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排序方式: 共有321条查询结果,搜索用时 15 毫秒
81.
Cutler MJ Swift NM Keller DM Wasmund WL Burk JR Smith ML 《American journal of physiology. Heart and circulatory physiology》2004,287(5):H2054-H2060
Obstructive sleep apnea is associated with sustained elevation of muscle sympathetic nerve activity (MSNA) and altered chemoreflex control of MSNA, both of which likely play an important role in the development of hypertension in these patients. Additionally, short-term exposure to intermittent hypoxic apneas can produce a sustained elevation of MSNA. Therefore, we tested the hypothesis that 20 min of intermittent hypoxic apneas can alter chemoreflex control of MSNA. Twenty-one subjects were randomly assigned to one of three groups (hypoxic apnea, hypercapnic hypoxia, and isocapnic hypoxia). Subjects were exposed to 30 s of the perturbation every minute for 20 min. Chemoreflex control of MSNA was assessed during baseline, 1 min posttreatment, and every 15 min throughout 180 min of recovery by the MSNA response to a single hypoxic apnea. Recovery hypoxic apneas were matched to a baseline hypoxic apnea with a similar nadir oxygen saturation. A significant main effect for chemoreflex control of MSNA was observed after 20 min of intermittent hypoxic apneas (P <0.001). The MSNA response to a single hypoxic apnea was attenuated 1 min postexposure compared with baseline (P <0.001), became augmented within 30 min of recovery, and remained augmented through 165 min of recovery (P <0.05). Comparison of treatment groups revealed no differences in the chemoreflex control of MSNA during recovery (P=0.69). These data support the hypothesis that 20 min of intermittent hypoxic apneas can alter chemoreflex control of MSNA. Furthermore, this response appears to be mediated by hypoxia. 相似文献
82.
Molecular mechanisms of polymorphic CYP3A7 expression in adult human liver and intestine 总被引:7,自引:0,他引:7
Burk O Tegude H Koch I Hustert E Wolbold R Glaeser H Klein K Fromm MF Nuessler AK Neuhaus P Zanger UM Eichelbaum M Wojnowski L 《The Journal of biological chemistry》2002,277(27):24280-24288
Human CYP3A enzymes play a pivotal role in the metabolism of many drugs, and the variability of their expression among individuals may have a strong impact on the efficacy of drug treatment. However, the individual contributions of the four CYP3A genes to total CYP3A activity remain unclear. To elucidate the role of CYP3A7, we have studied its expression in human liver and intestine. In both organs, expression of CYP3A7 mRNA was polymorphic. The recently identified CYP3A7*1C allele was a consistent marker of increased CYP3A7 expression both in liver and intestine, whereas the CYP3A7*1B allele was associated with increased CYP3A7 expression only in liver. Because of the replacement of part of the CYP3A7 promoter by the corresponding region of CYP3A4, the CYP3A7*1C allele contains the proximal ER6 motif of CYP3A4. The pregnane X and constitutively activated receptors were shown to bind with higher affinity to CYP3A4-ER6 than to CYP3A7-ER6 motifs and transactivated only promoter constructs containing CYP3A4-ER6. Furthermore, we identified mutations in CYP3A7*1C in addition to the ER6 motif that were necessary only for activation by the constitutively activated receptor. We conclude that the presence of the ER6 motif of CYP3A4 mediates the high expression of CYP3A7 in subjects carrying CYP3A7*1C. 相似文献
83.
Kangaroos and their relatives (family Macropodidae) are divided into the subfamilies Macropodinae (kangaroos, wallabies, pademelons) and Potoroinae (rat-kangaroos, potoroos, bettongs). The musky rat-kangaroo, Hypsiprymnodon moschatus, is traditionally allied with other potoroines, based primarily on the basis of osteological characters and aspects of the female reproductive system. Unlike other macropodids, however, which are capable of bipedal hopping, Hypsiprymnodon is a quadrupedal bounder and lacks several derived features of the pes and tarsus that are presumably adaptations for bipedal hopping. Other derived features, such as a complex stomach, loss of P2 with the eruption of P3, and reduction of litter size to one, are also lacking in Hypsiprymnodon but occur in all other macropodids. Thus, available evidence suggests that Hypsiprymnodon either is part of a monophyletic Potoroinae or is a sister taxon to other living macropodids. To test these hypotheses, we sequenced 1,170 bp base pairs of the mitochondrial genome for 16 macropodids. Maximum parsimony, minimum evolution, maximum likelihood, and quartet puzzling all support the hypothesis that macropodines and potoroines are united to the exclusion of Hypsiprymnodon. This hypothesis implies that characters such as bipedal hopping evolved only once in macropodid evolution. Aside from Hypsiprymnodon, the remaining macropodids separate into the traditional Macropodinae and Potoroinae. Macropodines further separate into two clades: one containing the New Guinean forest wallabies Dorcopsis and Dorcopsulus, and one consisting of the genera Macropus, Setonix, Thylogale, Onychogalea, Wallabia, Dendrolagus, Peradorcas, and Lagorchestes. Among potoroines, there is moderate support for the association of Bettongia and Aepyprymnus to the exclusion of Potorous. Divergence times were estimated by using 12S ribosomal RNA transversions. At the base of the macropodid radiation, Hypsiprymnodon diverged from other macropodids approximately 45 million years ago. This estimate is comparable to divergence estimates among families of Australasian possums based on single-copy DNA hybridization and 12S rRNA transversions. Macropodines and potoroines, in turn, diverged approximately 30 million years ago. Among macropodines, Dorcopsis and Dorcopsulus separated from other taxa approximately 10 million years ago. 相似文献
84.
