全文获取类型
收费全文 | 14330篇 |
免费 | 1650篇 |
国内免费 | 1854篇 |
专业分类
测绘学 | 5064篇 |
大气科学 | 2069篇 |
地球物理 | 2220篇 |
地质学 | 3056篇 |
海洋学 | 1330篇 |
天文学 | 1241篇 |
综合类 | 1446篇 |
自然地理 | 1408篇 |
出版年
2024年 | 76篇 |
2023年 | 148篇 |
2022年 | 459篇 |
2021年 | 599篇 |
2020年 | 602篇 |
2019年 | 686篇 |
2018年 | 469篇 |
2017年 | 761篇 |
2016年 | 678篇 |
2015年 | 697篇 |
2014年 | 805篇 |
2013年 | 1008篇 |
2012年 | 902篇 |
2011年 | 852篇 |
2010年 | 667篇 |
2009年 | 816篇 |
2008年 | 855篇 |
2007年 | 1012篇 |
2006年 | 930篇 |
2005年 | 748篇 |
2004年 | 709篇 |
2003年 | 549篇 |
2002年 | 464篇 |
2001年 | 391篇 |
2000年 | 318篇 |
1999年 | 284篇 |
1998年 | 227篇 |
1997年 | 168篇 |
1996年 | 162篇 |
1995年 | 147篇 |
1994年 | 135篇 |
1993年 | 114篇 |
1992年 | 76篇 |
1991年 | 65篇 |
1990年 | 43篇 |
1989年 | 46篇 |
1988年 | 34篇 |
1987年 | 20篇 |
1986年 | 21篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1977年 | 11篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
961.
962.
963.
舒宁 《武汉大学学报(信息科学版)》1989,(2)
本文论述了有关草资源调查的草原分类原理在计算机上实施的可能性,及如何利用辅助数据和影象数据复合技术问题,并以藏北高寒牧区大面积、高精度的草资源调查计算机分类的实例予以验证。 相似文献
964.
Precipitable water measurements made coincident in time and space with direct broadband solar irradiance measurements are used in conjunction with an atmospheric transmission model to derive a parameter whose major dependence is on total aerosol extinction. Irradiance measurements are used to calculate an atmospheric transmission factor (ATF) that is independent of the instrument calibration and the extraterrestrial solar constant. The dependency of the ATF on precipitable water is determined using LOWTRAN5, an atmospheric transmission model with high spectral resolution. Precipitable water measurements are then used to adjust the measured ATF to correspond to an ATF value obtained for a constant precipitable water amount. The remaining variability in the adjusted ATF is due mostly to aerosol extinction. The technique is applied to a 6-year period (1978–1983) for clear-sky mornings at Mauna Loa, Hawaii (MLO). MLO ATF aerosol residuals are compared with independently measured monochromatic aerosol optical depth. Results show that the ATF aerosol residual is nearly equal to the 500 nm aerosol optical depth prior to the eruption of E1 Chichon, at which time a nonlinear time-dependent relationship between the two quantities is evident. ATF aerosol residuals reflect the spectrally integrated aerosol influence on transmission and, therefore, could indicate better than monochromatic optical depth the radiation balance perturbations due to aerosols. The 6-year precipitable water record for MLO, determined from a dual-channel sunphotometer, has a mean value of 0.3 cm. An annual cycle in precipitable water is evident, as is a 4-month 5-standard-deviation drought from December 1982 through March 1983. 相似文献
965.
In this paper, the authors present the results of both macroscopic and microscopic investigations on structure development created by repeated ice lensing in various loamy experiments. Experimental data are compared with observations performed on active forms in High Arctic and Alpine Mountain environments. Those observations are also compared with phenomena observed in fossil periglacial formations of Western Europe. Platy and short prismatic structure formation is bonded to the hydraulic and thermal conditions during ice segregation. When a long series of alternating freezing and thawing affects platy structures, the fabric evolves, also being influenced by slope and drainage conditions: cryoturbations, frostcreep, and gelifluction can appear. They are characterized by specific microfabrics which are better developed with an increasing number of cycles: this is clear in experiments where hydraulic and thermal parameters are better controlled. Vesicles are also a prominent characteristic of the surface horizon in experiments and arctic soils. The genesis of vesicles is discussed on the basis of new observations and is related to the mechanical collapse of frost-created aggregates under the mechanical work of soil air escape during soil saturation by water at thaw. 相似文献
966.
本文对多元统计分析中目前应用的对应分析方法的原理公式作了重新推导,提出 z_(ij)=(p_(ij)/p_(i.)p_(.j))-1的数据变换公式;并对原始数据作了严格的预处理。最后应用一个实例计算和作图,与简单的因子分析及原用的对应分析成果作了比较。理论和算例都说明本文介绍的对应分析的数据预处理和分析方法较原用方法原理上更正确,应用上更合理,并克服了变量中对各种数据原有的局限性。 相似文献
967.
Isofactorial models for granulodensimetric data 总被引:1,自引:0,他引:1
Existing isofactorial models developed for disjunctive kriging using a cutoff grade on one variable are extended to the bivariate case which arises when dealing with granulo-densimetric data, such as are obtained from coal washing or mineral processing. 相似文献
968.
平面滑动标准化法是应用电子计算机处理(以下简体电算)大量区域水化资料的一种方法。它能够较好地反映水中各种元素的区域分布和圈定高背景区,准确地确定各类水异常的规模、强度和空间展布,有效地检出大量数据中的微弱信息,比传统整理方法具有显著的优越性。本文以65地区的应用效果加以说明。 相似文献
969.
J. Ricardo A. De França J. -M. Brustet J. Fontan 《Journal of Atmospheric Chemistry》1995,22(1-2):81-110
Remote sensing measurements provide a vauable means of determining the extent of burning areas and of estimating the overall distribution of pollutant sources (identified from experimental studies) in time and space. This distribution has to be taken into account in the boundary conditions of chemistry atmospheric models.Recent methods developed for the remote sensing of active fires in tropical or temperated forest zones, have been found to be completely inadequate for fire detection on West African savannas. In order to accurately estimate the active fire distribution in the function of different sorts of West African savannas (Sahelian, Sudanian and Guinean) and forests, a multispectral methodology has been developed based on NOAA/11-AVHRR satellite data, with the purpose of eliminating as much as possible the problems related to large surface heterogeneity, confusion and bias, produced by clouds, smoke, haze, background emissivities, etc.Unlike other methods, the results show that the multispectral method, in spite of its selectivity, provides realistic results, and does not under- or over-estimate the number of fires that can be sensed by the satellite. Consequently, this methodology is more appropriate than the simplest ones for a systematic sensing of this phenomenon. 相似文献
970.
应用考虑震级不确定笥和资料完整性估计地震危险性参数的极大似然法,分别采用1940年和1070年至1993年完整的地震资料,计算了汾渭地震带及陕南地区的地震危险性参数。结果表明:利用近几十年来的完整地震资料结合研究区历史上发生的最大地震,可以得到较为可靠的地震危险性参数;参数敏感性分析表明,完整震级不确定性对β的影响较小;随震级不确定性的增大地震年发生率减小;在资料完整的前提下,震级下限在一定范围内 相似文献