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31.
本文综述了IBDV的保护性抗原蛋白VP2与病毒形态、毒力变异、抗原变异间的关系及在诱导宿主细胞凋亡中的作用。同时也探讨了其在新型疫苗开发中的应用等方面的研究进展。 相似文献
32.
The ultimate body size that an individual fish achieves can be a function both of direct effects of growth or indirect effects
associated with the timing of sexual maturation (and associated energetic tradeoffs). These alternatives are often invoked
to explain variation in body size within and among fish populations, but have rarely been considered simultaneously. We assessed
how resource availability and timing of maturation interact to influence individual body size of bluegill (Lepomis macrochirus). Resource availability (high and low food) and the social structure of the population (presence or absence of large, mature
males) were varied in experimental ponds. Food ration affected growth (larger fish in the high food treatments) and the social
structure of the population affected timing of maturation (early maturation of males in the absence of large males). Treatment
effects, however, were sex-specific; males responded to the social structure of the population and females were more responsive
to resource availability. We also found individuals that became sexually mature were smaller than those that remained immature,
although results were sex-specific and resource dependent. For males, individuals that matured were smaller when resources
were limited; mature and immature females showed no difference in body size regardless of food ration. We show that both resource
availability and the processes that control timing of maturation interact in sex-specific ways to influence body size of bluegill.
These results suggest that a more robust explanation for variable body size requires consideration of sex-specific interactions
between ecological (food and growth) and evolutionary (timing of maturation) mechanisms. 相似文献
33.
Tibial condyle shape is alleged to vary among fossil tibiae attributed to Australopithecus, and has been argued to reflect functional differences of the knee. Convex anteroposterior curvature of the lateral tibial condyle in A. africanus has been interpreted to indicate a more chimpanzee-like locomotor repertoire than the flatter lateral tibial condyles of A. afarensis (Berger and Tobias, 1996, J. Hum. Evol. 30, 343). Alternatively, Latimer, Ohman, and Lovejoy (1987, Am. J. Phys. Anthropol. 74, 155) have suggested that in response to increased transarticular loads accompanied by larger body mass, joints should become flatter as size increases, both within and among species, so that the variation observed among hominin fossils reflects size alone rather than functional differences. In this study, three-dimensional surface areas of the lateral tibial condyle of humans, chimpanzees, and gorillas were computed using a Digibot II (Digibotics) laser scanner and the DataSculpt v.4.6 engineering software package to evaluate joint surface contours, and compared to two-dimensional surface area and arc and chord length measurements of the anteroposterior and mediolateral axes. Extant species measurements were then compared to those of A. afarensis (A.L. 129-1b, A.L. 288-1aq, A.L. 333x-26, A.L. 333-42) and A. africanus (Stw 514a). Results do not support the hypothesis that A. afarensis and A. africanus differ in condylar topology. They also do not support the hypothesis that joint surfaces become flatter with increased transarticular load accompanying increased body size, as curvature of the lateral tibial condyle in anteroposterior and mediolateral planes is not negatively allometric. However, femoral condylar shape is not included in this study, which may better reflect joint surface responses to increased body size. Finally, there is no basis from this study to reconstruct differences in locomotor behavior among fossil hominin taxa based on lateral tibial condyle morphology. 相似文献
34.
江孜沙棘[Hippophea gyantsensis(Rousi)Lian]是青藏高原特有的一种广生态幅的小乔木,在拉萨河谷地区的海拔3500~4200m范围内均有分布。前人工作多集中在江孜沙棘果实的开发利用方面,对其基础生态学研究较少。本研究旨在探讨江孜沙棘沿海拔梯度的群落组成和表型变异的规律。为此,在拉萨河谷上段沿海拔梯度由东向西设置了4个样带:3850m、3950m、4050m和4200m,每个样带设置2至3个10m×10m的样方进行研究。首先,详细记录了每个样方内林下维管植物的物种组成、样方内的沙棘盖度、海拔、样方与河岸的实际距离,并用DCA[detrended correspondence analysis(去势对应分析)]排序方法对群落及其组成物种进行排序分析。随机抽取了每个样方内的20个江孜沙棘植株个体,测定其胸径、基径、株高和叶片长度,用回归分析法分析这些变量和海拔之间的关系。研究结果表明,江孜沙棘在拉萨河谷内的主要生境分为4种类型,即:河边砾石滩地、河阶草滩、河边草甸和河边林缘,样方排序结果主要受海拔的影响;同时,江孜沙棘植株的基径、胸径和高度都随着海拔的升高而显著减小,而叶片长度与海拔之间无显著相关。本文研究结果表明,对江孜沙棘而言,海拔所代表的综合环境因子对其分布和表型有显著的影响,而局部光照可能也是影响其表型特征的重要生态因子。 相似文献
35.
