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   5435篇
  免费   2篇
  国内免费   1篇
电工技术   1篇
综合类   2篇
化学工业   14篇
建筑科学   2篇
轻工业   7篇
水利工程   1篇
无线电   6篇
一般工业技术   8篇
冶金工业   5382篇
自动化技术   15篇
  2017年   1篇
  2013年   3篇
  2012年   2篇
  2011年   4篇
  2010年   1篇
  2009年   1篇
  2008年   1篇
  2007年   4篇
  2006年   7篇
  2005年   4篇
  2004年   4篇
  2003年   4篇
  2002年   2篇
  2001年   1篇
  2000年   3篇
  1999年   165篇
  1998年   1668篇
  1997年   918篇
  1996年   581篇
  1995年   334篇
  1994年   293篇
  1993年   311篇
  1992年   40篇
  1991年   61篇
  1990年   70篇
  1989年   61篇
  1988年   68篇
  1987年   69篇
  1986年   54篇
  1985年   62篇
  1984年   1篇
  1983年   10篇
  1982年   27篇
  1981年   27篇
  1980年   53篇
  1979年   3篇
  1978年   13篇
  1977年   157篇
  1976年   340篇
  1975年   3篇
  1973年   1篇
  1972年   1篇
  1969年   1篇
  1955年   4篇
排序方式: 共有5438条查询结果,搜索用时 734 毫秒
241.
Delayed aorto-pulmonary artery fistula represents an uncommon delayed sequelae of penetrating cardiac trauma. A case is presented that demonstrates the need for a high index of suspicion, follow-up, and a complete evaluation of the patient who survives a penetrating heart injury. The mechanisms of delayed presentation, diagnosis, and management of the fistula are discussed.  相似文献   
242.
243.
Fluorescence in situ hybridization was performed on touch preparations from 55 primary infiltrating ductal carcinomas of the breast to determine numeric chromosome abnormalities. The frequency of aneusomy, measured by both nondisomy and chromosomal gain, was determined for chromosomes X, 4, 6-12, 17, and 18 with the use of chromosome-specific, alpha-satellite DNA probes. The presence of chromosome-specific numeric abnormalities was correlated with established clinicopathological parameters, including tumor size, lymph node involvement, tumor grade, estrogen receptor level, and menopause status. In addition, a case-control study was performed to explore a possible association between chromosome-specific aneusomy and recurrence in lymph-node-negative patients. Although chromosomes 8 and 6 were most frequently aneusomic, numeric abnormalities of chromosomes 4 and 11 were most strongly associated with established prognostic factors. For chromosomes 4 and 11, strong associations were found with tumor involvement of lymph nodes and increased tumor size, along with a weaker association with tumor grade. In addition, numeric abnormalities of the following chromosomes were associated with the corresponding prognostic factors: chromosomes X, 7, and 12 with lymph node status; chromosomes 10, 17, and 6 with tumor size; and chromosomes 7, 12, 17, and X with tumor grade. No correlations were observed with estrogen receptor level or menopause status. In the case-control study performed on isolated nuclei of paraffin-embedded tissue from lymph node-negative breast cancer patients (19 cases and 19 controls), the gain of chromosome 4 was correlated with disease progression. These findings suggest that chromosome-specific aneusomy is associated with certain established prognostic factors and may be associated with disease progression.  相似文献   
244.
BACKGROUND: Home oxygen therapy improves survival and quality of life in adults with chronic obstructive airways disease. The few studies about home oxygen therapy in children show improvements in weight gain, school performance and decreases in hospitalization expenses. AIM: To report our experience in home oxygen therapy in children followed for six months to four years. PATIENTS AND METHODS: Fifty five children, less than 15 years old, discharged from a University hospital with the diagnosis of chronic respiratory failure, were followed up at their homes. RESULTS: Discharge diagnoses were bronchopulmonary dysplasia in 36% of children, postinfectious pulmonary damage in 22%, neonatal distress in 13%, chronic aspiration in 9%, cystic fibrosis in 7% and miscellaneous in 13%. Forty six completed at least 6 months of follow up, five moved to other hospitals, three required ventilatory support and one died. Oxygen was discontinued in 33 patients, and this occurred before the ninth month of follow up in 88% of those children. Neonatal distress and bronchopulmonary dysplasia had the best prognoses, and oxygen was discontinued at 4 +/- 1 and 5.7 +/- 3 months respectively. Patients with postinfectious pulmonary disease had a higher incidence of bronchoneumoniae, and those with bronchopulmonary dysplasia a higher incidence of acute bronchiolitis, that motivated hospital admissions. Expenses due to home oxygen were lower than hospitalization costs. No adverse effects were detected. CONCLUSIONS: Infants and newborns on home oxygen therapy have a good prognosis, specially those with reversible diseases. This type of therapy allows an earlier hospital discharge with considerable cost reductions.  相似文献   
245.
It is proposed that both polar and radical reactions should be considered when discussing radical ion reactivity. The fact that only the polar reactivity has dominated previous discussions is pointed out. It is argued that if the configuration mixing model is applicable for the estimation of radical cation-nucleophile (or cation-nucleophile) combination reaction barriers, the theory should also explain the reactivity of the proton toward anionic nucleophiles. The model severely overestimates reaction barriers for the latter reactions. The discussion is centered around the following hypothesis: In the absence of severe steric effects, the reactivity of radical ions, especially evident in the reactions with radicals (for example very few radical cations react with dioxygen at measurable rates), is dominated by the degree of coupling between charge and radical centers. Evidence from the literature supporting the hypothesis is presented for a number of different classes of radical ion reactions. Further work to test the validity of the hypothesis is proposed for many of the reaction types. Triarylmethyl radicals and carbenium ions are suggested as models to which the radical and polar reactivities of 9,10-diarylanthracene radical cations may be compared. It is concluded that the radical cation/carbenium ion comparison (for the reaction with acetate ion) would show similar reactivities while the radical cation/free radical comparison (for the reaction with dioxygen) would fail, since no reaction at all would be observed with the radical cation while the free radical reacts rapidly.  相似文献   
246.
247.
We evaluated short-term systemic antimicrobial prophylaxis for catheter-associated bacteriuria in women undergoing elective gynecological operations in a prospective, controlled, double-masked study. Nine of 100 placebo-treated patients acquired bacteriuria during catheterization compared with 3 of 96 of the drug-treated group. However, at the time of hospital discharge, clean-voided urine specimens were positive as frequently in the drug-treated group (8 of 82 patients cultured) as in the placebo group (8 of 75 patients cultured). No difference in febrile morbidity due to bacteriuria was noted between the prophylaxis and placebo groups. The incidence of catheter-associated bacteriuria may be reduced by antimicrobial prophylaxis. However, because the protective effect is transient and is associated with the selection of resistant organisms, prophylaxis is not indicated for patients at low risk for acquired bacteriuria and in whom the sequelae of catheter-associated infections are infrequent.  相似文献   
248.
249.
250.
A 20-hear-old patient with mitral valve prolapse and minimal mitral regurgitation associated with intermittent marked sinus bradycardia and sinus arrhythmia, and atrioventricular block, proximal to the bundle of His, varying from first-degree to high-grade, is described. Both the murmur and the atrioventricular block had been documented since the age of eight years, and probably since the first year of life, and has shown no subsequent progression. The patient's symptoms of chest pain and severe lightheadedness and near syncope have been shown by telemetry electrocardiogrphic monitoring to be unrelated to changes in cardiac rhythm.  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