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71.
Abstract: Rögla is the northernmost locality yielding Mesozoic plant fossils in Scania, southern Sweden, and is one of the northernmost Rhaetian assemblages in Europe. The assemblage consists of over 500 specimens collected 50–60 years ago, of which 139 yielded identifiable plant remains referable to 15 plant species; another 19 specimens are tentatively assigned to four species because of their fragmentary preservation. The flora includes sphenophytes, ferns, cycads, bennettitaleans, seed ferns of uncertain alliance, conifers and some leaf remains that are tentatively assigned to ginkgophytes based on their epidermal anatomy. The species‐level composition of the assemblage is consistent with a Rhaetian age and is similar to well‐known floras from nearby Höganäs and Bjuv, except for the absence of cycads belonging to Nilssonia, which are very common in most other Scanian floras. The fossil assemblage is interpreted to derive from multi‐storey vegetation occupying moist habitats on a coastal plain. Strong affinities are evident with the coeval floras of Jameson Land, Greenland, reinforcing the concept of a distinctive North Atlantic floristic sub‐province at the close of the Triassic. 相似文献
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LARS E. HOLMER CHRISTIAN B. SKOVSTED CECILIA LARSSON GLENN A. BROCK ZHIFEI ZHANG 《Palaeontology》2011,54(2):235-239
Abstract: Brachiopods are marine Lophotrochozoa whose soft parts are enclosed in a bivalved shell. Although brachiopods are represented by a rich record from the Early Cambrian to the present, the origin of their bivalved body plan remains controversial. The Early Cambrian organophosphatic tommotiids Micrina and Paterimitra from Australia have been proposed as stem brachiopods. Here, we describe their earliest ontogeny, indicating that tommotiids possessed bivalved planktotrophic larvae. The curious combinations of characters in Micrina and Paterimitra indicate that they may belong to the stems of the Linguliformea and Rhynchonelliformea, respectively. The bivalved shell of adult living brachiopods may represent a plesiomorphic character retained from planktic tommotiid larvae; the crown group body plan of the Brachiopoda may have evolved through the paedomorphic retention of a bivalved larval state. 相似文献
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LISELOTTE W. ANDERSEN CHRISTIAN LYDERSEN ANNE K. FRIE AQQALU ROSING‐ASVID ERLINGUR HAUKSSON KIT M. KOVACS 《Biological journal of the Linnean Society. Linnean Society of London》2011,102(2):420-439
It is crucial to examine the genetic diversity and structure of small, isolated populations, especially those at the edge of their distribution range, because they are vulnerable to stochastic processes if genetic diversity is low and the isolation level is high, and because such populations provide insight into the consequences of population declines in a broader conservation context. The harbour seal (Phoca vitulina) population in Svalbard is the world's northernmost P. vitulina population. Nothing is known about the genetic diversity, distinctiveness, or origin of this small, marginalized mammalian population. Thus, the present study investigated its genetic status in the context of nearby P. vitulina in Iceland, south‐east Greenland, and northern Norway: this species is depleted/threatened in all of these regions. A total of 174 samples distributed between the four locations were analysed using 15 polymorphic microsatellites and variation in the displacement loop region (D‐loop). Each of the four locations was a genetically distinct population. The Svalbard population was highly genetically distinct, had reduced genetic diversity, received limited gene flow, had a rather low effective population size, and showed an indication of having experienced a bottleneck resulting from a recent population decline. The significant heterozygote excess observed in the Svalbard sample might be attributed to the low effective population size, which could initiate future population inbreeding effects. This phenomenon has not been reported earlier from other P. vitulina populations, but if the Svalbard population is experiencing inbreeding, this could reduce its resilience to climate change, disease outbreaks, or other perturbations. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 420–439. 相似文献
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Does the decline of gastropods in deep water herald ecosystem change in Lakes Malawi and Tanganyika?
BERT VAN BOCXLAER ROLAND SCHULTHEIß PIERRE‐DENIS PLISNIER CHRISTIAN ALBRECHT 《Freshwater Biology》2012,57(8):1733-1744
1. Ancient, deep lakes have traditionally been considered as stable, ecological islands, well buffered from environmental change because of their great depth. However, they are not immune to anthropogenic and climatic stress. Ecosystems of the permanently stratified warm Lakes Malawi and Tanganyika in the Great East African Rift are particularly delicate. Their stratification regime has historically limited the distribution of benthic biota to a ‘bathtub ring of biodiversity’, namely substrata in the upper, oxygenated water layer. 2. We use historical data on the endemic deep‐water molluscs of these lakes to assess present‐day stress on their benthic ecosystems. During the 20th century, these molluscs have probably decreased in abundance and migrated to shallower water. 3. These apparent trends have a significance beyond species‐based conservation, foremost because deep‐water organisms heavily rely on the position and temporal stability of the oxycline and therefore provide an early warning of large‐scale changes in the distribution of dissolved oxygen. Oxygen demands have increased in the East African Great Lakes over the last century whereas ventilation of deep water has remained the same or declined. 4. The combination of these factors is resulting in a narrowing of the ring of biodiversity and a changed nutrient flux through this ring. Reduction in the habitat available inevitably puts biota at risk, whereas changes in nutrient flux may cause shifts in the entire ecosystem or the collapse of parts of it. 5. Considering the socioeconomic value of these lakes and the potentially grave implications for their faunal biodiversity and entire ecosystems, existing evidence of faunal decline, especially in taxa that depend strongly on the stratification regime, is of great concern. Moreover, because the factors responsible are widespread and include surface‐water warming, increased run‐off and eutrophication, respiration stress may also develop in other tropical and subtropical lakes. 相似文献
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ANNE TOTET LEILA MELIANI; PHILIPPE LACUBE; JEAN CLAUDE PAUTARD; CHRISTIAN RACCURT PATRICIA ROUX GILLES NEVEZ 《The Journal of eukaryotic microbiology》2003,50(S1):668-669
ABSTRACT. We tested a real-time PCR assay targeting the Pneumocystis jirovecii mitochondria1 large subunit rRNA gene on 240 archival nasopharyngeal aspirates from non-immunosuppressed infants. The sensitivity of this assay appeared close to that of a conventional nested-PCR assay targeting the same locus. Because of its one-step procedure, and its sensitivity and rapidity, the real-time PCR assay is particularly suitable for screening individuals parasitized by P. jirovecii within large populations. 相似文献
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