全文获取类型
收费全文 | 818篇 |
免费 | 18篇 |
国内免费 | 69篇 |
专业分类
905篇 |
出版年
2015年 | 10篇 |
2013年 | 18篇 |
2012年 | 20篇 |
2011年 | 27篇 |
2010年 | 34篇 |
2009年 | 46篇 |
2008年 | 33篇 |
2007年 | 53篇 |
2006年 | 42篇 |
2005年 | 36篇 |
2004年 | 28篇 |
2003年 | 35篇 |
2002年 | 29篇 |
2001年 | 14篇 |
1999年 | 7篇 |
1998年 | 9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905条查询结果,搜索用时 0 毫秒
901.
ABSTRACT. 1. The effects of colony size and time of reproduction on the survival and size of offspring colonies and on drone production were examined for honey bees, Apis mellifera L. Drone and worker production and survival of parental and offspring colonies were monitored following swarming. Also, the temporal patterns of drone emergence and availability of unmated queens were examined.
2. Colony size at swarming was positively correlated with the number of workers invested in offspring colonies and the number of queens produced. However, colony size at swarming was not correlated with the number of offspring colonies produced.
3. Swarm size was positively correlated with drone and worker production after swarms were hived. Worker production of hived swarms was positively correlated with colony survival. Offspring queens which inherited a parental nest survived longer than queens in either primary swarms or afterswarms, presumably due to the advantage of inheriting a nest.
4. Drone emergence peaked just prior to swarming, the time when unmated queens were available. High drone production by colonies initiated by swarms probably reflected an attempt to reproduce prior to winter. The probabilities of a second swarming cycle within the same year and of surviving the winter were low for colonies initiated from swarms. 相似文献
2. Colony size at swarming was positively correlated with the number of workers invested in offspring colonies and the number of queens produced. However, colony size at swarming was not correlated with the number of offspring colonies produced.
3. Swarm size was positively correlated with drone and worker production after swarms were hived. Worker production of hived swarms was positively correlated with colony survival. Offspring queens which inherited a parental nest survived longer than queens in either primary swarms or afterswarms, presumably due to the advantage of inheriting a nest.
4. Drone emergence peaked just prior to swarming, the time when unmated queens were available. High drone production by colonies initiated by swarms probably reflected an attempt to reproduce prior to winter. The probabilities of a second swarming cycle within the same year and of surviving the winter were low for colonies initiated from swarms. 相似文献
902.
903.
A sulfur-containing lipid with chromatographic properties in several systems equal to the commercial sulfolipid (extracted from bovine spinal cord, Applied Science) has been isolated in 0.6 % yield (dry weight basis) from the mycelia of Glomerella cingulata. About 35 % of exogenous Na35SO4 incubated with the mycelial medium for 72 hours was recovered in the cerebroside sulfate fraction, with only traces of 35S activities in other lipid fractions. 相似文献
904.
DONG-JIN LEE GRAHAM A. YOUNG JAMES P. A. NOBEL 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1990,23(1):11-20
A study of the Heliolites interstinctus-decipiens lineage from the Silurian of the Chalcur Bay region, eastern Canada, indicates that most morphological characters of this lineage, including tabularium diameter, coenenchymal tubule diameter and corallite spacing, remain relatively invariate through a Llandovery to Pridoli interval of about 20 million years. In contrast, septal development and corallite wall erenulation show pronounced evolutionary changes due to heterochrony, as shown by comparison of astogenies throughout the lineage. The reduction of septa and the replacement of crenulate corallites by smooth ones in the 'decipiens' type descendent appear to have been by paedomorphosis from the 'interstinctus' type ancestor. The problems of speciation in this lineage are discussed including the alternative hypotheses of a speciation event in the early Ludlow or a phyletic trend within a single species whose longevity is due in part to the stabilization processes of niche separation. 相似文献
905.
R-index measures were obtained from judges who ranked black coffees for preferred drinking temperature. Preferred temperatures were above thermal pain and thermal damage thresholds. The least preferred temperature was below the oral thermal pain threshold. Similar results were obtained with a ranking for temperatures that judges felt were most likely to be served in a coffee shop. Observations of customers in coffee shops indicated that they began sipping coffee at similar high temperatures. 相似文献