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41.
42.
Bret B. Wagenhorst Ramji R. Rajendran Ellen E. Van Niel Richard B. Hessler Amir Bukelman Federico Gonzalez-Fernandez 《Journal of molecular evolution》1995,41(5):646-656
Vitamin A and fatty acids are critical to photoreceptor structure, function, and development. The transport of these nutrients between the pigment epithelium and neural retina is mediated by interphotoreceptor retinoid-binding protein (IRBP). IRBP, a 133-kDa (human) glycolipoprotein, is the major protein component of the extracellular matrix separating these two cell layers. In amphibians and mammals, IRBP consists of four homologous repeats of about 300 amino acids which form two retinol and four fatty acid-binding sites. Here we show that IRBP in teleosts is a simpler protein composed of only two repeats. Western blot analysis shows that goldfish IRBP is half the size (70 kDa) of IRBP in higher vertebrates. Metabolic labeling studies employing Brefeldin A taken together with in situ hybridization studies and the presence of a signal peptide show that goldfish IRBP is secreted by the cone photoreceptors. The translated amino acid sequence has a calculated molecular weight of 66.7 kDa. The primary structure consists of only two homologous repeats with a similarity score of 52.5%. The last repeats of human and goldfish IRBPs are 69.1% similar with hydrophobic regions being the most similar. These data suggest that two repeats were lost during the evolution of the ray-finned fish (Actinopterygii), or that the IRBP gene duplicated between the emergence of bony fish (Osteichthyes) and amphibians. Acquisition of a multirepeat structure may reflect evolutionary pressure to efficiently transport higher levels of hydrophobic molecules within a finite space. Quadruplication of an ancestral IRBP gene may have been an important event in the evolution of photoreceptors in higher vertebrates.
Correspondence to: F. Gonzalez-Fernandez 相似文献
43.
The A34R glycoprotein gene is required for induction of specialized actin-containing microvilli and efficient cell-to-cell transmission of vaccinia virus. 总被引:7,自引:5,他引:2 下载免费PDF全文
The mechanisms allowing vaccinia virus to spread from cell to cell are incompletely understood. The A34R gene of vaccinia virus encodes a glycoprotein that is localized in the outer membranes of extracellular virions. The small-plaque phenotype of an A34R deletion mutant was similar to that of mutants with deletions in other envelope genes that fail to produce extracellular vaccinia virions. Transmission electron microscopy, however, revealed that the A34R mutant produced numerous extracellular particles that were labeled with antibodies to other outer-envelope proteins and with protein A-colloidal gold. Fluorescence and scanning electron microscopy indicated that expression of the A34R protein was necessary for detection of vaccinia virus-induced actin tails, which provide motility to the intracellular enveloped form of vaccinia virus, and of virus-tipped specialized microvilli that project from the cell. The ability of vaccinia virus-infected cells to form syncytia after a brief exposure to a pH below 6, known as fusion from within, failed to occur in the absence of expression of the A34R protein; nevertheless, purified A34R- virions were capable of mediating low-pH-induced fusion from without. The present study provides genetic and microscopic evidence for the involvement of a specific viral protein in the formation or stability of actin-containing microvilli and for a role of these structures in cell-to-cell spread rather than in formation of extracellular virions. 相似文献
44.
This paper provides an analysis of infant body weights obtained from a sample of 38 rhesus monkey infants (Macaco mulatta) aged 29–165 days, i.e., animals still nutritionally dependent on their mothers. We examine the data on neonatal weights in relation to a number of factors, most notably, the sex of the infants, and the age and adiposity of their mothers. The infant body weights represent cross-sectional rather than longitudinal data; because they were mostly free-ranging animals, the infants were weighed just once each. Nevertheless, the results of our analysis strongly suggest that early postnatal growth in free-ranging rhesus is dependent on both maternal fatness and age. They also suggest that, although male infants are generally heavier than like-aged female infants, they do not grow any faster during the early postnatal period. Here, we speculate that the associations between infant size and both maternal age and adiposity are the result of between-mother differences in lactational output. © 1995 Wiley-Liss, Inc. 相似文献
45.
The extent of myocardial accumulation of tocainide, administered as single enantiomers and as well as racemate, was determined in the isolated, spontaneous beating rabbit heart. The heart was retrogradely perfused at a constant rate and fractions of the perfusate were collected during and after infusion. Kinetic parameters for myocardial accumulation and disposition of tocainide were indirectly determined from drug concentration/time course in the outflow perfusate. No stereoselectivity in myocardial accumulation was observed. A two compartment model with mean half-lives for distribution and elimination of 0.60 and 3.78 min, respectively, was fitted to the accumulation and disposition data. At steady-state, tocainide enantiomers were accumulated about three times in the myocardium relative to the perfusion liquid. © 1995 Wiley-Liss, Inc. 相似文献
46.
