全文获取类型
收费全文 | 355篇 |
免费 | 24篇 |
出版年
2013年 | 5篇 |
2011年 | 8篇 |
2010年 | 14篇 |
2009年 | 8篇 |
2008年 | 8篇 |
2007年 | 5篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2003年 | 3篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 6篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1971年 | 9篇 |
1969年 | 2篇 |
1959年 | 7篇 |
1958年 | 12篇 |
1957年 | 15篇 |
1956年 | 9篇 |
1955年 | 11篇 |
1954年 | 16篇 |
1953年 | 9篇 |
1952年 | 19篇 |
1951年 | 14篇 |
1950年 | 19篇 |
1949年 | 7篇 |
1948年 | 5篇 |
1946年 | 3篇 |
排序方式: 共有379条查询结果,搜索用时 15 毫秒
51.
There are few reports of the prevalence of psychotic disorders among isolated
population groups. Where present, variations in prevalence estimates raise
questions about the validity of methods of case ascertainment in such settings.
In a previous population-based survey of the Borana pastoralist community
in Ethiopia using the Composite International Diagnostic Interview, no cases
of schizophrenia were identified. In order to further explore this finding
and investigate how serious mental disorder is conceptualized, we conducted
focus group discussions with key members of the Borana pastoralist community.
Subsequently, focus group participants were used as key informants to identify
cases with possible psychotic disorder, based on their conceptualization.
Cases identified by key informants were interviewed by a trained psychiatrist
using the Schedules for Clinical Assessment in Neuropsychiatry (SCAN), to
confirm presence of disorder. Focus group discussions were subjected to thematic
analysis. The incongruity between local and psychiatric concepts lay mainly
in the fact that key informants described characteristics of marata (“madness”)
in terms of overt behavioural symptoms. Following the focus group discussions,
participants identified eight individuals with schizophrenia and 13 with a
psychotic mood disorder, confirmed through SCAN interview. Studies of psychotic
disorders in such communities are likely to benefit from combining structured
interviews with the key informant method. 相似文献
52.
DIRK KOEDAM E. DAVID MORGAN TÚLIO M. NUNES EDA FLÁVIA L. R. A. PATRICIO VERA L. IMPERATRIZ‐ FONSECA 《Physiological Entomology》2011,36(2):187-193
The specialist digger wasp Trachypus boharti Rubio‐Espina preys exclusively on males of the stingless bee Scaptotrigona postica Latreille 1807, although the hunting attacks involve both male and worker bees of S. postica and members of its own species. To understand the mechanism of prey selection, the cuticular hydrocarbon patterns of workers and males of S. postica are analyzed in detail, and the mandibular secretion of males is examined. The cuticular profiles of males and workers are distinctively different. The major group of cuticular compounds, heptacosene isomers, is twice as abundant in workers as in males. There is no clear distinction between worker and male mandibular secretions. Such a distinct and straightforward caste‐specific difference in cuticular hydrocarbons could function as a recognition cue by which T. boharti distinguishes between workers and males of S. postica. 相似文献
53.
Responses of a C3 and a C4 perennial grass to elevated CO2 and temperature under different water regimes 总被引:1,自引:0,他引:1
H. W. HUNT †‡ E. T. ELLIOTT † J. K. DETLING †§ J. A. MORGAN ¶ D.-X. CHEN† 《Global Change Biology》1996,2(1):35-47
An experiment was carried out to determine the effects of elevated CO2, elevated temperatures, and altered water regimes in native shortgrass steppe. Intact soil cores dominated by Bouteloua gracilis, a C4 perennial grass, or Pascopyrum smithii, a C3 perennial grass, were placed in growth chambers with 350 or 700 μL L?1 atmospheric CO2, and under either normal or elevated temperatures. The normal regime mimicked field patterns of diurnal and seasonal temperatures, and the high-temperature regime was 4 °C warmer. Water was supplied at three different levels in a seasonal pattern similar to that observed in the field. Total biomass after two growing seasons was 19% greater under elevated CO2, with no significant difference between the C3 and C4 grass. The effect of elevated CO2 on biomass was greatest at the intermediate water level. The positive effect of elevated CO2 on shoot biomass was greater at normal temperatures in B. gracilis, and greater at elevated temperatures in P. smithii. Neither root-to-shoot ratio nor production of seed heads was affected by elevated CO2. Plant tissue N and soil inorganic N concentrations were lower under elevated Co2, but no more so in the C3 than the C4 plant. Elevated CO2 appeared to increase plant N limitation, but there was no strong evidence for an increase in N limitation or a decrease in the size of the CO2 effect from the first to the second growing season. Autumn samples of large roots plus crowns, the perennial organs, had 11% greater total N under elevated CO2, in spite of greater N limitation. 相似文献
54.
