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   4550篇
  免费   2篇
综合类   1篇
化学工业   19篇
机械仪表   2篇
建筑科学   4篇
轻工业   13篇
无线电   5篇
一般工业技术   11篇
冶金工业   4483篇
自动化技术   14篇
  2019年   1篇
  2016年   3篇
  2015年   1篇
  2014年   7篇
  2013年   2篇
  2012年   4篇
  2011年   2篇
  2009年   2篇
  2007年   2篇
  2006年   6篇
  2005年   1篇
  2004年   2篇
  2003年   9篇
  2002年   4篇
  2001年   1篇
  2000年   2篇
  1999年   128篇
  1998年   1396篇
  1997年   851篇
  1996年   491篇
  1995年   268篇
  1994年   251篇
  1993年   278篇
  1992年   35篇
  1991年   49篇
  1990年   73篇
  1989年   61篇
  1988年   68篇
  1987年   63篇
  1986年   45篇
  1985年   35篇
  1984年   1篇
  1983年   8篇
  1982年   12篇
  1981年   29篇
  1980年   44篇
  1979年   3篇
  1978年   7篇
  1977年   93篇
  1976年   205篇
  1975年   5篇
  1964年   1篇
  1955年   3篇
排序方式: 共有4552条查询结果,搜索用时 0 毫秒
31.
This paper explains the Canadian decision process following the isolation and identification of A/New Jersey/8/76 at Fort Dix, New Jersey in February 1976. The cause for concern was the emergence of a swine-like strain related to that which caused the 1918-19 pandemic, together with proved man-to-man transmission. This concern was reinforced since all new influenza A strains known to have infected the number of persons involved at Fort Dix have become strains of epidemic importance. The Fort Dix outbreak gave sufficient warning to allow implementation of a national vaccination program, to prevent and protect against influenza. In the past such an opportunity had not occurred, and vaccine use had, at best, constituted an intervention in the course of an outbreak. The National Advisory Committee on Immunizing Agents had all available information when it reached its decision to recommend vaccination with bivalent (A/Victoria and A/New Jersey) or with monovalent (A/New Jersey) vaccine for selective, high-risk groups. This was an independent, scientifically based decision.  相似文献   
32.
33.
34.
Lung function and immunologic studies have been performed in 9 patients with bird breeder's hypersensitivity pneumonitis at the time of diagnosis and at intervals from 8 to 30 months after they ceased exposure to the provoking antigen. All 9 patients had evidence of small airway obstruction at the time of diagnosis. Complete recovery of lung function occurred in 4 patients. The other 5 all had evidence of interstitial damage; 3 of them had progressive increase in the degree of airway obstruction, and one had progressive loss of elastic recoil. The patients were nonsmokers, and these progressive changes could not be explained by occult exposure to antigen because the tests of immunologic sensitivity to relevant avian antigens became negative. Neither the nature or degree of lung function abnormality nor the form of clinical presentation was related to the development of residual damage. The period of exposure to antigen after symptoms developed and the age of the patient appeared to be the most important factors determining recovery of lung function.  相似文献   
35.
During International Biological Programme studies in Papua New Guinea, on Karkar Island and at Lufa in the Eastern Highlands, information on anthropometric, biochemical and genetic characteristics was collected from the same individuals. Use has been made of this special situation to investigate whether any associations exist between genetic markers and anthropometric and biochemical variation. Those found, and which satisfy criteria established to help in distinguishing real from chance associations, include: P with haemoglobin concentration and serum albumin and cholesterol levels; acid phosphatase with serum albumin level and haemoglobin concentration; anhaptoglobinaemia and serum globulin level; haemoglobin J-Tongariki with serum phosphorus level. The associations are discussed in terms of their arising from the direct result of environmental factors modifying gene expression, chance concordance of environmental and genetic variation, or pleiotropy.  相似文献   
36.
