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881.
882.
Metabolic effects of inhibitors of two enzymes of the branched-chain amino acid pathway in Salmonella typhimurium. 总被引:2,自引:1,他引:1 下载免费PDF全文
The metabolic effects of inhibitors of two enzymes in the pathway for biosynthesis of branched-chain amino acids were examined in Salmonella typhimurium mutant strain TV105, expressing a single isozyme of acetohydroxy acid synthase (AHAS), AHAS isozyme II. One inhibitor was the sulfonylurea herbicide sulfometuron methyl (SMM), which inhibits this isozyme and AHAS of other organisms, and the other was N-isopropyl oxalylhydroxamate (IpOHA), which inhibits ketol-acid reductoisomerase (KARI). The effects of the inhibitors on growth, levels of several enzymes of the pathway, and levels of intermediates of the pathway were measured. The intracellular concentration of the AHAS substrate 2-ketobutyrate increased on addition of SMM, but a lack of correlation between increased ketobutyrate and growth inhibition suggests that the former is not the immediate cause of the latter. The levels of the keto acid precursor of valine, but not of the precursor of isoleucine, were drastically decreased by SMM, and valine, but not isoleucine, partially overcame SMM inhibition. This apparent stronger effect of SMM on the flux into the valine arm, as opposed to the isoleucine arm, of the branched-chain amino acid pathway is explained by the kinetics of the AHAS reaction, as well as by the different roles of pyruvate, ketobutyrate, and the valine precursor in metabolism. The organization of the pathway thus potentiates the inhibitory effect of SMM. IpOHA has strong initial effects at lower concentrations than does SMM and leads to increases both in the acetohydroxy acid substrates of KARI and, surprisingly, in ketobutyrate. Valine completely protected strain TV105 from IpOHA at the MIC. A number of explanations for this effect can be ruled out, so that some unknown arrangement of the enzymes involved must be suggested. IpOHA led to initial cessation of growth, with partial recovery after a time whose duration increased with the inhibitor concentration. The recovery is apparently due to induction of new KARI synthesis, as well as disappearance of IpOHA from the medium. 相似文献
883.
Keren E. Shapira Tal Hirschhorn Lior Barzilay Nechama I. Smorodinsky Yoav I. Henis Marcelo Ehrlich 《Molecular biology of the cell》2014,25(10):1620-1628
Transforming growth factor-β (TGF-β) ligands activate Smad-mediated and noncanonical signaling pathways in a cell context–dependent manner. Localization of signaling receptors to distinct membrane domains is a potential source of signaling output diversity. The tumor suppressor/endocytic adaptor protein disabled-2 (Dab2) was proposed as a modulator of TGF-β signaling. However, the molecular mechanism(s) involved in the regulation of TGF-β signaling by Dab2 were not known. Here we investigate these issues by combining biophysical studies of the lateral mobility and endocytosis of the type I TGF-β receptor (TβRI) with TGF-β phosphoprotein signaling assays. Our findings demonstrate that Dab2 interacts with TβRI to restrict its lateral diffusion at the plasma membrane and enhance its clathrin-mediated endocytosis. Small interfering RNA–mediated knockdown of Dab2 or Dab2 overexpression shows that Dab2 negatively regulates TGF-β–induced c-Jun N-terminal kinase (JNK) activation, whereas activation of the Smad pathway is unaffected. Moreover, activation of JNK by TGF-β in the absence of Dab2 is disrupted by cholesterol depletion. These data support a model in which Dab2 regulates the domain localization of TβRI in the membrane, balancing TGF-β signaling via the Smad and JNK pathways. 相似文献
884.
885.
Ethanol, the choline requirement, methylation and liver injury 总被引:1,自引:0,他引:1
The findings obtained in this laboratory and others over the past decade are discussed in order to formulate a thesis, indicating the adverse action of ethanol on a vital methylation process in the liver. Evidence is shown that the rat may have a means of compensating for this impairment in methylation whereas humans do not have this same ability to protect against this action of ethanol. These considerations may offer a basis of why rats are apparently more resistant to alcoholic liver injury than humans. 相似文献
886.
Dalit Roth Rosenberg Markus Haber Joshua Goldford Maya Lalzar Dikla Aharonovich Ashraf Al-Ashhab Yoav Lehahn Daniel Segrè Laura Steindler Daniel Sher 《Environmental microbiology》2021,23(8):4295-4308
In the oceans and seas, environmental conditions change over multiple temporal and spatial scales. Here, we ask what factors affect the bacterial community structure across time, depth and size fraction during six seasonal cruises (2 years) in the ultra-oligotrophic Eastern Mediterranean Sea. The bacterial community varied most between size fractions (free-living (FL) vs. particle-associated), followed by depth and finally season. The FL community was taxonomically richer and more stable than the particle-associated (PA) one, which was characterized by recurrent ‘blooms’ of heterotrophic bacteria such as Alteromonas and Ralstonia. The heterotrophic FL and PA communities were also correlated with different environmental parameters: the FL population correlated with depth and phytoplankton, whereas PA bacteria were correlated primarily with the time of sampling. A significant part of the variability in community structure could, however, not be explained by the measured parameters. The metabolic potential of the PA community, predicted from 16S rRNA amplicon data using PICRUSt, was enriched in pathways associated with the degradation and utilization of biological macromolecules, as well as plastics, other petroleum products and herbicides. The FL community was enriched in predicted pathways for the metabolism of inositol phosphate, a potential phosphorus source, and of polycyclic aromatic hydrocarbons. 相似文献
887.
