全文获取类型
收费全文 | 4585篇 |
免费 | 334篇 |
专业分类
4919篇 |
出版年
2023年 | 26篇 |
2022年 | 68篇 |
2021年 | 129篇 |
2020年 | 79篇 |
2019年 | 98篇 |
2018年 | 132篇 |
2017年 | 109篇 |
2016年 | 175篇 |
2015年 | 256篇 |
2014年 | 272篇 |
2013年 | 373篇 |
2012年 | 412篇 |
2011年 | 392篇 |
2010年 | 237篇 |
2009年 | 237篇 |
2008年 | 307篇 |
2007年 | 257篇 |
2006年 | 219篇 |
2005年 | 224篇 |
2004年 | 201篇 |
2003年 | 185篇 |
2002年 | 145篇 |
2001年 | 32篇 |
2000年 | 16篇 |
1999年 | 29篇 |
1998年 | 25篇 |
1997年 | 29篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 24篇 |
1993年 | 14篇 |
1992年 | 21篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 15篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 9篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有4919条查询结果,搜索用时 15 毫秒
101.
Alessandro Minelli Diego Maruzzo Giuseppe Fusco 《Arthropod Structure & Development》2010,39(6):468-477
Size-related changes of form in animals with periodically patterned body axes and post-embryonic growth discontinuously obtained throughout a series of moulting episodes cannot be accounted for by allometry alone. We address here the relationships between body size and number and size of appropriately selected structural units (e.g., segments), which may more or less closely approximate independent developmental units, or unitary targets of selection, or both. Distinguishing between units fundamentally involving one cell only or a small and fixed number of cells (e.g., the ommatidia in a compound eye), and units made of an indeterminate number of cells (e.g., trunk segments), we analyze and discuss a selection of body features of either kind, both in ontogeny and in phylogeny, through a review of current literature and meta-analyses of published and unpublished data. While size/number relationships are too diverse to allow easy generalizations, they provide conspicuous examples of the complex interplay of selective forces and developmental constraints that characterizes the evolution of arthropod body patterning. 相似文献
102.
Viviana Lo Martire Alessandro Silvani Stefano Bastianini Chiara Berteotti Giovanna Zoccoli 《PloS one》2012,7(10)
The central neural pathways underlying the physiological coordination between thermoregulation and the controls of the wake-sleep behavior and cardiovascular function remain insufficiently understood. Growing evidence supports the involvement of hypocretin (orexin) peptides in behavioral, cardiovascular, and thermoregulatory functions. We investigated whether the effects of ambient temperature on wake-sleep behavior and cardiovascular control depend on the hypothalamic neurons that release hypocretin peptides. Orexin-ataxin3 transgenic mice with genetic ablation of hypocretin neurons (n = 11) and wild-type controls (n = 12) were instrumented with electrodes for sleep scoring and a telemetric blood pressure transducer. Simultaneous sleep and blood pressure recordings were performed on freely-behaving mice at ambient temperatures ranging between mild cold (20°C) and the thermoneutral zone (30°C). In both mouse groups, the time spent awake and blood pressure were higher at 20°C than at 30°C. The cold-related increase in blood pressure was significantly smaller in rapid-eye-movement sleep (REMS) than either in non-rapid-eye-movement sleep (NREMS) or wakefulness. Blood pressure was higher in wakefulness than either in NREMS or REMS at both ambient temperatures. This effect was significantly blunted in orexin-ataxin3 mice irrespective of ambient temperature and particularly during REMS. These data demonstrate that hypocretin neurons are not a necessary part of the central pathways that coordinate thermoregulation with wake-sleep behavior and cardiovascular control. Data also support the hypothesis that hypocretin neurons modulate changes in blood pressure between wakefulness and the sleep states. These concepts may have clinical implications in patients with narcolepsy with cataplexy, who lack hypocretin neurons. 相似文献
103.
Pereira RP Fachinetto R de Souza Prestes A Puntel RL Santos da Silva GN Heinzmann BM Boschetti TK Athayde ML Bürger ME Morel AF Morsch VM Rocha JB 《Neurochemical research》2009,34(5):973-983
Considering the important role of oxidative stress in the pathogenesis of several neurological diseases, and the growing evidence
of the presence of compounds with antioxidant properties in the plant extracts, the aim of the present study was to investigate
the antioxidant capacity of three plants used in Brazil to treat neurological disorders: Melissa officinalis, Matricaria recutita and Cymbopogon citratus. The antioxidant effect of phenolic compounds commonly found in plant extracts, namely, quercetin, gallic acid, quercitrin
and rutin was also examined for comparative purposes. Cerebral lipid peroxidation (assessed by TBARS) was induced by iron
sulfate (10 μM), sodium nitroprusside (5 μM) or 3-nitropropionic acid (2 mM). Free radical scavenger properties and the chemical
composition of plant extracts were assessed by 1′-1′ Diphenyl-2′ picrylhydrazyl (DPPH) method and by Thin Layer Chromatography
(TLC), respectively. M. officinalis aqueous extract caused the highest decrease in TBARS production induced by all tested pro-oxidants. In the DPPH assay, M. officinalis presented also the best antioxidant effect, but, in this case, the antioxidant potencies were similar for the aqueous, methanolic
and ethanolic extracts. Among the purified compounds, quercetin had the highest antioxidant activity followed by gallic acid,
quercitrin and rutin. In this work, we have demonstrated that the plant extracts could protect against oxidative damage induced
by various pro-oxidant agents that induce lipid peroxidation by different process. Thus, plant extracts could inhibit the
generation of early chemical reactive species that subsequently initiate lipid peroxidation or, alternatively, they could
block a common final pathway in the process of polyunsaturated fatty acids peroxidation. Our study indicates that M. officinalis could be considered an effective agent in the prevention of various neurological diseases associated with oxidative stress. 相似文献
104.
