全文获取类型
收费全文 | 34262篇 |
免费 | 3000篇 |
国内免费 | 3481篇 |
专业分类
40743篇 |
出版年
2024年 | 114篇 |
2023年 | 582篇 |
2022年 | 1156篇 |
2021年 | 1871篇 |
2020年 | 1269篇 |
2019年 | 1655篇 |
2018年 | 1425篇 |
2017年 | 1067篇 |
2016年 | 1551篇 |
2015年 | 2139篇 |
2014年 | 2605篇 |
2013年 | 2707篇 |
2012年 | 3226篇 |
2011年 | 2878篇 |
2010年 | 1831篇 |
2009年 | 1625篇 |
2008年 | 1832篇 |
2007年 | 1588篇 |
2006年 | 1385篇 |
2005年 | 1215篇 |
2004年 | 1052篇 |
2003年 | 1020篇 |
2002年 | 891篇 |
2001年 | 578篇 |
2000年 | 531篇 |
1999年 | 492篇 |
1998年 | 311篇 |
1997年 | 301篇 |
1996年 | 281篇 |
1995年 | 211篇 |
1994年 | 230篇 |
1993年 | 146篇 |
1992年 | 190篇 |
1991年 | 153篇 |
1990年 | 139篇 |
1989年 | 110篇 |
1988年 | 82篇 |
1987年 | 53篇 |
1986年 | 46篇 |
1985年 | 72篇 |
1984年 | 31篇 |
1983年 | 38篇 |
1982年 | 27篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1973年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
通过逆转录-聚合酶链反应从我国河南省2例重叠感染HCV或HBV/HDV的献血啼中,分离到HBVNS5区的部分cDNA,对其进行序列分析比较,结果表明,河南株HGVNS5工核苷酸与两中国HGV主同源性高于国外代表株(88.5-90.6%),但由核苷酸推导的氨基酸的同源性都无明显的地区性区别。HGVNS5区氨基酸序列较保守,缺乏明显高变区,中国4株HGV在7384位发生了由C→T的变异,从而导致一个人 相似文献
102.
103.
104.
105.
Revegetation is a traditional practice widely used for soil and water conservation on the Loess Plateau in China. However, there has been a lack of reports on soil microbial–biochemical indices required for a comprehensive evaluation of the success of revegetation systems. In this study, we examined the effects of revegetation on major soil nutrients and microbial–biochemical properties in an artificial alfalfa grassland, an enclosed natural grassland, and an artificial shrubland (Caragana korshinskii), with an abandoned cropland as control. Results showed that at 0–5, 5–20, and 20–40 cm depths, soil organic carbon, alkaline extractable nitrogen and available potassium were higher in natural grassland and artificial shrubland compared with artificial grassland and abandoned cropland. Soil microbial biomass C (Cmic) and phosphorous (Pmic) substantially decreased with depth at all sites, and in abandoned cropland was significantly lower than those of natural grassland, artificial grassland, and artificial shrubland at the depth of 0–5 cm. Soil microbial biomass N (Nmic) was higher in artificial shrubland and abandoned cropland compared with that in natural and artificial grasslands. Both Cmic and Pmic were significantly different between the 23‐year‐old and the 13‐year‐old artificial shrublands at the 0–5 cm depth. The activities of soil invertase, urease, and alkaline phosphatase in natural grassland and artificial shrubland were higher than those in artificial grassland and abandoned cropland. This study demonstrated that the regeneration of both natural grassland and artificial shrubland effectively preserved and enhanced soil microbial biomass and major nutrient cycling, thus is an ecologically beneficial practice for recovery of degraded soils on the Loess Plateau. 相似文献
106.
107.
Agnes Simonyi Yan He Wenwen Sheng Albert Y. Sun W. Gibson Wood Gary A. Weisman Grace Y. Sun 《Molecular neurobiology》2010,41(2-3):73-86
Alzheimer’s disease (AD) is marked by an increase in the production of extracellular beta amyloid plaques and intracellular neurofibrillary tangles associated with a decline in brain function. Increases in oxidative stress are regarded as an early sign of AD pathophysiology, although the source of reactive oxygen species (ROS) and the mechanism(s) whereby beta amyloid peptides (Aβ) impact oxidative stress have not been adequately investigated. Recent studies provide strong evidence for the involvement of NADPH oxidase and its downstream oxidative signaling pathways in the toxic effects elicited by Aβ. ROS produced by NADPH oxidase activate multiple signaling pathways leading to neuronal excitotoxicity and glial cell-mediated inflammation. This review describes recent studies demonstrating the neurotoxic effects of Aβ in conjunction with ROS produced by NADPH oxidase and the downstream pathways leading to activation of cytosolic phospholipase A2 (PLA2) and secretory PLA2. In addition, this review also describes recent studies using botanical antioxidants to protect against oxidative damage associated with AD. Investigating the metabolic and signaling pathways involving Aβ NADPH oxidase and PLA2 can help understand the mechanisms underlying the neurodegenerative effects of oxidative stress in AD. This information should provide new therapeutic approaches for prevention of this debilitating disease. 相似文献
108.
109.
110.
The function of NS4B is incompletely understood. The aim of the study is to understand the influence of NS4B on anti-viral response. After cell line stably expressing NS4B established, the influence of IFN-alpha of different concentration on VSV was studied using plaque assay; cell expression profiling caused by NS4B was studied using DNA microarray, and the IFNGR1 fluorescence intensity was analyzed. Our data showed that HCV-NS4B could suppress immuno-associated gene expression, in particular, IFN-gamma receptor signal transduction-related genes. Taken together, NS4B could play some roles in HCV resistance to IFN therapy. 相似文献