全文获取类型
收费全文 | 169篇 |
免费 | 0篇 |
出版年
2014年 | 4篇 |
2013年 | 5篇 |
2010年 | 3篇 |
2009年 | 3篇 |
2007年 | 6篇 |
2006年 | 3篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2001年 | 5篇 |
1999年 | 4篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1970年 | 4篇 |
1969年 | 2篇 |
1968年 | 6篇 |
1967年 | 5篇 |
1958年 | 4篇 |
1956年 | 3篇 |
1955年 | 2篇 |
1953年 | 2篇 |
1948年 | 1篇 |
1937年 | 1篇 |
1934年 | 1篇 |
1930年 | 1篇 |
1927年 | 1篇 |
1922年 | 1篇 |
1921年 | 1篇 |
1916年 | 1篇 |
1907年 | 1篇 |
1863年 | 1篇 |
排序方式: 共有169条查询结果,搜索用时 15 毫秒
1.
YONG-JIANG ZHANG FREDERICK C. MEINZER GUANG-YOU HAO FABIAN G. SCHOLZ SANDRA J. BUCCI FREDERICO S. C. TAKAHASHI RANDOL VILLALOBOS-VEGA JUAN P. GIRALDO KUN-FANG CAO WILLIAM A. HOFFMANN & GUILLERMO GOLDSTEIN 《Plant, cell & environment》2009,32(10):1456-1466
Size-related changes in hydraulic architecture, carbon allocation and gas exchange of Sclerolobium paniculatum (Leguminosae), a dominant tree species in Neotropical savannas of central Brazil (Cerrado), were investigated to assess their potential role in the dieback of tall individuals. Trees greater than ∼6-m-tall exhibited more branch damage, larger numbers of dead individuals, higher wood density, greater leaf mass per area, lower leaf area to sapwood area ratio (LA/SA), lower stomatal conductance and lower net CO2 assimilation than small trees. Stem-specific hydraulic conductivity decreased, while leaf-specific hydraulic conductivity remained nearly constant, with increasing tree size because of lower LA/SA in larger trees. Leaves were substantially more vulnerable to embolism than stems. Large trees had lower maximum leaf hydraulic conductance ( K leaf ) than small trees and all tree sizes exhibited lower K leaf at midday than at dawn. These size-related adjustments in hydraulic architecture and carbon allocation apparently incurred a large physiological cost: large trees received a lower return in carbon gain from their investment in stem and leaf biomass compared with small trees. Additionally, large trees may experience more severe water deficits in dry years due to lower capacity for buffering the effects of hydraulic path-length and soil water deficits. 相似文献
2.
LARSON KIRK D.; SCHAFFER BRUCE; DAVIES FREDERICK S. 《Journal of experimental botany》1993,44(3):665-671
A system was developed to test the effects of floodwater O2concentration on ethylene evolution and stem lenticel hypertrophy,and the effects of exogenous ethylene on stem lenticel hypertrophyin mango (Mangifera indica L.) trees. Dissolved O2 concentrationsof 17x109 m3 m3 generally resulted in hypertrophyof stem lenticels within about 6 d of flooding, whereas floodwaterO2 concentrations of 1315 x 109 m3 m3 delayedhypertrophy until about day 9. After 14d of flooding, therewere more than twice the number of hypertrophied lenticels pertree with floodwater O2 concentrations of 17 x 109m3 m3 than with floodwater O2 concentrations of 15 x109 m3 m3. Ethylene evolution from stem tissueimmediately above the floodline increased 4- to 8-fold in treesexposed to floodwater O2 concentrations of 12 x 109m3 m3, increased 2-fold for trees exposed to floodwaterO2 concentrations of 67 x 109 m3 m3, butremained constant with floodwater O2 concentrations of 1315x 109 m3 m3. Plants maintained in highly oxygenatedfloodwater (1315 x 109 m3 m3), and givenexogenous ethylene developed many hypertrophied lenticels, whereasplants in highly oxygenated water and not given ethylene developedfewer or nohypertrophied lenticels. These data suggest thatethylene plays a role in promotion of stem lenticel hypertrophyin flooded mango trees, and that floodwater dissolved oxygenconcentration can regulate stem lenticel hypertrophy and ethyleneevolution in this species. Key words: Flooding, hypoxia, hypertrophic cell swelling 相似文献
3.
