全文获取类型
收费全文 | 53693篇 |
免费 | 5133篇 |
国内免费 | 30篇 |
出版年
2023年 | 172篇 |
2021年 | 636篇 |
2020年 | 532篇 |
2019年 | 693篇 |
2018年 | 861篇 |
2017年 | 795篇 |
2016年 | 1345篇 |
2015年 | 2242篇 |
2014年 | 2366篇 |
2013年 | 3132篇 |
2012年 | 3658篇 |
2011年 | 3659篇 |
2010年 | 2439篇 |
2009年 | 2098篇 |
2008年 | 3055篇 |
2007年 | 3064篇 |
2006年 | 2812篇 |
2005年 | 2919篇 |
2004年 | 2843篇 |
2003年 | 2782篇 |
2002年 | 2732篇 |
2001年 | 612篇 |
2000年 | 497篇 |
1999年 | 620篇 |
1998年 | 750篇 |
1997年 | 543篇 |
1996年 | 496篇 |
1995年 | 521篇 |
1994年 | 468篇 |
1993年 | 427篇 |
1992年 | 508篇 |
1991年 | 425篇 |
1990年 | 359篇 |
1989年 | 362篇 |
1988年 | 341篇 |
1987年 | 330篇 |
1986年 | 308篇 |
1985年 | 395篇 |
1984年 | 419篇 |
1983年 | 335篇 |
1982年 | 450篇 |
1981年 | 393篇 |
1980年 | 342篇 |
1979年 | 279篇 |
1978年 | 311篇 |
1977年 | 286篇 |
1976年 | 258篇 |
1975年 | 213篇 |
1974年 | 259篇 |
1973年 | 259篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
Effects of Δ8- and Δ9-tetrahydrocannabinol (Δ8- and Δ9-THC) on three experimentally induced seizure models, i.e., audiogenic seizure (AS) test, maximal electroshock seizure (MES) test and pentylenetetrazol (PTZ)-induced seizure test were determined in the audiogenic rat. Both tetrahydrocannabinols possess a dose-related anticonvulsant effect against AS, MES and PTZ-induced maximal seizure. Although anticonvulsant potencies do not significantly differ, Δ8THC is three times more neurotoxic than Δ9THC. In addition, both THC's are without effect on minimal seizure and lethality induced by PTZ. Furthermore, the low protective indexes (TD50/ED50) determined in this study suggest that Δ8 and Δ9 THC may have poor therapeutic potentials as antiepileptic drugs. 相似文献
95.
Scytinostroma galactinum (Fr.)Donk is the fungus commonly known asCorticium galctinum (Fr.)Burt. Although it occurs as a saprobe on woody plants and plant debris, it also has been considered by several authors as an active pathogen that causes a white root and butt or collar rot. During the summer of 1970, it was found near Baltimore and also in Montgomery County, Maryland, under circumstances that seemingly provide additional records of pathogenicity. Several other Maryland records are cited, and many Canadian studies have been reviewed.S. galactinum has a distinctive dextrinoid mycelium, which is characteristic enough to permit a tentative identification even in the absence of other features. Outstanding elements of the basidiocarp are the dextrinoid hyphae and slender gloeocystidia. In culture, dextrinoid fiber hyphae and papillate oil-bearing hyphae with clamp connections are characteristic. These and other features of the basidiocarp and culture serve in the characterization of this fungus, which is economically significant and widely distributed. 相似文献
96.
97.
98.
99.
100.
Amy Chapman Gonzalo Gonzales Wayne R. Burrowes Paul Assanah Bernadette Iannone Michael K. Leung George B. Stefano 《Cellular and molecular neurobiology》1984,4(2):143-155
In Mytilus and Leucophaea the high-affinity binding site density is significantly lower in old animals than in young animals, whereas the low-affinity site density remains unchanged. In Mytilus the estimated met-enkephalin and met-enkephalin-Arg6-Phe7 levels are significantly higher in old than in young animals. In Leucophaea only the met-enkephalin level can be determined, and it is also higher in old animals. The decrease in the high-affinity binding site density and the corresponding increase in endogenous enkephalin levels suggest the existence of an opioid compensatory mechanism associated with the aging process. In Mytilus there is a demonstrated decrease with age in intraganglionic dopamine levels in response to applied opiates. In addition, the inhibition of dopamine-stimulated adenylate cyclase activity by opiates also decreases in older animals. In Leucophaea the sex difference in opioid binding densities diminishes with age. 相似文献