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241.
IRP1 [iron regulatory protein (IRP) 1] is a bifunctional protein with mutually exclusive end-states. In one mode of operation, IRP1 binds iron-responsive element (IRE) stem–loops in messenger RNAs encoding proteins of iron metabolism to control their rate of translation. In its other mode, IRP1 serves as cytoplasmic aconitase to correlate iron availability with the energy and oxidative stress status of the cell. IRP1/IRE binding occurs through two separate interfaces, which together contribute about two-dozen hydrogen bonds. Five amino acids make base-specific contacts and are expected to contribute significantly to binding affinity and specificity of this protein:RNA interaction. In this mutagenesis study, each of the five base-specific amino acids was changed to alter binding at each site. Analysis of IRE binding affinity and translational repression activity of the resulting IRP1 mutants showed that four of the five contact points contribute uniquely to the overall binding affinity of the IRP1:IRE interaction, while one site was found to be unimportant. The stronger-than-expected effect on binding affinity of mutations at Lys379 and Ser681, residues that make contact with the conserved nucleotides G16 and C8, respectively, identified them as particularly critical for providing specificity and stability to IRP1:IRE complex formation. We also show that even though the base-specific RNA-binding residues are not part of the aconitase active site, their substitutions can affect the aconitase activity of holo-IRP1, positively or negatively. 相似文献
242.
Dino J. Martins Steven D. Johnson 《Biological journal of the Linnean Society. Linnean Society of London》2013,110(1):199-213
Hawkmoths (Lepidoptera, Sphingidae) are considered important pollinators in tropical regions, but the frequency and degree of reciprocal specialization of interactions between hawkmoths and flowers remain poorly understood. Detailed observations at two sites in Kenya over a two‐year period indicate that adult hawkmoths are routinely polyphagous and opportunistic, regardless of their proboscis length. About 700 individuals of 13 hawkmoth species were observed visiting a wide range of plant species at the study sites, including 25 taxa that appear to be specifically adapted for pollination by hawkmoths. We estimate that 277 plant species in Kenya (c. 4.61% of the total angiosperm flora) are adapted for pollination by hawkmoths. Floral tube lengths of these plants have a bimodal distribution, reflecting the existence of two hawkmoth guilds differing in tongue length. Hawkmoths exhibited strongly crepuscular foraging patterns with activity confined to a 20‐min period at dusk and, in some cases, a similar period just before dawn. Corolla tube length appears to act as a mechanical filter as the longest‐tubed plants were visited by the fewest hawkmoth species and these were exclusively from the long‐tongued guild. Tube length showed a strong positive relationship with nectar volume, even after phylogenetic correction, which implies that plants with long corolla tubes are under selection to offer relatively large amounts of nectar to entice visits by polyphagous long‐tongued hawkmoths. Our study shows that diffusely co‐evolved pollination systems involving long‐tongued hawkmoths are clearly asymmetrical, with plants exhibiting a high degree of floral specialization, while hawkmoths exhibit polyphagous behaviour. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 199–213. 相似文献
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244.
Licia Carlson 《The Yale journal of biology and medicine》2013,86(3):303-314
This article examines the ethical issues surrounding the inclusion of people with
intellectual disabilities as research subjects. It explores subject selection,
competence, risk and benefits, and authority through three tensions that emerge
when considering these concepts in the context of the Disability Rights Movement
and critical disability scholarship. These tensions are defined as the double
dangers of inclusion and exclusion; the challenges of defining competence and
risk in terms of individuals vs. groups; and the conflicts that arise when
pursuing the dual goals of amelioration and elimination of disabilities. Though
these tensions are not resolved, they underscore the importance of researchers
engaging with critical disability perspectives in order to navigate these
complex ethical questions. 相似文献
245.
