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   245篇
  免费   27篇
  国内免费   46篇
测绘学   19篇
大气科学   33篇
地球物理   72篇
地质学   126篇
海洋学   35篇
天文学   1篇
综合类   15篇
自然地理   17篇
  2022年   5篇
  2021年   5篇
  2020年   4篇
  2019年   7篇
  2018年   4篇
  2017年   10篇
  2016年   10篇
  2015年   10篇
  2014年   12篇
  2013年   24篇
  2012年   13篇
  2011年   16篇
  2010年   10篇
  2009年   11篇
  2008年   16篇
  2007年   15篇
  2006年   26篇
  2005年   10篇
  2004年   17篇
  2003年   10篇
  2002年   10篇
  2001年   7篇
  2000年   10篇
  1999年   15篇
  1998年   6篇
  1997年   7篇
  1996年   4篇
  1995年   6篇
  1994年   5篇
  1993年   4篇
  1992年   4篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
排序方式: 共有318条查询结果,搜索用时 15 毫秒
91.
为了满足现场完成计算的需要,采用线路测量中桩、边桩放线的Casiofx-4800p计算器程序,运用该程序可以根据测量需要进行直线、圆曲线、缓和曲线中桩坐标和构筑物任意位置坐标计算,方便快捷,值得推广。  相似文献   
92.
MPI(Message Passing Interface)是消息传递并行程序设计的标准之一,概述了MPI的概念和组成,着重介绍了支持并行程序设计的消息传递接口(MPI)以及在MPI环境下的并行程序设计方法,并给出一个MPI并行程序设计实例,说明了MPI的程序设计流程和主从并行计算流程,由此提出了一个Master/Slave结构的设计模式。  相似文献   
93.
灰色聚类法在膨胀土分类中的应用   总被引:24,自引:3,他引:21  
介绍了灰色聚类法在膨胀土分类中的应用。以南水北调中线工程为例,利用灰色系统理论中的灰色聚类法对膨胀土的胀缩等级做了评判, 结果表明: 用灰色聚类法对膨胀土进行分类,使其分类数学化与定量化,对于解决常规多因子分类中,由于指标交叉而不能归类的问题更有其优越性。  相似文献   
94.
CINRAD/SB雷达伺服上电故障诊断分析   总被引:1,自引:1,他引:0  
在详细介绍CINRAD/SB雷达数字伺服系统加电控制、天线状态信号流程的基础上,分析出数字伺服系统无法上电3方面原因:负载过载导致空气开关保护性断电;伺服系统加电信号不正常;制动器过流导致温度超限。总结了CINRAD/SB雷达伺服系统无法上电故障的分析方法和诊断流程。通过诊断流程详细论述两例伺服无法上电的复杂故障分析和排除过程,以及在台站无配件更换情况下,充分利用雷达线路特点暂时采用应急方法尽快恢复雷达运转的方法,保证灾害性天气监测的需求。为新一代天气雷达技术支持和保障提供借鉴。  相似文献   
95.
In this paper, an improved method is presented to reduce vibrator harmonic distortion, one harmonic at a time and the method is illustrated with both simulated and field data. This method improves on the previous method that treated all the harmonics at once. The significant contribution in this procedure is a considerable reduction for the harmonics without any alteration for the weakest signals possibly present in positive and negative times. The core of the proposed technique depends on an accurate simulation for all the harmonics one by one existing in the positive and negative times of the data after cross‐correlation with the fundamental sweep and then subtracting the simulated harmonics from the original data using an optimization procedure. The steps and mathematical equations of the procedure are explained in detail in the body of the article in the section titled ‘harmonic by harmonic attenuation procedure’. Accordingly, a well‐developed procedure for enhancing the vibroseis data quality in both down‐ and up‐sweep data is illustrated. The procedure was tested on both synthetic and field data sets.  相似文献   
96.
In this paper we extend the generalized likelihood uncertainty estimation (GLUE) technique to estimate spatially distributed uncertainty in models conditioned against binary pattern data contained in flood inundation maps. Untransformed binary pattern data already have been used within GLUE to estimate domain‐averaged (zero‐dimensional) likelihoods, yet the pattern information embedded within such sources has not been used to estimate distributed uncertainty. Where pattern information has been used to map distributed uncertainty it has been transformed into a continuous function prior to use, which may introduce additional errors. To solve this problem we use here ‘raw’ binary pattern data to define a zero‐dimensional global performance measure for each simulation in a Monte Carlo ensemble. Thereafter, for each pixel of the distributed model we evaluate the probability that this pixel was inundated. This probability is then weighted by the measure of global model performance, thus taking into account how well a given parameter set performs overall. The result is a distributed uncertainty measure mapped over real space. The advantage of the approach is that it both captures distributed uncertainty and contains information on global likelihood that can be used to condition predictions of further events for which observed data are not available. The technique is applied to the problem of flood inundation prediction at two test sites representing different hydrodynamic conditions. In both cases, the method reveals the spatial structure in simulation uncertainty and simultaneously enables mapping of flood probability predicted by the model. Spatially distributed uncertainty analysis is shown to contain information over and above that available from global performance measures. Overall, the paper highlights the different types of information that may be obtained from mappings of model uncertainty over real and n‐dimensional parameter spaces. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
97.
