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   1155篇
  免费   102篇
  2022年   12篇
  2021年   26篇
  2020年   29篇
  2019年   33篇
  2018年   47篇
  2017年   35篇
  2016年   42篇
  2015年   60篇
  2014年   66篇
  2013年   58篇
  2012年   92篇
  2011年   78篇
  2010年   54篇
  2009年   54篇
  2008年   58篇
  2007年   57篇
  2006年   47篇
  2005年   44篇
  2004年   41篇
  2003年   38篇
  2002年   30篇
  2001年   24篇
  2000年   23篇
  1999年   23篇
  1998年   11篇
  1997年   6篇
  1996年   10篇
  1995年   11篇
  1994年   5篇
  1993年   10篇
  1992年   10篇
  1991年   4篇
  1990年   3篇
  1989年   7篇
  1988年   8篇
  1987年   4篇
  1986年   14篇
  1985年   7篇
  1984年   11篇
  1983年   4篇
  1982年   3篇
  1981年   7篇
  1980年   7篇
  1979年   3篇
  1978年   3篇
  1977年   5篇
  1975年   5篇
  1973年   8篇
  1972年   3篇
  1970年   3篇
排序方式: 共有1257条查询结果,搜索用时 31 毫秒
11.
12.
13.
The distribution of sulfated mucopolysaccharides in different tissues during growth and in cancer tissues is reported. It is shown that most of the tissues of 1 day-old rats and rabbits contain chondroitin sulfate A/C, chondroitin sulfate B and heparan sulfate in about the same proportions, whereas in adult animals chondroitin sulfate A/C decreases in concentration or disappears. Changes in the relative proportions of chondroitin sulfate B and heparan sulfate were also observed in most of the tissues. In rats, these changes occur in the first 25 days of extrauterine development. A great increase of chondroitin sulfate A/C was observed in human tumors of different origins when compared with the normal adjacent tissues. Changes in the relative proportions of chondroitin sulfate B and heparan sulfate were also observed in most of the tumors analysed. The possible role of chondroitin sulfate A/C in cell division is discussed in view of the present findings.  相似文献   
14.
15.
16.
In Vitro Cellular & Developmental Biology - Plant - Full-length and 5′ deletion fragments of three constitutively expressed gene promoters identified from the Citrus sinensis L. genome...  相似文献   
17.
BackgroundThis study evaluates an active search strategy for leprosy diagnosis based on responses to a Leprosy Suspicion Questionnaire (LSQ), and analyzing the clinical, immunoepidemiological and follow-up aspects for individuals living in a prison population.MethodsA cross-sectional study based on a questionnaire posing 14 questions about leprosy symptoms and signs that was distributed to 1,400 prisoners. This was followed by dermatoneurological examination, anti-PGL-I serology and RLEP-PCR. Those without leprosy were placed in the Non-leprosy Group (NLG, n = 1,216) and those diagnosed with clinical symptoms of leprosy were placed in the Leprosy Group (LG, n = 34).FindingsIn total, 896 LSQ were returned (64%), and 187 (20.9%) of the responses were deemed as positive for signs/symptoms, answering 2.7 questions on average. Clinically, 1,250 (89.3%) of the prisoners were evaluated resulting in the diagnosis of 34 new cases (LG), based on well-accepted clinical signs and symptoms, a new case detection rate of 2.7% within this population, while the NLG were comprised of 1,216 individuals. The confinement time medians were 39 months in the LG while it was 36 months in the NLG (p>0.05). The 31 leprosy cases who responded to the questionnaire (LSQ+) had an average of 1.5 responses. The symptoms “anesthetized skin area” and “pain in nerves” were most commonly mentioned in the LG while “tingling, numbness in the hands/feet”, “sensation of pricks and needles”, “pain in nerves” and “spots on the skin” responses were found in more than 30% of questionnaires in the NLG. Clinically, 88.2% had dysesthetic macular skin lesions and 97.1% presented some peripheral nerve impairment, 71.9% with some degree of disability. All cases were multibacillary, confirming a late diagnosis. Anti-PGL-I results in the LG were higher than in the NLG (p<0.0001), while the RLEP-PCR was positive in 11.8% of the patients.InterpretationOur findings within the penitentiary demonstrated a hidden prevalence of leprosy, although the individuals diagnosed were likely infected while living in their former communities and not as a result of exposure in the prison. The LSQ proved to be an important screening tool to help identify leprosy cases in prisons.  相似文献   
18.
Candeia (Eremanthus erythropappus (DC.) MacLeish), a native forest species from South America, has garnered commercial interest due to its production of essential oil that contains alpha-bisabolol. This compound is widely used in the pharmaceutical and cosmetics industry, with approximately 80% of Brazilian production being exported. Since candeia rust (Puccinia velata) has only been reported in Brazil, little is known about its epidemiology and control. There is no methodology to quantify rust severity in candeia, justifying the elaboration and validation of a diagrammatic scale containing eight levels of disease severity based on leaf area coverage (0.25%, 0.5%, 1%, 2%, 4%, 8%, 16% and 32%). In a natural sampling of disease in the field, 95% of the leaves showed severity below 16%, with the remaining 5% showing severities between 16% and 32% of leaf area. Validation of the proposed diagrammatic scale was performed by assessing the results from 10 inexperienced evaluators, performing evaluations of three leaves with different severity levels. The evaluations were performed at 7-day intervals; in the first instance, severity values were assigned without the diagrammatic scale, and for the second attempt, the scale proposed in this study was used. The accuracy and precision of the severity estimates produced by each evaluator compared to the real severity was analysed by linear regression and by Lin's statistics. The reproducibility of the estimates was evaluated by analysing the coefficient of determination of linear regressions by pairs of evaluators. The scale provided adequate levels of accuracy, precision, repeatability and reproducibility, indicating the proposed scale was a suitable method for quantifying the severity of candeia rust.  相似文献   
19.
Knowledge of how animal species use food resources available in the environment can increase our understanding of many ecological processes. However, obtaining this information using traditional methods is difficult for species feeding on a large variety of food items in highly diverse environments. We amplified the DNA of plants for 306 scat and 40 soil samples, and applied an environmental DNA metabarcoding approach to investigate food preferences, degree of diet specialization and diet overlap of seven herbivore rodent species of the genus Ctenomys distributed in southern and midwestern Brazil. The metabarcoding approach revealed that these species consume more than 60% of the plant families recovered in soil samples, indicating generalist feeding habits of ctenomyids. The family Poaceae was the most common food resource retrieved in scats of all species as well in soil samples. Niche overlap analysis indicated high overlap in the plant families and molecular operational taxonomic units consumed, mainly among the southern species. Interspecific differences in diet composition were influenced, among other factors, by the availability of resources in the environment. In addition, our results provide support for the hypothesis that the allopatric distributions of ctenomyids allow them to exploit the same range of resources when available, possibly because of the absence of interspecific competition.  相似文献   
20.
International Journal of Primatology - Some nonhuman primates use tools to modify the behavior of other animals in social contexts. For example, during their proceptive periods, female bearded...  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