888.
José Pablo Dundore-Arias Russell L. Groves Jeri D. Barak 《Applied and environmental microbiology》2015,81(18):6345-6354
Phytophagous insects can encounter Salmonella enterica on contaminated plant surfaces and transmit externally adhered and internalized bacteria on and among leaves. Excretion of ingested S. enterica by the leafhopper Macrosteles quadrilineatus has been previously reported; however, the sites of persistence of ingested bacteria remain undetermined. Fluorescence microscopy revealed the presence and persistence of S. enterica in various organs of M. quadrilineatus fed an inoculated diet for 12 h and then moved to two consecutive noninoculated diets for a total of 48 h. Ingested S. enterica was predominantly observed in the filter chamber, midgut, and Malpighian tubules of M. quadrilineatus dissected immediately after acquisition and at 24- and 48-h post-acquisition access periods (post-AAPs). Additionally, we examined the potential roles of the Salmonella pathogenicity island 1 (SPI-1) and SPI-2 type III secretion systems (T3SSs) in the persistence and excretion of ingested S. enterica. In competition assays, a prgH mutant lacking a functional SPI-1 T3SS was recovered at significantly lower levels than the WT in insect homogenates at 24 h post-AAP, and complementation with prgH restored S. enterica persistence in M. quadrilineatus. Moreover, expression of prgH inside M. quadrilineatus was observed up to 48 post-AAP. No differences were observed between the WT and an ssaK mutant lacking a functional SPI-2 T3SS in insect homogenates or between the WT and either mutant in insect excretions. This study provides novel insight into the presence and persistence of S. enterica inside M. quadrilineatus and demonstrates that the SPI-1 T3SS influences the persistence of the pathogen in the gut of a potential vector. 相似文献
889.
Nutrient limitation of phytoplankton growth in Waquoit Bay, Massachusetts, USA: a nutrient enrichment study 总被引:1,自引:0,他引:1
Gabrielle Tomasky Jeri Barak Ivan Valiela Peter Behr Lori Soucy Kenneth Foreman 《Aquatic Ecology》1999,33(2):147-155
We conducted nutrient enrichment experiments and field sampling to address three questions: (1) is there nutrient limitation
of phytoplankton accumulation within an estuary whose waters are exposed to relatively high nitrogen loading rates, (2) where
in the salinity gradient from fresh to seawater (0 to 32‰) is there a shift from phosphorus to nitrogen limitation of phytoplankton
accumulation, and (3) is there a seasonal shift in limiting function of phosphorus and nitrogen anywhere in the estuarine
gradient. Nitrogen and phosphorus enrichment experiments in the Childs River, an estuary of Waquoit Bay, Massachusetts, USA,
showed that the accumulation of phytoplankton biomass in brackish and saline water was limited by supply of nitrate during
warm months. The effects of enrichment were less evident in fresh water, with short-lived responses to phosphate enrichment.
There was no specific point along the salinity gradient where there was a shift from phosphorus- to nitrogen-limited phytoplankton
accumulation; rather, the relative importance of nitrogen and phosphorus changed along the salinity gradient in the estuary
and with season of the year. There was no response to nutrient additions during the colder months, suggesting that some seasonally-varying
factor, such as light, temperature or a physiological mechanism, restricted phytoplankton accumulation during months other
than May-Aug. There was only slight evidence of a seasonal shift between nitrogen- and phosphorus-limitation of chlorophyll
accumulation. Phytoplankton populations in nutrient-rich estuaries with short flushing times grow fast, but at the same time
the cells may be advected out of the estuaries while still rapidly dividing, thereby providing an important subsidy to production
in nearby deeper waters.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
890.
Effect of diet on survival,in the laboratory and the field,of sterile male Mediterranean fruit flies
To improve the effectiveness of the sterile insect technique against the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), our objectives in this study were two‐fold. First, to evaluate the ability of sterile males of the Vienna‐8 strain to survive starvation, we compared them to wild males under laboratory conditions. The second objective was to determine the effect of protein‐rich nutrition on sterile male fly survival, under starvation conditions in the laboratory, under semi‐natural conditions in a field enclosure, and under natural conditions in the open field. Therefore, we released marked sterile flies of the two diet regimes, protein‐fed or protein‐deprived, and monitored their survival by recapturing them after 4, 6, and 7 days. In the laboratory, wild males endured starvation significantly better than sterile ones and protein addition to sterile fly diet resulted in even greater reduced capability to endure starvation. On the other hand, the addition of protein to sterile‐male diet did not affect their ability to survive in a field enclosure or in the open field. We conclude that under natural conditions, where food is available, sterile male fly survival is unaffected by protein‐rich pre‐release diet. 相似文献