全文获取类型
收费全文 | 1318990篇 |
免费 | 148072篇 |
国内免费 | 862篇 |
出版年
2018年 | 11364篇 |
2016年 | 15993篇 |
2015年 | 22791篇 |
2014年 | 26571篇 |
2013年 | 37617篇 |
2012年 | 42393篇 |
2011年 | 42700篇 |
2010年 | 29173篇 |
2009年 | 26922篇 |
2008年 | 38245篇 |
2007年 | 39420篇 |
2006年 | 36957篇 |
2005年 | 35685篇 |
2004年 | 35437篇 |
2003年 | 34177篇 |
2002年 | 33282篇 |
2001年 | 56677篇 |
2000年 | 57011篇 |
1999年 | 45651篇 |
1998年 | 16882篇 |
1997年 | 17573篇 |
1996年 | 16575篇 |
1995年 | 16127篇 |
1994年 | 15770篇 |
1993年 | 15644篇 |
1992年 | 38378篇 |
1991年 | 37383篇 |
1990年 | 36690篇 |
1989年 | 35832篇 |
1988年 | 33233篇 |
1987年 | 31800篇 |
1986年 | 29501篇 |
1985年 | 29625篇 |
1984年 | 24759篇 |
1983年 | 21321篇 |
1982年 | 16763篇 |
1981年 | 15038篇 |
1980年 | 14179篇 |
1979年 | 23530篇 |
1978年 | 18645篇 |
1977年 | 16895篇 |
1976年 | 15803篇 |
1975年 | 17343篇 |
1974年 | 18642篇 |
1973年 | 18424篇 |
1972年 | 16557篇 |
1971年 | 15288篇 |
1970年 | 13127篇 |
1969年 | 12584篇 |
1968年 | 11372篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Numerous investigations have been carried out on the spectral distribution of the light of different species of fireflies. Here we record the emission spectrum of the Indian species of the firefly Luciola praeusta Kiesenwetter 1874 (Coleoptera : Lampyridae : Luciolinae) on a color film. Green and red color-sectors, with an intense yellow one in between, appear in this spectrum. Intensity profile of this spectrum reveals a hitherto undetected strong narrow yellow line, which lies within the full-width-at-half maximum (FWHM) of the intensity profile. The spectrum recorded in a high-resolution spectrometer confirms the presence of this sharp intense line. This finding lends support to an earlier drawn analogy between the in vivo emission of the firefly and laser light. 相似文献
992.
993.
M. A. RUBEGA 《Ibis》1997,139(3):488-493
Surface tension prey transport is a feeding mechanism employing the surface tension of water surrounding prey to transport prey from bill tip to mouth. Previously, it has been demonstrated only in the Red-necked Phalarope Phalaropus lobatus. On the basis of a model of the bill morphology necessary for this method of prey transport, I suggest that many species of shorebird should be capable of surface tension feeding. Laboratory investigations of the feeding mechanics of Wilson's Phalarope Phalaropus tricolor , Western Sandpiper Calidris mauri and Least Sandpiper Calidris minutilla demonstrated that all three use surface tension transport of prey when feeding in water. I examined interspecific variation in the performance of this feeding mechanism with a high-speed video system and a customized motion analysis system. Exploratory analyses indicated significant interspecific variation in distance the prey is transported per cycle of mandibular spreading, gape increase per unit transport, speed of transport, total number of cycles necessary to complete transport and total time to complete transport. The calidrid sandpipers also occasionally used other feeding mechanisms in conjunction with surface tension transport of prey. The discovery that these sandpipers, which normally obtain prey by probing, are capable of surface tension transport of prey implies that the capacity to employ this feeding mechanism may be widespread in the Scolopacidae and may have been a significant factor in the evolutionary radiation of phalaropes into aquatic environments. 相似文献
994.
Phytochrome A regulates red-light induction of phototropic enhancement in Arabidopsis. 总被引:20,自引:5,他引:15 下载免费PDF全文
Phytochrome A (phyA) and phytochrome B photoreceptors have distinct roles in the regulation of plant growth and development. Studies using specific photomorphogenic mutants and transgenic plants overexpressing phytochrome have supported an evolving picture in which phyA and phytochrome B are responsive to continuous far-red and red light, respectively. Photomorphogenic mutants of Arabidopsis thaliana that had been selected for their inability to respond to continuous irradiance conditions were tested for their ability to carry out red-light-induced enhancement of phototropism, which is an inductive phytochrome response. We conclude that phyA is the primary photoreceptor regulating this response and provide evidence suggesting that a common regulatory domain in the phyA polypeptide functions for both high-irradiance and inductive phytochrome responses. 相似文献
995.
Moment-based criteria for determining bioequivalence 总被引:1,自引:0,他引:1
996.
997.
998.
999.
The littoral microcrustacean fauna of Tivoli South Bay was studied from July to September, 1989. The effects of fish predation
on microcrustacean densities were tested in a short-term predator exclusion experiment. Fish were excluded from water chestnut
(Trapa natans) plots in four screened exclosures. An equal number of open cages allowed foraging. Fish predation did not have a significant
effect on densities of ostracods or other microcrustaceans. Ostracod densities increased in cages throughout the experimental
period, whereas cladoceran and copepod densities decreased in both treatments. Gut contents analysis of banded killifish (Fundulus diaphanus) revealed that ostracods and other microcrustaceans were commonly ingested by larval, juvenile, and adult killifish utilizing
T. natans as habitat. These results suggest that ostracods and other microcrustacean epifauna associated with T. natans may represent an important trophic link in the tidal freshwater wetlands of the Hudson River Estuary.
Deceased 相似文献
1000.