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91.
Hydrogen (H2) is a by-product of the symbiotic nitrogen fixation (N2 fixation) between legumes and root-nodule bacteria (rhizobia). Some rhizobial strains have an uptake hydrogenase enzyme (commonly referred to as Hup+) that recycles H2 within the nodules. Other rhizobia, described as Hup?, do not have the enzyme and the H2 produced diffuses from the nodules into the soil where it is consumed by microorganisms. The effect of this phenomenon on the soil biota and on the soil itself, and consequent stimulation of plant growth, has been demonstrated previously. Soybeans [Glycine max (L.) Merr.] cv. Leichhardt, inoculated with either a Hup+ strain (CB1809) or one of two Hup? strains (USDA442 or USDA16) of Bradyrhizobium japonicum and uninoculated soybeans, plus a non-legume control [capsicum (Capsicum annuum L.)] were grown in the field at Ayr, North Queensland, Australia. The objectives were to examine (1) relationships between N2 fixation and H2 emission, and (2) the influence H2-induced changes in soil might have during the legume phase and/or on the performance of a following crop. Strains CB1809 and USDA442 were highly effective in N2 fixation (“good” fixers); USDA16 was partly effective (“poor” fixer). The soil had a large but non-uniformly distributed naturalised population of B. japonicum and most uninoculated control plants formed nodules that fixed some N2. These naturalised strains were classified as “poor fixers” of N2 and were Hup+. H2 emissions from nodules were assessed for all treatments when the soybean crop was 62 days old. Other parameters of symbiotic N2 fixation and plant productivity were measured when the crop was 62 and 96 days old and at crop maturity. Immediately after final harvest, the land was sown to a crop of maize (Zea mays L.) in order to determine the consequences of H2 emission from the soybean crop on maize growth. It was estimated that soybeans inoculated with USDA442, the highly effective Hup– strain of B. japonicum, fixed 117 kg shoot N/ha (or about 195 kg total N/ha if the fixed N associated with roots and nodules was taken into account), and contributed about 215,000 l H2 gas per hectare to the ecosystem over the life of the crop. The volume of H2 evolved from soybeans nodulated by the Hup+ strain CB1809 was only 6% of that emitted by the USDA442 treatment, but there was no indication that soybean inoculated with USDA442 benefited from the additional H2 input. The shoot biomass, grain yield, and amounts of N fixed (105 kg shoot N/ha, 175 kg total N/ha) by the CB1809 treatment were little less than for USDA442 plants. Three days after the soybean crop was harvested, the plots were over-sown with maize along the same row lines in which the soybeans had grown. This procedure exposed the maize roots to whatever influence soybean H2 emission might have had on the soil and/or the soil microflora immediately surrounding soybean nodules. The evidence for a positive effect of soybean H2 emission on maize production was equivocal. While the consistent differences between those pre-treatments that emitted H2 and those that did not indicated a trend, only one difference (out of the 12 parameters of maize productivity that were measured) was statistically significant at P?<?0.05. The findings need substantiation by further investigation. 相似文献
92.
93.
Lazos-Monterrosa FA C Orantes-García O Farrera-Sarmiento AG Verdugo-Valdez MS Sánchez-Cortés LE Ruíz-Meza 《Phyton》2015,84(1):138-143
The tempisque (Sideroxylon capiri) is a tree native to Mexico used by the rural population for housing construction, poles and hedges, as fuel (wood) and also for fodder and ornamental purposes, among others. It is considered an endangered species. In order to contribute to its preservation and sustainable management, it was considered important to determine the proportion of viable seeds, the loss of viability due to storage period and the germination process by applying pregerminative treatments. We found that freshly collected seeds showed 100% viability, which decreased to 0% after 5 months of storage. According to the cumulative germination significant differences between treatments (p≤0.01) were found. It was observed that seeds can accelerate their time of germination with the previous exposure of 24 h in water at room temperature. The soaking treatment in water for 24 h at room temperature obtained final germination of 55%, while with the control 39% was reached. Soaking in hydrogen peroxide and scarification were the treatments with lower germination percentage (33 and 23%, respectively). To get a higher percentage of germinated seeds in a short time, it is necessary to give a soaking treatment in water for 24 h before sowing. 相似文献
94.
Diadenosine oligophosphates (Ap(n)A) have been proposed as intracellular and extracellular signaling molecules in animal cells. The ratio of diadenosine 5',5'-P1,P3-triphosphate to diadenosine 5',5'-P1,P4-tetraphosphate (Ap3A/Ap4A) is sensitive to the cellular status and alters when cultured cells undergo differentiation or are treated with interferons. In cells undergoing apoptosis induced by DNA topoisomerase II inhibitor VP16, the concentration of Ap3A decreases significantly while that of Ap4A increases. Here, we have examined the effects of exogenously added Ap3A and Ap4A on apoptosis and morphological differentiation. Penetration of Ap(n)A into cells was achieved by cold shock. Ap4A at 10 microM induced programmed cell death in human HL60, U937 and Jurkat cells and mouse VMRO cells and this effect appeared to require Ap4A breakdown as hydrolysis-resistant analogues of Ap4A were inactive. On its own, Ap3A induced neither apoptosis nor cell differentiation but did display strong synergism with the protein kinase C activators 12-deoxyphorbol-13-O-phenylacetate and 12-deoxyphorbol-13-O-phenylacetate-20-acetate in inducing differentiation of HL60 cells. We propose that Ap4A and Ap3A are physiological antagonists in determination of the cellular status: Ap4A induces apoptosis whereas Ap3A is a co-inductor of differentiation. In both cases, the mechanism of signal transduction remains unknown. 相似文献
95.
