全文获取类型
收费全文 | 74290篇 |
免费 | 1404篇 |
国内免费 | 1314篇 |
专业分类
测绘学 | 1903篇 |
大气科学 | 5315篇 |
地球物理 | 15137篇 |
地质学 | 26551篇 |
海洋学 | 6535篇 |
天文学 | 16955篇 |
综合类 | 329篇 |
自然地理 | 4283篇 |
出版年
2022年 | 480篇 |
2021年 | 806篇 |
2020年 | 832篇 |
2019年 | 886篇 |
2018年 | 1756篇 |
2017年 | 1656篇 |
2016年 | 2013篇 |
2015年 | 1243篇 |
2014年 | 1988篇 |
2013年 | 3746篇 |
2012年 | 2378篇 |
2011年 | 3186篇 |
2010年 | 2806篇 |
2009年 | 3774篇 |
2008年 | 3156篇 |
2007年 | 3204篇 |
2006年 | 3019篇 |
2005年 | 2249篇 |
2004年 | 2181篇 |
2003年 | 2026篇 |
2002年 | 1933篇 |
2001年 | 1687篇 |
2000年 | 1647篇 |
1999年 | 1363篇 |
1998年 | 1413篇 |
1997年 | 1355篇 |
1996年 | 1161篇 |
1995年 | 1143篇 |
1994年 | 1005篇 |
1993年 | 874篇 |
1992年 | 861篇 |
1991年 | 839篇 |
1990年 | 957篇 |
1989年 | 817篇 |
1988年 | 764篇 |
1987年 | 952篇 |
1986年 | 776篇 |
1985年 | 976篇 |
1984年 | 1137篇 |
1983年 | 1041篇 |
1982年 | 957篇 |
1981年 | 942篇 |
1980年 | 851篇 |
1979年 | 778篇 |
1978年 | 765篇 |
1977年 | 717篇 |
1976年 | 678篇 |
1975年 | 663篇 |
1974年 | 652篇 |
1973年 | 724篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
E. L. Stupitsky 《Geomagnetism and Aeronomy》2006,46(1):23-40
The analytical expressions for determining the deceleration region of plasma, produced during large-scale geophysical experiments of explosion type, and taking into account the effect of the rarefied ionosphere and geomagnetic field have been obtained. The possibility of the magnetosphere braking by plasma produced by a powerful explosion is analyzed. The simplified set of equations used to analyze the linear and non-linear stages of flute instability of explosive plasma expanding into the magnetic field has been obtained. The mass overflow between flutes and the viscous force is taken into account. The experimental studies of flute instability during laser plasma expansion into the magnetic field are theoretically substantiated. The mechanism explaining the formation of a jet stream and the main jet inclination of 11° with respect to the axis of symmetry has been proposed. 相似文献
952.
V. I. Trukhin V. I. Maksimochkin V. A. Zhilyaeva E. S. Kurochkina A. A. Shreider G. L. Kashintsev 《Izvestiya Physics of the Solid Earth》2006,42(11):928-941
Magnetic properties of young rift basalts in the southern Red Sea are studied in detail. It is found that basalt samples dredged in the rift zone are characterized by a large spread in magnetic parameters. The magnetic properties of the basalts are shown to indicate a complex evolution of the Red Sea rift zone. Titanomagnetite grains of the basalts are mostly affected by single-phase oxidation processes and have preserved paleomagnetic information. However, basalts discovered near the rift axis yield evidence of multiphase oxidation of titanomagnetite grains, which is untypical of young oceanic basalts. These basalts have high Curie points and large values of the natural remanent magnetization and Koenigsberger parameter. The corresponding samples were taken in nontransform zones where rocks have experienced the action of significant tectonic forces and, moreover, anomalous geomagnetic field patterns correlate with the position of these zones. Using the magnetic properties of the basalts, the northern segment of the rift axis is relocated. 相似文献
953.
