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   1077篇
  免费   0篇
化学工业   6篇
建筑科学   1篇
轻工业   3篇
无线电   1篇
一般工业技术   9篇
冶金工业   1052篇
自动化技术   5篇
  2013年   3篇
  2012年   1篇
  2010年   1篇
  2009年   2篇
  2008年   2篇
  2007年   5篇
  2006年   1篇
  2004年   2篇
  2003年   1篇
  2001年   1篇
  1999年   28篇
  1998年   339篇
  1997年   170篇
  1996年   139篇
  1995年   72篇
  1994年   55篇
  1993年   65篇
  1992年   5篇
  1991年   15篇
  1990年   8篇
  1989年   12篇
  1988年   15篇
  1987年   7篇
  1986年   8篇
  1985年   7篇
  1982年   5篇
  1981年   7篇
  1980年   6篇
  1979年   1篇
  1978年   2篇
  1977年   37篇
  1976年   54篇
  1975年   1篇
排序方式: 共有1077条查询结果,搜索用时 15 毫秒
951.
BACKGROUND: The granulocyte antigens NA1 and NA2 are the two recognized allelic forms of Fc gamma receptor IIIB. These antigens are clinically relevant, because they are the most frequent targets of neutrophil antibodies in alloimmune neonatal neutropenia, transfusion-related acute lung injury, and chronic benign autoimmune neutropenia of infancy. STUDY DESIGN AND METHODS: A genotyping assay for NA1 and NA2 using polymerase chain reaction with sequence-specific forward and reverse oligonucleotide primers has been developed and validated. Genomic DNA was isolated from the peripheral blood of 478 unrelated individuals of five ethnic groups and used as template for NA genotyping. RESULTS: A validation study of 22 serologically typed samples (2 NA1/NA1, 10 NA1/NA2, and 10 NA2/NA2) was performed. A concordance rate of 100 percent (22/22 samples) was observed between the genotyping assay and serologic typing. In the genotyping study conducted, the NA1 and NA2 gene frequencies observed were 0.31 and 0.69 for African Americans, 0.30 and 0.70 for Asian Indians, 0.37 and 0.63 for whites, 0.53 and 0.47 for Hispanics, and 0.55 and 0.45 for Native Americans, respectively. CONCLUSION: Polymerase chain reaction with sequence-specific primers provides a simple and rapid alternative to neutrophil antigen typing by serologic tests. The NA1 and NA2 gene frequencies observed in Asian Indians and African American populations are similar to those observed in white populations, while those observed in Native American and Hispanic populations are more similar to those previously reported for Asian populations.  相似文献   
952.
Two cases of fentanyl-induced muscle rigidity are presented. Significant features of these cases include the unusual pattern of rigidity and the use of fentanyl doses lower than those usually associated with muscle rigidity.  相似文献   
953.
Sixty leg ulcers were measured with two techniques, a common paper tape measure and a new technique, a plastic grid device. The plastic grid proved to be a reliable, valid, and feasible method to quickly assess wounds in a busy outpatient setting. The grid was superior to the tape measure in assessing large and/or irregular ulcers.  相似文献   
954.
Buffy coat smears prepared from peripheral blood and bone marrow aspirate obtained from proved 60 untreated cases of pulmonary tuberculosis were stained with Ziehl-Neelsen method and thoroughly screened for presence of tubercle bacilli. Acid-fast bacilli were detected in 55% cases in buffy coat, 48.3% cases in bone marrow, 38.3% cases both in buffy coat and bone marrow and 65% cases either in buffy coat or in bone marrow or in both. Considering the fact that demonstration of acid-fast bacilli may not be possible in more than 25-50% of the suspected cases of tuberculosis, these techniques are recommended for evaluation of their utility in establishing diagnosis of tuberculosis, particularly in reference to sputum negative cases of pulmonary tuberculosis and tuberculosis of inaccessible extrapulmonary sites.  相似文献   
955.
The psbA gene of the chloroplast genome has a codon usage that is unusual for plant chloroplast genes. In the present study the evolutionary status of this codon usage is tested by reconstructing putative ancestral psbA sequences to determine the pattern of change in codon bias during angiosperm divergence. It is shown that the codon biases of the ancestral genes are much stronger than all extant flowering plant psbA genes. This is related to previous work that demonstrated a significant increase in synonymous substitution in psbA relative to other chloroplast genes. It is suggested, based on the two lines of evidence, that the codon bias of this gene currently is not being maintained by selection. Rather, the atypical codon bias simply may be a remnant of an ancestral codon bias that now is being degraded by the mutation bias of the chloroplast genome, in other words, that the psbA gene is not at equilibrium. A model for the evolution of selective pressure on the codon usage of plant chloroplast genes is discussed.  相似文献   
956.