Historical Patterns of Developmental Integration in Piranhas 总被引:1,自引:1,他引:0
TO test the hypothesis that developmental integration coordinatesevolutionary change through history, we dissect the spatialand temporal integration of ontogenetic allometries of piranhabody form and examine the evolutionary coordination among ontogeneticfeatures by a phylogenetic analysis. Few of our characters provideevidence in support of the hypothesis. In general, we find thatdevelopmental integration is historically labile, being modifiedat virtually every speciation event. Most of the ontogeneticfeatures are dissociated in their phylogenetic changes and evolvein a mosaic fashion. Indeed, developmental integration is solabile that primitively integrated features of ontogeny usuallyevolve subsequently as independent characters. Evolutionarychanges in developmental integration can result in increasedor decreased integration on the ontogenetic time scale. Whenlocalized features are deleted from ontogeny, or when spatiallyintegrated features are gained, the derived ontogenies may bemore integrated in a spatial sense. The end result of phylogeneticdissociations may be a more highly developmentally integratedontogeny. Thus, in the piranhas we studied, we find a historicallycoupled increase in developmental integration caudally and adecrease indevelopmental integration cranially. 相似文献
55.
H. C. BIGGIN N. S. CHEN K. V. ETTINGER J. H. FREMLIN W. D. MORGAN R. NOWOTNY M. J. CHAMBERLAIN 《Nature: New biology》1972,236(67):187-188
THE technique of in vivo activation analysis has been used in the sequential study of whole-body calcium1. Neutrons are produced by bombarding a lithium target with 10 MeV protons from the 1.5 m Nuffield cyclotron. The patients, after being irradiated to a dose of about 1.5 rem, are transferred to a whole-body counter in which the activities induced in calcium, sodium and chlorine are monitored. We briefly describe here a new technique for making in vivo measurements on line by counting during the period of irradiation. In particular we have examined the feasibility of measuring the whole-body nitrogen content and of detecting trace amounts of the toxic element cadmium. Liquid phantoms simulating the conditions in the human body are used for these studies. 相似文献
56.
Photoperiodic time signals during twilight 总被引:5,自引:3,他引:2
J. E. HUGHES § D.C. MORGAN †‡ P.A. LAMBTON † C.R. BLACK H. SMITH† 《Plant, cell & environment》1984,7(4):269-277
Abstract. Although daylength has a major effect on flowering and several other aspects of plant development, the actual environmental time signals for the beginning and the end of day are obscure. An intensive spectroradiometric study was carried out in three contrasting environments: namely, unshaded sites, a mature oak woodland and a sugar beet crop. Spectral photon distributions were obtained describing numerous twilight phases and intervening photoperiods throughout the year. From each, absolute photon fluence rates, photon fluence rate ratios and phytochrome photoequilibria were calculated. Although substantial changes in spectral composition occurred during twilight, they were less capable of providing reliable and accurate time signals than the absolute fluence rate; this was especially apparent beneath the canopies. Thus, spectral changes are unlikely to be valuable in photoperiodic perception. The results are discussed in relation to the possible involvement of the known plant photoreceptors in photoperiodism. 相似文献
57.
KATY MORGAN YVONNE‐MARIE LINTON PRADYA SOMBOON PRASANTA SAIKIA VAS DEV DUONG SOCHEAT CATHERINE WALTON 《Molecular ecology》2010,19(11):2269-2285
Tropical forests have undergone repeated fragmentation and expansion during Pleistocene glacial and interglacial periods, respectively. The effects of this repeated forest fragmentation in driving vicariance in tropical taxa have been well studied. However, relatively little is known about how often this process results in allopatric speciation, since it may be inhibited by recurrent gene flow during repeated secondary contact, or to what extent Pleistocene‐dated speciation results from ecological specialization in the face of gene flow. Here, divergence times and gene flow between three closely‐related mosquito species of the Anopheles dirus species complex endemic to the forests of Southeast Asia, are inferred using coalescent based Bayesian analysis. An Isolation with Migration model is applied to sequences of two mitochondrial and three nuclear genes, and 11 microsatellites. The divergence of An. scanloni has occurred despite unidirectional nuclear gene flow from this species into An. dirus. The inferred asymmetric gene flow may result from the unique evolutionary adaptation of An. scanloni to limestone karst habitat, and therefore the fitness advantage of this species over An. dirus in regions of sympatry. Mitochondrial introgression has led to the complete replacement of An. dirus haplotypes with those of An. baimaii through a recent (~62 kya) selective sweep. Speciation of An. baimaii and An. dirus is inferred to have involved allopatric divergence throughout much of the Pleistocene. Secondary contact and bidirectional gene flow has occurred only within the last 100 000 years, by which time the process of allopatric speciation seems to have been largely completed. 相似文献
58.
