全文获取类型
收费全文 | 29881篇 |
免费 | 5873篇 |
国内免费 | 7416篇 |
专业分类
测绘学 | 2982篇 |
大气科学 | 3604篇 |
地球物理 | 6855篇 |
地质学 | 16942篇 |
海洋学 | 4853篇 |
天文学 | 474篇 |
综合类 | 2296篇 |
自然地理 | 5164篇 |
出版年
2024年 | 90篇 |
2023年 | 313篇 |
2022年 | 877篇 |
2021年 | 1150篇 |
2020年 | 1165篇 |
2019年 | 1490篇 |
2018年 | 1195篇 |
2017年 | 1338篇 |
2016年 | 1363篇 |
2015年 | 1555篇 |
2014年 | 1919篇 |
2013年 | 1710篇 |
2012年 | 2043篇 |
2011年 | 2089篇 |
2010年 | 1832篇 |
2009年 | 2067篇 |
2008年 | 1885篇 |
2007年 | 2220篇 |
2006年 | 2192篇 |
2005年 | 1927篇 |
2004年 | 1792篇 |
2003年 | 1598篇 |
2002年 | 1342篇 |
2001年 | 1102篇 |
2000年 | 964篇 |
1999年 | 906篇 |
1998年 | 795篇 |
1997年 | 716篇 |
1996年 | 654篇 |
1995年 | 545篇 |
1994年 | 498篇 |
1993年 | 402篇 |
1992年 | 366篇 |
1991年 | 269篇 |
1990年 | 176篇 |
1989年 | 252篇 |
1988年 | 120篇 |
1987年 | 88篇 |
1986年 | 49篇 |
1985年 | 30篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1954年 | 15篇 |
1877年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
921.
VICARIOUS RADIOMETRIC CALIBRATION OF SATELLITE FY-ID SENSORS AT VISIBLE AND NEAR INFRARED CHANNELS
下载免费PDF全文
![点击此处可从《Acta Meteorologica Sinica》网站下载免费的PDF全文](/ch/ext_images/free.gif)
ZHANG Yuxiang QIU Kangmu HU Xiuqing RONG Zhiguo ZHANG Lijun 《Acta Meteorologica Sinica》2004,18(4):505-516
For the problem of in-flight test site radiometric calibration for the FY-1D Meteorological Satellite onboard sensor's visible and near infrared channels,this paper described the calibration method,satellite-ground synchronous observation data acquired at China Dunhuang Calibration Test Site,parameter derivation and radiative transfer computation during the calibration,and the calibration result analysis.At FY-1D seven channels (with central wavelength at Channels 1:630 nm,2:865 nm;6:1610 nm;7:455 nm,8:505 nm;9:555 nm;10:932 nm),calibration coefficients obtained during the ground site calibration were compared with that respectively of prelaunch calibration.It is demonstrated that results of FY-1D onboard two sensors' (A and B) at channels 1,2,6 and 10 were close to pre-calibration,and the absolute difference of Gobi desert reflectance computed using test site and pre-launch calibration coefficients was no more than 2%. At other channels,large pre-launch calibration errors resulted in a poor consistency between the test site and pre-launch calibration.The errors can be corrected by the test site calibration results. Based on a rough estimation,the overall error of the calibration was about 6%. The paper also presented the in-flight vicarious calibration at the visible and near infrared channels of FY-1C sensor A which was launched in 1999 and has been put into operational mode since 2002.The results exhibit that FY-1C sensor's response has 23% attenuation at Channels 7 and 8,while only minor degradation at the other channels was found. During the mission,calibrations were also conducted at NOAA-17's Channels 1 and 2 (1:430-830 nm,2:500-1072 nm).A very good consistency has been achieved between the test site and pre-launched calibration results. 相似文献
922.
