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   58031篇
  免费   3400篇
  国内免费   83篇
电工技术   421篇
综合类   133篇
化学工业   12717篇
金属工艺   1092篇
机械仪表   1194篇
建筑科学   1744篇
矿业工程   135篇
能源动力   1315篇
轻工业   10239篇
水利工程   567篇
石油天然气   292篇
武器工业   7篇
无线电   2367篇
一般工业技术   9335篇
冶金工业   11617篇
原子能技术   248篇
自动化技术   8091篇
  2024年   120篇
  2023年   526篇
  2022年   1027篇
  2021年   1703篇
  2020年   1248篇
  2019年   1401篇
  2018年   2235篇
  2017年   2213篇
  2016年   2340篇
  2015年   1702篇
  2014年   2222篇
  2013年   4558篇
  2012年   3541篇
  2011年   3423篇
  2010年   2777篇
  2009年   2503篇
  2008年   2405篇
  2007年   2148篇
  2006年   1589篇
  2005年   1335篇
  2004年   1189篇
  2003年   1167篇
  2002年   1009篇
  2001年   793篇
  2000年   716篇
  1999年   777篇
  1998年   3698篇
  1997年   2453篇
  1996年   1609篇
  1995年   951篇
  1994年   745篇
  1993年   793篇
  1992年   313篇
  1991年   278篇
  1990年   219篇
  1989年   234篇
  1988年   243篇
  1987年   213篇
  1986年   175篇
  1985年   214篇
  1984年   190篇
  1983年   134篇
  1982年   168篇
  1981年   193篇
  1980年   216篇
  1979年   103篇
  1978年   102篇
  1977年   353篇
  1976年   740篇
  1973年   94篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Rolandic discharge (RD), noted in the electroencephalography (EEG) of patients with benign epilepsy in childhood with centrotemporal spikes (BECCT) has several unique features. One feature is that the amount or frequency of RDs does not correlate well with the incidence of seizures in BECCT although it is a key finding in the diagnosis of this epileptic syndrome. In this study, we examined the efficacy of antiepileptic drugs focusing on the disappearance of RDs in relationship with seizure control. Forty patients with BECCT who were not medically treated prior to this study were randomly sorted into three groups. Twenty patients were assigned for clonazepam (CZP) treatment, 10 patients for valproate (VPA) and the remaining 10 patients for carbamazepine (CBZ). Each drug was administered for 4 consecutive weeks. EEGs were recorded twice during the study, before and 4 weeks after the medication trial. The effects of each treatment on RDs were assessed. RDs disappeared in 15 of the 20 cases treated with CZP (75%) within 4 weeks while the same was observed in only one of the 10 cases treated with VPA (10%). CBZ failed to demonstrate any effect on RD. In the group treated with CZP, there were no differences in seizure incidence, seizure type and blood concentration of CZP between the patients whose RDs disappeared and those whose RDs remained.  相似文献   
102.
Gamma delta T-Cells represent a minor subpopulation of T-lymphocytes in man and their role in normal and diseased human skin is unknown. This article is a comprehensive review of T-lymphocytes bearing the gamma delta T-cell receptor in normal and pathological human skin. Firstly, we have documented the occurrence of gamma delta T-cells in normal skin and in a range of reactive and malignant skin conditions. We have then discussed the experimental findings regarding the repertoire used by gamma delta T-cells in normal human skin and in cutaneous disorders with an increased percentage of gamma delta T-cells.  相似文献   
103.
104.
105.
106.
107.
108.
109.
A cross-sectional study was performed to obtain risk factors for hepatitis B disease, HBsAg carriers and immunised personnel, among 2470 workers in a general hospital in Madrid, Spain. The data obtained were analyzed with multiple logistic regression to obtain beta coefficients for variables. The results of the analysis show that being a nurse or being regularly exposed to blood are the most important risk factors for hepatitis B acquisition. The length of time working at the same job activity was also a risk factor. The resulting beta coefficients allow the construction for a hepatitis non-immunised, HBsAg carrier and immunised HBV status, which can select subjects for a hepatitis B vaccination program.  相似文献   
110.
Si3N4powders coated with 6 wt% Y2O3and 4 wt% Al2O3were prepared by coprecipitation. The resulting powders were dispersed in water at different pH values and with addition of various amounts of ammonium polyacrylate (NH4PA) to produce 32 vol% slips. The influence of the amount of NH4PA solution added and pH on the rheological properties of 32 vol% coated Si3N4slips were studied. In addition, the sintered density of cast samples was determined and related to the degree of slip dispersion. The adsorption of the NH4PA on the coated particle surface was rather high and the surface became saturated near 0.86 mg/m2at pH 9.2. High NH4PA concentrations (1.7–3 wt%) were necessary to obtain well dispersed 32 vol% coated Si3N4slips at pH 9.2. The best stabilization was obtained with the addition of 2.3 wt% NH4PA; in this condition, the viscosity reached a minimum value of 35 mPa.s at 100 s–1. The slip viscosity increased with increasing pH from 9.2 to 10.2. Slips with low viscosities gave a more dense packing of cast samples and consequently higher sintered density values.  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