全文获取类型
收费全文 | 5270篇 |
免费 | 426篇 |
国内免费 | 1篇 |
出版年
2023年 | 24篇 |
2022年 | 60篇 |
2021年 | 133篇 |
2020年 | 52篇 |
2019年 | 78篇 |
2018年 | 103篇 |
2017年 | 96篇 |
2016年 | 160篇 |
2015年 | 272篇 |
2014年 | 269篇 |
2013年 | 357篇 |
2012年 | 459篇 |
2011年 | 426篇 |
2010年 | 264篇 |
2009年 | 213篇 |
2008年 | 335篇 |
2007年 | 322篇 |
2006年 | 292篇 |
2005年 | 276篇 |
2004年 | 266篇 |
2003年 | 235篇 |
2002年 | 255篇 |
2001年 | 49篇 |
2000年 | 48篇 |
1999年 | 53篇 |
1998年 | 57篇 |
1997年 | 49篇 |
1996年 | 22篇 |
1995年 | 39篇 |
1994年 | 33篇 |
1993年 | 35篇 |
1992年 | 32篇 |
1991年 | 18篇 |
1990年 | 25篇 |
1989年 | 28篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1977年 | 10篇 |
1976年 | 17篇 |
1974年 | 9篇 |
1973年 | 10篇 |
1969年 | 15篇 |
排序方式: 共有5697条查询结果,搜索用时 31 毫秒
931.
Jessica Erriquez Silvia Bernascone Monica Ciarletta Nicoletta Filigheddu Andrea Graziani Carla Distasi 《Cell calcium》2009,46(3):197-208
Ghrelin is a hormone regulating energy homeostasis via interaction with its receptor, GHSR-1a. Ghrelin activities in dorsal root ganglia (DRG) cells are unknown. Herein we show that ghrelin induces a change of cytosolic calcium concentration in both glia and neurons of embryonic chick DRG. Both RT-PCR and binding studies performed with fluorescent ghrelin in the presence of either unlabeled ghrelin or GHSR-1a antagonist D-Lys3-GHRP-6, indicate that DRG cells express GHSR-1a. In glial cells the response is characterized by a rapid transient rise in [Ca2+]i followed by a long lasting rise. The calcium elevation is dependent on calcium release from thapsigargin-sensitive intracellular stores and on activation of two distinct Ca2+ entry pathways, a receptor activated calcium entry and a store operated calcium entry. Surprisingly, D-Lys3-GHRP-6 exerts several activities in the absence of exogenous ghrelin: (i) it activates calcium release from thapsigargin-sensitive intracellular stores and calcium entry via voltage-operated channels in non-neuronal cells; (ii) it inhibits calcium oscillations in non-neuronal cells exhibiting spontaneous Ca2+ activity and iii) it promotes apoptosis of DRG cells, both neurons and glia. In summary, we provide the first evidence for ghrelin activity in DRG, and we also demonstrate that the widely used D-Lys3-GHRP-6 ghrelin antagonist features ghrelin independent activities. 相似文献
932.
Five anthocyanins, cyanidin 3-(2′′-(6′′′-caffeoyl-β-glucopyranosyl)-6′′-(E-p-coumaroyl)-β-glucopyranoside)-5-β-glucopyranoside, cyanidin 3-(2′′-(6′′′-E-sinapoyl-β-glucopyranosyl)-6′′-(E-p-coumaroyl)-β-glucopyranoside)-5-β-glucopyranoside, cyanidin 3-(2′′-(6′′′-feroyl-β-glucopyranosyl)-6′′-(E-p-coumaroyl)-β-glucopyranoside)-5-β-glucopyranoside, pelargonidin 3-(2′′-(6′′′-E-sinapoyl-β-glucopyranosyl)-6′′-(E-p-coumaroyl)-β-glucopyranoside)-5-β-glucopyranoside, and pelargonidin 3-(2′′-(6′′′-E-p-coumaroyl-β-glucopyranosyl)-6′′-(E-p-coumaroyl)-β-glucopyranoside)-5-β-glucopyranoside, together with five known anthocyanins have been identified in flowers of Cleome hassleriana Queen line. One monoacylated and four diacylated cyanidin 3-sophoroside-5-glucosides were identified as the main anthocyanins in flowers with mauve colouration, while a homologous glycosidic pattern based on pelargonidin was found in the five main anthocyanins from flowers with pink colouration. The anthocyanins identified in C. hassleriana share the same glycosidic pattern as anthocyanins isolated from the genera Raphanus, Brassica and Iberis in the sister family Brassicaceae. 相似文献
933.
934.
De los Reyes M Palomino J de Lange J Anguita C Barros C 《Animal reproduction science》2009,110(1-2):37-45
The aim of this study was to evaluate the effect of sperm cryopreservation and the maturation state of the oocyte on the time course of canine gamete interaction during co-culture for periods of 1-10 h. Semen samples were obtained by digital stimulation and ejaculates processed as fresh, chilled and frozen samples. Sperm were co-cultured with immature or in vitro mature bitch oocytes for up to 10 h. At hourly intervals, oocytes were evaluated for sperm penetration with epifluorescence microscopy. The results were analyzed statistically using generalized linear models. Spermatozoa treatments had a significant effect on the total percentage of oocyte penetration for both types of oocytes; fresh spermatozoa showed the highest average penetration rate, while frozen sperm showed the lowest value (p<0.05). At the 1st hour of co-culture, chilled and frozen dog sperm had a higher penetration percentage (p<0.05) of in vitro matured canine oocytes (43.6% and 45.7%, respectively) than the fresh sperm had (33.8%). Sperm penetration was directly proportional to the time of incubation, when fresh or chilled sperm were used (P<0.05); in contrast, frozen dog sperm did not change penetration rates with either immature or in vitro matured oocytes over time. There was a significant difference in the average of penetration rate between immature (47.3%) and in vitro matured oocytes (56.6%) throughout the 10h of culturing; irrespective of sperm treatment. The optimal incubation time in terms of maximizing penetration rates probably are dependent on how spermatozoa were processed prior to fertilization. 相似文献
935.
