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   6628篇
  免费   331篇
  国内免费   19篇
  2023年   75篇
  2022年   187篇
  2021年   390篇
  2020年   201篇
  2019年   333篇
  2018年   305篇
  2017年   223篇
  2016年   282篇
  2015年   330篇
  2014年   385篇
  2013年   564篇
  2012年   475篇
  2011年   477篇
  2010年   280篇
  2009年   239篇
  2008年   248篇
  2007年   238篇
  2006年   221篇
  2005年   182篇
  2004年   144篇
  2003年   117篇
  2002年   114篇
  2001年   63篇
  2000年   73篇
  1999年   54篇
  1998年   31篇
  1997年   20篇
  1996年   23篇
  1995年   20篇
  1994年   14篇
  1993年   20篇
  1992年   36篇
  1991年   51篇
  1990年   44篇
  1989年   34篇
  1988年   34篇
  1987年   42篇
  1986年   30篇
  1985年   39篇
  1984年   33篇
  1983年   21篇
  1982年   20篇
  1980年   15篇
  1979年   24篇
  1978年   24篇
  1977年   16篇
  1975年   14篇
  1974年   14篇
  1973年   21篇
  1968年   15篇
排序方式: 共有6978条查询结果,搜索用时 297 毫秒
991.
Autophagy is a cellular process for maintaining cellular homeostasis. This process can be induced by different factors, such as immune stimuli and pathogen-associated molecules. Autophagy has an important role in the control of IL-1β secretion by macrophages and other cell types. In present study, we describe a novel role for Iraqi propolis affecting autophagy in controlling the secretion of IL-1β in bone-marrow macrophages (BMDMs). After infection with Pseudomonas aeruginosa in the presence of propolis, the degradation of IL-1β was induced, and the activity of inflammasome was reduced. Iraqi propolis-induced autophagy in in vitro and in vivo models decreased the levels of IL-1β and caspase-1. Results indicated that IL-1β pathway production is regulated by autophagy via two different novel mechanisms, namely, regulation of the activation of NLRC4 inflammasome and IL-1β targeting for lysosomal degradation.  相似文献   
992.
The present study was conducted to elaborate vegetation composition structure to analyze role of edaphic and topographic factors on plant species distribution and community formation during 2013–14. A mixture of quadrat and transect methods were used. The size of quadrat for trees shrubs and herbs were 10 × 5, 5 × 2, 1 × 1 meter square respectively. Different phytosociological attribute were measured at each station. Primary results reported 123 plant species belong to 46 families. Asteraceae and Lamiaceae were dominant families with 8 species each. PCORD version 5 were used for Cluster and Two Way Cluster Analyses that initiated 4 plant communities within elevation range of 529–700 m from sea level. Indicator species analyses (ISA) were used to identify indicator species of each community. CANOCO Software (version 4.5) was used to measure the influence of edaphic and topographic variables on species composition, diversity and community formation. Whereas Canonical Correspondence Analysis (CCA) was used to measure the effect of environmental variables which showed elevation and aspect were the stronger environmental variable among topographic and CaCO3 contents, electric conductivity, soil pH were the stronger edaphic factors in determination of vegetation and communities of the Bheer Hills. Grazing pressure was one of the main anthropogenic factors in this regard.  相似文献   
993.
Odor sensation is a sensory modality of considerable significance in the foraging behavior and interactional organization of ants. In the food bait technology, smell is the basis of attraction, which, in turn, is the line of bait use and a key parameter for judging efficacy. Yet, the currently available baits possess low attractiveness to many ant pests. Hence, strategies to produce ant bait with increased attractiveness are needed. Despite evidence that coffee has a diverse aroma complex that affects the behavior of honey bees and ants, its attraction to house-invading ants has yet to be investigated. In a series of Y-tube olfactometer bioassays, we examined the behavioral responses of Tapinoma indicum (TI), Monomorium pharaonis (MP) and Solenopsis geminata (SG) to various coffee-induced odor stimuli, comprised of extracts from Arabica, Robusta and Liberica. All coffee extracts showed an influence on the behavior of TI, MP and SG workers, with Arabica showed the most significant influence to the tested ants. The workers of TI, MP and SG were more attracted to the odor of 0.01% Arabica extract (ONE), in comparison with 0.05% Arabica extract (TWO) or 0.10% Arabica extract (THREE). Arabica extract mixed with sugar (S) elicited a significant attraction from workers of all three species in a balanced competition with either unsweetened Arabica extract or water. These results indicated that coffee, particularly Arabica, was attractive to the foragers of TI, MP and SG, thus, the use of coffee as a novel stimulus agent seems plausible in ant bait development.  相似文献   
994.
