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   3834篇
  免费   6篇
电工技术   1篇
综合类   2篇
化学工业   12篇
建筑科学   2篇
轻工业   4篇
无线电   3篇
一般工业技术   15篇
冶金工业   3794篇
自动化技术   7篇
  2021年   2篇
  2019年   1篇
  2017年   3篇
  2016年   1篇
  2015年   1篇
  2014年   1篇
  2012年   1篇
  2011年   2篇
  2010年   2篇
  2008年   2篇
  2007年   3篇
  2006年   4篇
  2004年   2篇
  2003年   5篇
  2002年   1篇
  2001年   1篇
  2000年   1篇
  1999年   134篇
  1998年   1210篇
  1997年   666篇
  1996年   415篇
  1995年   217篇
  1994年   180篇
  1993年   243篇
  1992年   23篇
  1991年   46篇
  1990年   46篇
  1989年   60篇
  1988年   62篇
  1987年   52篇
  1986年   34篇
  1985年   36篇
  1984年   1篇
  1983年   8篇
  1982年   17篇
  1981年   21篇
  1980年   20篇
  1979年   2篇
  1978年   8篇
  1977年   98篇
  1976年   197篇
  1975年   9篇
  1974年   1篇
  1955年   1篇
排序方式: 共有3840条查询结果,搜索用时 15 毫秒
941.
OBJECTIVE: The purpose of these studies was to determine the effects of the essential fatty acid, linoleic acid, and the commonly used non-steroidal anti-inflammatory agents, aspirin and acetaminophen, on the rate of prostaglandin (PG) biosynthesis by human amnion cells. METHODS: Amnion cells were isolated from term, normal pregnancies and grown to confluence. Cells were incubated with control or medium containing 100 mumol/L linoleic acid. Cells were also incubated with control medium or medium containing 10 or 100 micrograms/mL aspirin or acetaminophen. RESULTS: Following an initial delay, amnion cells exposed to linoleic acid exhibited a significant increase in PGE synthesis. Both aspirin and acetaminophen in clinically relevant concentrations had a significant inhibitory effect on amnion cell PGE synthesis. CONCLUSIONS: Linoleic acid has a stimulatory effect and aspirin and acetaminophen have an inhibitory effect on PGE synthesis in human amnion cells in culture. We speculate that dietary habits, supplement ingestion, and over-the-counter drug use may affect amnion cell PG production. In view of the potential importance of intrauterine PG production in normal and abnormal labor, further study in this area is indicated.  相似文献   
942.
943.
944.
Thirty patients had 32 cementless total hip arthroplasty revisions and were evaluated postoperatively for clinical function (Harris Hip Score) and radiographic evidence of implant stability. Of the 26 femoral components revised, 16 were revised with anatomic long-stem femoral prostheses, and 10 were revised with straight mid-stem-length components. All components were collared and had circumferential proximal fiber-mesh porous coating. Seven of 16 patients had radiographic subsidence after revision with long-stem components (2 to 30 mm); 6 of 10 patients had subsidence after revision with mid-stem femoral components (2 to 25 mm). Of the 13 patients with femoral subsidence, 8 had calcar reconstruction with allograft bone; of the 13 patients without radiographic subsidence, 8 did not require calcar reconstruction. One of 27 fiber-mesh, porous-coated acetabular components migrated (30 mm). No components have been removed or revised. Even with circumferential proximal porous coating, femoral implant stability remains unpredictable in total hip arthroplasty revision.  相似文献   
945.
946.
PURPOSE: Chorioretinal toxoplasmosis can threaten visual function when located in the posterior pole. The aim of this study was to compare the advantages and disadvantage of combination of malocid-sulfadiazine and clindamycin subconjunctivally. METHODS: Two groups of patients affected by unilateral chorioretinal toxoplasmosis were studied. The diagnosis was performed in 77% of cases on acqueous humor analysis. The first group of twenty-six patients was treated with a combination of malocid-sulfadiazine while the second group (seventeen patients) was treated with clindamycin subconjunctivally. Local and general corticosteroids were associated in all cases. Mean follow-up was 19 months in the first group and 16.5 months in the second. RESULTS: Visual acuity was increased in 88.5% of cases in the first group and in 94% of cases in the second group. Cicatrization obtained in both groups was comparably delayed 1.68 months for the first and 1.26 months for the second. Recurrences were rarely observed in the two groups: respectively 8% and 6% of cases. No local and general complication was noted. CONCLUSION: These findings suggest the advantages of subconjunctival clindamycin treatment due to the absence of general hematological toxicity.  相似文献   
947.
