全文获取类型
收费全文 | 375篇 |
免费 | 14篇 |
国内免费 | 58篇 |
专业分类
系统科学 | 60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 | 349篇 |
出版年
2024年 | 5篇 |
2023年 | 16篇 |
2022年 | 6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447条查询结果,搜索用时 15 毫秒
351.
The utilization of traffic information received from intelligent vehicle highway systems(IVHS) to plan velocity and split output power for multi-source vehicles is currently a research hotspot. However, it is an open issue to plan vehicle velocity and distribute output power between different supply units simultaneously due to the strongly coupling characteristic of the velocity planning and the power distribution. To address this issue, a flexible predictive power-split control strategy based o... 相似文献
352.
McKay JD Hung RJ Gaborieau V Boffetta P Chabrier A Byrnes G Zaridze D Mukeria A Szeszenia-Dabrowska N Lissowska J Rudnai P Fabianova E Mates D Bencko V Foretova L Janout V McLaughlin J Shepherd F Montpetit A Narod S Krokan HE Skorpen F Elvestad MB Vatten L Njølstad I Axelsson T Chen C Goodman G Barnett M Loomis MM Lubiñski J Matyjasik J Lener M Oszutowska D Field J Liloglou T Xinarianos G Cassidy A;EPIC Study Vineis P Clavel-Chapelon F Palli D Tumino R Krogh V Panico S González CA 《Nature genetics》2008,40(12):1404-1406
We carried out a genome-wide association study of lung cancer (3,259 cases and 4,159 controls), followed by replication in 2,899 cases and 5,573 controls. Two uncorrelated disease markers at 5p15.33, rs402710 and rs2736100 were detected by the genome-wide data (P = 2 x 10(-7) and P = 4 x 10(-6)) and replicated by the independent study series (P = 7 x 10(-5) and P = 0.016). The susceptibility region contains two genes, TERT and CLPTM1L, suggesting that one or both may have a role in lung cancer etiology. 相似文献
353.
基于虚拟现实技术的某型导弹仿真训练系统研究 总被引:1,自引:0,他引:1
详细讨论了基于虚拟现实技术的某型号导弹仿真训练系统,从硬件和软件两个方面研究了仿真训练系统的具体设计、各功能模块以及所采用的技术和工作原理,分析了系统的工作流程、硬件组成和软件设计;最后,研究了仿真训练系统的总体结构和具体实现,详细介绍了组成系统的控制台和仿真训练单元的功能和应用。该系统能完全模拟导弹的训练过程,满足部队的需要。 相似文献
354.
弹丸侵彻混凝土的试验与仿真 总被引:2,自引:1,他引:1
通过直径125mm的模型弹对混凝土厚靶的垂直侵彻试验,得到了弹丸侵彻混凝土的最大侵彻深度、冲击漏斗坑、震塌漏斗坑尺寸和着靶姿态等参数值.采用ANSYS/LS-DYNA软件,对弹丸侵彻混凝土靶体试验进行了数值仿真,计算结果在侵彻过程、侵彻深度和靶体破坏现象等方面与试验结果吻合良好.为弹丸侵彻混凝土机理分析和模型试验成果扩展奠定了基础. 相似文献
355.
Adaptive detection of range-spread targets is considered in the presence of subspace interference plus Gaussian clutter with unknown covariance matrix. The target signal and interference are supposed to lie in two linearly independent subspaces with deterministic but unknown coordinates. Relying on the two-step criteria, two adaptive detectors based on Gradient tests are proposed, in homogeneous and partially homogeneous clutter plus subspace interference, respectively. Both of the proposed dete... 相似文献
356.
针对基坑群连续开挖存在的耦合效应,首先确定相似材料配比方案,其次通过正交试验得出合理的配比材料,进而设计基坑群模型试验,研究了两侧基坑叠加作用影响下车站基坑的围护结构和土体表层变形。研究结果表明:满足该软土地层相似常数的土层材料配比为石英砂:滑石粉:双飞粉:膨润土:水=0.27:0.27:0.232:0.058:0.17;相较于无邻近基坑开挖的地铁站,旁侧存在基坑开挖时由于相邻墙体引起的墙后土拱效应叠加而减小了坑间土体水平应力,进而减小开挖引起的围护结构受力和变形,但坑间土体沉降较大;基坑间距是支护结构变形的主要影响因素,两侧基坑间距位于1-2H之间(H为基坑深度),接近1倍开挖深度一侧的叠加影响大于接近2倍开挖深度一侧。基于所配相似材料开展的基坑群模型试验具有很好的试验效果,对相关基坑群模型试验有一定参考作用。 相似文献
357.
