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排序方式: 共有511条查询结果,搜索用时 15 毫秒
81.
Effects of xylem sap flow on carbon dioxide efflux from stems of birch (Betula pendula Roth) 总被引:2,自引:1,他引:2
The effect of xylem sap flow in stems of mature Betula pendula Roth on radial CO2 efflux was studied from April to October 2001. Temperature-controlled respiration cuvettes allowed measurements of CO2 efflux without interference from temperature gradients between stem surface and sapwood. Variations of sap flow in different stem sectors, and in a given sector at different heights were analysed. Daytime reduction of CO2 efflux caused by sap flow was expressed as the difference between gross and apparent CO2 release. Gross CO2 release was calculated from Arrhenius-equations derived from night-time data records of the same day, which were free from interference by sap flow. In mid-July, daytime reductions of CO2 efflux reached 1.8–3.9 μmol CO2 m−2 g−1 xylem sap transpired. Assuming tree-specific maximum transpiration rates of 30 kg H2O d−1 this is up to 40% of gross CO2 release. In relation to photosynthetic CO2 fixation the endogenous supply of dissolved CO2 to the leaves acccounted for 0.5–3.7%. This study indicates a negative correlation between sap flow velocity and radial CO2 efflux from B. pendula stems. Periods of unbalanced CO2 partial pressures between aqueous and gaseous pathways during increase and decrease of sap flow seem to affect gaseous CO2 release through lenticels. It is concluded that CO2 efflux rates are not simply equivalent to respiration rates because of the interference of aqueous CO2 transport by xylem sap flow in the wood-body of trees. 相似文献
82.
Chlor-alkali plants are known to be major sources of Hg emissions into the air. Therefore level of this metal in their surrounding must be carefully controlled. The aim of this work was to study the impact of the chlor-alkali industry in Brzeg Dolny (SW Poland) on the length of the vegetative short shoots of the pollution tolerant Betula pendula using the concentrations of Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn in the ubiquitous, terrestrial moss Brachythecium rutabulum as the pollution indicator of the environment. This investigation showed up to 14 mg kg−1 elevated concentrations of Hg in mosses from sites the most close (0–500 m) to the chlor-alkali factory. This concentration decreased with increasing distance from the factory. Two and half km away from the factory the Hg concentration falls to values of 0.1–0.2 mg kg−1 being still higher than background concentrations of 0.03–0.04 mg kg−1. Decreasing concentrations of Co, Cr, Fe and Ni were also correlated with increasing distance from the plant. The results indicate that B. rutabulum may be a suitable ecological indicator of metal pollution by chlor-alkali industry. Higher concentration of accumulated metals by this moss corresponds with longer vegetative short shoots of B. pendula. Vegetative short shoots may be used as bioindicators of metal pollution where mosses are absent. This study demonstrates the importance of controlling the emissions of chlor-alkali industry especially if situated in the midst of densely populated areas with potential risks to the inhabitants. 相似文献
83.
FLOR N. RIVERA RAMÓN CISNEROS CÉSAR HERNÁNDEZ-RODRÍGUEZ GERARDO ZÚÑIGA 《Biological journal of the Linnean Society. Linnean Society of London》2008,93(3):475-486
An in vitro evolution model was used to study changes in the genetic diversity of 24 strains of Pichia guilliermondii isolated from the midgut of bark beetles of the genus Dendroctonus . The genetic diversity of P. guilliermondii strains over 400 generations was analysed using multilocus enzyme electrophoresis (MLEE) and random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) markers. Resemblance relationships among strains were observed by cluster analysis. From the MLEE and RAPD markers, it was shown that the effective number of alleles, polymorphism and expected heterozygosity varied over the generations. The average heterozygosity among generations was statistically significant. Both the genetic diversity and the average heterozygosity were statistically significant among generations. The reduction in the population size from 109 to 105 yeast mL−1 associated with each transfer in P. guilliermondii strains and the clonal population structure observed along 400 generations suggest that genetic diversity changes and the observed replacement of genotypes are a consequence of a genetic drift process and not of the reproductive mode. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 475–486. 相似文献
84.
