全文获取类型
收费全文 | 5819篇 |
免费 | 1000篇 |
国内免费 | 1620篇 |
专业分类
测绘学 | 664篇 |
大气科学 | 1121篇 |
地球物理 | 1307篇 |
地质学 | 2920篇 |
海洋学 | 953篇 |
天文学 | 154篇 |
综合类 | 496篇 |
自然地理 | 824篇 |
出版年
2024年 | 27篇 |
2023年 | 103篇 |
2022年 | 180篇 |
2021年 | 265篇 |
2020年 | 180篇 |
2019年 | 271篇 |
2018年 | 271篇 |
2017年 | 232篇 |
2016年 | 336篇 |
2015年 | 301篇 |
2014年 | 347篇 |
2013年 | 360篇 |
2012年 | 408篇 |
2011年 | 417篇 |
2010年 | 392篇 |
2009年 | 392篇 |
2008年 | 352篇 |
2007年 | 404篇 |
2006年 | 318篇 |
2005年 | 329篇 |
2004年 | 307篇 |
2003年 | 245篇 |
2002年 | 383篇 |
2001年 | 313篇 |
2000年 | 260篇 |
1999年 | 221篇 |
1998年 | 122篇 |
1997年 | 115篇 |
1996年 | 85篇 |
1995年 | 98篇 |
1994年 | 86篇 |
1993年 | 48篇 |
1992年 | 50篇 |
1991年 | 44篇 |
1990年 | 37篇 |
1989年 | 24篇 |
1988年 | 25篇 |
1987年 | 22篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1976年 | 1篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1958年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有8439条查询结果,搜索用时 15 毫秒
991.
Mesozoic-Cenozoic tectonic transition in Kuqa Depression-Tianshan, Northwest China: Evidence from sandstone detrital and geochemical records 总被引:2,自引:0,他引:2
LI Zhong GUO Hong WANG Daoxuan & LIN Wei . Institute of Geology Geophysics Chinese Academy of Sciences Beijing China . Tarim Oilfield Branch CNPC Korla China . Hefei University of Industry Tunxilu Hefei China 《中国科学D辑(英文版)》2005,48(9):1387-1402
Succeeding to multiply collisions of different blocks in Late Paleozoic[1―5], complex intracontinental structural deformation occurred in the Tianshan area during Mesozoic-Cenozoic[6―16], which controlled coeval basin-range evolution and resulted in intensive modi- fication and adjustment of the Paleozoic oil-gas reser- voirs[17―19]. The Kuqa Depression is a secendary struc- tural unit of the Tarim basin, in which Mesozoic- Ce- nozoic deposits occur in thickness of 6000―7000 m. The Kuq… 相似文献
992.
根据渤海海域的构造演化背景和地质构造特征建立了该区的二维地质模型,用二维有限元方法计算模拟了渤海海域现代构造应力场,获得了该区构造应力场的分布特征;同时,根据计算结果把渤海海域的构造应力场分为辽东湾、渤中、渤东和渤西等4个区域,并对这4个区域在构造应力场上的差异性进行了描述。从渤海海域整体的应力分布可以看出,该区新近纪以来的断裂活动总体水平上西部较东部强烈,海域东部沿郯庐断裂带仍有较高的断裂发育程度及断裂张开性,而海域中部地区的断层发育程度、活动位移均较低 相似文献
993.
994.
995.
Jianhua Xu Yaning Chen Weihong Li Qin Nie Yulian Hong Yang Yang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(2):389-399
Based on the hydrologic and meteorological data in the Yarkand River Basin during 1957–2008, the nonlinear hydro-climatic process was analyzed by a comprehensive method, including the Mann–Kendall trend test, wavelet analysis, wavelet regression analysis and correlation dimension. The main findings are as following: (1) The annual runoff, annual average temperature and annual precipitation showed an increasing trend during the period of 1957–2008, and the average increase extent in runoff, temperature and precipitation was 2.234 × 108 m3/10 year, 0.223 °C/10 year, and 4.453 mm/10 year, respectively. (2) The nonlinear pattern of runoff, temperature and precipitation was scale-dependent with time. In other words, the annual runoff, annual average temperature and annual precipitation at five time scales resulted in five patterns of nonlinear variations respectively. (3) Although annual runoff, annual average temperature and annual precipitation presented nonlinear variations at different time scales, the runoff has a linear correlation with the temperature and precipitation. (4) The hydro-climatic process of the Yarkand River is chaotic dynamic system, in which the correlation dimension of annual runoff, annual average temperature and annual precipitation is 3.2118, 2.999 and 2.992 respectively. None of the correlation dimensions is an integer, and it indicates that the hydro-climatic process has the fractal characteristics. 相似文献
996.
