全文获取类型
收费全文 | 627篇 |
免费 | 82篇 |
国内免费 | 159篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 213篇 |
地球物理 | 129篇 |
地质学 | 313篇 |
海洋学 | 106篇 |
天文学 | 10篇 |
综合类 | 32篇 |
自然地理 | 56篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 21篇 |
2021年 | 22篇 |
2020年 | 12篇 |
2019年 | 19篇 |
2018年 | 13篇 |
2017年 | 15篇 |
2016年 | 18篇 |
2015年 | 19篇 |
2014年 | 34篇 |
2013年 | 57篇 |
2012年 | 26篇 |
2011年 | 24篇 |
2010年 | 26篇 |
2009年 | 42篇 |
2008年 | 58篇 |
2007年 | 46篇 |
2006年 | 51篇 |
2005年 | 34篇 |
2004年 | 34篇 |
2003年 | 18篇 |
2002年 | 23篇 |
2001年 | 20篇 |
2000年 | 30篇 |
1999年 | 25篇 |
1998年 | 25篇 |
1997年 | 30篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有868条查询结果,搜索用时 15 毫秒
211.
N. Glatthor C.E. Blom T. Blumenstock H. Fischer T. Gulde M. Höpfner W. Kimmig C. Piesch W. Bell B. Galle M. Wirth 《Journal of Atmospheric Chemistry》1998,30(1):81-101
In the winter of 1994/95 the German Transall research aircraft performed 5 campaigns in the European Arctic with 22 flights altogether. An extensive dataset of HNO3, ClONO2 and O3 column amounts was obtained by MIPAS-FT (Michelson Interferometer for Passive Atmospheric Sounding - Flugzeug Transall) onboard the aircraft. In this paper we present the variability of the ClONO2 reservoir gas in the course of the winter. We include groundbased FTIR measurements of HF, HCl and ClONO2 to discuss the airborne observations with regard to the partitioning of inorganic chlorine.From mid-December until the end of January, MIPAS measured a stable ClONO2 collar with constantly low column amounts inside the polar vortex and maxima at the edge. This observation reflected widespread conversion of ClONO2 to reactive chlorine inside the vortex for at least six weeks. In good accordance, the ground stations measured low in-vortex HCl and ClONO2 column amounts and conversion of HCl into ClONO2 in the region of the ClONO2 maxima. In the first week of February the ClONO2 amounts started to increase in the edge region as well as inside the vortex. Between March 21 and 27, just one week after the last cold period, MIPAS observed exclusively high ClONO2 column amounts inside the vortex, indicating fast deactivation of active chlorine. In the same period the ground stations measured an excess of ClONO2 over HCl. Further, the high ClONO2 implies that the polar vortex was renoxified in March. Lower ClONO2 values, observed inside the vortex on the flights of April 5 and 8, and an increased HCl/ClONO2 ratio, measured from ground, marked the starting redistribution within the chlorine reservoir species to the photochemically more stable HCl.In February, March and April, MIPAS observed mixing of ClONO2-rich air masses with midlatitude air at the vortex edge. A very clear event happened on March 27. On this flight a distinct ClONO2 minimum was measured at the vortex edge, which was closely correlated with a filament of midlatitude air observed by OLEX (Ozone Lidar EXperiment) onboard the Transall. 相似文献
212.
Ignacio Galindo Lev S. Ivlev Arturo Gonzlez Roberto Ayala 《Journal of Volcanology and Geothermal Research》1998,83(3-4)
Airborne and ground-based (correlation spectrometer, cascade impactor, and photoelectric counter together with intake filter probes) measurements are described for the volcanic emissions from Popocatépetl volcano (Mexico) from December 23, 1994 to January 28, 1995. Measurements of SO2 restarted 48 h after the eruption onset of December 21, 1994. Maximum sulfur dioxide (4560 t d−1) plus 3.8×104 t d−1 of particulate matter were ejected on December 24, 1994. The maximum rate of ejection occurred coincidentally with the maximum amplitude of harmonic tremor and the maximum number of seismic type B events. Sulfur dioxide emission rates ranged from 1790 to 2070 t d−1 (December 23–24, 1994). Afterwards, sulfur dioxide emission rates clearly indicated a consistent decline. However, frequent gas and ash emission puffs exhibited SO2 fluxes reaching values as high as 3060 t d−1. The emission SO2 baseline for the period of study (February 1994–January 1995) was about 1000 t d−1. Ejection velocity of particulate matter was approximately 270 m s−1 reaching a height of about 2.5 km over the summit. The immediate aerosol dispersion area was estimated at 6.0×104 km2 maximum. The microscopic structure of particles (aerosol and tephra) showed a fragile material, probably coming from weathered crustal layers. X-ray fluorescence and neutron-activation analysis from the impactor samples found the following elements: Si, Al, Ca, S, P, Cl, K, Ni, Fe, Ti, Sc, Cu, Zn, Mn, Sr, Cr, Co, Y, Br, Se, Ga, Rb, Hg and Pb. Morphological analysis shows that ash samples might be from pulverized basaltic rock indicating that the Popocatépetl eruption of December 21, 1994 was at low temperature. The microscopic structure of puff material showed substance aggregates consisted of fragile rock, water and adsorbed SO2. These aggregates were observed within water droplets of approximately 1 mm and even larger. Sulfur transformations in the droplets occurred intensively. Volcanic ash contained 5–6% of sulfur during the first expulsion hours. Elemental relative concentrations with respect to Al show that both Si and S have relative concentrations >1, i.e., 13.73 and 2.17, respectively in agreement with the photoelectric counter and COSPEC measurements. 相似文献
213.
