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71.
Economy is a central principle for understanding animal locomotion. Yet, compared with theoretical predictions concerning economy, animals run with compliant legs that are energetically costly. Here, we address this apparent paradox, highlighting two factors that predict benefits for compliant gaits: (i) minimizing cost of work associated with bouncing viscera; and (ii) leg control for robust stability in uneven terrain. We show that consideration of the effects of bouncing viscera predicts an energetic optimum for relatively compliant legs. To compare stability in uneven terrain, we introduce the normalized maximum drop (NMD), a measure based on simple kinematics, which predicts that compliant legs allow negotiation of relatively larger terrain perturbations without failure. Our model also suggests an inherent trade-off in control of leg retraction velocity (ω) for stability: low ω allows higher NMD, reducing fall risk, whereas high ω minimizes peak forces with terrain drops, reducing injury risk. Optimization for one of these factors explicitly limits the other; however, compliant legs relax this trade-off, allowing greater stability by both measures. Our models suggest compromises in leg control for economy and stability that might explain why animals run with compliant legs. 相似文献
72.
73.
从医院经济管理的现实出发,从理论上阐述了建立支出预算控制指标体系的必要性,其中重点说明了该体系对改善医院预算管理现状的现实意义,同时可增强预算控制的操作性,从而对提升医院管理发挥积极作用,达到降低成本,实施科学化管理的目的;另指出在实践中,如何分步骤地建立预算控制指标体系,并结合具体支出项目,提出一些将预算管理和支出控制相结合的思路与方法,与大家探讨。 相似文献
74.
Swire J 《Journal of molecular evolution》2007,64(5):558-571
Most investigations of the forces shaping protein evolution have focussed on protein function. However, cells are typically
50%–75% protein by dry weight, with protein expression levels distributed over five orders of magnitude. Cells may, therefore,
be under considerable selection pressure to incorporate amino acids that are cheap to synthesize into proteins that are highly
expressed. Such selection pressure has been demonstrated to alter amino acid usage in a few organisms, but whether “cost selection”
is a general phenomenon remains unknown. One reason for this is that reliable protein expression level data is not available
for most organisms. Accordingly, I have developed a new method for detecting cost selection. This method depends solely on
interprotein gradients in amino acid usage. Applying it to an analysis of 43 whole genomes from all three domains of life,
I show that selection on the synthesis cost of amino acids is a pervasive force in shaping the composition of proteins. Moreover,
some amino acids have different price tags for different organisms—the cost of amino acids is changed for organisms living
in hydrothermal vents compared with those living at the sea surface or for organisms that have difficulty acquiring elements
such as nitrogen compared with those that do not—so I also investigated whether differences between organisms in amino acid
usage might reflect differences in synthesis or acquisition costs. The results suggest that organisms evolve to alter amino
acid usage in response to environmental conditions.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
[Reviewing Editor: Hector Musto] 相似文献
75.
Thick sun leaves have a larger construction cost per unit leaf area than thin shade leaves. To re-evaluate the adaptive roles
of sun and shade leaves, we compared the photosynthetic benefits relative to the construction cost of the leaves. We drew
photosynthetically active radiation (PAR)-response curves using the leaf-mass-based photosynthetic rate to reflect the cost.
The dark respiration rates of the sun and shade leaves of mulberry (Morus bombycis Koidzumi) seedlings did not differ significantly. At irradiances below 250 μmol m−2 s−1, the shade leaves tended to have a significantly larger net photosynthetic rate (P
N) than the sun leaves. At irradiances above 250 μmol m−2 s−1, the P
N did not differ significantly. The curves indicate that plants with thin shade leaves have a larger daily CO2 assimilation rate per construction cost than those with thick sun leaves, even in an open habitat. These results are consistently
explained by a simple model of PAR extinction in a leaf. We must target factors other than the effective assimilation when
we consider the adaptive roles of thick sun leaves. 相似文献
76.