The lytB gene of Escherichia coli is essential and specifies a product needed for isoprenoid biosynthesis. 下载免费PDF全文
LytB and GcpE, because they are codistributed with other pathway enzymes, have been predicted to catalyze unknown steps in the nonmevalonate pathway for isoprenoid biosynthesis. We constructed a conditional Escherichia coli lytB mutant and found that LytB is essential for survival and that depletion of LytB results in cell lysis, which is consistent with a role for this protein in isoprenoid biosynthesis. Alcohols which can be converted to pathway intermediates beyond the hypothesized LytB step(s) support limited growth of E. coli lytB mutants. An informatic analysis of protein structure suggested that GcpE is a globular protein of the TIM barrel class and that LytB is also a globular protein. Possible biochemical roles for LytB and GcpE are suggested. 相似文献
96.
Sticklebacks are used as a model system in behavioral and evolutionary research, and therefore it is important to have a complete
understanding of their biology. Despite this, the presence of acoustic signals has never been explored. This study examines
acoustic cues in brook sticklebacks during courtship, spawning, egg guarding, and fry guarding. Although some fish produce
sounds during spine flaring, results of this experiment showed that brook sticklebacks do not. Females did produce incidental
sounds while depositing eggs in the nest. However, these were low intensity and seem unlikely to be heard over background
noise. 相似文献
97.
Elspeth A. McLennan Rebecca M. Gooley Phil Wise Katherine Belov Carolyn J. Hogg Catherine E. Grueber 《Conservation Genetics》2018,19(2):439-450
Tasmanian devils have experienced an 85% population decline since the emergence of an infectious cancer. In response, a captive insurance population was established in 2006 with a subpopulation later introduced onto Maria Island, Tasmania. We aimed to (1) examine the genetic parameters of the Maria Island population as a stand-alone site and within its broader metapopulation context, (2) assess the efficacy of assisted colonisations, and (3) inform future translocations. This study reconstructs the pedigree of 86 island-born devils using 31 polymorphic microsatellite loci. Combined molecular and pedigree analysis was used to monitor change in population genetic parameters in 4 years since colonisation. Molecular analysis alone revealed no significant change in genetic diversity, while DNA-reconstructed pedigree analysis revealed a statistically significant increase in inbreeding due to skewed founder representation. Pedigree modelling predicted that gene diversity would only be maintained above the threshold of 95% for a further 2 years, dropping to 77.1% after 40 years. Modelling alternative supplementation strategies revealed introducing eight new founders every 3 years will enable the population to retain 95% gene diversity until 2056, provided the translocated animals breed; to ensure this we recommend introducing ten new females every 3 years. We highlight the value of combining pedigree analyses with molecular data, from both a single-site and metapopulation viewpoint, for analysing changes in genetic parameters within populations of conservation concern. The importance of post-release genetic monitoring in an established population is emphasised, given how quickly inbreeding can accumulate and gene diversity be lost. 相似文献
98.
Infection of Tetrahymena pyriformis by Legionella longbeachae and other Legionella species found in potting mixes. 总被引:2,自引:0,他引:2 下载免费PDF全文
All Legionella longbeachae strains, both serogroups of L. bozemanii, and three strains of L. anisa reproducibly infected washed Tetrahymena pyriformis at 30 degrees C. L. pneumophila serogroup 1 strains infected T. pyriformis less reproducibly than did L. longbeachae. Low-level concentrations of nutrients in cocultures inhibited infection. Four L. micdadei strains and L. anisa ATCC 35292 failed to infect T. pyriformis. 相似文献
99.
Transfer RNAs isolated from E. coli grown in media where ferric iron is not freely available show well characterized chromatographic changes due to the absence of the methylthio moiety of ms2i6A. The altered tRNA molecules include tRNA trp tRNA tyr, tRNA phe and two minor tRNA ser species. It has been suggested that methylthiolation of tRNA affects its function in regulation. We now show iron-related changes in tRNA trp from S. typhimurium, Ps. aeruginosa and K. pneumoniae. tRNA trp from S. typhimurium contains ms2i6A and it seems probable that the availability of iron affects the synthesis of ms2i6A-tRNA trp from i6A-tRNA trp in this organism. An iron-related methylthiolating system may also be operative in K. pneumoniae. S. marcescens tRNA trp, however was not affected by the availability of iron. Neither ms2i6A nor i6A was found in S. marcescens tRNA, although an, as yet unidentified, hydrophobic nucleoside was present. 相似文献
100.
Historical ecological studies provide information about the origins of species in an area and the origins of traits characterizing the interactions between those species and their environment. Incorporating this evolutionary information into conservation policies will broaden the base of options for making effective decisions about the preservation of biodiversity. 相似文献