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31.
Estimates of Daily Energy Expenditure in Birds: The Time-Energy Budget as an Integrator of Laboratory and Field Studies 总被引:1,自引:1,他引:0
SYNOPSIS. Measures of energy expenditure by free-living birdscan provide quantitative testsof a number of ecological theories,regarding such diverse phenomena as foraging strategies, resourcecompetition, or parental investment. Our confidence in thesetests rests heavily on the confidence we have in the estimatedrates of energy expenditure. The most common approach to obtainingsuch estimates is the construction of time-energy budgets, inwhich the durations of ananimal's daily activities are multipliedby the respective energy costs of the activities, and thesecosts are summed. Our knowledge of the energy costs of activities,particularly locomotion, has greatly advanced in recent years,as has the ability to adequately assess thermoregulatory costs.Comparisons between timeenergy budgets and direct measures ofenergy expenditure obtained using doubly labeled water indicatethat time-energy budgets can yield accurate estimates of energyexpenditure. However, this is likely to be achieved only underfairly rigorous conditions in which resting costs, activitycosts, and thermoregulatory costs are all well described.Evidenceis accumulating to suggest that, under some conditions, energyexpenditure by birds reaches a maximum sustainable level, atwhich point it is limited by the physiological capacitiestoingest and assimilate energy. Under these conditions, behavioralresponses to changing physical environments and resource availabilitymay be critical to the maintenance of energy balance. 相似文献
32.
A rapid method for the detection of corynetoxins, tunicamycin-like antibiotics, is described. Test samples were applied to or grown on an agar medium and overlain with Clavibacter tritici which is highly sensitive to the toxins. The method could detect 50 ng of tunicamycin. Corynetoxins in a range of field and laboratory samples were readily detected. 相似文献
33.
The Influence of Carbon Dioxide and Daily Photon-flux Density on Optimal Leaf Nitrogen Concentration and Root: Shoot Ratio 总被引:5,自引:1,他引:4
Using a cost-benefit model, the leaf nitrogen concentrationand root : shoot ratio that maximize whole-plant relative growthrate are determined as a function of the above-ground environment(integrated daily photon flux density and the concentrationof carbon dioxide at the site of fixation within the leaf).The major advantage of this approach is that it determines theadaptive significance of leaf physiology by considering thefunctional integration of leaves and roots. The predicted responseto increasing daily photon flux densities is an increase inoptimal leaf N concentration (Nopt) and a concomitant increasein root: shoot ratio. Increased carbon dioxide concentrations,on the other hand, reduce Nopt and only slightly change root:shoot ratio. The observed increase in leaf nitrogen concentrationfound in plants growing at high altitudes (low CO2 partial pressure)is also predicted. Since these responses to light and CO2 maximizethe whole-plant relative growth rate, the observed adjustmentsthat plants make to light and carbon dioxide concentration appearto be adaptive. We show that the relationship between photosynthesis and leafnitrogen concentration is complex and depends on the light andCO2 levels at which photosynthesis is measured. The shape ofthis function is important in determining Nopt and the oppositeresponse of leaf nitrogen to light and carbon dioxide is shownto be the result of the different effects of light and CO2 onthe photosynthesis-leaf nitrogen curve. Plant growth, photosynthesis, leaf nitrogen, biomass allocation, optimization, carbon dioxide light 相似文献
34.
Two chilling-sensitive (Phaseolus vulgaris L., Zea mays L.)and two chilling-tolerant (Pisum sativum L., Spinacia oleraceaL.) species were raised in growth chambers under warm (28/18°Cday/night cycle) and cool (18/12°C) temperature regimes.Growth analysis techniques were used to evaluate leaf area andbiomass partitioning during early autotrophic growth. Plantsacclimated to both temperatures were measured for leaf gas exchangeand water potential ( 相似文献
35.
Cold shock and heat shock: a comparison of the protection generated by brief pretreatment at less severe temperatures 总被引:1,自引:0,他引:1
Abstract Brief exposure to low (0o C) or high (40o C) temperature elicits a protective response that prevents injury when the flesh fly, Sarcophaga crassipalpis Macquart, is subjected to more severe cold (-10o C) or heat (45o C). Both the low and high temperature responses were found in all developmental stages of the fly, but were most pronounced in the pupal and pharate adult stages. The protective responses generated by brief exposure to 0 or 40o C appear similar in that both result in a rapid acquisition of cold or heat tolerance and a loss of protection after the flies are returned to 25o C. The protection generated by chilling is obvious within 10 min of exposure to 0o C while a 30 min exposure to 40o C is required to induce the high temperature protection. High temperature protects against cold shock injury within a narrow range (around 36o C) but we have no evidence that low temperature can protect against heat injury. We previously demonstrated that the rapid increase in cold tolerance correlates with concomitant increases in glycerol concentration, but in this study we found no significant elevation in glycerol in heat-shocked flies. Thus the physiological and biochemical bases for the rapid responses to cold and heat appear to be different. 相似文献
36.