HENRIK GLENNER MARKJ. GRYGIER JENS T. HØEG PETER G.JENSEN FREDERICK R. SCHRAM F.L.S. 《Zoological Journal of the Linnean Society》1995,114(4):365-404
We present a cladistic analysis of the Cirripedia Thoracica using morphological characters and the Acrothoracica and Ascothoracida as outgroups. The list of characters comprised 32 shell and soft body features. The operational taxonomic units (OTUs) comprised 26 well-studied fossil and extant taxa, principally genera, since uncertainty about monophyly exists for most higher ranking taxonomic units. Parsimony analyses using PAUP 3.1.1 and Hennig86 produced 189 trees of assured minimal length. We also examined character evolution in the consensus trees using MacClade and Clados. The monophyly of the Balanomorpha and the Verrucomorpha sensu stricto is confirmed, and all trees featured a sister group relationship between the ‘living fossil Neoverruca and me Brachylepadomorpha. In the consensus trees the sequential progression of ‘pedunculate‘sister groups up to a node containing Neolepas also conforms to current views, but certain well-established taxa based solely on plesiomorphies stand out as paraphyletic, such as Pedunculata (= Lepadomorpha); Eolepadinae, Scalpellomorpha and Chthamaloidea. The 189 trees differed principally in the position of shell-less pedunculates, Neoverruca, the scalpelloid Capitulum, and the interrelationships within the Balanomorpha, although the 50% majority rule consensus tree almost fully resolved the latter. A monophyletic Sessilia comprising both Verrucomorpha and Balanomorpha appeared among the shortest trees, but not in the consensus. A tree with a monophyletic Verrucomorpha including Neoverruca had a tree length two steps longer than the consensus trees. Deletion of all extinct OTUs produced a radically different tree, which highlights the importance of fossils in estimating cirripede phylogeny. Mapping of our character set onto a manually constructed cladogram reflecting die most recent scenario of cirripede evolution resulted in a tree length five steps longer than any of our shortest trees. Our analysis reveals that several key questions in cirripede phylogeny remain unsolved, notably the position of shell-less forms and the transition from ‘pedunculate‘to ‘sessile‘barnacles. The inclusion of more fossil species at this point in our understanding of cirripede phylogeny will only result in even greater levels of uncertainty. When constructing the character list we also identified numerous uncertainties in the homology of traits commonly used in discussing cirripede evolution. Our study highlights larval ultrastructure, detailed studies of early ontogeny, and molecular data as the most promising areas for future research. 相似文献
4.
Genotypic, Developmental and Drought-Induced Differences in Root Hydraulic Conductance of Contrasting Sugarcane Cultivars 总被引:3,自引:0,他引:3
Hydraulic properties of entire root systems and isolated rootsof three contrasting sugarcane clones were evaluated using transpiration-induceddifferences in hydrostatic pressure across intact root systems,root pressure-generated xylem sap exudation, and pressure-fluxrelationships. Regardless of the measurement technique employed,the clones were ranked in the same order on the basis of theirleaf areaspecific total root system hydraulic conductance(Croot). All methods employed detected large developmental changesin Grootroot with maximum values occurring in plants with approximately02 m2 total leaf area. Genotypic ranking according to Groot,was reflected as a similar ranking according to root length-specifichydraulic conductance (L) of individual excised roots. Genotypicdifferences in Groot and L were consistent with anatomical characteristicsobserved in individual roots. Patterns of Groot, during soildrying and following re-irrigation suggested that the declinein Groot, observed during soil drying occurred within the rootsrather than at the soilroot interface and may have beencaused in part by xylem cavitation in the roots. Key words: Root hydraulic conductance, Saccharum spp, transpiration, root pressure, pressure-flux 相似文献
5.
1. The predatory caddisfly Rhyacophila vao Milne (Rhyacophilidae) displayed a 2-year, semivoltine life cycle in a small, spring-fed stream in southern Alberta, Canada. Three overlapping cohorts were identified throughout the 2-year sampling program, with five larval instars recognized. Larvae overwintered in instars I —ELI, developed to instar IV by summer and instar V by autumn. The second winter was spent in instar V, Pupation occurred from late May to August and did not commence until stream temperature exceeded 3°C. Adults were collected from mid-June to early September. 2. Larvae displayed a diphasic growth pattern: Phase I, a positive, non-linear growth rate for instars I-IV; Phase II, a constant growth rate during instar V. Phase I coincided with increasing stream temperatures in late winter and spring, where mean instantaneous growth rates (maximum of 2.78% dry wt day?1) were significantly correlated with stream temperatures. Although the duration of Phase II spanned a temperature range similar to that in Phase I, the instantaneous growth rate remained temperature-independent at 0.87% dry wt day?1. 3. Larvae exhibited a type III survivorship curve (i.e. an exponential decrease on an arithmetic scale), with the finite rate of mortality averaging 0.80% larvae day?1. 4. Cohort 1 (later part of 1983 year class) displayed lower total production compared with the equivalent growth phase in the 1984 year class (Cohort 2). In contrast, production of the non-linear and linear growth phases of Cohort 2 was similar. Periods of similar growth characteristics for Cohorts 1 and 2 had comparable P/B ratios for both the unadjusted and time-adjusted annual estimates, although higher ratios were observed for the non-linear growth phase of Cohort 2. Total cohort production (linear + non-linear growth phases) could only be calculated for Cohort 2, and was 870.2 ± 1011.4 mg dry wt m?2. The corresponding cohort P/B ratio was 5.01 and the adjusted annual P/B, 3.01. 5. Annual larval production (±SE) for the first and second years of the study was similar (Year 1, 480.0 ± 387.5mg dry wt m?2; Year 2, 526.9 ± 967.5mg dry wt m?2) as were unadjusted and annual P/B ratios. 相似文献
6.
