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排序方式: 共有390条查询结果,搜索用时 234 毫秒
41.
Bellincampi D Camardella L Delcour JA Desseaux V D'Ovidio R Durand A Elliot G Gebruers K Giovane A Juge N Sørensen JF Svensson B Vairo D 《Biochimica et biophysica acta》2004,1696(2):265-274
Carbohydrate-active enzymes including glycosidases, transglycosidases, glycosyltransferases, polysaccharide lyases and carbohydrate esterases are responsible for the enzymatic processing of carbohydrates in plants. A number of carbohydrate-active enzymes are produced by microbial pathogens and insects responsible of severe crop losses. Plants have evolved proteinaceous inhibitors to modulate the activity of several of these enzymes. The continuing discovery of new inhibitors indicates that this research area is still unexplored and may lead to new exciting developments. To date, the role of the inhibitors is not completely understood. Here we review recent results obtained on the best characterised inhibitors, pointing to their possible biological role in vivo. Results recently obtained with plant transformation technology indicate that this class of inhibitors has potential biotechnological applications. 相似文献
42.
Birte Töpper Aud Larsen Tron Frede Thingstad Runar Thyrhaug Ruth-Anne Sandaa 《Polar Biology》2010,33(11):1557-1565
In order to study interactions between microorganisms at different nutrient conditions in an arctic environment, a mesocosm
experiment was performed in Kongsfjorden, Svalbard (79°N). A phytoplankton bloom was initiated by daily additions of mineral
nutrients (ammonium and phosphate) to all mesocosm units. The addition of silicate and glucose, forming a factorial design
(+Si/+C, +Si/−C, −Si/+C, −Si/−C), was intended to produce different types of growth rate limitation for the bacterial community.
We here focus on the response in bacterial community composition to different nutrient situations. Phytoplankton, bacteria
and viruses were enumerated by flow cytometry, while denaturing gradient gel electrophoresis (DGGE) was used to track changes
in the bacterial community composition. Our results showed that both glucose and silicate addition affected the bacterial
community composition, with the largest effect from glucose. The initial increase in bacterial abundance was most pronounced
in the glucose units. After silicate addition, highest bacterial abundance was observed in the silicate treatments where mineral
nutrient competition by diatoms was expected to be highest. The major effect of glucose was expressed by the significant separation
of the +C and the −C samples at the end of the experiment, while silicate addition resulted in a more stable bacterial community
structure. In the unit, given both silicate and glucose, the diatoms were totally outcompeted by the bacterial community.
The competitive success of the heterotrophic bacteria in C-replete situations allows the conclusion that the bacteria were
not more negatively affected by low temperatures than phytoplankton. 相似文献
43.
Andrew D. Richardson T. Andy Black Philippe Ciais Nicolas Delbart Mark A. Friedl Nadine Gobron David Y. Hollinger Werner L. Kutsch Bernard Longdoz Sebastiaan Luyssaert Mirco Migliavacca Leonardo Montagnani J. William Munger Eddy Moors Shilong Piao Corinna Rebmann Markus Reichstein Nobuko Saigusa Enrico Tomelleri Rodrigo Vargas Andrej Varlagin 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2010,365(1555):3227-3246
We use eddy covariance measurements of net ecosystem productivity (NEP) from 21 FLUXNET sites (153 site-years of data) to investigate relationships between phenology and productivity (in terms of both NEP and gross ecosystem photosynthesis, GEP) in temperate and boreal forests. Results are used to evaluate the plausibility of four different conceptual models. Phenological indicators were derived from the eddy covariance time series, and from remote sensing and models. We examine spatial patterns (across sites) and temporal patterns (across years); an important conclusion is that it is likely that neither of these accurately represents how productivity will respond to future phenological shifts resulting from ongoing climate change. In spring and autumn, increased GEP resulting from an ‘extra’ day tends to be offset by concurrent, but smaller, increases in ecosystem respiration, and thus the effect on NEP is still positive. Spring productivity anomalies appear to have carry-over effects that translate to productivity anomalies in the following autumn, but it is not clear that these result directly from phenological anomalies. Finally, the productivity of evergreen needleleaf forests is less sensitive to phenology than is productivity of deciduous broadleaf forests. This has implications for how climate change may drive shifts in competition within mixed-species stands. 相似文献
44.
45.
Dispersal is a major factor regulating the number of coexisting species, but the relationship between species diversity and ecosystem processes has mainly been analysed for communities closed to dispersal. We experimentally investigated how initial local diversity and dispersal frequency affect local diversity and biomass production in open benthic microalgal metacommunities. Final local species richness and local biomass production were strongly influenced by dispersal frequency but not by initial local diversity. Both final local richness and final local biomass showed a hump-shaped pattern with increasing dispersal frequency, with a maximum at intermediate dispersal frequencies. Consequently, final local biomass increased linearly with increasing final richness. We conclude that the general relationship between richness and ecosystem functioning remains valid in open systems, but the maintenance of ecosystem processes significantly depends on the effects of dispersal on species richness and local interactions. 相似文献
46.
