全文获取类型
收费全文 | 364篇 |
免费 | 41篇 |
出版年
2021年 | 6篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 12篇 |
2015年 | 13篇 |
2014年 | 23篇 |
2013年 | 30篇 |
2012年 | 37篇 |
2011年 | 27篇 |
2010年 | 17篇 |
2009年 | 23篇 |
2008年 | 20篇 |
2007年 | 20篇 |
2006年 | 30篇 |
2005年 | 21篇 |
2004年 | 14篇 |
2003年 | 19篇 |
2002年 | 15篇 |
2001年 | 6篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 7篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有405条查询结果,搜索用时 15 毫秒
1.
2.
Soils contain two different activities for oxidation of hydrogen 总被引:1,自引:0,他引:1
Abstract Hydrogen oxidation rates were measured in a neutral compost soil and an acidic sandy loam at H2 mixing ratios of 0.01 to 5000 ppmv. The kinetics were biphasic showing two different K m values for H2 , one at about 10–40 nM dissolved H2 , the other at about 1.2–1.4 μM H2 . The low- K m activity was less sensitive to chloroform fumigation than the high- K m activity. If sterile soil was amended with Paracoccus denitrificans or a H2 -oxidizing strain isolated from compost soil, it exhibited only a high- K m (0.7–0.9 μM) activity. It also failed to utilize H2 mixing ratios below a threshold of 1.6–3.0 ppmv H2 (160–300 mPa). A similar result was obtained when fresh soil samples were suspended in water, and H2 oxidation was determined from the decrease of dissolved H2 . However, H2 was again utilized to mixing ratios lower than 0.05 ppmv, if the supernatant of the soil suspension or the settled soil particles were dried onto sterile soil or purified quarz sand. Obviously, soils contain two different activities for oxidation of H2 : (1) a high- K m , high-threshold activity which apparently is due to aerobic H2 -oxidizing bacteria, and (2) a low- K m , low-threshold activity whose origin is unknown but presumably is due to soil enzymes. 相似文献
3.
Rolf Altenburger Sibylle Abarzua Rainer Callies L. Horst Grimme Adalbert Mayer Dieter Leibfritz 《Archives of microbiology》1991,156(6):471-476
Cultures of the cyanobacterium Microcystis firma show rhythmic uptake and release of ammonia under conditions of carbon limitation. The massive removal of ammonia from the medium during the first light phase has little impact on the intracellular pH: a pH shift of less than 0.2 U towards the alkaline can be measured by in vivo 31P NMR. Furthermore, the energy status of the cells remains regulated. In vivo 15N NMR of M. firma, cultivated either with labelled nitrate or ammonia as the sole nitrogen source, reveals only gradual differences in the pool of free amino acids. Additionally both cultivation types show -aminobutyric acid, acid amides and yet unassigned secondary metabolites as nitrogen storing compounds. Investigating the incorporation of nitrogen under carbon limitation, however, only the amide nitrogen of glutamine is found permanently labelled in situ. While transamination reactions are blocked, nitrate reduction to ammonia can still proceed. Cation exchange processes in the cell wall are considered regarding the ammonia disappearance in the first phase, and the control of ammonia uptake is discussed with respect to the avoidance of intracellular toxification.Abbreviations GABA
-aminobutyric acid
- GOGAT
glutamate synthase
- GS
glutamine synthetase
- MDP
methylene diphosphonate
- MOPSO
3-(N-morpholino)-2-hydroxy-propanesulfonic acid
- NDPS
nucieoside diphosphosugars
- NOE
nuclear Overhauser effect
- NMR
nuclear magnetic resonance
For convenience, the term ammonia is used throughout to denote ammonia or ammonium ion when there is no good evidence as to which chemical species is involved 相似文献
4.
Of the nine species of Tropodiaptomus occurring in Equatorial East Africa, seven are redescribed and figured in great detail. Their relationships are discussed. A primary homonym is eliminated, and types are indicated wherever possible. 相似文献
5.
