首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   143篇
  免费   5篇
  148篇
  2023年   2篇
  2021年   3篇
  2020年   3篇
  2019年   5篇
  2018年   3篇
  2017年   5篇
  2016年   8篇
  2015年   4篇
  2014年   8篇
  2013年   13篇
  2012年   5篇
  2011年   16篇
  2010年   14篇
  2009年   9篇
  2008年   8篇
  2007年   7篇
  2006年   9篇
  2005年   7篇
  2004年   3篇
  2003年   3篇
  2002年   3篇
  2000年   1篇
  1996年   2篇
  1994年   1篇
  1993年   1篇
  1991年   1篇
  1985年   2篇
  1984年   1篇
  1976年   1篇
排序方式: 共有148条查询结果,搜索用时 22 毫秒
1.
Renewable energy (RE) technologies are looked upon favorably to provide for future energy demands and reduce greenhouse gas (GHG) emissions. However, the installation of these technologies requires large quantities of finite material resources. We apply life cycle assessment to 100 years of electricity generation from three stand‐alone RE technologies—solar photovoltaics, run‐of‐river hydro, and wind—to evaluate environmental burden profiles against baseline electricity generation from fossil fuels. We then devised scenarios to incorporate circular economy (CE) improvements targeting hotspots in systems’ life cycle, specifically (1) improved recycling rates for raw materials and (ii) the application of eco‐design. Hydro presented the lowest environmental burdens per kilowatt‐hour of electricity generation compared with other RE technologies, owing to its higher efficiency and longer life spans for main components. Distinct results were observed in the environmental performance of each system based on the consideration of improved recycling rates and eco‐design. CE measures produced similar modest savings in already low GHG emissions burdens for each technology, while eco‐design specifically had the potential to provide significant savings in abiotic resource depletion. Further research to explore the full potential of CE measures for RE technologies will curtail the resource intensity of RE technologies required to mitigate climate change.  相似文献   
2.
Salient sensory environments experienced by a parental generation can exert intergenerational influences on offspring. While these data provide an exciting new perspective on biological inheritance, questions remain about causes and consequences of intergenerational influences of salient sensory experience. We previously showed that exposing male mice to a salient olfactory experience, like olfactory fear conditioning, resulted in offspring demonstrating a sensitivity to the odor used to condition the paternal generation and possessing enhanced neuroanatomical representation for that odor. In this study, we first injected RNA extracted from sperm of male mice that underwent olfactory fear conditioning into naïve single‐cell zygotes and found that adults that developed from these embryos had increased sensitivity and enhanced neuroanatomical representation for the odor (Odor A) with which the paternal male had been conditioned. Next, we found that female, but not male offspring sired by males conditioned with Odor A show enhanced consolidation of a weak single‐trial Odor A + shock fear conditioning protocol. Our data provide evidence that RNA found in the paternal germline after exposure to salient sensory experiences can contribute to intergenerational influences of such experiences, and that such intergenerational influences confer an element of adaptation to the offspring. In so doing, our study of intergenerational influences of parental sensory experience adds to existing literature on intergenerational influences of parental exposures to stress and dietary manipulations and suggests that some causes (sperm RNA) and consequences (behavioral flexibility) of intergenerational influences of parental experiences may be conserved across a variety of parental experiences.  相似文献   
3.
Soluble guanylate cyclase (sGC), a heterodimeric heme protein, catalyses the conversion of GTP in to cyclic GMP, which acts as a second messenger in cellular signaling. Nitric oxide activates this enzyme several hundred folds over its basal level. Carbon monoxide, along with some activator molecules like YC-1 and BAY, also synergistically activate sGC. Mechanism of this synergistic activation is a matter of debate. Here we review the existing literature to identify the possible binding site for YC-1 and BAY on bovine lung sGC and its mechanism of activation. These two exogenous compounds bind sGC on α subunit inside a pocket and thus exert allosteric effect via subunit interface, which is relayed to the catalytic site. We used docking studies to further validate this hypothesis. We propose that the binding of YC-1/BAY inside the sensory domain of the α subunit modulates the interactions on the subunit interface resulting in rearrangements in the catalytic site into active conformation and this partly induces the cleavage of Fe-His bond.  相似文献   
4.
