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191.
We argue that phenotypic plasticity should be broadly construed to encompass a diversity of phenomena spanning several hierarchical levels of organization. Despite seemingly disparate outcomes among different groups of organisms (e.g., the opening/closing of stomata in leaves, adjustments of allocation to growth/reproduction, or the production of different castes in social insects), there are underlying shared processes that initiate these responses. At the most fundamental level, all plastic responses originate at the level of individual cells, which receive and process signals from their environment. The broad variations in physiology, morphology, behavior, etc., that can be produced by a single genotype, can be accounted for by processes regulating gene expression in response to environmental variation. Although evolution of adaptive plasticity may not be possible for some types of environmental signals, in many cases selection has molded responses to environmental variation that generate precise and repeatable patterns of gene expression. We highlight the example of responses of plants to variation in light quality and quantity, mediated via the phytochrome genes. Responses to changes in light at particular stages of plants' life cycles (e.g., seed germination, competition, reproduction) are controlled by different members of this gene family. The mechanistic details of the cell and molecular biology of phytochrome gene action (e.g., their effects on expression of other genes) is outlined. Plasticity of cells and organisms to internal and external environmental signals is pervasive, and represents not just an outcome of evolutionary processes, but also a potentially important molder of them. Phenotypes originally initiated via a plastic response, can be fixed through genetic assimilation as alternate regulatory pathways are shut off. Evolution of mechanisms of plasticity and canalization can both reduce genetic variation, as well as shield it. When the organism encounters novel environmental conditions, this shielded variation may be expressed, revealing hidden reaction norms that represent the raw material for subsequent evolution. 相似文献
192.
Oxygen Exchange in Relation to Carbon Assimilation in Water-stressed Leaves During Photosynthesis 总被引:10,自引:3,他引:7
In a study on metabolic consumption of photosynthetic electronsand dissipation of excess light energy under water stress, O2and CO2 gas exchange was measured by mass spectrometry in tomatoplants using 18O2 and 13CO2. Under water stress, gross O2 evolution(EO), gross O2 uptake (UO), net CO2 uptake (PN), gross CO2 uptake(TPS), and gross CO2 evolution (EC) declined. The ratio PN/EOfell during stress, while the ratios UO/EO and EC/TPS rose.Mitochondrial respiration in the light, which can be measureddirectly by 12CO2 evolution during 13CO2 uptake at 3000 µll1 13CO2, is small in relation to gross CO2 evolutionand CO2 release from the glycolate pathway. It is concludedthat PSII, the Calvin cycle and mitochondrial respiration aredown-regulated under water stress. The percentages of photosyntheticelectrons dissipated by CO2 assimilation, photorespiration andthe Mehler reaction were calculated: in control leaves morethan 50 % of the electrons were consumed in CO2 assimilation,23 % in photorespiration and 13 % in the Mehler reaction. Undersevere stress the percentages of electrons dissipated by CO2assimilation and the Mehler reaction declined while the percentageof electrons used in photorespiration doubled. The consumptionof electrons in photorespiration may reduce the likelihood ofdamage during water deficit. 相似文献
193.
Summary Physiological and biochemical responses of micropropagated tea plants grown under field conditions were investigated in comparison
to vegetatively propagated (VP) plants. No significant variation was observed between tissue culture raised (TC) and VP plants
in terms of photosynthetic carbon assimilation rate. However, clones showed significant variation among themselves. Carbon
assimilation studies carried out with a radiotracer technique revealed that ‘Assam’ cultivar UPASI-27 assimilated a higher
amount of labeled carbon dioxide followed by UPASI-3. However, UPASI-27 was marginally better than UPASI-3 in terms of mobilization
of assimilates to the growing sinks. Both, UPASI-3 and UPASI-27 reassimilated higher quantities of photosynthates followed
by BSB-1 and UPASI-26. Though there was a marginal variation in photosynthetic pigments of TC and VP plants, it was not statistically
significant. Similarly, no significant variations were observed in certain substrates (polyphenols, catechins and amino acids)
and enzymes (polyphenol oxidase, peroxidase and phenylalanine ammonia-lyase) except protease involved in the formation of
quality constituents of made tea. However, clonal variation was evident with respect to photosynthetic pigments, substrates/enzymes.
Under soil moisture stress, no significant variation was observed between VP and TC plants in terms of proline accumulation. 相似文献
194.
