全文获取类型
收费全文 | 1149篇 |
免费 | 124篇 |
国内免费 | 277篇 |
专业分类
测绘学 | 304篇 |
大气科学 | 30篇 |
地球物理 | 180篇 |
地质学 | 562篇 |
海洋学 | 139篇 |
天文学 | 144篇 |
综合类 | 138篇 |
自然地理 | 53篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 23篇 |
2021年 | 25篇 |
2020年 | 31篇 |
2019年 | 29篇 |
2018年 | 24篇 |
2017年 | 44篇 |
2016年 | 43篇 |
2015年 | 51篇 |
2014年 | 43篇 |
2013年 | 55篇 |
2012年 | 70篇 |
2011年 | 77篇 |
2010年 | 60篇 |
2009年 | 72篇 |
2008年 | 70篇 |
2007年 | 89篇 |
2006年 | 77篇 |
2005年 | 66篇 |
2004年 | 61篇 |
2003年 | 50篇 |
2002年 | 42篇 |
2001年 | 45篇 |
2000年 | 40篇 |
1999年 | 41篇 |
1998年 | 45篇 |
1997年 | 19篇 |
1996年 | 29篇 |
1995年 | 28篇 |
1994年 | 34篇 |
1993年 | 32篇 |
1992年 | 21篇 |
1991年 | 42篇 |
1990年 | 37篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1550条查询结果,搜索用时 15 毫秒
511.
研究了石墨炉原子吸收测定钛铁矿中微量元素 Cd 的方法,探索了在高含量的 Fe,Ti 基体干扰下以NH4H2PO4-H2NCSNH2-EDTA为混合基体改进剂的最佳仪器工作条件。在取样0.2000g,定容25 mL的条件下,方法检出限为0.006μg/g,用国家标准物质验证,其准确度(犚犈%)<10%,12次测定精密度(犚犛犇%)<10%,加标回收率90%~110%之间,符合国家相关要求。 相似文献
512.
P. Jenniskens P.S. Gural L. Dynneson B.J. Grigsby K.E. Newman M. Borden M. Koop D. Holman 《Icarus》2011,216(1):40-61
First results are presented from a newly developed meteoroid orbit survey, called CAMS – Cameras for Allsky Meteor Surveillance, which combines meteor detection algorithms for low-light video observations with traditional video surveillance tools. Sixty video cameras at three stations monitor the sky above 31° elevation. Goal of CAMS is to verify meteor showers in search of their parent comets among newly discovered near-Earth objects.This paper outlines the concept of operations, the hardware, and software methods used during operation and in the data reduction pipeline, and accompanies the data release of the first batch of meteoroid orbits. During the month of November 2010, 2169 precisely reduced meteoroid trajectories from 17 nights have an error in the apparent radiant of the trajectory <2° and error in speed <10%. Median values of the error are 0.31° and 0.53 km/s, respectively, sufficient to resolve the intrinsic dispersion of annual meteor showers and resolve minor showers from the sporadic background. The limiting visual magnitude of the cameras is +5.4, recording meteors of +4 magnitude and brighter, bright enough to stand out from the mostly fainter sporadic meteors detected as under dense radar echoes.CAMS readily detected all established showers (6) active during the clear nights in November. Of the showers that needed confirmation, we confirm the theta Aurigids (THA, IAU#390), the chi Taurids (CTA, IAU#388), and the omicron Eridanids (OER, IAU#338). We conclude that the iota November Aurigids (IAR, IAU#248) are in fact the combined activity of the theta Aurigids and chi Taurids, and this shower should be dismissed from the list. Finally, there is also a clustering consistent with the zeta Cancrids (ZCN, IAU#243), but we cannot exclude that this is lower perihelion dust belonging to the Orionid shower.Data are submitted to the IAU Meteor Data Center on a semi-regular basis, and can be accessed also at http://cams.seti.org. 相似文献
513.
514.
介绍目前常用的3种椭球变换方法并分析其特点,归纳E1-E6区域椭球元素及大地坐标变动量的公式.利用实测数据对多点法确定的E5椭球和定向定位调整法确定的E6椭球进行比较,结果表明:E6椭球面与投影面更加密切吻合,优于E5椭球. 相似文献
515.
516.
《水文科学杂志》2013,58(3):474-483
Abstract This study presents the measurement of streamflows by constant dilution of a yellow-orange food colorant (E110). Field measurements are carried out in the Doria River, a mountain torrent in the Savoie pre-Alps, France. A limnimetric station installed 12 years ago is periodically calibrated by mechanical and chemical measurements. Moreover, simultaneous mechanical and chemical methods allow the statistical validation of the proposed technique. The main advantages of this method are the lack of toxicity, the absence of visible river colouring, comparable to that of aquatic organic matter, and the low detection limit. This method allows high flow measurement under suitable conditions. 相似文献
517.
选用2010~2012年间新疆境内和边邻地区MS≥4.0地震41个,以中国地震台网给出的震级为标准震级,对新疆台网记录的数字记录波形使用不同仪器分析、仿真处理。用速度量记录直接计算,将速度量记录仿真为短周期WA位移记录、中长周期SK仪记录的勒夫波和长周期763仪记录的瑞利波位移记录计算震级,分别进行了震级偏差统计分析,初步得出震级偏差值的震级校正值,有利于提高新疆地震台网速报地震震级的准确性。 相似文献
518.
D. Van de Vlag B. Vasseur A. Stein R. Jeansoulin 《International journal of geographical information science》2013,27(10):1057-1072
An ontological approach in GIS serves as a framework for the conceptualization of processes in the real world. In this paper, we examine an application in coastal change in the Netherlands, whereby beaches are subject to artificial nourishment to offset the effect of severe erosion. The use of ontologies helps to define two scenarios: SI determined by the regulations from the Ministry for Public Works; SII grounded on the abilities from an existing spatial dataset. A comparison between SI and SII shows that 72.8% of the objects suitable and unsuitable for nourishment are correctly classified. A higher overlap is found in areas where actual beach nourishments were carried out. Inaccuracies in attributes influence the determination of the objects. A sensitivity analysis applied to altitude illustrates a significant increase of objects suitable for nourishment for both scenarios, when altitude is decreased within the lower limit of the root mean square error for the 95% confidence interval. Moreover, the sensitivity of altitude shows that artificial boundaries for beach nourishment objects are not reasonable and consequently should be treated as vague objects. 相似文献
519.
A modification of the spectrophotometric method for the determination of fluoride ions in iron‐rich materials is proposed. In this method the iron matrix was successfully removed using Diphonix® resin. The studied sample was a ferruginous mineral which contained about 38% of iron. The Euronorm certified reference material (ECRM) 676‐1 (Iron Ore Sinter), as a commercially available material having a similar matrix (39.76% w/w Fe) and fluoride level (0.1% w/w), was used to validate the method. After partial digestion in concentrated hydrochloric acid the samples were diluted and passed through Diphonix® resin. The concentration of fluoride ions was determined by a spectrophotometric method using a Zr:ER complex (λ = 540 nm). The result obtained for the ECRM was in good agreement with the certificate specification and thus proved the method to be applicable for the determination of fluoride ions in iron‐rich materials. Due to the easy digestion step and simple requirements for equipment, this method can be used in most laboratories. 相似文献
520.