Blumenberg M Krüger M Nauhaus K Talbot HM Oppermann BI Seifert R Pape T Michaelis W 《Environmental microbiology》2006,8(7):1220-1227
Sulfate reduction accounts for about a half of the remineralization of organic carbon in anoxic marine shelf regions. Moreover, it was already a major microbial process in the very early ocean at least 2.4 billion years before the present. Here we demonstrate for the first time the capability of sulfate-reducing bacteria (SRB) to biosynthesize hopanoids, compounds that are quantitatively important and widely distributed biomarkers in recent and fossil sediments dating back to the late Archean. We found high concentrations (9.8-12.3 mg per gram of dry cells) of non-extended and extended bacteriohopanoids (bacteriohopanetetrol, aminobacteriohopanetriol, aminobacteriohopanetetrol) in pure cultures of SRB belonging to the widely distributed genus Desulfovibrio. Biohopanoids were found--considered as membrane rigidifiers--in more than 50% of bacterial species analysed so far. However, their biosynthesis appeared to be restricted to aerobes or facultative anaerobes with a very few recently described exceptions. Consequently, findings of sedimentary hopanoids are often used as indication for oxygenated settings. Nevertheless, our findings shed new light on the presence of hopanoids in specific anoxic settings and suggests that SRB are substantial sources of this quantitatively important lipid class in recent but also past anoxic environments. 相似文献
47.
Rüst CA Knechtle B Wirth A Knechtle P Ellenrieder B Rosemann T Lepers R 《The Chinese journal of physiology》2012,55(3):156-162
"The aim of this study was to investigate whether the characteristics of anthropometry, training or previous performance were related to an Ironman race time in recreational female Ironman triathletes. These characteristics were correlated to an Ironman race time for 53 recreational female triathletes in order to determine the predictor variables, and so be able to predict an Ironman race time for future novice triathletes. In the bi-variate analysis, no anthropometric characteristic was related to race time. The weekly cycling kilometers (r = -0.35) and hours (r = -0.32), as well as the personal best time in an Olympic distance triathlon (r = 0.49) and in a marathon (r = 0.74) were related to an Ironman race time (< 0.05). Stepwise multiple regressions showed that both the personal best time in an Olympic distance triathlon ( P = 0.0453) and in a marathon (P = 0.0030) were the best predictors for the Ironman race time (n = 28, r2 = 0.53). The race time in an Ironman triathlon might be partially predicted by the following equation (r2 = 0.53, n = 28): Race time (min) = 186.3 + 1.595 × (personal best time in an Olympic distance triathlon, min) + 1.318 × (personal best time in a marathon, min) for recreational female Ironman triathletes." 相似文献
48.
Birte?Frech Melanie?Vogtsberger Christa?NeumeyerEmail author 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2012,198(1):53-60
Training experiments were performed to investigate the ability of goldfish to discriminate objects differing in spatial depth.
Tests on size constancy should give insight into the mechanisms of distance estimation. Goldfish were successfully trained
to discriminate between two black disk stimuli of equal size but different distance from the tank wall. Each stimulus was
presented in a white tube so that the fish could see only one stimulus at a time. For each of eight training stimulus distances,
the just noticeable difference in distance was determined at a threshold criterion of 70% choice frequency. The ratio of the
retinal image sizes between training stimulus and comparison stimulus at threshold was about constant. However, in contrast
to Douglas et al. (Behav Brain Res 30:37–42, 1988), goldfish did not show size constancy in tests with stimuli of the same visual angle. This indicates that they did not estimate
distance, but simply compared the retinal images under our experimental conditions. We did not find any indication for the
use of accommodation as a depth cue. A patterned background at the rear end of the tubes did not have any effect, which, however,
does not exclude the possibility that motion parallax is used as a depth cue under natural conditions. 相似文献
49.
Barley limit dextrinase (LD) that catalyses hydrolysis of α-1,6 glucosidic linkages in starch-derived dextrins is inhibited by limit dextrinase inhibitor (LDI) found in mature seeds. LDI belongs to the chloroform/methanol soluble protein family (CM-protein family) and has four disulfide bridges and one glutathionylated cysteine. Here, thioredoxin is shown to progressively reduce disulfide bonds in LDI accompanied by loss of activity. A preferential reduction of the glutathionylated cysteine, as indicated by thiol quantification and molecular mass analysis using electrospray ionisation mass spectrometry, was not related to LDI inactivation. LDI reduction is proposed to cause conformational destabilisation leading to loss of function. 相似文献
50.
Cuyvers S Dornez E Abou Hachem M Svensson B Hothorn M Chory J Delcour JA Courtin CM 《Analytical biochemistry》2012,420(1):90-92
Isothermal titration calorimetry and surface plasmon resonance were tested for their ability to study substrate binding to the active site (AS) and to the secondary binding site (SBS) of Bacillus subtilis xylanase A separately. To this end, three enzyme variants were compared. The first was a catalytically incompetent enzyme that allows substrate binding to both the AS and SBS. In the second enzyme, binding to the SBS was impaired by site-directed mutagenesis, whereas in the third enzyme, the AS was blocked using a covalent inhibitor. Both techniques were able to show that AS and SBS have a similar binding affinity. 相似文献