首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   577篇
  免费   67篇
  国内免费   46篇
  2023年   12篇
  2022年   11篇
  2021年   14篇
  2020年   23篇
  2019年   29篇
  2018年   19篇
  2017年   31篇
  2016年   30篇
  2015年   29篇
  2014年   38篇
  2013年   43篇
  2012年   27篇
  2011年   26篇
  2010年   27篇
  2009年   30篇
  2008年   25篇
  2007年   35篇
  2006年   17篇
  2005年   23篇
  2004年   22篇
  2003年   12篇
  2002年   12篇
  2001年   9篇
  2000年   8篇
  1999年   4篇
  1998年   6篇
  1997年   4篇
  1996年   10篇
  1995年   6篇
  1994年   6篇
  1993年   6篇
  1992年   6篇
  1991年   7篇
  1990年   4篇
  1989年   4篇
  1986年   4篇
  1985年   9篇
  1984年   3篇
  1983年   7篇
  1982年   3篇
  1981年   4篇
  1980年   7篇
  1979年   4篇
  1978年   4篇
  1977年   3篇
  1976年   4篇
  1975年   4篇
  1974年   3篇
  1972年   5篇
  1971年   4篇
排序方式: 共有690条查询结果,搜索用时 62 毫秒
81.
Saroglitazar, being a dual PPAR-α/γ agonist, has shown beneficial effect in diabetic dyslipidemia and hypertriglyceridemia. Fibrates are commonly used to treat severe hypertriglyceridemia. However, the effect of saroglitazar in patients with moderate to severe hypertriglyceridemia was not evaluated. We conducted a study to compare the efficacy and safety of saroglitazar (4 mg) with fenofibrate (160 mg) in patients with moderate to severe hypertriglyceridemia. This was a multicenter, randomized, double-blinded, double-dummy, active-control, and noninferiority trial in adult patients with fasting triglyceride (TG) levels of 500–1,500 mg/dl. The patients were randomized in a 1:1 ratio to receive daily dose of saroglitazar or fenofibrate for 12 weeks. The primary efficacy end point was the percent change in TG levels at week 12 relative to baseline. The study comprised of 41 patients in the saroglitazar group and 41 patients in the fenofibrate group. We found that the percent reduction from baseline in TG levels at week 12 was significantly higher in the saroglitazar group (least square mean = ?55.3%; SE = 4.9) compared with the fenofibrate group (least square mean = ?41.1%; SE = 4.9; P = 0.048). Overall, 37 treatment-emergent adverse events (AEs) were reported in 24 patients (saroglitazar: 13; fenofibrate: 11). No serious AEs were reported, and no patient discontinued the study because of AEs. We conclude that saroglitazar (4 mg) is noninferior to fenofibrate (160 mg) in reducing TG levels after 12 weeks of treatment, was safe, and well tolerated.  相似文献   
82.
Compounds from wild edible mushrooms has been reported to exert biological activities and contribute to the different flavors of mushrooms in our diet. Wild edible Boletus mushrooms are popular in Southwest China. In this study, we performed ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) based on widely targeted metabolomics analysis to identify key components. A total of 194 metabolites (113 upregulated, 81 downregulated) divided into 11 groups (49 metabolites in group lipids, 34 in amino acids and derivatives, 30 in organic acids, 18 in phenolic acids, 16 in nucleotides and derivatives, 13 in alkaloids, 6 in flavonoids, 3 in lignans and coumarins, 3 in tannins, 2 in terpenoids, and 20 in others) were found among Boletus bainiugan compared with B. subsplendidus. Through clustering analysis, principal component analysis (PCA), and orthogonal signal correction and partial least squares-discriminant analysis (OPLS-DA), different metabolites from fruiting bodies were clearly identified. Significant differences were observed in the metabolites between Boletus bainiugan and B. subsplendidus. These metabolites are involved in important biological functions. Our results provide new insights into important metabolites and theoretical basis for the taste difference of two wild edible Boletus mushrooms.  相似文献   
83.
Least squares estimation in dynamic-disturbance time series models   总被引:1,自引:0,他引:1  
PIERCE  DAVID A. 《Biometrika》1972,59(1):73-78
  相似文献   
84.
85.
Masking unmasked   总被引:1,自引:0,他引:1  
ATKINSON  A. C. 《Biometrika》1986,73(3):533-541
  相似文献   
86.
87.
结合南极磷虾渔业科学观察员收集的渔业数据和海洋环境数据,本研究利用地理加权回归模型(GWR),分析了具有空间属性的虾群深度和离岸距离两个因子,以及海水表温对南设得兰群岛北侧水域南极磷虾渔场空间分布的影响.结果表明:各年南极磷虾渔业单位捕捞努力量渔获量(CPUE)在空间上的分布无显著的集聚性;2010和2013年,3个因子之间存在空间自相关性(正相关),而2012和2016年则无自相关性.GWR模型结果显示,3个因子对CPUE的空间分布具有不同程度的影响,影响程度大小依次为虾群深度>离岸距离>温度.拟合结果发现,南设得兰群岛东、西两侧水域中表温对CPUE空间分布的影响与其他两个因子具有相反的趋势.虾群深度和离岸距离对CPUE的空间效应主要表现为负相关,但存在着年际和区域性差异.本研究结果可为南极磷虾渔场形成机制研究提供方法上的参考.  相似文献   
88.
89.

