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   2192篇
  免费   53篇
  国内免费   235篇
  2021年   5篇
  2020年   3篇
  2019年   5篇
  2018年   3篇
  2017年   9篇
  2016年   9篇
  2015年   15篇
  2014年   20篇
  2013年   17篇
  2012年   26篇
  2011年   353篇
  2010年   262篇
  2009年   72篇
  2008年   48篇
  2007年   47篇
  2006年   19篇
  2005年   168篇
  2004年   367篇
  2003年   149篇
  2002年   79篇
  2001年   101篇
  2000年   51篇
  1999年   48篇
  1998年   42篇
  1997年   69篇
  1996年   22篇
  1995年   36篇
  1994年   15篇
  1993年   113篇
  1992年   64篇
  1991年   38篇
  1990年   32篇
  1989年   35篇
  1988年   33篇
  1987年   23篇
  1986年   9篇
  1985年   17篇
  1984年   3篇
  1981年   2篇
  1979年   2篇
  1978年   3篇
  1977年   2篇
  1976年   4篇
  1975年   2篇
  1974年   6篇
  1973年   3篇
  1972年   5篇
  1971年   8篇
  1970年   2篇
  1955年   4篇
排序方式: 共有2480条查询结果,搜索用时 15 毫秒
61.
基于SIFT特征和近似最近邻算法的医学CT图像检索   总被引:1,自引:0,他引:1  
针对医学X线计算机断层(Computed Tomography,CT)图像,提出了一种基于尺度不变特征变换(Scale InvariantFeature Transform,SIFT)特征和近似最近邻算法的检索方法。首先通过SIFT算法得到图像的特征点和相应的特征向量,再采用近似最近邻算法进行SIFT特征向量的匹配搜索,得到数据库中与参考图像最相似的图像序列。实验结果表明,该法能检索到与目标图像细节相符的结果,大大提高了检索速度。与传统的基于纹理的检索方法相比,查准率和检索结果与目标图像的相似程度方面更佳,符合医学CT图像检索的要求。  相似文献   
62.
数字乳房X片中的伪彩色增强应用   总被引:1,自引:0,他引:1  
利用数字图像处理中伪彩色理论,讨论了灰度一彩色变换函数,并用合适的线性变换函数对数字乳房X片进行处理。处理后的图像与原数字灰度图像相比较,可分辨性明显提高。可以利用这种变换,辅助医疗诊断,从而降低乳房癌的漏诊和误诊率。经验证,经过伪彩色增强后的数字乳房X片病灶区域的可分辨性明显优于原数字图像,有较高的临床价值。  相似文献   
63.
E H South  R C Ritter 《Peptides》1988,9(3):601-612
Capsaicin treatment destroys small primary sensory neurons including a subpopulation of vagal afferents. Intraperitoneal, fourth ventricular or perivagal application of capsaicin attenuated or abolished cholecystokinin (CCK)-induced suppression of food intake. Capsaicin applied to the thoracolumbar spinal cord or to the pyloric region of the stomach did not alter CCK-induced reductions of food intake. Intraperitoneal capsaicin treatment reduced substance P-like immunoreactivity (SPLI) in the spinal dorsal horn and parts of the dorsal hindbrain. SPLI depletion, therefore, served as a histochemical indicator of the spread of capsaicin from its site of application. Capsaicin applied directly to the vagal trunks did not reduce SPLI in the spinal cord or hindbrain. Intraventricular capsaicin reduced SPLI in the hindbrain but not in the spinal cord. These data indicate that localized capsaicin application attenuates CCK-induced suppression of food intake by impairing the function of either central or peripheral portions of vagal afferent neurons. The data also support the conclusion that intraperitoneal capsaicin attenuates CCK-induced suppression of feeding by impairing vagal sensory function.  相似文献   
64.
65.
