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991.
As part of population dynamics studies of the South American fur seal (Arctophoca australis gracilis) rookery at Punta Weather in Guafo Island (43°36'S, 74°43’W), the causes and extent of pup mortality were monitored. During four breeding seasons, daily counts of live and dead pups were carried out to determine pup production and pup mortality. Dead pups were retrieved from the rookery to perform necropsies. The mean pup production was 1,735.5 ± 336 pups and the mean pup mortality up to 12 wk old was 6.0%± 2.6%. The major causes of death were enteritis with microscopic lesions of bacteremia (28.4%), starvation (23.5%), drowning (21%), trauma (19.8%), and stillbirths (2.5%). Enteritis with microscopic lesions of bacteremia, and starvation had higher incidence during January (beginning and middle of the breeding season) while most trauma and drowning occurred during February (end of the breeding season). In the 2006–2007 breeding season there was an increase in mortality due to starvation and trauma. Most pup deaths at Guafo Island are generated by extrinsic factors; therefore, additional studies that assess the impact of environmental changes and fishing activities, are needed in order to determine the exact causes of the decline of this species along Chilean coasts. 相似文献
992.
993.
Jose A. Estevez Tomás Landete-Castillejos Andrés J. García Enrique Gaspar-López Francisco Ceacero Laureano Gallego 《Acta theriologica》2011,56(4):323-328
Climate variability greatly affects animals through direct and indirect effects. Animals with slow reproductive adaptation to ecological changes such as large mammals are likely to have evolved mechanisms to anticipate early such impacts of climate variability on the environment. One of the adaptive mechanisms between reproductive costs and benefits in mammals affects parental investment through biases in sex ratio. Deer might be likely to show an early detection of climate variability because conception takes place in early autumn, but the main raising cost in deer concerns lactation, which takes place at the end of the following spring. The aim of this paper is to assess whether there is a relationship between global indices of climate variability such as El Niño-Southern Oscillation (ENSO) and sex ratio of a captive population of deer. Results showed that there was a negative correlation (r=?0.65) between sex ratio and ENSO indices between 1996 and 2008. El Niño enhances drier conditions during the summer in the Iberia Peninsula, which in turn favours a female bias. Results also suggest that the mechanism of early detection of climate variability exerts a strong effect on female reproductive physiology because the long-term stability of food resources in our setting has not markedly reduced it. 相似文献
994.
An understanding of the interplay between structure and energetics is crucial for the optimization of modern protein engineering techniques. In this context, the study of natural isoforms is a subject of major interest, as it provides the scenario for analyzing mutations that have endured during biological evolution. In this study, we performed a comparative analysis of the ligand-recognition and homodimerization energetics of bovine β-lactoglobulin variants A (βlgA) and B (βlgB). These variants differ by only two amino-acid substitutions: 64th (Asp(A) → Gly(B)), which is fully exposed to the solvent, and 118th (Val(A) → Ala(B)), immersed in the hydrophobic core of the protein. Calorimetric measurements revealed significant enthalpic and entropic differences between the isoforms in both binding processes. A structural comparison suggests that a variation in the conformation of the loop C-D, induced by mutation Asp/Gly, could be responsible for the differences in ligand-binding energetics. While recognition of lauric acid was entropically driven, recognition of sodium dodecyl sulfate was both entropically and enthalpically driven, confirming the key role of the ligand polar moiety. Because of a more favorable enthalpy, the dimerization equilibrium constant of βlgB was larger than that of βlgA at room temperature, while the two dimers became similarly stable at 35 °C. The isoforms exchanged the same number of structural water molecules and protons and shared similar stereochemistry at the dimer interface. MD simulations revealed that the subunits of both variants become more flexible upon dimer formation. It is hypothesized that a larger increase of βlgA mobility could account for the dimerization energetic differences observed. 相似文献
995.
Morphogenesis of plant cells is tantamount to the shaping of the stiff cell wall that surrounds them. To this end, these cells integrate two concomitant processes: 1), deposition of new material into the existing wall, and 2), mechanical deformation of this material by the turgor pressure. However, due to uncertainty regarding the mechanisms that coordinate these processes, existing models typically adopt a limiting case in which either one or the other dictates morphogenesis. In this report, we formulate a simple mechanism in pollen tubes by which deposition causes turnover of cell wall cross-links, thereby facilitating mechanical deformation. Accordingly, deposition and mechanics are coupled and are both integral aspects of the morphogenetic process. Among the key experimental qualifications of this model are: its ability to precisely reproduce the morphologies of pollen tubes; its prediction of the growth oscillations exhibited by rapidly growing pollen tubes; and its prediction of the observed phase relationships between variables such as wall thickness, cell morphology, and growth rate within oscillatory cells. In short, the model captures the rich phenomenology of pollen tube morphogenesis and has implications for other plant cell types. 相似文献
996.
The plains viscacha is a hystricognathi rodent with special reproductive characteristics. Despite poly-ovulation of 800 oocytes, it generates a high embryonic mortality since from 10 to 12 implantations only one or two offspring are born. The present work analyses the morphological, morphometrical, histochemical and lectinhistochemical characteristics of the uterus and uterine cervix of pregnant and non-pregnant viscacha. Anatomically, the uterus has two horns each one continued with a short cervix devoid of glands. The structure of the uterus is like that of other species; however, the proportion and size of its glands varies according to the physiological state. In viscacha, there is no uterine body and cervices cannot be differentiated externally. The formation of two sack bottoms is determined by the presence of a middle raphe in the cranial portion of the vagina. The so-described anatomy is different from that described in other hystricognathi such as guinea pig and coypu. The cervix presents two microscopically differentiable regions: the endocervix and the ectocervix lined by epithelia with different characteristics. The general characteristics of the uterus of L. maximus do not show specific differences with those of other mammals that might explain its peculiar gestation. 相似文献
997.
998.
María José Campos-Navarrete Víctor Parra-Tabla José Ramos-Zapata Cecilia Díaz-Castelazo Enrique Reyes-Novelo 《Arthropod-Plant Interactions》2013,7(6):607-617
The study of interaction networks between plants and pollinators allows us to explore interaction patterns at the community level, detect changes in visit frequency and evaluate the nestedness of the networks. The latter allows rare plant species to be visited by more abundant species of pollinators, potentially allowing community diversity to be maintained, and this approach makes it possible to discern the rewiring (changes in connections) of species when their preferred resource is not available. In this study, the topology, species identity and rewiring were compared between two contrasting sites, one within a conservation area and the other subjected to continuous disturbance. The networks of both sites were significantly nested and shared a high number of common species of both plants and pollinators. However, the sites differed notably in the number of exclusive interactions, suggesting a high percentage of interaction rewiring. The introduced bee species, Apis mellifera, was the most frequent species at both sites and also the most connected in terms of the number of its interactions. This is explained by its generalist foraging characteristics that allow it to form part of the networks’ core group. In general, our results underscore the importance of knowing the identity of the participating species when studying networks, and how connections change between them, as well as the potential effect of habitat destruction and the role of invasive species in the rearrangement of the interactions; all factors that can exert an influence on the functioning of plant–pollinator networks. 相似文献
999.
1000.
Vicente Andreu-Fernández Ainhoa Genovés Angel Messeguer Mar Orzáez Mónica Sancho Enrique Pérez-Payá 《PloS one》2013,8(2)