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211.
Price TD Brown CR Brown MB 《Evolution; international journal of organic evolution》2000,54(5):1824-1827
Abstract Estimates of the intensity of selection based on measurements of the living and the dead require knowledge of the fraction of the original population dying. We apply recently developed methods (Blanckenhorn et al. 1999) to estimate the intensity of selection in a population of cliff swallows. In this population the fraction of individuals dying was unknown, but certainly high. The inferred selection is very strong and impossible to achieve if the original population is assumed to have followed a normal distribution. We consider several alternative explanations for this result including measurement biases, undetected immigration, and sampling biases. Of these, sampling biases are perhaps the most likely. We conclude that the intensity of selection on the swallows was probably strong, but its absolute magnitude is unknown. 相似文献
212.
Crop-weed hybridization can potentially influence the evolutionary ecology of wild populations. Many crops are known to hybridize with wild relatives, but few studies have looked at the long-term persistence of crop genes in the wild. This study investigated one factor in the hybridization process in radish: differential pollinator visitation to wild radish (Raphanus raphanistrum) vs. crop-wild F1 hybrids (R. sativus x R. raphanistrum). Wild genotypes had yellow flowers, a recessive single-locus trait, whereas hybrids always had white or pale pink flowers. In experimental arrays in northern Michigan, total pollinator visitation was significantly biased toward wild plants when the frequencies of wild and hybrid plants were equal. Syrphid flies, the most frequent visitors, preferred wild plants while bumble bees showed no preference. This pattern was also observed when hybrid plants were overrepresented in the array (12 hybrid:2 wild). In contrast, when hybrid plants were rare (2 hybrid:12 wild), neither morph was preferred by any pollinator group. Later in the summer, pollinators were also observed in a large experimental garden with nearly equal frequencies of wild and hybrid plants. Cabbage butterflies (Pieris rapae) strongly overvisited wild plants, while bumble bees showed a slight preference for hybrids. Taken together, these studies suggest that F1 hybrids may not be at a disadvantage with regard to pollinator visits when they occur at low frequencies or when bumble bees are frequent flower visitors. Thus, variation in the proportion of white-flowered morphs among wild radish populations could be influenced by different histories of crop-to-wild hybridization, as well as by variation in the composition of local pollinator taxa. 相似文献
213.
The Turonian flora from Sayreville New Jersey includes one of the world's most diverse assemblages of Cretaceous angiosperm flowers. This flora is made even more interesting by its association with a large insect fauna that is preserved by charcoalification as well as in amber. Floral diversity includes numerous representatives of Magnoliidae, Hamamelididae, Rosidae, Dilleniidae, and Asteridae (Ericales sensu lato). Included are hypogynous, five-merous flowers with uniseriate hairs on the pedicels and stamens in bundles most frequently borne opposite the petals. There is considerable variation in filament length, and some filaments are branched. On some anthers, strands of residue, suggesting the former presence of a liquid of unknown nature, partially occlude the apparent zone of dehiscence. In other cases, open anthers are fully occluded by an amorphous substance. pollen is rarely found associated with anthers, but is common on stigmatic surfaces. pollen is prolate and tricolporate with reticulate micromorphology. The superior syncarpous ovary is five-carpellate with axile/intruded parietal placentation and numerous anatropous ovules/carpel. Ovary partitions have closely spaced, parallel ascending channels (secretory canals?), and there are apparent secretory canals/cavities in receptacles, sepals, and petals. Individual stigmas are cuneiform with a central groove and eccentrically peltate. Styles are short and fused. In aggregate, the stigmas form a secondarily peltate stigma. Seeds have a reticulate sculpture pattern, a pronounced raphe, and funicular arils with sculpture similar to the seeds. phylogenetic analyses of several data matrices of extant taxa place this fossil in a monophyletic group with the modern genera Garcinia and Clusia within the Clusiaceae. As such, these fossils represent the earliest fossil evidence of the family Clusiaceae. Some modern Clusiaceae are notable, in particular, for their close relationship with meliponine and other highly derived bee pollinators; the fossil flowers share several characters that suggest a similar mode of pollination. This possibility is consistent with other floral and insect data from the same locality. 相似文献
214.
A comparative analysis of heat waves and associated mortality in St. Louis, Missouri – 1980 and 1995
K. E. Smoyer 《International journal of biometeorology》1998,42(1):44-50
This research investigates heat-related mortality during the 1980 and 1995 heat waves in St. Louis, Missouri. St. Louis has
a long history of extreme summer weather, and heat-related mortality is a public health concern. Heat waves are defined as
days with apparent temperatures exceeding 40.6°C (105°F). The study uses a multivariate analysis to investigate the relationship
between mortality and heat wave intensity, duration, and timing within the summer season. The heat wave of 1980 was more severe
and had higher associated mortality than that of 1995. To learn if changing population characteristics, in addition to weather
conditions, contributed to this difference, changes in population vulnerability between 1980 and 1995 are evaluated under
simulated heat wave conditions. The findings show that St. Louis remains at risk of heat wave mortality. In addition, there
is evidence that vulnerability has increased despite increased air-conditioning penetration and public health interventions.
Received: 12 August 1997 / Revised: 12 January 1998 / Accepted: 13 February 1998 相似文献
215.