Kindler syndrome is an autosomal recessive disorder characterized by neonatal blistering, sun sensitivity, atrophy, abnormal pigmentation, and fragility of the skin. Linkage and homozygosity analysis in an isolated Panamanian cohort and in additional inbred families mapped the gene to 20p12.3. Loss-of-function mutations were identified in the FLJ20116 gene (renamed “KIND1” [encoding kindlin-1]). Kindlin-1 is a human homolog of the Caenorhabditis elegans protein UNC-112, a membrane-associated structural/signaling protein that has been implicated in linking the actin cytoskeleton to the extracellular matrix (ECM). Thus, Kindler syndrome is, to our knowledge, the first skin fragility disorder caused by a defect in actin-ECM linkage, rather than keratin-ECM linkage.  相似文献   
66.
Life history,ecology and longevity in bats   总被引:5,自引:1,他引:4  
Wilkinson GS  South JM 《Aging cell》2002,1(2):124-131
The evolutionary theory of aging predicts that life span should decrease in response to the amount of mortality caused by extrinsic sources. Using this prediction, we selected six life history and ecological factors to use in a comparative analysis of longevity among 64 bat species. On average, the maximum recorded life span of a bat is 3.5 times greater than a non-flying placental mammal of similar size. Records of individuals surviving more than 30 years in the wild now exist for five species. Univariate and multivariate analyses of species data, as well as of phylogenetically independent contrasts obtained using a supertree of Chiroptera, reveal that bat life span significantly increases with hibernation, body mass and occasional cave use, but decreases with reproductive rate and is not influenced by diet, colony size or the source of the record. These results are largely consistent with extrinsic mortality risk acting as a determinant of bat longevity. Nevertheless, the strong association between life span and both reproductive rate and hibernation also suggests that bat longevity is strongly influenced by seasonal allocation of non-renewable resources to reproduction. We speculate that hibernation may provide a natural example of caloric restriction, which is known to increase longevity in other mammals.  相似文献   
67.
Conversion of paper sludge to ethanol was investigated with the objective of operating under conditions approaching those expected of an industrial process. Major components of the bleached Kraft sludge studied were glucan (62 wt.%, dry basis), xylan (11.5%), and minerals (17%). Complete recovery of glucose during compositional analysis required two acid hydrolysis treatments rather than one. To avoid the difficulty of mixing unreacted paper sludge, a semicontinuous solids-fed laboratory bioreactor system was developed. The system featured feeding at 12-h intervals, a residence time of 4 days, and cellulase loading of 15 to 20 FPU/g cellulose. Sludge was converted to ethanol using simultaneous saccharification and fermentation (SSF) featuring a -glucosidase-supplemented commercial cellulase preparation and glucose fermentation by Saccharomyces cerevisiea. SSF was carried out for a period of 4 months in a first-generation system, resulting in an average ethanol concentration of 35 g/L. However, steady state was not achieved and operational difficulties were encountered. These difficulties were avoided in a retrofitted design that was operated for two 1-month runs, achieving steady state with good material balance closure. Run 1 with the retrofitted reactor produced 50 g/L ethanol at a cellulose conversion of 74%. Run 2 produced 42 g/L ethanol at a conversion of 92%. For run 2, the ethanol yield was 0.466 g ethanol/g glucose equivalent fermented and >94% of the xylan fed to the reactor was solubilized to a mixture of xylan oligomers and xylose.  相似文献   
68.
中国小头蓟马属二新种:缨翅目:蓟马科   总被引:2,自引:1,他引:1  
西方记述了中国小头蓟马属Microephalothrips2新种-中华小头蓟马M.chinensissp.nov。  相似文献   
69.
本文描述神经干复合动作电位实验的软件设计及其主要特点,友好的人机界面和简便的波形处理,并给出了实际实验结果,由于软件设计在智能化仪器中的重要作用,所以应加以仔细考虑。  相似文献   
70.
肺音信号分析系统研制   总被引:2,自引:0,他引:2  
本文研制的肺音信号检测与分析系统,具有肺音信号采集、肺音图显示、肺音信号的 时域分析等项功能。  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