Organotin compounds in surface sediments from selected fishing ports along the Chinese coast 总被引:1,自引:0,他引:1
The concentrations and species of organotin compounds(OTCs) in 52 surface sediment samples from nine fishing ports along the Chinese coast were studied.Butyltins(BTs) and phenyltins(PhTs) were derivatized using sodium tetraethylborate(NaBEt 4) and determined by head-space solid-phase microextraction(HS-SPME) gas chromatography coupled with a flame photometric detector(GC-FPD).The concentrations of OTCs ranged from <3.6 to 194 ng(Sn) g-1 dry weight(dw) for monobutyltin(MBT),<2.3 to 41.5 ng(Sn) g-1 dw for dibutyltin(DBT),<0.7 to 86.0 ng(Sn) g-1 dw for tributyltin(TBT) and <5.1 to 66.1 ng(Sn) g-1 dw for monophenyltin(MPhT),respectively.The concentrations of diphenyltin(DPhT) and triphenyltin(TPhT) were below the limit of detection(LOD).BTs were the main species in the sediments except for the samples collected from Shazikou fishing port in Qingdao.The concentrations of MBT were higher than DBT and TBT.The concentrations of OTCs in the sediments varied widely among different sampling locations.The concentrations of BTs were much higher in the samples collected from fishing ports close to the South China Sea than those in coast of the East China Sea and the Yellow Sea.MPhT was prevalent in most sampling stations except for those in coast of the East China Sea.The environmental and ecotoxicological risks of TBT in most sediment samples were low. 相似文献
358.
GAN Shu HE Daming FENG Yan 《科学通报(英文版)》2006,51(B11):33-38
Directing at the the longitudinal rangegorge region's special constituting condition of river basin geography landscape, the authors synthetically used the data analyses and spatial information treatment technique, selected corresponding measurable homology indicators, comparatively analyzed the characteristic difference of different river basin's landscape constitution patterns in the longitudinal range-gorge region, researched into different river net patterns and land cover conditions of each river basin landscape, and explored the river basin's landscape form and its spatial distributed chracters. Based on the analyses on river basin's landscape composition and its spatial distribution characters, this study researched into the main driving factor of modern earth surface process in the longitudinal range-gorge region, analyzed the relationship between the basin landscape changing and its modern earth surface process, finally completed a series of the potential ecological hydrology effect analyses. 相似文献
359.
A Fuzzy Set-Based Approach for Model-Based Internet-Banking System Security Risk Assessment 总被引:1,自引:1,他引:0
LI Hetian LIU Yun HE Dequan 《武汉大学学报:自然科学英文版》2006,11(6):1869-1872
A fuzzy set-based evaluation approach is demonstrated to assess the security risks for internet-banking System. The Internet-banking system is semi-formally described using Unified Modeling Language (UML) to specify the behavior and state of the system on the base of analyzing the existing qualitative risk assessment methods. And a quantitative method based on fuzzy set is used to measure security risks of the system, A case study was performed on the WEB server of the Internet-banking System using fuzzy-set based assessment algorithm to quantitatively compute the security risk severity. The numeric result also provides a method to decide the most critical component which should amuse the system administrator enough attention to take the appropriate security measure or controls to alleviate the risk severity. The experiments show this method can be used to quantify the security properties for the Internet-banking System in practice. 相似文献
360.
Climatic difference in dry and wet season under effect of the Longitudinal Range-Gorge and its influence on transboundary river runoff 总被引:1,自引:0,他引:1
YOU Weihong DUAN Changchun HE Daming 《科学通报(英文版)》2006,51(B11):69-79
Based on observed data of transboundary river runoffs in the Longitudinal Range-Gorge Region (LRGR) and those of precipitation and air temperature fields in Yunnan, climatic variability in dry and wet seasons under the impact of LRGR and its influence on transboundary river runoff are studied by means of statistical analysis and wavelet transforms. Results show that latitude variations of high correlation center for precipitation field and corresponding transboundary river runoff are not so notable due to the underlying topography of LRGR, while longitude variations are highly marked. In dry season, greater precipitation and slighter relative deviation are observed in the eastern part as compared to those in the western part of LRGR; while lower average temperature and greater standard deviation are found in the eastern part. In wet season, greater precipitation and slighter relative deviation are ob- served in the western part, while lower average temperature and similar standard deviation are found in the eastern part. Either in dry or wet season, relative deviation of eastern runoff is always greater than that of the western one. LRGR's barrier action is stronger for southwest monsoon but weaker for northeast one. Under the effect of LRGR, precipitation variations in the eastern and western parts are primarily found in smaller timescales, and the variations tend to be insignificant as timescales increase; whereas slighter temperature variations are observed In recent years, precipitation in wet season tended to increase, which in turn resulted in the greater runoff of transboundary rivers. While in the past decade, air temperature showed a climbing trend in both dry and wet season in the LRGR. 相似文献