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   1281篇
  免费   3篇
  国内免费   17篇
系统科学   97篇
丛书文集   25篇
教育与普及   29篇
理论与方法论   5篇
现状及发展   16篇
研究方法   5篇
综合类   1124篇
  2022年   1篇
  2020年   2篇
  2019年   2篇
  2018年   1篇
  2017年   5篇
  2016年   22篇
  2015年   22篇
  2014年   8篇
  2013年   4篇
  2012年   7篇
  2011年   100篇
  2010年   27篇
  2009年   61篇
  2008年   20篇
  2007年   29篇
  2006年   20篇
  2005年   25篇
  2004年   111篇
  2003年   102篇
  2002年   48篇
  2001年   38篇
  2000年   16篇
  1999年   26篇
  1998年   54篇
  1997年   46篇
  1996年   7篇
  1995年   11篇
  1994年   19篇
  1993年   97篇
  1992年   68篇
  1991年   65篇
  1990年   66篇
  1989年   44篇
  1988年   32篇
  1987年   53篇
  1986年   30篇
  1985年   1篇
  1984年   5篇
  1983年   3篇
  1982年   2篇
  1981年   1篇
排序方式: 共有1301条查询结果,搜索用时 578 毫秒
61.
To identify somatic mutations in pediatric diffuse intrinsic pontine glioma (DIPG), we performed whole-genome sequencing of DNA from seven DIPGs and matched germline tissue and targeted sequencing of an additional 43 DIPGs and 36 non-brainstem pediatric glioblastomas (non-BS-PGs). We found that 78% of DIPGs and 22% of non-BS-PGs contained a mutation in H3F3A, encoding histone H3.3, or in the related HIST1H3B, encoding histone H3.1, that caused a p.Lys27Met amino acid substitution in each protein. An additional 14% of non-BS-PGs had somatic mutations in H3F3A causing a p.Gly34Arg alteration.  相似文献   
62.
As end-stage renal disease (ESRD) has a four times higher incidence in African Americans compared to European Americans, we hypothesized that susceptibility alleles for ESRD have a higher frequency in the West African than the European gene pool. We carried out a genome-wide admixture scan in 1,372 ESRD cases and 806 controls and found a highly significant association between excess African ancestry and nondiabetic ESRD (lod score = 5.70) but not diabetic ESRD (lod = 0.47) on chromosome 22q12. Each copy of the European ancestral allele conferred a relative risk of 0.50 (95% CI = 0.39-0.63) compared to African ancestry. Multiple common SNPs (allele frequencies ranging from 0.2 to 0.6) in the gene encoding nonmuscle myosin heavy chain type II isoform A (MYH9) were associated with two to four times greater risk of nondiabetic ESRD and accounted for a large proportion of the excess risk of ESRD observed in African compared to European Americans.  相似文献   
63.
分析了当天线斜视角增大时,导致传统距离-多普勒成像算法性能下降的主要误差来源。提出了一种适合大斜视角星载SAR系统的改进距离-多普勒算法,并给出了处理仿真点目标数据得到图像质量的比较。结果表明,在大斜视角情况下,改进算法的性能远大于传统的距离-多普勒成像算法。  相似文献   
64.
In this paper,the effects of Si and Ce on the microstructure and hydrogen storage property of Ti26.5 Cr20V45Fe8.5Ce0.5 alloy were studied,respectively.First of all,effects of Si on the microstructure and hydrogen storage properties of Ti26.5Cr20(V45Fe8.5)1-xSixCe0.5(x=0,0.5,1.0,1.5 and 2.0 at%)alloys were studied by X-ray diffraction,scanning electron microscopy and P-C isotherm measurements.As the Si addition increases,the hydrogen absorption capacities of alloys decrease but the equilibrium pressure incre...  相似文献   
65.
为了使钢中全氧量控制在一个适当的水平,在武钢炼钢总厂RH真空脱气装置对低碳、超低碳钢进行了脱氧净化试验.结果表明,影响全氧去除的因素按作用高低依次是出钢溶解氧水平,溶解氧与钢包渣的交互作用,钢包渣,和真空处理净化时间.通过改进工艺生产了全氧量≤10×10-6,非金属夹杂物尺寸<10μm的清洁钢水,建立了一个钢包内钢水全氧浓度随时间变化的新方程,该方程考虑了全氧的表观平衡含量及环流、扩散传质对去除氧化物夹杂速率的影响.  相似文献   
66.
Content addressable storage (CAS) is a promising technology for improving storage efficiency as well as access throughput.Currently,many CAS products are implemented on the block level,which results in loss of file information.Thus,some sophisticated optimizations cannot be achieved,such as accurate fileprefetching.This paper presents a file-aware block-level storage system combined with the CAS function.In contrast with some existing file-level CAS,this system is transparent to upper-level applications,including the operating system and the file system.These features are achieved by using smart-disk technologies to help the storage system to learn the file-system layout.A prototype was implemented on an open-source virtual machine (VM) with the guest operating system being Windows XP.Tests show that this combination significantly reduces the size of the VM image file and improves the storage performance by discarding unused blocks and using a simple file-level prefetching strategy.  相似文献   
67.
Climate extremes, such as extreme hot temperatures and heat waves, can have dramatic societal, economic, and ecological consequences. China has experienced remarkable interannual and decadal changes in hot extremes during the last several decades. However, the underlying mechanisms responsible for changes in the hot extremes over China have not been clearly identified. In this study, we investigate the role of land-atmosphere coupling for hot days and heat waves during summer over China using two long-term ...  相似文献   
68.
69.
为了研究和开发增压循环床燃烧装置,在一个床体内径为80mm,高为6m的增压循环床内对其流动及操作特性进行了冷态试验研究。本文发表了床料粒径、筛分对床内空隙率分布的影响以及压力对增压循环流化床运行特性影响的试验结果,并讨论了它们对煤在增压循环流化床中燃烧可能产生的影响。  相似文献   
70.
扼要介绍了开展燃煤磁流体发电研究的各主要国家的研究现状,和燃煤磁流体发电装置的各主要部件研究的进展。根据已经取得的研究结果,对这项技术的实用化进程,提出了展望。  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