全文获取类型
收费全文 | 24495篇 |
免费 | 5077篇 |
国内免费 | 7400篇 |
专业分类
测绘学 | 2915篇 |
大气科学 | 4478篇 |
地球物理 | 5351篇 |
地质学 | 14152篇 |
海洋学 | 3652篇 |
天文学 | 742篇 |
综合类 | 2443篇 |
自然地理 | 3239篇 |
出版年
2024年 | 262篇 |
2023年 | 666篇 |
2022年 | 1455篇 |
2021年 | 1703篇 |
2020年 | 1400篇 |
2019年 | 1517篇 |
2018年 | 1649篇 |
2017年 | 1433篇 |
2016年 | 1597篇 |
2015年 | 1637篇 |
2014年 | 1795篇 |
2013年 | 1909篇 |
2012年 | 2017篇 |
2011年 | 2013篇 |
2010年 | 1966篇 |
2009年 | 1742篇 |
2008年 | 1645篇 |
2007年 | 1479篇 |
2006年 | 1262篇 |
2005年 | 1056篇 |
2004年 | 788篇 |
2003年 | 689篇 |
2002年 | 703篇 |
2001年 | 676篇 |
2000年 | 557篇 |
1999年 | 600篇 |
1998年 | 420篇 |
1997年 | 394篇 |
1996年 | 355篇 |
1995年 | 292篇 |
1994年 | 280篇 |
1993年 | 219篇 |
1992年 | 171篇 |
1991年 | 118篇 |
1990年 | 93篇 |
1989年 | 89篇 |
1988年 | 71篇 |
1987年 | 47篇 |
1986年 | 31篇 |
1985年 | 38篇 |
1984年 | 11篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 23篇 |
1978年 | 6篇 |
1958年 | 13篇 |
1957年 | 11篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
The ordinary kriging method, a geostatistical interpolation technique, was applied for developing contour maps of design storm depth in northern Taiwan using intensity–duration–frequency (IDF) data. Results of variogram modelling on design storm depths indicate that the design storms can be categorized into two distinct storm types: (i) storms of short duration and high spatial variation and (ii) storms of long duration and less spatial variation. For storms of the first category, the influence range of rainfall depth decreases when the recurrence interval increases, owing to the increasing degree of their spatial independence. However, for storms of the second category, the influence range of rainfall depth does not change significantly and has an average of approximately 72 km. For very extreme events, such as events of short duration and long recurrence interval, we do not recommend usage of the established design storm contours, because most of the interstation distances exceed the influence ranges. Our study concludes that the influence range of the design storm depth is dependent on the design duration and recurrence interval and is a key factor in developing design storm contours. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
2.
Chun-sheng Li Qi-jun Fu Yu-hua Yan Shu-ying Jiang Hong-wei Li 《Chinese Astronomy and Astrophysics》1985,9(2):128-133
We propose a model of two acceleration regions, which can explain, on the basis of microwave maser caused by a “hollow-beam” distribution of electrons, the presence of millisecond spikes in the event of 1981 May 16 and their absence in the event of 1981 October 12, and the enhanced continuous emission in the latter. We have also uncovered relations among the features, e.g. the Type IIIG, Type IVDCIM and hard x-ray bursts, that accompany the microwave millisecond spikes during the impulsive phase of a large flare. 相似文献
3.
The accuracy of the AE index as a measure of the joule heat production rate is examined for a typical substorm event on 18 March 1978 by estimating the global joule heat production rate, as a function of time, using data obtained from the IMS six meridian chains. In spite of the fact that the AE index had had an initial slow growth which was followed by a rapid growth, the joule heat production rate attained a high level during the slow growth and thus their variations were considerably different from those of the AE index. Therefore, although the AE index is statistically linearly related to the global joule heat production rate, one should be cautious in assuming that details of time variations of the AE index during individual events represent those of the joule heat production rate. 相似文献
4.
