全文获取类型
收费全文 | 811篇 |
免费 | 21篇 |
国内免费 | 67篇 |
出版年
2015年 | 10篇 |
2013年 | 17篇 |
2012年 | 20篇 |
2011年 | 27篇 |
2010年 | 33篇 |
2009年 | 46篇 |
2008年 | 33篇 |
2007年 | 53篇 |
2006年 | 42篇 |
2005年 | 35篇 |
2004年 | 28篇 |
2003年 | 35篇 |
2002年 | 29篇 |
2001年 | 14篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 17篇 |
1993年 | 14篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 15篇 |
1973年 | 6篇 |
1972年 | 7篇 |
1971年 | 11篇 |
1966年 | 6篇 |
1959年 | 9篇 |
1958年 | 18篇 |
1957年 | 18篇 |
1956年 | 10篇 |
1955年 | 16篇 |
1954年 | 17篇 |
1953年 | 11篇 |
1952年 | 8篇 |
1951年 | 9篇 |
排序方式: 共有899条查询结果,搜索用时 31 毫秒
841.
Increased use of conjoint analysis during the concept testing stage of food product development raises the question of whether conjoint analysis results translate into successful product development. Five food bar concepts from a previous conjoint analysis study targeted for the “Overall” panel, “Female” segment, “Male” segment, “Label Readers” segment and “Calorie Health Nuts” segment, were used for consumer testing. Standardized packaging was also developed to test elements not easily perceived from the product itself, i.e., low fat, low calorie and other nutritional information. The “Female #1 – commercial (Fiber One)” bar had the highest overall acceptance, 6.9 on a 9-point hedonic scale. Packaging significantly increased all ratings. Cluster analysis results were compared with segmentation from conjoint analysis. Similar results were found, showing there were clusters of consumers specifically interested in prototypes developed for specific conjoint analysis segments, which supports that conjoint analysis results translate into actual products. 相似文献
842.
Phospholipase C-mediated calcium signalling is required for fungal development and pathogenicity in Magnaporthe oryzae 总被引:1,自引:0,他引:1
Calcium signalling has profound implications in the fungal infection of plants and animals, during which a series of physiological and morphological transitions are required. In this article, using a model fungal pathogen, Magnaporthe oryzae , we demonstrate that the regulation of the intracellular calcium concentration ([Ca2+ ]int ) is essential for fungal development and pathogenesis. Imaging of [Ca2+ ]int showed that infection-specific morphogenesis is highly correlated with the spatiotemporal regulation of calcium flux. Deletion of the fungal phospholipase C gene ( M. oryzae phospholipase C 1, MoPLC1 ) suppressed calcium flux, resulting in a fungus defective in developmental steps, including appressorium formation and pathogenicity. Surprisingly, the PLC-δ1 gene of mouse was able to functionally substitute for MoPLC1 by restoring the calcium flux, suggesting the evolutionary conservation of the phospholipase C-mediated regulation of calcium flux. Our results reveal that MoPLC1 is a conserved modulator of calcium flux that is essential for the regulation of key steps in fungal development and pathogenesis. 相似文献
843.
YOUNG‐JOON PARK SUJIN KIM AEREE KIM SEUNG‐YEON HA YOUNG‐MEE LEE BONG‐KYUNG SHIN HYUN‐JOO LEE SOOJIN PARK HAN‐KYEOM KIM 《Bioethics》2010,24(6):309-322
This study assessed the knowledge and perception of human biological materials (HBM) and biorepositories among three study groups in South Korea. The relationship between the knowledge and the perception among different groups was also examined by using factor and regression analyses. In a self‐reporting survey of 440 respondents, the expert group was found more likely to be knowledgeable and positively perceived than the others. Four factors emerged: Sale and Consent, Flexible Use, Self‐Confidence, and Korean Bioethics and Biosafety Action restriction perception. The results indicate that those who are well aware of the existence of biobanks were more positively inclined to receive the Sale and Consent perception. As a result of the need for high quality HBMs and the use of appropriate sampling procedures for every aspect of the collection and use process, the biorepository community should pay attention to ethical, legal, and policy issues. 相似文献
844.
845.
THOMPSON ALISTAIR; VOGEL JOHN; LEE ROBERT EDWARD 《Journal of experimental botany》1977,28(4):1037-1041
Young leaves of Katanchoë pinnata Persoon fix CO2 by theC3 pathway while older leaves fix CO2 by the Crassulacean acidmetabolism pathway. The switchover from one system to the otheris associated with the disappearence of an inclusion body inthe chloroplasts of young leaves. 相似文献
846.
847.
Marine benthic communities in the Upper Devonian of New York 总被引:1,自引:0,他引:1
ZEDDIE P. BOWEN DONALD C. RHOADS A. LEE McALESTER 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1974,7(2):93-120
Four distinctive benthic communities occur in the mid-shelf deltaic deposits of the Upper Devonian Sonyea Group: the Bellerophon Community, dominated by herbivorous gastropods and deposit-feeding bivalves; the Prodrtctella Community, dominated by brachiopods with adaptations for life on muddy substrata; the Cypricardella Community, dominated by bivalves and brachiopods with a variety of adaptations; and the Rhipidomella Community, dominated by brachiopods adapted for life on sandy substrata. The geographic and stratigraphic occurrence of the communities suggest that their distribution was controlled by two principal sets of environmental variables: (1) onshore to offshore gradients in salinity, dissolved oxygen concentrations, and sedimentary substrata, and (2) rate of delta progradation. A change in the rate of delta build-out during mid-Sonyea time led to a dramatic change in onshore to offshore community patterns. The change suggests that great care must be used in constructing generalized community models for longer intervals of Paleozoic time. 相似文献
848.
849.
850.
1. Aposematic coloration in prey promotes its survival by conspicuously advertising unpalatability to predators. Although classical examples of aposematic signals involve constant presentation of a signal at a distance, some animals suddenly display warning colours only when they are attacked. 2. Characteristics of body parts suddenly displayed, such as conspicuous coloration or eyespot pattern, may increase the survival of the prey by startling the predator, and/or by signalling unpalatability to the predators at the moment of attack. 3. The adaptive value of such colour patterns suddenly displayed by unpalatable prey has not been studied. We experimentally blackened the red patch in the conspicuous red–white–black hindwing pattern displayed by an unpalatable insect Lycorma delicatula White (Hemiptera: Fulgoridae) in response to predator's attack. 4. There was no evidence that the presence of the red patch increased prey survival over several weeks. We hypothesise that predators generalised from the red–white–black patches on the hindwings of unpalatable L. delicatula to any similar wing display as a signal of unpalatability. Because a higher proportion of males than females stay put at their resting sites, displaying their wings in response to repeated attacks by predators, wing damage was more frequent in males than in females. 5. To our knowledge, this is the first experimental test of an adaptive role of aposematic signals presented by unpalatable prey during sudden displays triggered by direct predatory attack. 相似文献