全文获取类型
收费全文 | 701篇 |
免费 | 45篇 |
国内免费 | 50篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 6篇 |
2020年 | 25篇 |
2019年 | 13篇 |
2018年 | 23篇 |
2017年 | 17篇 |
2016年 | 17篇 |
2015年 | 26篇 |
2014年 | 24篇 |
2013年 | 57篇 |
2012年 | 13篇 |
2011年 | 23篇 |
2010年 | 19篇 |
2009年 | 25篇 |
2008年 | 33篇 |
2007年 | 27篇 |
2006年 | 29篇 |
2005年 | 37篇 |
2004年 | 40篇 |
2003年 | 31篇 |
2002年 | 18篇 |
2001年 | 24篇 |
2000年 | 24篇 |
1999年 | 8篇 |
1998年 | 17篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1993年 | 27篇 |
1992年 | 16篇 |
1991年 | 19篇 |
1990年 | 15篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 23篇 |
1986年 | 15篇 |
1985年 | 6篇 |
1983年 | 1篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1976年 | 1篇 |
排序方式: 共有796条查询结果,搜索用时 15 毫秒
91.
Manganese supplementation resulted in higher polysaccharide levels and reduced cellular pigmentation by more than 8- or 17-fold after growth for 7d of the fungus Aureobasidium pullulans ATCC 42023 on sucrose or corn syrup, respectively, as a carbon source. The melanin content of the polysaccharide elaborated by ATCC 42023 cells also decreased if MnCl2 was added to the medium. The pullulan content of the polysaccharide synthesized by ATCC 42023 on sucrose was found to increase with increasing levels of manganese, whereas it was lower during growth on corn syrup if manganese was present. 相似文献
92.
Josiane Arnaud Pierre Bourlard Bernard Denis Alain E. Favier 《Biological trace element research》1996,53(1-3):129-136
This study was carried out to assess manganese (Mn) status after an acute episode of myocardial infarction. Plasma and erythrocyte
Mn concentrations were measured from admission to hospital to day 15 postadmission in 21 patients suffering from acute myocardial
infarction and in three control groups. The determination of Mn in these biological fluids was performed by electrothermal
atomic absorption spectrometry. Plasma Mn was higher (p<0.01) and erythrocyte Mn was similar in the acute myocardial infarction group compared to healthy age-matched control group.
Plasma and erythrocyte Mn remained unchanged during the 2 wk after acute myocardial infarction and were not correlated to
enzyme activities. A decrease of erythrocyte Mn with age, expressed in nmol/L, was noted (p<0.02). These results suggest that plasma and erythrocyte Mn do not provide an indication of myocardial damage. Nonetheless,
Mn status in elderly merits further attention. 相似文献
93.
William J. Page 《Biometals》1995,8(1):30-36
The addition of manganese oxides to iron-limited medium promoted the formation of the pyoverdin siderophore azotobactin by Azotobacter vinelandii. When active-MnO2 was used, there was greatly decreased iron uptake into the cells, hyperproduction of azotobactin and the abiotic, chemical destruction or adsorbtion of the catechol siderophores azotochelin and aminochelin by this strong oxidizing agent. Although the iron content of the cells was the same as iron-limited cells, the growth of cells in medium with active-MnO2 was increased 1.5- to 2.5-fold over iron-limited controls. This growth promotion was not caused by iron contaminating the oxide or by manganese solubilized from the oxide. Soluble 0.05–4 mm Mn2+ inhibited the growth of iron-limited cells and had a minimal effect on iron uptake, but caused hyperproduction of azotobactin. This later effect was caused by the inhibition of soluble ferric reductase, in a manner identical to that previously observed for Zn2+. These results suggest that active-MnO2 may interfere with a surface-localized iron uptake site, possibly another ferric reductase. The reason for the growth promotion by active-MnO2 remains unknown, but is most likely related to decreased oxygen toxicity. 相似文献
94.
Summary Gonadotropin releasing hormone enhanced guanylate cyclase [E.C.4.6.1.2] two- to threefold in pituitary, testis, liver and kidney. Dose response relationships revealed that at a concentration of 1 nanomolar, gonadotropin releasing hormone caused a maximal augmentation of guanylate cyclase activity and that increasing its concentration to the millimolar range caused no further enhancement of this enzyme. There was an absolute cation requirement for gonadotropin releasing hormone's enhancement of guanylate cyclase activity as there was no increase without any cation present. Gonadotropin releasing hormone could increase guanylate cyclase activity with either calcium or manganese in the incubation medium but more augmentation was observed with manganese. The data in this investigation suggest that guanylate cyclase may play a role in the mechanism of action of gonadotropin releasing hormone. 相似文献
95.
Vigna radiata seedlings germinated in the presence of Mn2+ show an unusual increase in allantoinase activity which is proportional to Mn2+ concentration up to 5 mM. Though Mn2+ is not an activator for V. radiata allantoinase, it specifically protects allantoinase against thermal as well as papain-catalysed inactivation. Evidence is presented to show that the primary effect of Mn2+ is a protective one, both in vitro and in vivo, and that this is reflected in the observed enhancement of allantoinase activity in Mn2+ grown seedlings. That this unusual effect of Mn2+ is a specific one is indicated by the lack of a similar effect with Mg2+. Cu2+ is shown to destabilize V. radiata allantoinase in vitro as well as in vivo. 相似文献
96.