36.
Changwei Hu Mei Li Jianlong Li Qin Zhu Zhili Liu 《World journal of microbiology & biotechnology》2008,24(7):1209-1214
The marine microalga Pavlova viridis (Prymnesiophyceae) is widely used in marine aquaculture industries of China for feeding bivalves and has been proposed as
an alternative source of eicosapentaenoic acid (EPA). To investigate variation of its lipid and fatty acid compositions during
laboratory and outdoor cultivation, a 60-1 photobioreactor was established in Nanjing, China. Outdoor cultivation, paralleled
with laboratory cultures in mid-October, was performed from autumn through midwinter. The results showed that the total lipid
and EPA contents of outdoor cultures were both lower than those of indoor cultures. When the outdoor temperature and illumination
decreased, total lipid experienced no significant change. Although the level of saturated fatty acids decreased, polyunsaturated
fatty acids, especially EPA, increased. 相似文献
37.
How does forest landscape structure explain tree species richness in a Mediterranean context? 总被引:1,自引:0,他引:1
Although the strong relationship between vegetation and climatic factors is widely accepted, other landscape composition and
configuration characteristics could be significantly related with vegetation diversity patterns at different scales. Variation
partitioning was conducted in order to analyse to what degree forest landscape structure, compared to other spatial and environmental
factors, explained forest tree species richness in 278 UTM 10 × 10 km cells in the Mediterranean region of Catalonia (NE Spain).
Tree species richness variation was decomposed through linear regression into three groups of explanatory variables: forest
landscape (composition and configuration), environmental (topography and climate) and spatial variables. Additionally, the
forest landscape characteristics which significantly contributed to explain richness variation were identified through a multiple
regression model. About 60% of tree species richness variation was explained by the whole set of variables, while their joint
effects explained nearly 28%. Forest landscape variables were those with a greater pure explanatory power for tree species
richness (about 15% of total variation), much larger than the pure effect of environmental or spatial variables (about 2%
each). Forest canopy cover, forest area and land cover diversity were the most significant composition variables in the regression
model. Landscape configuration metrics had a minor effect on forest tree species richness, with the exception of some shape
complexity indices, as indicators of land use intensity and edge effects. Our results highlight the importance of considering
the forest landscape structure in order to understand the distribution of vegetation diversity in strongly human-modified
regions like the Mediterranean. 相似文献
38.
39.
Landscape diversity patterns and endemism of Araceae in Ecuador 总被引:1,自引:0,他引:1
Araceae is one of the largest herb families in tropical America, but its patterns of diversity and endemism are poorly known. We used predictive distribution modelling in GIS to study Araceae richness on a landscape scale in Ecuador. Modelling was based on georeferenced herbarium collections with humidity and mean annual temperature as climatic variables. Variation partitioning using multiple regression showed that humidity and altitude were main factors in explaining Araceae diversity patterns. Endemism was less well explained by present climatic factors. Unlike common diversity patterns of herbs or epiphytes, Araceae richness was highest in the eastern (Amazon) lowland rain forest with a secondary centre on the Andean foothills of northwestern Ecuador. The peak in endemism was on the western slopes of the Andes, corresponding to areas that have been severely affected by human activities and deforestation. Eastern lowland (Amazonian) forests were poor in endemic Araceae. 相似文献
40.
This paper aims to study the fertility rate of the migrant Tibetans residing in Northern India and finding out the factors
which are affecting the fertility level among them. Data are reported on age at menarche, age at marriage, first childbirth,
use of contraception, widowhood, migration and on various fertility measures in the Tibetan of Northern India living at low
and moderate altitude (600–2000 m), who have migrated from high altitude (4000 m above sea level) in Tibet. The migrant Tibetans
reported a relatively lower fertility as compared to the high and moderate altitude populations. This lower fertility is mostly
attributable to the use of contraception, the later mean age at marriage and first childbirth, and relatively high proportion
of widows in the migrant Tibetans. However, the social as well as biological changes in population during migration should
not be overlooked, which have a sufficient impact on fertility. 相似文献