47.
Grace A. Maresh Ellen A.G. Chernoff Lloyd A. Culp 《Archives of biochemistry and biophysics》1984,233(2):428-437
Human neuroblastoma cells (Platt) were detached from tissue culture substrata with a Ca2+ chelating agent, and then the suspended cells were extracted with a sodium dodecyl sulfate (SDS)-containing buffer to maximally solubilize their sulfate-radiolabeled proteoglycans. The majority of the high-molecular-weight material in these dissociative extracts was heparan sulfate proteoglycan, which resolves into two heterodisperse size classes upon gel filtration on columns of Sepharose CL4B. After removal of SDS from these extracts by hydrophobic chromatography on Sep-Pak C18 cartridges, extracts were further fractionated on various affinity matrices. All of the sulfate-radiolabeled material eluted as one peak from DEAE-Sephadex ion-exchange columns. In contrast, affinity fractionation on Sepharose columns derivatized with the heparan sulfate-binding protein, platelet factor-4, resolved three major and one minor subsets of these components. The nonbinding fraction contained some heparan sulfate proteoglycan and some chondroitin sulfate. The weak-binding fraction contained principally heparan sulfate proteoglycan, as well as a small amount of chondroitin sulfate proteoglycan; the gel-filtration properties of these proteoglycans before or after alkaline borohydride treatment indicated that they were small in size, containing perhaps 2 to 4 glycosaminoglycan chains. The high-affinity fraction eluted from platelet factor 4-Sepharose was composed entirely of “singlechain” heparan sulfate. A portion of the heparan sulfate proteoglycan of the original extract bound to the hydrophobic affinity matrix, octyl-Sepharose, and this hydrophobic proteoglycan partitioned into the nonbinding and weak-binding fractions of the platelet factor 4-Sepharose affinity columns. These studies reveal that the majority of the proteoglycan made by these neuronal cells in culture is of the heparan sulfate class, is small in size when compared to other characterized proteoglycans, and can be resolved into several overlapping subsets when fractionated on affinity matrices. 相似文献
48.
Summary Protoplasts isolated from cell suspension cultures of carrot (Daucus carota L.) and leaves of tobacco (Nicotiana tabacum L.) were treated with three lectins specific for galactosyl residues. After incubation with RCA I (Ricinus communis agglutinin, molecular weight 120,000) conjugated to ferritin or fluorescein, freshly isolated protoplasts displayed heavy labeling of their surfaces. Moreover, they agglutinated rapidly when exposed to low concentrations of RCA I. In parallel studies, PNA (peanut agglutinin) also bound extensively to the protoplast plasma membranes whileBandeiraea simplicifolia lectin I attached relatively weakly. When protoplasts were cultured for two days and then incubated with conjugates of RCA I and PNA, additional binding sites were revealed on the regenerating walls.The results indicate that galactosyl residues are distributed densely over the surface of plant protoplasts. They also allow inferences to be made regarding the positions and linkages of the galactose groups being recognized by the lectins. Moreover, they open up the question whether the galactosyl moieties detected in the wall derive from those labeled on the plasma membrane. To conclude, we make comparisons with binding by concanavalin A, and predict that galactose-recognizing lectins will join and in certain respects prove superior to concanavalin A as probes of the plant cell surface. 相似文献
49.
Techniques for estimating genetic admixture and applications to the problem of the origin of the Icelanders and the Ashkenazi Jews 总被引:5,自引:0,他引:5
Ellen M. Wijsman 《Human genetics》1984,67(4):441-448
Summary A method is introduced for simultaneously using multiple loci to estimate admixutre and test goodness of fit of the model of admixture. Deviation of observed frequencies from expectation caused by sources of error such as sampling and/or drift is allowed for all loci in all populations. This allows investigation of the effects of different assumptions about sources of error on the estimates. Admixture is then investigated for Icelanders and Ashkenazi Jews. Results indicate that the Icelanders have a large Norse contribution, and that the Jews may have a small to moderate contribution from the European gene pool. There are some indications that ABO and G6PD give abnormal estimates of admixture compared to other loci, and that the Jewish gene pool may be derived from additional populations in addition to the populations considered. 相似文献
50.
On the role of the bacteriophage lambda int gene product in site specific recombination 总被引:1,自引:0,他引:1
Integrative recombination of phage λ DNA occurs in extracts made from cells synthesizing int protein. In this paper we show that extracts of cells containing temperature-sensitive int protein are inactivated more rapidly by incubation at 38 °C than are wild-type extracts. This indicates that the int protein is directly involved in the recombination reaction. 相似文献