Geomagnetic storm effects at low latitudes 总被引:1,自引:0,他引:1
R. G. Rastogi 《Annales Geophysicae》1999,17(3):438-441
The geomagnetic horizontal (H) field from the chain of nine observatories in India are used to study the storm-time and disturbance daily variations. The peak decrease in storm-time variation in H showed significant enhancements at the equatorial electrojet stations over and above the normally expected decrease due to the ring current effects corrected for geomagnetic latitudes. The disturbance daily variation of H at equatorial stations showed a large decrease around midday hours over and above the usual dawn-maximum and dusk-minimum seen at any mid-latitude stations around the world. These slow and persistent additional decreases of H of disturbance daily variation at equatorial latitudes could be the effect of a westward electric field due to the Disturbance Ionospheric dynamo coupled with abnormally large electrical conductivities in the E region over the equator. 相似文献
954.
—?We test how well low-magnitude (m bLg 1.8 to 2.6), 25-ton chemical explosions at Balapan, Kazakhstan, can be located using IMS stations and standard earth models, relying on precisely determined relative arrival times of nearly similar, regional and teleseismic waveforms. Three 1997 Balapan explosions were recorded by a number of currently reporting and surrogate IMS stations. Three regional stations and two teleseismic arrays yielded consistent waveforms appropriate for relative picking. Master-event locations based on the AK135 model and ground-truth information from the first, shallowest and best-recorded explosion, fell under 1 km from known locations, for depths constrained to that of the master event. The resulting 90% confidence ellipses covered 12–13?km2 and contained the true locations; however, results for depth constrained to true depth were slightly less satisf actory. From predictions based on ground truth, we found a P g -coda phase at Makanchi, Kazakhstan to be misidentified and poorly modeled. After accounting for this, 90% ellipses shrank to 2–3?km2 and true-depth mislocation vectors became more consistent with confidence-ellipse orientations. These results suggest that a high level of precision could be provided by a tripartite array of calibration shots in cases where models are poorly known. We hope that the successful relocation of these small Balapan shots will support the role of calibration explosions in verification monitoring and special event studies, including on-site inspection. 相似文献
955.
Transport of three herbicides in ground water at Twin Lake test site,Chalk River,Ontario, Canada 总被引:2,自引:0,他引:2
A field tracer test performed under natural flow conditions at the Twin Lake test site, Chalk River Laboratories of the Atomic Energy of Canada Ltd. in Chalk River, Ontario, Canada, using tritium and three herbicides (Chlortoluron, Terbuthylazine, and Pendimethalin) was interpreted using the dispersion equation with a combined reaction model. The reaction model couples an instantaneous equilibrium reaction governed by a linear adsorption isotherm with a reversible or irreversible kinetic reaction of the first order, and decay. An improved interpretation method consists of a simultaneous fitting of theoretical concentration and mass-recovery curves to the experimental data, which leads to a more reliable determining of reaction models and improves the accuracy of fitting. Tritium served as the reference tracer to determine the flow velocity, dispersivity, and the recovery of the herbicides. Chlortoluron was slightly delayed by equilibrium exchange with strongly reduced concentration due to an irreversible kinetic reaction and/or decay. Terbuthilazine was slightly delayed by equilibrium exchange, with strongly reduced concentration due to a reversible kinetic reaction with some influence of decay. A strong equilibrium reaction and a strong reversible kinetic reaction without degradation governed the transport of Pendimethalin, reducing considerably its concentration. The results obtained show that simulations based only on Kd and decay constant, especially if these parameters are found in the laboratory, may considerably differ from those performed with reaction parameters determined in properly performed field tests. The dominant reaction types, and the values of parameters found in the study, supply useful information on the transport of the investigated herbicides in sandy aquifers under natural flow conditions. 相似文献
956.
