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   289篇
  免费   34篇
  国内免费   1篇
  324篇
  2020年   2篇
  2019年   2篇
  2017年   3篇
  2016年   2篇
  2015年   6篇
  2014年   4篇
  2013年   18篇
  2012年   13篇
  2011年   9篇
  2010年   13篇
  2009年   15篇
  2008年   17篇
  2007年   16篇
  2006年   16篇
  2005年   12篇
  2004年   15篇
  2003年   20篇
  2002年   15篇
  2001年   6篇
  2000年   8篇
  1999年   6篇
  1998年   3篇
  1997年   8篇
  1996年   2篇
  1994年   2篇
  1993年   2篇
  1992年   12篇
  1991年   3篇
  1990年   2篇
  1989年   13篇
  1988年   5篇
  1987年   5篇
  1986年   4篇
  1985年   5篇
  1984年   5篇
  1983年   5篇
  1982年   3篇
  1981年   2篇
  1980年   2篇
  1979年   5篇
  1978年   2篇
  1977年   3篇
  1969年   1篇
  1965年   1篇
  1964年   1篇
  1962年   1篇
  1957年   1篇
  1955年   1篇
  1950年   1篇
  1949年   1篇
排序方式: 共有324条查询结果,搜索用时 15 毫秒
61.
62.
63.
Skeletal abnormalities in neurofibromatosis type 1 syndrome (NF1) are observed in ~50% of patients. Here, we describe the phenotype of Nf1Ocl mouse model with Nf1‐deficient osteoclasts. Nf1Ocl mice with Nf1+/? or Nf1?/? osteoclasts in otherwise Nf1+/+ background were successfully generated by mating parental Nf1flox/flox and TRAP‐Cre mice. Contrary to our original hypothesis, osteoporotic or fragile bone phenotype was not observed. The µCT analysis revealed that tibial bone marrow cavity, trabecular tissue volume, and the perimeter of cortical bone were smaller in Nf1 mice compared to Nf1 control mice. Nf1 mice also a displayed narrowed growth plate in the proximal tibia. In vitro analysis showed increased bone resorption capacity and cytoskeletal changes including irregular cell shape and abnormal actin ring formation in Nf1?/? osteoclasts. Surprisingly, the size of spleen in Nf1 mice was two times larger than in controls and histomorphometric analysis showed splenic megakaryocytosis. In summary, Nf1Ocl mouse model presented with a mild but specific bone phenotype. This study shows that NF1‐deficiency in osteoclasts may have a role in the development of NF1‐related skeletal abnormalities, but Nf1‐deficiency in osteoclasts in Nf1+/+ background is not sufficient to induce skeletal abnormalities analogous to those observed in patients with NF1. J. Cell. Biochem. 113: 2136–2146, 2012. © 2012 Wiley Periodicals, Inc.  相似文献   
64.
65.
Seven years after fertilization the rate of CO2 production in the soil samples taken from the organic horizons of a poor pine forest site (Calluna vulgaris site type), treated with urea or ammonium nitrate with lime, was lower than that in the unfertilized soil. The same trend was also observed in samples of theEmpetrum-Calluna site type 14 years after fertilization. In the more fertileVaccinium myrtillus site type these rapidly-soluble N fertilizers had a long-term enhancing effect on the production of CO2. Apatite and biotite eliminated the decreasing effect of urea on the production of CO2. One reason for this might be the long-term increase in soil pH caused by apatite and biotite, or their constituents (Ca, Mg, K, P). Nitroform (a slow-releasing N fertilizer) had no statistically significant effect on the production of CO2 in soil samples from any of the forest types. Despite the high N mineralization in the samples from nitroform fertilized soils there was no nitrification, and the high content of total N indicated that after nitroform fertilization the losses of N were low.The correlation between the net mineralization values for C (CO2 production) and N was poor. However, multiple linear regression analysis, which also took into account the effect of nutrients and pH, indicated that there was a link between the mineralization of C and N.  相似文献   
66.
In printed circuit board (PCB) assembly, the majority of electronic components are inserted by high-speed placement machines. Although the efficient utilization of the machinery is important for a manufacturer, it is hard to fully realize in high-mix low-volume production environments. On the machine level, the component setup strategy adopted by the manufacturer has a significant impact on the overall production efficiency. Usually, the setup strategy is formulated as a part type grouping problem or a minimum setup problem. In this article, we consider a hybridization of these two problems for the single machine case: The object function to be minimized includes a weighted sum of the number of part type groups (giving the number of setup occasions) and the number of feeder changeovers. We present algorithms for the problem and compare their efficiency.  相似文献   
67.
OBJECTIVE: To examine the combined influence of workplace demands and changes in blood pressure induced by stress on the progression of carotid atherosclerosis. DESIGN: Population based follow up study of unestablished as well as traditional risk factors for carotid atherosclerosis, ischaemic heart disease, and other outcomes. SETTING: Eastern Finland. SUBJECTS: 591 men aged 42-60 who were fully employed at baseline and had complete data on the measures of carotid atherosclerosis, job demands, blood pressure reactivity, and covariates. MAIN OUTCOME MEASURES: Change in ultrasonographically assessed intima-media thickness of the right and left common carotid arteries from baseline to 4 year follow up. RESULTS: Significant interactions between workplace demands and stress induced reactivity were observed for all measures of progression (P < 0.04). Men with large changes in systolic blood pressure (20 mm Hg or greater) in anticipation of a maximal exercise test and with high job demands had 10-40% greater progression of mean (0.138 v 0.123 mm) and maximum (0.320 v 0.261 mm) intima-media thickness and plaque height (0.347 v 0.264) than men who were less reactive and had fewer job demands. Similar results were obtained after excluding men with prevalent ischaemic heart disease at baseline. Findings were strongest among men with at least 20% stenosis or non-stenotic plaque at baseline. In this subgroup reactive men with high job demands had more than 46% greater atherosclerotic progression than the others. Adjustment for atherosclerotic risk factors did not alter the results. CONCLUSIONS: Men who showed stress induced blood pressure reactivity and who reported high job demands experienced the greatest atherosclerotic progression, showing the association between dispositional risk characteristics and contextual determinants of disease and suggesting that behaviourally evoked cardiovascular reactivity may have a role in atherogenesis.  相似文献   
68.
69.
70.
A sensitive and specific radioimmunoassay was developed for detomidine, 4(5)-(2,3-dimethylbenzyl)imidazole. The antibodies were raised in rabbits against a conjugate of detomidine and bovine thyroglobulin prepared by diazo reaction. Detomidine was iodinated with chloramine-T and immunoreactive tracer was purified in cation exchange chromatography. The sensitivity of the RIA was 1.6 fmol/tube allowing direct detomidine measurements from minute serum and urine samples (0.1-0.2 microliter) as well as tissue homogenates (10 microliters). For concentrations below 16 pmol/ml chloroform extraction was used to extend the measurement range to 0.3 pmol/ml. Detomidine (80 micrograms/kg iv and im) was given to one horse and two calves and blood samples were taken and urine collected for 24 h whereafter the horse was slaughtered and tissue samples taken for RIA analyses. Serially diluted serum, urine and tissue samples produced a linear displacement curve parallel to synthetic detomidine in RIA. HPLC studies showed that serum and tissue immunoreactivity was unchanged detomidine whereas most immunoreactivity in the urine was due to an unknown metabolite.  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