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   7857篇
  免费   497篇
  国内免费   12篇
  2023年   17篇
  2022年   73篇
  2021年   150篇
  2020年   93篇
  2019年   115篇
  2018年   167篇
  2017年   152篇
  2016年   278篇
  2015年   409篇
  2014年   531篇
  2013年   556篇
  2012年   659篇
  2011年   600篇
  2010年   345篇
  2009年   335篇
  2008年   473篇
  2007年   461篇
  2006年   428篇
  2005年   389篇
  2004年   370篇
  2003年   315篇
  2002年   272篇
  2001年   194篇
  2000年   173篇
  1999年   121篇
  1998年   54篇
  1997年   41篇
  1996年   39篇
  1995年   49篇
  1994年   28篇
  1993年   18篇
  1992年   55篇
  1991年   30篇
  1990年   39篇
  1989年   36篇
  1988年   31篇
  1987年   23篇
  1986年   19篇
  1985年   26篇
  1984年   23篇
  1983年   15篇
  1982年   18篇
  1981年   10篇
  1979年   18篇
  1978年   15篇
  1976年   9篇
  1975年   8篇
  1974年   14篇
  1973年   13篇
  1972年   8篇
排序方式: 共有8366条查询结果,搜索用时 31 毫秒
921.
This study was aimed to search new genetic variants in the bovine FABP4 gene as molecular markers for meat quality and carcass traits. PCR–RFLP analysis revealed that three SNPs located at nucleotide positions g.2834C>G, g.3533T>A, and g.3691G>A were identified based on a GenBank accession number (NC_007312.4). Sequence analysis revealed that SNPs were located in intron 1 (g.2834C>G) and 2 (g.3533T>A), and an exon 3 (g.3691G>A), showing allele frequencies as 0.592, 0.579, and 0.789, respectively. Genetic variabilities of heterozygosity (He) and polymorphic information contents (PIC) were estimated for g.2834C>G (0.608 and 0.531), g.3533T>A (0.615 and 0.539), and g.3691G>A (0.498 and 0.401) loci, respectively. A SNP located in the exon 3 of FABP4 was characterized and associated with desirable increases of MS (marbling scores) and MG (meat quality grades) in Hanwoo. The statistical analysis revealed that additive effects by GG genotypes in g.3691G>A SNP were significantly greater than AA genotypes in MS and MG traits. These findings suggest that the FABP4g.3691G>A SNP will be a useful candidate locus to maximize economic benefits for cattle populations.  相似文献   
922.
923.
Although the underlying cause of Parkinson's disease (PD) is not well characterized, epidemiological studies suggest that exposure to agricultural chemicals is a risk factor for PD. Fluazinam (FZN) is a new active ingredient for the control of grey mould, belonging to the novel broad spectrum phenylpyridinamine fungicides. We used human neuroblastoma SH-SY5Y cells to investigate mechanisms of dopaminergic cell death in response to FZN. FZN treatment produced dose-dependent cytotoxicity, and decreased the tyrosine hydroxylase (TH) expression in SH-SY5Y cells. We provided evidence for the occurrence of oxidative stress and oxidative damage during FZN exposure on dopaminergic cells through the measurement of reactive oxygen species (ROS) in cells with DCFH-DA. The cytotoxic effects of FZN appear to involve an increase in ROS generation since pretreatment with N-acetyl cysteine (NAC), an anti-oxidant, reduced cell death. After FZN treatment, dopamine (DA) levels decreased in both cell and culture media, and oxidative effects of FZN were blocked by NAC pretreatment. We show that cell death in response to FZN was due to apoptosis since FZN exposure results in an increased in cytochrome c release into the cytosol and activated caspase-3 through p38 and JNK signaling. Furthermore, the blocking of p38 or JNK signaling inhibits FZN-induced cell death. Phosphorylation of mitogen-activated protein kinases precedes cytochrome c release and caspase-3 activation. This cellular response is characteristic of mitochondrial dysfunction. Therefore, we also investigated the effect of FZN on mitochondrial complex I activity in FZN-treated cell. Interestingly, we show that FZN inhibited the complex I activity. Thus in this study, we report a new mode of action by which the fungicide FZN could triggers apoptosis.  相似文献   
924.
Salmonella enterica and Escherichia coli O157:H7 are major food-borne pathogens causing serious illness. Phage SFP10, which revealed effective infection of both S. enterica and E. coli O157:H7, was isolated and characterized. SFP10 contains a 158-kb double-stranded DNA genome belonging to the Vi01 phage-like family Myoviridae. In vitro adsorption assays showed that the adsorption constant rates to both Salmonella enterica serovar Typhimurium and E. coli O157:H7 were 2.50 × 10−8 ml/min and 1.91 × 10−8 ml/min, respectively. One-step growth analysis revealed that SFP10 has a shorter latent period (25 min) and a larger burst size (>200 PFU) than ordinary Myoviridae phages, suggesting effective host infection and lytic activity. However, differential development of resistance to SFP10 in S. Typhimurium and E. coli O157:H7 was observed; bacteriophage-insensitive mutant (BIM) frequencies of 1.19 × 10−2 CFU/ml for S. Typhimurium and 4.58 × 10−5 CFU/ml for E. coli O157:H7 were found, indicating that SFP10 should be active and stable for control of E. coli O157:H7 with minimal emergence of SFP10-resistant pathogens but may not be for S. Typhimurium. Specific mutation of rfaL in S. Typhimurium and E. coli O157:H7 revealed the O antigen as an SFP10 receptor for both bacteria. Genome sequence analysis of SFP10 and its comparative analysis with homologous Salmonella Vi01 and Shigella phiSboM-AG3 phages revealed that their tail fiber and tail spike genes share low sequence identity, implying that the genes are major host specificity determinants. This is the first report identifying specific infection and inhibition of Salmonella Typhimurium and E. coli O157:H7 by a single bacteriophage.  相似文献   
925.
