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   413篇
  免费   39篇
  国内免费   30篇
儿科学   14篇
妇产科学   1篇
基础医学   43篇
口腔科学   54篇
临床医学   51篇
内科学   76篇
皮肤病学   8篇
神经病学   21篇
特种医学   114篇
外科学   14篇
综合类   24篇
预防医学   12篇
眼科学   5篇
药学   25篇
肿瘤学   20篇
  2021年   3篇
  2019年   3篇
  2018年   5篇
  2016年   5篇
  2015年   4篇
  2014年   3篇
  2013年   9篇
  2012年   9篇
  2011年   9篇
  2010年   9篇
  2009年   13篇
  2008年   7篇
  2007年   19篇
  2006年   9篇
  2005年   17篇
  2004年   4篇
  2003年   7篇
  2002年   14篇
  2001年   12篇
  2000年   7篇
  1999年   8篇
  1998年   21篇
  1997年   26篇
  1996年   22篇
  1995年   10篇
  1994年   25篇
  1993年   24篇
  1992年   3篇
  1991年   6篇
  1990年   4篇
  1989年   20篇
  1988年   17篇
  1987年   12篇
  1986年   7篇
  1985年   14篇
  1984年   6篇
  1983年   5篇
  1982年   6篇
  1981年   12篇
  1980年   4篇
  1979年   7篇
  1978年   5篇
  1977年   6篇
  1976年   6篇
  1975年   5篇
  1961年   2篇
  1960年   3篇
  1947年   2篇
  1943年   4篇
  1942年   2篇
排序方式: 共有482条查询结果,搜索用时 46 毫秒
1.
2.
以18-甲基-17β-羟基-17α-乙炔基-雌甾-4-烯-3-酮(18-甲基炔诺酮),17β-羟基-17α-乙缺基-雌甾-4-烯-3-酮(炔诺酮),17β-羟基-17α-乙炔基-雄甾-4-烯-3-酮(妊娠素)和17a-羟基孕甾-4-烯-3,20二酮(17α-羟基黄体酮)为原料,经NaBH,还原、脱水、双键转位和酯化等反应合成一系列3,5-甾二烯化合物,用1HNMR和MS证明了它们的结构。动物筛选结果表明,17β-丙酰氧基-17α-乙炔基-雌甾-3,5-二烯(IVb2有明显的抗早孕活性。中断早期妊娠的作用似与其雌激素活性有关。  相似文献   
3.
Bile duct calculi in patients with primary sclerosing cholangitis   总被引:1,自引:0,他引:1  
  相似文献   
4.
5.
Groups of 110 male and 110 female CD (Sprague-Dawley) rats were exposed to atmospheres containing 0 (control), 1000 or 8000 ppm v/v butadiene for 6 hr/day and 5 days/week. Ten of each sex from each group were killed at 52 weeks. The study was terminated when it was predicted that survival would drop to 20% to 25% (105 weeks for females and 111 weeks for males). High dose rats had wet, ruffled fur and showed slight incoordination during the first exposure each week. During the second year, mortality in both treated female groups was increased because of humanitarian sacrifice of animals with large subcutaneous masses, while increased mortality in the high dose males was accompanied by an increase of the severity of nephropathy. Body weight was slightly lower than controls in both sexes at the high dose, but statistically significant only over the first 12 weeks. There were no effects in hematological analyses or tests of neuromuscular function that definitely could be associated with treatment. Liver weights at both doses were increased in both sexes with no associated pathological change. Kidney weight was increased in males at the high dose, together with an increase in the severity of nephrosis. There were increases in the incidences of pancreatic exocrine adenoma (high dose, male); uterine sarcoma (both doses, female); Zymbal gland carcinoma (high dose, female); mammary tumors (both doses, female); thyroid follicular cell tumors; and testis Leydig-cell tumors (high dose). These data suggest that butadiene is a weak oncogen to the rat under the conditions of exposure used in this study.  相似文献   
6.
The rare apolipoprotein C-II (apoC-II) mutation, apoC-IILys19→Thr, also known as apoC-II-v, has been found previously in association with hyperlipoproteinemia. From a lipid clinic screening we identified three unrelated individuals who had the apoC-IILys19→Thr mutation. Among eight family members of one proband, we have found another four who were affected. None of the inviduals in this kindred is dyslipidemic and there is no difference in lipid levels between affected and unaffected family members. Therefore, we conclude that the presence of this apolipoprotein variant by itself has no effect on lipoprotein levels. In addition, the apolipoprotein E (apoE) isoform, apoE4 does not have a synergistic effect on lipoprotein levels in this kindred, in contrast to observations on the interaction of apoE4 with another apoC-II mutant (apoC-IIToronto). The single nucleotide substitution that causes the apoC-IILys19→Thr variant introduces a previously unrecognized restriction site (for Mae III), that provides for easy screening.  相似文献   
7.
