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41.

Background  

Microarray-based pooled DNA experiments that combine the merits of DNA pooling and gene chip technology constitute a pivotal advance in biotechnology. This new technique uses pooled DNA, thereby reducing costs associated with the typing of DNA from numerous individuals. Moreover, use of an oligonucleotide gene chip reduces costs related to processing various DNA segments (e.g., primers, reagents). Thus, the technique provides an overall cost-effective solution for large-scale genomic/genetic research. However, few publicly shared tools are available to systematically analyze the rapidly accumulating volume of whole-genome pooled DNA data.  相似文献   
42.

Background and Aims

Mycorrhizal specialization has been shown to limit recruitment capacity in orchids, but an increasing number of orchids are being documented as invasive or weed-like. The reasons for this proliferation were examined by investigating mycorrhizal fungi and edaphic correlates of Microtis media, an Australian terrestrial orchid that is an aggressive ecosystem and horticultural weed.

Methods

Molecular identification of fungi cultivated from M. media pelotons, symbiotic in vitro M. media seed germination assays, ex situ fungal baiting of M. media and co-occurring orchid taxa (Caladenia arenicola, Pterostylis sanguinea and Diuris magnifica) and soil physical and chemical analyses were undertaken.

Key Results

It was found that: (1) M. media associates with a broad taxonomic spectrum of mycobionts including Piriformospora indica, Sebacina vermifera, Tulasnella calospora and Ceratobasidium sp.; (2) germination efficacy of mycorrhizal isolates was greater for fungi isolated from plants in disturbed than in natural habitats; (3) a higher percentage of M. media seeds germinate than D. magnifica, P. sanguinea or C. arenicola seeds when incubated with soil from M. media roots; and (4) M. media–mycorrhizal fungal associations show an unusual breadth of habitat tolerance, especially for soil phosphorus (P) fertility.

Conclusions

The findings in M. media support the idea that invasive terrestrial orchids may associate with a diversity of fungi that are widespread and common, enhance seed germination in the host plant but not co-occurring orchid species and tolerate a range of habitats. These traits may provide the weedy orchid with a competitive advantage over co-occurring orchid species. If so, invasive orchids are likely to become more broadly distributed and increasingly colonize novel habitats.  相似文献   
43.
Serratia marcescens is a versatile opportunistic pathogen that can cause a variety of infections, including bacteremia. Our previous work established that the capsule polysaccharide (CPS) biosynthesis and translocation locus contributes to the survival of S. marcescens in a murine model of bacteremia and in human serum. In this study, we determined the degree of capsule genetic diversity among S. marcescens isolates. Capsule loci (KL) were extracted from >300 S. marcescens genome sequences and compared. A phylogenetic comparison of KL sequences demonstrated a substantial level of KL diversity within S. marcescens as a species and a strong delineation between KL sequences originating from infection isolates versus environmental isolates. Strains from five of the identified KL types were selected for further study and electrophoretic analysis of purified CPS indicated the production of distinct glycans. Polysaccharide composition analysis confirmed this observation and identified the constituent monosaccharides for each strain. Two predominant infection-associated clades, designated KL1 and KL2, emerged from the capsule phylogeny. Bacteremia strains from KL1 and KL2 were determined to produce ketodeoxynonulonic acid and N-acetylneuraminic acid, two sialic acids that were not found in strains from other clades. Further investigation of KL1 and KL2 sequences identified two genes, designated neuA and neuB, that were hypothesized to encode sialic acid biosynthesis functions. Disruption of neuB in a KL1 isolate resulted in the loss of sialic acid and CPS production. The absence of sialic acid and CPS production also led to increased susceptibility to internalization by a human monocytic cell line, demonstrating that S. marcescens phagocytosis resistance requires CPS. Together, these results establish the capsule genetic repertoire of S. marcescens and identify infection-associated clades with sialic acid CPS components.  相似文献   
44.
45.
Attempts to develop a vaccine to prevent genital herpes simplex virus 2 (HSV-2) disease have been only marginally successful, suggesting that novel strategies are needed. Immunization with HSV-2 glycoprotein C (gC-2) and gD-2 was evaluated in mice and guinea pigs to determine whether adding gC-2 to a gD-2 subunit vaccine would improve protection by producing antibodies that block gC-2 immune evasion from complement. Antibodies produced by gC-2 immunization blocked the interaction between gC-2 and complement C3b, and passive transfer of gC-2 antibody protected complement-intact mice but not C3 knockout mice against HSV-2 challenge, indicating that gC-2 antibody is effective, at least in part, because it prevents HSV-2 evasion from complement. Immunization with gC-2 also produced neutralizing antibodies that were active in the absence of complement; however, the neutralizing titers were higher when complement was present, with the highest titers in animals immunized with both antigens. Animals immunized with the gC-2-plus-gD-2 combination had robust CD4+ T-cell responses to each immunogen. Multiple disease parameters were evaluated in mice and guinea pigs immunized with gC-2 alone, gD-2 alone, or both antigens. In general, gD-2 outperformed gC-2; however, the gC-2-plus-gD-2 combination outperformed gD-2 alone, particularly in protecting dorsal root ganglia in mice and reducing recurrent vaginal shedding of HSV-2 DNA in guinea pigs. Therefore, the gC-2 subunit antigen enhances a gD-2 subunit vaccine by stimulating a CD4+ T-cell response, by producing neutralizing antibodies that are effective in the absence and presence of complement, and by blocking immune evasion domains that inhibit complement activation.  相似文献   
46.
Limitations associated with immunofluorescence enumeration of bacteria in soil derive largely from the efficiency with which cells can be separated from soil particles and collected on membrane filters for staining. Many tropical soils fix added bacteria tightly, resulting in low recoveries. Eight soils, representative of three of the major soil orders found in the tropics (oxisols, vertisols, and inceptisols), were tested for recovery of added Rhizobium strains. All except one Hawaiian andept (Typic Eutrandept) yielded recoveries ranging from <1 to 13%. Recovery from the andept was 100%. In soil-sand mixtures, addition of only a small amount of soil caused a dramatic decrease in recovery of added rhizobia. Increasing the soil content of the mixture from 0% (10 g of sand) to 50% (5 g of soil-5 g of sand) reduced recoveries from >90 to <1%. Varying the ionic strength and pH of the extracting solution did not cause marked increases in recovery. Protein solutions, ethylenediaminetetraacetate, and NaHCO3, on the other hand, improved release of bacteria. We report a modification to the usual membrane filter immunofluorescence procedure which yielded consistently high and reproducible recovery (coefficient of variation, 30%) of rhizobia from several tropical soils. In the modified procedure, partially hydrolyzed gelatin, diluted in ammonium phosphate, was used to suspend the soil. This caused dispersion of the soil and release of the bacteria from soil flocs. The efficiency of recovery of Rhizobium spp. from several tropical and two temperate soils remained high as the content of these soils in soil-sand mixtures was increased from 0 to 100%. The modified membrane filter immunofluorescence procedure was used to follow the growth of a strain of chickpea (Cicer arietinum) Rhizobium in a sterilized oxisol. The results showed a close agreement with viable counts at different stages during the growth cycle. Diluent for the hydrolyzed gelatin also had a marked effect on recovery. The efficiency of release of Rhizobium spp. from an oxisol was in the following order for the diluents used: 0.1 M (NH4)2HPO4 > 0.1 M Na2HPO4 = 0.1 M sodium-phosphate-buffered saline (pH 7.2) > 0.2 M NH4Cl > 0.2 KCl > NaCl = LiCl > water.  相似文献   
47.

