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991.
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993.
Brian D. Shaw Olga Kozlova Nick D. Read B. Gillian Turgeon H. C. Hoch 《Fungal genetics and biology : FG & B》2001,34(3):207-215
Conidia of Phyllosticta ampelicida germinate only after they have made contact with a substratum. Previous work has shown that external free calcium must be available to the spore for germination to be initiated. Transgenic strains of P. ampelicida expressing apo-aequorin, a calcium-sensitive luminescent protein, were developed to monitor cytoplasmic free Ca(2+) ([Ca(2+)]c). Transformants were verified by PCR and Southern hybridization. Apo-aequorin production was quantified for each of 21 transformants. The transformant that emitted the most light per unit of protein was found to contain 0.59 mg apo-aequorin/g total protein. To ascertain the feasibility of aequorin-based [Ca(2+)]c quantification, [Ca(2+)]c changes were measured in mycelia during various physiologically perturbing treatments: exposure to high concentrations of external Ca(2+), hypoosmotic shock, and mechanical perturbation. This is the first report of a plant pathogenic fungus for which aequorin-based Ca(2+) measurement protocols have been developed. 相似文献
994.
Nowacek DP Friedlaender AS Halpin PN Hazen EL Johnston DW Read AJ Espinasse B Zhou M Zhu Y 《PloS one》2011,6(4):e19173
Ecological relationships of krill and whales have not been explored in the Western Antarctic Peninsula (WAP), and have only rarely been studied elsewhere in the Southern Ocean. In the austral autumn we observed an extremely high density (5.1 whales per km(2)) of humpback whales (Megaptera novaeangliae) feeding on a super-aggregation of Antarctic krill (Euphausia superba) in Wilhelmina Bay. The krill biomass was approximately 2 million tons, distributed over an area of 100 km(2) at densities of up to 2000 individuals m(-3); reports of such 'super-aggregations' of krill have been absent in the scientific literature for >20 years. Retentive circulation patterns in the Bay entrained phytoplankton and meso-zooplankton that were grazed by the krill. Tagged whales rested during daylight hours and fed intensively throughout the night as krill migrated toward the surface. We infer that the previously unstudied WAP embayments are important foraging areas for whales during autumn and, furthermore, that meso-scale variation in the distribution of whales and their prey are important features of this system. Recent decreases in the abundance of Antarctic krill around the WAP have been linked to reductions in sea ice, mediated by rapid climate change in this area. At the same time, baleen whale populations in the Southern Ocean, which feed primarily on krill, are recovering from past exploitation. Consideration of these features and the effects of climate change on krill dynamics are critical to managing both krill harvests and the recovery of baleen whales in the Southern Ocean. 相似文献
995.
996.
Functional architecture of auditory cortex 总被引:13,自引:0,他引:13
Three complementary approaches demonstrate new types of organization in rodent, feline and primate auditory cortex, as well as differences in processing between auditory and visual cortex. First, connectional work reveals patterns of thalamocortical and corticocortical input unique to the auditory cortex. Second, physiological studies find multiple, interleaved auditory processing modules related to corticocortical connections and embedded in the isofrequency gradient. Third, functional analyses demonstrate independent processing streams for sound localization and identification analogous to the 'what' and 'where' streams in visual cortex, although the modular arrangements are modality-specific. Taken together, these data show that the auditory cortex has common and unique functional substrates. 相似文献
997.
mRNA degradation by the virion host shutoff (Vhs) protein of herpes simplex virus: genetic and biochemical evidence that Vhs is a nuclease 下载免费PDF全文
During lytic infections, the virion host shutoff (Vhs) protein (UL41) of herpes simplex virus destabilizes both host and viral mRNAs. By accelerating the decay of all mRNAs, it helps redirect the cell from host to viral gene expression and facilitates the sequential expression of different classes of viral genes. While it is clear that Vhs induces mRNA degradation, it is uncertain whether it is itself an RNase or somehow activates a cellular enzyme. This question was addressed by using a combination of genetic and biochemical approaches. The Vhs homologues of alphaherpesviruses share sequence similarities with a family of mammalian, yeast, bacterial, and phage nucleases. To test the functional significance of these similarities, Vhs was mutated to alter residues corresponding to amino acids known to be critical to the nuclease activity of cellular homologues. In every instance, mutations that inactivated the nuclease activity of cellular homologues also abolished Vhs activity. Recent experiments showed that Vhs interacts with the cellular translation initiation factor eIF4H. In this study, the coexpression of Vhs and a glutathione S-transferase (GST)-eIF4H fusion protein in bacteria resulted in the formation of a complex of the proteins. The wild-type Vhs/GST-eIF4H complex was isolated and shown to have RNase activity. In contrast, Vhs mutations that altered key residues in the nuclease motif abolished the nuclease activity of the recombinant Vhs/GST-eIF4H complex. The results provide genetic and biochemical evidence that Vhs is an RNase, either alone or as a complex with eIF4H. 相似文献
998.
The callose synthase (CalS) activity of membrane preparations from cultured Nicotiana alata Link & Otto pollen tubes is increased several-fold by treatment with trypsin in the presence of digitonin, possibly due to
activation of an inactive (zymogen) form of the enzyme. Active and inactive forms of CalS are also present in stylar-grown
tubes. Callose deposition was first detected immediately after germination of pollen grains in liquid medium, at the rim of
the germination aperture. During tube growth the 3-linked glucan backbone of callose was deposited at an increasing rate,
reaching a maximum of 65 mg h−1 in tubes grown from 1 g pollen. Callose synthase activity was first detected immediately after germination, and then also
increased substantially during tube growth. Trypsin caused activation of CalS throughout a 30-h time course of tube growth,
but the degree of activation was higher for younger pollen tubes. Over a 10-fold range of callose deposition rates, the assayed
CalS activity was sufficient to account for the rate of callose deposition without trypsin activation, implying that the form
of CalS active in isolated membranes is responsible for callose deposition in intact pollen tubes. Sucrose-density-gradient
centrifugation separated a lighter, intracellular membrane fraction containing only inactive CalS from a heavier, plasma-membrane
fraction containing both active and inactive CalS, with younger pollen tubes containing relatively more of the inactive intracellular
enzyme. The increasing rate of callose deposition during pollen-tube growth may thus be caused by the transport of inactive
forms of CalS from intracellular membranes to the plasma membrane, followed by the regulated activation of these inactive
forms in this final location.
Received: 1 December 1998 / Accepted: 21 January 1999 相似文献
999.
Read AF 《Trends in ecology & evolution》1998,13(12):516-517
Evolutionary Ecology of Parasites. From Individuals to Communities by Robert Poulin, Chapman & Hall, 1998. £55.00 hbk (x+212 pages) ISBN 0 412 80560 X 相似文献
1000.
Sarah Parker Read Siobhan M. Cashman Rajendra Kumar‐Singh 《The journal of gene medicine》2010,12(1):86-96