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   502篇
  免费   55篇
  2018年   5篇
  2017年   6篇
  2016年   13篇
  2015年   19篇
  2014年   20篇
  2013年   25篇
  2012年   19篇
  2011年   20篇
  2010年   18篇
  2009年   15篇
  2008年   13篇
  2007年   10篇
  2006年   12篇
  2005年   28篇
  2004年   22篇
  2003年   6篇
  2002年   11篇
  2001年   15篇
  2000年   15篇
  1999年   14篇
  1998年   7篇
  1997年   6篇
  1996年   8篇
  1994年   6篇
  1992年   14篇
  1991年   9篇
  1990年   7篇
  1989年   5篇
  1988年   4篇
  1987年   11篇
  1986年   8篇
  1984年   8篇
  1982年   5篇
  1981年   7篇
  1980年   7篇
  1979年   6篇
  1978年   13篇
  1977年   12篇
  1974年   7篇
  1973年   6篇
  1971年   4篇
  1970年   5篇
  1969年   3篇
  1968年   6篇
  1967年   3篇
  1966年   6篇
  1965年   10篇
  1956年   4篇
  1949年   3篇
  1944年   3篇
排序方式: 共有557条查询结果,搜索用时 15 毫秒
11.
E. N. MacKay  A. H. Sellers 《CMAJ》1966,94(17):889-899
For the 827 patients with malignant testicular tumours registered at the Ontario Cancer Foundation''s regional clinics in the period 1938-1961, the probability of surviving for five years after treatment was 59.8%; for the 731 patients who received all or part of their initial treatment at the clinics or were not treated anywhere, five-year survival probability was 62.7%. Most deaths from testicular cancer took place in the first two years after treatment, and 90% of recorded recurrences were diagnosed before the third anniversary. Survival rates were strongly influenced by histological type and extent of disease, and to some degree by age. Survival did not seem to be closely correlated with delay after first symptom, site or size of primary lesion, ectopia, surgical treatment of the abdominal nodes, site or dosage of radiation, or chemotherapy. The survival rates in this series of cases compare favourably with those of other large series.  相似文献   
12.
At the University Hospital, Saskatoon, over the last three years, pacemakers have been inserted in 40 patients with complete or incomplete heart block. Fourteen of the patients were females and 26 were males. The average age was 65 years; 12 were over 80 years of age, and the youngest patient was 8 years of age. In none was the heart block due to operation. Thirty-three patients are still alive and well. There have been seven deaths three early and four late. One patient died because of a “runaway” pacemaker, and two as a result of infection persisting around the pacemaker. Twenty-nine Medtronic pacemakers were used and 14 Atricor pacemakers; currently we favour the latter instrument.  相似文献   
13.
Treatment of human platelets with 162 nM 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in phosphorylation of a number of peptides, including myosin heavy chain and the 20-kDa myosin light chain. The site phosphorylated on the myosin heavy chain was localized by two-dimensional peptide mapping to a serine residue(s) in a single major tryptic phosphopeptide. This phosphopeptide co-migrated with a tryptic peptide that was produced following in vitro phosphorylation of platelet myosin heavy chain using protein kinase C. The sites phosphorylated in the 20-kDa myosin light chain in intact cells were analyzed by two-dimensional mapping of tryptic peptides and found to correspond to Ser1 and Ser2 in the turkey gizzard myosin light chain. In vitro phosphorylation of purified human platelet myosin by protein kinase C showed that in addition to Ser1 and Ser2, a third site corresponding to Thr9 in turkey gizzard myosin light chain is also phosphorylated. The phosphorylatable myosin light chains from human platelets were found to consist of two major isoforms present in approximately equal amounts, but differing in their molecular weights and isoelectric points. A third, minor isoform was also visualized by two-dimensional gel electrophoresis. Following treatment with TPA, both the mono- and diphosphorylated forms of each isoform could be visualized, and the sites of phosphorylation were identified. The phosphate content rose from negligible amounts found prior to treatment with TPA to 1.2 mol of phosphate/mol of myosin light chain and 0.7 mol of phosphate/mol of myosin heavy chain following treatment. These results suggest that TPA mediates phosphorylation of both myosin light and heavy chains in intact platelets by activation of protein kinase C.  相似文献   
14.
The structural development of the stems and basal anchorageroots of Galahad and Hereward winter wheat cultivars (Triticumaestivum L.) were investigated and related to their mechanicalfunction. Stem and root morphology, anatomy and mechanical propertieswere examined from tillering (March) up to maturity (August),together with plant weight distribution. This allowed us tocalculate a ‘factor of safety’ against root andstem failure throughout development. As the plants grew taller the stem and the anchorage ‘coronalroots’ increased in bending strength countering the increasingmechanical demands. The bending strength, in turn, was correlatedwith the amount of lignified material around the stem and rootperimeter. Structural development ceased by ear emergence, whenthe plant was at its tallest, but because the ear weight continuedto rise the ‘self-weight’ moment pushing the plantover continued to increase. This meant that the ‘safetyfactors’ of both cultivars against both root and stemmechanical failure decreased throughout development. In bothcultivars the safety factors against root failure were lowerthan for stem failure, and Galahad had lower factors of safetythan Hereward. All these findings were consistent with resultsof field trials; failure tends to occur late in development,during grain filling, and is localized to the root system, whilstGalahad is more prone to lodging than Hereward. The pattern of mechanical development of winter wheat seemsto be one which would maximize its reproductive success, maintainingits structural integrity especially early in development whileinvesting in a minimum of structural material. Key words: Safety factor, anchorage, lodging, biomechan-ics, structural development  相似文献   
15.