The effect of actinomycin-D (AMD) on radiation damage repair was studied in plateau phase V79 Chinese hamster cells. Sublethal radiation damage repair, as demonstrated by survival fluctuations following two x-ray exposures separted by time, was observed in our plateau phase cells. Plateau phase cells exposed to 0.01-0.04 mug/ml AMD (a nontoxic regimen to 8 hours) between x-ray exposures were less able to repair sublethal damage. If plateau phase cells were plated at low dilutions into fresh medium (conditions for resuming exponential growth) immediately after the first x-ray dose, and exposed to 0.01--0.04 mug/ml AMD until the second dose, inhibition of sublethal damage repair and additional cell killing were observed particularly at 0.04 mug/ml AMD. It is suggested that radiation-drug damage interactions should be studied in plateau phase cells and in cells resuming exponential growth after plateau phase (possibly analogous to "recruitment"), as well as in exponential phase cultures.  相似文献   
37.
1058 newborn infants were examined. Forty-one (3-9%) had clinically discernible pigmented lesions compatible with melanocytic naevi. Biopsy was performed on thirty-four of the forty-one and of these; eleven, representing 1-01% of the infants, proved to be melanocytic naevi. No giant (garment) naevi were seen in this series. Two of the eleven naevi pathologically examined showed histological changes similar to those that have been reported in some giant naevi, but the remaining nine were not only different from criteria usually assigned to giant naevi, but they also differed from the usual adult naevi, in that most were predominantly junctional. None of the melanocytic naevi in this series showed any suggestion of malignant change. In newborn infants it is often impossible clinically to distinguish naevi from other types of pigmented lesions, as only eleven out of the thirty-four pigmented lesions were melanocytic naevi. Seven of the eleven melanocytic naevi were under 1-5 cm in diameter. No pigmented lesions were found on the palms, soles or genitalia.  相似文献   
38.
Volatile free fatty acids (VFA) in blood increased approximately twofold in dogs subjected to total hepatectomy. The average total plasma VFA preoperatively was 1,585 mug percent and shortly before death, postoperatively, was 2,798 mug percent. The corresponding red cell concentrations were essentially the same. Acetic acid was 81 percent of the total VFA, propionic acid 7 percent, isobutyric acid 4 percent, butyric acid one percent, and isovaleric acid 5 percent. There was little or no isovalerate in red cells. The increments in the individual fatty acids after hepatectomy were highly variable, but the average increase with time was almost linear. The increase in VFA probably reflects an increased utilization of the branched-chain aminoacids by extrahepatic tissues.  相似文献   
39.
In stalk parenchyma tissue of WF9 X 38-11 single corn (Zea mays L.), there was a per cell increase in RNA synthesis and a slight increase in total RNA as cells became older. In cob parenchyma tissue of WF9 X 38-11 single cross corn, both total RNA content and RNA synthesis per cell decreased with the age of cells. In first developed leaf tissue of FR43 X FR14A single cross corn, RNA synthesis increased steadily but only slightly over its life span. The pattern of RNA synthesis and destruction in senescing leaf tissue of seedlings and two sources of parenchyma tissue of maturing plants appeared to differ.  相似文献   
40.
Affinity chromatography on agmatine-Sepharose was used for the separation of two active forms of urokinase (EC 3.4.99.26) from partially purified human urinary urokinase. The approximate molecular weight of the heavier form was 47 000 and of the lighter 33 400. Both forms were homogeneous by sodium dodecyl sulfate gel electrophoresis and by 3H-labeled diisopropylphosphorofluoridate and 14C-labeled p-nitrophenyl-p'-guanidinobenzoate incorporation studies. The 33 400 mol. wt. form had a single chain, and the 47 000 mol. wt. form had two chains (33 100 and 18 600 mol. wt.) linked by disulfide bonds. The specific activity of the heavier form was 104 000 CTA units/mg protein, compared with 226 000 units/mg for the lighter form but the activities per mmol of active site (molar activities) of the two forms were almost identical (9.6-10(9) and 10.2-10(9) CTA units/mmol). Isoelectric focusing on gels showed that the 47 000 material contained one major subform with a pI of 8.60 and a minor subform with a pI of 8.90, while the 33 400 material had three major subforms with pI values of 8.35, 8.60 and 8.70, respectively, and a minor subform with a pI of 8.05. 3H-labeled diisopropylphosphorofluoridate incorporation studies revealed an active-site serine residue in the heavy chain.  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