全文获取类型
收费全文 | 1858篇 |
免费 | 237篇 |
国内免费 | 197篇 |
出版年
2024年 | 5篇 |
2023年 | 45篇 |
2022年 | 35篇 |
2021年 | 67篇 |
2020年 | 72篇 |
2019年 | 96篇 |
2018年 | 88篇 |
2017年 | 88篇 |
2016年 | 123篇 |
2015年 | 92篇 |
2014年 | 94篇 |
2013年 | 150篇 |
2012年 | 94篇 |
2011年 | 122篇 |
2010年 | 88篇 |
2009年 | 100篇 |
2008年 | 117篇 |
2007年 | 121篇 |
2006年 | 100篇 |
2005年 | 69篇 |
2004年 | 60篇 |
2003年 | 53篇 |
2002年 | 45篇 |
2001年 | 40篇 |
2000年 | 47篇 |
1999年 | 41篇 |
1998年 | 28篇 |
1997年 | 19篇 |
1996年 | 31篇 |
1995年 | 26篇 |
1994年 | 16篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 3篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1971年 | 1篇 |
1950年 | 2篇 |
排序方式: 共有2292条查询结果,搜索用时 15 毫秒
131.
G. Taret M. Sevilla V. Wornoayporn A. Islam S. Ahmad C. Caceres A. S. Robinson M. J. B. Vreysen 《Journal of Applied Entomology》2010,134(3):207-215
The codling moth Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae) is a serious pest of pome fruit worldwide and the sterile insect technique (SIT) provides an environmentally acceptable approach for its control. As the pest is present in both the southern and northern hemispheres it would be possible for a rearing facility in the northern hemisphere to supply sterile moths to an SIT programme in the southern hemisphere during the northern winter and vice versa. This could greatly improve the economics of moth production and the running costs of rearing facilities. However in order to develop this concept, it is important to assess if populations of codling moth from different geographical regions share mating compatibility. Twelve different laboratory and field populations from both hemispheres were sampled and field cage bisexual mating compatibility tests were carried out between selected combinations. The index of sexual isolation (ISI) and the female and male relative performance index (FRPI and MRPI, respectively) were calculated for each mating combination. In only two of the combinations was there a slight but significant deviation from random mating. There were also some significant differences in mating duration between the homotypic matings and the duration of a particular homotypic mating seemed to depend on the origin of the other population in the cage. It was concluded that there exist no barriers to mating between populations of codling moth from many parts of the world and that it would be feasible for sterile moths to be shipped from one rearing facility to SIT programmes in other parts of the world. 相似文献
132.
Abstract Circadian mating rhythms, mating frequency, mating duration, and the effect of mating duration on fecundity and fertility in the cabbage beetle, Colaphellus bowringi were investigated in the laboratory. Mating occurred throughout the 24-h cycle but the majority of copulations occurred in the photophase with two apparent peaks, one at 8:00 and another at 16:00. Mating frequency observations for 10 consecutive days indicated that pre-mating period of C. bowringi was about 4 days, and pairs mated an average of 5 times per day and an average of 40 times during the first 10 days. There was a negative correlation between mating frequency and mating duration during the consecutive mating. The mean duration of the first copulation (136.24 ± 4.62 min) was significantly longer than those of the second (57.87 ± 2.03 min), third (53.05 ± 2.05 min) and fourth copulation (30.86 ± 2.98 min). Fecundity showed a slight increase with increasing mating duration but no significant difference among treatments. However, fertility was significantly influenced by the mating duration in this species. Mating of 20-min duration did not produce viable eggs. The mean percentage of fertile eggs with completed mating duration (204.43 ± 18.96 min, 56.75% fertile eggs) was significantly higher than those with 60 min (39.55%) and 30 min (17.91%) mating duration, suggesting that the longer mating duration might be associated with transfer of more sperm that are used to increase the fertility of eggs. 相似文献
133.
134.
