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281.
Brian R. Turner Issa Makhlouf 《Palaeogeography, Palaeoclimatology, Palaeoecology》2005,229(3):230-250
OSL dating of weakly consolidated, root-bound, non-calcareous quartz arenites in northeast Jordan, currently assigned to the Plio-Pleistocene Azraq Formation, suggests a Middle Pleistocene (652 ± 47 ka) age. The sandstones are up to 15.5 m thick and overlain by a 2.5 m thick Holocene gypcrete caprock. Facies and textural analyses suggest that the sandstones are predominantly aeolian in origin, mainly derived from Tertiary sediments exposed close to the depositional site. The sands were transported by the prevailing NW winds and deposited in a broad, relatively flat sand sheet environment. Rhizoliths occur throughout the sandstones, mainly as long, downward tapering, vertical tap roots, rarely branched and with few laterals. Microscopic examination of root cores replaced by carbonate reveals the presence of alveolar fabrics, possible needle fibre calcite, calcified organic filaments of fungal, root vessel and root hair origins, characteristic of low magnesium beta calcretes, typical of humid climates.Morphologically the roots resemble modern shrub-like species typical of desert environments where water availability at the surface and in the subsurface was sufficient to support an effective vegetation cover. Plots of stratigraphic variations in root length, root spacing and root frequency reflect temporal variations in the water table level and precipitation during sand deposition. All three parameters show a similar crude cyclicity consistent with fluctuations in the level of the water table with the most moist phase beneath the predominantly waterlain Holocene gypcrete when trees appeared for the first time. The gypcrete signifies a change to temporary wetter conditions and may mark the boundary between the Pleistocene and Holocene in this area. Although pedogenic horizonation is poorly developed, especially in desert sands, the beta calcretes and rhizocretions typically form within active soil zones. Soils do not form where rainfall is < 150 mm per year, and above 350 mm complete leaching of the edaphon occurs. However, above 300 mm per year shrubs are replaced by grassland, hence rainfall is inferred to have been 150-300 mm per year, much higher than the < 50 mm in the area today. The age of the sandstones may correlate with isotopic event 17, dated at 659 ka, when the Pleistocene climate in Jordan was characterised by arid to semi-arid phases interrupted by shorter more humid phases, when the water table was higher and the precipitation/evaporation balance greater than today. 相似文献
282.
Identification of mega‐environments in Europe and effect of allelic variation at maturity E loci on adaptation of European soybean 下载免费PDF全文
Alena K. Kurasch Volker Hahn Willmar L. Leiser Johann Vollmann Arnold Schori Claude‐Alain Bétrix Bernhard Mayr Johanna Winkler Klemens Mechtler Jonas Aper Aleksandra Sudaric Ivan Pejic Hrvoje Sarcevic Patrice Jeanson Christiane Balko Marco Signor Fabiano Miceli Peter Strijk Hendrik Rietman Eugen Muresanu Vuk Djordjevic Ana Pospišil Giuseppe Barion Peter Weigold Stefan Streng Matthias Krön Tobias Würschum 《Plant, cell & environment》2017,40(5):765-778
Soybean cultivation holds great potential for a sustainable agriculture in Europe, but adaptation remains a central issue. In this large mega‐environment (MEV) study, 75 European cultivars from five early maturity groups (MGs 000–II) were evaluated for maturity‐related traits at 22 locations in 10 countries across Europe. Clustering of the locations based on phenotypic similarity revealed six MEVs in latitudinal direction and suggested several more. Analysis of maturity identified several groups of cultivars with phenotypic similarity that are optimally adapted to the different growing regions in Europe. We identified several haplotypes for the allelic variants at the E1, E2, E3 and E4 genes, with each E haplotype comprising cultivars from different MGs. Cultivars with the same E haplotype can exhibit different flowering and maturity characteristics, suggesting that the genetic control of these traits is more complex and that adaptation involves additional genetic pathways, for example temperature requirement. Taken together, our study allowed the first unified assessment of soybean‐growing regions in Europe and illustrates the strong effect of photoperiod on soybean adaptation and MEV classification, as well as the effects of the E maturity loci for soybean adaptation in Europe. 相似文献
283.
Complexities of gene expression patterns in natural populations of an extremophile fish (Poecilia mexicana,Poeciliidae) 下载免费PDF全文
284.
《Saudi Journal of Biological Sciences》2017,24(5):1045-1050
Honeybees are critically important for the environment and to the economy. However, there are in substantial decline worldwide, leading to serious threat to the stability and yield of food crops. Beekeeping is of pivotal importance, combining the wide economical aspect of honey production and the important ecological services provided by honeybees. In this scenario, the prompt identification of beekeeping areas is strategic, since it maximised productivity and lowered the risks of colony losses. Fuzzy logic is an ideal approach for problem-solving tasks, as it is specifically designed to manage problems with a high degree of uncertainty. This research tested a novel GIS-based approach to assess beekeeping suitability of lands located in Calabria (Southern Italy), without relying to Analytic Hierarchy Process – Multiple Criteria Decision Making (AHP-MCDM), thus avoiding the constraints due to the technique and decision makers’ influences. Furthermore, the data used here were completely retrieved from open access sources, highlighting that our approach is characterized by low costs and can be easily reproduced for a wide arrays of geographical contexts. Notably, the results obtained by our experiments were validated by the actual beekeeping reality. Besides beekeeping, the use of this system could not only be applied in beekeeping land suitability evaluations, but may be successfully extended to other types of land suitability evaluations. 相似文献
285.