Wickramasinghe M. Bandaranayake 《Phytochemistry》1980,19(2):255-257
The following terpenoids were identified in the oleoresin, bark and timber of Canarium zeylanicum: 3β-hydroxyurs-12-en-11-one, 3β-hydroxyolean-12-en-11-one, olean-12-en-3,11-dione, urs-12-en-3,11-dione, α- and β-amyrin, α- and β-amyrenone, taraxerol, sitosterol, canaric acid, elemene, elemol, α-pinene, α- and β-phellandrene, limonene, terpineol and carvone. 相似文献
85.
Through a combination of spectroscopic techniques (UV, IR, mass spectrometry and NMR) it has been possible to show that strychnozairine, an alkaloid isolated from the root bark of Strychnos variabilis, is N1-acetyl-16-R-formyl-19-oxo-20,21-didehydrostrychnane. 相似文献
86.
O. Hovorka J. Kindl B. Kalinová M. Kníek P. Vrkoová B. Koutek 《Journal of Applied Entomology》2005,129(4):221-226
Abstract: To understand the role of chemical signals involved in Scolytus intricatus (Ratzeburg) (Col., Scolytidae) host colonization, the attractiveness of intact and beetle colonized host material was investigated in the field and in the laboratory. In the field, chemical signals operating at long range were investigated by means of sticky traps. In the laboratory, close-range chemical interactions were investigated with an arena olfactometer. Field experiments showed no differences in the attractiveness between infested and non-infested host material. On the contrary, laboratory experiments revealed higher attractiveness of infested host and beetle-produced frass in comparison with intact host and mechanically produced sawdust respectively. Laboratory data also disclosed the attractiveness of beetle extracts of both sexes. Our data show that: (1) host kairomones play an important role during host colonization, and that (2) S. intricatus does not use a sex-specific secondary attractant system. Differences between results of field and laboratory trials are discussed. 相似文献
87.
An homologous series of acylated flavan-3-ols and procyanidins have been isolated, together with the known procyanidins B-1, B-3 and trimer, from the bark of Salix sieboldiana. Chemical and spectroscopic evidence led to the assignments of their structures as the 3-O-(1,6-dihydroxy-2-cyclohexene-1-carboxylic acid ester) of (+)-catechin and the 1-hydroxy-6-oxo-2-cyclohexene carboxylic acid esters of (+)-catechin and procyanidins B-1, B-3 and trimer. 相似文献
88.
89.
Incorporating variability in simulations of seasonally forced phenology using integral projection models
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Devin W. Goodsman Brian H. Aukema Nate G. McDowell Richard S. Middleton Chonggang Xu 《Ecology and evolution》2018,8(1):162-175
Phenology models are becoming increasingly important tools to accurately predict how climate change will impact the life histories of organisms. We propose a class of integral projection phenology models derived from stochastic individual‐based models of insect development and demography. Our derivation, which is based on the rate summation concept, produces integral projection models that capture the effect of phenotypic rate variability on insect phenology, but which are typically more computationally frugal than equivalent individual‐based phenology models. We demonstrate our approach using a temperature‐dependent model of the demography of the mountain pine beetle (Dendroctonus ponderosae Hopkins), an insect that kills mature pine trees. This work illustrates how a wide range of stochastic phenology models can be reformulated as integral projection models. Due to their computational efficiency, these integral projection models are suitable for deployment in large‐scale simulations, such as studies of altered pest distributions under climate change. 相似文献
90.
A detailed study was made of the bark lectins of the legume tree Maackia amurensis using a combination of protein purification
and cDNA cloning. The lectins, which are the most abundant bark proteins, are a complex mixture of isoforms composed of two
types of subunits of 32 and 37 kDa, respectively. Isolation and characterization of the homotetrameric isoforms indicated
that the 32 kDa subunit exhibits a 100-fold stronger haemagglutinating activity than the 37 kDa subunit. Molecular cloning
confirmed that the two lectin subunits are encoded by different genes. The 32 kDa subunit is apparently encoded by a single
gene, whereas two highly homologous genes encode the 37 kDa subunit. A comparison of the deduced amino acid sequences of the
bark lectin cDNAs and the previously described cDNA encoding the seed haemagglutinin demonstrated that they are encoded by
different genes. Abbreviations: LECMAHb, cDNA clone encoding Maackia amurensis bark haemagglutinin; LECMALb, cDNA clone encoding
Maackia amurensis bark leucoagglutinin; MALb, Maackia amurensis bark leucoagglutinin; MAHb, Maackia amurensis bark haemagglutinin
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献