全文获取类型
收费全文 | 1129篇 |
免费 | 43篇 |
国内免费 | 75篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 18篇 |
2016年 | 18篇 |
2015年 | 19篇 |
2014年 | 31篇 |
2013年 | 38篇 |
2012年 | 28篇 |
2011年 | 31篇 |
2010年 | 25篇 |
2009年 | 40篇 |
2008年 | 44篇 |
2007年 | 48篇 |
2006年 | 38篇 |
2005年 | 53篇 |
2004年 | 46篇 |
2003年 | 45篇 |
2002年 | 43篇 |
2001年 | 43篇 |
2000年 | 28篇 |
1999年 | 32篇 |
1998年 | 33篇 |
1997年 | 32篇 |
1996年 | 22篇 |
1995年 | 39篇 |
1994年 | 40篇 |
1993年 | 40篇 |
1992年 | 43篇 |
1991年 | 20篇 |
1990年 | 31篇 |
1989年 | 22篇 |
1988年 | 15篇 |
1987年 | 17篇 |
1986年 | 9篇 |
1985年 | 26篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1981年 | 18篇 |
1980年 | 18篇 |
1979年 | 17篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1974年 | 6篇 |
1973年 | 3篇 |
排序方式: 共有1247条查询结果,搜索用时 78 毫秒
51.
From cells of Mucuna pruriens, grown in suspension, a monophenol monooxygenase (EC 1.14.18.1) was purified to homogeneity, as deduced from sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme appeared to have a native molecular weight of 90000±5000 dalton, and consisted of two subunits, each of 42000±1000 dalton. High-performance liquid chromatography with electrochemical detection for specific measurement of catecholes, was used to determine separately the tyrosinehydroxylating and catecholase activities of the enzyme. For the enzymatic activities, pH optima of, respectively, 7.5 and 5.5–6.5 were found; the effects of some inhibitors on both activities appeared to be different. Michaelis-Menten characteristics for some mono-and o-dihydroxysubstrates were determined.Abbreviations DEAE
diethylaminoethyl
- HPLC
high-performance liquid chromatography
- L-DOPA
L-3,4-dihydroxyphenylalanine 相似文献
52.
Stephen C. Fry 《Phytochemistry》1984,23(1):59-64
[14C]Cinnamate was taken up very rapidly by cultured spinach cells and completely incorporated into low-MW conjugates within 20 min. The 14C-labelled products were similar whether the [14C]cinnamate was supplied continuously over a period of hours via a peristaltic pump or instantaneously. Radioactivity was slowly recruited from the low-MW pool into aromatic components of the cell-wall fraction. Saponification of the radioactive wall fraction yielded, in addition to radioactive ferulate and p-coumarate, large amounts of ethyl acetate-soluble radioactive material with the properties of oxidatively coupled phenols. The coupled material was associated with the most highly ‘Driselase’-resistant fractions of the cell wall. In contrast, ‘Driselase’ released most of the wall's ferulate and p-coumarate on disaccharide fragments. It is suggested that the oxidatively coupled phenols are formed from simpler phenols by peroxidase and that they cross-link the polysaccharides to which they are attached, making these polysaccharides relatively ‘Driselase’-resistant. 相似文献
53.
Cell suspension cultures of Catharanthus roseus G. Don, Glycine max (L.) Merr. and Nicotiana tabacum L. were incubated with [14C]acetate, [14C]oleic acid and [14C]linoleic acid at five different temperatures ranging from 15 to 35° C. When the incubation temperature was increased, [14C]acetate was incorporated preferentially into [14C]palmitate, with a concomitant drop in [14C]oleate formation. Between 15 and 20° C, [14C]oleic acid accumulated in C. roseus cells. In all cultures, optimum desaturation of [14C]oleic acid to [14C]linoleic acid occurred between 20 and 25° C, and in G. max this was also the optimal range for desaturation of [14C]linoleic acid to [14C]linolenic acid. Elongation of [14C]palmitic acid was inhibited when cultures grown at 15° C for 25 h were subsequently incubated with [14C]acetate at 25° C. [14C]oleic acid accumulated in G. max and C. roseus cultures grown at 35° C for 25 h and subsequently incubated at 25° C. Desaturation of [14C]oleic acid increased up to 25° C, but then decreased or leveled off depending on the cell line and on the temperature prior to incubation. 相似文献
54.
Total RNA was extracted from fast growing suspension cells of bean, the mRNA was translated and the products of protein synthesis analysed by gel electrophoresis. Actinomycin D (20 g ml–1) added to the cultures 12 h before the induction of phenylalanine ammonia-lyase (PAL) activity by naphthylacetic acid (NAA) (1 mg/l) and kinetin (0.2 mg/l) failed to prevent the increased activity of the enzyme usually produced by this ratio of the plant growth hormones. PAL was isolated and purified from suspension cultured bean cells. The purified enzyme ran as a single band on polyacrylamide gel electrophoresis. The protein translated from RNA prepared from induced and non-induced cells was separated by gel electrophoresis and the bands of protein on the gels were compared. There was no evidence for an increase in the amount of PAL synthesised in vitro from the mRNA of induced cells even though these had 5 times the amount of activity of the enzyme compared with that of the non-induced cells. The results indicate that the induction of PAL activity is not immediately preceeded by an increase in the synthesis of PAL-mRNA by the cells. The control of the activity of the enzyme is discussed with respect to this finding.Abbreviations PAL
phenylalanine ammonia-lyase
- NAA
3naphthylacetic acid
- DEAE
Diethylamino ethyl
- EDTA
Ethylenediamine tetraacetate
- SDS
Sodium dodecyl sulphate 相似文献
55.
