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61.
JOHN MOYSE 《Zoological Journal of the Linnean Society》1984,80(1):323-336
Limb movements of restrained stage VI nauplii of Lepas pectinata were studied by cine-photography. Outline drawings were made of successive limb positions in both swimming and grooming activity. The antennae appeared to act as leaky paddles performing both propulsion and food gathering. Free-swimming nauplii averaged 120 limb beats min-1 and a speed of c. 4 mm s-1 . Grooming occurred every 7–20 beats.
It was concluded that lack of streamlining favours filtration at the expense of propulsion. The grooming sequence differs from that of balanid nauplii and is one method of transferring food to the vicinity of the mouth, where sorting and rejection take place prior to ingestion. Fine- and coarse-mesh filters presumably exploit different plankton types. The overall behaviour pattern is well-designed for exploitation of scarce food in the oligotrophic conditions of the ocean-surface habitat. 相似文献
It was concluded that lack of streamlining favours filtration at the expense of propulsion. The grooming sequence differs from that of balanid nauplii and is one method of transferring food to the vicinity of the mouth, where sorting and rejection take place prior to ingestion. Fine- and coarse-mesh filters presumably exploit different plankton types. The overall behaviour pattern is well-designed for exploitation of scarce food in the oligotrophic conditions of the ocean-surface habitat. 相似文献
62.
The effect of changes in the environment on lipid metabolismhas been studied in the brown alga, Fucus serratus L. Lightstimulated the incorporation of radioactivity from /{I4C/}acetateinto oleic and, especially, into linoleic acid. The same effectwas caused by lowering the incubation temperature from 15 °Cto 4 °C. Incubations in the presence of Cd + +, Pb + + orZn+ + had no effect on the total uptake of /{14C/}acetate intothe frond tip samples, but lowered the labelling of total lipidsrelative to aqueous-soluble components. However, pre-exposureof the algae to heavy metal cations caused changes in the uptakeof radioactivity but had less effect on the relative labellingof lipids than incubations in the presence of heavy metal cations.Algae collected from sites where the dissolved levels of heavymetals were elevated, showed a decrease in the relative labellingof lipids from /{14C/}acetate. Concentrations of Cd+ +, Pb++ or Zn+ + at 10 x levels found at the collection site had littleeffect on the pattern of fatty acids made by Fucus serratus. Key words: Lipid metabolism, Fucus serratus L., Environmental changes 相似文献
63.
SUMMARY. We describe a model of zooplankton population dynamics that accounts for differences in mortality and physiology among animals of different ages or sizes. The model follows changes in numbers of individuals and changes in individual and egg biomass through time and it expresses mortality and net assimilation as functions of animal size.
We investigated the effect of egg size, age at first reproduction, and size at first reproduction on the per capita growth rates of populations growing under different conditions. In the absence of predation or when exposed to vertebrate predators that prefer large prey, populations achieve maximum growth rates when animals hatch from small eggs and reach maturity quickly at small sizes. Populations exposed to invertebrate predators that concentrate on small animals may increase r in two different ways. One way is for animals to increase juvenile survivorship by hatching from large eggs and by shortening the juvenile period. An alternative strategy is for animals to hatch from small eggs and to postpone maturity until they grow beyond the range of sizes available to their predators. Certain life history strategies maximize r if animals continue to grow after they reach maturity. By growing larger, non-primiparous females are able to hatch larger clutches and thereby increase the overall rate of population growth.
The model analysis shows how to assess age-dependent mortality rates from field data. The net rate of population increase and the age distribution of eggs together provide specific, quantitative information about mortality. 相似文献
We investigated the effect of egg size, age at first reproduction, and size at first reproduction on the per capita growth rates of populations growing under different conditions. In the absence of predation or when exposed to vertebrate predators that prefer large prey, populations achieve maximum growth rates when animals hatch from small eggs and reach maturity quickly at small sizes. Populations exposed to invertebrate predators that concentrate on small animals may increase r in two different ways. One way is for animals to increase juvenile survivorship by hatching from large eggs and by shortening the juvenile period. An alternative strategy is for animals to hatch from small eggs and to postpone maturity until they grow beyond the range of sizes available to their predators. Certain life history strategies maximize r if animals continue to grow after they reach maturity. By growing larger, non-primiparous females are able to hatch larger clutches and thereby increase the overall rate of population growth.
