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   53186篇
  免费   985篇
  国内免费   317篇
电工技术   657篇
综合类   632篇
化学工业   4898篇
金属工艺   1020篇
机械仪表   930篇
建筑科学   880篇
矿业工程   393篇
能源动力   474篇
轻工业   2184篇
水利工程   632篇
石油天然气   60篇
武器工业   4篇
无线电   2169篇
一般工业技术   3576篇
冶金工业   21446篇
原子能技术   273篇
自动化技术   14260篇
  2024年   58篇
  2023年   202篇
  2022年   135篇
  2021年   132篇
  2019年   97篇
  2018年   484篇
  2017年   713篇
  2016年   1083篇
  2015年   806篇
  2014年   667篇
  2013年   679篇
  2012年   2929篇
  2011年   5464篇
  2010年   1815篇
  2009年   1772篇
  2008年   1259篇
  2007年   1201篇
  2006年   998篇
  2005年   3900篇
  2004年   3065篇
  2003年   2611篇
  2002年   1116篇
  2001年   735篇
  2000年   279篇
  1999年   635篇
  1998年   6222篇
  1997年   3822篇
  1996年   2512篇
  1995年   1452篇
  1994年   1073篇
  1993年   1101篇
  1992年   252篇
  1991年   306篇
  1990年   312篇
  1989年   280篇
  1988年   300篇
  1987年   227篇
  1986年   208篇
  1985年   173篇
  1984年   91篇
  1983年   96篇
  1982年   134篇
  1981年   186篇
  1980年   195篇
  1979年   62篇
  1978年   98篇
  1977年   610篇
  1976年   1321篇
  1975年   101篇
  1971年   49篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Here we present a case of a patient with a massive ossification of annulus fibrosus and longitudinal ligament at the level C3-C4, C4-C5 and C5-C6, also called the Van Swaay bridge. One can observe a propulsion of the pharingeal tissue at the level of the massive Van Swaay bridge between C5 and C6 which caused pressure and dysphagia.  相似文献   
112.
113.
Polyarteritis nodosa is a rare disorder and a form of systemic vasculitis. A 48 year-old female was admitted to the hospital because menorrhagia and pelvic pain in February 1993. The patient underwent exploratory laparotomy resulting in a total hysterectomy and bilateral salpingo-oophorectomy for myoma of uterus and a right adnexal cystic mass. Histopathologic examination revealed left ovarian periarteritis nodosa. Further investigation and 9 months follow-up failed to show any systemic involvement. To our knowledge the isolated ovarian polyarteritis nodosa is the first case in the literature.  相似文献   
114.
Suggests that it is difficult to get an exact account of gambling behavior in Norway. It appears that gambling behavior in Norway has increased 50% during the observed 5-yr period. Little is known about the prevalence of problematic gambling. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
115.
116.
Based on generalization and analysis of instructions and guidelines for therapeutical and prophylactic diets of workers, ways of its optimization were proposed, by using bifide-containing acid dairy products as a preventive agent against possible occupational diseases caused by occupational factors.  相似文献   
117.
OBJECTIVE: To investigate if unexpected behaviour of neonatal and paediatric patients connected to syringe pumps could be explained by transient elevation of these devices. DESIGN: Five different commercially available syringe-pumps were set at an infusion rate of 1 ml/h and then subjected to a vertical displacement manoeuvre (height 1 m). The actual delivered infusion volumes in association with the displacement manoeuvre were measured by a high precision weight scale connected to a computer. SETTING: A medical technology laboratory in a university hospital. MEASUREMENTS AND RESULTS: Elevation of the devices resulted in a rapid bolus injection of 0.19-2.28 ml. Returning the devices to their original positions resulted in an aspiration into the system of 0.06-0.34 ml. The times both for bolus injection and for aspiration into the system were less than 1 min in all cases. The updown manoeuvre was followed by a period with zero infusion ranging from 8 to 105 min. CONCLUSIONS: Design flaws in the construction of syringe pumps can expose patients to substantial danger following vertical displacement if potent drugs are being infused. If potent drugs are infused, care should be taken not to change the vertical position of the syringe pump even for short periods of time. Before buying new equipment, the authors recommend that the delivery characteristics of these devices should not only be tested during ordinary bench testing but should also include the reaction to a vertical displacement manoeuvre.  相似文献   
118.
119.
Cortical bone remodeling rates for rib samples from three archaeological populations and a modern autopsy sample were determined using an algorithm developed by Frost (Frost [1987a] Calcif. Tissue Res. 3:211-237). When plotted against the relative antiquities for population samples, histomorphometric variables; i.e., activation frequency (mu rc), net bone formation (netVf,r,t), and mean annual bone formation rate (Vf,r,t), exhibit a concordant trend of increased cortical bone remodeling activity levels over time. Two intensive foraging populations, Windover and Gibson, are similar for all bone remodeling parameters and have the lowest remodeling activity levels among the samples. The more recent Ledders sample, which is reported to practice agricultural subsistence, is consistently intermediate between these and a modern autopsy sample. Although there appear to be differences in bone formation rates among the populations it is concluded that these differences cannot be attributed to differences in bone remodeling rates among the populations, but rather are reflecting different effective ages of adult compacta for their ribs. These findings suggest that the earlier populations, particularly Windsor and Gibson, appear to have reached skeletal maturity at an older age than observed for modern.  相似文献   
120.
We report herein the phenotypic and functional analysis of human bone marrow and thymus derived early T cells. Commitment to T cell lineage is acquired during CD7 antigen expression by CD34+ precursors in human bone marrow and before thymus colonization. Early thymocytes show similar phenotypic characteristics as bone marrow T cells. They rapidly acquire CD4 before the dual expression of CD4 and CD8. Their expansion and differentiation is regulated by two major factors: thymic stroma and cytokines produced by these stroma cells or by thymocytes themselves. Among cytokines, IL1 and sCD23 produced by thymic epithelial cells support in vitro early T cell development.  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