全文获取类型
收费全文 | 43628篇 |
免费 | 8622篇 |
国内免费 | 11651篇 |
专业分类
测绘学 | 4801篇 |
大气科学 | 8529篇 |
地球物理 | 9714篇 |
地质学 | 22287篇 |
海洋学 | 6558篇 |
天文学 | 1491篇 |
综合类 | 4580篇 |
自然地理 | 5941篇 |
出版年
2024年 | 133篇 |
2023年 | 705篇 |
2022年 | 2094篇 |
2021年 | 2394篇 |
2020年 | 2013篇 |
2019年 | 2225篇 |
2018年 | 2420篇 |
2017年 | 2243篇 |
2016年 | 2554篇 |
2015年 | 2426篇 |
2014年 | 2727篇 |
2013年 | 2916篇 |
2012年 | 2937篇 |
2011年 | 2976篇 |
2010年 | 3093篇 |
2009年 | 2907篇 |
2008年 | 2862篇 |
2007年 | 2625篇 |
2006年 | 2369篇 |
2005年 | 2019篇 |
2004年 | 1536篇 |
2003年 | 1308篇 |
2002年 | 1323篇 |
2001年 | 1354篇 |
2000年 | 1381篇 |
1999年 | 1613篇 |
1998年 | 1228篇 |
1997年 | 1148篇 |
1996年 | 1049篇 |
1995年 | 926篇 |
1994年 | 802篇 |
1993年 | 720篇 |
1992年 | 578篇 |
1991年 | 455篇 |
1990年 | 331篇 |
1989年 | 309篇 |
1988年 | 273篇 |
1987年 | 163篇 |
1986年 | 147篇 |
1985年 | 97篇 |
1984年 | 111篇 |
1983年 | 86篇 |
1982年 | 71篇 |
1981年 | 58篇 |
1980年 | 34篇 |
1979年 | 41篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1958年 | 30篇 |
1954年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
The auriferous veins at Jinniushan occurs within the Jinniushan faulted zone in the Kunyushan Granite. Optical observation reveals that gold ore body formed during the main stage of hydrothermal activity. Detailed geothermometric studies of fluid inclusions from the veins show that the forming temperature ranges between 130℃ and 370℃ and the salinity is from 4.01 to 15.21 wvt percent NaCl. The ore-forming fluid is featured by low to moderate salinity, and low to moderate temperature. According to investigations of the values of vapor/liquid and temperatures of the ore-forming fluids, we propose that the boiling fluid inclusions exist in the main mineralization stages. Fluid boiling is suggested as a mechanism for the precipitation of gold from the hydrothermal fluid in the Jinniushan gold deposit. 相似文献
62.
青藏块体东北缘断层形变与中强地震 总被引:7,自引:4,他引:3
对祁连山-海原断裂带近期断层形变特征进行了初步研究,发现多场地,大范围的断层活动异常是中等强度地震发生的显著背景,并且往往与大陆地震活动的阶段性总体状况相呼应;区域形变存在明显的特征量,包括特征形态和特征时间,同一场地在不同地震前的异常特征具有重复性,但会受到背景差异显著的不同地震的影响,目前形变状况表明研究区仍具有发生中强地震的地壳运动背景。 相似文献
63.
We use the following numerical model for the collapse stage of a Type II supernova of 15 M⊙. Our electron capture rate includes the effects of the inverse reaction and the neutron-proton mass difference. This decreases the electron density at the collapse stage and led to rather large values of the maximum inward velocity and of the corresponding mass (Umax = 3.06 × 109cm/s, Mmax=0.76 M⊙). These larger values are more favourable for the propagation of shock after the rebounce and the triggering-off of a Type-II supernova explosion. For neutrino transport, we use a leakage model and an equilibrium diffusion model, respectively, for the thin and thick stages and a grey atmosphere model to assess the effect of neutrino precipitation on the collapse. We found this effect to be small, the energy precipitation to be not more than 10?5 the neutrino energy loss and the momentum precipitation not more than 10?6 the gravitational acceleration. 相似文献
64.
65.
66.
基于ArcSDE的地理数据入库技术研究 总被引:1,自引:0,他引:1
分析了GIS开发中空间数据的导入原理和技术,提出了一种基于ArcSDE的自建命令,实现了一种简单高效的空间数据入库方法。 相似文献
67.
基于直线感知增强的边缘提取算法 总被引:1,自引:1,他引:0
根据视觉识别边缘的感知特性,提出了一种基于直线感知增强的弱边缘的边缘提取算法。借鉴视觉的直线感知方式,针对弱边缘整体上呈直线分布的特点将其筛选出来,进行编组、连接和扩展。与Edison边缘提取算子的比较实验证明,本算法在对弱边缘的提取和虚假边缘的抑制上有显著增强。 相似文献
68.
Xie Rui-xiang Wang Min Shi Shuo-biao Xu Chun Li Wei-hua Yan Yi-hua 《Chinese Astronomy and Astrophysics》2003,27(4):426-434
Using the decimetric (700–1500 MHz) radio spectrometer and the synchronous observational system with high temporal resolution at four frequencies (1420, 2130, 2840 and 4260 MHz) of Yunnan Observatory, two rare events were observed on 2001 June 24 and 1990 July 30. The former was a small radio burst exhibiting pulsations with short periods (about 29, 40 and 100 ms) in the impulsive phase. The latter was a large radio burst, which at 2840 MHz produced radio pulsations with period of about 30 ms. This paper focuses on pulsations with very short periods in the range of 29–40 ms. The mechanism of generation of such pulsations may be modulation of radio radiation by the periodic trains of whistler packets originating in unstable regions of the corona. Alternatively, these pulsations can be attributed to wave-wave non-linear interactions of electrostatic upper hybrid waves driven by beams of precipitating electrons in flaring loops. 相似文献
69.
在GPS数据处理中 ,存在着误差影响、影响波的干扰、周跳和数据量大等问题。误差影响和影响波的干扰实质是在接收卫星信号时受到其它因素的影响 ;周跳是由于卫星信号的失锁而造成信号的不连续 ;数据量大是因为GPS观测需要采样间隔小又连续观测所致。由于小波理论具有时频分析、波形分解、特征提取和快速小波变换等特性 ,应用小波变换和波形分解可以解决误差影响和影响波的干扰的问题 ;应用特征提取可以解决周跳检测问题 ;应用快速小波变换可进行数据压缩 相似文献
70.
A synthesis of Holocene pollen records from the Tibetan Plateau shows the history of vegetation and climatic changes during the Holocene. Palynological evidences from 24 cores/sections have been compiled and show that the vegetation shifted from subalpine/alpine conifer forest to subalpine/alpine evergreen sclerophyllous forest in the southeastern part of the plateau; from alpine steppe to alpine desert in the central, western and northern part; and from alpine meadow to alpine steppe in the eastern and southern plateau regions during the Holocene. These records show that increases in precipitation began about 9 ka from the southeast, and a wide ranging level of increased humidity developed over the entire of the plateau around 8-7 ka, followed by aridity from 6 ka and a continuous drying over the plateau after 4-3 ka. The changes in Holocene climates of the plateau can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Indian Monsoon which expanded northwards 相似文献