Rapid thyroid-hormone effect on mitochondrial and cytosolic ATP/ADP ratios in the intact liver cell. 总被引:2,自引:2,他引:0 下载免费PDF全文
The effect of thyroid-hormone application on cytosolic and mitochondrial ATP/ADP ratio was investigated in rat liver in vivo and in the isolated perfused organ. In vivo the ATP/ADP ratio in livers from hypothyroid rats was 0.84 +/- 0.08 in the mitochondrial matrix and 5.6 +/- 0.9 in the cytosol, as was observed in euthyroid controls. In contrast, hyperthyroidism was followed by a significant decrease in the mitochondrial and by an increase in the cytosolic ATP/ADP ratio (to 0.34 +/- 0.06 and 11.3 +/- 2.8 respectively). In the perfused liver from hypothyroid animals, addition of L-3,3',5-tri-iodothyronine in the perfusate also provoked, within 2 h, a significant decrease in the mitochondrial ATP/ADP ratio, whereas the cytosolic ratio was unaffected. From these and previous data in the isolated perfused liver and in isolated mitochondria from hypothyroid and tri-iodothyronine-treated rats it is concluded that thyroid hormones increase mitochondrial respiration and ATP regeneration, which is associated with an acceleration of mitochondrial adenine nucleotide transport and significant alterations in the mitochondrial and cytosolic ATP/ADP ratios. 相似文献
6.
7.
dos Santos Silva Edinaldo N. Kakkassery Francy K. Maas Sibylle Dumont Henri J. 《Hydrobiologia》1994,288(2):119-128
Calanoid copepods, belonging to the new genus and species Keraladiaptomus rangareddyi, were collected from temporary ponds in Kerala State, India. The new genus belongs to the family Diaptomidae, subfamily Diaptominae. It is described in detail and its affinity to the related genera, Arctodiaptomus Kiefer, 1932 and Eodiaptomus Kiefer, 1932, discussed. 相似文献
8.
Wound-induced and developmental activation of a poplar tree chitinase gene promoter in transgenic tobacco 总被引:5,自引:0,他引:5
Howard R. G. Clarke John M. Davis Sibylle M. Wilbert Harvey D. Bradshaw Jr. Milton P. Gordon 《Plant molecular biology》1994,25(5):799-815
Wounding hybrid poplar (Populus trichocarpa × P. deltoides) trees results in the expression of novel wound-inducible (win) mRNAs thought to encode proteins involved in defense against pests and pathogens. Members of thewin6 gene family encode acidic multi-domain chitinases, with combined structure and charge characteristics that differ from previously described chitinases.Win6 expression has been shown to occur in pooled unwounded leaves of a wounded (on multiple leaves) poplar plant. Here we demonstrate that wounding a single leaf induceswin6 expression locally, in the wounded leaf, and remotely, in specific unwounded leaves with strong vascular connections to the wounded leaf. We also demonstrate that awin6 promoter--glucuronidase (GUS) gene fusion (win6-GUS) responds to wounding locally and remotely in transgenic tobacco. These data indicate that the poplarwin6 promoter has regulatory elements that are responsive to wound signals in the heterologous host. In addition,win6-GUS is developmentally activated in unwounded young leaves and floral tissues of transgenic tobacco. Similar developmental expression patterns are found to occur forwin6 in poplar trees, demonstrating that a herbaceous plant can serve as a host for woody tree transgene analysis and can accurately predict expression patterns in tree tissues (e.g. flowers) that would be difficult to study in free-living trees. 相似文献
9.
We used video microscopy techniques as a tool for live examination of the dynamic aspects of plant/fungus interactions. Early, dynamic responses of epidermal midrib cells of leaves from a potato cultivar (Solanum tuberosum L. cv. Datura) carrying resistance gene R1 to Phytophthora infestans (race 1: compatible interaction, race 4: incompatible interaction) were monitored. Similar responses were observed in both types of interaction, ranging from no visible reaction of invaded plant cells to hypersensitive cell death. The overall defense response of each individual cell exhibited a highly dynamic behavior that appeared to be tightly coordinated with the growth of the fungus. Initial localized reactions, including major rearrangements within the cytoplasm, occurred directly at the fungal penetration site, where rapid apposition of autofluorescent material and callose took place. If fungal invasion stopped at this stage, the host cell restored its normal cytoplasmic activity and survived. Hypersensitive cell death occurred only when fungal growth had proceeded to the formation of a clearly identifiable haustorium. In such cases, cytoplasm and nucleus conglomerated around the intracellular fungal structure, followed by a sudden collapse of the whole conglomerate and an instantaneous collapse of the fungal haustorium. Only small quantitative differences between the compatible and incompatible interactions of the two fungal races were observed for these early responses of epidermal cells. In the incompatible interaction, a slightly larger number of epidermal cells responded to fungal attack. More pronounced quantitative differences between compatible and incompatible interactions occurred upon fungal invasion of the mesophyll. These differences in the number of responding cells were not reflected at the level of gene expression: the spatial and temporal activation patterns of two defense-related genes, encoding phenylalanine ammonia-lyase and pathogenesis-related protein 1, were similar in both types of interaction.Dedicated to Professor Peter Sitte, Freiburg, Germany, on the occasion of his 65th birthday 相似文献
10.