Sediment pore water concentrations of Fe2+, Mn2+, NH
inf4
sup+
and CH4 were analyzed from both diver-collected cores and anin situ equilibration device (peeper) in Lake Erie's central basin. Sediment oxygen demand (SOD) was measured at the same station
with a hemispheric chamber (including DO probe and recorder) subtending a known area of sediments. The average SOD was 9.4
mM m−2 day−1 (0.3 g m−2 day−1). From pore water gradients within the near-surface zone, the chemical flux across the interface was calculated indirectly
using Fick's first law modified for sediments. These calculations, using core and peeper gradients, always showed sediment
loss to overlying waters, and variations between the two techniques differed by less than an order of magnitude for Fe2+ and CH4. The transport of these reduced constituents can represent a sizeable oxygen demand, ranging from less than 1% for Fe2+ and Mn2+ to as high as 26% for NH
inf4
sup+
, and 30% for CH4. The average flux of these constituents could account for about a third of the SOD at the sediment-water interface of this
station. 相似文献
97.
Summary Application of a granular formulation of hexachlorocyclohexane (HCH) to the potted soil at flooding decreased the concentration
of iron and. to some extent, manganese in rice plants, especially at concentrations above 3 ppm active ingredient (a.i.) Likewise,
HCH, applied to rice fields at transplanting (several days after submergence) caused a significant decrease in the concentration
of iron, and not manganese, in the rice plant but only at concentrations above 12.5 kg a.i./ha despite high levels of reduced
iron in the soil. Inhibition of iron reduction by HCH was more pronounced when applied at flooding than at several days after
flooding. 相似文献
98.
The effects of excess manganese on photosynthetic rate and concentration of chlorophyll in Triticum aestivum grown in solution culture 总被引:1,自引:0,他引:1
Manganese toxicity, which involves a broad array of physiological responses, has been identified as an important factor limiting plant growth on acid soils. In the experiments reported here, we examined the toxic effects of Mn on chlorophyll content, photosynthesis and respiration in two cultivars (Norquay and Columbus) of Triticum aestivum (wheat) which differ in tolerance of Mn. When grown over a range of concentrations of Mn (0–1 000 μ M ), the Mn-tolerant cultivar maintained higher rates of photosynthesis and respiration, and higher concentrations of chlorophyll a and chlorophyll b , than did the Mn-sensitive cultivar, despite greater accumulations of Mn in leaf tissues. After 5 days growth with 1 000 μ M Mn in solution, the photosynthetic rate fell to 25% of control in the sensitive cultivar and to only 75% of control in the tolerant cultivar. The concentration of chlorophyll a fell to 50% of control in the sensitive cultivar, but did not differ from control in the tolerant cultivar. Greater effects were seen on concentrations of chlorophyll b . which fell to 35% and 55% of control in the sensitive and tolerant cultivars, respectively. Rates of photosynthesis decreased in both cultivars as concentrations of chlorophyll decreased; however, the photosynthetic rate per unit chlorophyll remained constant or increased in the tolerant cultivar and decreased in the sensitive cultivar as concentrations of Mn in solution increased. Thus, in the sensitive cv. Columbus, Mn seemed to have a toxic effect on both chlorophyll content and photosynthesis per unit chlorophyll. In the tolerant cv. Norquay, the only clear effect of Mn was a reduction in chlorophyll content, although direct inhibition of photosynthesis could not be discounted. 相似文献
99.
Micro-element deficiencies have been implicated in the development of poor stem form in Pinus radiata plantations. Cu, Mn and B have been implicated in previous studies as influencing tree form and/or the process of lignification in plants. Therefore an experiment was initiated to examine the individual and interactive effects exhibited by these trace elements on stem form and lignification.The investigation showed that Cu deficiency reduced both lignification and stem form in seedlings. Mn, competing with Cu for uptake, enhanced the symptoms of Cu deficiency. Boron addition did not alleviate the expression of deformity or increase levels of lignification. There was a clear family influence on the development of seedling stem form in response to variations in mineral nutrition. 相似文献
100.
Take-all is a world-wide root-rotting disease of cereals. The causal organism of take-all of wheat is the soil-borne fungus Gaeumannomyces graminis var tritici (Ggt). No resistance to take-all, worthy of inclusion in a plant breeding programme, has been discovered in wheat but the severity of take-all is increased in host plants whose tissues are deficient for manganese (Mn). Take-all of wheat will be decreased by all techniques which lift Mn concentrations in shoots and roots of Mn-deficient hosts to adequate levels. Wheat seedlings were grown in a Mn-deficient calcareous sand in small pots and inoculated with four field isolates of Ggt. Infection by three virulent isolates was increased under conditions which were Mn deficient for the wheat host but infection by a weakly virulent isolate, already low, was further decreased. Only the three virulent isolates caused visible oxidation of Mn in vitro. The sensitivity of Ggt isolates to manganous ions in vitro did not explain the extent of infection they caused on wheat hosts. In a similar experiment four Australian wheat genotypes were grown in the same Mn-deficient calcareous sand and inoculated with one virulent isolate of Ggt. Two genotypes were inefficient at taking up manganese and were very susceptible to take-all, one was very efficient at taking up manganese and was resistant to take-all, and the fourth genotype was intermediate for both characters. All genotypes were equally resistant under Mn-adequate conditions. 相似文献