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   1650篇
  免费   131篇
  国内免费   46篇
电工技术   78篇
综合类   174篇
化学工业   174篇
金属工艺   99篇
机械仪表   108篇
建筑科学   108篇
矿业工程   57篇
能源动力   35篇
轻工业   203篇
水利工程   28篇
石油天然气   28篇
武器工业   17篇
无线电   88篇
一般工业技术   123篇
冶金工业   283篇
原子能技术   12篇
自动化技术   212篇
  2024年   3篇
  2023年   6篇
  2022年   21篇
  2021年   35篇
  2020年   36篇
  2019年   9篇
  2018年   21篇
  2017年   29篇
  2016年   18篇
  2015年   31篇
  2014年   61篇
  2013年   79篇
  2012年   105篇
  2011年   131篇
  2010年   114篇
  2009年   135篇
  2008年   132篇
  2007年   165篇
  2006年   126篇
  2005年   115篇
  2004年   73篇
  2003年   30篇
  2002年   36篇
  2001年   32篇
  2000年   34篇
  1999年   9篇
  1998年   67篇
  1997年   37篇
  1996年   36篇
  1995年   26篇
  1994年   6篇
  1993年   19篇
  1992年   4篇
  1991年   6篇
  1990年   3篇
  1989年   5篇
  1988年   2篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1983年   3篇
  1981年   3篇
  1980年   1篇
  1977年   4篇
  1976年   9篇
  1975年   1篇
  1970年   1篇
  1962年   1篇
  1961年   3篇
排序方式: 共有1827条查询结果,搜索用时 31 毫秒
1.
In the search for new risk factors for diabetic macroangiopathy the insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme gene was studied in 237 consecutive patients (125 men and 112 women) with non-insulin-dependent diabetes. The female population showed an excess of ischemic electrocardiographic changes or definite myocardial infarctions in the patients homozygous for the deletion [D/D; odds ratio (OR) 2.8; 95% confidence interval (CI) 1.4-5.3] and in the insertion/deletion heterozygotes (I/D; OR 1.8; CI 1.1-3.1) compared with the patients homozygous for the insertion (I/I). In the total series coronary heart disease, cerebrovascular disease, and claudication were more often observed in the patients with I/D (OR 1.5; CI 1.0-2.2) or the D/D genotype patients (OR 1.7; CI 1.1-2.6) than in those with the genotype I/I. The systolic blood pressure was lower in patients with genotype I/I (138 +/- 19 mmHg) than in those with the genotype I/D (149 +/- 22 mmHg) or D/D (150 +/- 21 mmHg; P < 0.02). The prevalence of hypertension and the median urinary albumin excretion rate also tended to be lowest in the I/I genotype patients. Multiple logistic analysis revealed that in women the angiotensin-converting enzyme D/D genotype is independently associated with coronary heart disease. Our findings suggest that variation at the angiotensin-converting enzyme gene locus is one of the factors involved in the predisposition of diabetic patients to the development of arterial disease and hypertension.  相似文献   
2.
The role of a depressor factor, atrial natriuretic peptide, in the development of arterial hypertension in adolescents with pubertal hypothalamic syndrome was studied in 52 patients and 13 healthy males aged 13-24 years. The duration of disease was 2-11 years. Radioimmunological methods were used to measure plasma atrial natriuretic peptide, plasma renin activity, and serum aldosterone. Patients with borderline arterial hypertension were found to have a significant reduction in their atrial natriuretic peptide levels, and this correlated directly with the renin-aldosterone system, demonstrating insufficiency of the depressor system in patients with pubertal hypothalamic syndrome and the involvement of atrial natriuretic peptide in the development of arterial hypertension, along with disturbances in the functional relationship between atrial natriuretic peptide and the renin-aldosterone system.  相似文献   
3.