Philip M. Service Charles A. Michieli Kirsten McGill 《Evolution; international journal of organic evolution》1998,52(6):1844-1850
A long-term laboratory selection experiment has produced replicated populations of fruit flies that differ in mean life span by more than twofold. An analysis of age-specific mortality rates indicated that differences in mean life span have been achieved principally by evolution of patterns of senescence. These results provide empirical confirmation that senescence can be modified within species by appropriate forms of natural selection, which is a fundamental prediction of theories regarding the genetic basis and evolution of senescence. Mortality data were fit to a model that accounts for the leveling off of cohort mortality rates at older ages, but that does not necessarily imply that very old individuals cease to senesce. 相似文献
216.
217.
Small benthic fish such as darters are frequently collected for stream inventory purposes or to document habitat use, with
the intent of releasing the fish unharmed following enumeration. The purpose of this study was to examine the injury and short
term mortality (8 d) of greenside darters captured by live wire pot trapping and electrofishing, using two different settings
(80Hz, 6ms and 60Hz, 6ms). Two different electrofishing techniques were used, spot electrofishing and sweep electrofishing.
Short term mortality was highest for fish collected in live pot traps. Abrasion from the wire traps appeared to remove scales
and irritate the skin. By the conclusion of the study, 74% of the fish caught in live pot traps were dead from fungal lesions.
Greenside darters captured by all electrofishing methods exhibited low short term mortality (< 10%). The only initial mortality,
hemorrhaging and spinal damage, occurred for fish collected using 80Hz, 6ms sweep technique, although the short term mortality
was still far less than that observed among trapped fish. The spot electrofishing technique resulted in no injury, with either
of the settings. Live trapping produces little initial mortality, and thus may be wrongly viewed as a safe alternative for
the collection of threatened benthic stream fishes, compared to electrofishing. We suggest that researchers studying small
fish in warmwater systems use caution when collecting and handling fish for subsequent release.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
218.
Long-term change in an unmanaged population of wych elm subjected to Dutch elm disease 总被引:1,自引:0,他引:1
1 Changes in a population of Ulmus glabra in Lady Park Wood (UK), a mixed deciduous native woodland, were studied by means of permanent transects. All individuals reaching 1.3 m height were recorded at irregular intervals from 1945 to 1993.
2 Dutch elm disease struck this population in about 1972. Most of the canopy and subcanopy stems were killed, but a few, slow-growing, subcanopy individuals survived unscathed.
3 Subsequent seedling regeneration and growth of sprouts from rootstocks of infected trees was substantial and vigorous. Twenty-three years after the outbreak of disease the number of elm individuals had increased by about 40%. Disease has, however, continued to afflict vigorous, exposed individuals.
4 The large-scale distribution of elm has been unaffected, but the small-scale pattern has changed due to the concentration of seedling regeneration in gaps.
5 The elm population appears to be differentiating into (i) a large high-turnover subpopulation of fast-growing, but repeatedly diseased maiden individuals and sprouts, and (ii) a small, low-turnover subpopulation of slow-growing individuals rooted in suboptimally dry, secluded sites. 相似文献
2 Dutch elm disease struck this population in about 1972. Most of the canopy and subcanopy stems were killed, but a few, slow-growing, subcanopy individuals survived unscathed.
3 Subsequent seedling regeneration and growth of sprouts from rootstocks of infected trees was substantial and vigorous. Twenty-three years after the outbreak of disease the number of elm individuals had increased by about 40%. Disease has, however, continued to afflict vigorous, exposed individuals.
4 The large-scale distribution of elm has been unaffected, but the small-scale pattern has changed due to the concentration of seedling regeneration in gaps.
5 The elm population appears to be differentiating into (i) a large high-turnover subpopulation of fast-growing, but repeatedly diseased maiden individuals and sprouts, and (ii) a small, low-turnover subpopulation of slow-growing individuals rooted in suboptimally dry, secluded sites. 相似文献
219.
Female Osmia repeatedly return to their nest to provision it with food and building material. The present study investigates the bees' nest localization performance by modifying visual cues in the near-vicinity of the nest. Each of several arrays of nesting holes was surrounded by four geometrical shapes. Removing some or all of the shapes reduced the proportion of direct returns but never prevented a bee from finding the appropriate array and, within that array, its own nest. The more the pattern was modified, the higher was the error score and the longer the delay, but no bee failed finally to find its nest. Shifting the pattern as well as the whole array of holes shifted homing orientation accordingly. There was no effect of the positions of the removed shapes, of contrast inversion, or of modifying the holes array. Our data are discussed in the light of the snapshot theory. 相似文献
220.
Daniel Pauly 《Reviews in Fish Biology and Fisheries》1998,8(3):307-334
The extension into tropical areas of Beverton and Holt's yield per recruit approach for stock assessment represents a straightforward case of normal science, the common Kuhnian counterpart to his much rarer paradigm shifts. It is shown that the normal science which, in recent decades, has led to new methods for estimating growth, mortality and other statistics required for yield per recruit analyses in data-sparse environments, has not only enriched fisheries science and aquatic biology as a whole, but has also contributed to identify the limitations of the single-species research programme originally defined by Beverton and Holt. The most likely prospect for that programme, in the tropics and elsewhere, is to become a component of the multispecies, or rather ecosystem approach that is emerging, and to which Beverton and Holt will have contributed many of the concepts, and much of the rigour. 相似文献