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We evaluated the direct and interactive effects of food and age on reproduction in the Montagu's Harrier Circus pygargus , to test whether variation in food supply was likely to affect age-specific breeding probability or success. Younger females were more frequently non-breeders than older females. When breeding, older females laid earlier, produced larger clutches, failed less often and had higher number of fledglings than younger females. Probability of breeding was higher, laying was earlier, and clutch size and number of fledglings per pair increased with increasing food abundance. A significant interaction between food and age was observed in both breeding probability and breeding performance: older females were more likely to breed than younger females when food abundance was low, and younger females performed less well in good food conditions than older females. Overall, differences between age groups were most marked in extreme food conditions, regardless of the quality of the conditions. 相似文献
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SUMMARY. 1. Phytoplankton production was measured during 1981–82 in Bahia de Puno. a large polymictic system that is part of LakeTiticaca in the tropical Andes (Peru-Bolivia), Photosynthesis followed aweak seasonal pattern through each 12-month cycle but the largestvariations occurrud between years. 2. The large temporal variations in productivity appeared to becontrolled by biological events rather than by the direct effeets ofseasonal or aseasonal physical processes. Major shifts in production overthe 2-year period were attributable to the proportional abundance andactivity of N2-fixing blue-green algae. Production was uncorrelated withthe seasonal radiation cycle. 3. In vivo fluorescence and photosynthetic assays revealed largechanges in phytoplankton community structure over time and depth.The shifts in vertical structure were associated with changes in transparency and water column stabilily.Physiological as well as floristiceffects dictated the variations in fluorescence per unit chlorophyll a. 4. An analysis of twenty-seven primary productivity data sets fromdifferent latitudes shtiwed that Bahia dc Puno resembled other tropicallakes in its relatively weak coupling between algal photosynthesis andseasonal variations in light. Productivity in the temperate zone correlated with the annual cycle of incoming radiation while the tropicalproduction data did not. For many of the tropical lakes, but fewtemperate lakes, the between-month variance in primary production wassignificantly higher than the between-month variance for incomingradiation. There was a significant positive relationship between maximum production variance explained hy light (maximum r2 for each dataset) and latitude. 5. As in many tropical lakes. Bahia de Puno experiences moderatelylarge variations in algal photosynthesis.The muted seasonal cycle of light explains only a small portion of the total variation In productivity, and other factors such as weuther-related events are disproportionately important. 相似文献
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MINAO FURUMURA CHIE SAKAI ZALFA ABDEL-MALEK GREGORY S. BARSH VINCENT J. HEARING 《Pigment cell & melanoma research》1996,9(4):191-203
Important regulatory controls of melanogenesis that operate at the subcellular level to modulate the structural and/or the functional nature of the melanins and melanin granules produced in melanocytes are reviewed. Melanocyte stimulating hormone and agouti signal protein have antagonistic roles and possibly opposing mechanisms of action in the melanocyte. In the mouse, melanocyte stimulating hormone promotes melanogenic enzyme function and elicits increases in the amount of eumelanins produced, while agouti signal protein reduces total melanin production and elicits the synthesis of pheomelanin rather than eumelanin. We are now beginning to understand the complex controls involved in regulating this switch at the molecular and biochemical levels. The quality and quantity of melanins produced by melanocytes have important physiological consequences for melanocyte function and undoubtedly play important roles in the various functions of the melanins per se, including hair and skin coloration and photoprotection. 相似文献
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TOSHIYUI KAIDOH JAYASREE NATH VINCENT OKOYE MASAMICHI AIKAWA 《The Journal of eukaryotic microbiology》1993,40(3):269-271
ABSTRACT. Using transmission electron microscopy, transverse dense bands were found to be associated with subpellicular microtubules and inner membraner in Plasmodium falciparum gametocytes. These dense bands may act as supportive structures to maintain the parallel arrangement of the microtubules, and/or to connect them to the inner membranes. 相似文献
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G. DASTE G. SERRE M-A. MAUDUYT C. VINCENT P. CAVERIVIERE J-P. SOLEILHAVOUP 《Cytopathology》1991,2(1):19-28
This paper presents an immunocytochemical study performed on cytocentrifuged deposits from 109 peritoneal and pleural effusions including 20 transudates, 43 malignant metastatic effusions and 46 effusions containing atypical cells, unidentifiable as reactive mesothelial or malignant epithelial cells on the classical morphological criteria. A panel of four monoclonal antibodies (MAb) was used, including KL1 directed to cytokeratins (KER), V9 to vimentin (VIM), NEO 723 to carcinoembryonic antigen (CEA) and E29 to epithelial membrane antigen (EMA). In most transudates the reactive mesothelial cells coexpressed VIM and KER with a ring-like pattern for the latter proteins. In contrast, they were unreactive to anti-CEA and weakly and inconsistently reactive to anti-EMA. In malignant effusions, most carcinoma cells coexpressed EMA, CEA and KER with a predominant diffuse cytoplasmic pattern for the latter. Only a few malignant epithelial cells from five metastatic adenocarcinomas weakly expressed VIM. When used on the 46 effusions with unidentifiable cells, the panel of MAb allowed reactive mesothelial cells and malignant epithelial cells to be distinguished from each other in 39 of 46 cases (85%). 相似文献