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71.
72.
Fort DJ Rogers RL McLaughlin DW Sellers CM Schlekat CL 《Biological trace element research》2002,90(1-3):117-142
The toxicity of boron has been understood for many years. However, limited data currently exist concerning the nutritional
essentiality of B in chordates. Results from an ongoing research program evaluating the nutritional essentiality of B in the
South African clawed frog, Xenopus laevis, found that X. laevis fed a low-B diet in a low-B culture media produced a substantially higher number of necrotic eggs and fertilized embryos
than frogs fed a boron-sufficient diet. Markedly decreased embryo cell counts at mid-blastula transition and an increased
frequency of abnormal gastrulation were also noted in embryos from adult frogs fed the B-deficient diet. By 96 h of development,
none of the larvae collected from the B-deficient adults and maintained in low-boron culture media developed normally. Reproductive
effects associated with B deficiency in female Xenopus included ovary atrophy, oocyte necrosis, and incomplete oocyte maturation. In males, a decrease in testis weight and sperm
count was noted. These studies suggest that these adverse effects resulting from B deficiency could be found during gametogenesis,
gamete maturation embryonic development, and larval maturation. The studies also confirmed that B deficiency was capable of
interrupting the X. laevis life cycle. Additional studies evaluating the role of B in the thyroid axis and the oocyte plasma membrane progesterone receptor
provide the first line of direct evidence for a biochemical role of boron in X. laevis. Combined together, this research program provides firm evidence that B is nutritionally essential in X. laevis. 相似文献
73.
Fort DJ 《Biological trace element research》2002,85(2):157-169
Processes of oocyte maturation that may be affected by boron (B) deficiency were studied to potentially determine a possible
biochemical role of B in the Xenopus laevis oocyte. More specifically, the Xenopus oocyte membrane progesterone receptor (OMPR) in B-deficient oocytes was characterized by evaluating progesterone affinity
for the OMPR and OMPR responsiveness to progesterone stimulation. The responsiveness of B-deficient oocytes to microinjection
of a purified oocyte cytoplasmic fraction (OCF) from B-adequate oocytes was also studied to evaluate which aspects of the
maturation process were affected by B deficiency. Results suggested that B deficiency resulted in incomplete oocyte maturation
and that maturation could not be induced by the administration of exogenous progesterone. Progesterone successfully induced
germinal vesicle breakdown (GVBD) in oocytes from females fed a B-supplemented diet (+B) and females administered a traditional
diet of beef liver and lung (B adequate). Addition of exogenous B to the -B oocytes increased the rate of progesterone-induced
GVBD slightly. The B-deficient X. laevis oocytes were capable of undergoing GVBD when endogenously stimulated by microinjected purified B-adequate OCF. These results
indicated that the inability of the B-deficient oocytes to undergo GVBD was not associated with the cytoplasmic induction
process specifically, but possibly in the progesterone receptor or signal transduction pathways. Radio-binding studies found
that progesterone binding to the B-deficient OPMR was greatly reduced compared to B-adequate or B-supplemented OMPR. Moreover,
washout studies determined that progesterone binding to the OMPR in B-deficient oocytes was more transient than the B adequate
or +B oocytes. 相似文献
74.
Fort DJ Propst TL Stover EL Strong PL Murray FJ 《Biological trace element research》1998,66(1-3):237-259
Frog embryo teratogenesis assay—Xenopus (FETAX) was utilized as a model system to evaluate the effects on embryo-larval development at various low boron (B) exposure
levels in the culture media. Concentrations tested ranged from <1 to 5000 μg B/L. A statistically significant (P < 0.05) increase
in malformations was observed at ≤ 3 μg B/L, but not at the greater concentrations. Abnormal development of the gut, craniofacial
region and eye, visceral edema, and kinking of the tail musculature (abnormal myotome development) and notochord were observed.
In subsequent studies, adult frogs were maintained for 28 d on two diets: (1) low B (LB, 62 μg B/kg) or (2) boric acid supplemented
(BA, 1851 μg B/kg); the frogs were subsequently mated, and their offspring were cultured in media containing various levels
of B. Results of the 28-d depletion studies indicated that frogs maintained under LB conditions produced a greater proportion
of (1) necrotic eggs and (2) fertilized embryos, which abnormally gastrulated at a greater rate and were substantially less
viable than embryos from frogs fed the BA diet. Malformations similar to those seen in the initial study were observed in
embryos from the B-depleted adults maintained in an LB environment; 28 d on the LB diet enhanced the incidence of malformations
associated with the LB culture media. These abnormalities were not observed in embryos cultured in ≥4 μg B/L from adults cultured
on the BA diet. These studies showed that insufficient B reproducibly interfered with normalXenopus laevis development during organogenesis, substantially impaired normal reproductive function in adult frogs, and thus represent
the first studies demonstrating the nutritional essentiality of B in an amphibian species. 相似文献
75.
