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   627篇
  免费   66篇
  693篇
  2024年   1篇
  2023年   8篇
  2022年   17篇
  2021年   46篇
  2020年   20篇
  2019年   26篇
  2018年   25篇
  2017年   17篇
  2016年   30篇
  2015年   44篇
  2014年   40篇
  2013年   37篇
  2012年   62篇
  2011年   46篇
  2010年   29篇
  2009年   20篇
  2008年   24篇
  2007年   19篇
  2006年   28篇
  2005年   20篇
  2004年   47篇
  2003年   26篇
  2002年   22篇
  2001年   8篇
  2000年   3篇
  1999年   2篇
  1998年   1篇
  1997年   4篇
  1995年   1篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1991年   6篇
  1990年   3篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1981年   1篇
  1979年   1篇
  1978年   1篇
  1948年   1篇
排序方式: 共有693条查询结果,搜索用时 0 毫秒
1.
Vaginal microbicides potentially empower women to protect themselves from HIV and other sexually transmitted infections (STIs), especially when culture, religion, or social status may prevent them from negotiating condom use. The open literature contains minimal information on factors that drive user acceptability of women’s health products or vaginal drug delivery systems. By understanding what women find to be most important with regard to sensory properties and product functionality, developers can iteratively formulate a more desirable product. Conjoint analysis is a technique widely used in market research to determine what combination of elements influence a consumer’s willingness to try or use a product. We applied conjoint analysis here to better understand what sexually-active woman want in a microbicide, toward our goal of formulating a product that is highly acceptable to women. Both sensory and non-sensory attributes were tested, including shape, color, wait time, partner awareness, messiness/leakage, duration of protection, and functionality. Heterosexually active women between 18 and 35 years of age in the United States (n = 302) completed an anonymous online conjoint survey using IdeaMap software. Attributes (product elements) were systematically presented in various combinations; women rated these combinations of a 9-point willingness-to-try scale. By coupling systematic combinations and regression modeling, we can estimate the unique appeal of each element. In this population, a multifunctional product (i.e., broad spectrum STI protection, coupled with conception) is far more desirable than a microbicide targeted solely for HIV protection; we also found partner awareness and leakage are potentially strong barriers to use.  相似文献   
2.
Antigenic differences between a wild-type virulent Candida albicans 4918 (wt) and its spontaneous avirulent mutant (m-10) were found with crossed immunoelectrophoresis. Yeast cell extracts as well as soluble protein and mannoprotein fractions obtained by affinity chromatography on concanavalin A (Con A) were analyzed. Sera from patients with candidiasis and antisera from rabbits infected with live wt cells and boosted with wt extracts or rabbits immunized with purified wt cell wall preparation were used as counter reactants. Qualitative differences in serum precipitins formed by patients with suspected or culture-proven candidiasis to polysaccharide antigens of wt and m-10 origin were observed. In comparison, except for a spike-formed precipitate detected only with the wt extract, the serum from infected rabbits precipitated the wt and m-10 cell wall polysaccharide antigens about equally. The same type of precipitate was also found with the Con A wt mannoprotein fractions but was again lacking with the m-10 mannoproteins. This precipitate, with extremely slow electromobility in the first dimension, may be related to some special immunodeterminant of the wt mannan molecule. No substantial differences in the precipitation patterns of the Con A wt and m-10 proteins were found when analyzed with patients' sera or rabbit anti-cell sera. However, using these protein fractions with anti-cell wall sera revealed a larger number of precipitates for the wt as opposed to the m-10 strain. The observed antigenic differences between the virulent- and the avirulent-derived strains seem to be mainly associated with cell wall determinants (components) and might be related to the greater adherence and infectivity of the wild strain.  相似文献   
3.