An Ustilago maydis ergosterol biosynthesis mutant (A14) which is partially blocked in sterol 14alpha-demethylase (P45014DM) activity is described. This mutant accumulated the abnormal 14alpha-methyl sterols, eburicol, 14alpha-methylfecosterol, and obtusifoliol, along with significant amounts of ergosterol. Although the A14 mutant grew nearly as well as the wild type, it was impaired in cell extension growth, which indicated a dysfunction in apical cell wall synthesis. The mutant was also found to be hypersensitive to the azole fungicides penconazole and tebuconazole.  相似文献   
16.
The use of short tandem repeat polymorphisms (STRPs) as marker loci for linkage analysis is becoming increasingly important due to their large numbers in the human genome and their high degree of polymorphism. Fluorescence-based detection of the STRP pattern with an automated DNA sequencer has improved the efficiency of this technique by eliminating the need for radioactivity and producing a digitized autoradiogram-like image that can be used for computer analysis. In an effort to simplify the procedure and to reduce the cost of fluorescence STRP analysis, we have developed a technique known as multiplexing STRPs with tailed primers (MSTP) using primers that have a 19-bp extension, identical to the sequence of an M13 sequencing primer, on the 5′ end of the forward primer in conjunction with multiplexing several primer pairs in a single polymerase chain reaction (PCR) amplification. The banding pattern is detected with the addition of the M13 primer-dye conjugate as the sole primer conjugated to the fluorescent dye, eliminating the need for direct conjugation of the infrared fluorescent dye tn the STRP primers. The use of MSTP for linkage analysis greatly reduces the number of PCR reactions. Up to five primer pairs can be multiplexed together in the same reaction. At present, a set of 148 STRP markers spaced at an average genetic distance of 28 cM throughout the autosomal genome can be analyzed in 37 sets of multiplexed amplification reactions. We have automated the analysis of these patterns for linkage using software that both detects the STRP banding pattern and determines their sizes. This information can then be exported in a user-defined format from a database manager for linkage analysis.  相似文献   
17.
18.
1. Homogenates of rat uteri removed 1 and 2 days post partum were centrifuged at 6000 g. Both pellets and supernatants degraded Azocoll, a general proteinase substrate, at pH 7.5. More than 80% of the total activity was in the pellet fraction. 2. Part of the pellet activity was in a latent form. Trypsin and 4-aminophenylmercuric acetate (a thiol-blocking agent) both activated this latent form, indicating that it is an enzyme--inhibitor complex. An endogenous serine proteinase activated part of the latent enzyme during the assay. 3. The enzyme activity was low before parturition and after involution; it was highest during the first 2 days post partum, when the largest losses of uterine wet weight and matrix macromolecules occur. 4. Up to 70% of the enzyme in the pellets was extracted by heating at 60 degrees C for 4 min in 0.1 M-CaCl2/0.05 M-Tris/HCl, pH 7.5. Approx. 30% of the extracted enzyme was still latent. 5. The extracted enzyme was a metalloproteinase, since it was inhibited completely by 1,10-phenanthroline, but not by inhibitors of thiol or serine proteinases. 6. The enzyme was further purified 15--30-fold by gel chromatography and precipitation with (NH4)2SO4. The apparent molecular weight, estimated by gel filtration, was 24000 for the latent form and 12000 for the active form. The pH optimum was 7--7.5. 7. The enzyme also degraded cartilage proteoglycan. This activity was studied by viscometry and the products were analysed by analytical ultracentrifugation. The major product had a mol.wt. of approx. 100000. The sites of cleavage were in the protein core, since no free oligosaccharides were detected. 8. This neutral metalloproteinase is distinct from uterine collagenase and from a uterine metal-dependent endopeptidase that hydrolyses a heptapeptide related to collagen.  相似文献   
19.
20.
Caldesmon is a calmodulin- and actin-binding protein present in both smooth and non-muscle tissue. The present study demonstrates that platelet caldesmon is a substrate for cAMP-dependent protein kinase (protein kinase A). Purified platelet caldesmon has an apparent molecular mass of 82 kDa on sodium dodecyl sulfate-polyacrylamide gels and can be phosphorylated in vitro by the catalytic subunit of protein kinase A to a level of 2 mol of phosphate/mol of caldesmon. Phosphorylation of caldesmon by protein kinase A results in a shift in the apparent molecular mass of the protein to 86 kDa. When caldesmon was immunoprecipitated from intact platelets treated with prostacyclin (PGI2) the same shift in apparent molecular mass of caldesmon was observed. Comparison of two-dimensional tryptic phosphopeptide maps of caldesmon phosphorylated in vitro by protein kinase A with caldesmon immunoprecipitated from intact platelets verified that protein kinase A was responsible for the observed increase in caldesmon phosphorylation in PGI2-treated platelets. The present study demonstrates that although caldesmon is basally phosphorylated in the intact platelet, activation of protein kinase A by PGI2 results in the significant incorporation of phosphate into two new sites. In addition, the effects of phorbol ester, collagen, and thrombin on caldesmon phosphorylation were also examined. Although phorbol ester treatment results in a significant increase in caldesmon phosphorylation apparently by protein kinase C, treatment of intact platelets with thrombin or collagen does not result in an increase in caldesmon phosphorylation.  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