Bradley RD; Adkins RM; Honeycutt RL; McDonald JH 《Molecular biology and evolution》1998,15(6):709-717
Using the strictly neutral model as a null hypothesis, we tested for
deviations from expected levels of nucleotide polymorphism at the alcohol
dehydrogenase locus (Adh-1) within and among four species of pocket gophers
(Geomys bursarius major, G. knoxjonesi, G. texensis llanensis, and G.
attwateri). The complete protein-encoding region was examined, and 10
unique alleles, representing both electromorphic and cryptic alleles, were
used to test hypotheses (e.g., the neutral model) concerning the
maintenance of genetic variation. Nineteen variable sites were identified
among the 10 alleles examined, including 9 segregating sites occurring in
synonymous positions and 10 that were nonsynonymous. Several statistical
methods, including those that test for within-species variation as well as
those that examine variation within and among species, failed to reject the
null hypothesis that variation (both within and between species of Geomys)
at the Adh locus is consistent with the neutral theory. However, there was
significant heterogeneity in the ratio of polymorphism to divergence across
the gene, with polymorphisms clustered in the first half of the coding
region and fixed differences clustered in the second half of the gene. Two
alternative hypotheses are discussed as possible explanations for this
heterogeneity: an old balanced polymorphism in the first half of the gene
or a recent selective sweep in the second half of the gene.
相似文献
85.
Adults of the human parasitic trematode Schistosoma mansoni, which causes
hepatosplenic/intestinal complications in humans, synthesize
glycoconjugates containing the Lewis x (Lex) Galbeta1-->4(Fucalpha1--
>3)GlcNAcbeta1-->R, but not sialyl Lewis x (sLex), antigen. We now
report on our analyses of Lexand sLexexpression in S.haematobium and
S.japonicum, which are two other major species of human schistosomes that
cause disease, and the possible autoimmunity to these antigens in infected
individuals. Antigen expression was evaluated by both ELISA and Western
blot analyses of detergent extracts of parasites using monoclonal
antibodies. Several high molecular weight glycoproteins in both S.
haematobium and S. japonicum contain the Lexantigen, but no sialyl
Lexantigen was detected. In addition, sera from humans and rodents infected
with S.haematobium and S.japonicum contain antibodies reactive with Lex.
These results led us to investigate whether Lexantigens are expressed in
other helminths, including the parasitic trematode Fasciola hepatica , the
parasitic nematode Dirofilaria immitis (dog heartworm), the ruminant
nematode Haemonchus contortus , and the free-living nematode Caenorhabditis
elegans . Neither Lexnor sialyl-Lexis detectable in these other helminths.
Furthermore, none of the helminths, including schistosomes, express Lea,
Leb, Ley, or the H- type 1 antigen. However, several glycoproteins from all
helminths analyzed are bound by Lotus tetragonolobus agglutinin , which
binds Fucalpha1-->3GlcNAc, and Wisteria floribunda agglutinin, which
binds GalNAcbeta1-->4GlcNAc (lacdiNAc or LDN). Thus, schistosomes may be
unique among helminths in expressing the Lexantigen, whereas many different
helminths may express alpha1,3-fucosylated glycans and the LDN motif.
相似文献
86.
Jain RK; Piskorz CF; Huang BG; Locke RD; Han HL; Koenig A; Varki A; Matta KL 《Glycobiology》1998,8(7):707-717
The selectins interact in important normal and pathological situations with
certain sialylated, fucosylated glycoconjugate ligands containing sialyl
Lewisx(Neu5Acalpha2-3Galbeta1-4(Fucalpha1-3)GlcN Ac). Much effort has gone
into the synthesis of sialylated and sulfated Lewisxanalogs as competitive
ligands for the selectins. Since the natural selectin ligands GlyCAM-1 and
PSGL-1 carry sialyl Lewisxas part of a branched Core 2 O-linked structure,
we recently synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(SE-3Galbeta1++
+-3)GalNAc1alphaOMe and found it to be a moderately superior ligand for L
and P-selectin (Koenig et al. , Glycobiology 7, 79-93, 1997). Other studies
have shown that sulfate esters can replace sialic acid in some selectin
ligands (Yeun et al. , Biochemistry, 31, 9126-9131, 1992; Imai et al. ,
Nature, 361, 555, 1993). Based upon these observations, we hypothesized
that Neu5Acalpha2-3Galbeta1-3GalNAc might have the capability of
interacting with L- and P-selectin. To examine this hypothesis, we
synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(Neu5Acalpha2++
+-3Galbeta1-3)- GalNAc alpha1-OB, which was found to be 2- to 3-fold better
than sialyl Lexfor P and L selectin, respectively. We also report the
synthesis of an unusual structure GalNAcbeta1-4(Fucalpha1-
3)GlcNAcbeta1-OMe (GalNAc- Lewisx-O-methyl glycoside), which also proved to
be a better inhibitor of L- and P-selectin than sialyl Lewisx-OMe.