David F. Gilmore Walter Godchaux III Edward R. Leadbetter 《Archives of microbiology》1989,152(4):387-392
We have studied the regulation of sulfate assimilation by the gliding bacterium Cytophaga johnsonae in which 20% of the total sulfur is in the sulfornate moiety of sulfonolipid. Added cystine inhibited sulfate uptake and growth with cystine as sulfur source resulted in a repression of sulfate uptake. However, low concentrations of cystine preferentially repressed the terminal reactions of sulfate assimilation responsible for cysteine synthesis while allowing the transport and activation of sulfate for sulfonolipid synthesis. The significance of this novel pattern of regulation in bacteria is discussed. 相似文献
195.
Joanna K. Norman Ann K. Sarai Stephen G. Weller Todd E. Dawson 《Evolution; international journal of organic evolution》1995,49(2):297-306
We compared inbreeding depression in hermaphroditic Schiedea lydgatei and its gynodioecious sister species, S. salicaria, to infer the level of inbreeding depression in their common ancestor. With measurements of selfing rates, this information can be used to assess the importance of inbreeding depression in the evolution of breeding systems in S. lydgatei and S. salicaria. Morphological and physiological characters related to fitness were compared for inbred and outcrossed S. lydgatei in high- and low-fertilizer environments in the greenhouse. Seed mass, number of seeds per capsule, germination, survival, biomass, number of flowers, and age at first flowering were compared for inbred versus outcrossed progeny. We also measured inbreeding depression in maximal rates of photosynthetic carbon assimilation and stomatal conductance to water vapor, traits that affect fitness through their influence on plant carbon balance and water-use efficiency (ratio of carbon gain to water loss). All traits except number of seeds per capsule in parents and survival showed inbreeding depression, with the magnitude depending on family and environment. High inbreeding depression is likely in the ancestor of S. lydgatei and S. salicaria, indicating that, with sufficiently high selfing rates, females could spread in populations. Hermaphroditism in S. lydgatei is probably favored by low selfing rates. In contrast, the evolution of gynodioecy in S. salicaria apparently has been favored by relatively high selfing rates in combination with high inbreeding depression. 相似文献
196.
197.
Substance P has been implicated as a neuronal mediator of inflammation in various inflammatory conditions. However, the exact role played by substance P in inflammatory bowel diseases or in experimental colonic vasculitis has not been clearly understood. In this study, we examined the effect of close superior mesenteric artery injection of substance P under prevailing inflammatory conditions induced by intravenous human albumin antialbumin immune complex followed by intracolonic perfusion of 2.5% formaldehyde in rats or intracolonic perfusion of 5% alcohol alone. The immune complex- and formaldehyde-treated rats showed severe microvascular changes such as microvascular plugging by red blood cells, endothelial breakage and extravasation of plasma proteins and red blood cells. The bolus injection of 10−8 M substance P reduced extravasation of Evans blue dye by 50% and the tissue wet to dry ratio by 20% in immune complex- and formaldehyde-perfused rats. Myeloperoxidase activity was not changed. Substance P also significantly inhibited (44%) the extravasation in alcohol-perfused rats. Pretreatment of immune complex- and formaldehyde-treated rats with substance P antagonist reversed the effect of substance P. These findings suggest that the most immediate effect of substance P may be vasodilation and clearing of vascular plugs induced by immune complex and formaldehyde. This effect of substance P differs from its chronic effect, which causes vasodilation and extravasation. 相似文献
198.
199.
David A. Cort 《Ethnic and racial studies》2013,36(2):313-314
While theoretical work focusing on immigrant language acculturation suggests that both parental and child's understanding of English are needed to measure acculturation, analysts have instead focused on child bilingualism. I develop a measure of familial acculturation and conceptually distinguish it from child bilingualism. I then determine whether several child and parental variables influence these measures differently, which would provide evidence supporting the conceptual distinction. Results show that child bilingualism is indeed independent of familial acculturation. Parental skills and resources significantly affect familial acculturation but not child bilingualism, whereas gender and Latino status affect child bilingualism but not familial acculturation. Additionally, modes of incorporation do not determine either child bilingualism or familial acculturation, suggesting that integrative forces external to the family may have little power to shape the internal workings that generate child or familial language acculturation. Together, these findings imply that researchers should avoid conflating child bilingualism with familial acculturation. 相似文献
200.