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91.
92.
Absence of 7-acetyl taxol binding to unassembled brain tubulin 总被引:1,自引:0,他引:1
The effect of taxol on microtubule proteins at 0 degrees C is controversial. In order to determine if taxol is unable to bind to unassembled tubulin, as has been hypothesized, the binding of [3H]acetyl taxol has been studied using equilibrium microdialysis. Ac-taxol bound to microtubules at 37 degrees C and the binding remained stable when the temperature was lowered to 0 degrees C. Ac-taxol bound also at 0 degrees C to microtubules stabilized with rhazinilam. In contrast, there was no binding of Ac-taxol to unassembled tubulin, either free tubulin at 0 degrees C or tubulin, complexed with several microtubule poisons, at 0 and 37 degrees C. 相似文献
93.
Christine No Jordi Hernandez-Borrell Stephen C. Kinsky Eiji Matsuura Lee Leserman 《生物化学与生物物理学报:生物膜》1988,946(2)
We have prepared liposomes containing methotrexate-γ-dimyristoylphosphatidylethanolamine (MTX-DMPE liposomes), to which protein A was covalently coupled, permitting specific association of these liposomes in vitro with murine cells preincubated with relevant protein A-binding monoclonal antibodies. In the absence of antibody the presence of externally-oriented methotrexate (MTX) in MTX-DMPE liposomes did not result in greater binding to cells than liposomes made without MTX-γ-DMPE. Derivation of methotrexate with phospholipid permits enhanced drug-liposome association. These liposomes are more resistant than conventional liposomes to repeated cycles of freezing and thawing. MTX-DMPE liposomes are comparable to antibody-targeted liposomes made with encapsulated water-soluble methotrexate both with respect to specific binding to target cells and drug effect. The inhibitory effects off MTX-liposomes, as well as free MTX, were reversible by either thiamin pyrophosphate (Tpp) or N5-formyltetrahydrofolate (F-THF), while the effects of MTX-DMPE liposomes were reversed only by N5-formyltetrahydrofolate. This suggests that the toxicity of non-targeted MTX-liposomes may be due to leakage of the encapsulated MTX. The absence of an effect of thiamin pyrophosphate on non-targeted MTX-DMPE liposomes indicates that they do not enter into the cell via the normal folate transport system. 相似文献
94.
J L Gu I D Goldfine J R Forsayeth P De Meyts 《Biochemical and biophysical research communications》1988,150(2):694-701
Two monoclonal antibodies to the insulin receptor, MA-5 and MA-20, unlike other monoclonal antibodies, do not mimick the accelerating effect of insulin on the dissociation of 125I-insulin from the receptors (negative cooperativity). On the contrary, MA-5 and MA-20 markedly slow down the dissociation rate. We show now that MA-5 and MA-20 are potent antagonists of the negative cooperativity induced by insulin, and reverse the insulin-induced acceleration whether added simultaneously with insulin or after insulin. The reversal of the insulin-induced acceleration is almost immediate. These data strengthen the concept therefore that the insulin-receptor complex has access to alternative conformational states that can be stabilized by ligand-induced site-site interactions. 相似文献
95.
Catherine Ferrand Dominique Clarous Christine Delteil Michel J. Weber 《Journal of neurochemistry》1986,46(2):349-358
The secretion and cellular localization of the molecular forms of acetylcholinesterase (AChE) were studied in primary cultures of rat sympathetic neurons. When cultured under conditions favoring a noradrenergic phenotype, these neurons synthesized and secreted large quantities of the tetrameric G4, and the dodecameric A12 forms, and minor amounts of the G1 and G2 forms. When these neurons adopted the cholinergic phenotype, i.e., in the presence of muscle-conditioned medium, the development of the cellular A12 form was completely inhibited. These neurons secreted only globular, mainly G4, AChE. Both cellular and secreted A12 AChE in adrenergic cultures aggregated at an ionic strength similar to that of the culture medium, raising the hypothesis that this form was associated with a polyanionic component of basal lamina. In noradrenergic neurons, 60-80% of the catalytic sites were exposed at the cell surface. In particular, 80% of G4 form, but only 60% of the A12 form, was external, demonstrating for the A12 form a sizeable intracellular pool. The hydrophobic character of the molecular forms was studied in relation to their cellular localization. As in muscle cells, most of the G4 form was membrane-bound. Whereas 76% of the cell surface A12 form was solubilized in the aqueous phase by high salt concentrations, only 50% of the intracellular A12 form was solubilized under these conditions. The rest of intracellular A12 could be solubilized by detergents and was thus either membrane-bound or entrapped in vesicles originating from, e.g., the Golgi apparatus. 相似文献
96.