In the United States, the Native American Graves Protection and Repatriation Act (NAGPRA) provides a specific framework for the disposition of Native American Ancestral remains within its purview. However, samples such as a bone fragment, tooth, or other biological tissue taken from the remains of these Ancestors have been treated by institutions and researchers as independent of the individual from whom they were removed and used in destructive research such as paleogenomic and other archaeometric analyses without consultation, consent, and collaboration from Native American communities; are not cared for in keeping with the current best practices for Indigenous Ancestors; and are not likely to be repatriated to their communities. Here, we demonstrate that any biological samples removed from Ancestors who are covered under NAGPRA must also be handled according to the stipulations defined for “human remains” within the legislation. As such, we are not proposing a change to existing legislation, but rather best practices, specific to the context of the United States and NAGPRA, relating to the use of and care for biological samples taken from Native American Ancestors.  相似文献   
4.
A cytoplasmic component which inhibited the activation of chitin synthetase was studied in the dimorphic fungus Candida albicans. The inhibitor was found to be heat stable and trypsin sensitive and was only effective when incubated with a vacuolar protease, an activator of chitin synthetase, before the activation of chitin synthetase. In addition, the particulate chitin synthetase from the yeast form of C. albicans was solubilized by a sodium cholate-digitonin extraction and subsequently was purified approximately 30-fold by Sepharose column chromatography and Amicon XM 100 filtration. Activity of the soluble enzyme was increased by the addition of trypsin or phosphatidyl serine. The molecular weight of the enzyme was estimated to be 400,000.  相似文献   
5.
6.
The whole-cell phospholipid composition of the six known polymorphic species of Tetrahymena has been examined by [(3)H]acetate and [(3)H]myristic acid radiolabeling, and by gas-liquid chromatography of total phospholipid-bound fatty acids. Five of the polymorphic species contained similar phospholipid profiles following radiolabeling in that phosphatidylethanolamine (PE) was the predominant phospholipid; however, in cells of Tetrahymena patula LFF, aminoethylphosphonolipid was present in amounts nearly equal to PE. Tetrahymena patula LFF contained an unusually large percentage of sphingolipid (16.2% by [(3)H]acetate radiolabeling). Substantial differences were found in the fatty acid profiles of the polymorphic species, which included the degree of fatty acid unsaturation and relative weight percentages of odd-chain fatty acids. Tetrahymena vorax contained a low ratio of unsaturated C(18) fatty acids to saturated C(18) fatty acids as compared with all other species examined. The differentiating species generally contained a lesser percentage of monoenoic fatty acids and a lower ratio of unsaturated C(16) fatty acids to saturated C(16) fatty acids as compared with the two monomorphic species examined.  相似文献   
7.
8.
Six baleen whale species are found in the temperate western North Atlantic Ocean, with limited information existing on the distribution and movement patterns for most. There is mounting evidence of distributional shifts in many species, including marine mammals, likely because of climate‐driven changes in ocean temperature and circulation. Previous acoustic studies examined the occurrence of minke (Balaenoptera acutorostrata) and North Atlantic right whales (NARW; Eubalaena glacialis). This study assesses the acoustic presence of humpback (Megaptera novaeangliae), sei (B. borealis), fin (B. physalus), and blue whales (B. musculus) over a decade, based on daily detections of their vocalizations. Data collected from 2004 to 2014 on 281 bottom‐mounted recorders, totaling 35,033 days, were processed using automated detection software and screened for each species' presence. A published study on NARW acoustics revealed significant changes in occurrence patterns between the periods of 2004–2010 and 2011–2014; therefore, these same time periods were examined here. All four species were present from the Southeast United States to Greenland; humpback whales were also present in the Caribbean. All species occurred throughout all regions in the winter, suggesting that baleen whales are widely distributed during these months. Each of the species showed significant changes in acoustic occurrence after 2010. Similar to NARWs, sei whales had higher acoustic occurrence in mid‐Atlantic regions after 2010. Fin, blue, and sei whales were more frequently detected in the northern latitudes of the study area after 2010. Despite this general northward shift, all four species were detected less on the Scotian Shelf area after 2010, matching documented shifts in prey availability in this region. A decade of acoustic observations have shown important distributional changes over the range of baleen whales, mirroring known climatic shifts and identifying new habitats that will require further protection from anthropogenic threats like fixed fishing gear, shipping, and noise pollution.  相似文献   
9.
10.
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