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   841篇
  免费   192篇
  国内免费   197篇
测绘学   49篇
大气科学   34篇
地球物理   328篇
地质学   507篇
海洋学   224篇
天文学   1篇
综合类   34篇
自然地理   53篇
  2024年   5篇
  2023年   8篇
  2022年   13篇
  2021年   37篇
  2020年   40篇
  2019年   27篇
  2018年   35篇
  2017年   44篇
  2016年   34篇
  2015年   53篇
  2014年   38篇
  2013年   44篇
  2012年   60篇
  2011年   70篇
  2010年   49篇
  2009年   58篇
  2008年   52篇
  2007年   73篇
  2006年   56篇
  2005年   53篇
  2004年   58篇
  2003年   49篇
  2002年   40篇
  2001年   36篇
  2000年   20篇
  1999年   18篇
  1998年   20篇
  1997年   20篇
  1996年   36篇
  1995年   16篇
  1994年   15篇
  1993年   17篇
  1992年   9篇
  1991年   5篇
  1990年   3篇
  1989年   2篇
  1988年   4篇
  1987年   5篇
  1986年   2篇
  1985年   1篇
  1984年   1篇
  1983年   2篇
  1982年   1篇
  1979年   1篇
排序方式: 共有1230条查询结果,搜索用时 187 毫秒
81.
柿竹园夕卡岩中有早、晚形成的两种产状石榴子石。本文为查明其形成物理化学条件及与矿化的关系,采用矿区天然花岗岩、灰岩和夕卡岩化早期形成的石榴子石为试样进行了模拟实验研究。实验结果表明:夕卡岩化早期石榴子石是在温度400—750℃,压力500—1000bar,pH=5—8条件下,由富含Si、Al、Fe、Cl、F等组分的热液与上泥盆统佘田桥组灰岩交代反应形成的;晚期石榴子石是在温度250—700℃,压力500—1000bar,pH=5—14条件下,由富含Si、Al、F等组分的带钨溶液与早期石榴子石交代反应产生重结晶作用形成的。  相似文献   
82.
The use of digital models has increased significantly in recent years with the accessibility of fast computing machines. A variable dimensioned digital model was constructed for the Shadnagar granite basin using SPECTRUM-7 micro computer to integrate various hydrogeological characteristics and for their quantitative evaluation. The basin has an areal extent of 437 sq km and is demarcated with clear water divides in all directions. Transmissivity, recharge and discharge at each cell of the basin area were estimated by trial and error simulation of the hydrogeological phenomenon under steady state condition. Dynamic simulation at representative nodes facilitated the estimation of storage coefficient. The capability of the constructed model was established by the conformance of the simulated hydrographs with the actual behaviour of the ground water system. The entire studies ammended the earlier arrived estimates of various input/output hydrogeological parameters and evolved a methodology for efficient processing of aquifer simulation data  相似文献   
83.
程先云  刘洪禄  郑凡东 《水文》2007,27(6):42-45
引入水箱模型进行城市地下排水设施降雨一侵入水的模拟,探讨了初期蓄流值对模拟结果的影响并提出了相应的解决办法;由于模型参数多、非线性,参数的率定采用通用优化分析计算平台PowerFit,并获得了满意的结果,表明:①水箱模型适用于地下排水设施雨洪模拟和预测,可为市政规划设计和城市灾害预报提供可靠依据;②PowerFit全局优化能力强、简单易用,可广泛应用于水利水电等工程领域中的优化计算。  相似文献   
84.
In this paper a spatially distributed model of the hillslope sediment delivery processes, named the sediment delivery distributed (SEDD) model, is initially reviewed; the model takes into account the sediment delivery processes due to both the hillslope sediment transport and the effects of slope curvature. Then the rainfall and sediment yield events measured at the experimental SPA2 basin, in Sicily, are used both to calibrate the SEDD model and to verify the predictive capability of the distributed sediment delivery approach at event scale. For the SPA2 basin discretized into morphological units and stream tubes, the SEDD model is calibrated at event scale using the measurements carried out at the outlet of the experimental basin in the period December 2000–January 2001. The model calibration is used to determine a relationship useful for estimating the unique coefficient βe of the model by rainfall erosivity factor Re at event scale. To test the predictive capability of the βe = f(Re) relationship, 20 events measured in the period September 2002–December 2005 are used; the comparison between measured sediment yield values and calculated ones for all monitored events shows that the sediment delivery distributed approach has a good predictive ability at event scale. The analysis also shows that estimating βe by the relationship βe = f(Re) gives a better agreement between measured and calculated sediment yields than obtained with the median value βe,m of all 27 calculated βe values. Finally the analysis at annual scale, for the period 2000–2005, allows the estimation of the median value βa,m representative of the annual behaviour. This analysis shows that the sediment delivery distributed approach also has a good predictive ability at annual scale. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
85.
