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41.
MICHAEL J. SIMMS 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1989,22(1):61-68
Simms, Michael J. 1969 01 15: Columnal ontogeny in articulate crinoids and its implications for their phylogeny. Lethaia , Vol. 22, pp. 61–68. Oslo. ISSN 0024–1164.
Detailed doamentation of columnal ontogeny in several Lower Jurassic isocrinids reveals a number of features which are of phylogenetic significance. Columnal proportions are determined by two largely independent growth vectors. Columnal diameter is primarily a function of cup size at the time of formation, though it may subsequently undergo considerable increase through lateral accretion. Columnal height is largely independent of cup size except for a gradual increase with the growth of the whole animal. Columnal diameter increases at a much greater rate than columnal height and so columnals are relatively lower in large individuals. Heterochronous variation in vertical growth rate or the extent of lateral accretion in columnals may significantly alter their shape. The smallest isocrinid columnals found (0.35 mm diameter) have synarthrial articula. The transformation to a typical pentaradiate symplexy, via a triradiate stage, occurs at a diameter of about 0.75 mm. Synarthrial articula are unknown in millericrinid columnals, which instead have symplectial articula at small diameters (0.45 mm). The presence of synarthrial articula in the stems of juvenile isocrinids, and their absence in millericrinids. supports previous hypotheses concerning derivation of bourgueticrinids from an isocrinid, rather than a millericrinid, ancestor. 相似文献
Detailed doamentation of columnal ontogeny in several Lower Jurassic isocrinids reveals a number of features which are of phylogenetic significance. Columnal proportions are determined by two largely independent growth vectors. Columnal diameter is primarily a function of cup size at the time of formation, though it may subsequently undergo considerable increase through lateral accretion. Columnal height is largely independent of cup size except for a gradual increase with the growth of the whole animal. Columnal diameter increases at a much greater rate than columnal height and so columnals are relatively lower in large individuals. Heterochronous variation in vertical growth rate or the extent of lateral accretion in columnals may significantly alter their shape. The smallest isocrinid columnals found (0.35 mm diameter) have synarthrial articula. The transformation to a typical pentaradiate symplexy, via a triradiate stage, occurs at a diameter of about 0.75 mm. Synarthrial articula are unknown in millericrinid columnals, which instead have symplectial articula at small diameters (0.45 mm). The presence of synarthrial articula in the stems of juvenile isocrinids, and their absence in millericrinids. supports previous hypotheses concerning derivation of bourgueticrinids from an isocrinid, rather than a millericrinid, ancestor. 相似文献
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43.
PHILIPPE GAUCHER PATRICK PAILLAT CLAUDE CHAPPUIS MICHEL SAINT JALME FATEMEH LOTFIKHAH MICHAEL WINK 《Ibis》1996,138(2):273-282
The Houbara Bustard Chlamydotis undulata is a polytypic species with three subspecies classified according size, colour and distribution: C. u. undulata, C. u. fuertaventurae and C. u. macqueenii. A comparative study of the male display behaviour of these three subspecies has shown similarities between C. u. undulata and C. u. fuertaventurae , whereas appreciable differences exist in the visual and auditory aspects of the display between C. u. undulata and C. u. macqueenii. These observations make the current taxonomy of Houbara Bustard questionable, particularly in view of the major importance of the sexual display in bird speciation processes. Furthermore, DNA analysis of the cytochrome b gene indicates the existence of a significant differentiation between the C. u. undulata and C. u. macqueenii populations. These findings indicate the need for a revision of the taxonomy of genus Chlamydotis which should separate the macqueenii and undulata populations at species rank. Until further investigations are completed, C. u. fuertaventurae should be kept as a subspecies of undulata since the courtship display is alike in both populations. 相似文献
44.
45.
MICHAEL SAVARESE 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1994,27(4):301-312
The Orientation of benthic marine organisms may be disturbed by flow-induced forces (i.e. drag and lift) caused by wave and current activity. Drag and lift are partly a function of organism size and shape. Consequently, morphology may affect stability (defined as resistance to reorientation, flipping, or entrainment) both during the life of an organism and after its death. An understanding of drag-and-lift effects is therefore essential to the interpretation of paleoecology and biostratinomic processes. An experimental method for quantifying the relative effects of flow-induced forces is described. These forces are measured during flume experiments using transducers and plaster replicas of fossils. As an illustration of the method's potential for taphonomic research, results from experiments investigating the effects of concavo-convex morphologies of articulate brachiopods are presented. Concave-up and convex-up orientations are commonly used to infer paleohydraulic conditions. Two geniculate brachiopods (Rafinesquina alternata and Leptaena richrnondensis) and three flattened forms (a second morphotype of Rafinesquina altemata, Strophodonta demissa , and Tropidoleptus carinatus) were tested in convex-up and concave-up postures and in three azimuthal orientations (hingeline oriented upstream, hingeline downstream, and hingeline parallel to flow). Concave-up orientations consistently exhibit higher drag than convex-up orientations, and this supports the common observation that valved fossils are typically found convex up in paleoenvironments dominated by traction transport. The presence of geniculation significantly increases drag. Lift is relatively insignificant for all models in most orientations. □ Taphonomy, paleoecology, brachiopods, flow-induced forces, transport. 相似文献
46.
Abstract.