Olga Mangoni Maria Saggiomo Monica Modigh Giulio Catalano Adriana Zingone Vincenzo Saggiomo 《Polar Biology》2009,32(3):311-323
The aim of this study was to assess the role of platelet ice microalgal communities in seeding pelagic blooms. Nutrient dynamics,
microalgal biomass, photosynthetic parameters, cell densities and species succession were studied in two mesocosm experiments,
designed to simulate the transition of microalgal communities from platelet ice habitat to pelagic conditions. The microalgal
assemblages were dominated by diatoms, 70% of which were benthic species such as Amphiprora kufferathii, Nitzschia stellata, and Berkeleya adeliensis. Photoacclimation of benthic species was inadequate also at relatively low irradiances. Exceptional growth capacity at different
light levels was observed for pelagic species such as Fragilariopsis cylindrus and Chaetoceros spp. which may be important in seeding blooms at ice breakup. Fragilariopsis cylindrus showed high growth rates both at 65 and 10% of incident light and in nutrient replete as well as in nutrient depleted conditions.
Five days after inoculation, phytoplankton biomass increased and nutrient concentrations decreased in both light conditions.
Nutrient uptake rates were up to 9.10 μmol L−1 d−1 of TIN in the high light tank and 6.18 μmol L−1 d−1 in the low light tank and nutrient depletion in the high light tank occurred 3 days prior to depletion in the low light tank.
At nutrient depletion, biomass concentrations were similar in both tanks, 30 and 34 μg Chla L−1.
This article belongs to a special topic: Five articles on Sea-ice communities in Terra Nova Bay (Ross Sea), coordinated by
L. Guglielmo and V. Saggiomo, appear in this issue of Polar Biology. The studies were conducted in the frame of the National
Program of Research in Antarctica (PNRA) of Italy. 相似文献
936.
937.
Caccamo D Di Mauro D Condello S Currò M Cutroneo G Anastasi GP Ientile R Trimarchi F 《Amino acids》2009,36(1):49-56
Several studies demonstrated that transglutaminases play a key role in extracellular matrix stabilization needed for cell
differentiation. We evaluated transglutaminase expression and activity in the pre-secretory stage of differentiation of the
continuously erupting rat incisor. We observed that transglutaminase-mediated incorporation of monodansylcadaverine into protein
substrates was specifically located in the apical loop, and along the basement membrane joining mesenchyme and inner dental
epithelium in the odontogenic organ. Enzyme activity was associated with mRNAs for transglutaminase 1 and 2. Notably, labelling
cells for these isoenzymes were observed in both mesenchymal and epithelial compartments, but not in the basement membrane,
in the ameloblast facing pulp anterior region, where ameloblast and odontoblast differentiation begins. These findings demonstrate
that transglutaminase 1 and transglutaminase 2 are expressed at a major extent in the pre-secretory stage of regenerating
rat incisor, where they probably play complementary roles in cell signalling between mesenchyme and epithelium and extracellular
matrix. 相似文献
938.
Cervellati C Franzoni L Squerzanti M Bergamini CM Spinozzi F Mariani P Lanzara V Spisni A 《Amino acids》2009,36(4):633-641
Activation of tissue transglutaminase by calcium involves a conformational change which allows exposition of the active site
to the substrate via movements of domains 3 and 4 that lead to an increase of the inter-domain distance. The inhibitor GTP
counteracts these changes. Here we investigate the possible existence of non-native conformational states still compatible
with the enzyme activity produced by chemical and thermal perturbations. The results indicate that chemical denaturation is
reversible at low guanidine concentrations but irreversible at high concentrations of guanidine. Indeed, at low guanidine
concentrations tissue TG-ase exists in a non-native state which is still affected by the ligands as in the native form. In
contrast, thermal unfolding is always irreversible, with aggregation and protein self-crosslinkage in the presence of calcium.
DSC thermograms of the native protein in the absence of ligands consist of two partly overlapped transitions, which weaken
in the presence of calcium and merge together and strengthen in the presence of GTP. Overall, the present work shows, for
the first time, the reversible denaturation of a TG-ase isoenzyme and suggests the possibility that also in in vivo, the enzyme
may acquire non-native conformations relevant to its patho-physiological functions. 相似文献
939.
John A. Lowe Xinjun Hou Christopher Schmidt F. David Tingley Stan McHardy Monica Kalman Shari DeNinno Mark Sanner Karen Ward Lorraine Lebel Don Tunucci James Valentine 《Bioorganic & medicinal chemistry letters》2009,19(11):2974-2976
The type 1 glycine transporter plays an important in regulating homeostatic glycine levels in the brain that are relevant to the activation of the NMDA receptor by the excitatory neurotransmitter glutamate. We describe herein the structure–activity relationships (SAR) of a structurally novel class of GlyT1 inhibitors following on a lead derived from high throughput screening, which shows good selectivity for GlyT1 and potent activity in elevating CSF levels of glycine. 相似文献
940.