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51.
Transport of amino acids (in vitro) in the rat pancreas is affected by the nutritional state of the animal. A fast of 24 h (young animals) or 48 h (adult animals) reduces the rate of amino acid uptake in the isolated rat pancreas in vitro. In contrast, refeeding of animals after a fast shows an increase in transport in young as well as adult animals.The effects of refeeding after a fast are mimicked to a significant extent by injection of mixtures of pancreozymin and carbamylcholine. Addition of these agents in vitro has no effect.The incorporation of amino acids into the total proteins of the rat pancreas follows the pattern of amino acid uptake. Even at high external levels of glycine (5 mM), incorporation increases although the glycine level in the cell is in excess of 25 mM. Reduction of glycine uptake by ouabain by 75% results in a substantial (44%) diminution of amino acid incorporation into proteins. The data suggest that inhibition of amino acid incorporation under the various metabolic conditions examined is due largely to a decreased availability of amino acids. 相似文献
52.
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54.
Emanuel Lebenthal Gregory W. Morrissey 《Biochimica et Biophysica Acta (BBA)/General Subjects》1977,497(2):558-566
The subcellular localization of enterokinase is controversial. In this study, enterokinase was extracted from a soluble fraction and a brush border fraction of rat small intestine by differential centrifugation. The soluble fraction contained 41% of the initial enterokinase activity while the brush border fraction contained only 4.6% of the initial activity. In contrast, alkaline phosphatase monitored as a brush border marker, yielded 26.3 in the brush border fraction and only 6% in the soluble fraction. Further separation of the soluble fraction on a Sepharose 4B column revealed three peaks of enterokinase activity. One small peak (3%) of a bound enzyme (Mr, 2·10?6) and two larger peaks of free enzyme (Mr, 3·105 and 9·105). In contrast, alkaline phosphatase major fraction was in a high molecular weight peak of bound enzyme. When the brush border fraction was chromatographed only a single peak of bound enterokinase and alkaline phosphatase were found. In the lower part of the small intestine, no brush border-bound enterokinase was found, while the peak of alkaline phosphatase was the same as in the upper intestine. These data suggest that enterokinase activity in the rat intestine is mainly in a free form localized in the mucin and soluble fraction and to a negligible extent in the brush border. 相似文献
55.
Automated determinations of 5-hydroxytryptamine and its main metabolite, 5-hydroxyindoleacetic acid, have been described (Technicon autoanalyzer). The determinations are based on an extraction procedure from deproteinized tissue extracts or cerebrospinal fluid by means of butanolheptane mixtures. The indoles are transferred from the organic phase to a water phase and determined fluormetrically with the cysteine-o-phthaldialdehyde method. The method is highly sensitive: solutions containing 1 ng/ml can be reproducibly determined. Twenty samples per hour can be passed through the system. The determination of both 5-hydroxyindoles is performed with the same manifold. 相似文献
56.
The radioautographs and statistical data presented herein indicate that the uptake of glucose [14C] into rat diaphragm sections does not depend solely on the insulin concentration of the incubation medium. It is shown that by taking into account the tissue weight of the diaphragm section, a linear relationship for uptake vs log (insulin concentration) may be obtained. This serves to emphasize how careful one must be when modifying a biological assay so that previously unimportant conditions do not become significant enough to invalidate the results. 相似文献
57.
In vitro growth of murine T cells. IV. Use of T-cell growth factor to clone lymphoid cells 总被引:3,自引:0,他引:3
Murine bone marrow cells can suppress the in vitro primary antibody response of normal spleen cells without apparent cytotoxicity. The bone marrow cells suppress the response to both T-dependent (SRBC) and T-independent (DNP-Ficoll) antigens. When bone marrow cells are fractionated on a sucrose density gradient, the suppressive activity is found in the residue rather than the lymphocyte fraction. The suppressive activity is either unaffected or enhanced by treatment with anti-T- and anti-B-cell serums. Pretreatment of mice with phenylhydrazine which reduces the number of pre-B cells did not reduce the suppressive activity of their bone marrow cells. Suppressive activity is abolished by irradiation of the marrow cells in vitro with 1000 R prior to assay. The activity is present in the marrow of thymus deficient (nude) mice, infant mice, and mice which have been made polycythemic by transfusion. Furthermore, the suppressor cell can phagocytize iron carbonyl particles, is slightly adherent to plastic and Sephadex G-10, and can bind to EA monolayers. We conclude that the suppressor cell is not a mature lymphocyte or granulocyte nor a member of the erythrocytic series, but is likely to be an immature cell possibly of the myeloid series. We speculate on the physiologic role of this cell. 相似文献
58.
Binding of Zn(II) to the carbon monoxide complex of human hemoglobin was shown by equilibrium sedimentation and sedimentation velocity experiments at pH 7.0 to induce the dissociation of liganded tetramers to dimers but not to monomers. These results provide direct confirmation of previous kinetic and gel filtration experiments (R. D. Gray, (1980) J. Biol. Chem.255, 1812–1818) that Zn(II) binding to liganded hemoglobin produces a change in aggregation state of liganded hemoglobin. 相似文献
59.
The coexistence of many species within ecological communities poses a long‐standing theoretical puzzle. Modern coexistence theory (MCT) and related techniques explore this phenomenon by examining the chance of a species population growing from rarity in the presence of all other species. The mean growth rate when rare, , is used in MCT as a metric that measures persistence properties (like invasibility or time to extinction) of a population. Here we critique this reliance on and show that it fails to capture the effect of temporal random abundance variations on persistence properties. The problem becomes particularly severe when an increase in the amplitude of stochastic temporal environmental variations leads to an increase in , since at the same time it enhances random abundance fluctuations and the two effects are inherently intertwined. In this case, the chance of invasion and the mean extinction time of a population may even go down as increases. 相似文献
60.
Different genetic stains of avian RNA tumor virus (ATV) were labeled with the fluorescent membrane probe R-18 (rhodamine conjugated
to a hydrocarbon chain) and cellular receptors for virus infection were analyzed on a rapid, single-cell basis by a multiparameter
cell sorter. Chicken cells genetically susceptible to various R-18 ATV were found to adsorb much more virus, as measured by
increased fluorescent binding, than did genetically resistant chicken cells. Virus binding to receptor sites could be saturated
with increased concentrations of labeled virus. This binding could be altered by removal of the polycation, polybrene, indicating
the important influence of electrostatic forces. Correlated time measurements of virus binding to single cells were taken
with these fluorescence measurements allowing for a minute-to-minute study of the kinetics of viral adsorption to resistant
and susceptible cells. The ratio of fluorescence (proportional to the number of virions bound per cell) to light scatter (proportional
to cell surface area) on a cell-to-cell basis was analyzed to examine the heterogeneity in fluorescent virion bound per unit
cell surface area within a given cell type. With these calculations, it was found that a large amount, but not all, of observed
fluorescence heterogeneity merely reflects differences in cell surface areas. However, there are significant differences in
viral receptor site densities within this supposedly homogeneous population of cells. This study represents a successful application
of fluorescent membrane probes and flow cytometry to the study of cellular responses to viral infection at the single-cell
level. Sine large numbers of cells can be examined rapidly, small subpopulations of live virally susceptible or resistant
cells can be cloned by multiparameter cell sorting. 相似文献