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Environmental indicators from lake sediments provide excellent opportunities to improve understanding of forest disturbance processes and corresponding changes in forest composition. Our research provides a methodology for assessing recent, historic, and prehistoric disturbances using lacustrine sediment records. We collected sediment cores from Blue Lake, a small subalpine lake on the Wasatch Plateau in central Utah. These cores record environmental changes caused by both spruce beetle ( Dendroctonus rufipennis Kirby) and human (logging and livestock grazing) modification. We observed deteriorated insect remains in the lake sediments. These remains correspond temporally with a historic spruce beetle outbreak, though alkaline conditions in the lake water may have inhibited preservation of bark beetle remains. Pollen data reveal that despite the unprecedented level of mortality among Engelmann spruce ( Picea engelmannii Parry ex Engelm.) resulting from the spruce beetle epidemic, logging activities subsequent to Euro-American settlement appear to be the most severe disturbance to the Blue Lake watershed over the last 750 years.  相似文献   
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As part of a larger study on the aquatic life of streams in central Colorado, efforts were made to determine the distribution of interstitial organisms, with emphasis on the subterranean amphipod Stygobromus . In a preliminary screening-level study, sampling for Stygobromus was conducted in 1985 at 47 sites along the Front Range of Colorado at elevations generally matching the type locale for S. coloradensis and S. pennaki at the confluence of the North Fork of the South Platte River and its mainstem. A more intensive follow-up study was conducted in 1988 at 30 sites concentrating on the upper South Platte River basin. In the follow-up study both hyporheic and shore zone (phreatic) habitats were sampled using a variety of techniques (Bou-Rouch pump, Karaman-Chappuis technique, and a coarsemesh wide-mouth net, as appropriate). In the preliminary study Stygobromus spp. were collected at only 12 of 47 study sites, with all collections in the vicinity of the type locale. In the follow-up study Stygobromus were found at 16 of 30 sites sampled, extending the known distribution in Colorado of S. coloradensis and S. pennaki well beyond the type locale. The use of multiple sampling techniques was important in locating these organisms. In addition to the amphipod Stygobromus , sampling sites in the follow-up study contained a rich interstitial community, including copepods, bathynellids, tardigrades, archiannelids, and ostracods.  相似文献   
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Complexity theory shares a common vocabulary with systems theory. Terms such as emergence, complexity, and adaptation appear in both traditions. Despite the similarities, complexity theory is not a misnomer for systems theory. Several points of departure exist in complexity's research agenda and methods. Moreover, while systems theory appears to have embraced interpretivist and critical philosophies, complexity theory remains firmly in the positivist camp, despite claims that it is a postmodern science.  相似文献   
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Sine SM  Engel AG 《Nature》2006,440(7083):448-455
Throughout the nervous system, moment-to-moment communication relies on postsynaptic receptors to detect neurotransmitters and change the membrane potential. For the Cys-loop superfamily of receptors, recent structural data have catalysed a leap in our understanding of the three steps of chemical-to-electrical transduction: neurotransmitter binding, communication between the binding site and the barrier to ions, and opening and closing of the barrier. The emerging insights might be expected to explain how mutations of receptors cause neurological disease, but the opposite is generally true. Namely, analyses of disease-causing mutations have clarified receptor structure-function relationships as well as mechanisms governing the postsynaptic response.  相似文献   
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After the completion of a draft human genome sequence, the International Human Genome Sequencing Consortium has proceeded to finish and annotate each of the 24 chromosomes comprising the human genome. Here we describe the sequencing and analysis of human chromosome 3, one of the largest human chromosomes. Chromosome 3 comprises just four contigs, one of which currently represents the longest unbroken stretch of finished DNA sequence known so far. The chromosome is remarkable in having the lowest rate of segmental duplication in the genome. It also includes a chemokine receptor gene cluster as well as numerous loci involved in multiple human cancers such as the gene encoding FHIT, which contains the most common constitutive fragile site in the genome, FRA3B. Using genomic sequence from chimpanzee and rhesus macaque, we were able to characterize the breakpoints defining a large pericentric inversion that occurred some time after the split of Homininae from Ponginae, and propose an evolutionary history of the inversion.  相似文献   
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Complement-mediated inflammation exacerbates the tissue injury of ischaemic necrosis in heart attacks and strokes, the most common causes of death in developed countries. Large infarct size increases immediate morbidity and mortality and, in survivors of the acute event, larger non-functional scars adversely affect long-term prognosis. There is thus an important unmet medical need for new cardioprotective and neuroprotective treatments. We have previously shown that human C-reactive protein (CRP), the classical acute-phase protein that binds to ligands exposed in damaged tissue and then activates complement, increases myocardial and cerebral infarct size in rats subjected to coronary or cerebral artery ligation, respectively. Rat CRP does not activate rat complement, whereas human CRP activates both rat and human complement. Administration of human CRP to rats is thus an excellent model for the actions of endogenous human CRP. Here we report the design, synthesis and efficacy of 1,6-bis(phosphocholine)-hexane as a specific small-molecule inhibitor of CRP. Five molecules of this palindromic compound are bound by two pentameric CRP molecules, crosslinking and occluding the ligand-binding B-face of CRP and blocking its functions. Administration of 1,6-bis(phosphocholine)-hexane to rats undergoing acute myocardial infarction abrogated the increase in infarct size and cardiac dysfunction produced by injection of human CRP. Therapeutic inhibition of CRP is thus a promising new approach to cardioprotection in acute myocardial infarction, and may also provide neuroprotection in stroke. Potential wider applications include other inflammatory, infective and tissue-damaging conditions characterized by increased CRP production, in which binding of CRP to exposed ligands in damaged cells may lead to complement-mediated exacerbation of tissue injury.  相似文献   
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