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1.
J. M. EDMONDS, 1984. Pollen morphology of Solanum L. section Solnnum . The pollen morphology of both dried and fresh, fixed material was examined using SEM. The work confirmed thc spheroidal to sub-prolate shape, the tricolporate nature and the granular surface sculpturing, typical of Solanurn pollen, but failed to demonstrate the occurrence of exine patterns which could bc of practical taxonomic use is differentiating the species belonging to the section Solanurn . Quantification of the exine sculpturing, by means of granule density counts, indicated a possible relationship between this feature and the morpho-genetic diversity of certain species.  相似文献   
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1. A 2 × 2 factorial design was employed to look at the influence of two levels of phosphorus (P; high and low) and two levels of light (high and low) and their interactions, on phytoplankton abundance, elemental tissue composition and community structure in two seasons (April and June) of 2005. 2. A novel feature of the experiment was the creation of high and low P levels by manipulating sediment core conditions in the laboratory. Sediment cores were incubated with their associated overlaying water column from four different sites in Mona Lake, Michigan, under anaerobic or aerobic conditions, respectively. 3. After 24 days, the water overlaying the sediment cores was collected and used as growth media for phytoplankton collected from Mona Lake. Phytoplankton communities were grown in the laboratory in the high or low P water, and subjected to high (250 μmol m?2 s?1) or low (10 μmol m?2 s?1) light for 9 (April) or 14 (June) days. 4. In the April experiment, high P treatments resulted in significantly higher chlorophyll‐a concentrations, significantly lower C : P ratios from two of the four sites, and greater dominance by Scenedesmus at all sites relative to low P treatments. High light generally led to higher chlorophyll‐a concentrations, higher C : P ratios and greater Scenedesmus and Fragilaria biovolume at all sites. A significant interaction was measured between P and light for chlorophyll‐a and Scenedesmus biovolume, suggesting the influence of P was more apparent at high light than at low light levels. 5. In the June experiment, high P increased ash‐free dry mass (AFDM), lowered C : P ratios and resulted in increased Pediastrum biovolume. High light levels led to greater chlorophyll‐a concentrations, AFDM and C : P ratios, as well as increased biovolumes of Scendesmus, Pediastrum and Fragilaria. A significant interaction was found between P and light for all three taxa, as the positive influence of P was more pronounced at high light levels. 6. The results of our study demonstrate that sediment‐derived P stimulates phytoplankton growth, but that its effect on phytoplankton dynamics is modulated by other factors, such as light.  相似文献   
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The structure of the cells forming the primitive streak was examined by SEM in a series of embryos at Hamburger and Hamilton's stages 2–5. Specimens were prepared by stripping the endoderm from fresh embryos in New Culture and by fracturing whole fixed embryos along and at right angles to the primitive streak. At all stages of examination the SEM appearance of cells within the primitive streak was quite different from that of ectodermal, endodermal or mesodermal cells away from the streak. Streak cells were closely packed, lay with their long axes directed from ectoderm to endoderm and possessed many flat leaf-like processes. By contrast the ectoderm formed a columnar epithelium, the endoderm a flat epithelium and the mesoderm was a layer of loosely arranged cells with long, thin processes.
