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981.
The potent antiulcer prostaglandin enprostil binds with high affinity to porcine gastric mucosal tissues. This binding is saturable, dissociable and displaceable by compounds with similar structures. Various characteristics of binding such as pH optimum and displacement potencies suggest that enprostil binds to mucosal PGE2 sites. Structure-activity and gastric mucosal binding relationships were also examined. 相似文献
982.
Molecular structure and polymorphic map of the human phenylalanine hydroxylase gene 总被引:32,自引:0,他引:32
Human phenylalanine hydroxylase is a liver-specific enzyme that catalyzes the conversion of phenylalanine to tyrosine. Absence of enzymatic activity results in phenylketonuria, a genetic disorder that causes development of severe mental retardation in untreated children. In this paper we report the cloning and structure of the normal human phenylalanine hydroxylase gene, which was isolated in four overlapping cosmid clones that span more than 125 kilobases (kb) of the genetic locus. The peptide coding region of the gene is about 90 kb in length and contains 13 exons, with intron sizes ranging from 1 to 23 kb. Exons at the 3' half of the gene are compact, whereas those at the 5' half are separated by large introns. The human phenylalanine hydroxylase gene codes for a mature messenger RNA of approximately 2.4 kb, and its noncoding to coding DNA ratio is one of the highest among eukaryotic genes characterized to date. The map positions of nine polymorphic restriction sites identified within the locus were established by restriction enzyme mapping of the cloned gene fragments. Two clusters of polymorphic sites were demonstrated: (1) BglII, PvuII(a), and PvuII(b) at the 5' end of the gene and (2) EcoRI, XmnI, MspI(a), MspI(b), EcoRV, and HindIII at the 3' end. The polymorphic site distribution within this gene is a useful tool for prenatal diagnosis and carrier detection of the genetic disorder, while knowledge of normal gene structure is a prerequisite for future characterization of mutant alleles. 相似文献
983.
This study examines the capacity of intact spinach (Spinacia oleracea L.) chloroplasts to fix 14CO2 when supplied with Benson-Calvin cycle intermediates in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Under these conditions, substantial 14CO2 fixation occurred in the light but not in the dark when either dihydroxyacetone phosphate, ribulose 5-phosphate, fructose 6-phosphate, or fructose bisphosphate was added. The highest rate of 14CO2 fixation (20-40 micromoles per milligram chlorophyll per hour) was obtained with dihydroxyacetone phosphate. In contrast, no 14CO2 fixation occurred when 3-phosphoglycerate was used. 14CO2 fixation in the presence of dihydroxyacetone phosphate and DCMU was inhibited by carbonylcyanide m-chlorophenylhydrazone, dl-glyceraldehyde, and pyridoxal 5′-phosphate. Low concentrations of O2 (25-50 micromolar) stimulated 14CO2 fixation, but the activity decreased with increasing O2 concentrations. The fixation of 14CO2 in the presence of DCMU and dihydroxyacetone phosphate was also observed in maize bundle sheath cells. These results provide direct evidence for cyclic photophosphorylation in intact chloroplasts. The activity measured is adequate to support all the extra ATP requirements for maximum rates of photosynthesis in these intact chloroplasts. 相似文献
984.
The need for better and longer lasting trileaflet valves has led to the design and development of the Abiomed polymeric trileaflet valve prosthesis. In-vitro fluid dynamic studies on sizes 25 and 21 mm valves in the aortic position indicate an overall improvement in performance compared to the Carpentier-Edwards and Ionescu-Shiley tissue valves in current clinical use. The pressure drop studies yielded effective orifice areas of 1.99 and 1.54 cm2, and performance indices of 0.41 and 0.45 for the Nos. 25 and 21 valves, respectively. Leaflet photography studies indicated that the two valve sizes had maximum opening areas of 225 and 145 mm2, respectively, at a normal resting cardiac output. Steady and pulsatile flow velocity measurements with a laser-Doppler anemometer (LDA) system indicate that the flow field downstream of the Abiomed valve is jetlike and turbulent. Maximum mean square axial velocity fluctuations of 55 and 83 cm/s, and turbulent shear stresses of 220 and 450 N/m2 were measured in the immediate vicinity of the nos. 25 and 21 valves, respectively. The Abiomed valves studied had been originally configured for use in valved conduits, and it is therefore our opinion that further improvements can be made to the valve and stent design, which would enhance its fluid dynamic performance. 相似文献
985.
