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11.
Summary In comparison to cassava grown in monoculture the root infection of cassava with vesicular-arbuscular mycorrhiza was increased by crop rotation with grain legumes in the field. This was also found when cassava was intercropped with legumes and fertilized. A possible specificity of mycorrhizal fungi to increase the yield of one species more than the other when grown in association, is discussed. 相似文献
12.
Abstract The growth, biomass δ13C values, and ability to accumulate titratable acidity at night were compared in eight environmental treatments for Cremnophila linguifolia, Sedum greggii, and their F1 hybrid. In the phytotron, differences in treatment daylength, day/night temperature and water availability were all found to have effects on total plant dry weight, nocturnal accumulation of titratable acidity and biomass δ13C value of at least some of the genotypes. However, there were differences between the genotypes both in the magnitude and direction of response of the phenotypic properties to the treatment variables. The phytotron δ13C values ranged from -12.9 to -19.2‰ for C. linguifolia, from -22.2 to -33.4‰ for S. greggii, and from -19.2 to -24.9‰ for the hybrid. After with-holding water for 76 h both C. linguifolia and the hybrid had midday Ψleaf values of -0.23 MPa; however, S. greggii had a value of -1.05 MPa. In contrast to past observations of other species, the daily watered plants of C. linguifolia had less negative δ13C values than did the plants watered only weekly. 相似文献
13.
14.
Summary To explain the decline of Hippopha? scrub in the vegetation succession in the dunes of The Netherlands, the growth and nodulation
of Hippopha? plants grown in pots, using soil from an early stage (site AH) and a post-optimum stage (site HP), were investigated.
In HP-soil nodulation, yield, and the nitrogen and phosphorus content of test plants were always lower and the number of necrotic
nodules and the dry matter content were always higher than in AH-soil, even after inoculation with crushed nodules and the
addition of a nutrient solution. Plants in HP-soil also had darker roots, less root hairs, a higher number of short lateral
roots and a higher percentage of dead roots than those in AH-soil. These characteristics of adverse growth conditions disappeared
upon ignition or gamma-irradiation of HP-soil.
Possible explanations of these results are discussed. The degeneration of Hippopha? scrub cannot be ascribed to the age of
the plants, the absence of sufficient infective endophyte particles or to abiotic factors such as unfavourable physical (particle
size) or chemical soil conditions but is caused by biotic factors. No indications were obtained that plant-pathogenic fungi
and bacteria are involved. HP-soil in contrast to AH-soil, however, contained large numbers of the nematodeLongidorus sp., a species known to cause root deformations. The conclusion was that this nematode is one of the biotic factors involved
in the degeneration of the Hippopha? scrub. This degeneration is due to a restriction of the root system resulting in a low
phosphate uptake, a low nodulation capacity and, as a consequence, a low nitrogen content. The results demonstrate that biotic
soil factors are important in influencing succession in higher plant communities. 相似文献
15.
Summary The VA-infected wheat varieties showed an increase of total (Lozano var.) and reducing (Lozano and Pane vars.) sugars in their root extracts. However, no clear relationship between sugar concentration in the root and VA mycorrhizal infection level could be established.In addition, the VA mycorrhizal hosts sorghum, alfalfa, sunflower and maize, and non-host radish and cabbage plants were tested for sugar content in their root extracts after fifteen days of growth. Sugars present in the root extracts of these plants did not seem to be a decisive factor in plant susceptibility to VA infection. 相似文献
16.
Horizontal primary roots of Zea mays L. were photographed during the course of their gravireaction and during a preceding growth period in the vertical orientation. The displacement, by root elongation, of marker particles on the root surface was recorded. The particle-displacement rates were used to estimate the distribution of elemental elongation rates along opposite sides of the growing root apex. In the temperature range 21–25°C there was a stimulation of local elongation rates along the upper side of a gravireacting root and a reduction (and sometimes a cessation) of elongation along the lower side. Elemental elongation rates have been related to the development of root curvature, and the magnitude of the differential growth between upper and lower sides required for a particular rate of bending has also been estimated. The results complement, and are compatible with, findings relating to the distribution of certain endogenous growth regulators believed to participate in the gravireaction.Abbreviation RELEL
relative elemental rate of elongation 相似文献
17.
Summary A rapid exchange procedure using ammonium acetate as an extractant was developed for measurement of cation exchange capacity
(CEC) of plant roots. The CEC values obtained with 1∶100 and 1∶200 root/solution ratios were almost equal, though the values
increased with length of the time of immersion in both the root/solution ratios. The method gave higher CEC values with fresh
roots as compared to dried roots. However, dried milled and dried unmilled roots gave identical values. 相似文献
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19.
Conclusion The greater tolerance of Dayton to A1 can be explained by a longer resistance of the plasmalemma towards A1 stress. Whether
a stronger mucigel production could be resonsible for increased A1 tolerance has to be examined in more detail. 相似文献
20.
Abstract. Fine-scale structure of a species-rich grassland was examined for seasonal changes caused by manipulated changes in the availability of above and below-ground resources (additional illumination with the help of mirrors and fertilization) in a field experiment. If changes induced by fertilization — which are expected to lead to a reduction in small-scale diversity —are due to intensified light competition, they should be compensated for by additional light input. Permanent plots of 40 cm × 40 cm were sampled by the point quadrat method at three angles (60°, 90° and 120° from the horizontal North-South direction), using a laser beam to position the quadrats, in early July and early September. The applied treatments did not cause apparent changes in plant leaf orientation. The degree of spatial aggregation of biomass increased seasonally in fertilized, non-illuminated plots: greater productivity at a constant light supply led to a faster growth rate of potentially dominant species, as compared to the subordinate ones. Additional illumination mitigated this effect of fertilization, indicating that the observed changes in biomass aggregation were due to increased light competition. There was a considerable seasonal decrease of variance ratio (ratio of observed variance of richness at a point and variance expected at random) in fertilized only and in illuminated only plots. In fertilized plots this was due to the positive relationship between biomass aggregation and expected variance of richness. Biomass constancy occurs to be inversely related to deficit in variance of richness. In illuminated plots, in contrast, only the observed variance of richness decreased seasonally, indicating a more uniform use of space by different species. Evidently, a deficit in variance of richness can be caused by drastically different processes, showing that the variance ratio statistic may not have a significant explanatory value in fine-scale community studies. 相似文献