全文获取类型
收费全文 | 1792篇 |
免费 | 168篇 |
国内免费 | 157篇 |
专业分类
2117篇 |
出版年
2024年 | 5篇 |
2023年 | 29篇 |
2022年 | 75篇 |
2021年 | 96篇 |
2020年 | 73篇 |
2019年 | 102篇 |
2018年 | 89篇 |
2017年 | 46篇 |
2016年 | 89篇 |
2015年 | 137篇 |
2014年 | 149篇 |
2013年 | 135篇 |
2012年 | 168篇 |
2011年 | 143篇 |
2010年 | 83篇 |
2009年 | 79篇 |
2008年 | 89篇 |
2007年 | 68篇 |
2006年 | 80篇 |
2005年 | 53篇 |
2004年 | 44篇 |
2003年 | 41篇 |
2002年 | 44篇 |
2001年 | 22篇 |
2000年 | 29篇 |
1999年 | 18篇 |
1998年 | 13篇 |
1997年 | 18篇 |
1996年 | 13篇 |
1995年 | 19篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有2117条查询结果,搜索用时 15 毫秒
71.
The common cold is most often a result of human rhinovirus (HRV) infection. Common cold symptoms including rhinorrhea and nasal obstruction frequently occur during HRV infection of the upper respiratory tract. Conversely, HRV may also infect the epithelial cells of the lower respiratory tract. Symptom severity associated with HRV infection ranges from mild to potentially serious depending on a person’s susceptibility and pre-existing condition, such as chronic obstructive pulmonary disease. An over active host immune response is believed to be the primary contributor to HRV pathogenesis. Enhanced activity of various host cell cytokines and granulocytes mediate specific cellular pathways inducing many of the symptoms associated with HRV infection. There are over 100 serotypes of HRV which can be further categorized based on the specific characteristics of each type. The two main categories of HRV consist of the major and minor groups. The unique host cell receptor is the distinguishing factor between these two groups. Yet, these viruses may also differ in mechanism of infection and replication. Due to the high frequency of hospital and clinical visits and the corresponding economic burden, novel therapies are of interest. Several different treatment options varying from herbal remedies to anti-viral drugs have been studied. However, the vast number of HRV serotypes complicates the progress of developing a universal treatment for attenuating HRV infection. 相似文献
72.
73.
Xiaoan Zuo Shaokun Wang Peng Lv Xin Zhou Xueyong Zhao Tonghui Zhang Jing Zhang 《Ecology and evolution》2016,6(1):318-328
The trait‐based approach shows that plant functional diversity strongly affects ecosystem properties. However, few empirical studies show the relationship between soil fungal diversity and plant functional diversity in natural ecosystems. We investigated soil fungal diversity along a restoration gradient of sandy grassland (mobile dune, semifixed dune, fixed dune, and grassland) in Horqin Sand Land, northern China, using the denaturing gradient gel electrophoresis of 18S rRNA and gene sequencing. We also examined associations of soil fungal diversity with plant functional diversity reflected by the dominant species' traits in community (community‐weighted mean, CWM) and the dispersion of functional trait values (FDis). We further used the structure equation model (SEM) to evaluate how plant richness, biomass, functional diversity, and soil properties affect soil fungal diversity in sandy grassland restoration. Soil fungal richness in mobile dune and semifixed dune was markedly lower than those of fixed dune and grassland (P < 0.05). Soil fungal richness was positively associated with plant richness, biomass, CWM plant height, and soil gradient aggregated from the principal component analysis, but SEM results showed that plant richness and CWM plant height determined by soil properties were the main factors exerting direct effects. Soil gradient increased fungal richness through indirect effect on vegetation rather than direct effect. The negative indirect effect of FDis on soil fungal richness was through its effect on plant biomass. Our final SEM model based on plant functional diversity explained nearly 70% variances of soil fungal richness. Strong association of soil fungal richness with the dominant species in the community supported the mass ratio hypothesis. Our results clearly highlight the role of plant functional diversity in enhancing associations of soil fungal diversity with community structure and soil properties in sandy grassland ecosystems. 相似文献
74.
