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   460篇
  免费   19篇
  国内免费   4篇
  2023年   3篇
  2022年   23篇
  2021年   26篇
  2020年   11篇
  2019年   14篇
  2018年   13篇
  2017年   11篇
  2016年   18篇
  2015年   33篇
  2014年   38篇
  2013年   29篇
  2012年   45篇
  2011年   34篇
  2010年   17篇
  2009年   12篇
  2008年   18篇
  2007年   13篇
  2006年   14篇
  2005年   7篇
  2004年   14篇
  2003年   8篇
  2002年   10篇
  2001年   3篇
  2000年   7篇
  1999年   12篇
  1998年   7篇
  1997年   6篇
  1996年   4篇
  1995年   3篇
  1994年   1篇
  1993年   1篇
  1992年   5篇
  1991年   1篇
  1990年   2篇
  1988年   1篇
  1987年   3篇
  1985年   2篇
  1983年   2篇
  1982年   1篇
  1979年   1篇
  1976年   1篇
  1974年   1篇
  1972年   2篇
  1969年   1篇
  1968年   3篇
  1967年   1篇
  1965年   1篇
排序方式: 共有483条查询结果,搜索用时 31 毫秒
1.
Transposon mutants of Bradyrhizobium japonicum 110 ARS were produced and screened for changes in attachment ability. Mutant CFK4 produced twice as many piliated cells, attached in 2.5-fold-higher numbers to soybean root segments, and colonized roots in about 2-fold-higher numbers than did the parental strain, 110 ARS. Mutants CFK35 and CFK38 were reduced in their attachment about 2-fold and 3.5-fold, respectively. This corresponded to reductions in piliated cells in their populations, reduced reaction with anti-pilus antiserum, and reduced hydrophobic attachment. Mutants CFK4 and CFK38 nodulated soybeans at about the same level as the parent strain, but CFK35 induced only pseudonodules. Two-dimensional gel analyses of the proteins from the mutants showed relatively few changes in proteins.  相似文献   
2.
3.
To investigate the occurrence of 17p (p53) loss of heterozygosity (LOH) and increased 4N or aneuploidy in gastric precancerous lesions (GPL), and their association with Helicobacter pylori (H pylori) infection. A total of 78 gastric mucosal biopsy specimens, including 10 normal mucosa and 68 gastric precancerous lesions [chronic atrophic gastritis (CAG, n = 20), intestinal metaplasia (IM, n = 12), low grade dysplasia (LGD, n = 15), and high grade dysplasia (HGD, n = 21)] were studied using PCR and flow cytometry. A modified Giemsa staining technique was used to detect H pylori. The study was performed in Erzurum Numune Hospital between 2007 and 2009. 17p (p53) LOH was observed in (1/20) 5% of CAG, in (2/12) 16% of IM, in (3/15) 20% of LGD and in (11/21) 53% of HGD. There was correlation between prevalence of 17p (p53) LOH and histological type of GPL (P = 0.004). Similarly, increased 4N or aneuploidy was detected in (1/20) 5% of CAG, in (1/12) 8% of IM, in (2/15) 13% of LGD and in (9/21) 43% of HGD. The correlation was found between aneuploidy and histological type of GPL (P = 0.009). However, there was no correlation between presence of H pylori infection in histological type of GPL (P = 0.921). On the other hand, a significant association was found between increased 4N or aneuploidy and 17p (p53) LOH in all of GPL (P = 0.0001). However, there was no statistically significant association between H pylori infection and 17p (p53) LOH or increased 4N/aneuplody in GPL. 17p (p53) LOH and increased 4N or aneuploidy are closely related to the early stages of gastric carcinogenesis.  相似文献   
4.
