全文获取类型
收费全文 | 9239篇 |
免费 | 830篇 |
国内免费 | 1483篇 |
出版年
2024年 | 36篇 |
2023年 | 145篇 |
2022年 | 291篇 |
2021年 | 530篇 |
2020年 | 379篇 |
2019年 | 487篇 |
2018年 | 493篇 |
2017年 | 344篇 |
2016年 | 420篇 |
2015年 | 698篇 |
2014年 | 753篇 |
2013年 | 753篇 |
2012年 | 939篇 |
2011年 | 849篇 |
2010年 | 538篇 |
2009年 | 504篇 |
2008年 | 564篇 |
2007年 | 496篇 |
2006年 | 418篇 |
2005年 | 377篇 |
2004年 | 339篇 |
2003年 | 273篇 |
2002年 | 210篇 |
2001年 | 95篇 |
2000年 | 109篇 |
1999年 | 96篇 |
1998年 | 72篇 |
1997年 | 83篇 |
1996年 | 62篇 |
1995年 | 46篇 |
1994年 | 35篇 |
1993年 | 20篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 14篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 12篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1950年 | 5篇 |
1911年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
171.
目的:探讨老年人活髓隐裂牙应用金属烤瓷全冠修复临床效果及适应症。方法:选取本院2006年1月至2011年1月期间收治的356例老年活髓隐裂牙合计621颗为研究对象,根据患牙疼痛程度随机将患者分为咬合疼痛组(A组)104例合计215颗患牙,咬合伴过敏性冷热刺激痛组(B组)122例合计232颗患牙,咬合伴延续性冷热刺激疼痛组(C组)130例合计174颗患牙,所有患者均接受金属烤瓷全冠修复,观察患者在治疗后1个月、6个月、12个月、18个月、24个月治愈情况以及牙髓及根尖周病变及牙髓发生情况。结果:与C组相比,A组、B组术后1个月、6个月、12个月、18个月、24个月治愈率以及总有效率较高,差异有统计学意义(P〈0.05)。结论:金属烤瓷全冠修复适合于轻微咬合疼痛以及咬合伴过敏性冷热刺激痛的患者,而对于咬舍伴延续性冷热刺激疼痛的患者则宜先行根管治疗术再进行全冠修复。 相似文献
172.
173.
174.
目的:基于基因拷贝数变异(CNV)区域网络识别神经胶质瘤的重要功能区域。方法:运用独特的计算样本的共相关性值的方法,使CNV数据与基因数据产生联系;基于蛋白质互作关系,在CNV区域与基因之间搭建桥梁,构建CNV区域网络;分析网络拓扑性质,识别出神经胶质瘤的重要功能CNV区域。结果:本文共识别出了11个与神经胶质瘤相关的候选重要功能CNV区域,通过功能注释和通路分析,确认了识别到的区域与神经胶质瘤有重要联系。结论:通过基因与表型之间的联系,利用已知表型基因在同源、功能、互作、结构域上的特征将CNV区域与基因联系起来,通过基因的功能可以了解到CNV区域的功能,对于疾病的预测和诊断有重要的意义。 相似文献
175.
Zhangwei Wang Bin Li Shishan Yu Xuewen Lai Bo Liu Jie Chen Toshimitsu Hayashi 《Phytochemistry letters》2013,6(3):461-466
Chemical investigation of the aqueous extract of the aerial portion of Sibiraea angustata led to the isolation of eight new monoterpene acylglucosides named sibiraglucoside A–H (1–8) and two known monoterpenes, sibiraic acid (9) and sibiskoside (10). Their structures were elucidated through extensive spectroscopic data analysis (including 1D and 2D NMR and HRESIMS experiments) and compared to literature data. In the in vitro bioassay, all of the compounds showed moderate hypolipidemic effects. 相似文献
176.
Xin Jia Tianshan Zha Bin Wu Yuqing Zhang Wenjing Chen Xiaoping Wang Haiqun Yu Guimei He 《PloS one》2013,8(2)
Although the temperature response of soil respiration (Rs) has been studied extensively, several issues remain unresolved, including hysteresis in the Rs–temperature relationship and differences in the long- vs. short-term Rs sensitivity to temperature. Progress on these issues will contribute to reduced uncertainties in carbon cycle modeling. We monitored soil CO2 efflux with an automated chamber system in a Pinus tabulaeformis plantation near Beijing throughout 2011. Soil temperature at 10-cm depth (Ts) exerted a strong control over Rs, with the annual temperature sensitivity (Q
10) and basal rate at 10°C (Rs
10) being 2.76 and 1.40 µmol m−2 s−1, respectively. Both Rs and short-term (i.e., daily) estimates of Rs
10 showed pronounced seasonal hysteresis with respect to Ts, with the efflux in the second half of the year being larger than that early in the season for a given temperature. The hysteresis may be associated with the confounding effects of microbial population dynamics and/or litter input. As a result, all of the applied regression models failed to yield unbiased estimates of Rs over the entire annual cycle. Lags between Rs and Ts were observed at the diel scale in the early and late growing season, but not in summer. The seasonality in these lags may be due to the use of a single Ts measurement depth, which failed to represent seasonal changes in the depth of CO2 production. Daily estimates of Q
10 averaged 2.04, smaller than the value obtained from the seasonal relationship. In addition, daily Q
10 decreased with increasing Ts, which may contribute feedback to the climate system under global warming scenarios. The use of a fixed, universal Q
10 is considered adequate when modeling annual carbon budgets across large spatial extents. In contrast, a seasonally-varying, environmentally-controlled Q
10 should be used when short-term accuracy is required. 相似文献
177.