Within the streak SEM did not show any differences between cells that could identify them specifically as future endoderm or mesoderm cells. It was concluded that during gastrulation all the cells migrating through the primitive streak have the same appearance regardless of their eventual destination in the embryo. This structure may be attributable to the type of movement made by cells during invagination.  相似文献   
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1. Insect oral secretions are important for the induction of a number of plant responses, but the relative role of mechanical damage in the induction of these responses is often not well understood. Damage from the frugivore Heliothis subflexa, a specialist on Physalis species, causes herbivore‐induced fruit abscission. In this field study, we examined the separate and combined effects of mechanical damage and H. subflexa oral secretions on Physalis fruit abscission. 2. To determine the relative role of mechanical and chemical factors, the following treatments were administered to fruit: (1) three levels of mechanical damage, (2) natural herbivore damage by control larvae and by larvae surgically treated to inhibit saliva secretion, and (3) injection of H.subflexa oral secretions and a water control. Abscission of mechanically damaged fruit with and without the addition of oral secretions was also compared. 3. Mechanical damage was sufficient to cause fruit abscission, and the addition of oral secretions to mechanically damaged fruit did not cause an increase in fruit abscission. Normal caterpillars and those treated to inhibit saliva secretion caused similar abscission rates. 4. Though most studies examining the effects of insect oral secretions on induced plant responses find these chemical stimuli to be important or essential, the results of the present study showed that oral secretions are not necessary for fruit abscission. Future work is needed to determine the relative importance of mechanical damage in herbivore‐induced plant responses in other systems.  相似文献   
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ABSTRACT Effects of silvicultural activities on birds are of increasing interest because of documented national declines in breeding bird populations for some species and the potential that these declines are in part due to changes in forest habitat. Silviculturally induced disturbances have been advocated as a means to achieve suitable forest conditions for priority wildlife species in bottomland hardwood forests. We evaluated how silvicultural activities on conservation lands in bottomland hardwood forests of Louisiana, USA, influenced species-specific densities of breeding birds. Our data were from independent studies, which used standardized point-count surveys for breeding birds in 124 bottomland hardwood forest stands on 12 management areas. We used Program DISTANCE 5.0, Release 2.0 (Thomas et al. 2006) to estimate density for 43 species with >50 detections. For 36 of those species we compared density estimates among harvest regimes (individual selection, group selection, extensive harvest, and no harvest). We observed 10 species with similar densities in those harvest regimes compared with densities in stands not harvested. However, we observed 10 species that were negatively impacted by harvest with greater densities in stands not harvested, 9 species with greater densities in individual selection stands, 4 species with greater densities in group selection stands, and 4 species with greater densities in stands receiving an extensive harvest (e.g., >40% canopy removal). Differences in intensity of harvest influenced densities of breeding birds. Moreover, community-wide avian conservation values of stands subjected to individual and group selection, and stands not harvested, were similar to each other and greater than that of stands subjected to extensive harvest that removed >40% canopy cover. These results have implications for managers estimating breeding bird populations, in addition to predicting changes in bird communities as a result of prescribed and future forest management practices.  相似文献   
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Tests with rainbow trout in mixtures of ammonium chloride with copper sulphate and of phenol with zinc sulphate have shown that the threshold of toxic concentration for a 50% mortality occurs in solutions for which a value of I is obtained by summing the concentrations of the individual poisons expressed as fractions of their individual threshold concentrations. With ammonia-copper mixtures this method of predicting the threshold concentration becomes progressively less adequate as lower percentage mortalities are considered.  相似文献   
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Abstract. 1. The hypotheses that genetic variation in host plant resistance of the arroyo willow affected leaf folder ( Phyllocolpa sp.) (Hymenoptera: Tenthredinidae) density and that genetic variation in shoot length and leaf length was correlated with resistance were tested.
2. Willows grown in pots and exposed to ovipojsition by the leaf folding sawfly in cages had significantly different densities among clones, indicating variation in resistance caused by genetic differences among conspecific host plants.
3. There was a general correspondence between leaf folder density on potted cuttings and on the plants in the field that were the sources of cuttings.
4. In behavioural choice experiments, susceptible clones (with highest leaf fold densities) had the highest oviposition activity of female leaf folders compared to clones that were resistant to the leaf folder.
5. Clones differed significantly in shoot length and leaf length among clones grown in pots, among clones in the field, and between shoots with galls and shoots without galls on clones in the field.
6. Leaf folder density was significantly positively correlated with mean shoot length on field clones in 1985 and 1986, but was not correlated with leaf length, although leaf length and shoot length were correlated.
7. Leaf length variation among willow clones accounted for a significant portion of the variation in resistance of potted willows, but shoot length was unimportant.  相似文献   
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Microsatellite data are widely used to test ecological and evolutionary hypotheses in wild populations. In this paper, we consider three typical sources of scoring errors capable of biasing biological conclusions: stuttering, large‐allele dropout and null alleles. We describe methods to detect errors and propose conventions to mitigate scoring errors and report error rates in studies of wild populations. Finally, we discuss potential bias in ecological or evolutionary conclusions based on data sets containing these scoring errors.  相似文献   
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