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101.
A full-size cDNA clone (1614 bp) encoding calreticulin was isolated from a PCR-based cDNA library of maize in vitro zygotes. Calreticulin is a major Ca2+ storage protein located mainly in the lumen of the endoplasmic reticulum but also in the nucleus and/or cytoplasm of some cells. A differential screening between cDNA libraries originating from 104 in vitro zygotes (18 h after in vitro fertilization) and 128 unfertilized egg cells was performed to isolated newly expressed genes or genes expressed more abundantly after fertilization. The expression of the isolated cDNA clone is enhanced after fertilization and strongly correlated to cell division. Sequence comparison to a shorter maize calreticulin cDNA isolated from a conventional cDNA library proves the ability and reproducibility of the recently described method for PCR based cDNA library construction from a few plant cells [12]. It is further shown that calreticulins in maize are probably transcribed from a small gene family differentially expressed in abundance in diverse tissues. The deduced amino acid sequence encodes an acidic protein (pI 4.17) of 48 kDa sharing 77–92% and 50–54% homology to other plant and animal calreticulins, respectively. The described calreticulin gene represents to our knowledge the first cDNA clone isolated from a RT/PCR cDNA library originating from only a few plant cells and is the first gene isolated from zygotes of higher plants.  相似文献   
102.
Pathotypes of Erysiphe graminis f. sp. hordei were monitored at fortnightly intervals in pure stands of cultivars Golf with Laevigatum resistance [gene Ml(La)], Steina with Arabische resistance (Mla 12) and Harry with Monte Cristo resistance (Mla9), as well as in two two-component mixtures [Golf + Steina (G + S) and Golf + Harry (G + H)] during the course of mildew epidemics in replicated field trials. The number of colonies per main tiller was also recorded. Virulence complexity (i.e. the average number of virulence genes per isolate with respect to the two matching resistance genes of the mixed cultivars) was always higher in mixtures than in pure stands. Linear regression of complexity on the number of elapsed mildew generations (based on actual temperature data) gave significant b-values (slopes) of 0.039, 0.034, 0.022 and 0.018 on Golf in G + S, Steina in G + S, Golf in G + H and Harry in G + H, respectively. In pure stands, there, was no significant complexity increase on any cultivar. The fact that b-values were higher on either component in the G + S than in the G + H mixture indicates stronger selection for the complex, i.e. two-virulence, pathotypes in G + S. Complex pathotypes had a higher relative fitness than simple (one-virulence) pathotypes in both mixtures but not in the pure stands. The absolute frequencies of complex pathotypes as measured by the area under the colony frequency curve (AUCFC) were higher on all cultivars in mixtures than in pure stands, except on Steina.  相似文献   
103.
Early events, such as formation of the cell wall, first nuclear division and first unequal division of the zygote, were examined following in vitro fusion of single egg and sperm protoplasts of maize ( Zea mays L.). The time course of these events was determined. The formation of cell wall components was observed 30 sec following egg—sperm fusion and proceeded continuously thereafter. Within 15 h after fusion most of the organelles became more densely grouped around the nucleus of the zygote. In the in vitro produced zygote the location of the cell organelles and of the dividing nucleus showed polarity. Two nucleoli were first observed 18 h after gamete fusion. The zygotic nucleus remained undivided for about 40 h. The first cell division was observed 40–60 h, generally 42–46 h, after egg—sperm fusion. The non-fused egg cell could be triggered to sporophytic development in vitro by pulses of high amounts of 2,4-D. Without such a treatment, cultured egg cells of different maize lines did not divide. Although nuclear fusion seemed to occur, fusion products of two egg cells also did not divide. Cell wall formation was incomplete and non-uniform, showing a polarity of cultured egg cells and fusion products of two egg protoplasts. Cell division was also induced after fusion of maize egg with sperms of genetically remote species, such as Coix, Sorghum, Hordeum or Triticum . These gametic heterologous fusion products developed to microcalli. Moreover, cell division occurred in fusion products of an egg and a diploid somatic cell-suspension protoplast from maize.  相似文献   
104.
