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   531890篇
  免费   7427篇
  国内免费   1483篇
电工技术   9632篇
综合类   528篇
化学工业   80235篇
金属工艺   20104篇
机械仪表   15323篇
建筑科学   12911篇
矿业工程   2281篇
能源动力   14735篇
轻工业   47652篇
水利工程   5279篇
石油天然气   9357篇
武器工业   43篇
无线电   60402篇
一般工业技术   103112篇
冶金工业   104179篇
原子能技术   10596篇
自动化技术   44431篇
  2022年   3261篇
  2021年   5030篇
  2020年   3611篇
  2019年   4668篇
  2018年   7968篇
  2017年   7778篇
  2016年   8147篇
  2015年   5705篇
  2014年   9476篇
  2013年   24613篇
  2012年   15006篇
  2011年   20615篇
  2010年   16116篇
  2009年   18011篇
  2008年   18509篇
  2007年   18136篇
  2006年   15817篇
  2005年   14472篇
  2004年   13841篇
  2003年   13600篇
  2002年   12809篇
  2001年   12940篇
  2000年   11951篇
  1999年   12693篇
  1998年   32914篇
  1997年   22984篇
  1996年   17533篇
  1995年   13115篇
  1994年   11380篇
  1993年   11040篇
  1992年   7971篇
  1991年   7465篇
  1990年   7303篇
  1989年   7068篇
  1988年   6508篇
  1987年   5789篇
  1986年   5683篇
  1985年   6299篇
  1984年   5935篇
  1983年   5194篇
  1982年   4921篇
  1981年   5001篇
  1980年   4725篇
  1979年   4628篇
  1978年   4431篇
  1977年   5345篇
  1976年   6978篇
  1975年   3805篇
  1974年   3570篇
  1973年   3679篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Basal cell carcinoma (BCC) is the most common type of skin cancer and the incidence of BCC is expected to rise, with increased demand on dermatology resources. Little is known of the effect on people's lives of having skin cancer. The aim of this study was to quantify the handicap caused gy basal cell carcinomas before and after therapy. Forty-four patients (22 males, mean age = 65 yrs, range = 35-81 yrs) with 48 BCCs were recruited and 37 patients completed the study. Each patient completed the UK Sickness Impact Profile (UKSIP) and the Dermatology Life Quality Index (DLQI) at the initial visit to the dermatology clinic, 1 week after treatment and 3 months after treatment. Lesions had been present for a mean of 25 months (range = 1-240 months), their mean diameter was 9.6mm (range = 3-35mm) and the sites were head and neck (79%), trunk (17%) and limbs (4%). There was no relationship between the quality of life score and size of lesion. Overall the scores at presentation were very low, rising 1 week after treatment and falling to below the initial scores at 3 months (mean UKSIP 0.4%, 0.7%, 0.13%; mean DLQI 5.3% 8.7%, 1.2%). BCCs cause little handicap. This may explain the delay in seeking medical attention and should be considered in planning public health education about BCCs.  相似文献   
993.
The growth in the number of dialysis patients in Canada is causing a critical shortage of resources. The low transplantation rate and an increase in the number of patients, combined with insufficient funding to expand facilities, threatens access to the expensive but life-sustaining therapy. Michel Martin, who recently underwent a kidney transplant, looks at the situation facing dialysis patients in Quebec and Ontario.  相似文献   
994.
In node-positive breast carcinoma, the presence of tumour cells in the efferent vessels (EV) of the axillary nodes (positive EV status) was shown to be of poor prognosis in 1979. Later the presence of nodal micrometastases was also related to survival. This report describes a new subgroup in this system that is of potential therapeutic interest. It consisted of the 40% of the EV-positive cases with micrometastases (< 0.2 cm2) in their nodes, in addition to nodes with macrometastases. In them the difference in prognosis associated with EV status no longer held. Their prognosis did not differ markedly from that in the EV-negative patients. In the absence of such 'additional' micrometastases, the prognostic difference was still highly significant. There was also some indication that the presence of micrometastases consisting of embolic tumour growth alone may be associated with early death in EV-negative cases, in keeping with the prognosis in cases with lone micrometastases.  相似文献   
995.
996.
The enhancement effects of some chemicals on the percutaneous absorption of alprazolam through human skin was investigated in vitro. Linoleic acid, oleic acid, Comperlan F® (linoleic acid diethanolamide), Comperlan KD® (coconut fatty acid diethanolamide) and Ethomeen C12® (bis-(2-hydroxyethyl)cocamine) were evaluated for their enhancing effect either as neat solvents or combined with propylene glycol. The effects of skin pretreatment with the enhancers on the percutaneous absorption of alprazolam from a drug suspension in an aqueous gel were also investigated: skin pretreatment with some enhancers has shown potentially interesting aspects. The determination of alprazolam partitioning into untreated and pretreated horny layer supported the idea that, with oleic and linoleic acid, a contribution to the modification of the diffusional resistance of the skin was given by an increase of the drug solubility in the stratum coraeum.  相似文献   
997.
998.
999.
1000.
This paper presents observations regarding the cracking behavior of tensile-loaded structural adhesive joints. Experiments showed that fracture occurred by the development and propagation of a damage zone, rather than a single, sharp crack, and that the presence of the adhesive spew fillet did not affect the fracture load of the adhesive joints studied. For joints bonded with the mineral-filled epoxy Cybond 4523GB (American Cyanamid), there was approximately 5 mm of subcritical crack propagation prior to final fracture. Fracture-load predictions based on the initial uncracked geometry made in previous papers were unaffected by this small change in geometry. For joints bonded with the rubber-toughened epoxy Permabond ESP 310, approximately 50 mm of subcritical crack propagation was observed. It was again found that predictions made in previous papers on the basis of the initial geometry gave a good estimate of the final fracture load even though this subcritical crack propagation significantly altered the geometry, and thus the applied energy release rates. The effect of shear deformations of the adherends was also investigated, and it was found that shear deformations could be neglected in engineering calculations for joints subject to remote tensile loading.  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