二氧化碳—水体系的拉曼光谱研究 总被引:1,自引:1,他引:0
研究了使用石英管熔融封闭法分别在酸性、中性以及碱性条件下,采用CaCO3或Na2CO3与HCl反应制备不同浓度的CO2标准系列,并对气相、液相中的CO2进行拉曼光谱研究,得出了定量分析气相CO2所遵循的规律,即CO2的浓度与拉曼位移(1388.9cm-1)强度呈线性相关,为定量分析流体包裹体中CO2的含量奠定了基础。 相似文献
214.
等离子体发射光谱法测定重晶石中钡铁和硅 总被引:3,自引:0,他引:3
重晶石经Na2CO3熔融,水浸取,过滤。沉淀经HCl溶解后,用电感耦合等离子体发射光谱法同时测定主成分BaSO4和次量成分Fe2O3以及滤液中的SiO2,结果与部颁标准方法符合。方法精密度好,主量组分BaSO4测定的RSD(n=6)为0.24%,次量组分Fe2O3和SiO2的RSD(n=6)分别是3.69%和1.45%。 相似文献
215.
216.
挥发性有机化合物及硫化物气体作指标勘查金属矿床的工作国内外均处于初试阶段。近几年我们用硫化氢、二氧化硫及轻烃气体(C1—C4烷烃和烯烃)作指标对十个不同景观条件不同地区的铅锌矿、铜钼矿、金矿、铜镍等多金属矿床进行了土壤及地表岩石测量勘查隐伏矿的方法试验,取得很好的结果。表明该方法是寻找多金属隐伏矿的一种有效的气体测量方法,它可用于寻找覆盖厚度几米到400多米运积物覆盖区隐伏矿及基岩面下埋藏400多米盲矿的地表土壤和岩石测量以及岩体评价找矿工作。试验结果还表明该方法用于岩石测量的效果优于土壤测量。 相似文献
217.
SO2排放,硫酸盐气溶胶和气候变化 总被引:3,自引:0,他引:3
工业SO2排放的增加使对流层大气中硫酸盐气溶胶浓度增大,硫酸盐气溶胶通过其直接和间接辐射强迫作用影响气候变化。有关的研究结果显示:硫到盐气溶胶的冷却效应在一定程度上抵消了温室效应,北半球增暖趋势的减缓和日较差的减小可能与大气中人为硫酸盐气溶胶浓度的增加有关。 相似文献
218.
Sensitive diffusive samplers for concentration measurements in ambient airhave been used successfully in Sweden for several years. The samplers have theadvantage of being stable at room temperature before, as well as after,sampling, easy to handle, and cost-efficient. Furthermore, they do not requireelectricity or field calibration. In order to test their use in tropical andsubtropical environments and to obtain a preliminary set of data to validateatmospheric chemistry transport models in this part of the world, duplicatesamples were collected at 11 sites every second month during one year. Eightof the sites were background sites in Asia. It was not possible within theproject to compare the measured concentrations with other measurementtechniques. However, the reproducibility of the duplicates was satisfactoryover the whole measuring range (almost three orders of magnitude of theconcentration for SO2) and reasonable agreement with modelcalculations was obtained at least for SO2 andNH3. Further testing of the measuring technique in tropicalareas is, however, warranted. 相似文献
219.
Acid Rain and Below-Cloud Scavenging in South-Western China 总被引:1,自引:0,他引:1
PETER A. TANNER HENG-CHI LEI MEI-YUAN HUANG ZHI-LAI SHEN 《Journal of Atmospheric Chemistry》1997,27(1):71-78
Major urban areas in south-western China exhibit unique air pollutionproblems due to increasing use of high sulphur-content fuels in an environmentof unfavourable topography and climate. Ambient levels of sulphur dioxideexceed the air quality objectives, and this gas is the major precursor of acidrain. Cloudwater chemistry studies are reported for urban, suburban andcountryside locations, during the period 1985–1989. Although cloudwateracidity was found to increase towards the cloud base, the acidity was muchgreater for rainwater samples collected simultaneously, and was morepronounced in urban rather than neighbouring suburban or countryside regions.The main contribution to the acidity arises from below-cloud scavenging of gasand aerosol and model calculations are able to simulate this behaviour. 相似文献
220.
This note describes simple procedural changes and corrections to gas pressure calculations for use with the Jakucs CO2 microanalyser. 相似文献