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   777篇
  免费   33篇
  2024年   1篇
  2023年   2篇
  2022年   9篇
  2021年   11篇
  2020年   7篇
  2019年   9篇
  2018年   10篇
  2017年   15篇
  2016年   17篇
  2015年   34篇
  2014年   46篇
  2013年   40篇
  2012年   51篇
  2011年   46篇
  2010年   36篇
  2009年   40篇
  2008年   46篇
  2007年   54篇
  2006年   51篇
  2005年   32篇
  2004年   37篇
  2003年   31篇
  2002年   49篇
  2001年   15篇
  2000年   13篇
  1999年   9篇
  1998年   10篇
  1997年   14篇
  1996年   7篇
  1995年   7篇
  1994年   7篇
  1993年   3篇
  1992年   12篇
  1991年   5篇
  1990年   9篇
  1989年   5篇
  1988年   3篇
  1987年   5篇
  1986年   3篇
  1983年   3篇
  1975年   2篇
  1974年   1篇
  1972年   3篇
排序方式: 共有810条查询结果,搜索用时 15 毫秒
751.
752.
753.
Abietic and dehydroabietic acid are interesting diterpenes with a highly diverse repertoire of associated bioactivities. They have, among others, shown antibacterial and antifungal activity, potentially valuable in the struggle against the increasing antimicrobial resistance and imminent antibiotic shortage. In this paper, we describe the synthesis of a set of 9 abietic and dehydroabietic acid derivatives containing amino acid side chains and their in vitro antimicrobial profiling against a panel of human pathogenic microbial strains. Furthermore, their in vitro cytotoxicity against mammalian cells was evaluated. The experimental results showed that the most promising compound was 10 [methyl N-(abiet-8,11,13-trien-18-yl)-d-serinate], with an MIC90 of 60 μg/mL against Staphylococcus aureus ATCC 25923, and 8 μg/mL against methicillin-resistant S. aureus, Staphylococcus epidermidis and Streptococcus mitis. The IC50 value for compound 10 against Balb/c 3T3 cells was 45 μg/mL.  相似文献   
754.
755.
756.
We examined the occurrence of carabid beetles along a forest successiongradient in central Finland (forest age classes: 5, 10, 20, 30 and 60years since clear-cutting). Species richness of carabids was higherin the two youngest age classes, while no clear differences were detected incarabid abundance. The high species richness in the young, open sites was due toinvasion of open-habitat species. Many forest species were absent from or scarcein the young sites and became gradually more abundant towards the older forestage classes. The catches indicated a drastic decrease and assemblage-levelchange in concert with canopy closure, i.e. 20–30 years afterclear-cutting. Some forest specialists with poor dispersal ability may facelocal extinction, if the proportion of mature forest decreases further and theremaining mature stands become more isolated. We recommend that, whileharvesting timber, connectivity between mature stands is ensured, mature standsare maintained close (a few tens of metres) to each other and the matrix qualityis improved for forest species by green tree retention.  相似文献   
757.
The goal of fish vaccination today is to protect fish against multiple bacterial fish pathogens simultaneously using polyvalent vaccines. However, many immunological processes such as antigenic cross-reaction, antigenic competition, affinity maturation and antigen-induced suppression may affect the specificity, avidity and level of antibodies. Consequently, the biological function of antibodies may be markedly different from that predicted by conventional serologic tests. Here, we investigated the effects of vaccination and composition of vaccine on the plasma antibody levels, biological function of antibodies in opsonophagocytosis as well as the effects of vaccination on the blood leucocyte counts. Rainbow trout were vaccinated with saline or with two different polyvalent, mineral oil-adjuvanted vaccines. Vaccine 1 contained Aeromonas salmonicida, Listonella anguillarum and both Th and Fd serotypes of Flavobacterium psychrophilum antigens and vaccine 2 contained A. salmonicida, L. anguillarum and only Fd serotype of Fl. psychrophilum. The antibody-mediated opsonophagocytosis was determined as the respiratory burst (RB) activity of blood monocytes and granulocytes against the tested bacterial antigens. Three weeks after vaccination both vaccine groups and the control group showed increased RB activity against all bacterial strains. However, the increase in RB activities was non-specific and originated from the increased number of circulating granulocytes and monocytes. On the other hand, at 6 weeks post-vaccination both specific antibodies and antibody-dependent opsonophagocytosis appeared in both vaccine groups. However, the composition of the vaccine had a marked effect on the magnitude of specific responses. The Fd+Th vaccine enhanced the target specific opsonophagocytosis, to a lesser extent than the Fd vaccine. Both polyvalent vaccines appeared to mainly affect the numbers of circulating monocytes and our results suggest that the monocytes play a more significant role than the granulocytes in antibody-dependent opsonophagocytosis. Our results also suggest that the presented opsonophagocytic assay is an advantageous method to predict vaccine efficiency and that the number, and properties, of bacterial antigens in polyvalent vaccines should be carefully selected in order to avoid inhibitory effects of antigens on the specific response of fish.  相似文献   
758.