Axenic crown gall tumor callus (from Vinca rosea L.) which is known to synthesize its own auxin is able to convert exogenous 14C-indole or tryptamine to indoleacetic acid [5.4 and 10 × 10−6μmol × h−1× (g fr wt)−1 respectively], but little or no 3H-tryptophan is converted [less than 6.4 × 10−8×μmol × h−1× (g fr wt)−1]. 相似文献
7.
FREDERICK C. COLLEY 《The Journal of eukaryotic microbiology》1967,14(2):217-220
SYNOPSIS. An electron microscope study of sporozoites of Eimeria nieschulzi Dieben, 1924 revealed that they have a pellicle which is thickened at the anterior end to form 2 polar rings. Radiating posteriorly from the rings, directly beneath the pellicle, are approximately 25 microtubules which may aid in support and locomotion of the sporozoite. Within the polar ring is a dense conoid. Numerous toxonemes extend posteriorly from the area of the conoid. Two paranuclear bodies are present and some toxonemes are closely associated with the anterior body. Numerous ribosomes, bodies containing granular material, and osmiophilic vesicle bounded bodies are also present. Each sporozoite has a single nucleus with a diffuse karyosome and distinct nuclear double membrane. 相似文献
8.
YONG‐JIANG ZHANG FREDERICK C. MEINZER JIN‐HUA QI GUILLERMO GOLDSTEIN KUN‐FANG CAO 《Plant, cell & environment》2013,36(1):149-158
Midday depressions in stomatal conductance (gs) and photosynthesis are common in plants. The aim of this study was to understand the hydraulic determinants of midday gs, the coordination between leaf and stem hydraulics and whether regulation of midday gs differed between deciduous and evergreen broadleaf tree species in a subtropical cloud forest of Southwest (SW) China. We investigated leaf and stem hydraulics, midday leaf and stem water potentials, as well as midday gs of co‐occurring deciduous and evergreen tree species. Midday gs was correlated positively with midday stem water potential across both groups of species, but not with midday leaf water potential. Species with higher stem hydraulic conductivity and greater daily reliance on stem hydraulic capacitance were able to maintain higher stem water potential and higher gs at midday. Deciduous species exhibited significantly higher stem hydraulic conductivity, greater reliance on stem capacitance, higher stem water potential and gs at midday than evergreen species. Our results suggest that midday gs is more associated with midday stem than with leaf water status, and that the functional significance of stomatal regulation in these broadleaf tree species is probably for preventing stem xylem dysfunction. 相似文献
9.
FREDERICK C. GAMST 《American anthropologist》1977,79(4):902-902
10.
FREDERICK C. PAGE 《The Journal of eukaryotic microbiology》1967,14(4):709-724
SYNOPSIS. Ten strains of Acanthamoeba from freshwater habitats were isolated in clonal cultures. Studies were made of trophic structure, nuclear division, cyst structure, some aspects of cytochemistry, and other characteristics. One strain was identified as A. castellanii (Douglas, 1930), one as A. astronyxis (Ray and Hayes, 1954), and 8 as A. polyphaga (Puschkarew, 1913). Strains of Acanthamoeba isolated by other workers were also examined comparatively.
The pattern of nuclear division in all strains resembled that in metazoan cells, with the exception that centrioles were never found. Trophic amoebae had a PAS-positive surface outline. Cyst walls were strongly PAS-positive and also gave a positive test for cellulose with zinc chloroiodide.
The genus Acanthamoeba Volkonsky, 1931 is re-defined, being distinguished from Hartmannella Alexeieff, 1912, emend. Volkonsky, chiefly by the formation of tapering, hyaline pseudopods (acanthopodia) and by a cyst made up of an ectocyst and a polyhedral or stellate endocyst, with excystment by removal of opercula. Other characteristics found in all strains include a distinctive food cup, the presence of many small refractile globules in the cytoplasm of trophic amoebae, and a cyst wall containing cellulose. The degree of spindle convergence, employed by Volkonsky as a generic criterion, was unusable.
Differential diagnoses based principally on cyst structure are offered for A. castellanii, A. astronyxis , and A. polyphaga. The strain previously called Mayorella palestinensis Reich, 1933 is a distinct species of Acanthamoeba. 相似文献
The pattern of nuclear division in all strains resembled that in metazoan cells, with the exception that centrioles were never found. Trophic amoebae had a PAS-positive surface outline. Cyst walls were strongly PAS-positive and also gave a positive test for cellulose with zinc chloroiodide.
The genus Acanthamoeba Volkonsky, 1931 is re-defined, being distinguished from Hartmannella Alexeieff, 1912, emend. Volkonsky, chiefly by the formation of tapering, hyaline pseudopods (acanthopodia) and by a cyst made up of an ectocyst and a polyhedral or stellate endocyst, with excystment by removal of opercula. Other characteristics found in all strains include a distinctive food cup, the presence of many small refractile globules in the cytoplasm of trophic amoebae, and a cyst wall containing cellulose. The degree of spindle convergence, employed by Volkonsky as a generic criterion, was unusable.
Differential diagnoses based principally on cyst structure are offered for A. castellanii, A. astronyxis , and A. polyphaga. The strain previously called Mayorella palestinensis Reich, 1933 is a distinct species of Acanthamoeba. 相似文献