BACKGROUND AND AIMS: Species of the Nepenthaceae family are under-represented in studies of leaf traits and the consequent view of mineral nutrition and limitation in carnivorous plants. This study is aimed to complement existing data on leaf traits of carnivorous plants. METHODS: Physico-chemical properties, including construction costs (CC), of the assimilatory organs (leaf and pitcher) of a guild of lowland Nepenthes species inhabiting heath and/or peat swamp forests of Brunei, Northern Borneo were determined. KEY RESULTS: Stoichiometry analyses indicate that Nepenthes species are nitrogen limited. Most traits vary appreciably across species, but greater variations exist between the assimilatory organs. Organ mass per unit area, dry matter tissue concentration (density), nitrogen (N), phosphorus (P), carbon, heat of combustion (H(c)) and CC values were higher in the leaf relative to the pitcher, while organ thickness, potassium (K) and ash showed the opposite trend. Cross-species correlations indicate that joint rather than individual consideration of the leaf and the pitcher give better predictive relationships between variables, signalling tight coupling and functional interdependence of the two assimilatory organs. Across species, mass-based CC did not vary with N or P, but increases significantly with tissue density, carbon and H(c), and decreases with K and ash contents. Area-based CC gave the same trends (though weaker in strength) in addition to a significant positive correlation with tissue mass per unit area. CONCLUSIONS: The lower CC value for the pitcher is in agreement with the concept of low marginal cost for carnivory relative to conventional autotrophy. The poor explanatory power of N, P or N : P ratio with CC suggests that factors other than production of expensive photosynthetic machinery (which calls for a high N input), including concentrations of lignin, wax/lipids or osmoregulatory ions like K(+), may give a better explanation of the CC variation across Nepenthes species. 相似文献
77.
78.
Producing sons reduces lifetime reproductive success of subsequent offspring in pre-industrial Finns 总被引:3,自引:0,他引:3
Rickard IJ Russell AF Lummaa V 《Proceedings. Biological sciences / The Royal Society》2007,274(1628):2981-2988
Life-history theory states that reproductive events confer costs upon mothers. Many studies have shown that reproduction causes a decline in maternal condition, survival or success in subsequent reproductive events. However, little attention has been given to the prospect of reproductive costs being passed onto subsequent offspring, despite the fact that parental fitness is a function of the reproductive success of progeny. Here we use pedigree data from a pre-industrial human population to compare offspring life-history traits and lifetime reproductive success (LRS) according to the cost incurred by each individual's mother in the previous reproductive event. Because producing a son versus a daughter has been associated with greater maternal reproductive cost, we hypothesize that individuals born to mothers who previously produced sons will display compromised survival and/or LRS, when compared with those produced following daughters. Controlling for confounding factors such as socio-economic status and ecological conditions, we show that those offspring born after elder brothers have similar survival but lower LRS compared with those born after elder sisters. Our results demonstrate a maternal cost of reproduction manifested in reduced LRS of subsequent offspring. To our knowledge, this is the first time such a long-term intergenerational cost has been shown in a mammal species. 相似文献
79.
Talita Lopes Honorato Maria Cristiane Rabelo Luciana Rocha Barros Gonçalves Gustavo Adolfo Saavedra Pinto Sueli Rodrigues 《World journal of microbiology & biotechnology》2007,23(10):1409-1415
The use of agriculture substrates in industrial biotechnological processes has been increasing because of its low cost. Cashew
apples are considered an agriculture low cost product in the Brazilian Northeast because the cashew cultivation is done mainly
to produce cashew nuts. About 90% of the cashew apples production is lost in the field after removing the nut. In this work,
the use of clarified cashew apple juice as substrate for microbial cultivation was investigated. The results showed that cashew
apple juice is a good source of reducing sugars and can be used to grow Leuconostoc mesenteroides to produce high added value products such as dextran, lactic acid, mannitol and oligosaccharides. 相似文献
80.
Life-history theory centres around trade-offs between current and future reproduction, but we have little understanding of how such trade-offs are mediated. We supplementary fed Ural owls (Strix uralensis) during the nestling period and quantified parents' current and future life-history components as well as their physiological health by monitoring haematocrit, leucocyte profile, intra- and extracellular blood parasites. Feeding led to reduced parental effort but did not improve offspring viability, male parasite defence, or parental survival. Intracellular leucocytozoan infection was reduced in fed females which lasted to the following year's reproductive season (carry-over effect), when fed females also laid larger and earlier clutches. Leucocytozoon infection therefore may mediate the life-history trade-off between current and residual reproduction in this species. 相似文献