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121.
Intra-specific competition defines the relationship between population density and the performance of individual organisms
(R-function). Observation of this relationship in nature shows it to be frequently nonlinear, and it has been argued, on intuitive
grounds, that this nonlinearity is due to the type of competition (scramble or contest) being expressed. Here, we use an individual-based
simulation model to investigate the effects of three resource partitioning schemes, representing different types of competition,
on the form of the R-function. Results indicate that all resource partitioning schemes can give rise to concave or convex functions depending
on the balance between maximum individual birth rate, maintenance cost, and demand for resources. Given high growth rates
and maintenance costs, contest competitors tend to exhibit less concavity than scramblers. Therefore, population stability
can be strongly affected by the strategy of resource partitioning. Life histories and environmental conditions that encourage
the homogeneous distribution of resources among individuals lead to complex and unstable dynamics. Stable dynamics is fostered
by heterogeneous resource distribution, which could result from such things as social hierarchies, individual and environmental
variability, and large, indivisible resource packets. 相似文献
122.
Much of applied and theoretical ecology is concerned with the interactions of habitat quality, animal distribution, and population
abundance. We tested a technique that uses resource selection functions (RSF) to scale animal density to the relative probability
of selecting a patch of habitat. Following an accurate survey of a reference block, the habitat-based density estimator can
be used to predict population abundance for other areas with no or unreliable survey data. We parameterized and tested the
technique using multiple years of radiotelemetry locations and survey data collected for woodland caribou across four landscape-level
survey blocks. The habitat-based density estimator performed poorly. Predictions were no better than those of a simple area
estimator and in some cases deviated from the observed by a factor of 10. We developed a simulation model to investigate factors
that might influence prediction success. We experimentally manipulated population density, caribou distribution, ability of
animals to track carrying capacity, and precision of the estimation equation. Our simulations suggested that interactions
between population density, the size of the reference block, and the pattern of distribution can lead to large discrepancies
between observed and predicted population numbers. Over- or undermatching patch carrying capacity and precision of the estimator
can influence predictions, but the effect is much less extreme. Although there is some empirical and theoretical evidence
to support a relationship between animal abundance and resource selection, our study suggests that a number of factors can
seriously confound these relationships. Habitat-based density estimators might be effective where a stable, isolated population
at equilibrium is used to generate predictions for areas with similar population parameters and ecological conditions. 相似文献
123.
Renzhong Wang Liang Chen Yuguang Bai Chunwang Xiao 《Journal of Plant Growth Regulation》2008,27(1):39-48
A natural grassland in northeastern China dominated by Leymus chinensis (Trin.) was subject to drought treatments to determine the seasonal dynamics in resource partitioning to shoot and storage
organs in response to drought. The growing season was divided into six stages according to the phenology of L. chinensis. Plant samples of L. chinensis were collected at each stage to determine biomass, gross calorific value, relative water content, and key mineral contents
of plant parts, including rhizomes, roots, leaves, and stems. Resource partitioning to shoot and storage organs as measured
by biomass, gross calorific value, and N, K+, and Na+ contents varied significantly among phenologic stages. Drought treatment (natural precipitation, 50–60 % of field capacity)
significantly reduced biomass, gross calorific value, relative water content of shoot, and N and K+ contents in both shoot and storage organs, but it enhanced rhizome : shoot ratio and Na+ content. A negative correlation in biomass, gross calorific value, and K+ and Na+ contents between shoot and storage organs was found throughout the growing season, which may have been accentuated by drought
when soil moisture was limited. Our results indicate that resource partitioning to storage plays an important role in regulating
plant growth of L. chinensis, especially under drought conditions. 相似文献
124.
The demand for monoclonal antibody for therapeutic and diagnostic applications is rising constantly which puts up a need to bring down the cost of its production. In this context it becomes a prerequisite to improve the efficiency of the existing processes used for monoclonal antibody production. This review describes various upstream processes used for monoclonal antibody production and evaluates critical parameters and efforts which are being made to enhance the efficiency of the process. The upstream technology has tremendously been upgraded from host cells used for manufacturing to bioreactors type and capacity. The host cells used range from microbial, mammalian to plant cells with mammalian cells dominating the scenario. Disposable bioreactors are being promoted for small scale production due to easy adaptation to process validation and flexibility, though they are limited by the scale of production. In this respect Wave bioreactors for suspension culture have been introduced recently. A novel bioreactor for immobilized cells is described which permits an economical and easy alternative to hollow fiber bioreactor at lab scale production. Modification of the cellular machinery to alter their metabolic characteristics has further added to robustness of cells and perks up cell specific productivity. The process parameters including feeding strategies and environmental parameters are being improved and efforts to validate them to get reproducible results are becoming a trend. Online monitoring of the process and product characterization is increasingly gaining importance. In total the advancement of upstream processes have led to the increase in volumetric productivity by 100-fold over last decade and make the monoclonal antibody production more economical and realistic option for therapeutic applications. 相似文献
125.
