全文获取类型
收费全文 | 1531篇 |
免费 | 188篇 |
专业分类
1719篇 |
出版年
2021年 | 38篇 |
2020年 | 18篇 |
2019年 | 21篇 |
2018年 | 25篇 |
2017年 | 16篇 |
2016年 | 41篇 |
2015年 | 50篇 |
2014年 | 58篇 |
2013年 | 71篇 |
2012年 | 71篇 |
2011年 | 87篇 |
2010年 | 49篇 |
2009年 | 44篇 |
2008年 | 55篇 |
2007年 | 72篇 |
2006年 | 64篇 |
2005年 | 48篇 |
2004年 | 49篇 |
2003年 | 54篇 |
2002年 | 47篇 |
2001年 | 36篇 |
2000年 | 36篇 |
1999年 | 38篇 |
1998年 | 21篇 |
1997年 | 18篇 |
1996年 | 28篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 16篇 |
1992年 | 25篇 |
1991年 | 16篇 |
1990年 | 19篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1987年 | 25篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 17篇 |
1983年 | 18篇 |
1982年 | 22篇 |
1981年 | 23篇 |
1980年 | 13篇 |
1979年 | 18篇 |
1978年 | 23篇 |
1977年 | 21篇 |
1976年 | 12篇 |
1975年 | 22篇 |
1974年 | 13篇 |
1973年 | 17篇 |
1972年 | 18篇 |
排序方式: 共有1719条查询结果,搜索用时 0 毫秒
91.
92.
93.
Pakistan, the second most populous Muslim nation in the world, has started to finally experience and confront the HIV/AIDS epidemic. The country had been relatively safe from any indigenous HIV cases for around two decades, with most of the infections being attributable to deported HIV positive migrants from the Gulf States. However, the virus finally seems to have found a home-base, as evidenced by the recent HIV outbreaks among the injection drug user community. Extremely high-risk behavior has also been documented among Hijras (sex workers) and long-distance truck drivers. The weak government response coupled with the extremely distressing social demographics of this South-Asian republic also helps to compound the problem. The time is ripe now to prepare in advance, to take the appropriate measures to curtail further spread of the disease. If this opportunity is not utilized right now, little if at all could be done later. 相似文献
94.
Krauss S Obert CA Franks J Walker D Jones K Seiler P Niles L Pryor SP Obenauer JC Naeve CW Widjaja L Webby RJ Webster RG 《PLoS pathogens》2007,3(11):e167
Migratory waterfowl of the world are the natural reservoirs of influenza viruses of all known subtypes. However, it is unknown whether these waterfowl perpetuate highly pathogenic (HP) H5 and H7 avian influenza viruses. Here we report influenza virus surveillance from 2001 to 2006 in wild ducks in Alberta, Canada, and in shorebirds and gulls at Delaware Bay (New Jersey), United States, and examine the frequency of exchange of influenza viruses between the Eurasian and American virus clades, or superfamilies. Influenza viruses belonging to each of the subtypes H1 through H13 and N1 through N9 were detected in these waterfowl, but H14 and H15 were not found. Viruses of the HP Asian H5N1 subtypes were not detected, and serologic studies in adult mallard ducks provided no evidence of their circulation. The recently described H16 subtype of influenza viruses was detected in American shorebirds and gulls but not in ducks. We also found an unusual cluster of H7N3 influenza viruses in shorebirds and gulls that was able to replicate well in chickens and kill chicken embryos. Genetic analysis of 6,767 avian influenza gene segments and 248 complete avian influenza viruses supported the notion that the exchange of entire influenza viruses between the Eurasian and American clades does not occur frequently. Overall, the available evidence does not support the perpetuation of HP H5N1 influenza in migratory birds and suggests that the introduction of HP Asian H5N1 to the Americas by migratory birds is likely to be a rare event. 相似文献
95.