The Persian Gulf and Oman Sea constitute one of the most important marine ecosystems and have many economically important aquatic species, including several coleoid cephalopods. Some coleoids are difficult to identify using traditional morphological characteristics. In this study, two mitochondrial fragments, cytochrome oxidase I (COI) and the large ribosomal subunit (16S rRNA), were used for identification of coleoid species in four regions in the northern Persian Gulf and Oman Sea. The study led to the identification of potential cryptic species of Sepia, Amphioctopus and Uroteuthis. Furthermore, Euprymna hyllebergi was reported for the first time from the Persian Gulf. A high diversity of Coeloidea was found in the study area. Mean intraspecific and interspecific nucleotide distances for COI were 0%–2% and 2%–7%, respectively, while these values for 16S rRNA sequences were 0%–1% and 1%–4%. Given the uncertainty about species identity and the high levels of intraspecific genetic diversity reported for some species in GenBank, a comprehensive global study will be needed to resolve the taxonomic status of several coleoid species.  相似文献   
995.
996.
997.
The alpha-toxin is one of the virulence factors of Clostridium perfringens for gas gangrene in humans and animals or necrotic enteritis in poultry. The C-terminal domain of this toxin ( cpa 247-370 ) was synthesized and cloned into pT1NX vector to construct the pT1NX-alpha plasmid. This surface-expressing plasmid was electroporated into Lactobacillus casei ATCC 393, generating the recombinant L. casei strain expressing alpha-toxoid (LC-α strain). Expression of this modified alpha-toxoid was confirmed by SDS-PAGE, immunoblotting, and direct immunofluorescence microscopy. BALB/c mice, immunized orally by the recombinant LC-α strain, elicited mucosal and significantly humoral immune responses (p < 0.05) and developed a protection against 900 MLD/mL of the standard alpha-toxin. This study showed that this recombinant LC-α strain could be a promising vaccine candidate against gas gangrene and necrotic enteritis.  相似文献   
998.
Floristic inventory of wild plants comprised of total 129 plant species belonging to 42 families and 101 genera. Location wise UAP contributed greater amount of plant species (53%), followed by PFI (29%), UoP (15%) and Islamia College (3%). Majority of the plants were annual herbs (58%), followed by perennial herbs (29%), trees (10%) and shrubs (3%), respectively. The leading families included Poaceae, contributed 18% of all the plant species. Habitat wise, 44% of them grew in grassy plains, abandoned lands and mismanaged lawns, followed by roadsides (34%), undulating grassy plains (15%) and stony grounds with uneven topography along with stream banks and drainage ditches (7%). Still some of plant species were used as ornamentals, while some shrubs were use in fencing around fields; others were utilized as green manure, for fishing, sheltering and religious purposes. Exploring and identifying the wild flora of the campus and compiling as a handbook would help to monitor new plants introductions particularly of noxious invasive weeds in the campuses in future.  相似文献   
999.
The paper describes the bio efficacy of a protease inhibitor; isolated from Allium sativumgarlic’ (ASPI); against Aedes aegypti mosquito, a well-known transmitter of dengue and Chikungunya. The purification of protease inhibitor from Allium sativumgarlic’ (ASPI) was carried out by ammonium sulfate precipitation followed by Fast Protein Liquid Chromatography using akta DEAE-Cellulose column. The protein fraction demonstrating trypsin inhibitory activity was further evaluated for its insecticidal activity using gut protease inhibition assay and larvicidal assay. ASPI is an inhibitor of porcine trypsin (IC50 of 650.726?μg/mL) and has molecular weight of ~15?kDa determined by SDS PAGE similar to other inhibitors of the Kunitz-type family (14–26?kDa). ASPI demonstrated 50% reduced activity of Ae. aegypti midgut proteases and showed a dose-dependent acute toxicity on Ae. aegypti 3rd instars exhibiting LC50 value of ~50.827?μg/mL. After ten days of larval exposure ASPI resulted in a 24-h delay of larval development and ~72% mortality at 61.5?μg/mL. These results suggest that ASPI may serve as potent insecticidal agent and hence opens a new gateway in the field of phyto-remediation.  相似文献   
1000.
Pink bollworm (Pectinophora gossypiella) is recognized as an important pest of cotton and can damage flowers and bolls of both Bt and non-Bt cultivars. Cry-1Ac in Bt cultivars is considered very effective in controlling lepidopterous larvae; therefore, the present study was carried out to investigate the impact of Cry1-Ac and the earliness index on the natural incidence of P. gossypiella at the Cotton Research Institute, Faisalabad. During 2015–2016, ten cultivars were used to determine the incidence of pink bollworm infestation. The experiment was repeated for 2 years. During the next year, Cry1-Ac and earliness traits of selected cultivars were also observed to determine their impact on pink bollworm. Correlation coefficient results regarding days to first flower (r value = 0.66) as well as the earliness index (r value = ? 0.62) exhibited a strong association with pink bollworm, but Cry1-Ac had a weak association (r value = ? 0.058) with pink bollworm. The coefficient of determination (R 2) explained that variability of pink bollworm due to Cry1-Ac, the earliness index, and days to first flower was 18.0, 38.5, and 43.5%, respectively. Principal component analysis results showed that the first two PCs expressed 87% of the total variability. Clusters made on the basis of the studied parameters revealed that clusters 2 and 3 comprised the cotton cultivars possessing earliness traits compared with cluster 1. Therefore, it can be concluded that the earliness index in cotton is an important component for the sustainable management of pink bollworm infestation, the need for which is endless to evade the pink bollworm problem in the era of climate change.  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