植物入侵会造成入侵地生态系统功能和稳定性的破坏。与原产地种源相比,入侵种源植物在生理学特性方面有所不同,使其在资源利用和抵抗环境胁迫具有较强的竞争优势。叶绿素荧光特性与植物光合作用效率密切相关,对植物生长具有重要作用。氮沉降加剧是全球变化的一个重要因子,土壤微生物对植物吸收利用土壤养分至关重要。通过施用细菌抑制剂(链霉素)和真菌抑制剂(扑海因)选择性抑制的土壤微生物活性,开展乌桕盆栽实验,在模拟氮沉降背景下,研究不同微生物群落如何影响入侵乌桕叶绿素荧光特性,有助于理解入侵植物的进化特征和入侵机制,为有效防控入侵植物并降低其对生态系统危害提供理论依据。以原产地地和入侵地两个种源乌桕(Triadica sebifera)为研究对象,在氮沉降条件下,通过调控土壤细菌和真菌,探讨两个种源乌桕叶绿素荧光参数差异。结果显示:氮沉降显著增加乌桕相对叶绿素含量(SPAD)、光系统II的最大量子产率(Fv/Fm)、非光化学猝灭(NPQ)和半饱和光强(Ik)。入侵种源乌桕比原产地具有较低SPAD。氮沉降与细菌抑制剂共同作用显著增强了Fv/Fm、NPQ和Ik,显著减弱了光能利用率(α)和SPAD。细菌抑制剂减缓了本地种源乌桕α,真菌抑制剂促进本地种源乌桕Ik,抑制入侵种源乌桕Ik,细菌和真菌抑制剂可显著降低原产地乌桕α。氮沉降与生物抑制剂可显著作用于乌桕叶片SPAD。氮沉降、土壤微生物和不同乌桕种源可共同作用于光系统Ⅱ实际光合量子产率Y(Ⅱ),α和潜在最大相对电子传递速率(ETRmax)。因此,氮沉降与生物抑制剂对乌桕叶绿素荧光特性具有协同作用,入侵种源乌桕对土壤微生物控制的响应不明显,在微生物控制条件下依然具有较强的适应能力,因而具有较强的入侵能力。  相似文献   
5.
BackgroundFamily involvement in overcoming the severity of leprosy is very important in the life of leprosy sufferers in communities who experience the clinical and, psychological, social and behavioral consequences of the disease. However, this need, psychosocial, is felt to be not optimal. This study is to identify how the experiences of family members as caregivers provide assistance to individuals with leprosy in improving healing and maintaining patterns of interaction in the family.MethodsThe design uses qualitative research with in-depth, face-to-face interviews with family members in a semi-structured manner with the hope of obtaining complete data. Using purposive sampling with Participatory Interpretative Phenomenology analysis, there are 12 families with 15 family members consisting of 4 men and 11 women.ResultsThis study produced a family theme that tried to follow what would happen to individuals with leprosy, with four sub-categories: 1) Using various coping alternatives to recognize the disease, 2) Family members in the shadow of leprosy, 3) Trying to empathize with other family members. sick, 4) Caring for the emotional response of the family and seeking support.ConclusionsThis analysis shows that deficiency in cognitive aspects can be closed by maintaining a lifestyle in the family through efforts to understand, support, establish communication, increase maximum involvement in restoring self-confidence, especially in individuals with leprosy with psychosocial problems in the family. The results of this study can be used as psychosocial support in maintaining communication between family members to support treatment programs and accelerate the recovery of leprosy.  相似文献   
6.
The maximum exponential growth rate, the Malthusian parameter (MP), is commonly used as a measure of fitness in experimental studies of adaptive evolution and of the effects of antibiotic resistance and other genes on the fitness of planktonic microbes. Thanks to automated, multi-well optical density plate readers and computers, with little hands-on effort investigators can readily obtain hundreds of estimates of MPs in less than a day. Here we compare estimates of the relative fitness of antibiotic susceptible and resistant strains of E. coli, Pseudomonas aeruginosa and Staphylococcus aureus based on MP data obtained with automated multi-well plate readers with the results from pairwise competition experiments. This leads us to question the reliability of estimates of MP obtained with these high throughput devices and the utility of these estimates of the maximum growth rates to detect fitness differences.  相似文献   
7.