We describe an objective method for evaluating the spatial distribution of water equivalents of the snow cover within a small catchment. Regression analysis is used to quantify the relationship between elevation, presence or absence of forest, and potential direct solar radiation as independent variables and water equivalent as measured at a number of sites. First, this regression relationship is used to interpolate water equivalent data all over the basin area. Then we interpolate the residuals of the regression using a geostatistical approach. Superimposing the results obtained by interpolating the regression relationship and the interpolated residuals eventually yields the water equivalent distribution over the test area. The advantages of the interpolation method used lie in the optimal (effective, unbiased) estimation of the interpolated values as well as in the possibility to quantify the associated estimation variances.  相似文献   
98.
Direct, partitioned, and projected (conjugate gradient‐like) solution approaches are compared on unsymmetric indefinite systems arising from the finite element integration of coupled consolidation equations. The direct method is used in its most recent and computationally efficient implementations of the Harwell Software Library. The partitioned approach designed for coupled problems is especially attractive as it addresses two separate positive definite problems of a smaller size that can be solved by symmetric conjugate gradients. However, it may stagnate and when converging it does not prove competitive with a global projection method such as Bi‐CGSTAB, which may take full advantage of its flexibility in working on scaled and reordered equations, and thus may greatly improve its computational performance in terms of both robustness and convergence rate. The Bi‐CGSTAB superiority to the other approaches is discussed and demonstrated with a few representative examples in two‐dimensional (2‐D) and three‐dimensional (3‐D) coupled consolidation problems. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
99.
王静  吴宇峰  王斌  张磊  王鑫  赵一 《岩矿测试》2015,34(4):464-470
毒性淋溶提取法(TCLP)是美国法定的一种生态环境风险评价方法,通过提取土壤中的重金属有效态判断土壤重金属污染状况和评估污染区域生态风险。本文应用TCLP法提取天津市某工业园区内及周围农田土壤中的有效态Cu、Pb、Zn、Cd,采用电感耦合等离子体质谱法和原子吸收光谱法分别测定重金属全量和有效态,结合单项污染指数和内梅罗综合污染指数评价了重金属生态风险。结果表明:研究区Zn是首要污染物,主要来源于镀锌厂、金属制品厂和电镀厂,其次是Pb和Cu污染,Cd无污染;Pb、Zn可能具有同源性或伴生关系;大部分土壤处于安全水平,重金属污染率不到30%,但农田土壤出现了Zn的轻度污染。重金属全量是影响重金属有效态含量较大的因素,当Zn全量大于环境质量标准限值(300 mg/kg),Pb全量大于80mg/kg时,有效态Zn、Pb与其全量均呈正相关。因此,可以使用TCLP法将土壤重金属全量与有效态进行量化评价重金属生态风险。  相似文献   
100.
王小华  杨玉琪  罗新雨  温涛 《地理学报》2022,77(8):1920-1936
高质量发展是中国“十四五”乃至更长时期经济社会发展的主题,也是适应社会主要矛盾变化的基本要求,更是建设社会主义现代化国家的关键路径和遵循经济实践规律的根本所在。本文从创新、协调、绿色、开放、共享5个维度构建经济高质量发展的评价指标体系,测度了2011—2018年中国31个省(自治区、直辖市)的经济高质量发展水平,在此基础上运用社会网络分析(SNA)和二次指派程序(QAP)分别对经济高质量发展的关联网络结构特征和经济高质量发展差异的作用机制进行分析。研究发现:① 空间关联网络的关联度一直为1,且网络密度稳定在0.2~0.26之间,省际经济高质量发展的空间关联网络通达性较强且存在多重叠加现象和一定的等级性,但关联紧密程度有待提高,各网络指标保持相对稳定。② 省际经济高质量发展的空间关联网络可以分为4个板块,其中以西部省份为主的“净溢出”板块获益最小;以中部省份为主的“经纪人”板块起着“中介”和“桥梁”的作用;以环渤海省份为主的“双向溢出”板块和以长三角、东南沿海省份为主的“净受益”板块在空间关联网络中的掌控和支配作用更大,且在全国经济高质量发展过程中所起的极化作用大于涓滴作用。③ 人力资本、城市化水平、金融科技和环境质量的地区差异都会直接造成地区间经济高质量发展水平的差异,人力资本差异对其贡献超过了90%。  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