A novel noninvasive genomic DNA isolation protocol from fecal tissue, by the proteinase K digestion and guanidine hydrochloride extraction method, was assessed for the genotyping of cattle and buffalo. The epithelial tissues present on the surface of the feces were used as source for isolation of genomic DNA. The DNA isolated from fecal tissue was found to be similar as those obtained from other body tissues such as skin, brain, liver, kidney, and muscle. The quality of DNA was checked by agarose gel electrophoresis and polymerase chain reaction (PCR). We successfully amplified a 320 bp MHC class II DRB gene and a 125 bp mt-DNA D-loop region from isolated genomic DNA of cattle. Thus, the DNA isolated using this method was suitable for common molecular biology methods, such as restriction enzyme digestion and genotyping of dairy animals through PCR.  相似文献   
5.
We have developed an efficient transformation system for Tylophora indica, an important medicinal plant in India, using Agrobacterium rhizogenes strains LBA9402 and A4 to infect excised leaf and stem explants and intact shoots at different sites. The induction of callus and transformed roots was dependent on the bacterial strain, explant type and inoculation site used. Transformed roots were induced only in explants infected with A. rhizogenes strain A4, while an optimal transformation frequency of up to 60% was obtained with intact shoots inoculated at the nodes. The presence of the left-hand transferred DNA (TL-DNA) in the genome of T. indica roots induced by A. rhizogenes was confirmed by PCR amplification of the rooting locus genes of A. rhizogenes. Root growth and the production of tylophorine, the major alkaloid of the plant, varied substantially among the nine root clones studied. Both parameters increased over time in liquid cultures, with maximum biomass and tylophorine accumulation occurring within 4–6 weeks of growth in fresh medium. Interestingly, in liquid culture, the culture medium also accumulated tylophorine up to concentrations of 9.78±0.21 mg l–1.  相似文献   
6.
Ledebouria revoluta are important ethnomedicinal plant found in India and South Africa. Micropropagation via indirect shoot organogenesis had been established from three types of explant (i.e. scale leaf, leaf lamina and root) of L. revoluta. Scale leaf was found superior as compared to leaf lamina and root explant with respect to their organogenic callus induction potentiality. Murashige and Skoog (1962) [MS] media supplemented with 3.0?mg?L?1 2,4-dichlorophenoxyacetic acid, 0.75?mg?L?1 β-naphthoxyacetic acid were best effective for inducing organogenic callus. Maximum 17.0?±?0.52 bulblets were induced from about 500?mg of callus within 42–46?days sub-culturing on a medium containing 0.75?mg?L?1 kinetin. The bulblets were matured (86.7% success) after one month culture on the same medium composition. The best result of in vitro root induction with 100% response and 8.4?±?0.31 roots per bulb was achieved after 18?days of implantation on MS medium containing 2.0?mg?L?1 indole-3-butyric acid. Plantlets were acclimatized with a 96.0% survival rate. Chromosomal studies revealed cytological stability of callus cells and all regenerants containing 2n?=?30 chromosomes, same as parental plants. Antimicrobial activity of L. revoluta was tested against two Gram-positive bacteria, three Gram-negative bacteria and two fungi. The methanol and ethanol extract proved more effective against bacteria, whereas acetone and chloroform extract shows potential anti-fungal activities. Present protocol can be applied reliably to produce uniform planting materials in large scale. In addition, this efficient indirect regeneration pathway via callus culture opens a way for improvement through genetic transformation.  相似文献   
7.
8.
Soluble guanylate cyclase (sGC), a physiological nitric oxide (NO) receptor, is a heme-containing protein and catalyzes the conversion of GTP to cyclic GMP. We found that 200 mM imidazole moderately activated sGC in the coexistence with 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1), although imidazole or YC-1 alone had little effect for activation. GTP facilitated this process. Resonance Raman spectra of imidazole complex of native sGC and CO-bound sGC (CO-sGC) have demonstrated that a simple heme adduct with imidazole at the sixth coordination position is not present for both sGC and CO-sGC below 200 mM of the imidazole concentration and that the Fe-CO stretching band (nuFe-CO)) appears at 492 cm(-1) in the presence of imidazole compared with 473 cm(-1) in its absence. Both frequencies fall on the line of His-coordinated heme proteins in the nuFe-CO vs nuC-O plot. However, it is stressed that the CO-heme of sGC becomes apparently photo-inert in a spinning cell in the presence of imidazole, suggesting the formation of five-coordinate CO-heme or of six-coordinate heme with a very weak trans ligand. These observations suggest that imidazole alters not only the polarity of heme pocket but also the coordination structure at the fifth coordination side presumably by perturbing the heme-protein interactions at propionic side chains. Despite the fact that the isolated sGC stays in the reduced state and is not oxidized by O(2), sGC under the high concentration of imidazole (1.2 M) yielded nu4 at 1373 cm(-1) even after its removal by gel-filtration, but addition of dithionite gave the strong nu4 band at 1360 cm(-1). This indicated that imidazole caused autoxidation of sGC.  相似文献   
9.