We tested the impacts of most common sample preservation methods used for aquatic sample materials on the stable isotope ratios of carbon and nitrogen in clams, a typical baseline indicator organism for many aquatic food web studies utilising stable isotope analysis (SIA). In addition to common chemical preservatives ethanol and formalin, we also assessed the potential impacts of freezing on δ13C and δ15N values and compared the preserved samples against freshly dried and analysed samples. All preservation methods, including freezing, had significant impacts on δ13C and δ15N values and the effects in general were greater on the carbon isotope values (1.3–2.2‰ difference) than on the nitrogen isotope values (0.9–1.0‰ difference). However, the impacts produced by the preservation were rather consistent within each method during the whole 1 year experiment allowing these to be accounted for, if clams are intended for use in retrospective stable isotope studies.  相似文献   
759.
Psychotic depression (PD) is a severe mental disorder leading to functional disability and high risk of suicide, but very little is known about the comparative effectiveness of medications used in its maintenance treatment. The objective of this study was to investigate the comparative effectiveness of specific antipsychotics and antidepressants, and their combinations, on the risk of psychiatric hospitalization among persons with PD in routine care. Persons aged 16-65 years with a first-time diagnosis of PD were identified from Finnish (years 2000-2018) and Swedish (years 2006-2021) nationwide registers of inpatient care, specialized outpatient care, sickness absence, and disability pension. The main exposures were specific antipsychotics and antidepressants, and the main outcome measure was psychiatric hospitalization as a marker of severe relapse. The risk of hospitalization associated with periods of use vs. non-use of medications (expressed as adjusted hazard ratio, aHR) was assessed by a within-individual design, using each individual as his/her own control, and analyzed with stratified Cox models. The two national cohorts were first analyzed separately, and then combined using a fixed-effect meta-analysis. The Finnish cohort included 19,330 persons (mean age: 39.8±14.7 years; 57.9% women) and the Swedish cohort 13,684 persons (mean age: 41.3±14.0 years; 53.5% women). Individual antidepressants associated with a decreased risk of relapse vs. non-use of antidepressants were bupropion (aHR=0.73, 95% CI: 0.63-0.85), vortioxetine (aHR=0.78, 95% CI: 0.63-0.96) and venlafaxine (aHR=0.92, 95% CI: 0.86-0.98). Any long-acting injectable antipsychotic (LAI) (aHR=0.60, 95% CI: 0.45-0.80) and clozapine (aHR=0.72, 95% CI: 0.57-0.91) were associated with a decreased risk of relapse vs. non-use of antipsychotics. Among monotherapies, only vortioxetine (aHR=0.67, 95% CI: 0.47-0.95) and bupropion (aHR=0.71, 95% CI: 0.56-0.89) were associated with a significantly decreased risk of relapse vs. non-use of both antidepressants and antipsychotics. In an exploratory analysis of antidepressant-antipsychotic combinations, a decreased relapse risk was found for amitriptyline-olanzapine (aHR=0.45, 95% CI: 0.28-0.71), sertraline-quetiapine (aHR=0.79, 95% CI: 0.67-0.93) and venlafaxine-quetiapine (aHR=0.82, 95% CI: 0.73-0.91) vs. non-use of antidepressants and antipsychotics. Benzodiazepines and related drugs (aHR=1.29, 95% CI: 1.24-1.34) and mirtazapine (aHR=1.17, 95% CI: 1.07-1.29) were associated with an increased risk of relapse. These data indicate that, in the maintenance treatment of PD, bupropion, vortioxetine, venlafaxine, any LAI, clozapine, and only few specific antidepressant-antipsychotic combinations are associated with a decreased risk of relapse. These findings challenge the current recommendation by treatment guidelines to combine an antipsychotic with an antidepressant (without further specification) as standard treatment in PD.  相似文献   
760.
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