全文获取类型
收费全文 | 4611篇 |
免费 | 52篇 |
国内免费 | 43篇 |
出版年
2023年 | 12篇 |
2022年 | 12篇 |
2021年 | 27篇 |
2020年 | 78篇 |
2019年 | 59篇 |
2018年 | 73篇 |
2017年 | 53篇 |
2016年 | 24篇 |
2015年 | 75篇 |
2014年 | 210篇 |
2013年 | 228篇 |
2012年 | 235篇 |
2011年 | 356篇 |
2010年 | 256篇 |
2009年 | 198篇 |
2008年 | 211篇 |
2007年 | 195篇 |
2006年 | 184篇 |
2005年 | 163篇 |
2004年 | 170篇 |
2003年 | 153篇 |
2002年 | 89篇 |
2001年 | 46篇 |
2000年 | 89篇 |
1999年 | 84篇 |
1998年 | 109篇 |
1997年 | 104篇 |
1996年 | 100篇 |
1995年 | 110篇 |
1994年 | 79篇 |
1993年 | 78篇 |
1992年 | 94篇 |
1991年 | 80篇 |
1990年 | 79篇 |
1989年 | 70篇 |
1988年 | 73篇 |
1987年 | 65篇 |
1986年 | 52篇 |
1985年 | 54篇 |
1984年 | 79篇 |
1983年 | 48篇 |
1982年 | 47篇 |
1981年 | 31篇 |
1980年 | 27篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 3篇 |
1972年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有4706条查询结果,搜索用时 15 毫秒
1.
《Saudi Journal of Biological Sciences》2017,24(5):1034-1037
Background: Propolis is a natural product of plant resins collected by honeybees from various plant sources. It is used as a remedy in folk medicine since ancient times because of its several biological and pharmacological properties. Recently, propolis has been used by dentist to treat various oral diseases. It was always mentioned as an anti-inflammatory agent. Cytokines are proteins that provide communication between cells and play a critical role in a wide variety of processes. It released from cells in an inflammatory process that active, mediate or potential actions of other cells or tissues. When dental pulp has inflammation, several pro-inflammatory cytokines including Interleukin-6 (IL-6) was released by innate immune cells. Objective: To analyse the expression of IL-6 on inflamed rat dental pulp tissue following application of propolis. Material and methods: Trigona sp. propolis was obtained from Luwu Regency, south Sulawesi Province, Indonesia. Flavonoid and non-flavonoid extracts were purified from propolis using thin layer chromatography. The study was applied on 80 male Sprague Dawley rats, 10–12 weeks of age, divided randomly and equally into 5 groups. Group I, as negative control group was not conducted any treatment. At group II, III, IV and V. A Class I cavity (Black Classification) were made on the occlusal surface of right maxillary first molar. The dental pulp was perforated using dental explorer and allowed in the oral environment for 1 h, after that, Ethanolic Extract Propolis (EEP) (Group II), Extract Flavonoid-Propolis (EFP) (Group III), Extract Non-Flavonoid Propolis (ENFP) (Group IV), or Calcium Hydroxide (Ca(OH)2) (Group V) were applied on dental pulp. All cavities were then filled with Glass Ionomer Cement as permanent filling. The rats being sacrificed in 6 h, 2 days, 4 days and 7 days. Sample biopsy were obtained, IL-6 expression was detected by using immunohistochemistry method. Data was analyzed statistically using Freidman and Kruskal Wallis tests with significance level of P < 0.05. Results: All agent showed IL-6 expression in inflamed rat dental pulp tissue, and this expression was decreased with the longer of observation time periods. EEP more stronger to decreased IL-6 expression on inflamed rat dental pulp tissue than other agent. There is significant difference (P < 0.05) of IL-6 expression between group I and other groups in 6 h and 2 days but not in 4 and 7 days time periods. Conclusion: Trigona sp. propolis from south Sulawesi, Indonesia could suppressed the expression of IL-6 on inflamed rat dental pulp tissue. 相似文献
2.
Oussama El Far Béatrice Marquèze Christian Leveque Nicole Martin-Moutôt Bethan Lang John Newsom-Davis †Akira Yoshida †Masami Takahashi Michael J. Seagar 《Journal of neurochemistry》1995,64(4):1696-1702
Abstract: In Lambert-Eaton myasthenic syndrome neurotransmitter release is reduced by an autoimmune response directed against the calcium channel complex of the nerve terminal. Autoantibodies were detected by immunoprecipitation assays using solubilized receptors labeled with ligands selective for N-type (125 I-ω conotoxin GVIA) and L-type ([3 H]PN200-110) calcium channels. Sera with a high antibody titer (>3 n M ) against rat brain N-type channels contained autoantibodies that immunoprecipitated neuronal and muscle L-type channels. These IgG fractions stained a 55-kDa protein in immunoblots of purified skeletal muscle dihydropyridine receptor, suggesting that they contain autoantibodies against the β subunit of the calcium channel. A distinct antibody population in the same fractions reacted with a nerve terminal 65-kDa protein that is unrelated to the β subunit and displays properties similar to those of synaptotagmin. 相似文献
3.
