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   222736篇
  免费   3170篇
  国内免费   646篇
电工技术   3768篇
综合类   183篇
化学工业   34310篇
金属工艺   8403篇
机械仪表   6506篇
建筑科学   6073篇
矿业工程   1396篇
能源动力   5712篇
轻工业   18819篇
水利工程   2502篇
石油天然气   4109篇
武器工业   8篇
无线电   24727篇
一般工业技术   44166篇
冶金工业   41427篇
原子能技术   5271篇
自动化技术   19172篇
  2021年   2136篇
  2020年   1492篇
  2019年   1974篇
  2018年   3075篇
  2017年   3082篇
  2016年   3375篇
  2015年   2320篇
  2014年   3781篇
  2013年   10269篇
  2012年   6133篇
  2011年   8426篇
  2010年   6617篇
  2009年   7300篇
  2008年   7526篇
  2007年   7525篇
  2006年   6463篇
  2005年   5937篇
  2004年   5701篇
  2003年   5496篇
  2002年   5043篇
  2001年   5052篇
  2000年   4917篇
  1999年   5100篇
  1998年   12067篇
  1997年   8629篇
  1996年   6820篇
  1995年   5060篇
  1994年   4618篇
  1993年   4409篇
  1992年   3471篇
  1991年   3253篇
  1990年   3119篇
  1989年   3188篇
  1988年   3022篇
  1987年   2601篇
  1986年   2510篇
  1985年   2965篇
  1984年   2711篇
  1983年   2556篇
  1982年   2285篇
  1981年   2385篇
  1980年   2179篇
  1979年   2306篇
  1978年   2273篇
  1977年   2532篇
  1976年   3405篇
  1975年   1979篇
  1974年   1874篇
  1973年   1866篇
  1972年   1523篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
91.
PURPOSE: To develop risk-based recommendations for mammographic screening for women in their 40s that take into account the woman's age, race, and specific risk factors. METHODS: We assumed that regular mammographic screening is justified for a 50-year-old woman, even one with no risk factors, and that a younger woman with an expected 1-year breast cancer incidence rate as great or greater than that of a 50-year-old woman with no risk factors would benefit sufficiently to justify regular screening. Recommendations under this criterion were based on age- and race-specific breast cancer incidence rates from the National Cancer Institute's (NCI's) Surveillance, Epidemiology, and End Results (SEER) Program; assessments of risk factors from the Breast Cancer Detection and Demonstration Project (BCDDP); and reports in the literature. RESULTS: Two methods, the exact-age procedure (EAP) and the grouped-age procedure (GAP), were developed. The less precise GAP only requires following a flow diagram. The proportion of white women recommended for screening by the EAP ranges from 10% for 40-year-old women to 95% for 49-year-old women, and the corresponding percentages for black women are 16% and 95%. The assumptions that underlie the guidelines are discussed critically. CONCLUSION: For women or physicians who prefer an individualized approach in deciding whether to initiate regular mammographic screening in the age range of 40 to 49 years, the present report offers recommendations based on individualized risk-factor data and clearly stated assumptions that have an empiric basis. These recommendations can be used to facilitate the counseling process.  相似文献   
92.
93.
94.
Chewing and acid on the tongue evoked a flow of saliva from the duct-cannulated parotid gland of the conscious rat despite pretreatment with atropine and adrenoceptor antagonists. This non-adrenergic, non-cholinergic (NANC) response depended on an intact parasympathetic innervation and was abolished by a tachykinin antagonist. The present findings are consistent with a physiological role for the secretory NANC mechanisms of the salivary glands.  相似文献   
95.
The electrochemical and corrosion behaviour of a nickel base super alloy (C-263) has been investigated in the deaerated binary and ternary solution mixture of concentrated phosphoric acid, acetic acid, sulphuric acid, nitric acid or water using potentiostatic technique at 35°C. The possibilities of electropolishing of this alloy in these solution mixtures have been also explored. The alloy showed distinct active, passive and transpassive behaviour in the experimental solutions. The alloy remained active and turned passive in the negative potential region. Transpassive dissolution of the alloy is observed and electropolishing is achieved in this region. The best electropolishing is obtained in 50% H3PO4 + 40% CH3COOH + 10% H2SO4. Higher content of water in the electrolytic solution is not useful for electropolishing of the alloy The experimental results also suggest that a current plateau in the transpassive potential region is not a sufficient condition to achieve electropolishing.  相似文献   
96.
97.
OBJECTIVES: To assess that neuromuscular relaxation onset of the adductor pollicis (AP) is related to neuromuscular stimulation rate. To assess that train-of-four (TOF) at 0.05 Hz is a more accurate indicator of optimal tracheal intubation time and conditions, than TOF at 0.08 Hz. STUDY DESIGN: Prospective, comparative, randomized double-blind study. PATIENTS: Forty adults, physical class ASA 1 or 2, undergoing general anaesthesia with tracheal intubation were allocated to two groups (n = 20) according to the sequence of stimulation of the AP: either TOF at 0.05 Hz (test group) or TOF at 0.08 Hz (control group). METHODS: Induction of anaesthesia was achieved with thiopentone, fentanyl and vecuronium (0.1 mg.kg-1). Neuromuscular monitoring was obtained with force displacement transducers attached to each AP. Tracheal intubation was performed once AP muscular response obtained with TOF at 0.05 Hz for test group and TOF at 0.08 Hz for control group was abolished. Results are expressed as mean +/- SEM. Fisher exact test was used for intubation conditions comparison. Curarization time between groups was compared with unpaired Student's t test (P < 0.05 accepted). RESULTS: TOF with 0.05 Hz stimulation significantly increased curarization time: 217 +/- 7 versus 162 +/- 6 s (P < 0.001). Intubation conditions were excellent in 95% and good in 5% of patients in the study group, compared to 15 and 40% in the control group, respectively (P < 0.01) in 45% of the control group patients coughing at intubation occurred. CONCLUSION: Low stimulation rate (TOF at 0.05 Hz) of AP is a reliable technique to determine the appropriate intubation time for patients paralyzed with vecuronium.  相似文献   
98.
99.
100.
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