Yilin Tang Jingjie Ge Fengtao Liu Ping Wu Sisi Guo Zhenyang Liu Yixuan Wang Ying Wang Zhengtong Ding Jianjun Wu Chuantao Zuo Jian Wang 《PloS one》2016,11(4)
PurposeTo characterize cerebral glucose metabolism associated with different cognitive states in Parkinson’s disease (PD) using 18F-fluorodeoxyglucose (FDG) and Positron Emission Tomography (PET).MethodsThree groups of patients were recruited in this study including PD patients with dementia (PDD; n = 10), with mild cognitive impairment (PD-MCI; n = 20), and with no cognitive impairment (PD-NC; n = 30). The groups were matched for age, sex, education, disease duration, motor disability, levodopa equivalent dose and Geriatric Depression Rating Scale (GDS) score. All subjects underwent a FDG-PET study. Maps of regional metabolism in the three groups were compared using statistical parametric mapping (SPM5).ResultsPD-MCI patients exhibited limited areas of hypometabolism in the frontal, temporal and parahippocampal gyrus compared with the PD-NC patients (p < 0.01). PDD patients had bilateral areas of hypometabolism in the frontal and posterior parietal-occipital lobes compared with PD-MCI patients (p < 0.01), and exhibited greater metabolic reductions in comparison with PD-NC patients (p < 0.01).ConclusionsCompared with PD-NC patients, hypometabolism was much higher in the PDD patients than in PD-MCI patients, mainly in the posterior cortical areas. The result might suggest an association between posterior cortical hypometabolism and more severe cognitive impairment. PD-MCI might be important for early targeted therapeutic intervention and disease modification. 相似文献
75.
76.
77.
78.
79.
Luo Lilan He Yajun Zhao Yannan Xu Qian Wu Jian Ma Haiyan Guo Hongyan Bai Lin Zuo Jianru Zhou Jian-Min Yu Hong Li Jiayang 《中国科学:生命科学英文版》2019,62(8):991-1002
Reactive oxygen species(ROS) play a crucial role in numerous biological processes in plants, including development, responses to environmental stimuli, and programmed cell death(PCD). Deficiency in MOSAIC DEATH 1(MOD1), a plastid-localized enoyl-ACP reductase essential for de novo fatty acid biosynthesis in Arabidopsis thaliana, leads to the increased malate export from chloroplasts to mitochondria, and the subsequent accumulation of mitochondria-generated ROS and PCD. In this study, we report the identification and characterization of a mod1 suppressor, som592. SOM592 encodes mitochondrion-localized NAD~+ transporter 2(NDT2). We show that the mitochondrial NAD pool is elevated in the mod1 mutant. The som592 mutation fully suppressed mitochondrial NADH hyper-accumulation, ROS production, and PCD in the mod1 mutant, indicating a causal relationship between mitochondrial NAD accumulation and ROS/PCD phenotypes. We also show that in wild-type plants, the mitochondrial NAD+uptake is involved in the regulation of ROS production in response to continuous photoperiod. Elevation of the alternative respiration pathway can suppress ROS accumulation and PCD in mod1, but leads to growth restriction. These findings uncover a regulatory mechanism for mitochondrial ROS production via NADH homeostasis in Arabidopsis thaliana that is likely important for growth regulation in response to altered photoperiod. 相似文献
80.
Yu‐Zuo Wang Xu‐Yi Shan Li‐Po Ma Jia‐Wei Wang Da‐Wei Wang Zhang‐Quan Peng Hui‐Ming Cheng Feng Li 《Liver Transplantation》2019,9(12)
Understanding the electric double layer is essential for achieving efficient electrochemical energy storage technologies. A conventional solid–liquid electrode interface suffers from serious self‐discharge and a narrow voltage window, which makes the development of a solid–solid interface imperative. However, an in‐depth understanding of the electric double layer with a solid–solid interface is lacking. Here, a solid–solid interfacial electric double layer is proposed with excellent electrochemical performance. The solid layer is constructed by the electrochemical decomposition of lithium difluoro(oxalate)borate, which provides a desolvated environment for the establishment of a electric double layer. This makes a stronger interaction between the electrode surface and the ions. Based on this unique property, it is found that the solid–solid interfacial electric double layer has an increased capacitance, which suggests a way to develop high‐energy electrochemical capacitors. 相似文献