105.
Binding of the 7SK snRNA turns the HEXIM1 protein into a P-TEFb (CDK9/cyclin T) inhibitor 总被引:12,自引:0,他引:12
Michels AA Fraldi A Li Q Adamson TE Bonnet F Nguyen VT Sedore SC Price JP Price DH Lania L Bensaude O 《The EMBO journal》2004,23(13):2608-2619
106.
Aliaksei?Kisialiou Giordana?Pelone Albino?Carrizzo Giovanni?Grillea Valentina?Trimarco Marina?Marino Michelangelo?Bartolo Alessandro?Marco?De Nunzio Rodolfo?Grella Alessandro?Landolfi Annibale?Puca Claudio?Colonnese Carmine?VecchioneEmail author 《Immunity & ageing : I & A》2012,9(1):22
Background
Thrombolytic therapy (TT) for acute ischemic stroke (AIS) can provoke bleeding’s complication depending on the ischemic lesion (IL) dimension. Inflammation involved in the setting of acute ischaemic stroke, is associated with infarct size. We aimed to study the independent correlation and association between clinical panel of routinely identified biomarkers, including inflammatory parameters, and cerebral IL dimension and site.Results
We evaluated eleven biomarkers in 105 unrelated patients during their hospitalization after acute stroke event. Our data indicate a significant association of: a) confluent IL size with 4th quartile of Erythrocyte Sedimentation Rate (ESR) (OR = 5.250; 95% CI, 1.002 to 27.514) and an independent correlation with sex; b) confluent IL size with 3rd quartile of fibrinogen (OR = 5.5; 95% CI, 1.027 to 29.451); c) confluent IL size with 3rd quartile of platelets (OR= 0.059; 95% CI, 0.003 to 1.175) and independent correlation with sex; d) smaller IL size (OR = 5.25; 95% CI, 1.351 to 20.396) with 3rd quartile of albumin levels and nodular and parenchimal IL size with 2nd (OR = 0.227; 95% CI, 0.053 to 0.981), 3rd (OR = 0.164; 95% CI, 0.038 to 0.711) and 4th (OR = 0.205; 95% CI, 0.048 to 0.870) quartiles albumin levels; e) smaller IL size with 3rd quartile triglycerides (TG) levels (OR = 9; 95% CI, 2.487 to 32.567) and an independent correlation with anterior location. Smaller IL size, anterior AIS turned out to be independently correlated with high serum albumin levels. Finally, high INR and PTT values were associated with worse NIHSS clinical outcomes in contrast to that observed with higher albumin level.Conclusions
We provide evidence of routine biomarkers levels correlation with acute IL size, independently of age and sex. In addition, we highlight the importance of differentiation of biomarkers normal interval levels for further improvement not only of the clinical decision making but also in post-acute clinical outcome management.107.
108.
Alessandro Chiarucci Marco Calderisi Francesca Casini Ilaria Bonini 《Folia Geobotanica》2008,43(1):19-33
The effects of the chemical and physical factors associated with geothermal activity on plant community structure and composition were investigated in one of the largest geothermal fields of central Italy. The study site was located in the geothermal area of Sasso Pisano – Monte Rotondo Marittimo, Southern Tuscany. The percentage cover of all vascular plant, bryophyte and lichen species was estimated within 119 circular plots of 0.25 m2. For each plot the soil pH, soil temperature, slope, aspect, incident radiation, soil nitrogen and carbon contents were also quantified. Two vascular plants, Calluna vulgaris and Agrostis castellana, were found to be the most widespread species tolerating the harshest conditions in terms of low soil pH and high soil temperature. The most widespread cryptogam species was Hypnum cupressiforme. Spatially autoregressive models showed that a proportion of about 41–51% of the variance in species richness of one group of plants (vascular or cryptogamic plants) could be modelled by using three or four uncorrelated environmental factors respectively (soil temperature, soil nitrogen and soil C/N ratio and these three plus incident radiation). For the total number of species (vascular and cryptogamic plants), the variance explained by the same three uncorrelated variables was about 57%. This study evidenced a strong environmental control of community composition and species richness, in a site subjected to extreme soil values of soil pH and temperature. The dominance of vascular over cryptogamic vegetation in this geothermal site can be explained by the combined effects of geothermal stress (low soil pH and high soil temperature) with the summer drought typical of the Mediterranean climate. 相似文献
109.
110.