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   222篇
  免费   27篇
  2022年   3篇
  2019年   3篇
  2018年   5篇
  2017年   7篇
  2016年   4篇
  2015年   7篇
  2014年   5篇
  2013年   11篇
  2012年   9篇
  2011年   6篇
  2010年   7篇
  2009年   9篇
  2008年   13篇
  2007年   11篇
  2006年   7篇
  2005年   7篇
  2004年   5篇
  2003年   5篇
  2002年   4篇
  2001年   4篇
  2000年   6篇
  1998年   4篇
  1997年   5篇
  1996年   3篇
  1994年   7篇
  1993年   8篇
  1992年   4篇
  1991年   6篇
  1990年   5篇
  1989年   6篇
  1988年   5篇
  1987年   4篇
  1986年   4篇
  1985年   7篇
  1984年   9篇
  1983年   4篇
  1982年   2篇
  1981年   3篇
  1980年   3篇
  1978年   2篇
  1977年   3篇
  1975年   2篇
  1974年   1篇
  1972年   4篇
  1971年   1篇
  1970年   2篇
  1969年   1篇
  1966年   1篇
  1964年   1篇
  1962年   1篇
排序方式: 共有249条查询结果,搜索用时 15 毫秒
91.
Coxiella burnetii is the agent of Q fever , an emergent worldwide zoonosis of wide clinical spectrum. Although C. burnetii infection is typically associated with acute infection, atypical pneumonia and flu-like symptoms, endocarditis, osteoarticular manifestations and severe disease are possible, especially when the patient has a suppressed immune system; however, these severe complications are typically neglected. This study reports the sequencing of the repetitive element IS1111 of the transposase gene of C. burnetii from blood and bronchoalveolar lavage (BAL) samples from a patient with severe pneumonia following methotrexate therapy, resulting in the molecular diagnosis of Q fever in a patient who had been diagnosed with active seronegative polyarthritis two years earlier. To the best of our knowledge, this represents the first documented case of the isolation of C. burnetii DNA from a BAL sample.  相似文献   
92.
A highly reproducible system was developed for efficient rooting of cultivars Boa Casta (BC) and Peneda and a BC seedling-derived clone (BC VII) of almond (Prunus dulcis Mill.). Twenty-four accessions derived from the clone BC VII and subjected to various in vitro culture treatments were screened. The long induction pre-treatment (LIP, 5 d), the brief induction pre-treatment (BIP, 16 h) and the hormonal shock by short dipping in hormone solution (1 min), were tested. BIP was the only that allowed rooting of cultivars. In BC VII, it induced high rooting frequencies (47–100 %) when using a solution of 0.4 mM indole-3-butyric acid solidified with 2 g dm−3 gellam gum for 16-h. The response to the auxin type was variable depending on the cultivar and the root induction pre-treatment used. Root number was significantly different between the two cultivars and BC VII. Root length was significantly higher when using 0.005 mM IBA in LIP but this concentration induced apical necrosis. The improved acclimatization procedure for up to 4 weeks increased the survival to 45 %. The initiation and development of adventitious roots were proved to be asynchronous.  相似文献   
93.
A bioterrorism attack could overwhelm medical personnel and facilities, suggesting a need for aid from nonmedical personnel. The American Dental Association suggests that dental professionals should assist in such cases, utilizing their strong scientific and technical skills. This study describes New England dental professionals' willingness, potential roles, motivators, and barriers to providing this aid. This cross-sectional study used a self-administered survey to collect data addressing the knowledge and opinions of dental professionals concerning acting as responders. The survey was distributed to 370 attendees of the 2005 Yankee Dental Conference, in Boston, Massachusetts. Most dental professionals expressed willingness to help during an attack (N = 340, 92%), reporting that dental professionals, in general, should perform a mean number of 6 roles. Three-quarters of dentists and dental students were personally willing, with proper training, to give immunizations, and 54% would perform triage. Knowledge was weak, but most dental professionals were interested in obtaining further education (83%). Since dental professionals are willing to assist during a bioterrorism attack and are motivated to obtain disaster response training, government officials and local directors and managers of disaster/emergency response agencies should consider incorporating dental professionals into their disaster management plans.  相似文献   
94.
