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21.
Cloning and expression of a cDNA encoding a catalytically active fragment of calf thymus DNA polymerase alpha 总被引:2,自引:0,他引:2
K Foster K Lüthi-Steinmann M Barnes G McMaster E Ferrari K Eliassen N Khan N Brown U Hübscher 《Biochemical and biophysical research communications》1986,140(1):21-27
A calf thymus cDNA expression library was constructed in the EcoRI site of lambda gt11 and probed with an antibody raised against calf thymus DNA polymerase alpha. Three classes of antibody-reactive clones were isolated. The largest class carried a 1.9 kilobase calf cDNA insert and expressed a 165-175 kilodalton beta-galactosidase:calf fusion protein which displayed DNA polymerase activity. The characteristic responses of the polymerase activity to alpha-specific inhibitors and antibodies identified the 1.9 kilobase cDNA as a sequence specifically derived from the structural gene encoding the pol alpha catalytic core. 相似文献
22.
E J Pisko S L Foster R E White M Panetti R A Turner 《Journal of immunology (Baltimore, Md. : 1950)》1986,136(6):2141-2150
The mechanisms whereby formed immune complexes (IC) or immunoglobulin aggregates can suppress further antibody production were explored by culturing normal human peripheral blood mononuclear leukocytes (PBL) with heat-aggregated IgG (HAIgG) and collecting the culture supernatants at 24 hr. These supernatants were found to suppress a pokeweed mitogen (PWM)-induced rheumatoid factor plaque-forming cell (RF-PFC) response in normal individuals. PWM-induced anti-trinitrophenylated sheep red blood cell (TNP-SRBC) PFC were also inhibited by suppressor supernatants from HAIgG-stimulated PBL, suggesting that the polyclonal PFC response was inhibited by a suppressor factor. The suppressor factor inhibited PWM stimulated RF-PFC throughout the culture period, but suppression was maximal at the peak of the RF-PFC response. Suppressor factor was only effective at the initiation of cultures, suggesting that it inhibited early events in the PWM-stimulated RF-PFC response. Molecular weight determination of the suppressor factor by differential membrane fractionation suggested a m.w. range of 30,000 to 50,000, and chromatography on Sephadex G-100 showed a peak activity at an approximate m.w. of 32,000. Studies suggested the factor was not an interferon. Depletion of T lymphocytes by E rosetting and macrophages/monocytes by G-10 adherence did not affect the generation of suppressor factor. Depletion of T lymphocytes (OKT4, OKT8) and NK cells (Leu-11b) by antibody-dependent, complement-mediated cytotoxicity also did not affect the generation of suppressor factor. Depletion of B lymphocytes with OKB7 resulted in the generation of significantly less suppressor factor. Suppression produced by unstimulated purified B lymphocytes was approximately one-half that seen when B lymphocytes were stimulated with HAIgG. Differential membrane fractionation studies suggested that only HAIgG-stimulated B cell cultures contained peak activity in the 30,000 to 50,000 m.w. fraction. Supernatants from unstimulated purified T cells also generated suppression, which was approximately one-half of that seen with HAIgG-stimulated B cells, but no increase in suppressor activity was seen in T cell cultures after incubation with HAIgG. These studies demonstrate that HAIgG is capable of stimulating B lymphocytes to produce a lymphokine, suppressive B cell factor (SBF), which is capable of suppressing a polyclonal PFC response. SBF may be important in feedback control of human immunoglobulin production. 相似文献
23.
Functional aspects of ano-rectal vascularity 总被引:4,自引:0,他引:4
The blood supply of the ano-rectum has been studied in cadaveric specimens by angiographic methods. The vascular anastomosis between the middle rectal and superior rectal vessels was found to be demonstrable on one side only. There appears to be a midline paucity of vessels in both the posterior and anterior rectal walls, and this may be important in the aetiology of anastomotic dehiscence in low anterior resection. 相似文献
24.
Cytokinin requiring cells of Nicotiana tabacum L. cv "Havana 425" can be induced in culture to become cytokinin autotrophic. This process is known as cytokinin habituation. Earlier we showed that pith parenchyma tissue consists of inducible cells, which habituate at high rates when treated with cytokinin, and noninducible cells, which remain cytokinin requiring under these conditions. The inducible and noninducible phenotypes are determined states that arise during the development of the tobacco plant and are inherited by individual cells. Here we show that pith tissue of plants regenerated from cloned lines of noninducible cells exhibits the inducible phenotype indicating that noninducible cells, or their descendants, can become inducible. This change in competence for habituation appears to have an epigenetic basis; it is reversible, occurs at high rates, and depends on the developmental state of the cells. The habituated state occurs in two forms that can be distinguished by their difference in developmental potential. Habituated cells derived from inducible pith cells give rise to normal plants whose leaf and pith tissues require cytokinin for growth in culture. In contrast, habituated cells obtained by transferring noninducible cells on media with progressively lower cytokinin concentrations give rise to plants whose leaf and pith tissues exhibit a cytokinin-habituated phenotype in culture. 相似文献
25.
26.
