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排序方式: 共有193条查询结果,搜索用时 31 毫秒
121.
Impaired calcium pump function does not slow relaxation in human skeletal muscle after prolonged exercise 总被引:2,自引:0,他引:2
Booth John; McKenna Michael J.; Ruell Patricia A.; Gwinn Tom H.; Davis Glen M.; Thompson Martin W.; Harmer Alison R.; Hunter Sandra K.; Sutton John R. 《Journal of applied physiology》1997,83(2):511-521
Booth, John, Michael J. McKenna, Patricia A. Ruell, Tom H. Gwinn, Glen M. Davis, Martin W. Thompson, Alison R. Harmer, Sandra K. Hunter, and John R. Sutton. Impaired calcium pump function doesnot slow relaxation in human skeletal muscle after prolonged exercise.J. Appl. Physiol. 83(2): 511-521, 1997.This study examined the effects of prolonged exercise on humanquadriceps muscle contractile function and homogenate sarcoplasmicreticulum Ca2+ uptake andCa2+-adenosinetriphosphataseactivity. Ten untrained men cycled at 75 ± 2% (SE) peak oxygenconsumption until exhaustion. Biopsies were taken from theright vastus lateralis muscle at rest, exhaustion, and 20 and 60 minpostexercise. Peak tension and half relaxation time of the leftquadriceps muscle were measured during electrically evoked twitch andtetanic contractions and a maximal voluntary isometric contraction atrest, exhaustion, and 10, 20, and 60 min postexercise. At exhaustion,homogenate Ca2+ uptake andCa2+ adenosinetriphosphataseactivity were reduced by 17 ± 4 and 21 ± 5%, respectively, andremained depressed after 60 min recovery (P 0.01). Muscle ATP, creatinephosphate, and glycogen were all depressed at exhaustion(P 0.01). Peak tension during a maximal voluntary contraction, a twitch, and a 10-Hz stimulation werereduced after exercise by 28 ± 3, 45 ± 6, 65 ± 5%,respectively (P 0.01), but noslowing of half relaxation times were found. Thus fatigue induced byprolonged exercise reduced muscleCa2+ uptake, but this did notcause a slower relaxation of evoked contractions. 相似文献
122.
Testing the covarion hypothesis of molecular evolution 总被引:14,自引:8,他引:6
The covarion hypothesis of molecular evolution states that the fixation of
mutations may alter the probability that any given position will fix the
next change. Tests of this hypothesis using the divergence of real
sequences are compromised because models of rate variation among sites
(e.g., the gamma version of the one-parameter equation) predict sequence
divergence values similar to those for the covarion process. This study
therefore focuses on the extent to which the varied and unvaried codons of
two well-diverged taxa are the same, because fewer are expected by the
covarion hypothesis than by the gamma model. The data for these tests are
the protein sequences of Cu, Zn superoxide dismutase (SOD) for mammals and
plants. Simulation analyses show that the covarion hypothesis makes better
predictions about the frequencies of varied and unhit positions in common
between these two taxa than does the gamma version of the one-parameter
model. Furthermore, the analysis of SOD tertiary structure demonstrates
that mammal and plant variabilities are distributed differently on the
protein. These results support the conclusions that the variable and
invariable codons of mammal and plant SODs are different and that the
covarion model explains the evolution of this protein better than the gamma
version of the one-parameter process. Unlike other models, the covarion
hypothesis accounts for rate fluctuations among positions over time, which
is an important parameter of molecular evolution.
相似文献
123.
124.
Andreas WM Dress Christoph Flamm Guido Fritzsch Stefan Grünewald Matthias Kruspe Sonja J Prohaska Peter F Stadler 《Algorithms for molecular biology : AMB》2008,3(1):7
Motivation
Sequence-based methods for phylogenetic reconstruction from (nucleic acid) sequence data are notoriously plagued by two effects: homoplasies and alignment errors. Large evolutionary distances imply a large number of homoplastic sites. As most protein-coding genes show dramatic variations in substitution rates that are not uncorrelated across the sequence, this often leads to a patchwork pattern of (i) phylogenetically informative and (ii) effectively randomized regions. In highly variable regions, furthermore, alignment errors accumulate resulting in sometimes misleading signals in phylogenetic reconstruction. 相似文献125.