Janvier Amy Joy Ulyshen Michael D. Braman Charles A. Traylor Clayton Edelkind-Vealey Miriam Braman S. Kristine 《Journal of Insect Conservation》2022,26(4):697-709
Journal of Insect Conservation - As urbanization continues throughout much of the world, there is great interest in better understanding the value of urban and residential environments to... 相似文献
96.
William Clayton 《International Review of Hydrobiology》1986,71(5):709-717
Ingestion time, digestion time, and assimilation efficiency by the sea anemone Aiptasia pallida were studied in the laboratory by feeding individual anemones preweighed pellets of freeze-dried Artemia salina nauplii. There was no significant correlation between anemone size, measured as dry weight, and either ingestion time, digestion time or assimilation efficiency. Similarly, there was no significant correlation between meal size (i.e., dry weight of ingested brine shrimp pellet) and either ingestion time, digestion time or assimilation efficiency. These results suggest that, under these conditions, assimilation efficiency is unaffected by either “meal” size or anemone size. 相似文献
97.
The California serogroup (CSG) of Orthobunyaviruses comprises several members capable of causing neuroinvasive disease in humans, including La Crosse orthobunyavirus (LACV), Jamestown Canyon orthobunyavirus (JCV), and Inkoo orthobunyavirus (INKV). Despite being genetically and serologically closely related, their disease incidences and pathogenesis in humans and mice differ. We have previously shown that following intraperitoneal inoculation of weanling mice, LACV was highly pathogenic while JCV and INKV were not. To determine why there were differences, we examined the ability of these viruses to invade the CNS and compared the host innate immune responses that regulated viral pathogenesis. We found that LACV was always neuroinvasive, which correlated with its high level of neuroinvasive disease. Interestingly, JCV was not neuroinvasive in any mice, while INKV was neuroinvasive in most mice. The type I interferon (IFN) response was critical for protecting mice from both JCV and INKV disease, although in the periphery JCV induced little IFN expression, while INKV induced high IFN expression. Despite their differing neuroinvasive abilities, JCV and INKV shared innate signaling components required for protection. The presence of either cytoplasmic Rig-I-Like Receptor signaling or endosomal Toll-Like Receptor signaling was sufficient to protect mice from JCV or INKV, however, inhibition of both pathways rendered mice highly susceptible to neurological disease. Comparison of IFN and IFN-stimulated gene (ISG) responses to INKV in the brains of resistant wild type (WT) mice and susceptible immune knockout mice showed similar IFN responses in the brain, but WT mice had higher ISG responses, suggesting induction of key ISGs in the brain is critical for protection of mice from INKV. Overall, these results show that the CSG viruses differ in neuroinvasiveness, which can be independent from their neuropathogenicity. The type I IFN response was crucial for protecting mice from CSG virus-induced neurological disease, however, the exact correlates of protection appear to vary between CSG viruses. 相似文献
98.
William S. Clayton 《International Review of Hydrobiology》1984,69(5):633-642
The effects of light regime, feeding regime and tentacle number on the zooplankton feeding capability of Hydra viridis were tested in the laboratory. Feeding was measured by exposing Hydra to a known volume of Artemia salina nauplii and recording the number captured and ingested. In all cases there was a correlation between the number of Artemia captured and the number ingested. H. viridis with 7 tentacles captured and ingested more Artemia than Hydra with 6 tentacles. However, changes in light and/or feeding regimes did not alter the number of tentacles/Hydra. Varying light and feeding regimes altered the number of Zoochlorellae/cell and Hydra growth rate. There was no effect on the number of Artemia captured or ingested and no effect on the percent ingestion of captured Artemia. These data suggest that, under these conditions, zooplankton feeding by H. viridis is independent of nutritional history. 相似文献
99.
100.
Nicole C. Thunes Rachel A. Conrad Haitham H. Mohammed Yongtao Zhu Paul Barbier Jason P. Evenhuis David Perez-Pascual Jean-Marc Ghigo Ryan S. Lipscomb John R. Schneider Nan Li Devon H. Erbes Clayton Birkett Benjamin R. LaFrentz Timothy J. Welch Mark J. McBride 《Applied and environmental microbiology》2022,88(3)