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91.
We assessed the short‐term effects of biotic (density, plant size) and abiotic factors (light), on the dynamics of physiognomically different plant groups (palms, tree ferns, lianas, and trees) in a hurricane‐impacted tropical wet montane forest, John Crow Mountains, Jamaica. All plants ≥2 cm (dbh) found within 45, 25 × 25 m permanent sample plots (2.8125 ha), established according to a randomized block design along an elevation gradient, were tagged and measured (dbh) in 2006 and re‐assessed in 2012 after Hurricane Dean (2007). Hemispheric light was measured in 2007 and 2008. Tree and liana size class distributions changed due to high mortality in the smallest size classes and their densities declined; however, palm and tree fern density remained unchanged. The dynamics of trees were only related to tree fern and liana dynamics (e.g., tree mortality was negatively related to liana recruitment etc.). Although pre‐ and posthurricane light was related to palm density and the density of the other plant groups, respectively, there were no significant changes in light. Tree survivorship increased with increasing dbh while posthurricane light and overall density influenced the growth and survivorship of tree species. Species importance value did not change, suggesting that direct regeneration may be the model of forest recovery following this small‐scale disturbance. Over the short term, tree species showed life history trade‐offs that aid species coexistence after this moderate/low disturbance event. Our study highlights that hurricanes with low impacts can have differential short‐ and possibly long‐term effects on different plant groups.  相似文献   
92.
Zinc finger proteins are polypeptides with sequence-specific, nucleic acid-binding properties. Substantial evidence has established them as a class of trans-acting molecules with regulatory roles in cellular growth and differentiation. We have screened an 11.5 day post coitum urogenital ridge cDNA library with an oligonucleotide encoding a sequence conserved between a variety of zinc finger proteins. By cDNA cloning and sequencing we show that a novel mouse gene, Zfp-35, encodes a protein with a block of 18 zinc finger domains and an N-terminal region rich in acidic residues. The 2.4 kb mRNA encoding this polypeptide is selectively expressed in adult testis, by comparison with other organs. We have analysed Zfp-35 expression in whole testes of sex-reversed mice, whole testes of prepuberal XY animals, germ cell fractions from XY adult testes and by in situ hybridization to sections from adult XY testes. Our studies show that a considerable increase in expression is restricted to spermatocytes at the pachytene stage of meiotic prophase. These experiments suggest that Zfp-35 may act to control gene activity during this particular stage of spermatogenesis.  相似文献   
93.
A survey to determine the prevalence of rheumatic heart disease (R.H.D.) in Black children was conducted in the creeches and primary schools of the South Western Townships of Johannesburg (Soweto). A total of 12 050 Black children were examined by 10 cardiologists in May to October 1972. The overal prevalence rate of R.H.D. was 6.9 per 1000, with a peak rate of 19.2 per 1000 in children of the seventh school grade. The maximal age incidence was 15-18 years and there was a female preponderance of 1 6:1. A rise in prevalence occurred with increasing family size. Most children (92%) were asymptomatic, and in 82.5% R.H.D. was diagnosed for the first time during the school survey. The commonest valve lesion was mitral regurgitation, which was present in 93% and occurred as an isolated lesion in 47.5%. Lancefield''s group A beta-haemolytic streptococcus was isolated from the throats of 52 per 1000 Soweto children. The auscultatory features of a non-ejection systolic click and late systolic murmur were prevalent (13.9 per 1000) and had several epidemiological factors in common with R.H.D. A comprehensive preventative campaign is urgently needed in South Africa, directed at both primary and secondary prophylaxis of R.H.D. The socioeconomic status of the community must be improved if optimal prevention is to be achieved.  相似文献   
94.
The entry of labelled calf-thymus histone, lysozyme, and poly-L-lysine into barley root tips was studied at concentrations which strongly inhibit root elongation. The macromolecules were suitably labelled and at these concentrations it was found, by autoradiography and fluorescence microscopy, that histone and lysozyme readily entered the roots and appeared to bind mainly to cell walls of the epidermis and cortex and to penetrate the cytoplasm occasionally. Except in cap cells, nuclei were rarely penetrated. Poly-L-lysine readily permeated cell walls and invaded cytoplasm and nuclei throughout the root tip. Some cells were damaged by contact with basic macromolecules, as evidenced by a change in appearance of protoplasts under phase contrast and by the inability of these same protoplasts to exclude labelled β-lactoglobulin. Such damage was restricted to cells in contact with the outer solution. Interior to the epidermis, development of many cells was inhibited without visible signs of damage. Evidence supports the conclusion that in the presence of polybasic polymers the integrity of cell membranes is altered, thereby allowing leakage of some cell constituents essential for normal development.  相似文献   
95.
Summary A naturally occurring, cross-linked fraction, constituting about 1% of the total DNA, has been isolated from the DNA of mice and rats. In sharp contrast to the rest of the rapidly renaturing DNA, this material shows poor binding ability during incubation in agar with DNA of the same species.  相似文献   
96.
