全文获取类型
收费全文 | 2219篇 |
免费 | 197篇 |
国内免费 | 82篇 |
出版年
2024年 | 8篇 |
2023年 | 41篇 |
2022年 | 31篇 |
2021年 | 68篇 |
2020年 | 96篇 |
2019年 | 104篇 |
2018年 | 86篇 |
2017年 | 80篇 |
2016年 | 95篇 |
2015年 | 84篇 |
2014年 | 127篇 |
2013年 | 173篇 |
2012年 | 78篇 |
2011年 | 96篇 |
2010年 | 104篇 |
2009年 | 90篇 |
2008年 | 118篇 |
2007年 | 98篇 |
2006年 | 91篇 |
2005年 | 84篇 |
2004年 | 76篇 |
2003年 | 73篇 |
2002年 | 64篇 |
2001年 | 59篇 |
2000年 | 35篇 |
1999年 | 50篇 |
1998年 | 37篇 |
1997年 | 36篇 |
1996年 | 34篇 |
1995年 | 25篇 |
1994年 | 34篇 |
1993年 | 24篇 |
1992年 | 30篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有2498条查询结果,搜索用时 656 毫秒
111.
112.
113.
Translating niche features: Modelling differential exposure of Argentine reptiles to global climate change
下载免费PDF全文
![点击此处可从《Austral ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Javier Nori Débora L. Moreno Azócar Felix B. Cruz Marcelo F. Bonino Gerardo C. Leynaud 《Austral ecology》2016,41(4):367-375
Global climate change affects the distributions of ectotherms and may be the cause of several conservation problems, such as great displacement of climatic suitable spaces for species and, consequently, important reductions of the extent of liveable places, threatening the existence of many of them. Species exposure (and hence vulnerability) to global climate change is linked to features of their climatic niches (such as the relative position of the inhabited localities of each species in the climatic space), and therefore to characteristics of their geographic ranges (such as the extent of the distributions or altitudinal range inhabited by the species). In order to analyze the pattern of response of Argentine reptiles to global climate change, we ran phylogenetic generalized least squares models using species exposure to global climate change as a response variable, and (i) niche properties (breadth and position of the species in the climate space) and (ii) general features of the distribution of species (maximum latitude, altitudinal range, maximum elevation, distributional range and proximity to the most important dispersal barrier) as predictors. Our results suggest that the best way to explain climate change exposure is by combining breadth and position of climatic niche of the species or combining geographic features that are indicators of both niche characteristics. Our best model shows that in our study area, species with the narrowest distributional ranges that also inhabit the highest elevations are the most exposed to the effects of global climate change. In this sense, reptile species from Yungas, Puna and Andes ecoregions could be especially vulnerable to the effects of climate change. We believe that these types of models may represent an interesting tool for determining species and places particularly threatened by the effects of global climate change, which should be strongly considered in conservation planning. 相似文献
114.
115.
目的:探讨参松养心胶囊对心房颤动(AF)患者P波离散度(Pd)及血清炎性因子水平的影响,为临床用药提供依据。方法:将西安交通大学第一附属医院2016年3月-2018年1月收治的AF患者纳入本研究,共148例。所有患者根据不同的治疗方式分为对照组和观察组。对照组(n=74)接受常规治疗,观察组(n=74)在对照组基础上加用参松养心胶囊,两组均治疗8周。比较两组患者治疗后的临床疗效,观察并比较两组患者治疗前及治疗后的Pd、最大P波时限(Pmax)变化情况,检测两组患者治疗前及治疗后的血清炎性因子水平,记录不良反应发生情况。结果:观察组总有效率为89.19%(66/74),高于对照组的70.27%(52/74)(P0.05)。两组患者治疗后的Pmax、Pd均明显降低,且观察组患者治疗后的Pmax、Pd均明显低于对照组(P0.05)。两组患者治疗后的血清炎性因子水平均明显降低,且与对照组相比,观察组患者治疗后的血清肿瘤坏死因子-α(TNF-α)、高敏C反应蛋白(hs-CRP)、白介素-6(IL-6)水平均降低(P0.05)。两组不良反应发生情况比较无统计学差异(P0.05)。结论:参松养心胶囊治疗AF患者安全有效,能明显减轻炎性反应,改善患者心功能。 相似文献
116.
