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981.
Nicholas J. G. Pearce Joanna S. Denton William T. Perkins John A. Westgate Brent V. Alloway 《第四纪科学杂志》2007,22(7):721-736
Laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) is a high spatial resolution analytical method which has been applied to the analysis of silicic tephras. With current instrumentation, around 30 trace elements can be determined from single glass shards as small as ~ 40 µm, separated from tephra deposits. As a result of element fractionation during the ablation process using a 266 nm laser, a relatively complex calibration strategy is required. Nonetheless, such a strategy gives analyses which are accurate (typically within ±5%) and have an analytical precision which varies from ~ ±2% at 100 ppm, to ~ ±15% at 1 ppm. Detection limits for elements used in correlation and discrimination studies are well below 1 ppm. Examples of the application of trace element analysis by LA‐ICP‐MS in tephra studies are presented from the USA, New Zealand and the Mediterranean. Improvements in instrumental sensitivity in recent years have the potential to lower detection limits and improve analytical precision, thus allowing the analysis of smaller glass shards from more distal tephras. Laser systems operating at shorter wavelengths (e.g. 193 nm) are now more widely available, and produce a much more controllable ablation in glasses than 266 nm lasers. Crater sizes of <10 µm are easily achieved, and at 193 nm many of the elemental fractionation issues which mar longer wavelengths are overcome. By coupling a short wavelength laser to a modern ICP‐MS it should be possible to determine the trace element composition of glass shards as small as 20 µm and, providing sample preparation issues can be overcome, the determination of the more abundant trace elements in glass shards as small as 10 µm is within instrumental capabilities. This will make it possible to chemically fingerprint tephra deposits which are far from their sources, and will greatly extend the range over which geochemical correlation of tephras can be undertaken. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
982.
983.
用中国卫星激光测距资料解算地球定向参数 总被引:1,自引:0,他引:1
利用我国SLR网卫星Lageosl的激光测距资料独立测定地球定向参数EOP的可能性和可达到的精度,选取了2001年4月19日—5月30日,2001年9月1日—10月30日这两时段国内SLR网对Lageosl卫星激光测距资料,用SHORDE软件估算地球定向参数,并在同样的时间段内用全球的Lageosl卫星的激光测距资料也测定地球定向参数,分别将两序列的地球定向参数与IERS的EOPc04序列进行比较,其外符精度分别为:X_p、Y_p4—5mas、D_r-0.32ms(用目内资料解算的),X_p、Y_p1—0.35mas、D_(r1)-0.03ms(用全球的激光资料解算的). 相似文献
984.
The use of predictive models for the understanding and management of sediment and contaminant transport generally requires knowledge of particle size and settling velocity. Particle size is often obtained by direct measurements, and the settling velocities are usually predicted using the Stokes' law (or a modification thereof) for single‐grained spherical particles. Such measurements and estimates are not satisfactory measures for cohesive sediments, which exist as agglomerated particles called flocs and whose behaviour is significantly different from that of the single‐grained particles. Direct measurement of settling velocity and size using optical methods in settling columns has also been employed to improve these predictions; however, the subjectivity in determining which particles are in focus results in unreliable size data. An out‐of‐focus particle will generally possess a larger size than in reality. This paper evaluates a laser‐assisted particle sizing/settling velocity determination technique's ability to eliminate the subjectivity and improve particle‐sizing accuracy during settling column experiments. Although the diffraction of light by the translucent standard beads (used for evaluating the technique's accuracy for determining particle size) posed a problem, the results suggest that this technique has potential for assisting researchers to obtain the most accurate settling particle size data possible. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
985.
机载激光影像制图系统中的3维定位技术 总被引:4,自引:0,他引:4
介绍了利用863ADHH“机载激光影像制图系统”获得的激光测距数据,飞机GPS位置数据和姿态数据进行3维直接对地定位的一系列技术,及其在计算机视觉方面的应用^「1」。致力于解决如下3个方面的问题:1.如何解算激光测距点末端的3维坐标;2.如何解算已识别目标(高程已知)中每一点的3维坐标;3.影像存在扭曲,如何将现实空间中的直线映射成影像空间中的曲线。本文方法适用于线扫描方式与扫描方式。 相似文献
986.
叙述了大地测量有关国际组织和科学规划的动态及其发展趋势。由此我们可以了解有关国际组织正在做的工作、要达到的目标和有关科学规划的最新进展及已获得成果。这对我国的大地测量工作者来说 ,无疑是很有价值的。 相似文献
987.
回顾了过去20年,特别是近10年来云南天文台人造卫星的观测与应用情况。介绍在观测仪器的研制、改进和观测方法研究以及有关激光测月资料的归算与应用方面所作过的工作。根据既有的条件,就今后若干年内可能进行的几项工作提出了粗浅的看法。 相似文献
988.
989.
介绍一种新的超近距离 (小于 1m)靶距测量技术。该技术已于 1999年 5月和 1999年 7月成功地用于武汉固定卫星激光测距站和“中国地壳运动观测网络”的流动卫星激光测距系统中 ,校准卫星激光测距系统内各种光路、电路的延时。经这两个系统长期观测 ,证明此技术运行可靠 ,效果很好 ,校准精度优于 1cm 相似文献
990.
M. Jank D. Plaienka M. Frey M. Cosca S. TH. Schmidt B. Luptk . Mres 《Journal of Metamorphic Geology》2001,19(2):197-216
Alpine metamorphism, related to the development of a metamorphic core complex during Cretaceous orogenic events, has been recognized in the Veporic unit, Western Carpathians (Slovakia). Three metamorphic zones have been distinguished in the metapelites: 1, chloritoid + chlorite + garnet; 2, garnet + staurolite + chlorite; 3, staurolite + biotite + kyanite. The isograds separating the metamorphic zones have been modelled by discontinuous reactions in the system K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH). The isograds are roughly parallel to the north‐east‐dipping foliation related to extensional updoming along low‐angle normal faults. Thermobarometric data document increasing P–T conditions from c. 500 °C and 7–8 kbar to c. 620 °C and 9–10 kbar, reflecting a coherent metamorphic field gradient from greenschist to middle amphibolite facies. 40Ar/39Ar data obtained by high spatial resolution in situ ultraviolet (UV) laser ablation of white micas from the rock slabs constrain the timing of cooling and exhumation in the Late Cretaceous. Mean dates are between 77 and 72 Ma; however, individual white mica grains record a range of apparent 40Ar/39Ar ages indicating that cooling below the blocking temperature for argon diffusion was not instantaneous. The reconstructed metamorphic P–T–t path is ‘clockwise’, reflecting post‐burial decompression and cooling during a single Alpine orogenic cycle. The presented data suggest that the Veporic unit evolved as a metamorphic core complex during the Cretaceous growth of the Western Carpathian orogenic wedge. Metamorphism was related to collisional crustal shortening and stacking, following closure of the Meliata Ocean. Exhumation was accomplished by synorogenic (orogen‐parallel) extension and unroofing in an overall compressive regime. 相似文献