This article reports on the full genome sequence of Paenibacillus terrae HPL-003, which is a gram-positive, endospore-forming, xylanase-producing bacterium isolated from soil found in forest residue on Gara Mountain. The strain HPL-003 contains 6,083,395 bp with a G+C content of 46.77 mol%, 2,633 protein-coding genes, and 117 structural RNAs.  相似文献   
926.
A novel Gram-positive, aerobic, motile, hemolytic, endospore-forming and rod-shaped bacterium TW25T was isolated from a dead ark clam during a mass mortality event on the South coast of Korea. The strain grew optimally at 30°C, at pH 8–9, and with 1% (w/v) NaCl. The 16S rRNA gene sequence analysis indicated that strain TW25T was associated with the genus Ornithinibacillus and that it was most closely related to the type strain of Ornithinibacillus californiensis (98.5% similarity). The dominant cellular fatty acids were iso-C15:0, anteiso-C15:0 and C16:0. The peptidoglycan amino acid type was A4β, containing l-ornithine and d-aspartic acid. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, four unidentified phospholipids, two unidentified aminolipids and two unidentified lipids. The major respiratory quinone was menaquinone-7 (MK-7). The G + C content of genomic DNA was 36.7 mol%. DNA–DNA hybridization experiments with related strains revealed lower than 11 ± 3% relatedness. Based on this polyphasic taxonomic study, strain TW25T represents a novel species in the genus Ornithinibacillus, for which the name Ornithinibacillus scapharcae sp. nov. is proposed. The type strain is TW25T (=KACC 15116T = JCM 17314T).  相似文献   
927.
Transient receptor potential melastatin 7 (TRPM7) channels are divalent cation-selective ion channels that are permeable to Ca(2+) and Mg(2+). TRPM7 is ubiquitously expressed in vertebrate cells and contains both an ion channel and a kinase domain. TRPM7 plays an important role in regulating cellular homeostatic levels of Ca(2+) and Mg(2+) in mammalian cells. Although studies have shown that the kinase domain of TRPM7 is required for channel activation and can phosphorylate other target proteins, a systematic analysis of intact TRPM7 channel phosphorylation sites expressed in mammalian cells is lacking. We applied mass spectrometric proteomic techniques to identify and characterize the key phosphorylation sites in TRPM7 channels. We identified 14 phosphorylation sites in the cytoplasmic domain of TRPM7, eight of which have not been previously reported. The identification of phosphorylation sites using antibody-based immunopurification and mass spectrometry is an effective approach for defining the phosphorylation status of TRPM7 channels. The present results show that TRPM7 channels are phosphorylated at multiple sites, which serves as a mechanism to modulate the dynamic functions of TRPM7 channels in mammalian cells.  相似文献   
928.
Choi GE  Cho YJ  Koh WJ  Chun J  Cho SN  Shin SJ 《Journal of bacteriology》2012,194(10):2756-2757
Mycobacterium abscessus subsp. bolletii is an increasing cause of human pulmonary disease and infections of the skin and soft tissues. Consistent reports of human infections indicate that M. bolletii is a highly pathogenic, emerging species of rapidly growing mycobacteria (RGM). Here we report the first whole-genome sequence of M. abscessus subsp. bolletii BD(T).  相似文献   
929.
This data paper reports litter fall data collected in a network of 21 forest sites in Japan. This is the largest litter fall data set freely available in Japan to date. The network is a part of the Monitoring Sites 1000 Project launched by the Ministry of the Environment, Japan. It covers subarctic to subtropical climate zones and the four major forest types in Japan. Twenty-three permanent plots in which usually 25 litter traps were installed were established in old-growth or secondary natural forests. Litter falls were collected monthly from 2004, and sorted into leaves, branches, reproductive structures and miscellaneous. The data provide seasonal patterns and inter-annual dynamics of litter falls, and their geographical patterns, and offer good opportunities for meta-analyses and comparative studies among forests.  相似文献   
930.
Outlier detection and cleaning procedures were evaluated to estimate mathematical restricted variogram models with discrete insect population count data. Because variogram modeling is significantly affected by outliers, methods to detect and clean outliers from data sets are critical for proper variogram modeling. In this study, we examined spatial data in the form of discrete measurements of insect counts on a rectangular grid. Two well-known insect pest population data were analyzed; one data set was the western flower thrips, Frankliniella occidentalis (Pergande) on greenhouse cucumbers and the other was the greenhouse whitefly, Trialeurodes vaporariorum (Westwood) on greenhouse cherry tomatoes. A spatial additive outlier model was constructed to detect outliers in both the isolated and patchy spatial distributions of outliers, and the outliers were cleaned with the neighboring median cleaner. To analyze the effect of outliers, we compared the relative nugget effects of data cleaned of outliers and data still containing outliers after transformation. In addition, the correlation coefficients between the actual and predicted values were compared using the leave-one-out cross-validation method with data cleaned of outliers and non-cleaned data after unbiased back transformation. The outlier detection and cleaning procedure improved geostatistical analysis, particularly by reducing the nugget effect, which greatly impacts the prediction variance of kriging. Consequently, the outlier detection and cleaning procedures used here improved the results of geostatistical analysis with highly skewed and extremely fluctuating data, such as insect counts.  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