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1.
Sperm competition experiments between lines of crickets producing different sperm lengths. 总被引:5,自引:0,他引:5
Sperm numbers can be important determinants of fertilization success in sperm competition. However, the importance of variation in sperm size is less well understood. Sperm size varies significantly both between and within species and comparative studies have suggested that some of this variance can be explained by sperm competition. In this study we examine whether variation in sperm length has consequences for fertilization precedence using controlled sperm competition experiments in the field cricket Gryllus bimaculatus. This species is an ideal model for such investigations because the mechanism of sperm competition generates complete mixing of different males' spermatozoa in the female (thereby allowing individual sperm to express their own competitive abilities). We successfully bred lines of crickets, the males of which produced short, medium and long sperm types with narrow and non-overlapping distributions. Males of different lines were then sequentially mated with control females in order to create two-male sperm competitions. The paternity outcomes of these competitions were measured after matings using an irradiated male technique (with a full reciprocal design that controls for natural fertility and any irradiation effects on gamete competitiveness) over a 12 day oviposition period. However, having successfully bred diverging sperm length lines and competing males that differed in sperm length, we found no evidence that a male's sperm size explained any of the variation in their relative fertilization success. Males from lines producing longer sperm showed no fertilization advantage over males producing shorter sperm across 97 double matings. There was also no advantage for males producing a sperm length close to the population mean over those competitors whose sperm length had been selectively diverged across 63 matings. 相似文献
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Mortality statistics for 25 populations of the larger Old World monkeys (members of the subfamily Cercopithecinae) were evaluated with a competing hazard model of mortality. The best eight of these life tables were combined to generate a standard model life table representative of the mortality patterns of these primates. Two applications of the standard model to smooth, graduate, and compare life tables based on limited and defective data are presented. 相似文献
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Jeremy T. Starr Richard J. Sciotti Debra L. Hanna Michael D. Huband Lisa M. Mullins Hongliang Cai Jeffrey W. Gage Mandy Lockard Mark R. Rauckhorst Robert M. Owen Manjinder S. Lall Mark Tomilo Huifen Chen Sandra P. McCurdy Michael R. Barbachyn 《Bioorganic & medicinal chemistry letters》2009,19(18):5302-5306
Dual inhibitors of bacterial gyrB and parE based on a 5-(2-pyrimidinyl)-imidazo[1,2-a]pyridine template exhibited MICs (μg/mL) of 0.06–64 (Sau), 0.25–64 (MRSA), 0.06–64 (Spy), 0.06–64 (Spn), and 0.03–64 (FQR Spn). Selected examples were efficacious in mouse sepsis and lung infection models at <50 mg/kg (PO dosing). 相似文献
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1. A dose-dependent decrease in male fertility occurs in the Indian Meal Moth, Plodia interpunctella , when sub-lethally infected with granulovirus during the larval stage.
2. Here, the causes for this decline are investigated by examining eupyrene and apyrene sperm numbers and sizes produced by males across four levels of viral challenge.
3. The results could not explain how reduced male fertility is caused in this host–pathogen interaction. While a reduction in both eupyrene and apyrene sperm numbers from all virus-treated males was found, this was not significant and neither was there a difference in sperm lengths across the four treatments. There were also no differences in the variances of sperm numbers or lengths between the doses, and no associations between sperm numbers or lengths and body size were found.
4. A significant correlation between eupyrene and apyrene numbers was found, but this was independent of dose. Significant between-male variance in apyrene sperm lengths was found, indicating that individual males differ in the range of apyrene sperm sizes they produce.
5. It is suggested that further intracellular and behavioural study is needed to identify the causes of the granulovirus-induced reduction in fertility of P. interpunctella . 相似文献
2. Here, the causes for this decline are investigated by examining eupyrene and apyrene sperm numbers and sizes produced by males across four levels of viral challenge.
3. The results could not explain how reduced male fertility is caused in this host–pathogen interaction. While a reduction in both eupyrene and apyrene sperm numbers from all virus-treated males was found, this was not significant and neither was there a difference in sperm lengths across the four treatments. There were also no differences in the variances of sperm numbers or lengths between the doses, and no associations between sperm numbers or lengths and body size were found.
4. A significant correlation between eupyrene and apyrene numbers was found, but this was independent of dose. Significant between-male variance in apyrene sperm lengths was found, indicating that individual males differ in the range of apyrene sperm sizes they produce.
5. It is suggested that further intracellular and behavioural study is needed to identify the causes of the granulovirus-induced reduction in fertility of P. interpunctella . 相似文献
7.
Phalloidin tightly binds to actin and converts soluble actin into depolymerization-resistant actin filaments. Phalloidin promotes the potassium-dependent, calcium-independent efflux of γ-amino butyric acid and nore-pinephrine from synaptosomes but inhibits the potassium-facilitated, calcium-dependent release of these neurotransmitters. This suggests that an actomyosin system is involved in synaptic transmission. 相似文献
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The impacts that predators have on prey behavior, growth, survival, and ultimately the composition of many ecological communities
are mediated by prey defenses and the susceptibility of prey to predators. We hypothesized that prey populations inhabiting
short-lived, species-poor, aquatic environments should lack significant morphological, developmental, and behavioral responses
to predators and are therefore highly susceptible to predation. Furthermore, we predicted that the resultant decrease in prey
density and increase in per capita resources due to high susceptibility to predators should enhance overall cohort survival
because of enhanced growth of surviving prey. To test these ideas, we performed laboratory and outdoor mesocosm experiments
to disentangle multiple effects of predators on an anuran (Scaphiopus couchii); a species highly adapted to breeding in ephemeral habitats and that has one of the shortest larval periods of all anurans.
Chemical (presence of predator) and lethal predator cues (predator plus consumed conspecific) elicited no response in behavior,
development, or morphology, indicating a lack of defensive mechanisms. Survivorship was significantly reduced in treatments
where tadpoles were exposed to predators. However, this reduction in prey density led to accelerated time to metamorphosis,
conferring an advantage to survivors who must metamorphose before ephemeral ponds dry. Our experiments demonstrated that in
short-lived environments, prey may exhibit little or no response to the presence of predators presumably because selection
for anti-predator defenses is countered by selection for rapid metamorphosis. However, predation actually resulted in an increase
in overall cohort survival. Although predators are relatively rare in highly ephemeral aquatic environments, they may play
an important role in facilitating the long-term persistence of their prey by reducing prey density. 相似文献