This paper outlines the application of a new data‐based mechanistic (DBM) modelling methodology to the characterization of the sediment transmission dynamics in a small upland reservoir, Wyresdale Park, Lancashire. The DBM modelling strategy exploits advanced statistical procedures to infer the dynamic model structure and its associated parameters directly from the instrumented data, producing a parametrically efficient, continuous time, transfer function model which relates suspended sediment load at the reservoir inflow to the outflow at the event scale. The associated differential equation model parameters have physical attributes which can be interpreted in terms of sediment transmission processes and associated reservoir trap efficiency. Sedigraph analysis suggests that wind‐induced resuspension episodically supplies an additional load to the reservoir outlet. The stochastic nature of the DBM model makes it ideal for evaluating the effects of uncertainty through Monte Carlo simulations (MCS) for discharge and sediment transmission. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
957.
D. Bocchiola C. Mihalcea G. Diolaiuti B. Mosconi C. Smiraglia R. Rosso 《Advances in water resources》2010
We develop a simple model to evaluate the daily flow discharges in the ablation season for the 11 km2 Pantano basin in the Retiche Italian Alps, based upon the data gathered during a three years field campaign. The Pantano basin embeds the Venerocolo debris covered and the Avio debris free glaciers, covering 2.14 km2 in the Adamello Group, where the widest Italian glacier Adamello is located. First, degree-day models based upon air temperature are tuned to calculate snow and ice melt at daily scale. Glaciers’ meteorological data are collected from an automatic weather station (AWS), operating on the glacier during summer 2007. The melt factors in the debris covered areas of the glacier are estimated against debris thickness, using a data driven parameterization. The flow discharge from the catchment is estimated using semi distributed flow routing for the ablation seasons of four years, from 2006 to 2009. The predicted discharges are compared to those derived from inverse reservoir's routing at the Benedetto lake, catching the basin outflow. The proposed approach is valuable as a tool to investigate the hydrology of poorly gauged glacierized areas, including those with debris covered ice, widely diffused and yet poorly understood. Pending accurate parameterization the approach is usable for water resources evaluation and for long term assessment of the climate change impact on the glacierized areas within the Alps. 相似文献
958.
郭履灿 《CT理论与应用研究》2005,14(4):45-49
本文阐述”多维体视方法论”,主张立体透视与动态、多维地看问题;它起源于医学CT(计算机层析学)透视成像、核磁共振(MRI)等体视学方法研究疾病的生理解剖结构、病理特征、监测人体有关器官的各种变化,是行之有效的方法;已成功地应用于检测工业器械、航天器及地下结构等物体的内部结构,从而发展和演绎出来的认识论方法。在医学领域将CT、MRI所得二维信息和断面图像、对病灶区引入“体显示”和“面显示”等可视化技术,将能充分反映不同疾病的病理、药理特征;在航天、地学等领域同样应用着CT多维“可视化技术”。本文试图发扬综合预测的学术思想,将医学临床应用CT、核磁共振、体视学方法结合研究其他制约因素指标,从而区分出疾病的原发、继发分期,导致绝症的进程和前兆,概括为“多维体视预测方法”;也适用于地震孕育、强震发生与火山喷发预测的研究。 相似文献
959.
960.
花山复式岩体位于华北地块南缘,采用LA-ICP-MS技术测得复式岩体中的中细粒似斑状黑云二长花岗岩的锆石U-Pb年龄为128±1Ma,此年龄被解释为成岩年龄。该岩体及邻近的五丈山岩体中花岗岩具有高硅、富碱特征,为准铝-弱过铝质高钾钙碱性系列;在稀土和微量元素上,富集LREE、Rb、Ba、K、Sr等大离子亲石元素,亏损HREE、Zr、Hf、Ta、Nb、P、Ti等高场强元素,总体上Eu异常不明显,显示出I-A过渡型花岗岩的特征。锆石Lu-Hf同位素组成表明,花山花岗岩的εHf(t)主要变化于-25.8~-19.6之间,tDM2为2.81~2.43Ga,显示源区物质以古老的壳源物质为主,有年轻组分的参与。与岩体外围多金属成矿年龄的对比分析发现,外围金、钼矿床与花山复式岩体的年龄一致,比五丈山岩体晚20~25Ma,表明金、钼矿的形成与花山岩体在时空上联系密切,该岩体可能为成矿提供了热源。 相似文献