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   826篇
  免费   2篇
化学工业   6篇
机械仪表   1篇
无线电   2篇
冶金工业   818篇
自动化技术   1篇
  2014年   1篇
  2011年   1篇
  2008年   1篇
  2006年   1篇
  2003年   1篇
  1999年   28篇
  1998年   260篇
  1997年   133篇
  1996年   85篇
  1995年   53篇
  1994年   58篇
  1993年   51篇
  1992年   3篇
  1991年   6篇
  1990年   4篇
  1989年   6篇
  1988年   6篇
  1987年   9篇
  1986年   9篇
  1985年   4篇
  1982年   3篇
  1981年   2篇
  1980年   10篇
  1978年   1篇
  1977年   24篇
  1976年   61篇
  1975年   2篇
  1966年   1篇
  1960年   1篇
  1955年   3篇
排序方式: 共有828条查询结果,搜索用时 15 毫秒
151.
To evaluate the application of radionuclide infarct scintigraphy to diagnose myocardial infarction after revascularization, we obtained postoperative technetium 99m pyrophosphate myocardial scintigrams, serial electrocardiograms and CPK-MB isoenzymes in ten control and 51 revascularized patients. All control patients had negative electrocardiograms and scintigrams, but eight had positive isoenzymes. Eight revascularized patients had positive electrocardiograms, images and enzymes and two had positive scintigrams and enzymes with negative electrocardiograms. Thirty-four patients with negative electorcardiograms and scintigrams had positive isoenzymes; in only seven patients were all tests negative. Our data suggest radionuclide infarct scintigraphy is a useful adjunct to the electrocardiogram in diagnosing perioperative infarction. The frequent presence of CPK-MB in postoperative patients without other evidence of infarction suggests that further studies are required to identify all factors responsible for its release.  相似文献   
152.
The present investigation was designed to evaluate whether end-stage cardiac failure in patients affected by dilated cardiomyopathy (DC) was dependent upon extensive myocyte cell death with reduction in muscle mass or was the consequence of collagen accumulation in the myocardium independently from myocyte cell loss. In addition, the mechanisms of ventricular dilation were analysed in order to determine whether the changes in cardiac anatomy were important variables in the development of intractable congestive heart failure. DC is characterized by chamber dilation, myocardial scarring and myocyte hypertrophy in the absence of significant coronary atherosclerosis. However, the relative contribution of each of these factors to the remodeling of the ventricle is currently unknown. Moreover, no information is available concerning the potential etiology of collagen deposition in the myocardium and the changes in number and size of ventricular myocytes with this disease. Morphometric methodologies were applied to the analysis of 10 DC hearts obtained from patients undergoing cardiac transplantation. An identical number of control hearts was collected from individuals who died from causes other than cardiovascular diseases. DC produced a 2.2-fold and 4.2-fold increase in left ventricular weight and chamber volume resulting in a 48% reduction in mass-to-volume ratio. In the right ventricle, tissue weight and chamber size were both nearly doubled. Left ventricular dilation was the result of a 59% lengthening of myocytes and a 20% increase in the transverse circumference due to slippage of myocytes within the wall. Myocardial scarring represented by segmental, replacement and interstitial fibrosis occupied approximately 20% of each ventricle, and was indicative of extensive myocyte cell loss. However, myocyte number was not reduced and average cell volume increased 2-fold in both ventricles. In conclusion, reactive growth processes in myocytes and architectural rearrangement of the muscle compartment of the myocardium appear to be the major determinants of ventricular remodeling and the occurrence of cardiac failure in DC.  相似文献   
153.
154.
An asymptomatic skin nodule in a patient with myelofibrosis was shown to consist of extramedullary hematopoiesis. It was a soft bluish nodule that resembled a hemangioma. Microscopically, both erythroid and myeloid cells, but not megakaryocytes, were found. This case demonstrates the ability of the skin to recapitulate dermal hematopoiesis seen in a stage of human fetal development.  相似文献   
155.