Summary Accurate volume determination of the encephalic ventricles is of importance in several clinical conditions, including Alzheimer's presenile dementia, schizophrenia, and benign intracranial hypertension. Previous studies have investigated the accuracy with which magnetic resonance imaging (MRI) can be used in clinical practice to evaluate the encephalic ventricles. However, adequate evaluation of pathological conditions depends on a sufficient amount of morphometric data from normal subjects. To begin establishing this data base for normal subjects, we evaluated the MRI scans of 38 subjects found to have no apparent pathology and calculated the ventricular volume in each case by using methods previously developed in our laboratory. The results were then compared with published volumes determined from studies that used either ventricular casts or computerized tomographic scans. The average total ventricular volume for all 38 subjects was 17.4 cm3, while that for males was 16.3 cm3 and that for females was 18.0 cm3. A small but significant correlation was found between age of subject and ventricular volume, with ventricular size increasing with age.
Evaluation du volume des ventricules cérébraux à partir des images obtenues en résonance magnétique nucléaire chez 38 sujets humains
Résumé La détermination exacte du volume des ventricules cérébraux est importante en clinique comme par exemple dans la démence présénile d'Alzheimer, la schizophrénie et l'hypertension intracrânienne bénigne. Des études antérieures ont étudié la fiabilité de la résonance magnétique nucléaire en pratique clinique pour évaluer le volume des ventricules cérébraux. Toutefois une évaluation correcte dans les conditions pathologiques implique une bonne connaissance des données morphométriques du sujet normal. Pour établir ces données sur « le sujet normal », nous avons étudié les coupes obtenues en IRM chez 38 sujets apparemment indemnes de toute pathologie; nous avons calculé le volume ventriculaire dans chaque cas en utilisant des méthodes mises au point auparavant dans notre laboratoire. Les résultats ont été ensuite comparés avec ceux obtenus par d'autres études utilisant soit des moules ventriculaires, soit des coupes tomographiques computérisées. Le volume ventriculaire total moyen chez 38 sujets est de 17,4 cm3, mais il est chez les sujets masculins de 16,3 cm3 et chez les sujets de sexe féminin de 18 cm3. Une corrélation faible mais significative a été trouvée entre l'âge du sujet et le volume ventriculaire, étant entendu que la taille du ventricule augmente avec l'âge.
  相似文献   
8.
9.
Davis  GD; Fulton  RE; Ritter  DG; Mair  DD; McGoon  DC 《Radiology》1978,128(1):133-144
Of 181 patients with severe congenital pulmonary atresia and ventricular septal defect or "type IV truncus" (an obsolete term), all but 11% had true central pulmonary arteries. These arteries were demonstrable by large serial biplane angiograms using multiple selective injections into collateral vessels, frequent photographic subtraction, and occasional pulmonary vein-wedge angiograms. These techniques are extremely important for accurate diagnosis and in planning corrective or palliative surgery, which was done in 77% of patients with pulmonary arteries.  相似文献   
10.
Conventional methods for the analysis of in vivo hyperpolarized 13C NMR data from the lactate dehydrogenase (LDH) reaction usually make assumptions on the stability of rate constants and/or the validity of the two‐site exchange model. In this study, we developed a framework to test the validity of the assumption of stable reaction rate constants and the two‐site exchange model in vivo via ratiometric fitting of the time courses of the signal ratio L(t)/P(t). Our analysis provided evidence that the LDH enzymatic kinetics observed by hyperpolarized NMR are in near‐equilibrium and satisfy the two‐site exchange model for only a specific time window. In addition, we quantified both the forward and reverse exchange rate constants of the LDH reaction for the transgenic and mouse xenograft models of breast cancer using the ratio fitting method developed, which includes only two modeling parameters and is less sensitive to the influence of instrument settings/protocols, such as flip angles, degree of polarization and tracer dosage. We further compared the ratio fitting method with a conventional two‐site exchange modeling method, i.e. the differential equation fitting method, using both the experimental and simulated hyperpolarized NMR data. The ratio fitting method appeared to fit better than the differential equation fitting method for the reverse rate constant on the mouse tumor data, with less relative errors on average, whereas the differential equation fitting method also resulted in a negative reverse rate constant for one tumor. The simulation results indicated that the accuracy of both methods depends on the width of the transport function, noise level and rate constant ratio; one method may be more accurate than the other based on the experimental/biological conditions aforementioned. We were able to categorize our tumor models into specific conditions of the computer simulation and to estimate the errors of rate quantification. We also discussed possible approaches to the development of more accurate rate quantification methods for hyperpolarized NMR. Copyright © 2013 John Wiley & Sons, Ltd.  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