Background

Questions about the reliability of parametric standard errors (SEs) from nonlinear least squares (LS) algorithms have led to a general mistrust of these precision estimators that is often unwarranted.

Methods

The importance of non-Gaussian parameter distributions is illustrated by converting linear models to nonlinear by substituting eA, ln A, and 1/A for a linear parameter a. Monte Carlo (MC) simulations characterize parameter distributions in more complex cases, including when data have varying uncertainty and should be weighted, but weights are neglected. This situation leads to loss of precision and erroneous parametric SEs, as is illustrated for the Lineweaver-Burk analysis of enzyme kinetics data and the analysis of isothermal titration calorimetry data.

Results

Non-Gaussian parameter distributions are generally asymmetric and biased. However, when the parametric SE is < 10% of the magnitude of the parameter, both the bias and the asymmetry can usually be ignored. Sometimes nonlinear estimators can be redefined to give more normal distributions and better convergence properties.

Conclusion

Variable data uncertainty, or heteroscedasticity, can sometimes be handled by data transforms but more generally requires weighted LS, which in turn require knowledge of the data variance.

General significance

Parametric SEs are rigorously correct in linear LS under the usual assumptions, and are a trustworthy approximation in nonlinear LS provided they are sufficiently small — a condition favored by the abundant, precise data routinely collected in many modern instrumental methods.  相似文献   
90.
Understanding the key aspects of plant regeneration from seeds is crucial in assessing species assembly to their habitats. However, the regenerative traits of seed dormancy and germination are underrepresented in this context. In the alpine zone, the large species and microhabitat diversity provide an ideal context to assess habitat‐related regenerative strategies. To this end, seeds of 53 species growing in alpine siliceous and calcareous habitats (6230 and 6170 of EU Directive 92/43, respectively) were exposed to different temperature treatments under controlled laboratory conditions. Germination strategies in each habitat were identified by clustering with k‐means. Then, phylogenetic least squares correlations (PGLS) were fitted to assess germination and dormancy differences between species’ main habitat (calcareous and siliceous), microhabitat (grasslands, heaths, rocky, and species with no specific microhabitats), and chorology (arctic–alpine and continental). Calcareous and siliceous grasslands significantly differ in their germination behaviour with a slow, mostly overwinter germination and high germination under all conditions, respectively. Species with high overwinter germination occurs mostly in heaths and have an arctic–alpine distribution. Meanwhile, species with low or high germinability in general inhabit in grasslands or have no specific microhabitat (they belong to generalist), respectively. Alpine species use different germination strategies depending on habitat provenance, species’ main microhabitat, and chorotype. Such differences may reflect adaptations to local environmental conditions and highlight the functional role of germination and dormancy in community ecology.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号