Makihiko Ikegami Sander van Hal Jan W. A. van Rheenen Dennis F. Whigham Marinus J. A. Werger 《Plant Ecology》2008,199(1):55-64
If connected ramets are growing in heterogeneous environments, Division of Labour (DoL) among ramets potentially will result
in more efficient sharing of resources and an overall benefit to the plants. As a result of DoL, connected ramets growing
in a heterogeneous environment might achieve more biomass than ramets growing in a homogeneous environment. DoL has been demonstrated
to occur in a few clonal plant species, although most studies simply focussed on biomass allocation, not on actual resource
capturing such as water and nutrient consumption. The model system for our study is one in which two connected ramet groups
of Schoenoplectus americanus were placed into contrasting environments. In one treatment, the connected ramets grew in heterogeneous environments and
in the other treatment, the connected ramets grew in the same (i.e. homogeneous) environment. We manipulated two variables
(light and salinity) in the experiment. We hypothesized that ramets growing in a shaded and fresh water condition in a heterogeneous
environment would use more water than ramets growing in a similar condition but in a homogeneous environment. We further hypothesized
that ramets growing in a light and saline condition in a heterogeneous environment would assimilate less water than ramets
growing in a similar condition but in a homogeneous environment. These hypotheses are based on the assumption that ramets
in a heterogeneous environment would translocate water from ramets growing in a shaded and fresh water condition to ramets
growing in a light and saline water condition. We also hypothesized that ramets growing in heterogeneous environments achieve
larger biomass than ramets in homogeneous environments. Ramets grown in light and saline conditions in heterogeneous environments
allocated more biomass to aboveground parts, had taller shoots, larger Specific Green (leaf) Area and consumed less water
than ramets grown in similar conditions but in a homogeneous environment. Results confirm the hypothesis that connected ramets
in heterogeneous environments are specialised to capture locally abundant resources and share these with connected ramets
growing in other habitats. The result of DoL is that the entire connected ramet system benefits and achieves higher biomass. 相似文献
286.
Do alien plants on Mediterranean islands tend to invade different niches from native species? 总被引:1,自引:0,他引:1
In order to understand invasions, it is important to know how alien species exploit opportunities in unfamiliar ecosystems. For example, are aliens concentrated in niches under-exploited by native communities, or widely distributed across the ecological spectrum? To explore this question, we compared the niches occupied by 394 naturalized alien plants with a representative sample from the native flora of Mediterranean islands. When niche structure was described by a functional group categorization, the distribution of native and alien species was remarkably similar, although “succulent shrubs” and “trees with specialized animal pollination mechanisms” were under-represented in the native species pool. When niche structure was described by Grime’s CSR strategy, the positioning of aliens and natives differed more strongly. Stress-tolerance was much rarer amongst the aliens, and a competitive strategy was more prevalent at the habitat level. This pattern is similar to previous findings in temperate Europe, although in those regions it closely reflects patterns of native diversity. Stressed environments are much more dominant in the Mediterranean. We discuss a number of factors which may contribute to this difference, e.g., competitive and ruderal niches are often associated with anthropogenic habitats, and their high invasibility may be due partly to introduction patterns rather than to a greater efficiency of aliens at exploiting them. Thus far, the reasons for invasion success amongst introduced species have proved difficult to unravel. Despite some differences, our evidence suggests that alien species naturalize across a wide range of niches. Given that their ecologies therefore vary greatly, one may ask why such species should be expected to share predictable traits at all? 相似文献
287.
288.
Responses of soluble amino acids and organic acids to either ambient (36 Pa) or elevated (100 Pa) CO2 treatments were determined using barley primary leaves (Hordeum vulgare L. cv. Brant). Total soluble amino acids were increased 33% by CO2 enrichment 9 days after sowing (DAS), but a decrease relative to the ambient CO2 treatment was observed with increasing leaf age. Marked declines of glutamine and asparagine were observed under CO2 enrichment, both diurnally and with advancing leaf age. Consequently, total soluble amino acids were 59% lower in the elevated compared to the ambient CO2 treatment 17 DAS. It was likely that chlorosis in response to CO2 enrichment negatively impacted soluble amino acid levels in older barley primary leaves. In contrast to the ambient CO2 treatment, glutamine and most other soluble amino acids decreased as much as 60% during the latter half of a 12 h photoperiod in primary leaves of 13-day-old seedlings grown under enhanced CO2. Malate was decreased about 9 percent by CO2 enrichment and citrate and succinate were increased by similar amounts when measured 9 and 13 DAS. Malate accumulation was also decreased about 20% by CO2 enrichment on a diurnal basis. The onset of CO2-dependent leaf yellowing had much less of an effect on organic acids than on soluble amino acids. This above results emphasized the sensitivity of N metabolism to CO2 enrichment in barley. Increased levels of citrate and succinate in response to CO2 enrichment suggested that the tricarboxylic acid cycle was upregulated in barley by CO2 enrichment. In summary, organic and amino acid levels in barley primary leaves were dynamic and were altered by age, diurnally and in response to CO2 enrichment. 相似文献
289.
Marcelo Gleiser Joel Thorarinson Sara Imari Walker 《Origins of life and evolution of the biosphere》2008,38(6):499-508
Most biomolecules occur in mirror, or chiral, images of each other. However, life is homochiral: proteins contain almost exclusively L-amino acids, while only D-sugars appear in RNA and DNA. The mechanism behind this fundamental asymmetry of life remains an open problem. Coupling the spatiotemporal evolution of a general autocatalytic polymerization reaction network to external environmental effects, we show through a detailed statistical analysis that high intensity and long duration events may drive achiral initial conditions towards chirality. We argue that life's homochirality resulted from sequential chiral symmetry breaking triggered by environmental events, thus extending the theory of punctuated equilibrium to the prebiotic realm. Applying our arguments to other potentially life-bearing planetary platforms, we predict that a statistically representative sampling will be racemic on average. 相似文献
290.