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   410篇
  免费   50篇
  460篇
  2022年   8篇
  2021年   3篇
  2020年   6篇
  2019年   6篇
  2018年   4篇
  2017年   8篇
  2016年   9篇
  2015年   10篇
  2014年   11篇
  2013年   22篇
  2012年   9篇
  2011年   14篇
  2010年   12篇
  2009年   14篇
  2008年   11篇
  2007年   13篇
  2006年   13篇
  2005年   9篇
  2004年   14篇
  2003年   8篇
  2002年   12篇
  2001年   9篇
  2000年   17篇
  1999年   14篇
  1998年   15篇
  1997年   3篇
  1996年   8篇
  1995年   4篇
  1994年   7篇
  1993年   4篇
  1992年   8篇
  1991年   4篇
  1990年   4篇
  1989年   10篇
  1988年   4篇
  1987年   9篇
  1986年   8篇
  1985年   8篇
  1984年   7篇
  1983年   5篇
  1981年   6篇
  1980年   4篇
  1979年   3篇
  1978年   4篇
  1977年   8篇
  1975年   3篇
  1974年   3篇
  1972年   4篇
  1961年   3篇
  1910年   3篇
排序方式: 共有460条查询结果,搜索用时 0 毫秒
111.
A cDNA was isolated from a zebra finch telencephalon cDNA library that encodes the myelin proteolipid protein. The clone was 2874 nucleotides long containing an open reading frame of 831 nucleotides that encoded a 277 amino acid myelin proteolipid protein. The 5-and 3 untranslated regions were 112 and 1931 nucleotides, respectively. In Northern blots the clone hybridized to 3 bands of 3.5, 2.4 and 1.5 Kb in mouse brain RNA, but to only a single band of 3.0 kb in zebra finch brain RNA, suggesting the lack of alternative polyadenylation sites within the 3 untranslated region of the zebra finch PLP mRNAs. There was a small degree of homology between the zebra finch and chicken PLP 5 untranslated regions, but relatively little homology of the 5 untranslated regions of the zebra finch PLP cDNA clone with the homologous regions of PLP cDNAs of many mammalian species. Except for a small stretch of considerable homology, there was little overall homology with the 3 untranslated regions of mammalian PLP mRNAs. Approximately 10% (i.e. 28) of the amino acids in the zebra finch PLP differed from mammalian PLP, with most of these changes located within exon 3. There were 16 amino acid changes between zebra finch and chicken, suggesting that greater sequence variation in PLP structure is tolerated among avian species than among mammalian species.Abbreviations DM20 25 kDa proteolipid protein in myelin - PLP classic 30 kDa myelin proteolipid protein Special issue dedicated to Dr. Marjorie B. Lees.  相似文献   
112.
113.
Payseur BA, Covert HA, Vinyard CJ, Dagosto M. 1999. New Body Mass Estimates for Omomys carteri, a Middle Eocene Primate From North America. Am J Phys Anthropol 109:41–52. This article included an incomplete Table 2. The final two columns, showing “Intercept” and “SEE” data were omitted. The complete Table 2, with these two columns included, is provided below.  相似文献   
114.
Initial adhesion of fungi to plasticized polyvinyl chloride (pPVC) may determine subsequent colonization and biodeterioration processes. The deteriogenic fungus Aureobasidium pullulans was used to investigate the physicochemical nature of adhesion to both unplasticized PVC (uPVC) and pPVC containing the plasticizers dioctyl phthalate (DOP) and dioctyl adipate (DOA). A quantitative adhesion assay using image analysis identified fundamental differences in the mechanism of adhesion of A. pullulans blastospores to these substrata. Adhesion to pPVC was greater than that to uPVC by a maximum of 280% after a 4-h incubation with 10(8) blastospores ml(-1). That plasticizers enhance adhesion to PVC was confirmed by incorporating a dispersion of both DOA and DOP into the blastospore suspension. Adhesion to uPVC was increased by up to 308% in the presence of the dispersed plasticizers. Hydrophobic interactions were found to dominate adhesion to uPVC because (i) a strong positive correlation was observed between substratum hydrophobicity (measured by using a dynamic contact angle analyzer) and adhesion to a range of unplasticized polymers including uPVC, and (ii) neither the pH nor the electrolyte concentration of the suspension buffer, both of which influence electrostatic interactions, affected adhesion to uPVC. In contrast, adhesion to pPVC is principally controlled by electrostatic interactions. Enhanced adhesion to pPVC occurred despite a relative reduction of 13 degrees in the water contact angle of pPVC compared to that of uPVC. Furthermore, adhesion to pPVC was strongly dependent on both the pH and electrolyte concentration of the suspension medium, reaching maximum levels at pH 8 and with an electrolyte concentration of 10 mM NaCl. Plasticization with DOP and DOA therefore increases adhesion of A. pullulans blastospores to pPVC through an interaction mediated by electrostatic forces.  相似文献   
115.
116.
We studied roosting and foraging behavior of two Neotropical gleaning bats, ?Orbigny's round-eared bat, Tonatia silvicola, and the fringe-lipped bat, Trachops cirrhosus (Phyllostomidae). Techniques included radio-tracking in a tropical lowland forest in Panama and analysis of data from long-term studies in Panama and Venezuela. Day roosts of T. silvicola were in arboreal termite nests. T. cirrhosus roosted in a hollow tree. T. silvicola emerged late (ca 60 min after sunset), and foraged close to the roosts (maximum distance 200–500 m). T. cirrhosus emerged early (ca 30 min after local sunset), and foraged farther from its roost (>1.5 km). Both bats used small foraging areas (3–12 ha) in tall, open forest. They foraged in continuous flight (maximum 27–36 min) or in short sally flights (<1 minute) from perches (“hang-and-wait” strategy). The small foraging areas of these bats and their sedentary foraging mode most likely make them vulnerable to habitat fragmentation.  相似文献   
117.
The history, origin, identity, chemistry and use of Evans blue dye are described along with the first application to staining by Herbert McLean Evans in 1914. In the 1930s, the dye was marketed under the name, Evans blue dye, which was profoundly more acceptable than the ponderous chemical name.  相似文献   
118.
The coaggregation ability of bacteria isolated from a freshwater biofilm was compared to those derived from the coexisting planktonic population. Twenty-nine morphologically distinct bacterial strains were isolated from a 6-month-old biofilm, established in a glass tank under high-shear conditions, and 15 distinct strains were isolated from the associated re-circulating water. All 44 strains were identified to genus or species level by 16S rDNA sequencing. The 29 biofilm strains belonged to 14 genera and 23.4% of all the possible pair-wise combinations coaggregated. The 15 planktonic strains belonged to seven genera and only 5.8% of all the possible pair-wise combinations coaggregated. Therefore, compared to the planktonic population, a greater proportion of the biofilm strains coaggregated. It is proposed that coaggregation influences biofilm formation and species diversity in freshwater under high shear.  相似文献   
119.
120.