在北京东灵山地区,沿一定海拔梯度,对藜芦(Veratrum nigrum)这一雄花两性花同株的多年生草本植物的繁殖特征进行了初步研究。结果表明:藜芦开花植株的生物量显著大于未开花植株的生物量。藜芦开花植株大小存在最小临界值,总种群的最小临界值为2.61 g,不同种群的繁殖临界值存在一定的差异。根据花粉/胚珠比(Pollen / ovule ratio,P/O比)推测,藜芦应属于以异交为主的混合交配系统。雄花的大小与生物量都比两性花小,而且其开放时间也晚于两性花,但二者的花粉生产量却没有显著差异。这种现象与人们针对雄花两性花同株植物的雄花功能所提出的最优资源分配假说(Optimal resource allocation hypothesis)是一致的。 相似文献
126.
2005年4月至2006年11月,对雷公山自然保护区的鱼类资源状况进行了调查.调查表明,保护区共有鱼类35种,隶属4目10科30属.该区的鱼类多数为适应于山区溪流生活的种类,鲤科鱼类是其中最大的类群,构成鱼类区系成分的主体.该区有一定经济价值的鱼类包括泥鳅(Misgurnus anguillicandatus)、马口鱼(Opsariichthys bidens)、鲤(Cyprinus carpio)、瓦氏黄颡鱼(Pelteobagrus vachelli)、黄鳝(Monopterus albus)、草鱼(Ctenopharyngodon idellus)、刺鲃(Spinibarbus caldwelli)、南方白甲鱼(Onychostoma gerlachi)、月鳢(Channa asiatica)等.通过实地调查,对保护区内两条主要水系(长江水系和珠江水系)的物种相似度进行了对比. 相似文献
127.
We have previously reported that the exposure to an abnormal magnetic field simulating the one encountered by the International Space Station (ISS) orbiting around the Earth may enhance autonomic response to emotional stimuli. Here we report the results of the second part of that study which tested whether this field also affects cognitive functions. Twenty-four volunteers participated in the study, 12 exposed to the natural geomagnetic field and 12 to the magnetic field encountered by ISS. The test protocol consisted of a set of eight tests chosen from a computerized test battery for the assessment of attentional performance. The duration of exposure was 90 min. No effect of exposure to ISS magnetic field was observed on attentional performance. 相似文献
128.
Mary Jane West-Eberhard has suggested that plasticity may be of primary importance in promoting evolutionary innovation and
diversification. Here, we explore the possibility that the diversification of phytophagous insects may have occurred through
such a process, using examples from nymphalid butterflies. We discuss the ways in which host plant range is connected to plasticity
and present our interpretation of how West-Eberhard’s scenario may result in speciation driven by plasticity in host utilization.
We then review some of the evidence that diversity of plant utilization has driven the diversification of phytophagous insects
and finally discuss whether this suggests a role for plasticity-driven speciation. We find a close conceptual connection between
our theory that the diversification of phytophagous insects has been driven by oscillations in host range, and our personal
interpretation of the most efficient way in which West-Eberhard’s theory could account for plasticity-driven speciation. A
major unresolved issue is the extent to which a wide host plant range is due to adaptive plasticity with dedicated modules
of genetic machinery for utilizing different plants. 相似文献
129.
130.
David J. Janetski Dominic T. Chaloner Scott D. Tiegs Gary A. Lamberti 《Oecologia》2009,159(3):583-595
Pacific salmon (Oncorhynchus spp.) disturb sediments and fertilize streams with marine-derived nutrients during their annual spawning runs, leading researchers
to classify these fish as ecosystem engineers and providers of resource subsidies. While these processes strongly influence
the structure and function of salmon streams, the magnitude of salmon influence varies widely across studies. Here, we use
meta-analysis to evaluate potential sources of variability among studies in stream ecosystem responses to salmon. Results
obtained from 37 publications that collectively included 79 streams revealed positive, but highly inconsistent, overall effects
of salmon on dissolved nutrients, sediment biofilm, macroinvertebrates, resident fish, and isotopic enrichment. Variation
in these response variables was commonly influenced by salmon biomass, stream discharge, sediment size, and whether studies
used artificial carcass treatments or observed a natural spawning run. Dissolved nutrients were positively related to salmon
biomass per unit discharge, and the slope of the relationship for natural runs was five to ten times higher than for carcass
additions. Mean effects on ammonium and phosphorus were also greater for natural runs than carcass additions, an effect attributable
to excretion by live salmon. In contrast, we observed larger positive effects on benthic macroinvertebrates for carcass additions
than for natural runs, likely because disturbance by live salmon was absent. Furthermore, benthic macroinvertebrates and biofilm
associated with small sediments (<32 mm) displayed a negative response to salmon while those associated with large sediments
(>32 mm) showed a positive response. This comprehensive analysis is the first to quantitatively identify environmental and
methodological variables that influence the observed effects of salmon. Identifying sources of variation in salmon–stream
interactions is a critical step toward understanding why engineering and subsidy effects vary so dramatically over space and
time, and toward developing management strategies that will preserve the ecological integrity of salmon streams.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献