Cytokine requirements for induction of systemic and mucosal CTL after nasal immunization. 总被引:9,自引:0,他引:9
H F Staats C P Bradney W M Gwinn S S Jackson G D Sempowski H X Liao N L Letvin B F Haynes 《Journal of immunology (Baltimore, Md. : 1950)》2001,167(9):5386-5394
Cholera toxin (CT) is frequently used as an experimental adjuvant intranasally for the induction of systemic and mucosal immunity. However, CT is highly reactogenic and not approved for use in humans. To define the cytokine requirements for the nasal activation of the systemic and mucosal immune system, and to design new adjuvants with efficacy similar to CT, we defined the cytokines that were able to replace CT as a nasal adjuvant for the induction of CTL. BALB/c mice were nasally immunized with an HIV immunogen that contains an MHC class I-restricted CTL epitope +/- cytokines and tested for HIV-specific immune responses. We found that combinations of IL-1alpha plus IL-18, IL-1alpha plus IL-12, and IL-1alpha plus IL-12 plus GM-CSF each induced optimal splenocyte anti-HIV CTL responses in immunized mice (range 60-71% peptide-specific (51)Cr release). Peak H-2D(d)-peptide tetramer-binding T cell responses induced by cytokine combinations were up to 5.5% of CD8(+) PBMC. Nasal immunization with HIV immunogen and IL-1alpha, IL-12, and GM-CSF also induced Ag-specific IFN-gamma-secreting cells in the draining cervical lymph node and the lung. The use of IL-1alpha, IL-12, and GM-CSF as nasal adjuvants was associated with an increased expression of MHC class II and B7.1 on nonlymphocytes within the nasal-associated lymphoid tissue/nasal mucosa. Thus, IL-1alpha, IL-12, IL-18, and GM-CSF are critical cytokines for the induction of systemic and mucosal CTL after nasal immunization. Moreover, these cytokines may serve as effective adjuvants for nasal vaccine delivery. 相似文献
126.
Previous investigations on the monkey kidney COS cell line demonstrated the
weak expression of fucosylated cell surface antigens and presence of
endogenous fucosyltransferase activities in cell extracts. RT-PCR analyses
have now revealed expression of five homologs of human fucosyltransferase
genes, FUT1, FUT4, FUT5, FUT7, and FUT8, in COS cell mRNA. The enzyme in
COS cell extracts acting on unsialylated Type 2 structures is closely
similar in its properties to the alpha1,3- fucosyltransferase encoded by
human FUT4 gene and does not resemble the product of the FUT5 gene.
Although FUT1 is expressed in the COS cell mRNA, it has not been possible
to demonstrate alpha1,2- fucosyltransferase activity in cell extracts but
the presence of Le(y) and blood-group A antigenic determinants on the cell
surface imply the formation of H-precursor structures at some stage. The
most strongly expressed fucosyltransferase in the COS cells is the
alpha1,6-enzyme transferring fucose to the innermost N -acetylglucosamine
unit in N - glycan chains; this enzyme is similar in its properties to the
product of the human FUT8 gene. The enzymes resembling the human FUT4 and
FUT8 gene products both had pH optima of 7.0 and were resistant to 10 mM
NEM. The incorporation of fucose into asialo-fetuin was optimal at 5.5 and
was inhibited by 10 mM NEM. This result initially suggested the presence of
a third fucosyltransferase expressed in the COS cells but we have now shown
that triantennary N- glycans with terminal nonreducing galactose units,
similar to those present in asialo-fetuin, are modified by a weak
endogenous beta-galactosidase in the COS cell extracts and thereby rendered
suitable substrates for the alpha1,6- fucosyltransferase.
相似文献
127.
128.
Although the reproductive ecology of marine turtles has beenthe subject of numerous long-range studies, the reproductivephysiology of these unique animals is little known. Recently,however, preliminary anatomical and endocrinological studieshave provided a good basis on which to begin to attempt to explainseveral of their unusual biological systems. New findings relatedto the anatomy of Chelonia mydas and Lepidochelys olivacea arepresented. The female, although having a very massive pair ofsimultaneously functioning ovaries, appears in most ways verysimilar to other chelonians. Corpora hemorrhagica, corpora luteaand corpora atretica from active ovaries are briefly described.Ovulation coincides with a luteinizing hormone and progesteronesurge. Sperm are probably stored for the season after a singlemating period which appears to occur prior to the first ovulation.Males may also cycle and mating as well as nesting are seenas more or less seasonal. The seasonality could be controlledin part by melatonin or other endocrines from the sea turtle'smassive pineal complex. A hypothetical model for reproductionis presented in hopes of stimulating interest in physiologicalapproaches to the study of marine turtle reproduction. 相似文献
129.
130.