The structural gene for V antigen (lcrV) is known to be encoded within the lcrGVH-yopBD operon of the approximately 70-kb low-calcium-response or Lcr plasmid of Yersinia pestis. This 37-kDa monomeric peptide was reported to provide active immunity in mice, suppress inflammatory cytokines, and regulate expression of the low calcium response (Lcr+). Here we describe pVHB62, encoding a polyhistidine-V antigen fusion peptide (Vh) and linked LcrH. Vh underwent degradation from both the C terminus and N terminus during classical chromatographic fractionation but remained intact within two compartments during Ni2+ affinity chromatography. The first was homogeneous, capable of active immunization (mouse intravenous 50% lethal dose, > 10(7) bacteria), and stable at 4 degrees C. The second remained bound to the affinity column but could be eluted as a mixture of Vh, LcrH, and low-molecular-weight material by application of 6 M guanidine HCl. This mixture was dialyzed, denatured in 8 M urea, and again applied to the affinity column, which then hound Vh but not LcrH. The latter was recovered and renatured, and low-molecular-weight material was removed by biochemical fractionation. The resulting homogeneous LcrH bound protein AN antigen fusion peptide but not protein A in a sandwich enzyme-linked immunosorbent assay, and this reaction was inhibited by Vh. These observations indicate that LcrH normally binds V antigen in bacterial cytoplasm and suggest that only free LcrH down-regulates expression of the low calcium response.  相似文献   
4.
Mental health supplement to the Ontario Health Survey: methodology   总被引:1,自引:0,他引:1  
OBJECTIVE: To describe the methodology of a province-wide, cross-sectional, epidemiologic study of psychiatric disorder among those aged 15 years and over living in household dwellings in Ontario. METHOD: Respondents for the survey were drawn from households (N = 13002) participating in a province-wide health survey. One person per household was selected, and 9953 (76.5%) participated. RESULTS: Participants and nonparticipants were similar to each other. An extensive array of data, including measures of psychiatric disorder classified using a revised version of the Composite International Diagnostic Interview (CIDI), are available for all respondents. CONCLUSIONS: The Ontario Health Supplement is contained in a public-use data file at the Ontario Ministry of Health and is available to investigators for study. A strong survey design, careful measurement, and acceptable levels of response provide the rationale for our inviting researchers to access and use the Ontario Health Supplement data base.  相似文献   
5.
介绍一种利用氧化铝生产过程的中间物料———铝酸钠溶液 ,生产高纯超细氧化铝的方法 ,即利用钡盐净化铝酸钠溶液 ,得到A/S >10 0 0 0的精制溶液 ,再进行种分分解 ,得到超细Al(OH) 3 ,经过酸洗 ,最终得到纯度达 99 99% ,粒度 90 %小于 2 μm高纯超细氧化铝。  相似文献   
6.
基于EPP模式下的数据采集系统   总被引:2,自引:0,他引:2  
介绍了一种基于并口EPP模式通讯的数据采集系统的设计方法,该系统以ADSP2 1 81、E PLD为核心器件,AD7331 1芯片为模拟信号输入输出接口,非常适合便携式数据采集系统  相似文献   
7.
Since the advent of computed tomography (CT) traumatic intraventricular haemorrhage (IVH) has been diagnosed more often. It has reportedly been associated with a poor prognosis, but pure or solitary IVH is rare, suggesting that other lesions occurring concurrently with it may contribute to the poor outcome. In a series of 65 patients with severe head injury (GCS < or = 8), 14 (22%) had IVH on initial CT. Death rate in these 14 was 21%, not significantly different from that in patients without IVH (14%), although a significantly higher proportion of patients without IVH had a good outcome. These results suggest that mortality is related to other lesions associated with IVH rather than to IVH alone and that the presence of IVH does not necessarily lead to a poor outcome.  相似文献   
8.
本文提出一种从军用地图中提取铁路、道路的半自动方法和自动恢复显示其在地图中标识方式的算法,从而进一步实现地图图形显示系统的多层次结构。  相似文献   
9.
10.
激光粒度分析仪测定氢氧化铝细颗粒方法的探讨   总被引:1,自引:0,他引:1  
针对马尔文2000型激光粒度分析仪在氢氧化铝分析中对25μm粒径以下细颗粒的分析不太敏感,难以满足氧化铝生产分解过程对粒度控制的要求,对试验样品采用一些非常规的特殊处理方法,以提高细小颗粒在处理过样品中所占的体积百分比;研究了不同的样品处理方式对分析结果的影响。试验结果表明,只有对洗涤、过滤后的湿样进行分析,才能对分解料浆样品中的细颗粒的粒度分布进行准确地分析,得到满足试验和生产过程控制精度的结果。  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