Patterns of mobilization of calcium,magnesium, and phosphorus by embryonic yellow-headed blackbirds(Xanthocephalus xanthocephalus) 总被引:1,自引:0,他引:1
Mary J. Packard Gary C. Packard 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,160(6):649-654
Summary Embryonic blackbirds(Xanthocephalus xanthocephalus) obtain most of their calcium from the eggshell (85 90%), but all of their phosphorus comes from reserves in the yolk (80–85%) and albumen (15–20%). Approximately equal amounts of magnesium are supplied by the eggshell, the yolk, and the albumen. Yolk is depleted of magnesium and phosphorus during embryogenesis, but excess calcium absorbed from the eggeshell is stored in the yolk. Consequently reserves of calcium in the yolk actually increase 8-fold during embryonic development. Our results reveal that altricial birds manifest patterns of mobilization and deposition of calcium and other elements similar to those described for precocial species. Evolution of altriciality from precocity evidently did not entail major changes in how embryonic birds meet the challenge of obtaining the calcium, magnesium, and phosphorus required for development. 相似文献
4.
Abstract: Bovine adrenal chromaffin cells (BCC) were used to compare histamine- and angiotensin II-induced changes of inositol mono-, bis-, and trisphosphate (InsP1, InsP2, and InsP3, respectively) isomers, intracellular free Ca2+ ([Ca2+]i), and the pathways of inositol phosphate metabolism. Both agonists elevated [Ca2+]i by 200 nM 3–4 s after addition, but afterwards the histamine response was much more prolonged. Histamine and angiotensin II also produced similar four- to fivefold increases of Ins(1,4,5)P3 that peaked within 5 s. Over the first minute of stimulation, however, Ins(1,4,5)P3 formation was monophasic after angiotensin II, but biphasic after histamine, evidence supporting differential regulation of angiotensin II- and histamine-stimulated signal transduction. The metabolism of Ins(1,4,5)P3 by BCC homogenates was found to proceed via (a) sequential dephosphorylation to Ins(1,4)P2 and Ins(4)P, and (b) phosphorylation to inositol 1,3,4,5-tetrakisphosphate, followed by dephosphorylation to Ins(1,3,4)P3, Ins(1,3)P2, and Ins(3,4)P2, and finally to Ins(1 or 3)P. In whole cells, Ins(1 or 3)P only increased after histamine treatment. Additionally, Ins(1,3)P2 was the only other InsP2 besides Ins(1,4)P2 to accumulate within 1 min of agonist treatment [Ins(3,4)P2 did not increase]. These results support a correlation between the time course of Ins(1,4,5)P3 formation and the time course of [Ca2+]i transients and illustrate that Ca2+-mobilizing agonists can produce distinguishable patterns of inositol phosphate formation and [Ca2+], changes in BCC. Different patterns of second-messenger formation are likely to be important in signal recognition and may encode agonist-specific information. 相似文献
5.
Johan C. Sunryd Banyoon Cheon Jill B. Graham Kristina M. Giorda Rafael A. Fissore Daniel N. Hebert 《The Journal of biological chemistry》2014,289(23):16085-16099
The endoplasmic reticulum (ER) is organized in part by adapter proteins that nucleate the formation of large protein complexes. Tetratricopeptide repeats (TPR) are well studied protein structural motifs that support intermolecular protein-protein interactions. TMTC1 and TMTC2 were identified by an in silico search as TPR-containing proteins possessing N-terminal ER targeting signal sequences and multiple hydrophobic segments, suggestive of polytopic membrane proteins that are targeted to the secretory pathway. A variety of cell biological and biochemical assays was employed to demonstrate that TMTC1 and TMTC2 are both ER resident integral membrane proteins with multiple clusters of TPR domains oriented within the ER lumen. Proteomic analysis followed by co-immunoprecipitation verification found that both proteins associated with the ER calcium uptake pump SERCA2B, and TMTC2 also bound to the carbohydrate-binding chaperone calnexin. Live cell calcium measurements revealed that overexpression of either TMTC1 or TMTC2 caused a reduction of calcium released from the ER following stimulation, whereas the knockdown of TMTC1 or TMTC2 increased the stimulated calcium released. Together, these results implicate TMTC1 and TMTC2 as ER proteins involved in ER calcium homeostasis. 相似文献
6.
