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   4353篇
  免费   269篇
  国内免费   1篇
  2023年   22篇
  2022年   28篇
  2021年   101篇
  2020年   55篇
  2019年   59篇
  2018年   111篇
  2017年   65篇
  2016年   131篇
  2015年   213篇
  2014年   234篇
  2013年   328篇
  2012年   383篇
  2011年   337篇
  2010年   223篇
  2009年   179篇
  2008年   279篇
  2007年   257篇
  2006年   225篇
  2005年   213篇
  2004年   195篇
  2003年   179篇
  2002年   193篇
  2001年   45篇
  2000年   32篇
  1999年   34篇
  1998年   42篇
  1997年   32篇
  1996年   45篇
  1995年   24篇
  1994年   37篇
  1993年   31篇
  1992年   21篇
  1991年   30篇
  1990年   20篇
  1989年   18篇
  1988年   16篇
  1987年   18篇
  1986年   10篇
  1985年   12篇
  1984年   24篇
  1983年   18篇
  1982年   10篇
  1981年   6篇
  1980年   11篇
  1979年   11篇
  1978年   9篇
  1974年   9篇
  1973年   6篇
  1967年   3篇
  1949年   3篇
排序方式: 共有4623条查询结果,搜索用时 93 毫秒
71.
Molecular and Cellular Biochemistry - Chronic kidney disease (CKD) is a renal dysfunction that can lead to high rates of mortality and morbidity, particularly when coupled with late diagnosis. CKD...  相似文献   
72.
Molecular Biology Reports - Serine hydrolases play crucial roles in many physiological and pathophysiological processes and a panel of these enzymes are targets of approved drugs. Despite this,...  相似文献   
73.
Biodiversity and Conservation - The complex biology and specialized relationships between orchids and both fungi and pollinators can complicate orchid conservation and management. Some terrestrial...  相似文献   
74.

The effects of invaders on native species are usually tested using species mean trait values over long time scales. However, considering individual variation over short timescales can help us better understand the interaction between invaders and native species. We compared trophic traits of the non-native guppy (Poecilia reticulata) and the native Brazilian poeciliid Phalloceros harpagos using experiments simulating the early stages of an invasive process. We used short-term mesocosms to simulate an early invasion scenario, where the two species were placed together, and a pre-invasion scenario, where species were kept separated, and analyzed interspecific and intraspecific trophic variability. We also compared the foraging efficiency of species in laboratory experiments. We found no differences on the mean diet of both species between pre and early invasion treatments. At the individual level, in the early invasion scenario, individuals of both species reduced their trophic niche as a probable effect of the presence of the heterospecific. Phalloceros harpagos had higher consumption rates than guppies indicating greater efficiency in feeding on invertebrates. Our results suggest that non-native species were not intrinsically better consumers of high-quality resources. Instead, intraspecific variation might be playing an overlooked role in shaping interactions between species during the early stages of invasion.

  相似文献   
75.
Probiotics and Antimicrobial Proteins - Probiotics represent a possible strategy for controlling intestinal infections in livestock. Members of the Weissella genus are increasingly being studied...  相似文献   
76.
Landscape and Ecological Engineering - The relationship between beech (Fagus crenata) reproductive-organ (female flowers: FFs, male inflorescences: MIs, and filled masts: FMs) production and the...  相似文献   
77.
Parkinson''s disease (PD) is a neurodegenerative disorder that affects adult people whose treatment is palliative. Thus, we decided to test three dammarane triterpenes 1, 1a, 1b, and we determined that 1 and 1a inhibit β-aggregation through thioflavine T rather than 1b. Since compound 1 was most active, we determined the interaction between α-synuclein and 1 at 50 µM (Kd) through microscale thermophoresis. Also, we observed differences in height and diameter of aggregates, and α-synuclein remains unfolded in the presence of 1. Also, aggregates treated with 1 do not provoke neurites'' retraction in N2a cells previously induced by retinoic acid. Finally, we studied the potential sites of interaction between 1 with α-synuclein fibrils using molecular modelling. Docking experiments suggest that 1 preferably interact with the site 2 of α-synuclein through hydrogen bonds with residues Y39 and T44.  相似文献   
78.
Castilleja tenuiflora is a facultative root hemiparasitic plant that has colonized a disturbed lava field in central Mexico. To determine the effects of hemiparasitism on the population dynamics of the parasite, we identified a set of potential hosts and quantified their effects on the vital rates of C. tenuiflora during 2016–2018. Connections between the roots of the hemiparasite and the hosts were confirmed with a scanning electron microscope. Annual matrices considering two conditions (with and without potential hosts) were built based on vital rates for each year, and annual stochastic finite rate growth rates (λs) were calculated. Plants produced more reproductive structures with hosts than without hosts. A Life Table Response Experiment (LTRE) was performed to compare the contributions of vital rates between conditions. We identified 19 species of potential hosts for this generalist hemiparasite. Stochastic lambda with hosts λs = 1.02 (CI = 0.9999, 1.1) tended to be higher than without them λs = 0.9503 (CI = 0.9055, 0.9981). The highest elasticity values correspond to survival. LTRE indicated that the most important parameters are survival and fecundity; the total contribution of fecundity (0.0192) to the difference in growth was three times lower than that of survival (0.0603). Piqueria trinervia was the most abundant host, and C. tenuiflora had a higher lambda with it than with other species. Individuals can grow alone, but hosts can have a positive effect on the vital parameters of C. tenuiflora and on λ.  相似文献   
79.
Riassunto

L'A. deserive la vegetazione di due stazioni delle serpentine dell'Impruneta e riporta le osservazioni condotte negli anni 1938–40 sul ritmo di vegetazione delle specie che popolano tali stazioni.

Dalle osservazioai fenologiche risulta che il risveglio della vegetazione sulle serpentine non è ritardato alla primavera per le specie pi[ugrave] tipiche, mentre lo è per talune specie banali; che le parti secche delle piante tendono a rimanere lungamente in posto; che la disseminazione è lenta e si protrae spesso fino all'autunno inoltrato od anche fino alla primavera successiva.  相似文献   
80.
The contribution that oxidative damage to DNA and/or RNA makes to the aging process remains undefined. In this study, we used the hMTH1‐Tg mouse model to investigate how oxidative damage to nucleic acids affects aging. hMTH1‐Tg mice express high levels of the hMTH1 hydrolase that degrades 8‐oxodGTP and 8‐oxoGTP and excludes 8‐oxoguanine from both DNA and RNA. Compared to wild‐type animals, hMTH1‐overexpressing mice have significantly lower steady‐state levels of 8‐oxoguanine in both nuclear and mitochondrial DNA of several organs, including the brain. hMTH1 overexpression prevents the age‐dependent accumulation of DNA 8‐oxoguanine that occurs in wild‐type mice. These lower levels of oxidized guanines are associated with increased longevity and hMTH1‐Tg animals live significantly longer than their wild‐type littermates. Neither lipid oxidation nor overall antioxidant status is significantly affected by hMTH1 overexpression. At the cellular level, neurospheres derived from adult hMTH1‐Tg neural progenitor cells display increased proliferative capacity and primary fibroblasts from hMTH1‐Tg embryos do not undergo overt senescence in vitro. The significantly lower levels of oxidized DNA/RNA in transgenic animals are associated with behavioral changes. These mice show reduced anxiety and enhanced investigation of environmental and social cues. Longevity conferred by overexpression of a single nucleotide hydrolase in hMTH1‐Tg animals is an example of lifespan extension associated with healthy aging. It provides a link between aging and oxidative damage to nucleic acids.  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