmic membrane was detected. This, together with the substrate specificity displayed, near neutral pH optimum and irreversible inactivation at low pH, suggests a role for CelA as a cytoplasmic enzyme for the degradation of imported oligosaccharides. 相似文献
45.
We have used affinity chromatography in combination with mass spectrometry to isolate, identify, and assign a preliminary functional annotation to a large number of both known and novel proteins from rice. Rice (Oryza sativa) leaf, root, and seed tissue extracts were fractionated by column affinity chromatography using alpha-D-mannose as the ligand. Bound fractions were eluted and subjected to one-dimensional electrophoresis, followed by high-performance liquid chromatography-tandem mass spectrometric analysis of separated proteins. This multiplexed technology resulted in the isolation and identification of 136 distinct mannose binding proteins from rice. A comparative analysis demonstrates very little overlap of identified proteins between the respective tissues, and confirms the correctly compartmentalized presence of a significant number of proteins from largely tissue-specific biochemical pathways. Over 30% of the identified proteins with a previously annotated function are directly involved in sugar metabolism, including several highly expressed known rice lectins. Direct comparison of the peptide sequences identified in this study to those peptides identified in the most comprehensive survey of the rice proteome to date indicates that our current data represents a significant enrichment of proteins unique to this dataset. Nearly 15% of the identified proteins, identified on the basis of exact peptide matching to sequences in the rice genomic database, represent proteins without a previously known functional annotation, indicating the potential of this combined chromatographic approach to assign a preliminary function to novel proteins in a high-throughput fashion. 相似文献
46.
Echinococcosis: an emerging or re-emerging zoonosis? 总被引:24,自引:0,他引:24
The aim of this review is a critical discussion of factors actually or potentially contributing to persistence or emergence of echinococcosis in humans. Alveolar echinococcosis (AE), a life-threatening infection of humans, is caused by a larval stage of Echinococcus multilocularis. The adult parasite inhabits the intestine of foxes and other carnivores and has a wide distribution in the northern hemisphere (North America and northern and central Eurasia). Recent surveys in central Europe have extended the known geographical occurrence of E. multilocularis in foxes from four countries at the end of the 1980s to at least 11 countries in 1999. Cases of human AE previously regularly reported from only four countries are now recorded from seven countries, but the annual incidences are low. Since adequate information from earlier surveys is not available, it is not possible to conclude if the new findings reflect a recent extension of the parasite's range or just the first identification of hitherto unnoticed endemic areas. Evidence of parasite spreading has been reported from North America and Japan. Factors with the potential of enhancing the infection risk for humans in the future include increasing fox populations and parasite prevalences, progressing invasion of cities by foxes, the establishment of urban cycles of the parasite, and the spill-over of the E. multilocularis infection from wild carnivores to domestic dogs and cats. In view of the potential severity and fatality of AE in humans health authorities should initiate internationally coordinated countermeasures. Although control programmes against human cystic echinococcosis (CE), caused by E. granulosus, have been established in some countries and effective control strategies are available, the parasite has still a wide geographical distribution affecting many countries of all continents. Thus, human CE is persisting in many parts of the world with high incidences, and in some areas it is a re-emerging problem. For example, alarming increases of the number of human cases have been reported from Bulgaria and Kazakhstan, and the People's Republic of China. Progress in control can only be expected if health authorities attribute a higher priority to this disease and if all modern diagnostic and control options (for example vaccination of intermediate host animals) can be used. 相似文献
47.
Dichogamy is very common in flowering plants and is widely thought to reduce pollen-pistil interference, especially self-pollination. Yet, the functional significance of dichogamy has rarely been studied. We investigated the nature and functioning of dichogamy in eastern Ontario populations of Aquilegia canadensis, a highly selfing columbine previously described as protogynous. We then manipulated flowers to determine whether increased protogyny would reduce self-fertilization. Contrary to previous reports, A. canadensis is not dichogamous. Controlled pollinations in a greenhouse showed that pollen tubes generally begin to develop after anther dehiscence. Although stigmas can collect pollen early in floral development, naturally pollinated flowers collected from four populations had few pollen grains on stigmas and almost no pollen tubes in styles until after anther dehiscence. Limited pollen deposition before anther dehiscence was also associated with low nectar availability and limited sepal expansion. Because inbreeding depression is strong in this species, selection may favor increased protogyny if it reduces selfing. We tested this hypothesis by comparing the level of selfing in flowers rendered protogynous by the removal of the first 19 (of 39) anthers to develop, with nonprotogynous control flowers. Contrary to expectations, protogyny did not reduce selfing. Our results emphasize the importance of detailed field observations and manipulative experiments in understanding the nature and functional significance of dichogamy. 相似文献
48.