This study was carried out to investigate the nature of the immunological responses which took place in a child who had recently recovered from toxocariasis. She had developed a marked eosinophilia and had high titers of toxocara antibodies. Experiments were performed to examine whether Toxocara canis infective larvae could be killed in the presence of her serum and human eosinophils. Eosinophils with human complement, or this patient's serum, adhered to the surface of the larvae within 10 min. By 40 min, using both light and electron microscopy, it was shown that the cells had flattened against the cuticle and degranulated. However, by 3 hr, eosinophils had begun to detach, and the larvae remained alive for at least 1 week afterward. Further addition of serum or of eosinophils, which were shown to be able to immobilize T. spiralis infective larvae, failed to kill the T. canis larvae. It was concluded that, in this patient, the development of an inflammatory response to a T. canis infection was not associated with the appearance of antibodies capable of inducing eosinophil dependent toxicity to the larvae in vitro. Eosinophil dependent killing mechanisms may be less important than other components of the immune response, in immunity to this parasite in humans.  相似文献   
97.
Half embryos produced from 8-cell or compacted stages were cultured in vitro for 1-2 days and transferred to oviducts or uteri of recipients at different stages of pseudopregnancy. The proportion of live fetuses was low (8-12%), except for one group (27%) in which half embryos were cultured in vitro for 1 day and transferred into oviducts on the 1st day of pregnancy. Monozygotic twin production rate, however, was low (1 out of 10) even in this group. Fetal weight on the 18th day of gestation was significantly lower after transfer of half embryos than after transfer of similarly treated but undivided embryos. Half embryos produced from the 2-cell stage were inserted into empty zonae, embedded in agar, cultured in ligated mouse oviducts for 2-4 days and transferred to oviducts of recipient females on the 1st day of pregnancy or pseudopregnancy. When twin embryos cultured for 2-3 days were transferred to pseudopregnant recipients together with control embryos, 4 sets of monozygotic twins and 5 singletons out of 10 sets of twin embryos were obtained on Days 18-19 of gestation, giving a survival rate of 65%.  相似文献   
98.
A dramatic difference is observed in the intracellular distribution of the high mobility group (HMG) proteins when chicken embryo fibroblasts are fractionated into nucleus and cytoplasm by either mass enucleation of cytochalasin-B-treated cells or by differential centrifugation of mechanically disrupted cells. Nuclei (karyoplasts) obtained by cytochalasin B treatment of cells contain more than 90 percent of the HMG 1, while enucleated cytoplasts contain the remainder. A similar distribution between karyoplasts and cytoplasts is observed for the H1 histones and the nucleosomal core histones as anticipated. The presence of these proteins, in low amounts, in the cytoplast preparation can be accounted for by the small percentage of unenucleated cells present. In contrast, the nuclei isolated from mechanically disrupted cells contain only 30-40 percent of the total HMGs 1 and 2, the remainder being recovered in the cytosol fraction. No histone is observed in the cytosol fraction. Unike the higher molecular weight HMGs, most of the HMGs 14 and 17 sediment with the nuclei after cell lysis by mechanical disruption. The distribution of HMGs is unaffected by incubating cells with cytochalasin B and mechanically fractionating rather than enucleating them. Therefore, the dramatic difference in HMG 1 distribution observed using the two fractionation techniques cannot be explained by a cytochalasin-B-induced redistribution. On reextraction and sedimentation of isolated nuclei obtained by mechanical cell disruption, only 8 percent of the HMG 1 is released to the supernate. Thus, the majority of the HMG 1 originally isolated with these nuclei, representing 35 percent of the total HMG 1, is stably bound, as is all the HMGs 14 and 17. The remaining 65 percent of the HMGs 1 and 2 is unstably bound and leaks to the cytosol fraction under the conditions of mechanical disruption. It is suggested that the unstably bound HMGs form a protein pool capable of equilibrating between cytoplasm and stably bound HMGs.  相似文献   
99.
100.
Summary In order to study any Conformational changes associated with ultraviolet irradiation of TMV-RNA, methods of circular dichroism and absorbance-temperature profile were applied. RNA irradiated in water at 254 nm showed a distinct change in CD spectrum, but there was only a slight change accompanying irradiation in phosphate buffer.A small change in absorbance-temperature profile at 258 nm is associated with irradiation of RNA in water; RNA irradiated in phosphate buffer and Mg++ solutions showed essentially no changes.It is concluded that conformational changes accompanying irradiation of RNA in water are greater than those taking place in phosphate or magnesium solutions, and the enhanced change in water is related to the larger quantum yield for inactivation found in water than in buffer solutions.Photochemistry of Macromolecules XXXIII, supported in part by the U.S. Atomic Energy Commission, contract AT(11-1)-34, Project 116.  相似文献   
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