利用降水平均递增率求山地最大降水高度 总被引:6,自引:0,他引:6
本文引入降水平均递增率的概念,改进了文献中的计算方法,可以一次求出山地降水量与海拔的经验关系式中全部参数的最佳值,其中包括山地最大降水高度。并用实例说明了本法的步骤及特点。 相似文献
5.
Kathleen A. Radloff Anya R. Manning Brian Mailloux Yan Zheng M. Moshiur Rahman M. Rezaul Huq Kazi M. Ahmed Alexander van Geen 《Applied Geochemistry》2008
Microbial Fe reduction is widely believed to be the primary mechanism of As release from aquifer sands in Bangladesh, but alternative explanations have been proposed. Long-term incubation studies using natural aquifer material are one way to address such divergent views. This study addresses two issues related to this approach: (1) the need for suitable abiotic controls and (2) the spatial variability of the composition of aquifer sands. Four sterilization techniques were examined using orange-colored Pleistocene sediment from Bangladesh and artificial groundwater over 8 months. Acetate (10 mM) was added to sacrificial vials before sterilization using either (1) 25 kGy of gamma irradiation, (2) three 1-h autoclave cycles, (3) a single addition of an antibiotic mixture at 1× or (4) 10× the typical dose, and (5) a 10 mM addition of azide. The effectiveness of sterilization was evaluated using two indicators of microbial Fe reduction, changes in diffuse spectral reflectance and leachable Fe(II)/Fe ratios, as well as changes in P-extractable As concentrations in the solid phase. A low dose of antibiotics was ineffective after 70 days, whereas autoclaving significantly altered groundwater composition. Gamma irradiation, a high dose of antibiotics, and azide were effective for the duration of the experiment. 相似文献
6.
Vertical variations of wave-induced radiation stress tensor 总被引:3,自引:0,他引:3
INTRODUcrIONThe concept of radiation stress was deve1oPed by tonguet--Higgins and Stewart (1964 ),who intreduced the definition of radiation stress as the excess mornentum due to the presence ofwaves, on the basis of time-averaged laws of Newtonian fluid mechanics and the assmption ofa unifOrm velocity distribution over depth. Subequently, the theory has been applied success-fully in the investigation of phenomena such as wave set-up and set--down (Bowen et al.,l968), longshore currents … 相似文献
7.
在浅层工程折射地震测量中 ,通常采用相遇观测系统采集数据和相应的解释方法进行解释 ;对于单边观测采集方法由于与其相应的解释方法较少而少被采用。本文提出 1种方法简单、精度可靠、可直接利用同一点相邻 2排列 2次观测的初至折射时间并适合于海洋走航式单边连续观测系统的折射初至资料解释方法。其精度基本与同观测段的采用相遇观测的差异时距方法解释的精度十分接近。该方法即适合于人工解释又适合于计算机自动解释。 相似文献
8.
9.
雪宝顶碱性花岗岩岩石地球化学与成矿控制 总被引:7,自引:0,他引:7
对雪宝顶碱性花岗岩具有高丰度的W、Sn、Be含量和W、Sn矿化花岗岩的微量元素组合特征进行了分析,结果显示:稀土元素具有∑REE含量与LREE/HREE比值偏低和负Eu异常的特点;元素比值K/Rb,U/Th,Nb/Ta的规律性变化以及矿脉产状特征等表明W-(Sn)-Be脉状矿床形成于岩浆演化晚期,与岩浆期后的热液活动有关。 相似文献
10.
黄海海域陆相中生界地震反射特征及靶区优选 总被引:1,自引:0,他引:1
利用前人对黄海海域油气勘探成果,作者对北黄海盆地,南黄海盆地北部坳陷陆相中生界进行了研究。结果认为:黄海海域陆相中生界分布广、厚度大、具有良好的生、储、盖组合,是该区下步油气战略性调查的首选目标。并提出北黄海陆相中生界油气勘探应以东部凹陷为主,同时兼顾中部凹陷。南黄海北部坳陷近期油气勘探重点应选择北部凹陷和加大东北凹陷的研究力度。南黄海南部坳陷陆相中生界油气勘探重点放在南五和南七凹陷。 相似文献