Photoinhibition as a function of the ambient redox potential in Tris-washed PS II membrane fragments
The mode of photoinhibition as a function of the ambient redox potential (Eambient) in suspensions of Tris-washed PS II membrane fragments has been analyzed by monitoring flash-induced absorption changes
at 830 nm. It was found: (a) the detectable initial amplitude, ΔAtotal
830, as a measure of the capacity to form the `stable' radical pair, P680+ċ Q−ċ
A, drastically decreases during a 10 min photoinhibition at Eambient values below +350 mV; (b) conversely, the normalized extent of the 18 μs relaxation kinetics, ΔA18 μ s
830 as a measure of the electron transfer from YZ to P680+ċ becomes highly susceptible to light stress when Eambient exceeds values of about +350 mV; (c) effects of the ambient redox potentials are highly pronounced during light exposure
under anaerobic conditions, while much smaller differences arise under aerobic conditions; (d) the extent of damage does not
correlate with the total concentration of K3[Fe(CN)6] and K4[Fe(CN)6] in the suspension during photoinhibition but rather depends on the Em-values; (e) qualitatively similar features are observed when the redox buffer system K3[Fe(CN)6]/Na2S2O4 is replaced by K2[IrCl6]/Na2S2O4; (f) the characteristic Eambient-dependence of photoinhibition is observed only under anaerobic conditions. The results are discussed with respect to different
redox components that might be involved, including brief comments on a possible role of Cyt b559.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
49.
Effect of Pasture Trees on Soil Nitrogen and Organic Matter: Implications for Tropical Montane Forest Restoration 总被引:4,自引:0,他引:4
In lower-montane ecosystems of Ecuador, Setaria sphacelata (foxtail grass), the predominant introduced pasture species, forms a tussock grassland that reduces soil nitrogen and resists recolonization of forest vegetation. We compared the influence of individual trees or small clusters of nitrogen-fixing ( Inga sp., Fabaceae) and non-nitrogen-fixing trees ( Psidium guajava L., guava) on the soil and abiotic conditions that affect further regeneration of forest vegetation within pastures. Pasture trees ameliorated air temperature and light intensity to levels similar to those in adjacent intact forest. Beneath Inga , soil NO3 − -N was four times higher than in open pasture. Nitrification was five times higher under Inga canopies than in open pastures for both field and laboratory incubations. This suggests that the increased soil N transformations under Inga are derived mainly from improved soil rather than microenvironmental conditions. Psidium canopies slightly increased field nitrification but had no effect under laboratory conditions. We also compared the natural abundance 13 C signature and the carbon and nitrogen content of subcanopy soil with adjacent open pasture soil. Inga increased the C and N content of the upper 5 cm of soil and increased by 7% the fraction of soil organic matter derived from C3 plants. The improved soil and abiotic conditions beneath the canopies of N-fixing pasture trees favor the establishment and growth of woody montane species, suggesting that these trees could be used to accelerate forest regeneration within abandoned pastures. 相似文献
50.
The density and dispersion of individuals, nonequilibrium demographics, and habitat fragmentation all affect the magnitude and extent of spatial genetic structure within forest tree populations. Here, we investigate the link between historical demography and spatial genetic structure within ecologically contrasting stands of foxtail pine (Pinus balfouriana) in the Klamath Mountains of northern California. We defined two stand types a priori, based largely on differences in foxtail pine density and basal area, and for each type we sampled two stands. Population expansions, likely from Pleistocene bottlenecks, were detected in three of the four stands. The magnitude and extent of spatial autocorrelation among genotypes at five nuclear microsatellites differed dramatically among stands, with those having lower foxtail pine density exhibiting strong patterns of isolation by distance. Moran's I statistics were 7-fold higher for the first distance class (<25 m) in these stands relative to those observed in stands with higher foxtail pine density (I(25) = 0.14 vs. 0.02). We conclude that differences in spatial genetic structure between stand types are due to differences in ecological attributes that affected expansion from inferred bottlenecks. 相似文献