首页 | 官方网站   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   1094篇
  免费   10篇
  国内免费   5篇
医药卫生   1109篇
  2023年   3篇
  2021年   15篇
  2020年   8篇
  2018年   10篇
  2017年   10篇
  2016年   18篇
  2015年   32篇
  2014年   26篇
  2013年   29篇
  2012年   58篇
  2011年   77篇
  2010年   49篇
  2009年   53篇
  2008年   99篇
  2007年   83篇
  2006年   77篇
  2005年   87篇
  2004年   84篇
  2003年   69篇
  2002年   54篇
  2001年   8篇
  2000年   5篇
  1998年   8篇
  1997年   3篇
  1996年   3篇
  1995年   4篇
  1994年   8篇
  1992年   3篇
  1991年   4篇
  1990年   4篇
  1989年   4篇
  1987年   3篇
  1985年   3篇
  1981年   6篇
  1980年   4篇
  1979年   4篇
  1970年   3篇
  1969年   3篇
  1968年   4篇
  1967年   5篇
  1966年   4篇
  1965年   4篇
  1939年   4篇
  1936年   7篇
  1933年   3篇
  1932年   2篇
  1906年   2篇
  1903年   6篇
  1898年   2篇
  1894年   5篇
排序方式: 共有1109条查询结果,搜索用时 46 毫秒
1.
Conclusion In Switzerland, infants weighing 500–999 g at birth seem to have a relatively high mortality and a relatively low risk for handicap. This impression has to be confirmed by assessing outcome at school age.  相似文献   
2.
3.
Summary The Lifetime and 6 month DSM-III prevalence rates of mental disorders from an adult general population sample of former West Germany are reported. The most frequent mental disorders (lifetime) from the Munich Follow-up Study were anxiety disorders (13.87%), followed by substance (13.51%) and affective (12.90%) disorders. Within anxiety disorders, simple and social phobia (8.01%) were the most common, followed by agoraphobia (5.47%) and panic disorder (2.39%). Females had about twice the rates of males for affective (18.68% versus 6.42%), anxiety (18.13% versus 9.07%), and somatization disorders (1.60% versus 0.00%); males had about three times the rates of substance disorders (21.23% versus 6.11%) of females. Being widowed and separated/divorced was associated with high rates of major depression. Most disordered subjects had at least two diagnoses (69%). The most frequent comorbidity pattern was anxietyand affective disorders. Simple and social phobia began mostly in childhood or early adolescence, whereas agoraphobia and panic disorder had a later average age of onset. The majority of the cases with both anxiety and depression had depression clearly after the occurrence of anxiety. The DIS-DSM-III findings of our study have been compared with both ICD-9 diagnoses assigned by clinicians independently as well as other epidemiological studies conducted with a comparable methodology.  相似文献   
4.
5.
The genetic transformation of plastids of higher plants has developed into a powerful approach for both basic research and biotechnology. Due to the high copy number of the plastid genome per plastid and per cell, repeated cycles of shoot regeneration under conditions selective for the modified plastid chromosome are required to obtain transformants entirely lacking wild-type plastid genomes. The presence of promiscuous plastid DNA in nuclear and/or mitochondrial genomes that generally contaminate even gradient-purified plastid fractions reduces the applicability of the highly sensitive PCR approach to monitor the absence of residual wild-type plastid chromosomes in transformed lines. It is therefore difficult, or even impossible, to assess reliably the hetero- or homoplastomic state of plastid transformants in this manner. By analysing wild-type and transplastomic mutants of tobacco, we demonstrate that separation of plastid chromosomes isolated from gradient-purified plastid fractions by pulsed-field gel electrophoresis can overcome the problem of (co)amplification of interfering promiscuous plastid DNA. PCR analyses with primers specific for plastid, mitochondrial and nuclear genes reveal an impressive purity of such plastid DNA fractions at a detection limit of less than one wild-type plastid chromosome copy per ten transplastomic cells.  相似文献   
6.
7.
Histological samples of autopsy or biopsy tissue provide the best available evidence that autoreactive T cells are involved in the immunopathogenesis of many autoimmune diseases. However, morphology alone does not provide information on the antigen-specific T-cell receptor (TCR) of these cells, let alone on their antigen specificity. In this review article we discuss a number of emerging possibilities for identifying TCR sequences directly from biopsy tissue. We also review the methods for expressing presumably autoreactive TCR molecules and speculate on how the expressed TCR might be used to identify target antigens. Such information should eventually provide new insights into disease pathogenesis which lead to better therapies.  相似文献   
8.
The acoustic startle response is enhanced during states of fear and attenuated during pleasant ones. Our question was whether pharmacological stimulation of the reward system disrupts the learning and retrieval of conditioned fear as measured by fear-potentiated startle. We therefore injected the dopamine agonist amphetamine into the nucleus accumbens (NAC) immediately before either acquisition or expression of conditioned fear and measured the effect of these injections on fear-potentiated startle and baseline startle response. This study clearly showed that amphetamine injections into the NAC had no effect on baseline startle amplitude and acquisition/expression of conditioned fear. In contrast, amphetamine injections into the nucleus accumbens clearly enhanced spontaneous motor activity. These results suggest that dopamine within the NAC is not involved in modulation of fear-potentiated startle and baseline startle.  相似文献   
9.
Among more than 200 human papillomavirus (HPV) types presumed to exist, 18 "high-risk" HPV types are frequently found in anogenital cancer. The best studied types are HPV-16 and 18, which are only distantly related to one another and form two separate phylogenetic branches, each including six closely related types. HPV-30, 53, 56, and 66 form a third phylogenetic branch unrelated to HPV-16 and 18. Worldwide comparison of HPV-16 and 18 isolates revealed a distribution of variant genomes that correlated with the geographic origin and the ethnicity of the infected cohort and led to the concept of unique African, European, Asian, and Native American HPV-16 and 18 variants. Here, we address the question whether similar phylogenies are found for HPV-53, 56, and 66 by determining the sequence of the long control regions (LCR) of these HPVs in samples from Europe, Asia, and Africa, and from immigrant societies in North and South America. Phylogenetic trees calculated from point mutations and a few insertions/deletions affecting 2-4.2% of the nucleotide sequences were distinct for each of the three HPVs and divergent from HPV-16 and 18. In contrast to the "star-phylogenies" formed by HPV-16 and 18 variants, 44 HPV-53 isolates represented nine variants, which formed two deep dichotomic branches reminiscent of the beginning split into two new taxa, as recently observed for subtypes of HPV-44 and 68. A total of 66 HPV-56 isolates represented 17 variants, which formed three branches preferentially containing European, Asian, and African variants. Variants of a fourth branch, deeply separated from the other three, were characterized by a 25 bp insertion and created a dichotomy rather than star-like phylogeny. As it contained isolates from cohorts in all continents, it may have evolved before the spread of humans into all continents. 18 of 31 HPV-66 isolates represented the prototype clone, which was found in all parts of the world, while the remaining 13 clones formed 11 branches without any geographic association. Our findings confirm the notion of a quantitatively limited genomic diversity of each HPV type with some correlation to the geographic origin of the sample. In addition, we observed in some variants of these three HPV types mutations that affect the amino acid sequence of the E6 oncoproteins and the L1 capsid protein, supporting the possibility of immunogenic and oncogenic diversity between variants of any HPV type.  相似文献   
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-23

京公网安备 11010802026262号