A DNA polymerase activity was isolated from cells of Oryza sativa L. grown in suspension culture. Molecular mass ( 180,000), optimal requirements for pH (neutral), Mg2+ (5–10 mM), Mn2+ (1 mM), template preference (activated DNA), lack of activity with native or denatured DNA, and sensitivity to N-ethylmaleimide and ionic strength are similar to those of the vertebrate -polymerase. Like DNA polymerase , the DNA polymerase described in this work is the most abundant in proliferating cells of Oryza sativa L., Parthenocissus tricuspidata (Siebold et Zucc.) Planchon, Acer pseudoplatanus L., and Medicago sativa L. and responds to changes in the rate of cell multiplication. We therefore postulate that this -like DNA polymerase is the replicating enzyme of plant cells.Abbreviations BSA
bovine serum albumin
- EDTA
ethylendiamino-tetracetic acid
- DTT
dithiothreitol
- PTSF
p-toluenesulfonyl fluoride 相似文献
56.
Somatic embryoids differentiated in suspension cultures of G. klotzschianum after 3–4 weeks of culture in a liquid medium containing glutamine (optimally, 10–15 mM). Embryogenesis occurred after a preculture of callus on a medium containing 10 mg/l of the cytokinin, 2iP. The embryoids had meristematic regions, a well formed epidermis, and formed roots and vestigial leaves. Asparagine was much less effective than glutamine in promoting embryoid differentiation. The presence of 2,4-D in the medium resulted in increased vigor of the suspension cultures and subsequently in the formation of many embryoids, but does not seem to be necessary for somatic embryogenesis in cotton.Technical Article 14646 from the Texas Agricultural Experiment Station 相似文献
57.
William R. Tolbert Joseph Peder Richard C. Kimes 《In vitro cellular & developmental biology. Plant》1981,17(10):885-890
Summary A system has been developed for growth and maintenance of mammalian cells in suspension culture at high density. In principle,
the maintenance of constant levels of required nutrients coupled with the removal of toxic cell byproducts can support much
higher suspension cell densities than may be obtained in conventional spinners. The system consisted of 4- or 40-liter reaction
vessels equipped with a vertically supported rotating cylindrical filter. Agitation was provided by the magnetically driven,
rotating filter. Fresh medium was supplied at a rate of 10 to 20 ml/h per 109 cells and the expended medium free of cells was withdrawn through the rotating filter. Both pH and dissolved O2 and CO2 were monitored and regulated. Walker 256 carcinosarcoma cells have been grown in these reactors to densities 10-to 30-fold
greater than that obtained in Bellco spinners. In addition to high cell densities, the yield of cells per liter of medium
used was 2- to 3-fold that obtained in the conventional systems. Both 4-and 40-liter versions of this reactor have been operated
without the use of antibiotics. The 40-liter reactor also has been modified for chemostat operation. In a single run, for
example, the Walker cell density was maintained between 6 and 10×106 cells/ml with a total yield of 8.7×1011 cells from 360 liters of medium. 相似文献
58.
Chromatography of soluble polyphenols of p-fluorophenylalanine-sensitive and -resistant tobacco cells revealed that the 10-fold increased level found in the resistant line was largely due to the accumulation of two unidentified polyphenols. The uptake of Phe-[U-14C] and Tyr-[U-14C] by the resistant line was ca 10 % that by the sensitive line. About 90 % of the phenylalanine-[14C] which was taken up by both cell lines could be accounted for as free phenylalanine in protein, soluble polyphenols or CO2. The fate of Tyr-[14C] was similar to that of phenylalanine except that the incorporation was into insoluble polymeric forms of polyphenols rather than into soluble polyphenols. The resistant line incorporated 9-times more phenylalanine-[14C] into soluble polyphenols than did the sensitive line. The different 14C-aromatic amino acid accumulation and incorporation patterns noted with the two cell lines indicates that there are different active pools. Differential uptake rates by the two cell lines might affect the distribution of the absorbed amino acid among the different pools. 相似文献
59.
Ubiquinone (UQ) formation in BY-2 tobacco cells was especially promoted by a high concentration of 2,4-D. 2,4,5-T, MCP and NAA also promoted UQ formation in these cells. The UQ content in the cells cultured at high concentrations of 2,4-D was higher than that of controls throughout the culture period. The addition of 2,4-D at an early period in cell growth was very effective in promoting UQ formation, but addition at the stationary phase was ineffective. Cell growth was improved by adding phosphate to the medium but UQ content was decreased. UQ content decreased slowly during subculturing, whereas cell growth recovered gradually. 相似文献
60.
Cell suspension cultures of parsley and soybean were incubated for 38 h with 14C-labeled benzo[a]pyrene; autoclaved cultures were used as controls. Metabolites were isolated by a sequential extraction procedure and further studied by chromatography or by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The soluble metabolites amounted to 1–2.2% in the case of parsley cells, and 19–28% in the case of soybean cells. These metabolites varied in polarity, some being soluble in organic solvent or aqueous buffer while other metabolite fractions were soluble only in hot aqueous sodium dodecylsulphate. In addition, a significant amount of an insoluble metabolite fraction was isolated from the culture fluid as well as the cellular material of soybean suspension cultures.Abbreviations BP
benzo[a]pyrene
- SDS
sodium dodecyl sulfate
- TCA
trichloroacetic acid 相似文献