Guoliang Wang Yuhua Xue Yanzi Wang Fei Dong Mei Shen Rongrong Zong Zuguo Liu Cheng Li 《Journal of cellular and molecular medicine》2019,23(6):4217-4228
Incomplete tear film spreading and eyelid closure can cause defective renewal of the ocular surface and air exposure‐induced epithelial keratopathy (EK). In this study, we characterized the role of autophagy in mediating the ocular surface changes leading to EK. Human corneal epithelial cells (HCECs) and C57BL/6 mice were employed as EK models, respectively. Transmission electron microscopy (TEM) evaluated changes in HCECs after air exposure. Each of these models was treated with either an autophagy inhibitor [chloroquine (CQ) or 3‐methyladenine (3‐MA)] or activator [Rapamycin (Rapa)]. Immunohistochemistry assessed autophagy‐related proteins, LC3 and p62 expression levels. Western blotting confirmed the expression levels of the autophagy‐related proteins [Beclin1 and mammalian target of rapamycin (mTOR)], the endoplasmic reticulum (ER) stress‐related proteins (PERK, eIF2α and CHOP) and the PI3K/Akt/mTOR signalling pathway‐related proteins. Real‐time quantitative PCR (qRT‐PCR) determined IL‐1β, IL‐6 and MMP9 gene expression levels. The TUNEL assay detected apoptotic cells. TEM identified autophagic vacuoles in both EK models. Increased LC3 puncta formation and decreased p62 immunofluorescent staining and Western blotting confirmed autophagy induction. CQ treatment increased TUNEL positive staining in HCECs, while Rapa had an opposite effect. Similarly, CQ injection enhanced air exposure‐induced apoptosis and inflammation in the mouse corneal epithelium, which was inhibited by Rapa treatment. Furthermore, the phosphorylation status of PERK and eIF2α and CHOP expression increased in both EK models indicating that ER stress‐induced autophagy promoted cell survival. Taken together, air exposure‐induced autophagy is indispensable for the maintenance of corneal epithelial physiology and cell survival. 相似文献
117.
Menthol is known for its analgesic properties, but relatively little information is available on its potential as an anaesthetic on fish. The purpose of this study was to assess anaesthetic and sedative effectiveness of menthol and its safety in rainbow trout (Oncorhynchus mykiss). Juvenile rainbow trout 180 ± 28 g (mean ± SD) within a range of 152–208 g fish?1 were individually exposed to menthol concentrations between 10 and 150 mg l?1 and observed for behavioural responses, induction time to anaesthesia and recovery time. Menthol concentrations of 40–150 mg l?1 induced anaesthesia with varying exposure times. There was an exponential relationship (p < 0.001) between induction time and menthol concentration. Menthol concentrations of 80–150 mg l?1 induced anaesthesia within three minutes of exposure and fish recovered within three minutes. Induction and recovery data showed that 80 mg l?1 was most suitable for anaesthesia in juveniles of this species. Concentrations of 10–20 mg l?1 had sedative effects. Menthol stock solutions prepared using ethanol and acetone and storage time of stock solutions at room temperature for up to 48 h showed no significant differences in anaesthetic efficiency. When exposure time to menthol was kept constant at three minutes, 22% of fish had temporary cessation of gill ventilation. These fish had longer recovery times than those that did not show that response. Menthol was an effective anaesthetic and could be tested as a sedative for trout. 相似文献
118.
Jiyu Wang Lun Pan Hengyu Guo Binbin Zhang Rongrong Zhang Zhiyi Wu Changsheng Wu Lijun Yang Ruijin Liao Zhong Lin Wang 《Liver Transplantation》2019,9(8)
Water wave energy is a promising renewable energy source that may alleviate the rising concerns over current resource depletion, but it is rarely exploited due to the lack of efficient energy harvesting technologies. In this work, a hybrid system with a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG) based on an optimized inner topological structure is reported to effectively harvest water wave energy. The TENG with etched polytetrafluoroethylene films and Cu electrodes utilizing the contact‐freestanding mode is designed into a cubic structure, in which the EMG is well hybridized. An integration of TENG and EMG achieves mutual compensation of their own merits, enabling the hybrid system to deliver satisfactory output over a broad range of operation frequency. The output performance of TENG with varied inner topological structures is experimentally and theoretically compared, and a concept is proposed to further clarify the energy conversion efficiency, which should be considered in designing energy harvesting devices. The influences of oscillation frequency, amplitude, and dielectric materials on the output performance of the hybrid system are comprehensively studied on different platforms. Furthermore, the optimum operation frequency ranges for TENG and EMG are concluded. The proposed hybrid nanogenerator renders an effective approach toward large‐scale blue energy harvesting over a broad frequency range. 相似文献
119.
120.