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   370篇
  免费   14篇
  国内免费   58篇
系统科学   58篇
教育与普及   6篇
理论与方法论   2篇
现状及发展   5篇
研究方法   25篇
综合类   346篇
  2024年   5篇
  2023年   16篇
  2022年   1篇
  2021年   3篇
  2018年   2篇
  2015年   3篇
  2013年   30篇
  2012年   10篇
  2011年   17篇
  2010年   7篇
  2009年   6篇
  2008年   38篇
  2007年   55篇
  2006年   73篇
  2005年   35篇
  2004年   14篇
  2003年   31篇
  2002年   15篇
  2001年   10篇
  2000年   19篇
  1999年   3篇
  1997年   3篇
  1996年   2篇
  1995年   13篇
  1994年   4篇
  1993年   2篇
  1992年   1篇
  1989年   4篇
  1984年   1篇
  1970年   1篇
  1966年   1篇
  1959年   1篇
  1958年   5篇
  1957年   6篇
  1956年   3篇
  1954年   1篇
  1948年   1篇
排序方式: 共有442条查询结果,搜索用时 15 毫秒
61.
62.
TheOptimalControlModelofEconomicDevelopmentinQingchuanCountyXUJiuping;LIUGuangzhong;HEChangzheng(Dept.ofAppliedMathematics.Ch...  相似文献   
63.
64.
The problem of D-pseudoconvex programming with operator con-straints is discussed in this paper.Some new optimality conditions are presentedand an error made by V.Barbu in [4] is pointed out.  相似文献   
65.
66.
The main problems in drawing causal inferences from epidemiological case-control studies are confounding by unmeasured extraneous factors, selection bias and differential misclassification of exposure. In genetics the first of these, in the form of population structure, has dominated recent debate. Population structure explained part of the significant +11.2% inflation of test statistics we observed in an analysis of 6,322 nonsynonymous SNPs in 816 cases of type 1 diabetes and 877 population-based controls from Great Britain. The remainder of the inflation resulted from differential bias in genotype scoring between case and control DNA samples, which originated from two laboratories, causing false-positive associations. To avoid excluding SNPs and losing valuable information, we extended the genomic control method by applying a variable downweighting to each SNP.  相似文献   
67.
η?Carinae is one of the most massive binary stars in the Milky Way. It became the second-brightest star in our sky during its mid-nineteenth-century 'Great Eruption', but then faded from view (with only naked-eye estimates of brightness). Its eruption is unique in that it exceeded the Eddington luminosity limit for ten years. Because it is only 2.3 kiloparsecs away, spatially resolved studies of the nebula have constrained the ejected mass and velocity, indicating that during its nineteenth-century eruption, η?Car ejected more than ten solar masses in an event that released ten per cent of the energy of a typical core-collapse supernova, without destroying the star. Here we report observations of light echoes of η?Carinae from the 1838-1858 Great Eruption. Spectra of these light echoes show only absorption lines, which are blueshifted by -210?km?s(-1), in good agreement with predicted expansion speeds. The light-echo spectra correlate best with those of G2-to-G5 supergiants, which have effective temperatures of around 5,000?kelvin. In contrast to the class of extragalactic outbursts assumed to be analogues of the Great Eruption of η?Carinae, the effective temperature of its outburst is significantly lower than that allowed by standard opaque wind models. This indicates that other physical mechanisms such as an energetic blast wave may have triggered and influenced the eruption.  相似文献   
68.
The construction of basic wavelet was discussed and many basic analyzing wavelets was compared. A complex analyzing wavelet which is continuous, smoothing, orthogonal and exponential decreasing was presented, and it was used to decompose two blasting seismic signals with the continuous wavelet transforms (CWT). The result shows that wavelet analysis is the better method to help us determine the essential factors which create damage effects than Fourier analysis.  相似文献   
69.
 设计了一个针对多发性硬化症患者的三维步态分析实验,利用三维光学捕捉系统对实验被试身体不同部位标记点的三维坐标进行追踪和记录,成功发现了多个步态参数发生的变化,这些变化不仅能反映实验被试细微的步态功能上的变化,而且还与接受治疗的时间密切相关。此套基于步态数据的量化评估体系能够弥补目前广泛应用的评估方法主观和不够准确的缺点,为临床医生改进治疗方案以及制定更加有效的治疗方法提供帮助。  相似文献   
70.
The East Asian winter monsoon (EAWM) consists of subsystems such as the Siberian high, Aleutian low, East Asian trough, low-level northerly wind and high-level East Asian jet stream. It is revealed that the interannual variation of the EAWM-related atmospheric circulation has exhibited an obvious weakening since the mid-1980s. During 1956-1980, significant negative correlations between the EAWM and sea surface temperature are observed in the oceans along the east coast of East Asia, accompanied by significant positive correlations in the western Warm Pool. However, the significant interannual relationship in the previous period is found to have been disrupted during 1986-2010. Further analysis reveals that the Arctic Oscillation after the mid-1980s tends to suppress the interannual variability of the EAWM. In addition, it was found that the large-scale warming after the mid-1980s is favorable to reduce the land-sea thermal contrast variability on both the interdecadal and interannual time scales.  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