Drosophila melanogaster stock consisting of meiotic recombination deficient (Rec−) double mutant mei-9a mei-41D5 males and Rec+ females was exposed at the larval stage to an aromatic amine or a polycyclic aromatic hydrocarbon. After emergence as adult flies, the males and the females were scored separately. When the treatment caused a dose-dependent reduction in the male to female ratio from the control level, the experiment was repeated with a larval stock consisting of Rec+ males and Rec+ females under comparable conditions. A preferential killing effect upon Rec− larvae was taken as evidence of DNA damaging effect of the test compound. Among 16 compounds tested, 1-AP, B(a)P, 2-AF, DAF, 4-AAF, 2-AAF, 1-AA, 2-AA, DMA, B(a)A and DMBA were registered as positive; Py and 3-MC were weakly positive; and B(e)P, Fluo and Ant were negative. The selective killing effects of the compounds in each of the pyrene, fluorene and anthracene series varied drastically as a function of structure in a way similar to that reported for the genotoxicity in Drosophila and the carcinogenicity in rodents. The Drosophila DNA repair assay will serve as a simple adjunct to the already available means for studying the genotoxic potency of aromatic amines and polycyclic aromatic hydrocarbons. 相似文献
76.
Genetic variability in HIV-1 gp120 affects interactions with HLA molecules and T cell receptor 总被引:3,自引:0,他引:3
K M Callahan M M Fort E A Obah E L Reinherz R F Siliciano 《Journal of immunology (Baltimore, Md. : 1950)》1990,144(9):3341-3346
The propensity of HIV-1 to undergo sequence variation, particularly in the envelope glycoprotein gp120, complicates vaccine development and may enable the virus to evade ongoing immune responses in infected individuals. We present here a molecular analysis of the effects of this variability on human T cell recognition of HIV-1 gp120. Synthetic peptides representing a defined CD4+ human T cell epitope in gp120 were used to survey gp120 molecules from various HIV-1 strains for the capacity to be recognized in the context of a single human MHC molecule, DR4. Variation affected recognition at two levels. For some strains, variation in this epitope was sufficient to alter the interaction of Ag receptors on gp120-specific human T cell clones with peptide-DR4 complexes on APC. In the case of two strains, the natural variation was sufficient to prevent the critical initial interaction between the relevant gp120 peptides and DR4 on the APC. However, these strains were highly divergent from the reference strain. Thus it is encouraging to note that the range of natural sequence variation in this T cell epitope falls, for the most part, within the range of peptide sequences that can be accommodated by the relevant human MHC molecule. 相似文献
77.
Anders Mosbech Kasper L. Johansen Nikolaj I. Bech Peter Lyngs Ann M. A. Harding Carsten Egevang Richard A. Phillips Jerome Fort 《Polar Biology》2012,35(2):305-311
Seabirds are important components in marine ecosystems. However, knowledge of their ecology and spatial distribution during
the non-breeding season is poor. More investigations during this critical period are required urgently, as marine environments
are expected to be profoundly affected by climate change and human activities, with both direct and indirect consequences
for marine top predators. Here, we studied the distribution of little auks (Alle alle), one of the most abundant seabird species worldwide. We found that after the breeding season, birds from East Greenland
quickly travelled north-east to stay for several weeks within a restricted area in the Greenland Sea. Activity patterns indicated
that flying behaviour was much reduced during this period, suggesting that this is the primary moulting region for little
auks. Birds then performed a southerly migration to overwinter off Newfoundland. These preliminary results provide important
information for the conservation of this species and emphasise the need for further studies at a larger spatial scale. 相似文献
78.
79.
80.
Kinectin Is a Key Effector of RhoG Microtubule-Dependent Cellular Activity 总被引:4,自引:0,他引:4 下载免费PDF全文
E. Vignal A. Blangy M. Martin C. Gauthier-Rouvire P. Fort 《Molecular and cellular biology》2001,21(23):8022-8034
RhoG is a member of the Rho family of GTPases that activates Rac1 and Cdc42 through a microtubule-dependent pathway. To gain understanding of RhoG downstream signaling, we performed a yeast two-hybrid screen from which we identified kinectin, a 156-kDa protein that binds in vitro to conventional kinesin and enhances microtubule-dependent kinesin ATPase activity. We show that RhoG(GTP) specifically interacts with the central domain of kinectin, which also contains a RhoA binding domain in its C terminus. Interaction was confirmed by coprecipitation of kinectin with active RhoG(G12V) in COS-7 cells. RhoG, kinectin, and kinesin colocalize in REF-52 and COS-7 cells, mainly in the endoplasmic reticulum but also in lysosomes. Kinectin distribution in REF-52 cells is modulated according to endogenous RhoG activity. In addition, by using injection of anti-kinectin antibodies that challenge RhoG-kinectin interaction or by blocking anti-kinesin antibodies, we show that RhoG morphogenic activity relies on kinectin interaction and kinesin activity. Finally, kinectin overexpression elicits Rac1- and Cdc42-dependent cytoskeletal effects and switches cells to a RhoA phenotype when RhoG activity is inhibited or microtubules are disrupted. The functional links among RhoG, kinectin, and kinesin are further supported by time-lapse videomicroscopy of COS-7 cells, which showed that the microtubule-dependent lysosomal transport is facilitated by RhoG activation or kinectin overexpression and is severely stemmed upon RhoG inhibition. These data establish that kinectin is a key mediator of microtubule-dependent RhoG activity and suggest that kinectin also mediates RhoG- and RhoA-dependent antagonistic pathways. 相似文献