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   1452篇
  免费   20篇
  国内免费   1篇
电工技术   8篇
综合类   1篇
化学工业   146篇
金属工艺   30篇
机械仪表   20篇
建筑科学   9篇
能源动力   16篇
轻工业   38篇
石油天然气   2篇
无线电   66篇
一般工业技术   171篇
冶金工业   894篇
原子能技术   3篇
自动化技术   69篇
  2023年   4篇
  2022年   4篇
  2021年   17篇
  2020年   7篇
  2019年   5篇
  2018年   10篇
  2017年   7篇
  2016年   18篇
  2015年   11篇
  2014年   14篇
  2013年   36篇
  2012年   22篇
  2011年   25篇
  2010年   20篇
  2009年   22篇
  2008年   17篇
  2007年   24篇
  2006年   21篇
  2005年   22篇
  2004年   18篇
  2003年   28篇
  2002年   18篇
  2001年   11篇
  2000年   12篇
  1999年   47篇
  1998年   257篇
  1997年   171篇
  1996年   114篇
  1995年   70篇
  1994年   62篇
  1993年   59篇
  1992年   24篇
  1991年   22篇
  1990年   30篇
  1989年   21篇
  1988年   29篇
  1987年   32篇
  1986年   11篇
  1985年   15篇
  1984年   12篇
  1983年   12篇
  1982年   9篇
  1981年   8篇
  1978年   4篇
  1977年   15篇
  1976年   22篇
  1973年   6篇
  1972年   6篇
  1971年   3篇
  1970年   5篇
排序方式: 共有1473条查询结果,搜索用时 15 毫秒
31.
32.
The etiology of liver disease remains unknown in about 4 to 23% of dialysis patients and 10 to 16% of renal transplant recipients. A search for other causative agents of liver disease led to the discovery of the GB group of viruses. We studied the association between the presence of GB virus C (GBV-C) infection, known risk factors for parenterally-transmitted infections and history or laboratory evidence of liver disease among end-stage renal disease (ESRD) patients referred for renal transplantation to the New England Organ Bank, MA. Stored sera from patients on the renal transplantation waiting list between November 1986 and June 1990 were tested for antibody to hepatitis C virus (HCV). Sera were available in 1544 of 3243 (48%) patients, and anti-HCV was detected by ELISA3 in 287 (19%). All 287 anti-HCV positive patients formed the anti-HCV positive cohort and 286 randomly selected anti-HCV negative patients formed the anti-HCV negative cohort (573 patients overall). Additional sera were available for GBV-C RNA testing in 465 of 573 (81%) patients, and GBV-C RNA was detected by RT-PCR in 146. The overall extrapolated prevalence of serum GBV-C RNA was 29%. The prevalence of serum GBV-C RNa among anti-HCV positive patients (35%) was not significantly different from that among anti-HCV negative patients (29%; P = 0.22). In a univariate analysis, compared to patients without GBV-C RNA, patients with serum GBV-C RNA were younger [odds ratio (OR) 0.98 per year of age, P = 0.01], had a lower proportion of males (OR 0.64, P = 0.03), lower proportion of patients with diabetes mellitus (OR 0.44, P = 0.01), higher proportion of patients with a previous transplantation (OR 1.53, P = 0.04), longer duration of dialysis at the time of enrollment (OR 1.004 per month on dialysis, P = 0.03), and a higher proportion of patients with history of transfusions (OR 4.58, P = 0.01). Serum GBV-C RNA was not associated with a significantly increased OR for history of liver disease or non-A, non-B hepatitis, or elevated serum alanine aminotransferase levels. In a step-wise multivariate regression analysis, a younger age (OR 0.98 per year of age, P = 0.03), and history of blood transfusions (OR 3.89, P = 0.03) were associated with an increased OR for serum GBV-C RNA, while diabetes mellitus was associated with a decreased OR for GBV-C RNA (OR 0.47, P = 0.01). Anti-HCV was not a predictor of serum GBV-C RNA (OR 1.07, P = 0.77). The results of this study support the fact that GBV-C is a parenterally transmitted virus and shed light on the modes of transmission of GBV-C among ESRD patients. However, the association with liver disease remains to be established.  相似文献   
33.
