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   102篇
  免费   16篇
  2022年   1篇
  2021年   4篇
  2020年   3篇
  2019年   3篇
  2018年   4篇
  2017年   2篇
  2016年   1篇
  2015年   6篇
  2014年   12篇
  2013年   6篇
  2012年   5篇
  2011年   5篇
  2010年   4篇
  2009年   3篇
  2008年   6篇
  2007年   2篇
  2006年   1篇
  2005年   3篇
  2004年   3篇
  2003年   2篇
  2002年   4篇
  2001年   4篇
  2000年   2篇
  1999年   2篇
  1998年   8篇
  1997年   3篇
  1996年   1篇
  1995年   1篇
  1994年   1篇
  1992年   3篇
  1990年   1篇
  1988年   1篇
  1986年   2篇
  1984年   1篇
  1979年   2篇
  1977年   1篇
  1975年   3篇
  1971年   1篇
  1954年   1篇
排序方式: 共有118条查询结果,搜索用时 15 毫秒
111.
The synthesis and biological evaluation of about one dozen 7-silylcamptothecin derivatives are described. Most new compounds show potencies comparable to or better than camptothecin itself. The best compound, 11-fluoro-10-amino-7-trimethylsilylcamptothecin, is more than 20 times more potent than camptothecin in cell assays.  相似文献   
112.
Visceral leishmaniasis (VL) in Brazil is transmitted by the phlebotomine Lutzomyia longipalpis and in some midwestern regions by Lutzomyia cruzi. Studies of the phlebotomine fauna, feeding habits and natural infection rate by Leishmania contribute to increased understanding of the epidemiological chain of leishmaniases and their vectorial capacity. Collections were performed in Jaciara, state of Mato Grosso from 2010-2013, during which time 2,011 phlebotomines (23 species) were captured (68.70% Lu. cruzi and 20.52% Lutzomyia whitmani). Lu. cruzi females were identified by observing the shapes of the cibarium (a portion of the mouthpart) and spermatheca, from which samples were obtained for polymerase chain reaction to determine the rates of natural infection. Engorged phlebotomines were assessed to identify the blood-meal host by ELISA. A moderate correlation was discovered between the number of Lu. cruzi and the temperature and the minimum rate of infection was 6.10%. Twenty-two females were reactive to the antisera of bird (28%), dog (3.30%) and skunk (1.60%). We conclude that Lu. cruzi and Lu. whitmani have adapted to the urban environment in this region and that Lu. cruzi is the most likely vector of VL in Jaciara. Moreover, maintenance of Leishmania in the environment is likely aided by the presence of birds and domestic and synanthropic animals.  相似文献   
113.
114.
Objectives To compare the effects of vaginal hysterectomy, subtotal abdominal hysterectomy, and total abdominal hysterectomy on sexual wellbeing.Design Prospective observational study over six months.Setting 13 teaching and non-teaching hospitals in the Netherlands.Participants 413 women who underwent hysterectomy for benign disease other than symptomatic prolapse of the uterus and endometriosis.Main outcome measures Reported sexual pleasure, sexual activity, and bothersome sexual problems.Results Sexual pleasure significantly improved in all patients, independent of the type of hysterectomy. The prevalence of one or more bothersome sexual problems six months after vaginal hysterectomy, subtotal abdominal hysterectomy, and total abdominal hysterectomy was 43% (38/89), 41% (31/76), and 39% (57/145), respectively (χ2 test, P = 0.88).Conclusion Sexual pleasure improves after vaginal hysterectomy, subtotal abdominal hysterectomy, and total abdominal hysterectomy. The persistence and development of bothersome problems during sexual activity were similar for all three techniques.  相似文献   
115.
116.
Plant and Soil - The aim of this study was to evaluate the effects of long-term mineral and organic fertilisation on crop performance and soil fertility. The Long-Term Nutrient Depletion Trial...  相似文献   
117.
118.
We examined annual variation in the timing of conception andparturition in the African buffalo (Syncerus caffer) and thesynchrony of birth timing with resource cues, using 8 yearsof monthly birth, rainfall, and vegetation data, measured asNormalized Difference Vegetation Index (NDVI). Monthly birthshad the strongest significant correlations with NDVI and rainfalllevels 12 and 13 months in the past, respectively. In addition,the synchrony of current year births corresponds most stronglyto the synchrony of the previous year's NDVI distribution. Becausethe gestation period of buffalo has been estimated to be around11 months, these findings suggest that improved protein levels,occurring approximately a month after the first green flushof the wet season, are either a trigger for conception or conceptionhas evolved to be synchronous with correlated environmentalcues that ensure females enter a period of peak body conditionaround the time of conception and/or parturition. With a gestationperiod of approximately 340 days, parturition occurs to takeadvantage of the period when forage has its highest proteincontent. A comparative analysis of gestation periods withinthe subfamily Bovinae indicates that African buffalo have aprotracted gestation for their body size, which we suggest isan adaptation to their seasonal environment. We also found thatinterannual variation in the birth distribution suggests a degreeof plasticity in the date of conception, and variation in thenumber of calves born each year suggest further synchrony ata timescale longer than a single year.  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