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   116篇
  免费   30篇
  国内免费   47篇
化学   69篇
晶体学   6篇
力学   10篇
综合类   3篇
数学   28篇
物理学   77篇
  2023年   2篇
  2022年   7篇
  2021年   3篇
  2020年   4篇
  2019年   6篇
  2018年   2篇
  2017年   4篇
  2016年   4篇
  2015年   7篇
  2014年   7篇
  2013年   6篇
  2012年   13篇
  2011年   15篇
  2010年   19篇
  2009年   20篇
  2008年   7篇
  2007年   13篇
  2006年   12篇
  2005年   11篇
  2004年   6篇
  2003年   3篇
  2002年   2篇
  2001年   1篇
  2000年   6篇
  1999年   2篇
  1997年   4篇
  1996年   2篇
  1992年   2篇
  1990年   3篇
排序方式: 共有193条查询结果,搜索用时 15 毫秒
131.
冷却储存环主环磁铁的准直测量   总被引:5,自引:2,他引:3       下载免费PDF全文
 采用激光跟踪仪及配套带软件Insight对兰州重离子加速器冷却储存环主环磁铁进行了安装和准直。首先建立全局坐标系,用来确定从源体到实验环各子系统的理论原点的位置;而各个子系统又分别以各自的理论原点为基础建立局部坐标系,用来安装定位本系统内的各个元件;对各个子系统中的每一个元件还采用了元件坐标系。准直测量时,先在每块磁铁上焊接8个测量基准;然后对磁铁上的基准进行测量,以确定其在元件坐标系中的位置;再架设激光跟踪仪,测量主环控制网点,恢复主环局部坐标系,根据元件在主环局部坐标系中的位置及理论坐标,计算出相关的变换参数;转入元件坐标系,采用激光跟踪仪及Insight 软件显示实时测量坐标及其与理论值之差,其精度达到0.15 mm。  相似文献   
132.
ABSTRACT. In this paper, we present a nonrenewable resource model including environmental pollution as a state variable. The model is analyzed to identify some of the characteristics of the optimal paths. In addition, we present a numerical example on the basis of the algebraic solutions of our qualitative model, and identify some of characteristics of the optimal time paths for two sets of social costs of the pollutant. These results are consistent with the proposition of the previous literature that levying the shadow cost of the pollution stock reduces the consumption of resource; hence, it slows the accumulation of the pollutant in the atmosphere. One quirk in the results, however, is that extractions will persist longer in the higher pollution cost scenario. The costate variable for the resource stock is decomposed into a scarcity effect and a cost effect; and the costate variable for the pollution stock is decomposed into an undesirable abundance effect and a cost effect. Both of these, however, are cost effects.  相似文献   
133.
Fresnel incoherent correlation holographic (FINCH) microscopy is a recently developed new technique, which employs a spatial light modulator (SLM) as the beam splitter. Light originating from the same object point is split into two beams by the wavefront-division phase mask displayed on SLM, and a Fresnel-zone plate-like hologram is formed by the interference of the two beams. The numerical aperture NAH of the recorded Fresnel hologram is introduced as a comprehensive parameter for evaluating the imaging characteristics in the FINCH scheme. The effect of wavefront properties on NAH of the hologram is investigated theoretically in the sense of optimizing imaging resolution. The variation trends of NAH are described and an optimal NAH is achieved by implementing an appropriate phase mask for a given recording distance between SLM and CCD; thus optimized imaging resolution and signal-to-noise ratio are demonstrated experimentally.  相似文献   
134.
智能车辆捷联视线稳定跟踪平台设计与实现   总被引:1,自引:0,他引:1  
基于智能车辆环境识别传感器系统的特点,设计了隔离车体角运动,提供稳定传感器视线给智能车辆环境识别传感器系统的捷联稳定跟踪平台系统.详细分析了稳定平台系统的机械结构、伺服机构和捷联稳定算法,实时通信测试和动态性能检测试验表明,车载捷联视线稳定跟踪平台系统的设计满足智能车辆使用要求,为智能车辆的自主驾驶奠定了应用基础.  相似文献   
135.
为观察C4烯烃转化制丙烯过程中影响催化剂稳定性的因素,对经历不同反应时间(即新鲜、反应48h、反应650h、反应650h后再生和再生后再进行反应48h)的系列ZSM-5分子筛催化剂进行了表征。结果表明,经历长期反应后,催化剂微孔体积和BJH吸附累积孔体积明显降低;再生后,孔体积可以恢复到新鲜催化剂的初始值。与此同时,NH3-TPD酸量不仅降低,而且再生后也不能得到恢复。与高温水蒸气处理的催化剂相比较,27Al MAS NMR表征结果说明,积炭因素对催化剂孔体积的影响可通过再生消除,而分子筛骨架铝丢失和分子筛晶胞参数的降低对催化剂酸量的持续减少起主要作用。长期在高温水蒸气条件下运行后,催化剂酸量可维持在一定水平,使催化剂长期稳定运行成为可能。  相似文献   
136.
