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   1082425篇
  免费   116053篇
  国内免费   682篇
  2018年   9829篇
  2016年   13248篇
  2015年   18132篇
  2014年   21255篇
  2013年   30822篇
  2012年   33973篇
  2011年   34660篇
  2010年   23569篇
  2009年   21598篇
  2008年   30789篇
  2007年   31738篇
  2006年   29980篇
  2005年   28829篇
  2004年   28759篇
  2003年   27700篇
  2002年   26866篇
  2001年   47587篇
  2000年   47954篇
  1999年   38111篇
  1998年   13416篇
  1997年   13945篇
  1996年   13018篇
  1995年   12748篇
  1994年   12439篇
  1993年   12280篇
  1992年   32023篇
  1991年   31194篇
  1990年   30579篇
  1989年   29959篇
  1988年   27899篇
  1987年   26278篇
  1986年   24511篇
  1985年   24706篇
  1984年   20493篇
  1983年   17438篇
  1982年   13410篇
  1981年   11984篇
  1980年   11224篇
  1979年   19145篇
  1978年   14949篇
  1977年   13778篇
  1976年   12699篇
  1975年   14065篇
  1974年   15043篇
  1973年   14911篇
  1972年   13582篇
  1971年   12407篇
  1970年   10707篇
  1969年   10482篇
  1968年   9567篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
11.
12.
13.
14.
15.
New scientific frontiers and emerging technologies within the life sciences pose many global challenges to society. Big Data is a premier example, especially with respect to individual, national, and international security. Here a Special Agent of the Federal Bureau of Investigation discusses the security implications of Big Data and the need for security in the life sciences.  相似文献   
16.
17.
Volatile organic compounds (VOCs) are secondary metabolites acting as a language for the communication of plants with the environment. In orange fruits, the monoterpene D-limonene accumulates at very high levels in oil glands from the peel. Drastic down-regulation of D-limonene synthase gene expression in the peel of transgenic oranges harboring a D-limonene synthase transgene in antisense (AS) configuration altered the monoterpene profile in oil glands, mainly resulting in reduced accumulation of D-limonene. This led to fruit resistance against Penicillium digitatum (Pd), Xanthomonas citri subsp. citri (Xcc) and other specialized pathogens. Here, we analyze resistance to pathogens in independent AS and empty vector (EV) lines, which have low, medium or high D-limonene concentrations and show that the level of resistance is inversely related to the accumulation of D-limonene in orange peels, thus explaining the need of high D-limonene accumulation in mature oranges in nature for the efficient attraction of specialized microorganism frugivores.  相似文献   
18.
Physicians considering stereotactic ablative body radiation therapy (SBRT) for the treatment of extracranial cancer targets must be aware of the sizeable risks for normal tissue injury and the hazards of physical tumor miss. A first-of-its-kind SBRT platform achieves high-precision ablative radiation treatment through a combination of versatile real-time imaging solutions and sophisticated tumor tracking capabilities. It uses dual-diagnostic kV x-ray units for stereoscopic open-loop feedback of cancer target intrafraction movement occurring as a consequence of respiratory motions and heartbeat. Image-guided feedback drives a gimbaled radiation accelerator (maximum 15 x 15 cm field size) capable of real-time ±4 cm pan-and-tilt action. Robot-driven ±60° pivots of an integrated ±185° rotational gantry allow for coplanar and non-coplanar accelerator beam set-up angles, ultimately permitting unique treatment degrees of freedom. State-of-the-art software aids real-time six dimensional positioning, ensuring irradiation of cancer targets with sub-millimeter accuracy (0.4 mm at isocenter). Use of these features enables treating physicians to steer radiation dose to cancer tumor targets while simultaneously reducing radiation dose to normal tissues. By adding respiration correlated computed tomography (CT) and 2-[18F] fluoro-2-deoxy-ᴅ-glucose (18F-FDG) positron emission tomography (PET) images into the planning system for enhanced tumor target contouring, the likelihood of physical tumor miss becomes substantially less1. In this article, we describe new radiation plans for the treatment of moving lung tumors.  相似文献   
19.
The aim of this work is to show a quick and simple procedure able to identify the geometrical parameters of the intervertebral disc that strongly affect the behavior of the FEM model. First, we allocated a selection criterion for the minimum number of geometrical parameters that describe, with a good degree of approximation, a healthy human vertebra. Next, we carried out a sensitivity analysis using the ‘Taguchi orthogonal array’ to arrive at a quick identification of the parameters that strongly affect the behavior of the Fem model.  相似文献   
20.
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