对某些类型的主震事件, 进行中短期预测也许是可能的. 利用Varnes, Bufe和Varnes提出的破裂时间法模拟前兆地震能量加速释放模型,通过实际观测资料与理论公式的拟合, 可以建立主地震事件的中短期预测技术, 用以确定表示主震的地点、时间和震级大小. 本文使用的是云南区域台网的地震目录资料,覆盖的时间段为1965~2002年. 统计分析表明,在此37年时间内,等于或大于2.5级地震资料是相当完整的. 本文对云南地区的30次主震事件进行了模拟,其中25次主震事件由前兆序列模拟得到的预测时间和震级与实际值相当接近,主震震级预测精度约0.57个震级单位,假定已知前兆序列中最后一次事件,则预测主震发生时间误差约0.64年.对另外的5次主震事件,由于没有足够的前兆事件来充分确定前兆能量加速曲线或是存在对能量加速释放曲线的干扰事件,而不能进行破裂时间法模拟.本文的研究结果还表明,由于云南是破坏性地震和中小地震活跃的地区,因此,主地震与前兆事件最佳搜索半径不存在明显的线性关系.主震矩与系数k,m之间存在强烈的相关性,利用主震地震矩与系数的关系和限制指数m的取值范围,可进一步缩小预测时间和预测震级的最佳拟合区范围,提高了模拟主震事件的预测精度. 本文采用破裂时间法对30次主震事件进行拟合,80%以上获得了较好的结果. 显示出该方法在预测已知主震事件序列的能力方面大有希望,因此,利用前兆事件对未来主震事件进行中短期预测的前景是令人鼓舞的. 相似文献
923.
The characteristics of atmospheric heat source associated with the summer monsoon onset in the South China Sea (SCS) are studied using ECMWF reanalysis data from 1979 to 1993. A criterion of the SCS summer monsoon onset is defined by the atmospheric hea… 相似文献
924.
925.
Environmental Properties of Minerals and Contaminants Purified by the Mineralogical Method 总被引:2,自引:0,他引:2
The investigation of the environmental properties of minerals, i.e., environmental mineralogy, is a branch of science dealing with interactions between natural minerals and spheres of the Earth surface as well as a reflection of global change, prevention of ecological destruction, participation in biomineralogy, and remediation of environmental pollution. Pollutant treatment by natural minerals is based on the natural law and reflects natural self-purification functions in the inorganic world, similar to that of the organic world - a biological treatment. A series of case studies related to natural self-purification, which were mostly completed by our group, are discussed in this paper. In natural cryptomelane there is a larger pseudotetragonal tunnel than that formed by [MnO6] octahedral double chains, with an aperture of 0.462-0.466 nm2, filled with K cations. Cryptomelane might be a real naturally-occurring mineral of the active octahedral molecular sieve (OMS-2). CrⅥ-bearing wastewater can be treate 相似文献
926.
927.
Geologic marks related to extraterrestrial impact events, such as impact split gravels, impact brecciate layers, impact dikes, microirghizites, microtektites, especially meteoritic residues, were discovered on the boundary between Sinian/Cambrian at Tianmenshan of Western Hunan, which may possibly demonstrate that an extraterrestrial impact event has ever occurred there on the S/C boundary. 相似文献
928.
The Wahongshan fault zone in Qinghai province is one of the most important faults in westem China. In this paper, deformation and X-ray petrofabrics have been studied in the middle segment of the fault. The results show that the formation of the fault zones can be divided into two major stages: ductile shear deformation stage and brittle deformation stage. The early stage ductile shearing leads to the formation of the NW-NNW trending mylonite zones along the fault, which is intensely cut by the late-formed brittle faults. X-ray petrofabrics of rocks near the faults indicate that the minerals in the tectonites show a great degree of orientation in the alignment. The quartz, which is a very important mineral in the tectonites, is deformed by basal face gliding or near basal face gliding, and sometimes by prismatic face sliding, which indicates that the rocks are deformed in epithermal to mesothermal or mesothermal environment, and the dynamic recrystallization also plays an important role in the formation 相似文献
929.
930.
NHC硅化法及其应用 总被引:1,自引:0,他引:1
NHC硅化加固方法 ,已在数十项工程中推广应用 ,均取得满意效果 ,介绍了这一方法的作用原理及其特性 ,并列举了在几项工程中的应用实例。 相似文献