Combining this with our knowledge of Core 2 branched structures, we have
synthesized a molecule that is 5- to 6-fold better at inhibiting L- and
P-selectin than sialyl Lewisx-OMe, By contrast to unbranched structures,
substitution of a sulfate ester group for a sialic acid residue in such a
molecule resulted in a considerable loss of inhibition ability. Thus, the
combination of a sialic acid residue on the primary (beta1-3) arm, and a
modified Lexunit on the branched (beta1-6) arm on an O-linked Core 2
structure generated a monovalent synthetic oliogosaccharide inhibitor
superior to SLexfor both L- and P-selectin.
相似文献
87.
M S Springer M Westerman J R Kavanagh A Burk M O Woodburne D J Kao C Krajewski 《Proceedings. Biological sciences / The Royal Society》1998,265(1413):2381-2386
Alternative hypotheses in higher-level marsupial systematics have different implications for marsupial origins, character evolution, and biogeography. Resolving the position of the South American monito del monte (Order Microbiotheria) is of particular importance in that alternate hypotheses posit sister-group relationships between microbiotheres and taxa with disparate temporal and geographic distributions: pediomyids; didelphids; dasyuromorphians; diprotodontians; all other australidelphians; and all other marsupials. Among Australasian marsupials, the placement of bandicoots is critical; competing views associate bandicoots with particular Australasian taxa (diprotodontians, dasyuromorphians) or outside of a clade that includes all other Australasian forms and microbiotheres. Affinities of the marsupial mole are also unclear. The mole is placed in its own order (Notoryctemorphia) and sister-group relationships have been postulated between it and each of the other Australasian orders. We investigated relationships among marsupial orders by using a data set that included mitochondrial and nuclear genes. Phylogenetic analyses provide support for the association of microbiotheres with Australasian marsupials and an association of the marsupial mole with dasyuromorphs. Statistical tests reject the association of diprotodontians and bandicoots together as well as the monophyly of Australasian marsupials. The origin of the paraphyletic Australasian marsupial fauna may be accounted for by (i) multiple entries of australidelphians into Australia or (ii) bidirectional dispersal of australidelphians between Antarctica and Australia. 相似文献
88.
Treva Rice Ingrid B. Borecki Claude Bouchard RD.C. Ruo 《Obesity (Silver Spring, Md.)》1993,1(4):288-294
Interest in a single gene etiology for obesity, as assessed by the body mass index (BMI), has been spurred recently by reports of a putative recessive major gene for extreme values, which accounts for as much as 40% of the variance. The major gene hypothesis was evaluated here in the Québec Family Study, a random sample of 375 French-Canadian volunteer families. This report represents one component in a more complete investigation of obesity in these families. In contrast to the recent studies, a major gene hypothesis for BMI was not verified here. Although there was a major effect, it did not conform to a Mendelian pattern of transmission. A multifactorial component (i.e., polygenic and/or common environmental factors) accounted for 42% of the phenotypic variance. In addition, evidence of heterogeneity between the generations was found. The heterogeneity was traced to the major non-Mendelian component (which accounted for 0.01% of the variance in parents and over 40% in offspring) rather than to the multifactorial one. These results would suggest that a simple recessive gene mixed model may not be sufficient to explain the familial distribution of the BMI. Several factors which may have contributed to these results include temporal trends and surrogate effects such as those related to variation in body composition and energy balance components. (OBESITY RESEARCH 1993; 1:288–294) 相似文献
89.
The developmental origin of arsenate-induced renal agenesis was investigated. Pregnant Wistar rats were each injected once ip with 45 mg/kg sodium arsenate at day 10 (sperm day = day 0). Pregnancy was terminated at various times following injection and the embryos recovered and serially sectioned. Renal agenesis resulted when the mesonephric duct failded to give rise to a ureteric bud with subsequent failure of induction of the metanephric blastema. The underlying defect was retardation in growth of the mesonephric duct, first observed 48 hours after arsenate injection. A shortened mesonephric duct also resulted in a failure of the mesonephros to attain normal size and in the male resulted in absence of the ductus deferens, seminal vesicle a variable portion of the epididymis. Due to the intimate association of the mesonephric and growing paramesonephric ducts, a shortened mesonephric duct resulted in a shortened paramesonephric duct with resultant lack of a uterine horn. 相似文献
90.