The distribution and persistence of iprodione applied by thermal fogging in a glasshouse tomato crop
WALTER M. MORGAN 《The Annals of applied biology》1981,98(1):93-99
Deposits collected on filter paper after application of a ready-to-fog formulation of iprodione and the residues of iprodione washed from tomato leaves after fog and HV spray application were analysed by gas-liquid-chromatography. Relatively heavy deposits were found close to the fogging machine but the deposit became lighter with increasing distance from the machine and in positions lateral to the stream of fog. The deposit collected within the leaf canopy was considerably lighter than that collected above the plants. Residues of iprodione on plants treated with HV sprays were always considerably higher than on fogged plants given a comparable rate of application. After repeated treatment, a substantial build-up of residue was found, but the amount on fogged plants was approximately half that on plants treated with HV sprays. There was a good correlation between the residue found on plants at six positions within the glasshouses and the incidence of infection from artificial inoculations of Botrytis cinerea on petioles. 相似文献
59.
Cotton (Gossypium hirsutum L. cv. Deltapine 15) seedlings were grown in solution culture in which the Mn2+ level was varied. Following an initial period, a series of shifts in manganese nutrition were employed, each lasting 14 days. Appearance was observed and fresh weight, IAA oxidase (IAAO), peroxidase and IAAO inhibitor levels were determined. After the initial 3 weeks of treatment, growth was negatively correlated with IAAO (or peroxidase) activity. All shifts in manganese nutrition resulted in predicted changes in IAAO activity, growth and plant appearance during a second 2-week period of the experiment. Continuously deficient plants exhibited highest leaf abscission and IAA oxidase activity, and lowest growth of all treatments. Plants shifted from deficient to control levels of Mn2+ exhibited a marked decline in IAAO activity, increase in growth and absence of leaf abscission. Plants shifted from borderline deficiency to deficient Mn2+ exhibited a major increase in IAAO activity, reduction in growth and extensive leaf abscission. Control and borderline toxicity plants maintained normal IAAO activity, growth, and appearance. During a final 2-week period, symptom expression was intensified. In particular, the initial borderline deficiency plants shifted to deficient levels of Mn2+ abscised most of those leaves that expanded after the shift in treatment. In addition, shifts of some plants to toxic Mn2+ levels during the third phase of the experiment produced a complete cycle of manipulation. Plants initially deficient in Mn2+ with high IAAO and low growth recovered growth and declined in IAAO when shifted to control Mn2+ and then suffered severe inhibition of growth and toxicity symptoms when shifted to high Mn2+. In all cases changes in enzyme activity, growth, leaf abscission and similar symptoms were most strongly expressed in the youngest tissue or that with the greatest potential for growth during the interval of a particular treatment. Since total growth, IAAO, leaf abscission, internode length and similar symptoms were consistently manipulated in both directions (increase or decrease in intensity or degree) by raising or lowering Mn2+ levels in the plant culture medium, we conclude that there is a causal relationship between IAAO and these responses that involves destruction of auxin. 相似文献
60.
EVANS J. C.; GREVILLE R. W.; MORGAN A. J.; ROWLANDS C. C. 《Journal of Molluscan Studies》1989,55(1):23-29
E.P.R. spectroscopy was used to detect and characterise transitionmetal ions, notably Fe and Mn, and organic free radicals withinthe tissues of the slug Deroceras reticulatum. Tissue Cu wasE.P.R. silent. The calcium complexes found within the varioussoft tissues and the shell were shown to be of the calcite configuration.It was suggested that the presence of the organic free radicalswithin the digestive gland and reproductive organ may be dueto the peroxidation of subcellular membrane lipids. (Received 15 October 1987; accepted 2 January 1988) 相似文献