Marie-Jeanne Holveck Claire Doutrelant Romain Guerreiro Philippe Perret Doris Gomez Arnaud Grégoire 《Biology letters》2010,6(4):453-457
Eggshell colouration is thought to function as a female-specific secondary sexual trait. While tests of this idea are rapidly accumulating in cavity-nesting birds, some fundamental underlying assumptions remain rarely investigated: namely, can males see eggshell coloration and perceive colour differences between the eggs of different females? We tested these two key assumptions in a natural population of blue tits (Cyanistes caeruleus). Using transponders, we tracked male nest visits and found that all males visited their nest-boxes while eggs were present and often visually accessible. Interestingly, some males also visited neighbouring nests. We then tested whether birds could detect eggshell coloration using models of avian colour vision; models were performed with and without limitations on visual performance owing to dim light. Both models found that differences in eggshell brightness were often easier to discriminate than differences in colour; there was more contrast in white eggshell background between clutches than within and its contrast against nest background was repeatable within clutches, suggesting these features could act as signals. Yet, the detectability of these contrasts depended entirely on model assumptions of visual limitations. Consequently, we need a better understanding of underlying visual mechanisms in dim-light environments and behavioural discrimination experiments before confirming the signalling potential of eggshell coloration. 相似文献
135.
THOMAS R. STANLEY 《The Journal of wildlife management》2010,74(8):1825-1833
ABSTRACT Grassland birds endemic to the central shortgrass prairie ecoregion of the United States have experienced steep and widespread declines over the last 3 decades, and factors influencing reproductive success have been implicated. Nest predation is the major cause of nest failure in passerines, and nesting success for some shortgrass prairie birds is exceptionally low. The 3 primary land uses in the central shortgrass prairie ecoregion are native shortgrass prairie rangeland (62%), irrigated and nonirrigated cropland (29%), and Conservation Reserve Program (CRP, 8%). Because shortgrass–cropland edges and CRP may alter the community of small mammal predators of grassland bird nests, I sampled multiple sites on and near the Pawnee National Grasslands in northeast Colorado, USA, to evaluate 1) whether small mammal species richness and densities were greater in CRP fields and shortgrass prairie–cropland edges compared to shortgrass prairie habitats, and 2) whether daily survival probabilities of ground-nesting grassland bird nests were negatively correlated with densities of small mammals. Small mammal species richness and densities, estimated using trapping webs, were generally greater along edges and on CRP sites compared to shortgrass sites. Vegetation did not differ among edges and shortgrass sites but did differ among CRP and shortgrass sites. Daily survival probabilities of artificial nests at edge and CRP sites and natural nests at edge sites did not differ from shortgrass sites, and for natural nests small mammal densities did not affect nest survival. However, estimated daily survival probability of artificial nests was inversely proportional to thirteen-lined ground squirrel (Spermophilus tridecemlineatus) densities. In conclusion, these data suggest that although land-use patterns on the shortgrass prairie area in my study have substantial effects on the small mammal community, insufficient data existed to determine whether land-use patterns or small mammal density were affecting grassland bird nest survival. These findings will be useful to managers for predicting the effects of land-use changes in the shortgrass prairie on small mammal communities and avian nest success. 相似文献
136.
SARA C. GREGORY W. MATTHEW VANDER HAEGEN WAN YING CHANG STEPHEN D. WEST 《The Journal of wildlife management》2010,74(1):18-25
ABSTRACT The western gray squirrel (Sciurus griseus) in Washington, USA, is limited to 3 disjunct areas and is a state threatened species. Information is lacking for the North Cascades population, which is the northernmost population for the species. Squirrels in this population exist without oaks (Quercus spp.) that provide forage and cavities for maternal nests elsewhere in their range. During May 2003 to August 2005, we studied selection of nest sites and nest trees by 18 radiocollared squirrels in Okanogan County, Washington. Without oak cavities, females reared their young in dreys. General nest-tree characteristics were similar to characteristics of western gray squirrel nest trees in Southeastern Cascades: relatively tall ponderosa pines (Pinus ponderosa) ≥ 40 cm diameter at breast height. Results from conditional logistic models determined that the odds of a squirrel selecting a tree for nesting increased with greater diameter at breast height and with infection by dwarf mistletoe (Arceuthobium spp.). Nest sites with high selection probability by squirrels had greater basal area and number of tree species than available unselected sites. Retention of forest patches that include a mix of conifer species or conifer and deciduous trees and moderate to high basal area could promote nesting opportunities, connectivity for arboreal travel, as well as abundance and diversity of hypogeous fungi. Experiments to test the efficacy of retaining untreated patches of varying size (including trees infected with mistletoe) on nesting by western gray squirrels within stands managed for fire suppression and forest health would provide important information about the effects of forest fuel management on arboreal wildlife. 相似文献
137.