Ankylosing spondylitis (AS) results in disease-specific inflammation at the site of ligamentous insertion into the bone. Atlantoaxial joint subluxation and vertical subluxation of the axis may occur as a consequence of instability resulting from the inflammatory process. Spontaneous anterior atlantoaxial subluxation is a well recognized complication in about 2% of patients with AS, and presents with or without signs of spinal cord compression. Vertical subluxation may follow anterior or posterior subluxation. It was noted in 3-8% of patients with rheumatoid arthritis, but is an exceedingly rare complication of AS. Moreover, it has never been reported that multiple cerebellar infarction and bulbar symptoms developed spontaneously due to atlanto-occipital subluxation and vertical subluxation in a patient with a long [corrected] history of AS. We describe a man with AS who developed multiple cerebellar infarction due to vertebral artery obstruction and bulbar symptoms associated with atlanto-occipital subluxation and vertical subluxation.  相似文献   
34.
35.
Neural Computing and Applications - Induction machines have extensive demand in industries as they are used for large-scale production and, therefore, vulnerable to both electrical and mechanical...  相似文献   
36.
The photopolymerization of styrene with a well‐defined molecular architecture and a low polydispersity index and with methyl and phenylseleno (? SePh) groups at α‐ and ω‐chain ends, respectively, was performed via a controlled/living radical polymerization with a new initiating system, 1‐(phenylseleno)ethyl benzene/tert‐butyl diphenyl (phenylseleno) silane, through the absorption of visible light at room temperature. A novel initiating living radical polymerization was examined. The yield and number‐average molecular weight (Mn) of the resulting polymer increased with the reaction time. Furthermore, a linear relationship was found in a plot of Mn versus the polymer yield. These results indicated that this polymerization proceeded through a living radical mechanism. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 348–355, 2004  相似文献   
37.
Seed oils of Stachytarpheta mutabilis, Petrea volubilis, Gmelina hystrix were examined for their component acids and were found to contain the following acids (wt. %): Capric (0.5, -, 1.3), Lauric (0.5, 5.9, 1.5), Myristic (1.0, 8.9, 2.3), Palmitic (7.7, 10.7, 29.2), Stearic (5.4, 20.9, 21.1), Arachidic (1.1, 3.5, 6.3), Behenic (1.0, 4.2, 4.7), Oleic (9.1, 42.1, 2.9) and Linoleic (73.7, 3.8, 30.7) respectively.  相似文献   
38.
Addition of plasticizers to poly(vinyl chloride) generally increases its flammability and frequently increases smoke production during its burning. Flame retardants added to plasticized PVC can reduce flammability, but increase smoke production. This study shows that proper choice of combined use of other polymers, phosphate plasticizers, fillers and other flame retardants, produces measured synergistic improvements in flame retardance and smoke suppression which could benefit applications such as PVC wire and cable insulation.  相似文献   
39.
Thermal barrier coatings (TBCs) are improving the performance and efficiency of advanced gas turbine engines by allowing higher inlet temperature and insulation of critical hot-section components. Monitoring the integrity of TBCs prior to failure is critical to the overall performance of gas turbine en gines and requires a robust nondestructive evaluation (NDE) technique. In this paper, changes in electrochemical impedance with microstructural degradation of critical constituents in TBCs are summarized for the development of electrochemical impedance spectroscopy as an NDE technique for TBCs.  相似文献   
40.
A.c. impedance behaviour of MnO2 and doped -MnO2 electrodes in H2SO4 medium was assessed with a view to explaining the mechanism of the discharge behaviour of MnO2 electrodes in 4m H2SO4 electrolyte. The electrodes used in this work appear to be intermediate cases of planar and porous electrodes as the angles, , made by the low frequency part with the real axis are found to be in the range (30–60°). The Nyquist plots and the Randle plots tend to reinforce the observation made by Tye that the capacity yield is essentially diffusion controlled. The depression and flattening of semi-circles observed reveals a link with the heterogeneity of the planar electrode and with the porosity of the pitted electrode. The deviation from a 45° angle made by the low frequency part with the real axis may either be explained by the roughness of the electrode surface or the shallow pores on the surface of the electrodes; in other words due to the difference between the apparent and true surface areas. The double layer capacitance values of the electrodes seem to subsume adsorption capacitances and diffusion factors. Hence, the relative increase in magnitude. The electrodes appear to behave like planar electrodes when 10 µF is introduced into the circuit as a parallel capacitance since angles 0 vary between 40–58°. The undoped -MnO2 electrode, as well as those prepared from Li-MnO2, Ag-MnO2, and I.C.8, appear to be planar electrodes.  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