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A theoretical rheological model for agar gels, based on the bead spring model for linear flexible random coils and the model for crosslinked polymers, is successfully fitted to experimental gelation curves obtained over a wide range of cooling rates (0.5–20 °C min−1) and agar concentration (1–3 wt%). The theoretical gelation temperature, Tgelmodel increases with increasing agar concentration and decreasing cooling rate. The intrinsic net association rate increases significantly with increasing cooling rate. This increase is related to the higher probability of association of the non-associated agar molecules at higher cooling rates. 相似文献
104.
Bees are essential pollinators for many flowering plants, including agriculturally important crops such as apple. As geographic ranges of bees or their host plants change as a result of human activities, we need to identify pathogens that could be transmitted among newly sympatric species to evaluate and anticipate their effects on bee communities. We used PCR screening and DNA sequencing to evaluate exposure to potentially disease-causing microorganisms in a pollinator of apple, the horned mason bee (Osmia cornifrons). We did not detect microsporidia, Wolbachia, or trypanosomes, which are common pathogens of bees, in any of the hundreds of mason bees screened. We did detect both pathogenic and apathogenic (saprophytic) fungal species in the genus Ascosphaera (chalkbrood), an unidentified species of Aspergillus fungus, and a strain of bacteria in the genus Paenibacillus that is probably apathogenic. We detected pathogenic fungal strains in asymptomatic adult bees that therefore may be carriers of disease. We demonstrate that fungi from the genus Ascosphaera have been transported to North America along with the bee from its native range in Japan, and that O. cornifrons is exposed to fungi previously only identified from nests of other related bee species. Further study will be required to quantify pathogenicity and health effects of these different microbial species on O. cornifrons and on closely-related native North American mason bees that may now be exposed to novel pathogens. A global perspective is required for pathogen research as geographic ranges of insects and microorganisms shift due to intentional or accidental introductions. 相似文献
105.
The binding of luxol fast blue ARN by various biological lipids 总被引:1,自引:0,他引:1
106.
Two anorectic drugs commonly prescribed as adjuncts in weight control and a third experimental drug were studied in rats for their anorectic and possible thermogenic activities. Diethylpropion, a congener of amphetamine, mazindol, which is chemically unrelated to amphetamine, and ciclazindol, an experimental drug structurally similar to mazindol, were given in graded doses to determine their effect on food and oxygen consumption (VO2). Anorectic effects exhibited by diethylpropion and mazindol were similar and more potent than ciclazindol. Both resting and anesthetized VO2 measurements were done to assess the thermogenic activity of the drugs. Anesthetized VO2 was performed in an attempt to seperate peripheral from centrally-mediated actions of the drugs. Amphetamine was also tested at 1.0 mg/kg in order to correlate relative potencies. Mazindol, but not diethylpropion or ciclazindol, produced a dose response increases in resting VO2. At the 1.0 mg/kg dose, amphetamine produced a greater increase in resting VO2 than mazindol. At this dose, both drugs elicited centrally-induced alertness, although amphetamine elicited greater activity than mazindol. Mazindol and diethylpropion, but not ciclazindol, caused a dose-related increase in anesthetized VO2. The anesthetized VO2 response to amphetamine at 1 mg/kg was greater than the responses of mazindol and diethylpropion at 3.0 mg/kg. These findings confirm the previously recognized anorectic effects of mazindol and diethylpropion and also demonstrate that mazindol and diethylpropion but not ciclazindol (at the doses used) produced dose-related increases in VO2 (energy expenditure) by stimulating directly peripheral mechanisms and in the case of mazindol central mechanisms as well. 相似文献
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108.