Selective deposition of BaSO4 in the tight junctions (TJs) of frog skins led to profound and reversible functional alterations of these structures, as revealed by changes of tissue conductance (G), clamping current (I), and fluxes of extracellular markers (sulfate (JSO
4) and sucrose (JSUC)). Experiments were performed with nominally Ca2+ -free simple salt solutions on the apical side (usually KCl) and Na2SO4-Ringer on the inner side of skins. The deposition of BaSO4 in the TJs was obtained by diffusion and/or migration through the paracellular path of Ba2+ from the apical solution and SO
4
2–
from the inner solution. A brief presence (2 to 6 min) of apical Ba2+ (Ba2+ pulse) is followed (i.e., when Ba2+ is removed from the apical fluid) by a large increase of G, I, JSO
4 and JSUC, above pre-Ba2+ levels. These attain a steady state within 15 to 30 min (overshoot phase), characterizing a conspicuous increase of the paracellular permeability. During the overshoot phase, a second Ba2+ pulse blocks the paracellular route while apical Ba2+ is present, leading to a new and larger overshoot when the Ba2+ pulse is terminated. Addition of apical Ca2+ triggers the resealing of the TJs, resulting in a full recovery of G, I, JSO
4 and JSUC. This Ca2+ -induced recovery persists when apical Ca2+ is removed. The presence of a normal Ca2+ concentration in the inner bathing Ringer does not induce the recovery process. Tissues remain viable after being submitted to the Ba2+ treatment and the subsequent overshoot. Experiments performed in the urinary bladder of Rana catesbeiana and skins and urinary bladders of Bufo marinus indicate that Ba2+ effect can also be elicited in these tissues. The above results seem to report general properties of the TJs. Incidentally, they warn about the use of Ba2+ as an ion channel blocker in epithelial membranes in association with SO
4
2–
-containing solutions on the contralateral side.This project was supported by grants from Fundação de Amparo à Pesquisa do Estado de São Paulo (91/0293-7 to F.L.V., and 90/1788-1 to A.S.), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (410068/90-0 and 303633-85/BF to F.L.V.). J.A.C. received a doctoral fellowship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior/Fundação Universidade do Rio Grande. We thank Dr. Alice T. Ferreira for help in the measurements of free Ca2+ concentration. 相似文献
7.
Judy A. Garner 《Journal of neurochemistry》1990,54(5):1700-1708
Rises in intracellular calcium cause several events of physiological significance, including the regulated release of neuronal transmitters. In this study, the effects of divalent cations on the structural organization of cytomatrix in presynaptic terminals was examined. [35S]Methionine-radiolabeled guinea pig retinal ganglion cell cytomatrix proteins were axonally transported [in slow component b (SCb) of axonal transport] to the neuron terminals in the superior colliculus. When the peak of radiolabeled cytomatrix proteins reached the terminals, synaptosomes containing the radiolabeled cytomatrix proteins were prepared. Approximately 40% of each SCb protein was soluble after hypoosmotic lysis of the radiolabeled synaptosomes in the presence of divalent cation chelators. Lysis of synaptosomes in the presence of calcium ions over a range of concentrations, however, caused a dramatic decrease in solubility of the presynaptic SCb proteins. The cytoplasmic effects may result from a calcium-dependent condensation of cytoplasm around presynaptic terminal membrane systems. There are two major presynaptic SCb proteins (at 60 and 35 kDa), that exhibited exceptional behavior: they remained as soluble in the presence of calcium as under control conditions, suggesting that they were relatively unaffected by the mechanism causing the decrease in SCb protein solubility. Also examined were the effects of other alkaline earth and transition metal divalent cations on the presynaptic SCb proteins. 相似文献
8.
9.
Abstract: Elevated concentrations of extracellular K+ increased inositol phosphate accumulation in primary cultures of chick retinal photoreceptors and multipolar neurons. K+ -evoked stimulation of inositol phosphate accumulation was greater in photoreceptor-enriched cell cultures than in cultures where multipolar neurons were the predominant cell type. Destroying multipolar neurons, but not photoreceptors, with kainic acid and N -methyl- d -aspartate did not reduce the K+ -evoked stimulation of inositol phosphate accumulation. Both of these observations indicate that the observed effects occur in photoreceptor cells. The K+ -evoked stimulation of inositol phosphate accumulation was blocked by omitting Ca2+ from the incubation medium or by adding the dihydropyridine-sensitive Ca2+ -channel antagonists, nitrendipine and nifedipine. Bay K 8644, a dihydropyridine agonist, stimulated inositol phosphate accumulation and enhanced the effect of K+ . ω-Conotoxin GVIA, an inhibitor of N-type Ca2+ channels, had no significant effect on K+ -stimulated inositol phosphate accumulation. Pretreatment with pertussis toxin neither blocked K+ -evoked inositol phosphate accumulation nor altered the inhibitory effect of nifedipine. K+ -evoked inositol phosphate accumulation appears to reflect activation of phosphatidylinositol-specific phospholipase C, as it is inhibited by U-73122. These results indicate that Ca2+ influx through voltage-gated, dihydropyridine-sensitive channels activates phospholipase C in photoreceptor inner segments and/or synaptic terminals. 相似文献
10.