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   4474篇
  免费   211篇
  国内免费   3篇
电工技术   58篇
化学工业   1315篇
金属工艺   146篇
机械仪表   78篇
建筑科学   93篇
矿业工程   12篇
能源动力   134篇
轻工业   573篇
水利工程   10篇
石油天然气   9篇
无线电   96篇
一般工业技术   678篇
冶金工业   1063篇
原子能技术   23篇
自动化技术   400篇
  2023年   37篇
  2022年   172篇
  2021年   277篇
  2020年   99篇
  2019年   88篇
  2018年   158篇
  2017年   155篇
  2016年   170篇
  2015年   125篇
  2014年   170篇
  2013年   287篇
  2012年   183篇
  2011年   230篇
  2010年   156篇
  2009年   137篇
  2008年   123篇
  2007年   130篇
  2006年   77篇
  2005年   62篇
  2004年   65篇
  2003年   55篇
  2002年   47篇
  2001年   30篇
  2000年   32篇
  1999年   28篇
  1998年   186篇
  1997年   207篇
  1996年   141篇
  1995年   96篇
  1994年   47篇
  1993年   71篇
  1992年   22篇
  1991年   13篇
  1990年   19篇
  1989年   20篇
  1988年   19篇
  1987年   15篇
  1986年   16篇
  1985年   20篇
  1984年   33篇
  1983年   24篇
  1982年   43篇
  1981年   50篇
  1980年   56篇
  1979年   29篇
  1978年   41篇
  1977年   110篇
  1976年   242篇
  1975年   15篇
  1973年   13篇
排序方式: 共有4688条查询结果,搜索用时 12 毫秒
971.
972.
973.
974.
975.
976.
To study the mechanisms of dorsal axis specification, the alteration in dorsal cell fate of cleavage stage blastomeres in axis-respecified Xenopus laevis embryos was investigated. Fertilized eggs were rotated 90 degrees with the sperm entry point up or down with respect to the gravitational field. At the 8-cell stage, blastomeres were injected with the lineage tracers, Texas Red- or FITC-Dextran Amines. The distribution of the labeled progeny was mapped at the tail-bud stages (stages 35-38) and compared with the fate map of an 8-cell embryo raised in a normal orientation. As in the normal embryos, each blastomere in the rotated embryos has a characteristic and predictable cell fate. After 90 degrees rotation the blastomeres in the 8-cell stage embryo roughly switched their position by 90 degrees, but the fate of the blastomeres did not simply show a 90 degrees switch appropriate for their new location. Four types of fate change were observed: (i) the normal fate of the blastomere is conserved with little change; (ii) the normal fate is completely changed and a new fate is adopted according to the blastomere's new position: (iii) the normal fate is completely changed, but the new fate is not appropriate for its new position; and (4) the blastomere partially changed its fate and the new fate is a combination of its original fate and a fate appropriate to its new location. According to the changed fates, the blastomeres that adopt dorsal fates were identified in rotated embryos. This identification of dorsal blastomeres provides basic important information for further study of dorsal signaling in Xenopus embryos.  相似文献   
977.
In the recent years the number of diagnosed cases of Lyme Disease has tended to increase. This is due to the possibility of serological examinations. Between 1992-95 at the Neurological Department of 2nd Chair of Pediatrics Silesian Medical Academy in Katowice 7 children with Lyme Disease were hospitalized. The authors analysed the clinical course, important laboratory and serological data and treatment effects.  相似文献   
978.
979.
The incidence of bladder cancer continues to increase, with an estimated 53,000 new cases diagnosed in the United States in 1996-90% of which are transitional cell carcinomas. The male-to-female ratio is 3:1. A number of etiological factors are associated with the development of bladder cancer, but in industrialized countries, cigarette smoking is the most important. Specific chemicals have also been identified as causing bladder cancer, as have a number of occupational exposures to less well-defined specific agents. Treatment with cytostatic drugs, especially cyclophosphamide, is associated with increased risk of bladder cancer, as is treatment with radiotherapy for uterine cancer. In developing countries, especially in the Middle East and parts of Africa, infections with members of the genus Schistosoma are responsible for a high incidence of bladder cancer-75% of which are squamous cell carcinomas. Arsenic has been indicated as a bladder carcinogen in Argentina, Chile, and Taiwan. The reason for the high incidence of urinary tract cancer in individuals suffering from Balkan nephropathy has yet to be determined. A careful history of patients with bladder cancer is an important and useful process in helping to identify causal factor and, in more than one-half the cases, a known relationship is found. Bladder cancer is a potentially preventable disease, with a significant morbidity and mortality in many parts of the world.  相似文献   
980.
We presented in our study methods and results of blood flow measurements with Doppler ultrasound in uterine and arcuate arteries in relation to localization of placenta in physiological pregnancy. We performed examinations in 154 pregnant women with pregnancy age of 32-42 wk. On the basis of qualitative analysis of blood flow waveforms we discovered the difference in the blood flow in utero-placental compartment in relation to placental localization and we proved that this change takes place in uterine as well an in arcuate arteries.  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