全文获取类型
收费全文 | 60920篇 |
免费 | 11605篇 |
国内免费 | 14373篇 |
专业分类
测绘学 | 4180篇 |
大气科学 | 12577篇 |
地球物理 | 16069篇 |
地质学 | 29975篇 |
海洋学 | 7127篇 |
天文学 | 3102篇 |
综合类 | 6460篇 |
自然地理 | 7408篇 |
出版年
2024年 | 197篇 |
2023年 | 776篇 |
2022年 | 2365篇 |
2021年 | 2791篇 |
2020年 | 2358篇 |
2019年 | 2870篇 |
2018年 | 3287篇 |
2017年 | 3076篇 |
2016年 | 3559篇 |
2015年 | 3056篇 |
2014年 | 3717篇 |
2013年 | 3755篇 |
2012年 | 3505篇 |
2011年 | 3687篇 |
2010年 | 3836篇 |
2009年 | 3669篇 |
2008年 | 3361篇 |
2007年 | 3193篇 |
2006年 | 2576篇 |
2005年 | 2401篇 |
2004年 | 1879篇 |
2003年 | 1839篇 |
2002年 | 1786篇 |
2001年 | 1808篇 |
2000年 | 2069篇 |
1999年 | 2754篇 |
1998年 | 2248篇 |
1997年 | 2259篇 |
1996年 | 1996篇 |
1995年 | 1785篇 |
1994年 | 1582篇 |
1993年 | 1413篇 |
1992年 | 1156篇 |
1991年 | 863篇 |
1990年 | 614篇 |
1989年 | 617篇 |
1988年 | 537篇 |
1987年 | 341篇 |
1986年 | 288篇 |
1985年 | 195篇 |
1984年 | 186篇 |
1983年 | 141篇 |
1982年 | 131篇 |
1981年 | 103篇 |
1980年 | 76篇 |
1979年 | 58篇 |
1978年 | 27篇 |
1977年 | 18篇 |
1976年 | 8篇 |
1958年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Methyl-galactosides were oxidized at room temperature by galactose oxidase in a one-step reaction and afforded methyl-galactoaldehyde
in excellent yield and high purity. The resulting galactoaldehyde as a useful intermediate can be directly used in glycopeptide
synthesis. 相似文献
42.
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
43.
A formula for the thickness of a shear band formed in saturated soils under a simple shear or a combined stress state has been proposed. It is shown that the shear band thickness is dependent on the pore pressure properties of the material and the dilatancy rate, but is independent of the details of the combined stress state. This is in accordance with some separate experimental observations. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
44.
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
45.
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
46.
47.
Zhan-Le Du Hua-Ning Wang Xiang-Tao He National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Astronomy Beijing Normal University Beijing 《中国天文和天体物理学报》2006,6(4):489-494
The maximum amplitudes of solar activity cycles are found to be well anti-correlated (r = -0.72) with the newly defined solar cycle lengths three cycles before (at lag -3) in 13-month running mean sunspot numbers during the past 190 years. This result could be used for predicting the maximum sunspot numbers. The amplitudes of Cycles 24 and 25 are estimated to be 149.5±27.6 and 144.3±27.6, respectively. 相似文献
48.
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
49.
昆仑山8.1级地震前中国大陆的构造应变背景 总被引:10,自引:4,他引:6
利用“网络工程”1998~2001年累积的1181个测站的GPS重复观测资料,采用双三次样条函数模型建立中国大陆水平运动模型速度场,用大地坐标在椭球面上计算各类应变场,详细分析了2001年昆仑山8.1级地震前中国大陆水平构造应变场空间分布特征。各类构造应变场的最高值都出现在喜马拉雅构造带与昆仑山地块内(地震断裂带南侧),鲜水河—安宁河断裂带次之。分析表明,昆仑山8.1级地震正好发生在张性面膨胀应变率的高值区,第一、第二和最大剪应变率高值区边缘的突变区和最大、最小主应变率的高值区。 相似文献
50.
Wavelet Analysis of Space Solar Telescope Images 总被引:1,自引:0,他引:1
Xi-An Zhu Sheng-Zhen Jin Jing-Yu Wang Shu-Nian NingNational Astronomical Observatories Chinese Academy of Science Beijing Department of Mechanical Electric Engineering China College of Mining Technology Beijing 《中国天文和天体物理学报》2003,3(6):587-596
The scientific satellite SST (Space Solar Telescope) is an important research project strongly supported by the Chinese Academy of Sciences. Every day, SST acquires 50 GB of data (after processing) but only 10GB can be transmitted to the ground because of limited time of satellite passage and limited channel volume. Therefore, the data must be compressed before transmission. Wavelets analysis is a new technique developed over the last 10 years, with great potential of application. We start with a brief introduction to the essential principles of wavelet analysis, and then describe the main idea of embedded zerotree wavelet coding, used for compressing the SST images. The results show that this coding is adequate for the job. 相似文献