Activation of the transformation potential of the cellular fps gene 总被引:27,自引:0,他引:27
Chicken cellular-fps (c-fps) sequences were substituted for viral-fps (v-fps) sequences in two retroviral genome structures, one that expressed a c-fps gene product that was indistinguishable from the normal c-fps gene product expressed in chicken bone marrow cells, and another that expressed a gag-fps fusion protein. When c-fps gene sequences (without linked gag gene sequences) were expressed at high levels in a viral vector, no transformation of fibroblasts was detected. It was previously demonstrated that the corresponding v-fps sequences could transform fibroblasts. When the same c-fps sequences were expressed in a form linked to gag gene sequences, transformation of fibroblasts and induction of tumors were observed. The data suggest that the c-fps gene product lacks transformation potential by itself even when overexpressed and that the transformation potential of the c-fps gene can be activated by either mutation (or mutations) in the fps coding region or by fusion with viral gag gene sequences. 相似文献
27.
Localization of Tamm-Horsfall-glycoprotein-like immunoreactivity in cultured baby-hamster kidney cells, shown by immunofluorescence and by light- and electron-microscopic immunoperoxidase techniques. 下载免费PDF全文
Tamm-Horsfall glycoprotein was isolated from hamster urine, and antiserum against it was produced in rabbits. IgG was isolated from the antiserum. Immunocytochemical methods were used to localize Tamm-Horsfall-like immunoreactivity in three substrains of baby-hamster kidney (BHK) cells. Indirect immunofluorescence techniques showed that, in two substrains (BHK-21/C13/2P and BHK-21/C13/3P), a proportion of the cells fluoresced brilliantly, whereas those of the third substrain (BHK-21/ICRF) were totally negative. Related findings were obtained by the immunoperoxidase optical-microscopic technique. From the results of immunoperoxidase techniques using the electron microscope, it was concluded that the substance was present in association with the plasma membranes of the reacting cells. Our data suggest that the line of baby-hamster kidney cells, BHK-21/C13, may contain cells of renal-tubular epithelial origin, and that the proportion of these may be variable from one subculture to another. 相似文献
28.
Basement membrane components in healing rabbit corneal epithelial wounds: immunofluorescence and ultrastructural studies 总被引:10,自引:3,他引:7 下载免费PDF全文
The nature of the substrate that supports epithelial migration in vivo is of interest, particularly with respect to mechanisms of wound healing. Immunofluorescence and electron microscopy were used to search for common substrate components in prototype rabbit corneal wounds: epithelial scrape wounds, in which the corneal or conjunctival epithelium migrated over the denuded lamina densa of the corneal basement membrane (CBM), and superficial keratectomy, in which the corneal epithelium migrated over a bare stroma without CBM. The corneal epithelium moved rapidly over the CBM or stroma to cover the defect within 2-3 d, whereas the conjunctival epithelium required 1-2 wk. In all wounds, fibronectin and fibrin/fibrinogen were deposited onto the bare surface within 8 h after wounding and persisted under the migrating epithelium until migration was complete. Bullous pemphigoid antigen (BPA), a normal component of the CBM, was removed with the epithelium upon scrape wounding and reappeared in the CBM after migration was completed. In contrast, the conjunctival epithelium had a continuous subepithelial band of BPA out to the migrating tip. Laminin, also a normal component of the CBM, was not removed in the scrape wounds, indicating that the region of least resistance to shear stress was between the BPA and laminin layers. Laminin was removed by superficial keratectomy and was not detectable under the leading edge of the migrating cells. Laminin and BPA were restored in the CBM by 2-4 wk. Type IV collagen could not be detected in normal CBM, but was conspicuously present in conjunctival basement membrane and in blood vessels. Focal bands of type IV collagen did appear in the newly synthesized CBM 2-4 wk after keratectomy. These results argue that BPA, laminin, and type IV collagen are not essential for the migration of corneal epithelium during wound healing and support the hypothesis that fibronectin and fibrin/fibrinogen are the common, perhaps the essential, components of the provisional matrix that serves as a substrate until the permanent attachment components are regenerated. 相似文献
29.
The development and testing of an integrated kinetic model describing both short and long term zinc metabolism in humans is discussed. The development took place in two stages. The first, based on a five day turnover study, details the early phases of zinc metabolism in several body tissues together with absorption and excretion. This model, however, accounts for only 10% of total body zinc. To describe the kinetics of total body zinc, a long term model which contains a reduced version of the five day model was developed. This model required an additional compartment for the liver system, but as postulated in the short term model, 90% of body zinc turns over slowly in a single compartment. The models are then used to describe the effect on zinc metabolism of different disease states and lietary perturbations. These additional studies enhance the models' validity while providing physiological insights. 相似文献
30.
In previous experiments two extreme modes of visual discrimination performance have been investigated by measuring small differences in pattern shape at points along a continuum of pattern shapes. These two modes, associated with discrete and continuous encoding processes, were obtained by simultaneously manipulating the number of pattern components in the display and the effective duration of the display. In this experiment, discrimination performance was measured for a fixed number of pattern components, namely three, and variable display time course. The stimuli used were curved lines drawn from a continuum with curvature parameter s. There were three stimulus time courses: (1) 2-s stimulus display, (2) 100-ms stimulus display, and (3) 100-ms stimulus display followed by a post-stimulus mask. Discrimination performance declined smoothly and monotonically with s for (1), but varied non-monotonically with s revealing a central peak for (3). Performance for (2) was intermediate between that for (1) and that for (3). A reduction in effective stimulus duration alone was thus sufficient to cause a transition from continuous to discrete modes of discrimination performance, a result which may be compatible with an explanation of variable discrimination modes based on a method of successive internal approximations of the stimulus. 相似文献