Jennifer E. Sanner Lorraine Frazier Malini Udtha 《The Yale journal of biology and medicine》2013,86(1):5-13
Platelet serotonin has been associated with depression and coronary artery
disease. Understanding the association between platelet serotonin and depressive
symptoms during acute coronary syndrome (ACS) may explain some of the ACS events
seen in depressed individuals. The objectives were to evaluate whether levels of
platelet serotonin during an ACS event differ between individuals who screen
positive or negative for depressive symptoms and to determine if a linear
relationship exists. In this cross-sectional study, data were collected on 51
patients with ACS. Multiple linear regression models were examined. Platelet
serotonin levels were not significantly different between the depressed and
non-depressed groups (β = -4.093 and p = .293); a linear relationship was not
found (β = -.254 and p = .250). In conclusion, a relationship between platelet
serotonin and depressive symptoms was not found. It remains unclear if an
association exists between platelet serotonin levels and depressive symptoms
during hospitalization for ACS. 相似文献
246.
Srdjan Ljubisavljevic Ivana Stojanovic Slobodan Vojinovic Dragan Stojanov Svetlana Stojanovic Tatjana Cvetkovic Dejan Savic Dusica Pavlovic 《Neurochemistry international》2013
Advanced oxidation protein products (AOPP) and total thiol (SH) groups levels in plasma and CSF were studied in a cohort of 50 clinically isolated syndrome (CIS) and 57 relapsing remittent multiple sclerosis (RRMS) patients related to 20 control group (CG) patients’ values. The obtained results were compared regarding patients demographic, biochemical, clinical (EDSS) and MRI features (total T2 weighted lesions number and Gd enhancement lesion volume). 相似文献
247.
248.
Katharina Stein Mathias Templin Isabell Hensen Markus Fischer Diethart Matthies Matthias Schleuning 《Biotropica》2013,45(3):325-332
Plant reproductive success is usually positively related to conspecific floral density, but neutral or negative effects of floral density on reproduction have also been reported. Differences in the relationship between reproduction and floral density largely originate from a trade‐off between increasing attractiveness versus increasing competition for pollinators at high floral densities. Although floral densities strongly vary in the understory of tropical forests, for instance, due to variation in light availability, little is known about the density dependence of reproduction in tropical understory plants. We used path analyses to disentangle direct and indirect effects of canopy openness and floral density on fruit set and analyzed the relationship between pollen load and floral density for two Neotropical understory plants, Heliconia metallica and Besleria melancholica. In both species, fruit set was not directly related to canopy openness, but decreased with increasing floral density. In H. metallica, canopy openness had an indirect negative effect on reproduction mediated by its effects on floral density. Effects of floral density on pollen loads were species‐specific. In B. melancholica, pollen loads linearly decreased with increasing floral density, indicating competition for pollinators at high densities. In H. metallica, pollen loads were reduced at both low and high densities, indicating an interplay of facilitative and competitive effects of floral density on pollen deposition. In contrast to other studies, we found negative density dependence of reproduction in both understory species. Negative effects of floral density on reproduction appear to be related to pollinator‐mediated effects on reproduction rather than to variation in abiotic conditions. 相似文献
249.
Rachel L. Vannette Marie-Pierre L. Gauthier Tadashi Fukami 《Proceedings. Biological sciences / The Royal Society》2013,280(1752)
Mutualistic interactions are often subject to exploitation by species that are not directly involved in the mutualism. Understanding which organisms act as such ‘third-party’ species and how they do so is a major challenge in the current study of mutualistic interactions. Here, we show that even species that appear ecologically similar can have contrasting effects as third-party species. We experimentally compared the effects of nectar-inhabiting bacteria and yeasts on the strength of a mutualism between a hummingbird-pollinated shrub, Mimulus aurantiacus, and its pollinators. We found that the common bacterium Gluconobacter sp., but not the common yeast Metschnikowia reukaufii, reduced pollination success, seed set and nectar consumption by pollinators, thereby weakening the plant–pollinator mutualism. We also found that the bacteria reduced nectar pH and total sugar concentration more greatly than the yeasts did and that the bacteria decreased glucose concentration and increased fructose concentration whereas the yeasts affected neither. These distinct changes to nectar chemistry may underlie the microbes'' contrasting effects on the mutualism. Our results suggest that it is necessary to understand the determinants of microbial species composition in nectar and their differential modification of floral rewards to explain the mutual benefits that plants and pollinators gain from each other. 相似文献
250.