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991.
高频电磁波传播速度在水及淤积砂土中影响因素实验研究 总被引:1,自引:1,他引:1
水及淤积土中电磁波传播速度是实现水上探地雷达(GPR)探测数据准确时深转换的关键因素.论文基于探地雷达实测结果分析了水温、盐度、浊度对水中电磁波速的影响和粒径组成、含水量变化对砂土介电常数(电磁波速)的影响,建立了淤积砂土介电常数模型并给出了相应速度计算方法.研究表明水中电磁波速主要受水体盐度影响,随盐度增大而指数减小.淤积砂土介电常数符合Looyenga模型,现场探测时可根据土样三相体积比确定土体介电常数,进而确定土体电磁波速,实现GPR数据时深准确转换. 相似文献
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分析了几种常见的变化检测算法的鲁棒性,在此基础上提出一种光谱量值和形状优化组合的地表覆盖变化检测方法。以西安市及其周边为研究区域,分析该区域2000~2009年的地表覆盖变化。变化检测的总体精度为92.313%,Kappa系数为0.844,优于其他传统算法。 相似文献
993.
Normal Reference Value of Red Blood Cell Count of Chinese Presenile Men and Geographical Factors 总被引:1,自引:0,他引:1
HE Jinwei GE Miao SU Huimin LIANG Wei CHEN Hongfei 《中国地理科学(英文版)》2007,17(1):92-98
This paper aims at providing a scientific basis for unifying the normal reference value standards of red blood cell count of Chinese presenile men. The paper, using microscopical counting method, studies the relationship between the normal reference values of 38,061 samples of red blood cell count of presenile men and eight geographical factors in 297 units in China. It is found that the correlation of geographical factors and the normal reference value of red blood cell count of presenile men is quite significant (F=303.00, P=0.000). By using the method of stepwise regression analysis, one regression equation is inferred. It is concluded that if geographical data are obtained in a certain area, the normal reference value of red blood cell count of presenile men in this area can be reckoned by using the regression analysis. Furthermore, according to the geographical factors, China can be divided into eight regions: Northeast China Region, North China Region, Shanxi-Shaanxi-Inner Mongolia Region, Middle and Lower Reaches of the Changjiang River Region, Southeast China Region, Northwest China Region, Southwest China Region and Qinghai-Tibet Plateau Region. 相似文献
994.
Huayu Lu Joseph A. Mason Thomas Stevens Yali Zhou Shuangwen Yi Xiaodong Miao 《地球表面变化过程与地形》2011,36(12):1590-1603
This paper draws on recent optically stimulated luminescence (OSL) dating to evaluate the long‐held assumption that dust accumulation rates in the Loess Plateau and the extent of active aeolian sand in the dunefields to the north have varied together over time, because both are controlled by the strength of the Asian monsoons and also possibly because the dunefields are proximal loess sources. The results show there is little evidence that high rates of loess accumulation coincided with well‐dated episodes of extensive dune activity in the Mu Us, Otindag, and Horqin dunefields, at 11–8 ka and 1–0 ka. Explanations for the apparent lack of coupling include local variation in the trapping of dust and post‐depositional preservation of the loess and dune sediments, in response to varying local environmental conditions. In addition, a substantial portion of the loess may be transported directly from source areas where dust emission has somewhat different climatic and geomorphic controls than aeolian sand activity within the dunefields. The results of this study cast doubt on the use of loess accumulation rate as a palaeoclimatic proxy at millennial timescale. The dunefield and loess stratigraphic records are interpreted as primarily recording changes in effective moisture at a local scale, but the timing of late Quaternary dune activity, along with a variety of other evidence, indicates that moisture changes in many of the drylands of northern China may not be in phase with precipitation in core regions of the Asian monsoons. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Future changes of terrestrial ecosystems due to changes in atmospheric CO2 concentration and climate are subject to a large degree of uncertainty, especially for vegetation in the Tropics. Here, we evaluate the natural vegetation response to projected future changes using an improved version of a dynamic vegetation model (CLM-CN-DV) driven with climate change projections from 19 global climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5). The simulated equilibrium vegetation distribution under historical climate (1981–2000) has been compared with that under the projected future climate (2081–2100) scenario for Representative Concentration Pathway 8.5 (RCP8.5) to qualitatively assess how natural potential vegetation might change in the future. With one outlier excluded, the ensemble average of vegetation changes corresponding to climates of 18 GCMs shows a poleward shift of forests in northern Eurasia and North America, which is consistent with findings from previous studies. It also shows a general “upgrade” of vegetation type in the Tropics and most of the temperate zones, in the form of deciduous trees and shrubs taking over C3 grass in Europe and broadleaf deciduous trees taking over C4 grasses in Central Africa and the Amazon. LAI and NPP are projected to increase in the high latitudes, southeastern Asia, southeastern North America, and Central Africa. This results from CO2 fertilization, enhanced water use efficiency, and in the extra-tropics warming. However, both LAI and NPP are projected to decrease in the Amazon due to drought. The competing impacts of climate change and CO2 fertilization lead to large uncertainties in the projection of future vegetation changes in the Tropics. 相似文献
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大兴安岭地区加格达奇东部发育一套安山质凝灰角砾熔岩、安山质晶屑岩屑凝灰岩、安山岩,1:20万加格达奇幅区调将其划分为中晚侏罗世壮志组(J2-3z)和二叠纪星火组(P2x).本研究在加格达奇东部大黑山地区和额尔格奇地区安山岩中获得锆石LA-ICP-MS U-Pb谐和年龄分别为120±2.1 Ma和123.1±2.3 Ma,结合岩石组合特征,将原上述划分厘定为下白垩统龙江组(K1l),为大杨树盆地北部火山岩地层提供了新的同位素定年资料. 相似文献
1000.
分析苏北里下河地区排水入海的最大干河--射阳河在本流域中的地位和作用,目前河道淤积,工程老化和水污染严重等现状,以及射阳河蕴藏着的河海联运,水源充足,自然和人文景观众多潜在优势;阐述了整治和综合开发利用射阳河的重要性和迫切性;提出了整治和开发利用的3条总体原则,大体思路及保证顺利实施的关键措施。 相似文献