The morphogenetic movements of neural ectoderm cells associated with neural plate development and neural fold fusion were examined in notochord-defective embryos. Those movements were apparently normal in embryos which displayed a notochord reduced in size or which completely lacked a notochord. Likewise, axial stretching in the anterior-posterior direction was also normal in “notochord-defective” embryos. A role for the anuran notochord in directing neural fold fusion and axial stretching can, therefore, be ruled out. 相似文献
986.
987.
金龟子在武功一带发生者,种类颇多,据笔者调查,发生普遍而为害较烈者,计有四种。一为棕色金龟子Rhizotrogus(Amphimallus)sp.;二为酱色金龟子Holo-trichia diomphalia Bates;三为黑色金龟子Trematodes tenebrioides Pall.,本种为 相似文献
988.
Young cells produced in LK sheep during rapid hematopoiesis after massive hemorrhage contain more K than the cells which are normally released into the circulation. The K content in these new cells falls to that characteristic of mature LK cells after a few days in the circulation. K transport properties in young and old cells before and after massive bleeding were studied. Young and old cells were separated by means of a density gradient centrifugation technique. Evidence showing that younger cells are found in the lower density fractions is presented. Active transport of K in the lightest fraction as measured by strophanthidin-sensitive influx was four to five times greater in red cells drawn 6 days after massive bleeding while the K leak as measured by strophanthidin-insensitive influx was only slightly larger. No change after bleeding was observed in older cells which had been present in the circulation prior to the hemorrhage. It is concluded that the high K content of young cells produced in LK sheep after bleeding is due to temporary retention of membrane K transport properties characteristic of HK cells. Thus, genetically determined modification of membrane transport properties has been shown to occur in nondividing circulating red cells. 相似文献
989.
Associations between mutations and a VNTR in the human phenylalanine hydroxylase gene. 总被引:4,自引:1,他引:3 下载免费PDF全文
A A Goltsov R C Eisensmith D S Konecki U Lichter-Konecki S L Woo 《American journal of human genetics》1992,51(3):627-636
The HindIII RFLP in the human phenylalanine hydroxylase (PAH) gene is caused by the presence of an AT-rich (70%) minisatellite region. This region contains various multiple of 30-bp tandem repeats and is located 3 kb downstream of the final exon of the gene. PCR-mediated amplification of this region from haplotyped PAH chromosomes indicates that the previously reported 4.0-kb HindIII allele contains three of these repeats, while the 4.4-kb HindIII allele contains 12 of these repeats. The 4.2-kb HindIII fragment can contain six, seven, eight, or nine copies of this repeat. These variations permit more detailed analysis of mutant haplotypes 1, 5, 6, and, possibly, others. Kindred analysis in phenylketonuria families demonstrates Mendelian segregation of these VNTR alleles, as well as associations between these alleles and certain PAH mutations. The R261Q mutation, associated with haplotype 1, is associated almost exclusively with an allele containing eight repeats; the R408W mutation, when occurring on a haplotype 1 background, may also be associated with the eight-repeat VNTR allele. Other PAH mutations associated with haplotype 1, R252W and P281L, do not appear to segregate with specific VNTR alleles. The IVS-10 mutation, when associated with haplotype 6, is associated exclusively with an allele containing seven repeats. The combined use of this VNTR system and the existing RFLP haplotype system will increase the performance of prenatal diagnostic tests based on haplotype analysis. In addition, this VNTR may prove useful in studies concerning the origins and distributions of PAH mutations in different human populations. 相似文献