Type 2 diabetes mellitus is a complex metabolic disorder with adverse cardiovascular risk. The role of micronutrients has not yet been well clarified in this condition, especially in India.THE OBJECTIVES OF THIS STUDY WERE TO: (1) evaluate chromium status in Indian subjects with type 2 diabetes mellitus, (2) assess the effect of chromium picolinate (200 &mgr;g trivalent chromium twice daily) administration on glycaemic control and lipid profile in these subjects and (3) comment on the possible mechanism of any beneficial effect noted above.Fifty subjects were studied in a double blind, placebo-controlled, crossover fashion, with each treatment arm (chromium/placebo) lasting 12 weeks and 4 weeks' wash-off period in between. 50 healthy age- and sex-matched volunteers served as controls. Serum chromium level appeared to be higher in the general population in our country compared to western countries (36.5-59.5 nmol/L as compared to 2.3-40.3 nmol/L) However, the local diabetics were found to have a lower serum chromium level than the healthy controls (32.3 nmol/L against 44.7 nmol/L; p < 0.0001) and a mean increase of 3.5 nmol/L was noted after 12 weeks of chromium supplementation that was, expectedly, not seen in the placebo phase (p < 0.0001).Significant improvement in glycaemic control was noted in the chromium-treated group (DeltaFasting serum glucose = 0.44 mmol/L, p < 0.001; DeltaPost-prandial serum glucose = 1.97 mmol/L, p < 0.001; Deltaglycated hemoglobin = 0.01; p = 0.04, in comparison to placebo) This was accompanied by a significant greater fall in fasting serum insulin in the chromium-treated group, p < 0.05.The change in lipid parameters (total serum cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol and triglycerides) did not show significant difference between the chromium and placebo groups.Clinically significant hematological, renal or hepatic toxicity were excluded by routine hemogram, serum urea, creatinine, alanine amino transferase (ALT) and alkaline phosphatase estimations.In conclusion, chromium supplementation seems to improve glycaemic control in type 2 diabetic patients, which appears to be due to an increase in insulin action rather than stimulation of insulin secretion.  相似文献   
10.
Surplus male proboscis monkeys at the Singapore Zoo pose a considerable problem for maintenance and maximizing of exhibition potential. In 2008, a new exhibit was constructed to house and display a group of six proboscis monkey males born in Singapore Zoo. To document and monitor the all‐male group establishment in the new exhibit, we conducted observations on intragroup interactions between the monkeys, spatial use of their new exhibit, and visitor effects on their behavior. We found contact aggressive interactions between the monkeys to be consistently lower than noncontact aggressive interactions and by week six of introduction to the new exhibit, contact aggression was almost nonevident. Affiliative interactions also developed between individuals in the group, with an interface of aggressive and socioreconcilatory behavior influenced by food competition and a dominance hierarchy. This was evident from significantly higher overall aggression and affiliation during feeding times compared to nonfeeding times, and this was reduced when food competition was mitigated by modifying the feeding regime. We measured the groups’ spatial use of the exhibit and the relation to behavior, crowd size, and density. Our results showed that the proboscis monkeys utilized the available exhibit space, were largely unaffected by visitor crowd size and density, and were able to exhibit a variety of natural behaviors, including swimming. Our accomplishment in maintaining and displaying an all‐male group of proboscis monkeys in captivity provides viable options for more comprehensive captive management and breeding programs for this endangered species. Zoo Biol. 32:281‐290, 2013. © 2012 Wiley Periodicals, Inc.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号