首页 | 官方网站   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   3033篇
  免费   2篇
工业技术   3035篇
  2022年   3篇
  2020年   2篇
  2017年   3篇
  2016年   2篇
  2015年   1篇
  2014年   2篇
  2013年   9篇
  2012年   4篇
  2011年   3篇
  2010年   3篇
  2009年   2篇
  2007年   4篇
  2006年   1篇
  2005年   2篇
  2004年   1篇
  2003年   2篇
  2002年   8篇
  2001年   3篇
  2000年   2篇
  1999年   86篇
  1998年   825篇
  1997年   452篇
  1996年   291篇
  1995年   186篇
  1994年   125篇
  1993年   198篇
  1992年   34篇
  1991年   39篇
  1990年   38篇
  1989年   54篇
  1988年   45篇
  1987年   47篇
  1986年   46篇
  1985年   49篇
  1984年   1篇
  1983年   3篇
  1982年   13篇
  1981年   34篇
  1980年   32篇
  1979年   2篇
  1978年   7篇
  1977年   106篇
  1976年   246篇
  1975年   14篇
  1963年   1篇
  1955年   4篇
排序方式: 共有3035条查询结果,搜索用时 953 毫秒
41.
42.
43.
We conducted a retrospective review of 155 spinal operations at our institution to determine the efficacy of intraoperative salvage. Addition of intraoperative salvage had little effect on the success of a preoperative autologous donation program. Only patients with operative blood loss > 2,000 ml (12% of patients) benefited from this expensive source of autologous blood. The technique tended to be most effective in children aged 16-18 years. Use of intraoperative salvage for all pediatric spinal procedures is neither necessary nor cost effective.  相似文献   
44.
The National Cancer Institute's program to help dentists reduce tobacco use among their patients is part of the Community Intervention Trial for Smoking Cessation, a 22-community, randomly controlled trial of an intervention program for smoking cessation. Results of COMMIT baseline surveys of dentists in the 11 intervention communities are presented.  相似文献   
45.
46.
Molecular analysis of cellulose biosynthesis in Arabidopsis   总被引:1,自引:0,他引:1  
Cellulose, an abundant, crystalline polysaccharide, is central to plant morphogenesis and to many industries. Chemical and ultrastructural analyses together with map-based cloning indicate that the RSW1 locus of Arabidopsis encodes the catalytic subunit of cellulose synthase. The cloned gene complements the rsw1 mutant whose temperature-sensitive allele is changed in one amino acid. The mutant allele causes a specific reduction in cellulose synthesis, accumulation of noncrystalline beta-1,4-glucan, disassembly of cellulose synthase, and widespread morphological abnormalities. Microfibril crystallization may require proper assembly of the RSW1 gene product into synthase complexes whereas glucan biosynthesis per se does not.  相似文献   
47.
In enteric bacteria, chromosomally encoded permeases specific for lactose, maltose, and melibiose are allosterically regulated by the glucose-specific enzyme IIA of the phosphotransferase system. We here demonstrate that the plasmid-encoded raffinose permease of enteric bacteria is similarly subject to this type of inhibition.  相似文献   
48.
The effects of not breastfeeding on mortality due to diarrhea and acute lower respiratory infection (ALRI) in children under 2 years of age were examined using data from a 1988-1991 longitudinal study of 9,942 children in Metro Cebu, The Philippines. Cox regression methods were used to study the magnitude of the risks, possible interactions with birth weight and nutritional status, and the effect of additional confounding factors. Not breastfeeding had a greater effect on diarrheal mortality than on ALRI mortality. In the first 6 months of life, failing to initiate breastfeeding or ceasing to breastfeed resulted in an 8- to 10-fold increase in the rate of diarrheal mortality. The rate of mortality associated with both ALRI and diarrhea was increased nearly six times by not breastfeeding, but the rate of ALRI mortality alone was not increased. The data also suggested that the risk of mortality associated with not breastfeeding was greater for low birth weight infants and infants whose mothers had little formal education. After age 6 months, the protective effects of breastfeeding dropped dramatically. These findings underscore the importance of promoting breastfeeding, especially during the first 6 months of life, and of targeting high risk groups such as low birth weight babies and those of low socioeconomic status.  相似文献   
49.
We recently diagnosed subcutaneous fat necrosis in a newborn female infant using fine needle aspiration cytology. The neonate had perinatal asphyxia and her mother a difficult labor, but otherwise the neonate was well developed and healthy and within a few days developed well-defined areas of subcutaneous induration all over. On cytologic examination of the aspirated material, many necrotizing fat cells were found with refractile, needle-shaped crystals arranged in a sheaflike or starburst pattern. Subcutaneous fat necrosis of the newborn is uncommon today, and although the histologic findings from excised tissue are known, this appears to be the first case in which the diagnosis was possible from a sample of fine needle aspirate.  相似文献   
50.
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-23

京公网安备 11010802026262号