Background and Aims

Recent phylogenetic analysis has placed the aquatic family Hydatellaceae as an early-divergent angiosperm. Understanding seed dormancy, germination and desiccation tolerance of Hydatellaceae will facilitate ex situ conservation and advance hypotheses regarding angiosperm evolution.

Methods

Seed germination experiments were completed on three species of south-west Australian Hydatellaceae, Trithuria austinensis, T. bibracteata and T. submersa, to test the effects of temperature, light, germination stimulant and storage. Seeds were sectioned to examine embryo growth during germination in T. austinensis and T. submersa.

Key Results

Some embryo growth and cell division in T. austinensis and T. submersa occurred prior to the emergence of an undifferentiated embryo from the seed coat (‘germination’). Embryo differentiation occurred later, following further growth and a 3- to 4-fold increase in the number of cells. The time taken to achieve 50 % of maximum germination for seeds on water agar was 50, 35 and 37 d for T. austinensis, T bibracteata and T. submersa, respectively.

Conclusions

Seeds of Hydatellaceae have a new kind of specialized morphophysiological dormancy in which neither root nor shoot differentiates until after the embryo emerges from the seed coat. Seed biology is discussed in relation to early angiosperm evolution, together with ex situ conservation of this phylogenetically significant group.  相似文献   
48.
Summary Aeration of tissue cultured rare Australian plantsConostylis wonganensis S.D. Hopper (Haemodoraceae);Diplolaena andrewsii Ostenf.;Drummondita ericoides Harvey (Rutaceae);Eremophila resinosa F. Muell. (Myoporaceae);Eucalyptus ‘graniticola’ (Myrtaceae);Lechenaultia pulvinaris C. Gardner (goodeniaceae); andSowerbaea multicaulis E. Pritzel (Liliaceae) has been found to reduce vitrification in sensitive species as well as significantly improving shoot quality and transfer to soil in most study species. A simple 7-mm hole with a double-layer insert of filter paper in the polypropylene screw lids of the culture vessel decreased shoot vitrification over a 4-wk culture period. The method has implications for facilitating the tissue culture of other rare Australian plants and reducing the occurrence of this developmental abnormality.  相似文献   
49.
Summary : FT is a tool written in C++, which implements the Fourier analysis method to locate periodicities in aminoacid or DNA sequences. It is provided for free public use on a WWW server with a Java interface. Availability : The server address is http://o2.db. uoa.gr/FT Contact : shamodr@atlas.uoa.gr   相似文献   
50.
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