JUAN DIEGO IBÁÑEZ‐ÁLAMO MANUEL SOLER 《Biological journal of the Linnean Society. Linnean Society of London》2010,101(4):759-766
Urbanization, one of the most extreme land‐use alterations, is currently spreading, and the number of species confronting these changes is increasing. However, contradictory results of previous studies impede a clear interpretation of which selective pressure (nest predation or food limitation) is more important in urban habitats compared with natural situations, and whether birds can confront them by adjusting their life‐history strategies. We investigated life‐history syndromes of three common blackbird (Turdus merula) populations differing in their human influence (urban, rural, and woodland). We analysed daily nest predation and nestling starvation rates to assess the relative importance of these selection pressures in each habitat. Simultaneously, several life‐history traits were investigated to determine if T. merula seem adapted to their main source of selection. Food limitation was more important in the city, whereas nest predation was the most important selective force in the forest. The rural habitat was characterized by an intermediate influence of these two factors. Life‐history syndromes, as the covariation of a suite of traits, confirmed these results because T. merula seem well adapted to the main cause of selection in each habitat. Our results are consistent with urbanization imposing new challenges on birds, and that they adaptively respond to them. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 759–766. 相似文献
138.
Mbangi N. Mulavwa Kumugo Yangozene Mikwaya Yamba‐Yamba Balemba Motema‐Salo Ndunda N. Mwanza Takeshi Furuichi 《American journal of primatology》2010,72(7):575-586
We examined the location of nest groups, spatial distribution of nests within a nest group, and attributes of individual nests of wild bonobos at Wamba, Democratic Republic of Congo. We also examined the seasonal factors influencing nesting behavior and compared the nest group size with the 1 hr party size during daytime. We defined a nest group to be a cluster of nests that were built in the same evening and found within 30 m from the other nearest nest. Examination of the largest gap within a nest group suggested that 30 m was an acceptable cutoff value. Monthly rainfall or fruit abundance did not significantly influence the monthly mean nest group size. Nests were built in the swamp forest for as many as 13% observation days, suggesting the need for reevaluation of the use of swamp forest by bonobos. The use of swamp forest was influenced not by seasonal rainfall or fruit abundance, but by the fruiting of specific species. Preferred tree species for building nests accounted for 19.8% of standing trees, which suggested that the selection of sleeping sites was not largely restricted by the distribution of specific species. The mean 1 hr party size was almost identical through the day and was similar to the mean nest group size. Parties of bonobos sometimes split into smaller nest groups, especially when feeding on non‐preferred fruits during fruit scarcity. By contrast, when feeding on preferred fruits while ranging in large parties, they often aggregated to form even larger nest groups. When sleeping in small‐ or middle‐sized nest groups, they tended to aggregate the next morning. These tendencies may reflect the gregarious nature of bonobos who prefer to range or sleep together as far as circumstances allow. Am. J. Primatol. 72:575–586, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
139.
Selena Humphreys Chris S. Elphick Carina Gjerdrum Margaret Rubega 《Journal of Field Ornithology》2007,78(2):152-158
ABSTRACT. Saltmarsh Sharp-tailed Sparrows ( Ammodramus caudacutus ) build ground nests, often with a closely-woven dome, in marshes that frequently flood during high tides. To test the hypothesis that domed nests help reduce the loss of eggs and chicks due to flooding or predation, we examined the characteristics and fate of 102 nests at sites along the coast of Connecticut. To test whether nest structure was tailored to suit microhabitat conditions, we also measured vegetation characteristics around nests. Finally, we conducted artificial nest-flooding experiments to determine whether removal of domes reduced egg retention during flooding. We found no significant effects of nest structure on breeding success or failure, and few significant correlations between nest structure and microhabitat. The height of nests above the ground, however, increased with vegetation height, supporting the hypothesis that nest construction is influenced by flooding, but not supporting the hypothesis that predation risk is important. Dome removal experiments showed that domes have a highly significant effect on the retention of eggs during flooding, suggesting that domes help eggs survive the regular tidal flooding of marshes. 相似文献
140.
There was an allometry between length of nesting male Pomatoschistus microps and the size of the nest. There was also a positive relationship between parasite load and pectoral fin asymmetry. There was no marked relationship between the number of eggs in the nest and parasitism or level of asymmetry. These results are discussed in terms of energy allocation and fish reproductive success. 相似文献