The HelA protein of Rhodobacter capsulatus is the ATP-binding-cassette subunit of an exporter complex required for cytochrome c biogenesis. By primary sequence comparisons the F88 residue of HelA is similar to the F508 residue of the cystic fibrosis transmembrane regulator (CFTR) protein. Previous studies have established that CFTR F508delta or F508R proteins are defective but F508C is functional. Our results demonstrate that the HelA F88 mutants functionally mimic the phenotypes of known CFTR F508 mutants. The phenotypes of additional HelA mutants and the in vivo steady-state levels of these proteins are also reported.  相似文献   
105.
Cytochrome c oxidase (COX) consists of 13 subunits, 3 encoded in the mitochondrial genome and 10 in the nucleus. Little is known of the role of the nuclear-encoded subunits, some of which exhibit tissue-specific isoforms. Subunit VIa is unique in having tissue-specific isoforms in all mammalian species examined. We examined relative evolutionary rates for the COX6A heart (H) and liver (L) isoform genes along the length of the molecule, specifically in relation to the tissue-specific function(s) of the two isoforms. Nonsynonymous (amino acid replacement) substitutions in the COX6AH gene occurred more frequently than in the ubiquitously expressed COX6AL gene. Maximum-parsimony analysis and sequence divergences from reconstructed ancestral sequences revealed that after the ancestral COX6A gene duplicated to yield the genes for the H and L isoforms, the sequences encoding the mitochondrial matrix region of the COX VIa protein experienced an elevated rate of nonsynonymous substitutions relative to synonymous substitutions. This is expected for relaxed selective constraints after gene duplication followed by purifying selection to preserve the replacements with tissue-specific functions.   相似文献   
106.
Direct embryogenesis and plant regeneration were obtained by implantation of individual wheat ( Triticum aestivum L.) zygotes into cultured ovules of wheat or barley. The zygotes were isolated mechanically from emasculated spikes, 3–9 h after hand-pollination. In 13 independent experiments, a total of 186 zygotes were implanted into excised ovules obtained from emasculated spikes which had been treated previously with 2,4-dichlorophenoxyacetic acid to induce parthenocarpic, embryoless ovary development. On average, 17.2% of the implanted zygotes gave rise to dorsiventrally differentiated embryos. The embryos resembled those growing in planta with no obvious deviation from the zygotic embryogenesis pathway. In contrast to previously described regeneration systems from individual zygotes of higher plants, this is the first study in which direct embryo formation is reproducibly obtained without intermediate tissue dedifferentiation. Most embryos germinated when transferred to regeneration medium, and later formed phenotypically normal, fully fertile plants. Regenerants were confirmed to be derived from the implanted zygotes by means of AFLP and/or morphological analyses. Although zygote implantation has long been established as a useful method in sexual animal reproduction, an equivalent technique for plants is described here for the first time. Since the zygotes enter the embryogenic pathway directly, the genome is presumably as stable as during embryogenesis in planta . With this new approach, isolated wheat zygotes are accessible to micromanipulation without affecting their subsequent embryonic development.  相似文献   
107.
108.
109.
A bacterial homolog to the mitochondrial enoyl-CoA hydratase.   总被引:6,自引:0,他引:6  
D L Beckman  R G Kranz 《Gene》1991,107(1):171-172
A 257-amino acid (aa) open reading frame in the photosynthetic bacterium, Rhodobacter capsulatus, shows significant homology to the mitochondrial enoyl-CoA hydratase (290 aa). This similarity in size and sequence suggests that R. capsulatus oxidizes fatty acids using specific components, more like the mitochondrial system than the multifunctional component system of Escherichia coli.  相似文献   
110.
Immunological methods were used to obtain information about Escherichia coli heme proteins. There is a membrane-bound catalase which consists of a single subunit (as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis) which is also present in the soluble fraction. Antibodies raised against purified, soluble cytochrome b562 showed that this cytochrome is not related to any of the membrane-bound cytochromes, including the b562 component of the cytochrome o complex. Cytochrome b556 is immunologically unrelated to the cytochrome b556 NR associated with the nitrate reductase system. Cytochrome b556 and cytochrome o are not present in a constant ratio in the membrane.  相似文献   
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