箭载双臂式电场仪的原理与设计   总被引:1,自引:0,他引:1  
在介绍双臂式电场仪探测原理的基础上,给出了子午工程探空火箭搭载的双臂式电场仪的具体设计.为了降低探针的不对称和不一致性,采用了铝制球形探针设计,使用石墨涂层以减少表面不均匀性,并采用独特的外形设计来消除支撑臂阴影影响;在信号处理部分,为了能提高系统动态范围,采用了分频段处理的方法.最后,结合整体系统设计的需要提出了几点误差考虑,并给出了系统性能测试结果.所设计的电场仪带宽0~5MHz,直流探测范围为0.1mV/m~±1V/m,交流探测范围为10μV/m~50mV/m,可以实现对电场强度为0~±1V/m的空间电场进行二维测量.  相似文献   
137.
100kA快脉冲直线变压器驱动源模块   总被引:11,自引:9,他引:2       下载免费PDF全文
介绍了100 kA快脉冲直线变压器驱动源原型模块及其采用的200 kV多级多通道气体开关的设计和初步实验结果。该模块由20台100 kV/20 nF电容器按10个支路并联组成,其中每个支路包括2台电容器、1只多级多通道开关以及相应的传输线。模块直径约1.5 m,厚度仅为20 cm。采用B-dot探针诊断负载电流。当充电电压为±90 kV时,在1.1Ω负载上可得到102.2 kA的峰值电流,上升时间为53.6 ns,脉冲宽度为133 ns。实验结果表明,该快脉冲直线变压器驱动源模块具有较好的快脉冲输出能力。  相似文献   
138.
自从20世纪50年代开始利用微束辐照生物活细胞以来,由于微束独特的辐照特征, 其在生物学、 材料学、 生物医学、航空航天科学、环境科学、地质学、微加工等领域得到了广泛的应用。 在前人大量研究的基础上, 对微束装置及其应用进行总结概括。 展望了微束的发展趋势并简单介绍中国科学院近代物理研究所正在兴建的中高能重离子微束辐照装置。 Collimated proton microbeam has been used to irradiate the biological living cells since 1850s. Due to its unique characteristic in irradiation, microbeam has been extensively applied to many research fields,such as biology, material science, biomedicine,aeronautics and stronautics, environmental science, geology,micromachining and so on. Based on the much research of predecessors, the microbeam facilities and their corresponding applications are summarized in this paper. At last,prospects on the development trend of microbeam are made, and the intermediate energy and high energy heavy ion microbeam irradiation facility being constructed at the Institute of Modern Physics of Chinese Academy of Sciences is briefly introduced.  相似文献   
139.
A state-of-the-art high energy heavy ion microbeam irradiation system is constructed at the Institute of Modern Physics of the Chinese Academy of Sciences. This microbeam system operates in both full current intensity mode and single ion mode. It delivers a predefined number of ions to pre-selected targets for research in biology and material science. The characteristic of this microbeam system is high energy and vertical irradiation. A quadrupole focusing system, in combination with a series of slits, has been designed to optimize the spatial resolution. A symmetrically achromatic system leads the beam downwards and serves simultaneously as an energy analyzer. A high gradient quadrupole triplet finally focuses a C^6+ ion beam to 1 μm in the vacuum chamber within the energy range from 10 MeV/u to 100 MeV/u. In this paper, the IMP microbeam system is described in detail. A systematic investigation of the ion beam optics of this microbeam system is presented together with the associated aberrations. Comparison is made between the IMP microbeam system and the other existing systems to further discuss the performance of this microbeam. Then the optimized initial beam parameters are given for high resolution and high hitting efficiency. At last, the experiment platform is briefly introduced.  相似文献   
140.
The construction and commissioning of HIRFL-CSR were finished in 2007. From 2000 to 2005 the subsystem and key devices of CSR were successfully fabricated, such as magnet, power supply, UHV system, e-cooler, electric-static deflector with the septum of 0.1 mm, and the fast-pulse kicker with the rise time of 150 ns. After that the CSR commissioning activities were performed in 2006 and 2007, including the accumulation of those heavy ions of C, At, Kr and Xe by the combination of stripping injection (STI) or multiple multi-turn injection (MMI) and e-cooling with a hollow e-beam, wide energy-range synchrotron ramping by changing the RF harmonic-number at mid-energy, the beam stacking in the experimental ring CSRe, the RIBs mass-measurement with the isochronous-mode in CSRe by using the time-of-flight method, and the ion beam slow-extraction from CSRm.  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