Senyo Ofori Christine Bretton Patrick Hof Michel Schorderet† 《Journal of neurochemistry》1986,47(4):1199-1206
The basal catecholamine content of rabbit retina was determined by liquid chromatography with electrochemical detection (LC-EC) and 3,4-dihydroxyphenylethylamine (dopamine, DA) found to be the major catecholamine. The immediate DA precursor, 3,4-dihydroxyphenylalanine (L-DOPA), and the metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), were also detected at about 2.8% and 17% of DA levels, respectively. When added exogenously, L-tyrosine did not increase the rate of DA synthesis over the basal level. In contrast, exogenous L-DOPA led to a 3.5-fold increase in DA, and to a 20-fold increase in DOPAC content. The monoamine oxidase inhibitors pargyline and (-)-deprenyl differentially affected the degradation of DA, since 100 microM pargyline was apparently more effective than 100 microM (-)-deprenyl. Reserpine and (+/-)-amphetamine each induced a Ca2+-independent decrease of DA stores. The separate actions of reserpine and (+/-)-amphetamine in lowering tissue DA levels were additive, suggesting two separate pools of DA available for release from presynaptic stores. The present study demonstrates that the LC-EC technique may be used to investigate the modulation of the synthesis and release of retinal DA in vitro, without the prior uptake of radiolabelled transmitter. 相似文献
97.
D. Christine Sigurdson Robert K. Herman Cynthia A. Horton Claire K. Kari Steven E. Pratt 《Molecular & general genetics : MGG》1986,202(2):212-218
Summary The translocation mnT12(IV;X) is a fusion of holocentric chromosomes IV and X, the breakpoints occurring near the left end of IV and the right end of X. Animals homozygous for mnT12 are viable and fertile; they contain five pairs of chromosomes rather than the normal set of six pairs. The mnT12 chromosome is larger than all wild-type chromosomes and thus identifies linkage groups IV and X cytologically. Hermaphrodites heterozygous for mnT12 show high frequency meiotic nondisjunction both between mnT12 and the X chromosome, which results in a high incidence of male self progeny (27% compared to the wild-type incidence of 0.2%), and between mnT12 and chromosome IV, which results in a high incidence of self progeny essentially trisomic for chromosome IV (karyotype IV/mnT12/mnT12). The viability of chromosome IV trisomics has been confirmed by constructing animals trisomic for only normal copies of chromosome IV; these animals are morphologically wild type. Meiotic chromosome disjunction in mnT12 homozygotes appears to be normal, although the frequency of recombination between markers that are normally X-linked is significantly reduced. Males of genotype IV/mnT12/0 are fertile. They can be thought of as having a neo-X(mnT12) neo-Y(normal IV) karyotype since it is possible to maintain a male-hermaphrodite stock of C. elegans consisting of such males and hermaphrodites carrying two neo-X chromosomes and no neo-Y; the organism is thus converted from an XO:XX type of sex determination to an XX:XX system. 相似文献
98.
Lack of correlation between extensive accumulation of bisnucleoside polyphosphates and the heat-shock response in eukaryotic cells 总被引:4,自引:0,他引:4
G F Guédon G J Gilson J P Ebel N M Befort P M Remy 《The Journal of biological chemistry》1986,261(35):16459-16465
The accumulation in large amounts of bisnucleoside polyphosphates (Ap4X) after heat shock in Xenopus laevis oocytes or cultured hepatoma cells (HTC cells) is observed after exposure to temperatures of 45 degrees C or higher. The accumulation is a transient phenomenon, with the collapse in cellular ATP concentration severely affecting the rate of synthesis of Ap4X, allowing degrading activities to empty the pool of these compounds under prolonged heat shock. This accumulation of Ap4X to high levels, compared to the basic content, is only observed under conditions leading to irreversible damage, ultimately resulting in the death of the cell. It is shown that the increase in Ap4X after hyperthermia is due to the partial or almost complete inhibition of their degradation pathways, rather than to a stimulation of their rate of synthesis. Finally, the synthesis of heat-shock proteins could be observed under conditions which do not lead to important accumulation of Ap4X, therefore ruling out the possibility that these adenylylated nucleotides would behave as chemical signals ("alarmones") triggering the synthesis of heat-shock proteins. Nevertheless, on the basis of our earlier results (Guédon, G., Sovia, D., Ebel, J. P., Befort, D., and Remy, P. (1985) Embo J. 4, 3743-3749), it cannot be excluded that Ap4X might play a role in the regulation of the heat-shock response; this would, however, rely on variations in Ap4X concentrations which do not exceed a factor of 2. 相似文献
99.
The survival of Salmonella typhimurium after a standard heat challenge at 55°C for 25 min increased by several orders of magnitude when cells grown at 37°C were pre-incubated at 42°, 45° or 48°C before heating at the higher temperature. Heat resistance increased rapidly after the temperature shift, reaching near maximum levels within 30 min. Elevated heat resistance persisted for at least 10 h. Preincubation of cells at 48°C for 30 min increased their resistance to subsequent heating at 50°, 52°, 55°, 57° or 59°C. Survival curves of resistant cells were curvilinear. Estimated times for a '7D' inactivation increased by 2.6- to 20-fold compared with cells not pre-incubated before heat challenge. 相似文献
100.