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21.
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
22.
Enhancer sequences responsible for DNase I hypersensitivity in polyomavirus chromatin. 总被引:5,自引:2,他引:3 下载免费PDF全文
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
23.
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
24.
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
25.
This paper describes the isolation and amino acid analysis of un-cross-linked elastin obtained by neutral salt extraction from the ligamentum nuchae of a calf fed from birth to 9 months on a diet low in copper. 相似文献
26.
Synergistic effects of metabolically related amino acids on the growth of a multicellular plant 总被引:2,自引:2,他引:0 下载免费PDF全文
The effects of several amino acids related to the metabolism of aspartic acid on the growth and development of gemmalings of the liverwort Marchantia polymorpha were investigated under axenic conditions. Lysine and theonine synergistically inhibit the growth of these plants and cause a loss of normal pigmentation at concentrations as low as 1 μm. These effects are highly specific for this pair of amino acids, are partially reversible upon removal of the effectors, and can be prevented by low concentrations of methionine or its metabolic precursor, homoserine. Alterations in the growth and development of gemmalings in the presence of natural amino acids are discussed in relation to metabolic regulatory mechanisms which have been well established in microorganisms. 相似文献
27.
28.
"Further-processed" turkey products, prepared from chilled, eviscerated, and thawed carcasses at two commercial turkey-processing plants, were evaluated, for the presence of salmonellae. These organisms were isolated from swab samples from 12% of chilled, eviscerated turkey carcasses, 27% of finished products, and 24% of processing equipment. The same serotypes as those found throughout a plant on any one visit were recovered from 31% of rinse-samples taken from hands and gloves of processing personnel. Salmonellae were found in samples taken on 37 of 48 visits; a greater number of recoveries were made on days when freshly killed turkeys were processed (87%) than when frozen-defrosted carcasses were processed (59%). The predominant serotype isolated from meat and environment usually changed from visit to visit. Salmonella sandiego and Salmonella anatum were the most frequent among 23 serotypes recovered. Most of the isolated serotypes are commonly associated with turkeys and have been incriminated as causative agents of human salmonellosis. The implication is that further-processed turkey products, if inadequately cooked by the consumer and if improperly refrigerated between the time of manufacture and consumption, could directly transmit salmonellae. These same products might also contaminate other foods by introducing salmonellae into food-preparation areas. 相似文献
29.
30.
The distribution of hyaluronate-binding activity was determined in the soluble and membrane fractions derived from adult mouse brain by sonication in low-ionic-strength buffer. Approximately 60% of the total activity was recovered in the soluble fraction and 33% in membrane fractions. In both cases, the hyaluronate-binding activities were found to be of high affinity (KD = 10(-9) M), specific for hyaluronate, and glycoprotein in nature. Most of the hyaluronate-binding activity from the soluble fraction chromatographed in the void volume of Sepharose CL-4B and CL-6B. Approximately 50% of this activity was highly negatively charged, eluting from diethylaminoethyl (DEAE)-cellulose in 0.5 M NaCl, and contained chondroitin sulfate chains. This latter material also reacted with antibodies raised against cartilage link protein and the core protein of cartilage proteoglycan. Thus, the binding and physical characteristics of this hyaluronate-binding activity are consistent with those of a chondroitin sulfate proteoglycan aggregate similar to that found in cartilage. A 500-fold purification of this proteoglycan-like, hyaluronate-binding material was achieved by wheat germ agglutinin affinity chromatography, molecular sieve chromatography on Sepharose CL-6B, and ion exchange chromatography on DEAE-cellulose. Another class of hyaluronate-binding material (25-50% of that recovered) eluted from DEAE with 0.24 M NaCl; this material had the properties of a complex glycoprotein, did not contain chondroitin sulfate, and did not react with the antibodies against cartilage link protein and proteoglycan. Thus, adult mouse brain contains at least three different forms of hyaluronate-binding macromolecules. Two of these have properties similar to the link protein and proteoglycan of cartilage proteoglycan aggregates; the third is distinguishable from these entities. 相似文献