香港地区活动断裂的初步探讨 总被引:1,自引:0,他引:1
香港地区的断裂构造颇为发育,主要有北东、北东东和北西向三组断裂。在现今构造应力场作用之下,北东东和北西向断裂组成共轭断裂系统。由于本地区地震活动水平不高,尚难确定哪组断裂与地震活动密切相关。断层泥的热释光资料表明,断裂的最新活动应在晚更新世,断裂的复发周期应在10万年左右。目前尚不能肯定哪条断裂为活动断裂。 相似文献
997.
Hong Hao 《地震工程与结构动力学》1998,27(1):91-103
During the recent major earthquakes, some bridges suffered severe damage due to the pull-off-and-drop collapse of their decks. This is due to the large differential movements of the adjacent spans of bridges during strong shaking compared to the seating lengths provided. The differential movements are primarily due to the different vibration properties of adjacent spans and non-uniform ground excitations at the bridge supports. This paper analyses the effects of various bridge and ground motion parameters on the required seating lengths for bridge decks to prevent the pull-off-and-drop collapse. The random vibration method is used in the analysis. A two-span bridge model with different span lengths and vibration frequencies and subjected to various spatially varying ground excitations is analysed. Non-uniform spatial ground motions are modelled by the filtered Tajimi–Kanai power spectral density function and an empirical coherency function. Ground motions with different intensities, different cross-correlations and different site conditions are considered in the study. The required seating lengths for bridge decks are calculated. Numerical results are presented and discussed with respect to different bridge vibration and ground motion properties. © 1998 John Wiley & Sons, Ltd. 相似文献
998.
目前钻孔应变观测一般为水平应变,使用无限岩石平板中的钻孔应力集中模型,可反演出水平应力场分布及变化.如果在此基础上加上垂向应力测量,就可反演出三维应力场分布.本文介绍的RZB型深井宽频带地形变综合观测系统的垂向应变测量单元,外钢筒为波纹管结构,并通过螺旋刻丝、热处理等技术,其垂向等效弹性模量比耦合水泥低一个数量级,同时垂向应变钢筒的水平向等效弹性模量高于垂向弹性模量一个数量级.垂向应变探头的力学结构可以被形象地看成是一个螺旋柱形弹簧,其轴向极易产生弹性形变,而水平向的硬度却得到了极大的加强,因此可在竖井中较为准确地测量轴向应变. 相似文献
999.
This paper discusses the growth stages,spatial structures,quantitative fitting relationships among various parameters,growth patterns and influencing factors of mud cracks by field survey,core observation and SEM analysis.The study shows that:(1) Mud crack growth can go through three stages,i.e.the syndiagenetic stage,the burial diagenetic stage(including early diagenetic stage,middle-late diagenetic stage) and the epidiagenetic stage.(2) Quantitative fitting relationships among various parameters allow a great significance to describe the spatial structure,the regional distribution and the growth environment of mud cracks.(3) Mud crack growth has three models,such as the unilateral growth model including the linear growth pattern,the curvilinear growth pattern and the bifurcation growth pattern,the multilateral growth model including the inteisectional growth pattern,the join growth pattern and the dispersed growth pattern,and the mixed growth model including the combination of any patterns listed above.(4) Modern mud crack growth usually undergoes four stages.Sand beds in sand-mud rhythmic strata can play a lubricative role on crack growth and provide enough sandy deposits for filling cracks.(5) Mud crack growth usually produces bifurcation and bifurcation angles which are mostly 120° or 90° that are related to sediment heterogeneity and released energy.(6)Factors affecting mud crack growth cover many aspects:clay content and salinity can control the number of mud cracks in different areas;terrain can control mud crack morphology;and different sedimentary cycles can control the growth patterns and filling models of mud cracks. 相似文献
1000.
人工地震测深和天然地震流动观测兼用的轻便数字地震仪系统 总被引:7,自引:1,他引:7
本文介绍一种新的轻便数字地震仪DAS-1。其设计特点是:双微处理器硬件结构;过采样AD转换技术的运用;线性相位和最小相位FIR数字滤波的运用;大容量CMOS快闪存贮器作数据存储介质;GPS授时和内部高精度数字钟相结合的时间服务系统;采集器功耗低于0.65W。该仪器有3个信号输入通道,0 ̄40Hz的带宽和16位字长。它可方便地用于人工地震测深及天然地震流动观测。 相似文献