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41.
A decline in the calcium-dependent release of neurotransmitters appears to underlie the decreased neuronal function that accompanies reduced oxygen tensions (hypoxia). To determine if alterations in calcium uptake are primary to these changes, synaptosomal calcium uptake was measured in the presence of 100%, 2.5%, or 0% oxygen. Calcium uptake declined 60.2 +/- 0.1 and 82.4 +/- 2.5% with 2.5% and 0% when compared with 100% oxygen, respectively. 3,4-Diaminopyridine stimulated calcium uptake by synaptosomes when they were incubated in low-potassium media. It also diminished the hypoxic-induced decline in calcium uptake to 30.6 +/- 3.1 and 33.5 +/- 3.1% with 2.5% and 0% oxygen, respectively. External binding to the synaptosomal plasma membrane declined to 29.2 +/- 0.3 or 11.8 +/- 0.9% when the oxygen tension was reduced to 2.5% or 0% oxygen. 3,4-Diaminopyridine increased this superficial binding from 111.7 +/- 0.3 to 86.5 +/- 0.9 or 23.4 +/- 0.9% with 100%, 2.5%, or 0% oxygen when compared with 100% oxygen without 3,4-diaminopyridine, respectively. Thus, the decline in neuronal processing that accompanies acute hypoxia may be due to altered calcium homeostasis, which diminishes neurotransmitter release. 相似文献
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Ribonucleic Acid Synthesis During the Differentiation of Sporangia in the Water Mold Achlya 总被引:6,自引:2,他引:4 下载免费PDF全文
The role of ribonucleic acid (RNA) synthesis in the development of sporangia in the saprolegniaceous mold Achlya was studied. Methods were developed for growing and treating large populations of mycelia so that the hyphal tips would differentiate into sporangia with considerable synchrony. Under the starvation conditions imposed for the differentiation of sporangia, net RNA, deoxyribonucleic acid (DNA), and protein synthesis ceased. However, incorporation of radioactive precursors into RNA continued at a high rate throughout the period of differentiation, showing that the enzymatic mechanism for RNA synthesis was still in an active state. Actinomycin D inhibited the differentiation of sporangia and the incorporation of labeled precursors into RNA. The level of actinomycin used did not inhibit the normal outgrowth and branching of the mycelia that occurred during differentiation. Thus, DNA-dependent RNA synthesis was required for the differentiation of sporangia. Sucrose gradient analysis of newly synthesized RNA showed that only the ribosomal and soluble fractions of RNA were labeled during vegetative growth. During the differentiation of sporangia, ribosomal and soluble RNA fractions were also labeled, and, in addition, a heterodisperse fraction of labeled RNA which was heavier than ribosomal RNA appeared; this fraction was not evident in the newly synthesized RNA from vegetative mycelia. 相似文献
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48.
Philip S. Rudland Christine M. Hughes Sharon A. Ferns Michael J. Warburton 《In vitro cellular & developmental biology. Plant》1989,25(1):23-36
Summary Parenchymal organoidal structures that were obtained from collagenase digestion of reduction mammoplasty specimens of apparently
normal human breasts have been grown in short-term primary cultures, either on plastic or on floating gels of polymerized
rat-tail collagen. Three morphologically distinct major cell types are readily observed in both systems: cuboidal cells, which
occupy apical positions on collagen gels; larger, epithelioid, or basal cells on gels; and elongated cells which penetrate
into the gel. In addition, a fourth cell type, that of a large, flat cell, is observed less readily by phase contrast microscopy
on the surface of cultures grown on plastic. Immunofluorescent and immunocytochemical staining of cultures on plastic or histologic
sections of cultures on gels have been undertaken with antisera and other histochemical reagents that stain the different
parenchymal cell types in vivo. Thus antisera to epithelial membrane antigen(s), monoclonal antibodies (MABs) to the defatted
mammary milk fat globule membrane, peanut lectin, and keratin MAB LE61, which preferentially stain the epithelial cells of
ducts in vivo, also stain the cuboidal/apical cells in vitro. The large, flat cells are stained intensely by the first three
reagents but not by the last one. Antisera to collagen IV, laminin, fibronectin, actin, keratin MAB LP34, MABs to the common
acute lymphoblastic leukemia antigen, and MAB LICR-LON-23.10, which showed enhanced staining for the ductal myoepithelial
cells in vivo, also stain the epithelioid/elongated cells in vitro. However, the effect of the last four reagents is reduced
considerably in most elongated cells, and MAB LP34 stains the large, flat cells intensely. Heterogeneous cells of intermediate
morphologies and staining patterns between the cuboidal/flat cells and large epithelioid cells have also been identified.
The results suggest that the cuboidal cells and large, flat cells are related to mammary epithelial cells, whereas the large
epithelioid/elongated cells have some characteristics of myoepithelial cells, and that intermediate forms may exist in culture
between the two parenchymal cell types.
This work was supported in part by the Ludwig Institute for Cancer Research and the Cancer and Polio Research Fund. Dr. M.
J. Warburton is supported by the Cancer Research Campaign. 相似文献
49.
The development and structure of secondary haustoria of Nuytsia floribunda are described and compared with other Santalalean haustoria. After establishing contact with the host root, cortical folds of the haustorium grow around the root in separate directions and fuse forming a ring around it. At an early stage of development, meristematic tissue differentiates in the interior proximal part of the haustorium. Zones of collapsed layers are present in the outer cortical region. Subsequently, in the proximal part, two vascular cores, two lysigenous cavities and extensive masses of sclerenchyma develop prior to penetration of the host root. The sclerenchymatous cells form a characteristic structure, described as the sclerenchyma prong. During penetration the intrusive part of the haustorium reaches not only the host xylem but continues growing downwards until it entirely splits the host root. Comparable to a guillotine, the sclerenchyma prong is directly involved in this remarkable process. The sclerenchyma prong finally lies in the distal part of the haustorium. Following this mechanical slicing of the host root, tube-like cells of the intrusive part actively penetrate the host xylem in an axial direction. 相似文献
50.
Hugo P. Montiero Glenn F. Vile Christine C. Winterbourn 《Free radical biology & medicine》1989,6(6):587-591
The cytotoxicity of many xenobiotics is related to their ability to undergo redox reactions and iron dependent free radical reactions. We have measured the ability of a number of redox active compounds to release iron from the cellular iron storage protein, ferritin. Compounds were reduced to their corresponding radicals with xanthine oxidase/hypoxanthine under N2 and the release of Fe2+ was monitored by complexation with ferrozine. Ferritin iron was released by a number of bipyridyl radicals including those derived from diquat and paraquat, the anthracycline radicals of adriamycin, daunorubicin and epirubicin, the semiquinones of anthraquinone-2-sulphonate, 1,5 and 2,6-dihydroxyanthraquinone, 1-hydroxyanthraquinone, purpurin, and plumbagin, and the nitroaromatic radicals of nitrofurantoin and metronidazole. In each case, iron release was more efficient than with an equivalent flux of superoxide. Introduction of air decreased the rate of iron release, presumably because the organic radicals reacted with O2 to form superoxide. In air, iron release was inhibited by superoxide dismutase. Semiquinones of menadione, benzoquinone, duroquinone, anthraquinone 1,5 and 2,6-disulphonate, 1,4 naphthoquinone-2-sulphonate and naphthoquinone, when formed under N2, were unable to release ferrin iron. In air, these systems gave low rates of superoxide dismutase-inhibitible iron release. Of the compounds investigated, those with a single electron reduction potential less than that of ferritin were able to release ferritin iron. 相似文献