- 1 The effects of resource limitation and the lethal and sublethal effects of a granulosis virus on a lepidopteran host, the Indian meal moth, Plodia interpunctella, were examined.
- 2 The food quality was manipulated by the addition of an inert bulking agent (methyl cellulose) which caused the size, development rate and fecundity of the moths to be reduced.
- 3 The resource quality had no effect on the mortality due to the virus. In contrast, sublethal effects of the virus on pupal weight were more apparent under conditions of resource limitation.
- 4 Considerable variation between the sublethal effects after challenge with different doses of the virus was found. The balance between deleterious sublethal effects of the virus and the selection of more robust individuals by the bioassays is proposed as a mechanism to explain this variation.
- 5 Implications for the dynamics of insect hosts and their pathogens are discussed.
47.
Michael J. Carvan III MICHAEL SANTOSTEFANO STEPHEN SAFE DAVID BUSBEE 《Marine Mammal Science》1994,10(1):52-69
Abstract: An epithelial cell line, Carvan dolphin kidney (CDK), isolated from a prematurely born female bottlenose dolphin, Tursiops truncatus , exhibited growth characteristics not previously reported for cetacean cells in culture. CDK cells were cytokeratin positive and demonstrated a maximum doubling time of 1.31 days, with plating and colony forming efficiencies approaching 100% for the early population doublings. Despite an unusually efficient colony-forming ability and rapid growth, these cells were neither transformed nor immortal, displaying normal contact inhibition, anchorage dependence, and the requirement for high concentrations of fetal bovine serum in the growth medium. CDK cells exhibited age-dependent changes in growth rate, colony-forming efficiency, and cytoplasmic profile, and showed a finite lifespan of about 50 population doublings and a stable 2N = 44 karyotype which correlates with previously reported cytogenetic analyses. Velocity sedimentation analysis showed that CDK cells contained nuclear aryl hydrocarbon receptor (Ah), indicating their potential to be induced for cytochrome P450. These data suggest that CDK cells may have utility as an in vitro toxicological model for evaluating hydrocarbon contaminant effects on Tursiops truncatus , a protected marine mammal. 相似文献
48.
MICHAEL P. KOONCE PAULA M. GRISSOM MARY LYON THERESA POPE J. RICHARD McINTOSH 《The Journal of eukaryotic microbiology》1994,41(6):645-651
Cytoplasmic dynein is a high molecular weight, microtubule-based mechanochemical ATPase that is believed to provide motive force for a number of intracellular motilities, including transport of membrane-bound organelles. Cytoplasmic dynein also localizes to the mitotic spindles of some organisms and to the kinetochore regions of some condensed chromosomes, where it may play an active role in spindle assembly, spindle position, and/or chromosome movement during cell division. Despite active research efforts from a number of laboratories, little detail is yet available about dynein-based cellular activities. This paper describes our efforts to characterize cytoplasmic dynein from Dictyostelium and to use this protist as a molecular genetic factory to probe structure-function relationships of this molecule. 相似文献
49.
The influence of ferricyanide on transmembrane electron transfer,proton secretion, membrane potential, and cytoplasmic pH ofLimnobium stoloniferum (G.F. Mey) Griseb. root cells was investigatedat different external pH HCF III reduction by the roots was accompanied by membrane depolarization,an increase in proton secretion and by alkalinization of thecytoplasm. Change of membrane potential and cytoplasmic pH aswell as transmembrane e transfer was more pronouncedat acid external pH. The rate of proton flux was linearly dependenton the rate of electron transfer. The slope of the relationshipwas around 1, independent of external pH The data are in agreement with the hypothesis that electrontransfer at the plasma membrane is directly coupled to protonsecretion. It is suggested that both e and redox-coupledH+ transport are activated by acid external pH Key words: Plasmalemma redox system, electron transfer, proton transport, pH, membrane potential, Limnobium stoloniferum 相似文献
50.
ELIANA M. M. ROCHA MICHAEL R. HOLLINGDALE BARBARA SINA PAMELA LELAND JOSÉ D. LOPES ANTONIANA U. KRETTLI 《The Journal of eukaryotic microbiology》1993,40(1):61-63
ABSTRACT. Monoclonal antibodies that react with the circumsporozoite protein of the avian malaria Plasmodium gallinaceum sporozoites also reacted with circumsporozoite protein of the rodent malaria Plasmodium berghei. Two types of reactivity were identified: 1) two monoclonal antibodies reacted with P. berghei sporozoite protein by enzyme-linked immunosorbent assay, Western blot and indirect immunofluorescence antibody, 2) six other monoclonal antibodies reacted with P. berghei sporozoites by ELISA and Western blot only. We studied whether these differences could be explained by reactivity in enzyme-linked immunosorbent assay with different P. berghei circumsporozoite peptides. Although all P. gallinaceum monoclonal antibodies reacted with the P. berghei repeats, the first group reacted with a conserved peptide sequence, N1, whereas the second group did not. These results suggest that circumsporozoite proteins from P. gallinaceum and P. berghei share common epitopes. the biological significance of our finding is not yet clear. Indeed, the cross-reactive monoclonal antibodies giving a positive indirect immunofluorescence antibody with the P. berghei sporozoites only caused a borderline effect on the living P. berghei parasites in vitro as measured by inhibition of sporozoite infectivity. 相似文献