Shiu Lun Au Yeung Chaoqiang Jiang Kar Keung Cheng Benjamin J. Cowling Bin Liu Weisen Zhang Tai Hing Lam Gabriel M. Leung C. Mary Schooling 《PloS one》2013,8(7)
Background
Observational studies show moderate alcohol use negatively associated with ischemic heart disease (IHD) and cardiovascular disease (CVD). However, healthier attributes among moderate users compared to never users may confound the apparent association. A potentially less biased way to examine the association is Mendelian randomization, using alcohol metabolizing genes which influence alcohol use.Methods
We used instrumental variable analysis with aldehyde dehydrogenase 2 (ALDH2) genotypes (AA/GA/GG) as instrumental variables for alcohol use to examine the association of alcohol use (10 g ethanol/day) with CVD risk factors (blood pressure, lipids and glucose) and morbidity (self-reported IHD and CVD) among men in the Guangzhou Biobank Cohort Study.Results
ALDH2 genotypes were a credible instrument for alcohol use (F-statistic 74.6). Alcohol was positively associated with HDL-cholesterol (0.05 mmol/L per alcohol unit, 95% confidence interval (CI) 0.02 to 0.08) and diastolic blood pressure (1.15 mmHg, 95% CI 0.23 to 2.07) but not with systolic blood pressure (1.00 mmHg, 95% CI -0.74 to 2.74), LDL-cholesterol (0.03 mmol/L, 95% CI -0.03 to 0.08), log transformed triglycerides (0.03 mmol/L, 95% CI -0.01 to 0.08) or log transformed fasting glucose (0.01 mmol/L, 95% CI -0.006 to 0.03), self-reported CVD (odds ratio (OR) 0.98, 95% CI 0.76 to 1.27) or self-reported IHD (OR 1.10, 95% CI 0.83 to 1.45).Conclusion
Low to moderate alcohol use among men had the expected effects on most CVD risk factors but not fasting glucose. Larger studies are needed to confirm the null associations with IHD, CVD and fasting glucose. 相似文献178.
Myosin VI (encoded by the Myo6 gene) is highly expressed in the inner and outer hair cells of the ear, retina, and polarized epithelial cells such as kidney proximal tubule cells and intestinal enterocytes. The Myo6 gene is thought to be involved in a wide range of physiological functions such as hearing, vision, and clathrin-mediated endocytosis. Bats (Chiroptera) represent one of the most fascinating mammal groups for molecular evolutionary studies of the Myo6 gene. A diversity of specialized adaptations occur among different bat lineages, such as echolocation and associated high-frequency hearing in laryngeal echolocating bats, large eyes and a strong dependence on vision in Old World fruit bats (Pteropodidae), and specialized high-carbohydrate but low-nitrogen diets in both Old World and New World fruit bats (Phyllostomidae). To investigate what role(s) the Myo6 gene might fulfill in bats, we sequenced the coding region of the Myo6 gene in 15 bat species and used molecular evolutionary analyses to detect evidence of positive selection in different bat lineages. We also conducted real-time PCR assays to explore the expression levels of Myo6 in a range of tissues from three representative bat species. Molecular evolutionary analyses revealed that the Myo6 gene, which was widely considered as a hearing gene, has undergone adaptive evolution in the Old World fruit bats which lack laryngeal echolocation and associated high-frequency hearing. Real-time PCR showed the highest expression level of the Myo6 gene in the kidney among ten tissues examined in three bat species, indicating an important role for this gene in kidney function. We suggest that Myo6 has undergone adaptive evolution in Old World fruit bats in relation to receptor-mediated endocytosis for the preservation of protein and essential nutrients. 相似文献
179.
180.
Shumei Li Bin Wang Pengfei Xu Qixiang Lin Gaolang Gong Xiaoling Peng Yuanyuan Fan Yong He Ruiwang Huang 《PloS one》2013,8(8)
Diffusion-weighted MRI (DW-MRI), the only non-invasive technique for probing human brain white matter structures in vivo, has been widely used in both fundamental studies and clinical applications. Many studies have utilized diffusion tensor imaging (DTI) and tractography approaches to explore the topological properties of human brain anatomical networks by using the single tensor model, the basic model to quantify DTI indices and tractography. However, the conventional DTI technique does not take into account contamination by the cerebrospinal fluid (CSF), which has been known to affect the estimated DTI measures and tractography in the single tensor model. Previous studies have shown that the Fluid-Attenuated Inversion Recovery (FLAIR) technique can suppress the contribution of the CSF to the DW-MRI signal. We acquired DTI datasets from twenty-two subjects using both FLAIR-DTI and conventional DTI (non-FLAIR-DTI) techniques, constructed brain anatomical networks using deterministic tractography, and compared the topological properties of the anatomical networks derived from the two types of DTI techniques. Although the brain anatomical networks derived from both types of DTI datasets showed small-world properties, we found that the brain anatomical networks derived from the FLAIR-DTI showed significantly increased global and local network efficiency compared with those derived from the conventional DTI. The increases in the network regional topological properties derived from the FLAIR-DTI technique were observed in CSF-filled regions, including the postcentral gyrus, periventricular regions, inferior frontal and temporal gyri, and regions in the visual cortex. Because brain anatomical networks derived from conventional DTI datasets with tractography have been widely used in many studies, our findings may have important implications for studying human brain anatomical networks derived from DW-MRI data and tractography. 相似文献