Two phylogenetic methods (multilocus sequence typing [MLST] and a multiplex PCR) were investigated to determine whether phylogenetic classification of verocytotoxin-producing Escherichia coli serotypes correlates with their classification into groups (seropathotypes A to E) based on their relative incidence in human disease and on their association with outbreaks and serious complications. MLST was able to separate 96% of seropathotype D and E serotypes from those that cause serious disease (seropathotypes A to C), whereas the multiplex PCR lacked this level of seropathotype discrimination.  相似文献   
95.
A myeloperoxidase inhibitory kaempferol derivative, namely pterogynoside (1), was isolated from fruits of Pterogyne nitens, along with six known flavonols, kaempferol, afzelin, kaempferitrin, quercetin, isoquercetrin and rutin. The structures of all compounds were elucidated primarily from 1D and 2D NMR spectroscopic analyses, as well as by high resolution mass spectrometry. All flavonols were screened to identify secondary metabolites as potential myeloperoxidase (MPO) inhibitors, and at concentrations of 0.50–50 nM, quercetin (5), isoquercitrin (6) and rutin (7) exhibited strong inhibitory effects with IC50 values of 1.22 ± 0.01, 3.75 ± 0.02 and 3.60 ± 0.02, respectively. The MPO activity detected for the new derivative 1 was markedly decreased (IC50 10.3 ± 0.03) when compared with known flavonols 5–7, and interestingly increased when tested against ABTS scavenging activity.  相似文献   
96.
This study describes the genetic relationships of the first human astrovirus type-8 (HAstV-8) detected in Belém-Brazil, during a public hospital-based study. This strain was compared with other HAstV-8 strains identified elsewhere which have sequences available at GeneBank. The regions ORF1a (primers Mon348/Mon340) and ORF2 (primers Mon269/Mon270) were analyzed by nucleotide sequencing and a high similarity rate was observed among the Belém strain and other HAstV-8 strains. In ORF1a, homology values of 93-100% were detected, and in ORF2 96-99%. Considering the sequence variation (7%) observed in ORF2 region, it was suggested that HAstV-8 strains could be divided in three different lineages.  相似文献   
97.
98.
Molecular Mechanisms of Pollen Tube Growth and Differentiation   总被引:23,自引:0,他引:23       下载免费PDF全文
Mascarenhas JP 《The Plant cell》1993,5(10):1303-1314
  相似文献   
99.
Summary This report describes a protocol for regeneration ofBrassica nigra in vitro from unorganized callus to a highly differentiated stage of flowering. Callus is initiated from seedling hypocotyl, and root explants and plantlets are obtained via somatic embryogenesis. Shoot cultures can be established from these plantlets. These shoots can either be induced to flower in vitro or rooted to produce plants which flower ex vitro. Each stage of development is marked with a specific growth regulator requirement. This has potential as a model system to understand the cellular and molecular mechanisms involved in morphogenesis, and it can be used to understand the mechanism of change of phase from vegetative to reproductive. An advantage of this system is that in vitro flowering can be obtained repeatedly in the shoots raised from the axillary buds of the flowering shoots. The protocol can also be used to procureB. nigra gametes under aseptic condition.  相似文献   
100.
Multiple shoots were induced from nodal segments of mature Eucalyptus torelliana F. Muell. and E. camaldulensis Dehnh trees on Murashige and Skoog's medium supplemented with Kn, BAP, Cal.Pan and Bio. Incubation in semi-solid media at 15°C with continuous illumination followed by growth in agitated liquid media was essential for shoot induction and development in primary explants of E. camaldulensis. For culture of E. gorelliana, growth in agitated liquid media alone was sufficient. Rooting could be induced in shoot cultures of E. torelliana by treatment with NAA whereas treatment with a mixture of IAA, IBA, IPA and NAA was essential for E. camaldulensis. After auxin treatment, transfer to a charcoal-containing medium was necessary. Rooted plantlets could be successfully transferred to pots and field. By this method it is estimated that about 50,000 plantlets of E. torelliana and 20,000 of E. camaldulensis can be produced, in a year, from a single nodal segment of a mature tree.Abbreviations Kn Kinetin - BAP 6-Benzylaminopurine - Ca.Pan Calcium Pantothenate - Bio Biotin - NAA -Naphthalene acetic acid - IAA Indole-3-acetic acid - IBA Indole-3-butyric acid - IPA Indole-3-propionic acid Communication No. 3315  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