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   3227篇
  免费   13篇
  国内免费   13篇
电工技术   17篇
综合类   12篇
化学工业   37篇
金属工艺   21篇
机械仪表   11篇
建筑科学   14篇
矿业工程   1篇
能源动力   6篇
轻工业   74篇
水利工程   2篇
石油天然气   2篇
无线电   3篇
一般工业技术   42篇
冶金工业   2970篇
自动化技术   41篇
  2023年   2篇
  2022年   10篇
  2021年   9篇
  2020年   5篇
  2019年   4篇
  2018年   3篇
  2017年   4篇
  2015年   11篇
  2014年   6篇
  2013年   43篇
  2012年   23篇
  2011年   17篇
  2010年   15篇
  2009年   22篇
  2008年   15篇
  2007年   13篇
  2006年   6篇
  2005年   9篇
  2004年   4篇
  2003年   10篇
  2001年   2篇
  2000年   2篇
  1999年   98篇
  1998年   930篇
  1997年   563篇
  1996年   349篇
  1995年   170篇
  1994年   143篇
  1993年   206篇
  1992年   25篇
  1991年   12篇
  1990年   21篇
  1989年   17篇
  1988年   20篇
  1987年   18篇
  1986年   18篇
  1985年   20篇
  1983年   9篇
  1982年   15篇
  1981年   20篇
  1980年   26篇
  1979年   2篇
  1978年   12篇
  1977年   94篇
  1976年   208篇
  1975年   7篇
  1973年   2篇
  1964年   1篇
  1955年   4篇
  1954年   1篇
排序方式: 共有3253条查询结果,搜索用时 0 毫秒
941.
We present a force plate system which measures low-magnitude vertical reaction forces generated by small laboratory animals. The force plate mechanical design minimizes radiated transverse waves, acoustic reverberation, and standing waves caused by impacts on the force plate surface. A secondary force plate and PC-based software algorithm minimize floor vibrational artifact. The force plate was used to measure function of rats during two tests: forelimb/hindlimb hopping reaction and surface righting reaction. In control rats, forelimb hopping rate exceeded hindlimb hopping rate during 16 weeks of repeated testing. Subchronic intraperitoneal (i.p.) dosing of 10 mg/kg/day acrylamide produced a selective impairment of hindlimb hopping. In contrast, single doses of haloperidol (1-5 mg/kg, i.p.) slowed the righting reaction and produced a relatively selective impairment of forelimb hopping. The force plate system presents new opportunities for performing quantitative neurological assessments of small laboratory animals when previously such tests had been performed subjectively and qualitatively.  相似文献   
942.
943.
We present a case of microlaryngoscopy in a patient with an unexpectedly difficult airway. The airway was managed by using an oesophageal-tracheal Combitube (Kendall-Sheridan, Argyle, NY) (ETC) and a fibre-optic bronchoscope (Pentax-Japan-5 mm).  相似文献   
944.
945.
946.
OBJECTIVE: To investigate the alterations in autonomic control of heart rate at high altitude and to test the hypothesis that hypoxaemic stress during exposure to high altitude induces non-linear, periodic heart rate oscillations, similar to those seen in heart failure and the sleep apnoea syndrome. SUBJECTS: 11 healthy subjects aged 24-64. MAIN OUTCOME MEASURES: 24 hour ambulatory electrocardiogram records obtained at baseline (1524 m) and at 4700 m. Simultaneous heart rate and respiratory dynamics during 2.5 hours of sleep by fast Fourier transform analysis of beat to beat heart rate and of an electrocardiographically derived respiration signal. RESULTS: All subjects had resting hypoxaemia at high altitude, with an average oxyhaemoglobin saturation of 81% (5%). There was no significant change in mean heart rate, but low frequency (0.01-0.05 Hz) spectral power was increased (P < 0.01) at high altitude. Time series analysis showed a complex range of non-linear sinus rhythm dynamics. Striking low frequency (0.04-0.06 Hz) heart rate oscillations were observed during sleep in eight subjects at high altitude. Analysis of the electrocardiographically derived respiration signal indicated that these heart rate oscillations correlated with low frequency respiratory oscillations. CONCLUSIONS: These data suggest (a) that increased low frequency power during high altitude exposure is not simply attributable to increased sympathetic modulation of heart rate, but relates to distinctive cardiopulmonary oscillations at approximately 0.05 Hz and (b) that the emergence of periodic heart rate oscillations at high altitude is consistent with an unstable cardiopulmonary control system that may develop on acute exposure to hypoxaemic stress.  相似文献   
947.
Microwave effects on drosophila morphogenesis were studied. Drosophila embryo were exposed by continuous wave 460 MHz at SAR = 1-5 Wt/kg. It was found that irradiation induced some morphosis such as imago legs and wings form alterations. These effects depended on embryo age, SAR and period exposure. It was proposed that the local microwave heating is responsible for describe effects.  相似文献   
948.
The lymphocyte blast transformation test (LBTT) with three tuberculin dilutions was used to examine 190 patients with varying pulmonary tuberculosis activity, of them 63 patients received chemotherapy. According to the blast formation in the patients' cultured peripheral blood cells by three tuberculin dilutions, a correlation was found between the clinical manifestations of the process and the functional activity of T lymphocytes. Thus, the greatest percentage (500 TU) of blasts in LBTT per mean PPD dose was detectable in patients with low LBTT results by three tuberculin dilutions with positive dynamics during chemotherapy. With further positive dynamics, the proportion of blasts in the cultured peripheral blood cells was highest per high PPD doses (5000 TU). On the contrary, patients with progressive tuberculosis displayed a oppositely directed phasic pattern.  相似文献   
949.
LA Gaudette  A Richardson  S Huang 《Canadian Metallurgical Quarterly》1998,10(3):35-45 (ENG); 35-47 (FRE)
OBJECTIVES: This article examines differences by occupation in daily cigarette smoking prevalence and intensity among full-time workers, and how these differences are associated with smoking restrictions at work. DATA SOURCES: Most of the data are from a Health Canada-sponsored Supplement to the 1994/95 National Population Health Survey (NPHS). The analysis is based on 5,674 respondents aged 15 to 64 who were full-time workers at the time of their interview. Comparable information is presented from the 1978/79 Canada Health Survey and the 1986 Labour Force Survey Smoking Supplement. MAIN RESULTS: In 1994/95, 28% of full-time workers were daily smokers, and about a third of them smoked 25 or more cigarettes a day. Smoking prevalence and intensity were lowest among white-collar workers and highest among blue-collar workers. Since 1978/79, there has been an overall decline in smoking prevalence, and since 1986, a decline in smoking intensity among all workers except those in outdoor blue-collar occupations. About 6 in 10 full-time workers who smoked daily encountered restrictions at work.  相似文献   
950.
We have compared the ability of two mammalian Notch homologs, mouse Notchl and Notch2, to inhibit the granulocytic differentiation of 32D myeloid progenitor cells. 32D cells undergo granulocytic differentiation when stimulated with either granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF). Expression of the activated intracellular domain of Notch1 inhibits the differentiation induced by G-CSF but not by GM-CSF; conversely, the corresponding domain of Notch2 inhibits differentiation in response to GM-CSF but not to G-CSF. The region immediately C-terminal to the cdc10 domain of Notch confers cytokine specificity on the cdc10 domain. The cytokine response patterns of Notch1 and Notch2 are transferred with this region, which we have termed the Notch cytokine response (NCR) region. The NCR region is also associated with differences in posttranslational modification and subcellular localization of the different Notch molecules. These findings suggest that the multiple forms of Notch found in mammals have structural differences that allow their function to be modulated by specific differentiation signals.  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