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   505篇
  免费   37篇
  国内免费   16篇
儿科学   32篇
妇产科学   1篇
基础医学   87篇
口腔科学   8篇
临床医学   80篇
内科学   109篇
皮肤病学   6篇
神经病学   9篇
特种医学   98篇
外科学   29篇
综合类   33篇
预防医学   20篇
眼科学   1篇
药学   34篇
中国医学   1篇
肿瘤学   10篇
  2021年   3篇
  2020年   2篇
  2019年   5篇
  2018年   12篇
  2017年   3篇
  2016年   4篇
  2015年   9篇
  2014年   15篇
  2013年   19篇
  2012年   21篇
  2011年   11篇
  2010年   27篇
  2009年   18篇
  2008年   10篇
  2007年   18篇
  2006年   14篇
  2005年   10篇
  2004年   2篇
  2003年   8篇
  2002年   7篇
  2001年   9篇
  2000年   13篇
  1999年   18篇
  1998年   24篇
  1997年   28篇
  1996年   26篇
  1995年   20篇
  1994年   19篇
  1993年   16篇
  1992年   2篇
  1991年   7篇
  1990年   11篇
  1989年   26篇
  1988年   21篇
  1987年   16篇
  1986年   12篇
  1985年   7篇
  1984年   6篇
  1983年   9篇
  1982年   3篇
  1981年   9篇
  1980年   11篇
  1979年   2篇
  1978年   5篇
  1977年   2篇
  1976年   4篇
  1975年   3篇
  1972年   2篇
  1968年   2篇
  1919年   2篇
排序方式: 共有558条查询结果,搜索用时 15 毫秒
1.
Sonoelasticity imaging of prostate cancer: in vitro results   总被引:2,自引:0,他引:2  
  相似文献   
2.
Screening for early ovarian cancer   总被引:5,自引:0,他引:5  
Taylor  KJ; Schwartz  PE 《Radiology》1994,192(1):1
  相似文献   
3.
Tumor vascular signals in renal masses: detection with Doppler US   总被引:3,自引:0,他引:3  
Ramos  IM; Taylor  KJ; Kier  R; Burns  PN; Snower  DP; Carter  D 《Radiology》1988,168(3):633-637
The vascularity of 49 renal masses (26 malignant and 23 benign lesions) was investigated with duplex Doppler ultrasound. Doppler signals obtained at the margins of renal masses were defined as "tumor signals" when the Doppler-shifted frequency of the lesion exceeded the frequency shift in the ipsilateral main renal artery. These exceeded 2.5 kHz with a 3-MHz insonating frequency. Among the 26 renal masses that subsequently proved to be malignant, tumor signals were obtained in 15 of 18 (83%) untreated renal cell carcinomas, in three of four Wilms tumors, and in two patients with metastases to the kidney, but not in the one patient with lymphoma. None of the 23 benign renal masses demonstrated tumor signals. Tumor vascularity in malignant lesions gives rise to abnormal, high-velocity, Doppler-shifted signals that can help in the differential diagnosis of renal masses.  相似文献   
4.
Salmonella enterica serotype Typhi differs from nontyphoidal Salmonella serotypes by its strict host adaptation to humans and higher primates. Since fimbriae have been implicated in host adaptation, we investigated whether the serotype Typhi genome contains fimbrial operons which are unique to this pathogen or restricted to typhoidal Salmonella serotypes. This study established for the first time the total number of fimbrial operons present in an individual Salmonella serotype. The serotype Typhi CT18 genome, which has been sequenced by the Typhi Sequencing Group at the Sanger Centre, contained a type IV fimbrial operon, an orthologue of the agf operon, and 12 putative fimbrial operons of the chaperone-usher assembly class. In addition to sef, fim, saf, and tcf, which had been described previously in serotype Typhi, we identified eight new putative chaperone-usher-dependent fimbrial operons, which were termed bcf, sta, stb, ste, std, stc, stg, and sth. Hybridization analysis performed with 16 strains of Salmonella reference collection C and 22 strains of Salmonella reference collection B showed that all eight putative fimbrial operons of serotype Typhi were also present in a number of nontyphoidal Salmonella serotypes. Thus, a simple correlation between host range and the presence of a single fimbrial operon seems at present unlikely. However, the serotype Typhi genome differed from that of all other Salmonella serotypes investigated in that it contained a unique combination of putative fimbrial operons.  相似文献   
5.
In human in-vitro fertilization (IVF)-embryo transfer, the in-vitro culture environment differs from in-vivo conditions in that the oxygen concentration is higher, and in such conditions the mouse embryos show a higher concentration of reactive oxygen species (ROS) in simple culture media. ROS are believed to cause damage to cell membranes and DNA fragmentation in somatic cells. This study was conducted to ascertain the level of H2O2 concentration within embryos and the morphological features of cell damage induced by H2O2. A total of 62 human oocytes and embryos (31 fragmented, 15 non-fragmented embryos, 16 unfertilized oocytes) was obtained from the IVF-embryo transfer programme. The relative intensity of H2O2 concentrations within embryos was measured using 2',7'-dichlorodihydrofluorescein diacetate by Quanti cell 500 fluorescence imaging and DNA fragmentation was observed with transmission electron microscopy and an in-situ apoptosis detection kit. The H2O2 concentrations were significantly higher in fragmented embryos (72.21 +/- 9.62, mean +/- SEM) compared to non-fragmented embryos (31.30 +/- 3.50, P < 0.05) and unfertilized oocytes (30.75 +/- 2.67, P < 0.05). Apoptosis was observed only in fragmented embryos, and was absent in non-fragmented embryos. Electron microscopic findings confirmed apoptotic bodies and cytoplasmic condensation in the fragmented blastomeres. We conclude that there is a direct relationship between increased H2O2 concentration and apoptosis, and that further studies should be undertaken to confirm these findings.   相似文献   
6.
Structural properties of the H-2Db and H-2Kd murine major histocompatibility complex (MHC) antigens were examined by radiochemical methods. Radiolabelled preparations of the H-2Db and H-2Kd antigens were obtained by indirect immune precipitation of NP-40 lysates of the lymphoid tumor cell lines EL-4 (H-2b) and C14 (H-2d), respectively. After preparation of the 37,000 molecular weight papain fragment the antigens were cleaved with CNBr. The H-2Kd antigen yielded four major CNBr fragments whereas the H-2Db molecule provided six. These CNBr fragments were subjected to partial NH2-terminal amino acid sequence analysis and aligned by homology to the H-2Kb glycoprotein. Comparison of the structural properties of the H-2Kd and H-2Db molecules with previously published data on the other known major transplantation antigens of the b and d haplotypes (H-2Kb, H-2Dd and H-2Ld) reveal a marked structural similarity. First, the data show that certain methionine residues have been highly conserved and that cleavage by CNBr at these positions provides an initial strategy for the study of these molecules. Secondly, disulfide-linked peptides obtained after CNBr cleavage could be aligned and the data suggest the presence of disulfide bridges in homologous positions. Third, after CNBr cleavage both the H-2Kd and H-2Db molecules yielded two glycopeptides which were homologous to glycopeptides from the H-2Kb molecule. Fourth, overall homology for a limited number of comparable positions is about 81% between the H-2Kb and H-2Kd gene products and 88% between the H-2Kb and H-2Db gene products.  相似文献   
7.
8.
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