Temporal patterns of happiness and information in a global social network: hedonometrics and Twitter 总被引:3,自引:0,他引:3
Individual happiness is a fundamental societal metric. Normally measured through self-report, happiness has often been indirectly characterized and overshadowed by more readily quantifiable economic indicators such as gross domestic product. Here, we examine expressions made on the online, global microblog and social networking service Twitter, uncovering and explaining temporal variations in happiness and information levels over timescales ranging from hours to years. Our data set comprises over 46 billion words contained in nearly 4.6 billion expressions posted over a 33 month span by over 63 million unique users. In measuring happiness, we construct a tunable, real-time, remote-sensing, and non-invasive, text-based hedonometer. In building our metric, made available with this paper, we conducted a survey to obtain happiness evaluations of over 10,000 individual words, representing a tenfold size improvement over similar existing word sets. Rather than being ad hoc, our word list is chosen solely by frequency of usage, and we show how a highly robust and tunable metric can be constructed and defended. 相似文献
109.
Christina M. Kennedy Eric Lonsdorf Maile C. Neel Neal M. Williams Taylor H. Ricketts Rachael Winfree Riccardo Bommarco Claire Brittain Alana L. Burley Daniel Cariveau Luísa G. Carvalheiro Natacha P. Chacoff Saul A. Cunningham Bryan N. Danforth Jan‐Hendrik Dudenhffer Elizabeth Elle Hannah R. Gaines Lucas A. Garibaldi Claudio Gratton Andrea Holzschuh Rufus Isaacs Steven K. Javorek Shalene Jha Alexandra M. Klein Kristin Krewenka Yael Mandelik Margaret M. Mayfield Lora Morandin Lisa A. Neame Mark Otieno Mia Park Simon G. Potts Maj Rundlf Agustin Saez Ingolf Steffan‐Dewenter Hisatomo Taki Blandina Felipe Viana Catrin Westphal Julianna K. Wilson Sarah S. Greenleaf Claire Kremen 《Ecology letters》2013,16(5):584-599
Bees provide essential pollination services that are potentially affected both by local farm management and the surrounding landscape. To better understand these different factors, we modelled the relative effects of landscape composition (nesting and floral resources within foraging distances), landscape configuration (patch shape, interpatch connectivity and habitat aggregation) and farm management (organic vs. conventional and local‐scale field diversity), and their interactions, on wild bee abundance and richness for 39 crop systems globally. Bee abundance and richness were higher in diversified and organic fields and in landscapes comprising more high‐quality habitats; bee richness on conventional fields with low diversity benefited most from high‐quality surrounding land cover. Landscape configuration effects were weak. Bee responses varied slightly by biome. Our synthesis reveals that pollinator persistence will depend on both the maintenance of high‐quality habitats around farms and on local management practices that may offset impacts of intensive monoculture agriculture. 相似文献
110.
Annalaura Mancia Spyropoulos DD McFee WE Newton DA Baatz JE 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2012,155(1):136-142
Current models for in vitro studies of tissue function and physiology, including responses to hypoxia or environmental toxins, are limited and rely heavily on standard 2-dimensional (2-D) cultures with immortalized murine or human cell lines. To develop a new more powerful model system, we have pursued methods to establish and expand cultures of primary lung cell types and reconstituted tissues from marine mammals. What little is known about the physiology of the deep-sea diving pygmy sperm whale (PSW), Kogia breviceps, comes primarily from stranding events that occur along the coast of the southeastern United States. Thus, development of a method for preserving live tissues and retrieving live cells from deceased stranded individuals was initiated. This report documents successful cryopreservation of PSW lung tissue. We established in vitro cultures of primary lung cell types from tissue fragments that had been cryopreserved several months earlier at the stranding event. Dissociation of cryopreserved lung tissues readily provides a variety of primary cell types that, to varying degrees, can be expanded and further studied/manipulated in cell culture. In addition, PSW-specific molecular markers have been developed that permitted the monitoring of fibroblast, alveolar type II, and vascular endothelial cell types. Reconstitution of 3-D cultures of lung tissues with these cell types is now underway. This novel system may facilitate the development of rare or disease-specific lung tissue models (e.g., to test causes of PSW stranding events and lead to improved treatments for pulmonary hypertension or reperfusion injury in humans). Also, the establishment of a "living" tissue bank biorepository for rare/endangered species could serve multiple purposes as surrogates for freshly isolated samples. 相似文献