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61.
The Catalasemetre, for assessing the quality of raw and pasteurized milk, has been studied. No correlation was found between catalase activity and bacterial counts for farm bulk tank milks within the range 5.2 ± 102 -5.4 ± 105 cfu/ml. Similarly, no relation was observed between catalase activity and somatic cell counts of milk (range of counts from 0.08 to 3.5). However, the catalase activity and bacterial count of pasteurized milks which had been pre-incubated at 21.C for 25 h in the presence of crystal violet-penicillin-nisin to inhibit Gram-positive bacterial growth were significantly related. Thus, the use of this pre-incubation procedure coupled with the Catalasemetre to estimate bacterial growth, has potential in assessing the keeping quality of pasteurized milk samples within 25.5 h of production. Results on the thermostability of native milk catalase are also presented. 相似文献
62.
Bryan B. Fuller 《In vitro cellular & developmental biology. Plant》1987,23(9):633-640
Summary Tyrosinase activity increased in Cloudman S-91 mouse melanoma cell homogenates incubated at 37°C for a minimum of 8 h. Enzyme
activity continued to increase for 48h at which time the maximal level of activation was observed. Activation did not occur
at 4°C and did not occur in the cytosol fraction of the cell, suggesting that the response was localized to melanosomes. The
activated enzyme was resistant to solubilization with the nonionic detergent, Triton X-100, and preparation of homogenates
in this detergent did not inhibit the temperature-dependent activation of the melanosomal fraction of the cell. The activation
process increased the V
Max
of tyrosinase 10-fold and lowered the K
M
by a factor of 2 as determined by the tyrosine hydroxylase assay. The increase in tyrosinase activity was detectable by three
assay methods: tyrosine hydroxylation, melanin synthesis, and by tyrosine decarboxylation. The formation of melanin, however,
was found to be 1/20 that of either tyrosine hydroxylation or decarboxylation, a finding which suggests that the melanin pathway
may be blocked at 5,6-dihydroxyindole. The “self-activation” response could not be mimicked by incubating cell homogenates
with cyclic AMP-dependent protein kinase. Activated tyrosinase could be inhibited by the addition of fresh cell extracts,
a finding which suggests that tyrosinase inhibitors may be present in these cells.
This investigation was supported by Public Health Service grants CA41425 and CA30393 awarded by the National Cancer Institute,
Bethesda, MD and by a research grant from the Proctor and Gamble Company. 相似文献
63.
Enhancer sequences responsible for DNase I hypersensitivity in polyomavirus chromatin. 总被引:5,自引:2,他引:3
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DNase I preferentially cleaves polyomavirus minichromosomes at two sites in the enhancer, each of which comprises the sequence AAGCAPuPuAAG flanked by short inverted repeats. A tandem duplication of this sequence generates an additional hypersensitive locus. Mutations which alter either the AAGCAPuPuAAG or flanking repeats diminish hypersensitivity. This region must determine the chromatin conformation recognized by DNase I. 相似文献
64.
65.
Abstract: The concentration of γ-aminobutyrate (GABA) and the activity of glutamate decarboxylase and GABA-transaminase were measured in extracts of mouse brain before the onset and during the course of generalized seizures induced by systemic administration of homocysteine thiolactone. The results indicate that whole brain GABA metabolism is unaffected by subconvulsive and convulsive doses of homocysteine at all stages of the generalized seizure. Electroencephalographic monitoring of rat brain electrical activity via hippocampal electrode implantation allowed the course of homocysteine-induced seizures to be followed and afforded a means of quantifying such seizures. 相似文献
66.
Soybean (Glycine max L. Merrill) nodules are usually more enriched in 15N than other tissues. We show that both bacteroids and nodule cortex are considerably more enriched in 15N than nodule cytosol, with bacteroids being slightly more enriched than the cortex. Hence, 15N enrichment occurs in cells of both plant and bacterial origin. 相似文献
67.
68.
69.
Identification and purification of calcium ion dependent modulators of actin polymerization from bovine thyroid 总被引:2,自引:0,他引:2
We describe the purification of Ca2+-dependent actin modulator proteins from bovine thyroid using DNase I affinity chromatography and diethylaminoethylcellulose chromatography. The 40K actin modulator has been purified to 98% homogeneity. It is a single polypeptide chain with a molecular weight of approximately 40 000 and an isoelectric point of 8.1. Its amino acid composition is different from previously described actin-associated proteins and thyroid actin. On the basis of the centrifugation assay and the DNase I inhibition assay, the actin complexed with the 40K protein is G-actin in its conformation rather than F-actin oligomers. Substoichiometric concentrations of the 40K protein rapidly inhibit actin polymerization in the presence of physiological concentrations of Ca2+ and Mg2+. An 80K actin modulator also has been purified to 98% homogeneity. It is a single polypeptide chain with a molecular weight of approximately 80 000 and an isoelectric point of 6.35-7.0. Its amino acid composition is different from those of villin, gelsolin, and leukocyte actin polymerization inhibitor. On the basis of the DNase inhibition assay and the centrifugation assay, the nonprecipitable actin associated with the 80K protein was F-actin in its conformation. The 80K protein acts very efficiently as a Ca2+-dependent nucleator for actin assembly and reduces its viscosity. In addition to the 40K and 80K actin modulators, 91K and 95K actin-associated proteins were partially purified. The 91K-95K fraction has similar activity to the 80K protein regarding precipitation of F-actin. The 125I-G-actin polyacrylamide gel overlay technique [Snabes, M. C., Boyd, A.E., & Bryan, J. (1981) J. Cell Biol. 90, 809-812] revealed that both the 91K and 95K proteins bind 125I-actin after sodium dodecyl sulfate (NaDodSO4) electrophoresis while the 80K and 40K proteins do not. Thyroid 91K protein comigrated with a human platelet 91K actin binding protein on NaDodSO4 gels and may be similar to macrophage gelsolin. The 95K protein may be similar to villin, the intestinal cytoskeletal protein. 相似文献
70.
A. G. Nash D. R. Dance V. R. McCready J. D. Griffiths 《BMJ (Clinical research ed.)》1972,3(5825):508-510
The uptake of 67Ga in biopsy specimens of normal and abnormal tissue was measured in 20 cases of colonic and rectal disease and the ratio between the 67Ga uptake in these diseases and in the normal colon or rectum was determined. Uptake of the isotope was high in most of the 14 primary malignant tumours, being highest in poorly differentiated tumours. This uptake was found to be concentrated at the active tumour edge. Uptake of the isotope was generally low in non-malignant lesions. 相似文献