The model analysis shows how to assess age-dependent mortality rates from field data. The net rate of population increase and the age distribution of eggs together provide specific, quantitative information about mortality. 相似文献
64.
Temperature Regulation of Anthocyanin Accumulation in Apple Skin 总被引:1,自引:0,他引:1
The regulation of anthocyanin accumulation in apple skin (cv.Jonathan) by temperature was studied. In the field the increasein anthocyanin in the skin before harvest coincided with decreasingtemperatures and with increasing ethylene production by thefruit. In detached apples held under continuous white light,the optimum temperatures for anthocyanin accumulation were 12°C in unripe apples and 1624 °C in ripe apples.These effects were explained by corresponding changes in thelevel of phenylalanine ammonia-lyase (PAL), a key enzyme offlavonoid synthesis. PAL levels were higher at low than at hightemperatures and higher in ripe than in unripe apples. In intermittentlight the effects of temperature were similar but levels ofPAL and anthocyanin were lower, particularly in unripe apples.It is concluded that temperature, in conjunction with ripeningand light, is an important factor regulating anthocyanin accumulationand that its effects are mediated by effects on the level ofPAL activity. Key words: Apple, Anthocyanin, Phenylalanine ammonia-lyase 相似文献
65.
SYNOPSIS Cyclic epidermal cellular prohfeiation,with or withoutkeratinization is a vertebrate characteristic Such activityprobably obeys an autonomous rhythm which is legulated throughneuro humoral S)stcms in response to envnonmental (piox imate)stimuliand related to adaptive (ultimate) factors In seeking causeand effect lelationships, however, it becomes apparent thatthe same environmental parameter may be both an ultimate anda pioximate factor, the latter also regulating the rate of lesponseWith regard to molting in homoio'heims, tempeiatuie acts insuch a capacity in many species Peiiodic shedding of the outer epidermis in fish amphibiansand reptiles does not appear to be coirelated with seasonalfactors to the extent that avian and mammalian molts are The evolution of vertebrate molting cycles has amounted to theentraining of inherent epidermal C)cles with seasonal demandsby the organism itself and the environment,these demands actas regulating mechanisms Pieadapted structures such as feathersand hairs function collectively as plumage and pelage in theirvarious roles but separately in their growth and leplacementcycles which, however, are coordinated for maximum functionalefficiency Molting is also synchionized with the seasonal cycleaccording to the availability of energy resources and time tocomplete the essential functions (in addition to molting) Theevolved molting systems as manifested in the gieat variety ofpatterns and types in the vertebrates, may thus be legardedas almost individual responses to selective piessures actingon a umveisil vertebrate chaiacter The basic regulatoiy system involves the neuro hvpophyseal complexwhich contiols target endocrines affecting various functionswhich themselves influence epidermal mitosis and, ultimately,molting 1 he mechanism in its simplest form controls the animalsmetabolism through the thyroid acting independently in a permissivecapacity or synergistically with the adrenal and gonadal hormoneswhich are regulated directly and/or indirectly through negativefeedback 相似文献
66.
67.
68.
The influence of temperature was studied in relation to nitrate reductase activity of creeping bentgrass (Agrostis palustris Huds. cv. ‘Toronto’) a cool season grass and bermudagrass (Cynodon dactylon L. cv. ‘Tifgreen’) a warm season grass. Maximum nitrate reductase activity of both species occurred at 20°C. The nitrate reductase level in bentgrass leaves was reduced when grown at 35°C while bermudagrass leaves were relatively unaffected. The activity per se of the bentgrass enzyme preparation was inhibited rather than synthesis of the enzyme. 相似文献
69.
Synthesis of Substance P 总被引:3,自引:0,他引:3
GEOFFREY W. TREGEAR HUGH D. NIALL JOHN T. POTTSJUN. SUSAN E. LEEMAN MICHAEL M. CHANG 《Nature: New biology》1971,232(29):87-89
SUBSTANCE P has been synthesized by the solid-phase procedure of Merrifield1,2 according to the sequence H-Arg-Pro-LysPro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2 reported in the previous letter. 相似文献
70.
SEVERAL mouse alloantigens described recently are expressed solely or chiefly on lymphoid cells. This indicates that the programme of selective gene action responsible for cyto-differentiation includes instructions for the synthesis of unique cell surface conformations characteristic of particular cell types1, 2. 相似文献