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21.
Corinna Richter Ron L. Dy Rebecca E. McKenzie Bridget N.J. Watson Corinda Taylor James T. Chang Matthew B. McNeil Raymond H.J. Staals Peter C. Fineran 《Nucleic acids research》2014,42(13):8516-8526
Clustered regularly interspaced short palindromic repeats (CRISPR), in combination with CRISPR associated (cas) genes, constitute CRISPR-Cas bacterial adaptive immune systems. To generate immunity, these systems acquire short sequences of nucleic acids from foreign invaders and incorporate these into their CRISPR arrays as spacers. This adaptation process is the least characterized step in CRISPR-Cas immunity. Here, we used Pectobacterium atrosepticum to investigate adaptation in Type I-F CRISPR-Cas systems. Pre-existing spacers that matched plasmids stimulated hyperactive primed acquisition and resulted in the incorporation of up to nine new spacers across all three native CRISPR arrays. Endogenous expression of the cas genes was sufficient, yet required, for priming. The new spacers inhibited conjugation and transformation, and interference was enhanced with increasing numbers of new spacers. We analyzed ∼350 new spacers acquired in priming events and identified a 5′-protospacer-GG-3′ protospacer adjacent motif. In contrast to priming in Type I-E systems, new spacers matched either plasmid strand and a biased distribution, including clustering near the primed protospacer, suggested a bi-directional translocation model for the Cas1:Cas2–3 adaptation machinery. Taken together these results indicate priming adaptation occurs in different CRISPR-Cas systems, that it can be highly active in wild-type strains and that the underlying mechanisms vary. 相似文献
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Raymond L. White Jean-Marc Lalouel G. Mark Lathrop Mark F. Leppert Yusuke Nakamura Peter O'Connell 《The Western journal of medicine》1987,147(4):423-427
Although a number of human genes that cause disease have been traced through the defective product, most genetic defects are recognized only by phenotype. When the biochemical defect is unknown, a gene can be located only through molecular approaches based on coinheritance (genetic linkage) of the disease phenotype with a particular allele of a polymorphic DNA marker that has already been mapped to a specific chromosomal region. Linkage studies in affected families have already localized genes for several important diseases, including cystic fibrosis. Finding a genetic linkage in families in which a disease segregates requires that the human genetic map have a large number of polymorphic markers; when the map is dense enough, any disease gene can be located by linkage to a known marker. Many DNA segments with a high degree of polymorphism are being found and mapped as markers in normal reference pedigrees. Genetic linkage mapping has implications even broader than its application to prenatal diagnosis or therapeutic strategy; analyzing mutations in important genes will illuminate basic mechanisms in molecular biology and the early events that lead to cancer and other disorders. 相似文献
29.
Ludo Filez Willy Stalmans Freddy Penninkx Raymond Kerremans Karel Geboes 《Bioscience reports》1987,7(12):917-923
Lactate dehydrogenase has been measured in the small-intestinal mucosa in order to assess its value as a marker for the effects of ischemia and of reperfusion. The decrease in specific activity of the enzyme illustrates the deleterious effect of reperfusion on the quality of the remaining epithelial cells. However, this parameter fails to detect the loss of epithelial cells, which is the major event during ischemia as well as during reperfusion. In contrast, the expression of enzyme activity per g protein of the underlying intestinal muscle allowed us, in addition, to assess quantitatively the loss of epithelial cells, in good agreement with the histological data. 相似文献
30.
Roy E. Weber Frank B. Jensen Raymond P. Cox 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1987,157(2):145-152
Summary The allosteric effects of the erythrocytic nucleoside triphosphates (NTP) and of proton concentrations were investigated by precise measurement of Hb–O2 equilibria of tench hemoglobin (including extreme, high and low saturation ranges) and analysed in terms of the MWC two state model and the Adair four step oxygenation theory.At low concentrations (NTP/Hb ratio=1.0, and pH>7.3) ATP, GTP and protons decrease Hb–O2 affinity by increasing the allosteric constantL and reducingK
T, the association constant1 of the deoxy, tense state of the Hb, without significantly affecting that (K
R) of the oxy state, increasing the free energy of cooperativity (G). High concentrations of these effectors, however, also reduceK
R. The greater sensitivity of the half-saturation O2 tension (P
50) of the Hb to GTP than to ATP at the same concentration, correlates with greater effects of GTP on bothK
T andK
R. The pH and NTP dependence of the four Adair association constants and the calculated fractional populations of Hb molecules in different stages of oxygenation show that the autochthonous NTP effectors and protons stabilize the T structure and postpone the TR transition basic to cooperativity in fish Hb.The possible implications of the findings for aquatic respiration are discussed.Abbreviations
ATP
adenosine triphosphate
-
DPG
2,3-diphosphoglycerate (glycerate-2,3-bisphosphate)
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GTP
guanosine triphosphate
-
IHP
inositol hexaphosphate
-
NTP
nucleoside triphosphates
In this paperK
T andK
R are defined as theassociation equilibrium constants instead of dissociation constants (as originally defined by Monod et al. 1965) to facilitate comparison with the Adair constants 相似文献