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61.
Reaction of the lung to air pollutant exposure 总被引:1,自引:0,他引:1
Urban air pollutants, when administered to laboratory animals, adversely affect pulmonary structure and function. Effects include decrease in airway caliber, changes in lung elasticity, degeneration or destruction of tissue, and impaired pulmonary defense mechanisms. Urban dwellers subjected to pollutant exposures might incur similar health risks. The substances reviewed are: a) reducing pollutants — SO2 and associated particulates and b) oxidizing (or photochemical) pollutants — NO2 and O3. 相似文献
62.
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64.
Variation in the ribosomal internal transcribed spacers (ITS1 and ITS2) among eight taxa of the Mimulus guttatus species complex 总被引:1,自引:0,他引:1
The internal transcribed spacer region (ITS1 and ITS2) of the 18S-25S
nuclear ribosomal DNA sequence and the intervening 5.8S region were
sequenced from three individuals in each of eight taxa of the Mimulus
guttatus species complex. Three discrete variants, or "types," of ITS
sequences were found, among which 30%-40% of sites differed, compared with
1%-2% within types. Dot plots indicate that these types were not related by
conspicuous rearrangements or inversions. More than one ITS type was often
found in the same taxon, and two of three ITS types span species
boundaries, indicating their presence prior to speciation. These ITS
sequences showed essentially no positional homology with the nearest
sequenced relative, tomato. In contrast, the 5.8S region was relatively
unvaried, with 8 of 162 sites varied in the sample among all eight taxa.
The phylogeny inferred by the most common ITS sequence type, rooted by the
two other ITS types, agreed with isozymes in showing the distinctness of M.
nudatus, M. laciniatus, and M. tilingii from the other five taxa.
相似文献
65.
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67.
Incubation of prolamellar bodies (PLB) in high-salt media leads to changes in PLB structure and properties of their protochlorophyllide
oxidoreductase–protochlorophyllide (POR–PChlide) complex. The paracrystalline organisation typical of PLB is disrupted and NADPH dissociates from photoconvertible POR–PChlide, with absorption maxima at 640 and 650 nm (POR–PChlide
640/650
), and a non-photoconvertible form, with absorption maxima at 635 nm (POR–PChlide
635
), is formed. These effects are strongly dependent on the valence of the cation of the perturbing salt, indicating that they
involve surface double layers effects. They are also influenced by the nature of the anion and by high concentrations of non-electrolytes,
suggesting the involvement of surface hydration effects. The structural changes are largely, if not entirely, independent
of the presence of excess NADPH. Changes to the POR–PChlide complex, however, are strongly inhibited by excess NADPH suggesting that the two sets of changes may not be causally linked.
As long as the disruption is not too great, the structural changes seen on incubation of PLB in high salt media lacking excess
NADPH are reversed on removal of the high salt perturbation. This reversal is independent of the presence or absence of added
NADPH. Reformation of photoconvertible POR–PChlide, however, requires the presence of NADPH. The reformation of paracrystalline PLB in the absence of NADPH strongly indicates
that preservation of PLB structure, in isolated PLB preparations at least, is independent of the presence or absence of POR–PChlide
650
. 相似文献
68.
Variation in heat shock proteins within tropical and desert species of poeciliid fishes 总被引:8,自引:0,他引:8
Norris CE; diIorio PJ; Schultz RJ; Hightower LE 《Molecular biology and evolution》1995,12(6):1048-1062
The 70-kilodalton heat shock protein (hsp70) family of molecular
chaperones, which contains both stress-inducible and normally abundant
constitutive members, is highly conserved across distantly related taxa.
Analysis of this protein family in individuals from an outbred population
of tropical topminnows, Poeciliopsis gracilis, showed that while
constitutive hsp70 family members showed no variation in protein isoforms,
inducibly synthesized hsp70 was polymorphic. Several species of
Poeciliopsis adapted to desert environments exhibited lower levels of
inducible hsp70 polymorphism than the tropical species, but constitutive
forms were identical to those in P. gracilis, as they were in the
confamilial species Gambusia affinis. These differences suggest that
inducible and constitutive members of this family are under different
evolutionary constraints and may indicate differences in their function
within the cell. Also, northern desert species of Poeciliopsis synthesize a
subset of the inducible hsp70 isoforms seen in tropical species. This
distribution supports the theory that ancestral tropical fish migrated
northward and colonized desert streams; the subsequent decrease in
variation of inducible hsp70 may have been due to genetic drift or a
consequence of adaptation to the desert environment. Higher levels of
variability were found when the 30- kilodalton heat shock protein (hsp30)
family was analyzed within different strains of two desert species of
Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In
both cases the distribution of hsp30 isoform diversity was similar to that
seen previously with allozyme polymorphisms.
相似文献
69.
柠檬酸合酶的分子生物学研究进展 总被引:1,自引:0,他引:1
柠檬酸合酶(citrate synthase,CS)是细胞内多种重要代谢途径的关键酶。CS可催化草酰乙酸和乙酰辅酶A之间的缩合反应生成柠檬酸和辅酶A。通常革兰氏阳性细菌、古菌以及真核细胞的CS为同源二聚体,而革兰氏阴性细菌的CS为同源六聚体。根据其在细胞内的定位不同,CS可分为线粒体CS、乙醛酸循环体CS、过氧化物酶体CS。这些同工酶在能量代谢、植物脂肪的代谢、脂肪酸的氧化及细胞解毒过程中起着重要作用。不同来源的CS空间结构、催化机制和动力学性质十分相似。针对其生化特性、空间结构特点、催化机制以及分子进化等研究进展进行综述。 相似文献
70.