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   6083篇
  免费   39篇
  国内免费   1篇
电工技术   45篇
综合类   2篇
化学工业   527篇
金属工艺   36篇
机械仪表   59篇
建筑科学   140篇
矿业工程   4篇
能源动力   59篇
轻工业   223篇
水利工程   28篇
石油天然气   3篇
无线电   361篇
一般工业技术   466篇
冶金工业   3783篇
原子能技术   35篇
自动化技术   352篇
  2021年   31篇
  2019年   22篇
  2018年   39篇
  2017年   35篇
  2016年   31篇
  2015年   18篇
  2014年   46篇
  2013年   161篇
  2012年   67篇
  2011年   100篇
  2010年   82篇
  2009年   80篇
  2008年   102篇
  2007年   94篇
  2006年   81篇
  2005年   90篇
  2004年   77篇
  2003年   79篇
  2002年   68篇
  2001年   71篇
  2000年   64篇
  1999年   155篇
  1998年   1099篇
  1997年   636篇
  1996年   428篇
  1995年   282篇
  1994年   240篇
  1993年   267篇
  1992年   80篇
  1991年   76篇
  1990年   105篇
  1989年   96篇
  1988年   92篇
  1987年   87篇
  1986年   78篇
  1985年   74篇
  1984年   43篇
  1983年   43篇
  1982年   36篇
  1981年   54篇
  1980年   70篇
  1979年   38篇
  1978年   28篇
  1977年   118篇
  1976年   238篇
  1975年   28篇
  1974年   24篇
  1973年   18篇
  1972年   19篇
  1971年   18篇
排序方式: 共有6123条查询结果,搜索用时 15 毫秒
41.
An investigation into a system linking a computer solid modeler to an active stereo imaging inspection station is presented. Given the computer solid model of a surface, a projected pattern can be encoded so that the reflections from the object's surface exhibit a uniformly simple pattern when the object's surface and the modeled surface are identical. Research concerning the method of generating projection patterns, as well as the sensitivity of the system, is discussed. A prototype system consisting of a computer graphics workstation; a flexible projector, and a machine vision system was used to inspect two different manufactured parts  相似文献   
42.
43.
This article is a discussion of the use of narrow-band light sources coupled with cameras equipped with band-pass filters to document patterned injuries on human skin. Several case reports are included.  相似文献   
44.
45.
1. Effects of feeding condition from birth were examined on the sensitivity of neuromuscular transmission to d-tubocurarine (dTc) in vitro in male mice of the ddY strain. 2. Mice were trained to climb two separated cylindrical steel-wire tubes for feeding and drinking, respectively, from 16 days of age. Some mice were conventionally fed, from 99 days of age. Nerve-muscle preparations were made from the left phrenic nerve diaphragm muscle (DPH), the sciatic nerve soleus muscle (SOL), and the sciatic nerve extensor digitorum longus muscle (EDL) of 99-day-old and 155-day-old mice. The nerve trunk was electrically activated with trains of four pulses and tetanic pulses. 3. The sensitivity to the effects of dTc decreased in the order EDL, SOL, and DPH. This result held true in all mice tested. 4. This sensitivity was significantly potentiated by the compulsory movement. 5. The supersensitivity remained even when mice were conventionally fed after 99 days of age. 6. The compulsion rendered EDL antifatigable on tetanic stimulation. This property was also retained after a return to conventional feeding. 7. These results suggest that the effects of feeding condition from birth might remain on neuromuscular functions after termination of the conditioning.  相似文献   
46.
Two international trials of potential biomass species families and clones planted in 1985 have been analyzed to determine changing patterns in growth, diseases, and insects. In the Swedish trial, with close spacing and short rotations, Salix viminalis clones gave the best average yield of 17.4 Mg/Ha/yr on the first coppice rotation. In the Minnesota, USA trial, with wider spacings and a longer rotation Populus alba hybrid clones gave the best average yields of 5.5 Mg/Ha/yr. The most important disease and insect problems encountered were Septoria musiva stem cankers on some Populus clones; frost die back in some Salix clones; and the leaf blotch miner, Fenusa dohrnii, on most Alnus families. Recommendations for future international cooperation in field trials are presented.  相似文献   
47.
48.
A multi-technique approach, incorporating nuclear magnetic resonance (NMR), elemental analysis, differential scanning calorimetry (DSC), thermogravimetric analysis and surface area determination, has been used to investigate the formation of chars by oxidized cellulose. It was found that oxidation of the cellulose tends to increase the surface area of the resulting char. NMR, elemental analysis and DSC show how cellulose oxidation tends to increase aromaticity and cross-linking. This, in turn, decreases diffusion rates of volatiles out of the oxidized cellulose during pyrolysis, giving denser carbons and higher BET surface areas.  相似文献   
49.
A nation-wide cross-sectional survey of 816 children 3-4 years old was carried out in The Gambia between September 1990 and July 1991 to assess the seroprevalence of antibodies against 3 diseases included in the expanded programme on immunization: measles, poliomyelitis and tetanus. Among 689 children whose records were available, 94.5% were fully immunized. Measles vaccine was administered to 97% of the children and 91% of these had detectable antibodies at the time of the survey. Antibodies against type 1 and type 3 polioviruses, after up to 6 doses of oral polio vaccine, were present in 88.1% and 89.3% of the children respectively. Ninety-seven percent of the children who had received 4 doses of diphtheria-pertussis-tetanus vaccine (DPT) and 91% of those who received 3 doses had detectable tetanus toxoid antibodies at the age of 3-4 years. This study shows that serological responses to EPI vaccines given in infancy persist at very satisfactory levels throughout early childhood.  相似文献   
50.
Exp I, with 12 male hooded rats, demonstrated that Ss with caudate-putamen lesions exhibited an impairment in the acquisition and reversal of a spatial maze task when compared with unoperated control Ss. Exp II, with 24 Ss, investigated leverpress responding supported by a VI schedule in 3 groups of Ss: a group with caudate-putamen lesions, a group with lesions of the posterior cortex, and an unoperated control group. The presentation of a 0.5-sec, response-contingent light correlated with reinforcement generated an elevated response rate in the 2 operated groups but tended to suppress responding in the control group, perhaps by overshadowing the response–reinforcer relation. Only the group with cortical lesions maintained the elevated rate when the light was uncorrelated with food delivery. Exp III confirmed for these same Ss that caudate-putamen lesions produced a spatial learning deficit. No deficit was observed in the posterior cortex group. It is suggested that caudate-putamen lesions disrupt the mechanism underlying the response–reinforcer association on which spatial maze learning and free operant responding in part depend. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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