This study investigated the effects of dietary Bifidobacterium bifidum (BFD) and mannan-oligosaccharide (MOS), as a synbiotic, on the production performance, gut microbiology, serum biochemistry, antioxidant profile and health indices of broiler chicken. Six dietary treatments were T1 (negative control), T2 (positive control-20 mg antibiotic BMD kg−1 diet; BMD: bacitracin methylene disalicylate), T3 (0·1% MOS + 106 CFU BFD per g feed), T4 (0·1% MOS + 107 CFU BFD per g feed), T5 (0·2% MOS + 106 CFU BFD per g feed) and T6 (0·2% MOS + 107 CFU BFD per g feed). Significantly (P < 0·01) better growth performance and efficiency was observed in birds supplemented with 0·2% MOS along with 106 CFU BFD per g of feed compared to BMD and control birds. Supplementation with 0·2% MOS along with either 106 or 107 CFU BFD per g feed reduced (P < 0·01) the gut coliform, Escherichia coli, total plate count, and Clostridium perfringens count and increased the Lactobacillus and Bifidobacterium count. Significantly (P < 0·01) higher serum and liver antioxidant enzyme pool, serum HDL cholesterol and lower serum glucose, triglyceride, total cholesterol, cardiac risk ratio, atherogenic coefficient and atherogenic index of plasma were observed in birds supplemented with 0·2% MOS along with 106 CFU BFD per g of feed compared to control or BMD supplemented birds. Better production performance, gut microbial composition, serum biochemistry, antioxidant profile and health indices were depicted by broiler chicken supplemented with 0·2% MOS and 106 CFU BFD per g of feed.  相似文献   
8.
In human‐modified landscapes, important ecological functions such as predation are negatively affected by anthropogenic activities, including the use of pesticides and habitat degradation. Predation of insect pests is an indicator of healthy ecosystem functioning, which provides important ecosystem services, especially for agricultural systems. In this study, we compare predation attempts from arthropods, mammals, and birds on artificial caterpillars in the understory, between three tropical agricultural land‐use types: oil palm plantations, rubber tree plantations, and fruit orchards. We collected a range of local and landscape‐scale data including undergrowth vegetation structure; elevation; proximity to forest; and canopy cover in order to understand how environmental variables can affect predation. In all three land‐use types, our results showed that arthropods and mammals were important predators of artificial caterpillars and there was little predation by birds. We did not find any effect of the environmental variables on predation. There was an interactive effect between land‐use type and predator type. Predation by mammals was considerably higher in fruit orchards and rubber tree than in oil palm plantations, likely due to their ability to support higher abundances of insectivorous mammals. In order to maintain or enhance natural pest control in these common tropical agricultural land‐use types, management practices that benefit insectivorous animals should be introduced, such as the reduction of pesticides, improvement of understory vegetation, and local and landscape heterogeneity.  相似文献   
9.
Background: The present study examined the contribution of ethnicity to the association of leptin receptor gene (LEPR) gene variants with polycystic ovary syndrome (PCOS) in Tunisian and Bahraini Arabic-speaking women.Methods: Subjects consisted of 320 women with PCOS, and 446 eumenorrhic women from Tunisia, and 242 women with PCOS and 238 controls from Bahrain. Genotyping of (exonic) rs1137100 and rs1137101 and (intronic) rs2025804 LEPR variants was done by allelic exclusion.Results: The minor allele frequencies (MAFs) of rs1137100 and rs1137101 were significantly different between PCOS cases and control women from Bahrain but not Tunisia, and LEPR rs1137101 was associated with increased PCOS susceptibility only in Bahraini subjects. Furthermore, rs1137100 was associated with decreased PCOS risk among Bahrainis under codominant and recessive models; rs1137100 was negatively associated with PCOS in Tunisians after controlling for testosterone. In addition, rs2025804 was associated with increased PCOS risk among Tunisian but not Bahraini women, after adjusting for key covariates. Negative correlation was seen between rs1137101 and triglycerides in Tunisians, while homeostasis model assessment of insulin resistance (HOMA-IR) and insulin correlated with rs2025804 and rs1137101 among Bahraini subjects, and rs1137101 correlated with estradiol and prolactin. Taking TAG haplotype as common, positive association of TAA and negative association of TGG haplotype with PCOS was seen among Bahraini women; no three-locus PCOS-associated haplotypes were found in Tunisians.Conclusions: The present study is the first to demonstrate the contribution of ethnicity to the association of LEPR gene variants with PCOS, thereby highlighting the significance of controlling for ethnicity in gene association investigations.  相似文献   
10.
Three new eremophilane sesquiterpenes phomadecalins G−I ( 1 – 3 ) and two new benzene derivatives microdiplzenes A and B ( 12 and 13 ), together with nine known eremophilane sesquiterpenes ( 4 – 11 and 14 ) were isolated from an endophytic fungus, Microdiplodia sp. WGHS5. Their structures were elucidated by the interpretation of HR-ESI-MS and NMR data; meanwhile, the absolute configurations of new compounds were determined on the base of ECD calculations. All compounds were evaluated for the antimicrobial activities and antiproliferative effect on human gastric cancer cell lines (BGC-823).  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