BACKGROUND: Desmoplastic fibroma is a benign, locally aggressive, intraosseous neoplasm with a propensity for local recurrence. Desmoplastic fibroma most commonly originates within the mandible (70% of cases), and long bones with rare lesions reported in the maxillary, frontal, and parietal bones. We report two patients with desmoplastic fibroma arising within the temporal bone. STUDY DESIGN: Case report and literature review. PATIENTS: Two patients with desmoplastic fibroma with intracranial and extra cranial growth patterns are presented. Both were young females with aural fullness and decreased hearing. INTERVENTIONS: Diagnostic and therapeutic. RESULTS: Both tumors were surgically extirpated and the patients have remained disease free for 18-48 months. Neither tumor expressed estrogen or progesterone receptors. CONCLUSION: Desmoplastic fibroma is a highly invasive local destructive lesion which is best treated by nondestructive surgical intervention. Immunohistochemical analysis may demonstrate hormonal receptors, in which case Tamoxifen may reduce recurrence.  相似文献   
957.
One hundred eighty three patients (73.8%) in the SFNC series received radiation therapy alone, for 60 patients and with additional chemotherapy for 129 patients. From this review, a dose-response relationship with an improved survival time with doses greater than 50 Gy could not be demonstrated (p = 0.97). The multivariate risk analysis identified the radiation therapy as one of the factors which has the most favorable impact on survival. Radiation therapy remains the treatment method of choice. These results are compared with data from the literature.  相似文献   
958.
BACKGROUND: Nitrates are widely used in the treatment of angina in patients with acute myocardial infarction (AMI). Short-term administration prevents left ventricular (LV) dilation and infarct expansion. However, little information is available regarding their long-term effects on LV remodeling in patients surviving Q-wave AMI. METHODS AND RESULTS: This was a randomized, double-blind, placebo-controlled trial designed to investigate the long-term (6-month) efficacy of intermittent transdermal nitroglycerin (NTG) patches on LV remodeling in 291 survivors of AMI. Patients meeting entry criteria had baseline gated radionuclide angiography (RNA) followed by randomization to placebo or active NTG patches delivering 0.4-, 0.8-, or 1.6-mg/h. RNA was repeated at 6 months and 6.5 days after withdrawal of double-blind medication. The primary study end point was the change in end-systolic volume index (ESVI). Both ESVI and end-diastolic volume index (EDVI) were significantly reduced with 0.4-mg/h NTG patches (-11.4 and -11.6 mL/m2, respectively, P<.03). This beneficial effect was observed primarily in patients with a baseline LV ejection fraction < or =40% (deltaESVI, -31 mL/m2; deltaEDVI, -33 mL/m2; both P<.05) and only at the 0.4-mg/h dose. After NTG patch withdrawal, ESVI significantly increased but did not reach pretreatment values. CONCLUSIONS: Transdermal NTG patches prevent LV dilation in patients surviving AMI. The beneficial effects are limited to patients with depressed LV function and only at the lowest (0.4-mg/h) dose. Continued administration is necessary to maintain efficacy. Whether these remodeling effects confer a clinical or survival advantage will need to be addressed in an adequately powered cardiac event trial.  相似文献   
959.
960.
Dietary protein restriction decreases plasma concentrations of insulin-like growth factor-I (IGF-I) and reduces IGF-I mRNA levels in the liver. In addition to the actions of systemic IGF-I, locally produced IGF-I is thought to mediate autocrine and paracrine growth effects in the colon. The objectives of the present study were to investigate the IGF-I pathway in the colon and liver of adult rats under conditions of dietary protein restriction, surgical stress, and dietary protein repletion. Two groups of rats were placed on either a 20% or 2% casein diet for 19 days. Two additional groups of rats underwent gastrostomy after a 2% casein diet for 2 weeks, and then were either kept on the 2% casein diet or changed to a 20% casein diet until day 19. Dietary protein restriction reduced plasma concentrations of IGF-I and IGF-binding proteins (IGFBPs) and hepatic IGF-I mRNA content, while increasing colonic IGF-I receptor mRNA. Gastrostomy in protein-depleted animals had no effect on hepatic IGF-I mRNA, but led to a marked increase in colonic IGF-I mRNA levels. Dietary protein repletion resulted in a decrease in colonic IGF-I receptor mRNA. The distinct effects of dietary protein depletion and operative stress on the IGF pathway in the colon as compared with the liver may serve to maintain the level of IGF-I signaling in the colon by autocrine or paracrine mechanisms under these conditions.  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