In implantable cardioverter-defibrillator therapy with endocardial lead systems, certain clinical variables are associated with defibrillation energy requirements. Because of the weak correlation coefficients, these variables cannot predict defibrillation thresholds in individual patients.  相似文献   
948.
949.
OBJECTIVE: The characteristics of 3 patients with longstanding rheumatoid arthritis (RA) and consecutive evolution of limited cutaneous systemic sclerosis (IcSSc) were evaluated and compared with those of patients with IcSSc alone (n = 20) or with RA alone (n = 120). METHODS: Clinical features of the different patient populations were compared. Serologic analyses included tests for antinuclear antibodies (ANA) and ANA subsets, in particular anticentromere antibodies (ACA) and anti-heterogeneous nuclear RNP (hnRNP)-A2/RA33 (anti-A2/RA33). RESULTS: The 3 patients with RA developed IcSSc 11, 29, or 50 years after the onset of RA. Features of IcSSc were Raynaud's phenomenon, sclerodactyly, and telangiactasias in all 3 patients, and esophageal dysmotility in 1 patient. Rheumatoid factor (RF) and anti-A2/ RA33 were each found in 2 patients, and 1 of these patients was seropositive for both RF and anti-A2/RA33. ACA titers were positive in all cases. However, similar to the development of RA prior to IcSSc, the occurrence of autoantibodies typical of RA preceded the occurrence of ACA, at least in 2 of the patients. Using affinity-purified antibodies, cross-reactivities between anti-centromere protein A (CENP-A) and anti-CENP-B antibodies with anti-A2/RA33 antigens were seen in the 2 anti-A2/RA33-positive patients. Such cross-reactivities were not found in IcSSc patients without concomitant RA. Epitope mapping revealed that both autoantibody specificities recognized the known major epitopes: anti-CENP-B reacted with the C-terminal region and anti-A2/RA33 with the second RNA binding domain in the N-terminal region of hnRNP-A2. CONCLUSION: The RA-lcSSc overlap syndrome in these 3 patients with longstanding RA was characterized by an incomplete CREST (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasias) syndrome. The study demonstrated the presence of autoantibodies typical of both diseases and cross-reactivity of ACA with hnRNP-A2/RA33 in the sera of these patients.  相似文献   
950.
Particulate air pollution, including coal fly ash, contains iron, and some of the pathological effects after inhalation may be due to reactive oxygen species produced by iron-catalyzed reactions. The objective of this study was to determine whether iron, present in coal fly ash, was mobilized, leading to ferritin induction in human airway epithelial cells, and whether the size of the particles affected the amount of iron mobilized. Three types of coal were used to generate the three size fractions of fly ash collected. The Utah coal fly ash was generated from a bituminous b coal, the Illinois coal fly ash from a bituminous c coal, and the North Dakota coal fly ash from a lignite a coal. Three size fractions were studied to compare the amount of iron mobilized in human airway epithelial (A549) cells and by citrate in cell-free suspensions. The size fractions selected were fine (<2.5 microm) and coarse (2.5-10 microm) components of PM10, airborne particulate matter <10 microm in diameter, and the fraction greater than 10 microm. Coal fly ash samples were incubated with 1 mM citrate to determine if iron associated with coal fly ash could be mobilized. Iron was mobilized by citrate from all three size fractions of all three coal types to levels as high as 56.7 nmol of Fe/mg of coal fly ash after 24 h. With all three coal types, more iron was mobilized by citrate from the <2.5 microm fraction than from the >2.5 microm fractions. Further, the mobilized iron was in the Fe(III) form. To determine if iron associated with the coal fly ash could be mobilized by A549 cells, cells were treated with coal fly ash, and the amount of the iron storage protein ferritin was determined after 24 h. Ferritin levels were increased by as much as 11.9-fold in cells treated with coal fly ash. With two of the three types of coal studied, more ferritin was induced in cells treated with the <2.5 microm fraction than with the >2.5 microm fractions. Further, inhibition of the endocytosis of the coal fly ash by the cells resulted in ferritin levels that were near that of the untreated cells, suggesting that iron was mobilized intracellularly, not in the culture medium. The results of this study suggest that differences in particle size and speciation of iron may affect the release of iron in human airway epithelial cells.  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