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J. Carlos Cervera José Luis Andrade Eric A. Graham Rafael Durán Paula C. Jackson J. Luis Simá 《Biotropica》2007,39(5):620-627
Mammillaria gaumeri , an endemic cactus from Yucatan, is threatened due to human-mediated habitat fragmentation but knowledge regarding factors that would inform management plans is limited, including information on optimal microhabitats and growth. We studied seasonal patterns of microclimate, net CO2 uptake and growth of adult individuals during the dry, rainy and northwind (late fall to winter) seasons in separate populations located in a coastal dune and in a dry forest. To provide an assay of primary productivity, we measured the production of new axillary buds (areoles) from the apex. We found that patterns of net CO2 uptake in the three seasons were consistent with obligate crassulacean acid metabolism. The reduction in soil water potential and the increase in water vapor pressure deficit led to a reduction in 24-h net CO2 uptake from 18.0 to 1.3 mmol CO2 /m2 , after 30 d of drought. Dry-weight gain was maximal during the rainy season and there was no growth during the dry season, thus seasonal patterns of net CO2 uptake and growth for M. gaumeri reflected soil and atmospheric water contents. Annual dry-weight gain increased linearly with plant size and with total daily photosynthetic photon flux density (PPFD) up to 80 percent of ambient. Maximal growth was in exposed microhabitats receiving 60–80 percent of total ambient PPFD. We hypothesize that low-magnitude disturbances, resulting in more exposed microhabitats, might be beneficial for growth and conservation of adult individuals of this rare species. 相似文献
993.
Andrea J Robinson Jomana Elaridi Bianca J Van Lierop Selma Mujcinovic W Roy Jackson 《Journal of peptide science》2007,13(4):280-285
Microwave irradiation dramatically improves the efficiency of ring closing metathesis (RCM) reactions of resin-attached peptides and the technology is illustrated by the highly selective synthesis of dicarba analogues of alpha-conotoxin IMI. 相似文献
994.
Downward flux of water through roots (i.e. inverse hydraulic lift) in dry Kalahari sands 总被引:17,自引:0,他引:17
E.-D. Schulze M. M. Caldwell J. Canadell H. A. Mooney R. B. Jackson D. Parson R. Scholes O. E. Sala P. Trimborn 《Oecologia》1998,115(4):460-462
Downward transport of water in roots, in the following termed “inverse hydraulic lift,” has previously been shown with heat
flux techniques. But water flow into deeper soil layers was demonstrated in this study for the first time when investigating
several perennial grass species of the Kalahari Desert under field conditions. Deuterium labelling was used to show that water
acquired by roots from moist sand in the upper profile was transported through the root system to roots deeper in the profile
and released into the dry sand at these depths. Inverse hydraulic lift may serve as an important mechanism to facilitate root
growth through the dry soil layers underlaying the upper profile where precipitation penetrates. This may allow roots to reach
deep sources of moisture in water-limited ecosystems such as the Kalahari Desert.
Received: 1 January 1998 / Accepted: 1 April 1998 相似文献
995.
Molecular and biochemical characterisation of DNA-dependent protein kinase-defective rodent mutant irs-20. 总被引:5,自引:2,他引:3 下载免费PDF全文
A Priestley H J Beamish D Gell A G Amatucci M C Muhlmann-Diaz B K Singleton G C Smith T Blunt L C Schalkwyk J S Bedford S P Jackson P A Jeggo G E Taccioli 《Nucleic acids research》1998,26(8):1965-1973
The catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs) is a member of a sub-family of phosphatidylinositol (PI) 3-kinases termed PIK-related kinases. A distinguishing feature of this sub-family is the presence of a conserved C-terminal region downstream of a PI 3-kinase domain. Mutants defective in DNA-PKcs are sensitive to ionising radiation and are unable to carry out V(D)J recombination. Irs-20 is a DNA-PKcs-defective cell line with milder gamma-ray sensitivity than two previously characterised mutants, V-3 and mouse scid cells. Here we show that the DNA-PKcs protein from irs-20 cells can bind to DNA but is unable to function as a protein kinase. To verify the defect in irs-20 cells and provide insight into the function and expression of DNA-PKcs in double-strand break repair and V(D)J recombination we introduced YACs encoding human and mouse DNA-PKcs into defective mutants and achieved complementation of the defective phenotypes. Furthermore, in irs-20 we identified a mutation in DNA-PKcs that causes substitution of a lysine for a glutamic acid in the fourth residue from the C-terminus. This represents a strong candidate for the inactivating mutation and provides supportive evidence that the extreme C-terminal motif is important for protein kinase activity. 相似文献
996.
Molecular and biochemical characterization of new X-ray-sensitive hamster cell mutants defective in Ku80. 总被引:2,自引:0,他引:2 下载免费PDF全文
A Errami N J Finnie B Morolli S P Jackson P H Lohman M Z Zdzienicka 《Nucleic acids research》1998,26(19):4332-4338
Ku, a heterodimer of approximately 70 and approximately 80 kDa subunits, is a nuclear protein that binds to double-stranded DNA ends and is a component of the DNA-dependent protein kinase (DNA-PK). Cell lines defective in Ku80 belong to group XRCC5 of ionizing radiation-sensitive mutants. Five new independent Chinese hamster cell mutants, XR-V10B, XR-V11B, XR-V12B, XR-V13B and XR-V16B, that belong to this group were isolated. To shed light on the nature of the defect in Ku80, the molecular and biochemical characteristics of these mutants were examined. All mutants, except XR-V12B, express Ku80 mRNA, but no Ku80 protein could clearly be detected by immunoblot analysis in any of them. DNA sequence analysis of the Ku80 cDNA from these mutants showed a deletion of 252 bp in XR-V10B; a 6 bp deletion that results in a new amino acid residue at position 107 and the loss of two amino acid residues at positions 108 and 109 in XR-V11B; a missense mutation resulting in a substitution of Cys for Tyr at position 114 in XR-V13B; and two missense mutations in XR-V16B, resulting in a substitution of Met for Val at position 331 and Arg for Gly at position 354. All these mutations cause a similar, 5-7-fold, increase in X-ray sensitivity in comparison to wild-type cells, and a complete lack of DNA-end binding and DNA-PK activities. This indicates that all these mutations lead to loss of the Ku80 function due to instability of the defective protein. 相似文献
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