Equilibrium and disequilibrium degassing of a volatile phase from a magma of K-phonolitic composition was investigated to assess its behavior upon ascent. Decompression experiments were conducted in Ar-pressurized externally heated pressure vessels at superliquidus temperature (1050 °C), in the pressure range 10–200 MPa using pure water as fluid phase. All experiments were equilibrated at 200 MPa and then decompressed to lower pressures with rates varying from 0.0028 to 4.8 MPa/s. Isobaric saturation experiments were performed at the same temperature and at 900–950 °C to determine the equilibrium water solubility in the pressure range 30–250 MPa. The glasses obtained from decompression experiments were analyzed for their dissolved water content, vesicularity and bubble size distribution. All decompressed samples presented a first event of bubble nucleation at the capsule–melt interface. Homogeneous bubble nucleation in the melt only occurred in fast-decompressed experiments (4.8 and 1.7 MPa/s), for ΔP ≅ 100 MPa. For these decompression rates high water over-saturations were maintained until a rapid exsolution was triggered at ΔP > 150 MPa. For slower rates (0.0028, 0.024, 0.17 MPa/s) the degassing of the melt took place by diffusive growth of the bubbles nucleating at the capsule–melt interface. This process sensibly reduced water over-saturation in the melt, preventing homogeneous nucleation to occur. For decompression rates of 0.024 and 0.17 MPa/s low water over-saturations were attained in the melt, gradually declining toward equilibrium concentrations at low pressures. A near-equilibrium degassing path was observed for a decompression rate of 0.0028 MPa/s. Experimental data combined with natural pumice textures suggest that both homogeneous and heterogeneous bubble nucleations occurred in the phonolitic magma during the AD 79 Vesuvius plinian event. Homogeneous bubble nucleation probably occurred at a depth of ∼ 3 km, in response to a fast decompression of the magma during the ascent.  相似文献   
86.
裂隙概化模型的非饱和渗流试验研究   总被引:4,自引:1,他引:4       下载免费PDF全文
借鉴多孔介质非饱和渗流试验的研究成果,研制出一套可同时测定单裂隙毛细压力-饱和度以及非饱和渗透系数-毛细压力关系的试验装置.为检验试验装置的可信度和试验原理的正确性,并初步探讨单裂隙非饱和渗流的机理,特制作了一阶梯开度的裂隙概化模型(本文称之为“S-H”裂隙模型),并在上述试验装置上进行了“S-H”裂隙模型的非饱和渗流试验,初步阐明了单裂隙非饱和渗流的一些基本水力特性,同时试验结果也表明本文试验装置和试验原理合理可靠.  相似文献   
87.
DUT-1合成模型冰的弯曲强度和弹性模量实验分析   总被引:3,自引:0,他引:3       下载免费PDF全文
依据渤海海冰物理和力学特征值和国内水池实验室能力,以1:10~1:30比尺要求,发展了DUT-1合成模型冰.文中简介该模型冰的理想参数、成分和制备过程.就其弯曲强度和弹性模量进行系统的实验分析.通过500多次弯曲实验,获得该模型冰在不同加载速度下的破坏方式,各向同性证据和弯曲强度为35~65kPa和弹性模量平均53MPa的结果.并且得到弯曲强度和弹性模量在实测湿密度范围内呈递增关系,浸水模型冰性能稳定时间超过4h,弹性模量与弯曲强度之比82%超过2000.  相似文献   
88.
本文采用液压阻尼系统(HDS)控制立式圆柱钢制储罐的地震反应,建立了安装HDS储罐的力学分析模型,并进行了数值计算,从频域对安装HDS后储罐的地震响应进行了分析,研究了HDS的减震效果和HDS和HDS参数对储罐地震反应的影响。  相似文献   
89.
二级结构地震反应的实验研究   总被引:2,自引:0,他引:2  
本文针对结构顶部的附属结构在正弦激励和地震动作用下的反应,设计了多层结构模型并研究了附属结构的多种情况。实验结果表明,附属结构在地震作用下可对主体结构产生不同的影响,根据附属结构的参数的不同可能导致主体结构的反应增大或减小,因此得出结论:在结构设计时对主体结构和附属结构进行整体考虑,能使结构的地震反应控制在最佳的水平。  相似文献   
90.
DUT-1非冻结合成模型冰的弯曲强度   总被引:1,自引:4,他引:1  
简介了DUT-1非并结合成模型冰的功能,给出DUT-1模型冰的弯曲强度的测试装置和设备,讨论该模型冰在不同加载速度下的破坏方式和发生峰值弯曲强度的条件,通过悬臂梁上弯和下湾实验结果,说明DUT-1模型冰的各向同性,检验了浸水模型冰性能的稳定性和模型冰湿密度对峰值弯曲强度的效应。  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