The photodynamic effects of temoporfin (meso-tetrahydroxyphenylchlorin, mTHPC) and merocyanine 540 (MC540) in murine myeloid leukemia M1 and WEHI 3B (JCS) cells were compared. The mTHPC was found to be more potent and selective. At a lethal dosage of 90% killing (LD90), only 1.3 microM of mTHPC and 4.2 kJ/m2 of light irradiation was required, which was a 20-fold lower drug concentration and 11-fold smaller light dose than that required when using MC540. Meanwhile, three times less, or 15%, of the coincubated erythrocytes were destroyed by mTHPC than by MC540. Confocal micrographs showed that both drugs accumulated diffusely inside the cytoplasm in a very similar fashion, but mTHPC induced a more extensive apoptosis in photosensitized JCS cells. For example, at LD90, mTHPC practically killed all JCS cells via apoptosis and cleaved the DNA to extremely small 150 base-pair fragments. In contrast, among the JCS cells killed by MC540, about 88% died via apoptosis and large DNA fragments were abundant. Relative to MC540, the ability of mTHPC to trigger large-scale and thorough apoptosis in leukemia cells may help explain its potency and selectivity.  相似文献   
156.
In a retrospective study, the prognostic value of monitoring the decay of alpha-fetoprotein (AFP) was assessed. Serum AFP was determined serially in 18 children with malignant germ-cell or hepatic tumors: 7 endodermal sinus tumor, 3 embryonal carcinoma, 5 malignant teratoma, 2 hepatoblastomas, and 1 hepatocellular carcinoma. The actual half-life (AHL) of AFP was computed after surgical resection of the tumor. In group 1, which had complete resection and no recurrence during follow-up (n = 13), the AHL of AFP was 4.0 +/- 0.9 days. In group 2, which had incomplete resection or recurrence during follow-up (n = 5), the AHL of AFP was 24.8 +/- 20 days, significantly longer than that of group 1 (P = 0.0026). The increased AHL of AFP indicated residual active tumor after surgical resection. The AHL of AFP may be more sensitive than serial monitoring of AFP in detecting preclinical recurrence after surgical resection of AFP-secreting tumors. Treatment strategies can be based on AFP clearance, and prospective clinical trials are warranted.  相似文献   
157.
A developmental chronometry hypothesis of early brain damage is suggested in which regions of the brain with a protracted course of postnatal development will be more vulnerable than earlier maturing areas to deleterious effects of early insult and, therefore, may become common sites of abnormality across many disorders originating in early childhood. Initial investigations of the cerebellum and frontal lobes are presented using MRI and neuropsychological measures. Planimetric measures of the cerebellar vermis (lobuli I-V and VI-VII) and pons, and neuropsychological frontal lobe measures were obtained from high functioning individuals with autism (A), survivors of acute lymphoblastic leukemia (ALL) with brain sequelae following radiation and chemotherapy, and from rigorously selected healthy controls (C). The neuropsychological results were clustered according to functions commonly related to frontal brain, posterior brain, and left and right hemispheres. The A and ALL groups, as compared to C, yielded modest but consistently reduced MRI measures for vermal lobuli I-V and VI-VII. Hypoplasia of lobuli VI-VII was more marked than I-V. Performance on neuropsychological tests for frontal lobe functions was generally depressed in both groups, with more severe deficits in A. Between-group differences in verbal, visual-spatial, and emotional-social skills are discussed. The cerebellar and frontal brain deficits that are present in both clinical groups (A and ALL) may be common to other developmental and acquired disorders of early childhood. Such joint manifestation of cerebellar and frontal lobe abnormalities is in agreement with the concept of cerebellar significance for the development of higher cognitive functions.  相似文献   
158.
159.
160.
An acromegalic patient with galactorrhea-amenorrhea who conceived following long-term 2-bromo-alpha-ergocryptine (CB-154) therapy is described. During CB-154 therapy, determinations of serum prolactin (PRL), luteinizing hormone (LH)-human chorionic gonadotropin, follicle-stimulating hormone a reduction in PRL level followed by an LH peak, a rise in basal body temperature and menstruation. The patient became pregnant during the next cycle, but therapeutic abortion was performed because of the active acromegaly. These results demonstrate that CB-154 can restore ovulatory function not only to the patient with a hypothalamic disorder but also to the acromegalic patient with an enlarged sella turcica.  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