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   7280篇
  免费   30篇
  国内免费   12篇
电工技术   154篇
综合类   15篇
化学工业   461篇
金属工艺   268篇
机械仪表   350篇
建筑科学   41篇
矿业工程   82篇
能源动力   6篇
轻工业   89篇
水利工程   97篇
石油天然气   120篇
武器工业   1篇
无线电   434篇
一般工业技术   804篇
冶金工业   4109篇
原子能技术   105篇
自动化技术   186篇
  2023年   4篇
  2022年   55篇
  2021年   79篇
  2020年   67篇
  2019年   93篇
  2018年   194篇
  2017年   217篇
  2016年   260篇
  2015年   127篇
  2014年   178篇
  2013年   235篇
  2012年   173篇
  2011年   213篇
  2010年   193篇
  2009年   225篇
  2008年   191篇
  2007年   200篇
  2006年   190篇
  2005年   114篇
  2004年   70篇
  2003年   39篇
  2002年   50篇
  2001年   32篇
  2000年   97篇
  1999年   182篇
  1998年   1299篇
  1997年   789篇
  1996年   418篇
  1995年   251篇
  1994年   195篇
  1993年   211篇
  1992年   41篇
  1991年   24篇
  1990年   45篇
  1989年   39篇
  1988年   49篇
  1987年   37篇
  1986年   36篇
  1985年   38篇
  1983年   5篇
  1982年   17篇
  1981年   21篇
  1980年   28篇
  1979年   6篇
  1978年   17篇
  1977年   82篇
  1976年   154篇
  1975年   12篇
  1974年   11篇
  1973年   5篇
排序方式: 共有7322条查询结果,搜索用时 15 毫秒
81.
82.
83.
A man with double inlet left ventricle and severe subpulmonary stenosis underwent a Fontan operation at the age of 29 years. Eight years later he developed atrial flutter with complete heart block. To avoid a further thoracotomy, a unipolar carbon tipped electrode was placed into the posterior cardiac vein via the coronary sinus. More than 8 years after implantation of the original lead, and after two generator changes, telemetric thresholds remain between 1.8-2.1 volts. Percutaneous transvenous ventricular pacing via the coronary sinus can produce an excellent long-term result and should be the initial approach of choice after a Fontan-type operation.  相似文献   
84.
85.
BACKGROUND: Desflurane (difluoromethyl 1-fluoro 2,2,2-trifluoroethyl ether) is a new inhalational anesthetic currently under investigation for use in humans. Recently, the authors showed that desflurane is a trigger of malignant hyperthermia (MH) in susceptible swine. To date, there has been no in vivo comparison of the relative ability of inhalational anesthetics to trigger MH. The effects of desflurane, isoflurane, and halothane on six MH-susceptible purebred and six MH-susceptible mixed-bred Pietrain swine were examined. METHODS: The animals were exposed to 1 MAC and 2 MAC (if MH was not triggered after 1 MAC hour) doses of each of the three volatile anesthetics in random sequence at 7-10-day intervals and changes in end-tidal CO2, arterial blood gases, serum lactate, core and muscle temperature, blood pressure, and heart rate were measured. RESULTS: There was a statistical difference between anesthetics in the time required to trigger MH; halothane exposure resulted in the fastest onset of an MH episode (20 +/- 5 min), compared with isoflurane (48 +/- 24 min) and desflurane (65 +/- 28 min), both of which required significantly longer exposures. There was no statistical difference between the MH purebred and mixed-bred swine in the time required to trigger MH (defined as a PaCO2 of 70 mmHg) with a given agent, and time to triggering was also independent of the order of exposure to the three anesthetics. Malignant hyperthermia susceptibility was confirmed in ten surviving animals, by both in vivo succinylcholine challenge and in vitro contracture testing. CONCLUSIONS: Although all three volatile anesthetics triggered MH, exposure to halothane resulted in significantly shorter times to MH triggering when compared with desflurane and isoflurane.  相似文献   
86.
In male Syrian hamsters, short days induce regression of the reproductive system, but eventually spontaneous recrudescence occurs ensuing from refractoriness to the inhibitory photoperiod. Although the photoperiod of 12 L:12 D (12 h light:12 h dark) may act like a short day by inducing the testicular cycle outlined above, it may fail to evoke the increase of circulating concentrations of prolactin that accompanies testicular recrudescence. This photoperiod may fail to induce photorefractoriness, as indicated by the prolonged low concentrations of prolactin in the blood. Herein, hamsters were exposed to either 8 L:16 D or 12 L:12 D from weaning and by 28 weeks exposure to either photoperiod, the hamsters had large testes following recrudescence from a photoperiod induced-regression). Transfer to 8 L:16 D from 12 L:12 D at 28 weeks resulted in a second testicular regression and recrudescence. In a second experiment, the testes of hamsters moved to 8 L:16 D from 12 L:12 D after 29 weeks exposure to the latter photoperiod similarly regressed and then regrew. Serum concentrations of prolactin decreased in these males after transfer to the shorter daylength but also decreased in hamsters kept under 12 L:12 D both groups were usually below those of hamsters moved to 14 L:10 D. These results show that exposure for 28 or 29 weeks to 12 L:12 D was insufficient to induce photorefractoriness, despite the recrudescence of the testes following involution.  相似文献   
87.
The results of investigations performed by specialists at Research and Design Institute of Electrical Technology together with other enterprises, institutes, and organizations concerning the formulation of a strategy for the development of nuclear power in Russia in the first half of the 21st century are presented. The individual stages of the work, key assumptions, ideas, and recommendations, on which the strategy is based, the initiatives which the President of the Russian Federation advanced at the millennium summit held at the United Nations, and the international INPRO project initiated by Russia are examined. It is concluded that innovative development and a transition to building as quickly as possible nuclear power objects that meet the requirements and demands of the new century are necessary. __________ Translated from Atomnaya énergiya,Vol. 103, No. 1, pp. 5–15, July, 2007.  相似文献   
88.
89.
The influence of the internal gettering process on the large-scale defects in Czochralski-grown boron-doped single-crystal silicon is investigated by low-angle mid-infrared light scattering. The large-scale defects in the as-grown material and crystals subjected to the internal gettering procedure are classified. The applicability of low-angle light scattering in laboratory investigations and in the industrial inspection of the operations in an internal gettering production cycle is demonstrated. Fiz. Tekh. Poluprovodn. 31, 1158–1163 (October 1997)  相似文献   
90.
Meeting a person with AIDS in the classroom was evaluated to determine if it had an impact on students' perceived susceptibility to HIV infection and attitudes toward persons with AIDS. The meeting was incorporated into the Grade 9 AIDS education program of a school district in Nova Scotia. Four schools participated in this study. Two schools were randomly assigned to the treatment group, which met the person with AIDS, and the remaining two schools formed the comparison group. Measures of the two attitudinal variables were collected using a self-report questionnaire that was administered both prior to and two weeks after the educational intervention. Meeting a person with AIDS in the classroom had no measurable impact on students perceived susceptibility to HIV infection nor on their attitudes toward persons with AIDS. Suggestions for using the educational intervention more effectively and for further research are made.  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