DAVID C. HOUSTON 《Ibis》1988,130(4):402-417
Carcasses were provided at a gallery forest site in Venezuela to compare the feeding methods of four vulture species. Turkey Vultures or Lesser Yellow-headed Vultures were always the first species to arrive. Black Vultures were most likely to arrive at large carcasses or those in open situations and were the only species to form large feeding groups. King Vultures were equally likely to arrive at small or large carcasses. There were marked differences in feeding technique, food selection, rate of feeding and bill morphology between Turkey, Black and King Vultures, and the level of aggression between species was low compared to intra-specific aggression. 相似文献
37.
38.
A dual-surface leaf chamber was used to investigate the responsesof net photosynthesis and leaf conductance to independent changesin the humidity environments of the upper and lower surfacesof leaves of sunflower and soybean. In sunflower decreasingthe humidity around the upper leaf surface while maintainingthat of the lower surface constant and high reduced both thephotosynthetic rate and the conductance of the lower surface.These reductions could not be attributed to changes in bulkleaf water potential since the transpiration rate of the wholeleaf remained constant. Similarly, the reductions were not relatedto localized water deficits in the lower epidermis or lowermesophyll since the transpiration rate of the lower surfacewas reduced. Possible mechanisms whereby the gas exchange characteristicsof the lower leaf surface of sunflower respond to the humidityenvironment of the upper surface are discussed. In contrastto sunflower, the photosynthetic rate of the lower surface ofsoybean was insensitive to the humidity environment of the uppersurface. In leaves of sunflower grown under a moderate temperature anda medium light level, simultaneous decreases of humidity atboth leaf surfaces reduced the photosynthetic rate of the wholeleaf without affecting the substomatal partial pressure of CO2.In contrast, with leaves developed under a cool temperatureand a high light level, both the photosynthetic rate and thesubstomatal partial pressure of CO2 were reduced. Evidently,the occurrence in sunflower of the response pattern suggestinga non-stomatal inhibition of photosynthesis by low humiditydepends upon the environment during growth. The possibilitythat this non-stomatal inhibition may be an artifact due toan error in the assumption of water vapour saturation withinthe leaf airspace is considered. Key words: Vapour pressure deficit, photosynthesis, conductance, non-stomatal inhibition, Helianthus annuus, Glycine max 相似文献
39.
The xylem vessels of excised adventitious roots of onion, Alliumcepa, were perfused with unbuffered nutrient solution adjustedinitially to either pH 9·3 or 3·9; the pH of thesolution after passage through the xylem, at rates not lessthan 2 xylem volume changes min1, was close to pH 6·5in both instances. The flux of H+ across the xylem/symplastboundary into mildly alkaline, phosphate-buffered solutionsperfusing the vessels could be increased greatly with increasingbuffer strength, up to a maximum value between 0·51·0pmol H+ mm2 s1. The apparent neutralization ofacidic malic acid buffers had a slightly lower maximum capacity,equivalent to 0·3 to 0·5 pmol H+mm2 s1. The addition of 5·0 pmol m3fusicoccin (FC) to the xylem perfusion solution stimulated theentry of H+ into the xylem; in unbuffered perfusion solutionsthe pH fell to pH 3·6 after a lag of 2535 min.FC additions to phosphate-buffered solutions also stimulatedthe H+ flux to an extent similar to that in unbuffered solution,viz. 0·20·4 pmol mm2 s1. The release of K+ (36Rb-labelled) into xylem sap transientlyincreased as the [K+] in weakly buffered perfusion solutionswas raised stepwise; a very marked increase being seen whenthe concentration was raised to 100 mol m3 from 40 molm3. The addition of 5·0 mmol m3 FC to theperfusing solution containing 100 mol m3 K+ rapidly decreasedthe K+ flux to the xylem as the H+ flux increased. Fusicoccinalso inhibited the flux of K+ into unbuffered perfusion solutionsbut the effect appeared reversible. Addition of 10 mmol m3abscisic acid (ABA) to the perfusion solution quickly producedtransient increases in both K+ and H+ fluxes into the xylem.In this and other experiments using weakly phosphate-bufferedperfusing solutions, H+ fluxes were comparable in size to thoseof K+ The results are consistent with the idea that the stele of onionroots contains a proton trarislocating ATPase whose activityresponds to the pH of the xylem sap. It is evident that theactivity of the proton secreting and proton neutralizing mechanismsin the xylem parenchyma control the movement of other ions acrossthe xylem/symplast boundary. Key words: Xylem perfusion, fusicoccin, abscisic acid, pH gradient 相似文献
40.
A Consumer-Resource Approach to Community Structure 总被引:9,自引:0,他引:9
Because all species are consumers and all, eventually, are consumedby other species, consumer-resource interaction is one of themost fundamental processes of ecology. Simple models that includethe direct mechanisms of consumer-resource interactions maythus be the fundamental building-block for models of communitystructure. These models are easily extended to include suchcomplexity as the effects of physical limiting factors, spatialheterogeneity in resource supply, fluctuating resource supply,and multiple trophic levels. Each such modification places constraintson the traits of species that can persist. Consumer-resourcemodels make predictions about many aspects of community structure,including species richness, species composition, species dominance,population dynamics, morphological or physiological traits ofspecies, and patterns of phenotypic variation within species.Thus, each model affords numerous opportunities to test andmodify or reject it. A review of a variety of communities suggeststhat much of the structure of each community can be explainedby a relatively simple consumer-resource model, but that differentelements of complexity may be important in different communities. 相似文献