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101.
102.
Oestradiol uptake and retention, and high-affinity binding sites in cultured rabbit uterus 下载免费PDF全文
Oestradiol uptake and turnover was examined in rabbit uterus maintained in organ culture for up to 3 days. Serum decreased the uptake of [(3)H]oestradiol, whereas insulin had no significant effect. During the first 24h of culture unoccupied high-affinity receptors for oestradiol were markedly depleted in the cytosol. Nuclear binding sites remained high during the first day of culture, and were still present after 3 days. The stability of nuclear-bound oestradiol was confirmed by examining the turnover of radioactivity during culture of uteri of rabbits injected with [(3)H]oestradiol 6h before death. Over half of the radioactivity was retained for as long as 3 days in tissue cultured in the absence of oestrogen. In tissue cultured for 24h with unlabelled oestrogen, there was a progressive increase in the displacement of [(3)H]oestradiol as the concentration of unlabelled hormone in the medium was increased from 0.1 to 5nm. Higher concentrations of oestradiol had little additional effect. The oestradiol involved in this displacement reaction was associated with macromolecules, characterized by Sephadex G-25 chromatography and sucrose-density-gradient ultracentrifugation of the 0.4m-KCl extract of the nuclear pellet. 相似文献
103.
The thermal denaturation of DNA: average length and composition of denatured areas 总被引:1,自引:0,他引:1 下载免费PDF全文
A spectral study of melting curves of DNA ranging from 73 to 32% AT indicates that the base ratio of sequences melting within DNA are a linear function of temperature. A study of partially denatured DNA by electron microscopy, reversible renaturation and fractionation on hydroxylapatite suggests that the melting curve of DNA represents the melting of sequences which average 3-4 million daltons in length. These sequences appear to be a combination of two areas, one which is high in AT and denatures in the first three-quarters of the melting curve, and one which is high in GC and denatures in the final quarter. The length of these sequences appears to vary between 1.5-6 million daltons. 相似文献
104.
105.
Determination of Melting Sequences in DNA and DNA-Protein Complexes by Difference Spectra 总被引:1,自引:0,他引:1 下载免费PDF全文
A graphical formula is presented for determining the base ratio of melted DNA. By use of this formula, the composition of sequences which melt in different portions of the melting curves of Clostridium DNA, Escherichia coli DNA, and mouse DNA were determined. As the DNA melts, the per cent of adenine and thymine (AT) in the melted sequences decreases linearly with temperature. The average composition of sequences which melt in a given part of the melting curve is proportional to the base ratio of the DNA. The concentration and average composition of sequences were determined for three parts of the melting curves of the DNA samples, and a frequency distribution curve was constructed. The curve is symmetrical and has a maximum at about 56% AT. The distribution of GC-rich sequences on the E. coli chromosome was estimated by shearing, partially melting, and fractionating the DNA on hydroxylapatite. GC-rich sequences appear to occur every thousand base pairs, and have a maximum length of about 180 base pairs. The graphical formula was applied to the determination of the composition of sequences which melt in different parts of the melting curve of chromatin. Throughout the melting curve, the composition of the melting sequences is about 60% AT, which appears to suggest that relatively long sequences are melting simultaneously. Their melting temperature may be a function of the composition of the protein on different parts of the DNA. The problem of light scattering in DNA-protein and DNA was also investigated. A formula is presented which corrects for light scattering by relating the intensity of the scattered light to the rate of change of absorbance of DNA with wavelength. 相似文献
106.
Two forms of the glucoamylase of Aspergillus niger 总被引:3,自引:0,他引:3
107.
108.
Rolf E. Flygare Stevan H. Broderson E. Russell Hayes 《Biotechnic & histochemistry》1970,45(4):149-153
A neutralized Schiff's reagent (pH 6.7) was prepared and used to investigate the role of the acidic nature of the routine Schiff's reagent (pH 2.6) in the plasmal reaction. The neutralized reagent was satisfactory as an aldehyde reagent in the nucleal reaction on gut and, although giving a less intense reaction than the routine reagent in the PAS reaction on the gut and plasmal reaction on the aorta, was satisfactory here in respect to localization and thus to aldehyde specificity. Control sections for the plasmal reaction of unfixed nerve and aorta gave positive results when placed in the routine Schiff's, this increasing with time left in the reagent. Similar control sections in the neutralized Schiff's reagent remained consistently negative even though left in this reagent for 0.5 hr. The positive reaction of such control sections is apparently due to acid hydrolysis of labile plasmalogens by the routine Schiff's reagent in myelin and elastin and not to the presence of “free” aldehydes in these tissue elements 相似文献
109.
Factors Influencing the Survival and Revival of Heat-treated Escherichia coli 总被引:4,自引:3,他引:1 下载免费PDF全文
Maximal revival of heat-damaged Escherichia coli occurred in nutrient media containing 0.8 to 1.0% (w/v) of Difco yeast extract. Vitamins did not appear to be involved in the recovery process. The situation with amino acids was less clear-cut, and, although certain of these may be essential for revival, proof for this is as yet inconclusive. Replica plating, in which colonies (from cells which had survived a heating process) on a rich medium were replicated onto minimal agar, revealed that no auxotrophic mutants had been formed as a result of heat treatment. Bacteria which were heated in 1% (w/v) yeast extract were killed more slowly than those heated in water. 相似文献
110.
Quantitative Analyses of Certain Enteric Bacteria and Bacterial Extracts: II. Discrimination of Sonic Extracts by Interfacial Densitometry of Precipitin Systems 总被引:1,自引:1,他引:0 下载免费PDF全文
Bacterial extracts prepared by ultrasonic disruption were reacted with both narrow- and broad-spectrum reference (homologous) and cross-reacting (heterologous) precipitins produced in rabbits. Quantitation of the reaction was obtained by densitometry of the antigen-antibody interface. Comparisons were made of sonic extracts from various starting populations all equated to the same nitrogen concentrations, and of various nitrogen levels derived from five bacterial population levels prepared separately. Sources of error are probed to show under what circumstances cross-reactions would be of greater magnitude than reference ones. The feasibility was shown of using quantitative densitometry of the interface combined with broadly reacting precipitins to identify bacteria on an intergeneric and interspecies scale. Problems associated with the use of absorbed or monospecific precipitins are explained. 相似文献