全文获取类型
收费全文 | 7836篇 |
免费 | 329篇 |
国内免费 | 119篇 |
出版年
2024年 | 9篇 |
2023年 | 66篇 |
2022年 | 99篇 |
2021年 | 168篇 |
2020年 | 133篇 |
2019年 | 205篇 |
2018年 | 191篇 |
2017年 | 147篇 |
2016年 | 152篇 |
2015年 | 197篇 |
2014年 | 309篇 |
2013年 | 475篇 |
2012年 | 274篇 |
2011年 | 361篇 |
2010年 | 221篇 |
2009年 | 307篇 |
2008年 | 394篇 |
2007年 | 394篇 |
2006年 | 354篇 |
2005年 | 306篇 |
2004年 | 317篇 |
2003年 | 294篇 |
2002年 | 264篇 |
2001年 | 209篇 |
2000年 | 169篇 |
1999年 | 161篇 |
1998年 | 158篇 |
1997年 | 142篇 |
1996年 | 152篇 |
1995年 | 163篇 |
1994年 | 154篇 |
1993年 | 138篇 |
1992年 | 135篇 |
1991年 | 130篇 |
1990年 | 127篇 |
1989年 | 110篇 |
1988年 | 100篇 |
1987年 | 65篇 |
1986年 | 88篇 |
1985年 | 95篇 |
1984年 | 85篇 |
1983年 | 57篇 |
1982年 | 56篇 |
1981年 | 55篇 |
1980年 | 28篇 |
1979年 | 18篇 |
1978年 | 17篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1971年 | 4篇 |
排序方式: 共有8284条查询结果,搜索用时 15 毫秒
1.
《Cell reports》2020,30(1):164-172.e4
- Download : Download high-res image (143KB)
- Download : Download full-size image
2.
目的:观察不同酸中毒条件下正常大鼠和脓毒性休克大鼠胸主动脉对多巴胺反应性的变化。方法:采用离体血管灌流方法,观察对照组和脓毒性休克组大鼠胸主动脉在不同pH条件下的反应性变化。结果:pH值依次降低,对照组及脓毒性休克组离体胸主动脉对多巴胺反应性均下降,在相同pH值条件下脓毒性休克组比对照组离体血管对多巴胺反应性下降更为明显。结论:①环境pH值的下降会导致正常大鼠和脓毒性休克大鼠离体动脉对多巴胺反应性的下降。②在相同的酸性环境中脓毒性休克大鼠的血管对多巴胺刺激的反应性更差,更易失去活性。 相似文献
3.
4.
Numerous data suggested that the pharmacological and biochemical properties of 5-hydroxytryptamine1A (5-HT1A) receptors exhibit some regional differences in the CNS, notably within the raphe nuclei compared with various forebrain areas (such as the hippocampus). This possibility has been further investigated in the dorsal raphe nucleus and two areas within the hippocampus, the dentate gyrus and the CA1 area, using the quantitative autoradiographic technique. The potencies of 5'-guanylylimidodiphosphate to inhibit the specific binding of 125I-Bolton-Hunter-8-methoxy-2-(N-propyl-N-propylamino)tetralin (125I-BH-8-MeO-N-PAT) to 5-HT1A sites and of N-ethylmaleimide to block these sites irreversibly were identical in the dorsal raphe nucleus and the hippocampal areas in rat brain sections. In contrast, slight but significant differences were noted in the pH dependence and pharmacological properties of 5-HT1A sites labeled by 125I-BH-8-MeO-N-PAT in these three regions. Similarly, heat denaturation experiments and tissue exposure to either phospholipase A2 or the alkylating agent 8-methoxy-2-(N-2'-chloropropyl,N-propyl)aminotetraline revealed regional differences in the properties of 5-HT1A sites. However, in most cases, the observed variations were of greater amplitude between the CA1 area and the dentate gyrus, where 5-HT1A sites are located postsynaptically, than between any one of these areas and the dorsal raphe nucleus where they act as (presynaptic) somatodendritic autoreceptors. These data further support that subtypes of 5-HT1A receptors probably exist in the rat brain, but this heterogeneity seems unrelated to the pre- or post-synaptic location of these receptors. 相似文献
5.
《Developmental cell》2020,52(6):714-730.e5
- Download : Download high-res image (188KB)
- Download : Download full-size image
6.
Mandy L. Roberts-Crowley Tora Mitra-Ganguli Liwang Liu Ann R. Rittenhouse 《Cell calcium》2009,45(6):589-601
Great skepticism has surrounded the question of whether modulation of voltage-gated Ca2+ channels (VGCCs) by the polyunsaturated free fatty acid arachidonic acid (AA) has any physiological basis. Here we synthesize findings from studies of both native and recombinant channels where micromolar concentrations of AA consistently inhibit both native and recombinant activity by stabilizing VGCCs in one or more closed states. Structural requirements for these inhibitory actions include a chain length of at least 18 carbons and multiple double bonds located near the fatty acid's carboxy terminus. Acting at a second site, AA increases the rate of VGCC activation kinetics, and in CaV2.2 channels, increases current amplitude. We present evidence that phosphatidylinositol 4,5-bisphosphate (PIP2), a palmitoylated accessory subunit (β2a) of VGCCs and AA appear to have overlapping sites of action giving rise to complex channel behavior. Their actions converge in a physiologically relevant manner during muscarinic modulation of VGCCs. We speculate that M1 muscarinic receptors may stimulate multiple lipases to break down the PIP2 associated with VGCCs and leave PIP2's freed fatty acid tails bound to the channels to confer modulation. This unexpectedly simple scheme gives rise to unanticipated predictions and redirects thinking about lipid regulation of VGCCs. 相似文献
7.
Bone morphogenetic protein 2 (BMP-2) has been known for decades as a strong osteoinductive factor and for clinical applications is combined solely with collagen as carrier material. The growing concerns regarding side effects and the importance of BMP-2 in several developmental and physiological processes have raised the need to improve the design of materials by controlling BMP-2 presentation. Inspired by the natural cell environment, new material surfaces have been engineered and tailored to provide both physical and chemical cues that regulate BMP-2 activity. Here we describe surfaces designed to present BMP-2 to cells in a spatially and temporally controlled manner. This is achieved by trapping BMP-2 using physicochemical interactions, either covalently grafted or combined with other extracellular matrix components. In the near future, we anticipate that material science and biology will integrate and further develop tools for in vitro studies and potentially bring some of them toward in vivo applications. 相似文献
8.
Larval hemolymph tyrosinase activity in Drosophila melanogaster was detected with high performance liquid chromatography with electrochemical detection. The enzyme hydroxylated L-tyrosine, and oxidized the diphenol substrates L-dopa and dopamine. In larvae of a selected immune-reactive strain the rates of tyrosine hydroxylation, dopa oxidation, and dopamine oxidation were markedly increased during the early stages of melanotic encapsulation of the eggs of the parasitic wasp Leptopilina boulardi. Tyrosinase activity was not modified in parasitized larvae of a selected susceptible strain of D. melanogaster, in which hosts the parasitoids developed unmolested. During the same period of parasitization, the amount of free tyrosine in immune reactive larvae was approximately three times higher than in susceptible hosts. These data indicate that the tyrosinase system of the immune reactive strain is activated during parasitization, and this results in the synthesis of some precursors which ultimately produce a melanotic and sclerotic capsule around the eggs of the parasite. Based on known genetic information of the enzyme system in Drosophila, it appears that at least two genes may be involved in the activation process, one associated with the proenzyme for monophenol oxidase activity, and the second with the proenzyme for diphenol oxidase activity. 相似文献
9.
10.