Background

Frequent exacerbations induce a high burden to Chronic Obstructive Pulmonary Disease (COPD). We investigated the course of exacerbations in the published COSMIC study that investigated the effects of 1-year withdrawal of fluticasone after a 3-month run-in treatment period with salmeterol/fluticasone in patients with COPD.

Methods

In 373 patients, we evaluated diary cards for symptoms, Peak Expiratory Flow (PEF), and salbutamol use and assessed their course during exacerbations.

Results

There were 492 exacerbations in 224 patients. The level of symptoms of cough, sputum, dyspnea and nocturnal awakening steadily increased from 2 weeks prior to exacerbation, with a sharp rise during the last week. Symptoms of cough, sputum, and dyspnea reverted to baseline values at different rates (after 4, 4, and 7 weeks respectively), whereas symptoms of nocturnal awakening were still increased after eight weeks. The course of symptoms was similar around a first and second exacerbation. Increases in symptoms and salbutamol use and decreases in PEF were associated with a higher risk to develop an exacerbation, but with moderate predictive values, the areas under the receiver operating curves ranging from 0.63 to 0.70.

Conclusions

Exacerbations of COPD are associated with increased symptoms that persist for weeks and the course is very similar between a first and second exacerbation. COPD exacerbations are preceded by increased symptoms and salbutamol use and lower PEF, yet predictive values are too low to warrant daily use in clinical practice.  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