全文获取类型
收费全文 | 2725篇 |
免费 | 626篇 |
国内免费 | 1119篇 |
专业分类
测绘学 | 73篇 |
大气科学 | 1876篇 |
地球物理 | 466篇 |
地质学 | 222篇 |
海洋学 | 936篇 |
天文学 | 250篇 |
综合类 | 105篇 |
自然地理 | 542篇 |
出版年
2024年 | 21篇 |
2023年 | 76篇 |
2022年 | 120篇 |
2021年 | 140篇 |
2020年 | 151篇 |
2019年 | 226篇 |
2018年 | 144篇 |
2017年 | 169篇 |
2016年 | 154篇 |
2015年 | 165篇 |
2014年 | 210篇 |
2013年 | 223篇 |
2012年 | 235篇 |
2011年 | 225篇 |
2010年 | 171篇 |
2009年 | 228篇 |
2008年 | 173篇 |
2007年 | 231篇 |
2006年 | 193篇 |
2005年 | 154篇 |
2004年 | 131篇 |
2003年 | 127篇 |
2002年 | 114篇 |
2001年 | 80篇 |
2000年 | 93篇 |
1999年 | 69篇 |
1998年 | 65篇 |
1997年 | 50篇 |
1996年 | 70篇 |
1995年 | 51篇 |
1994年 | 39篇 |
1993年 | 52篇 |
1992年 | 32篇 |
1991年 | 27篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4470条查询结果,搜索用时 359 毫秒
271.
272.
城内外屋顶面附近风.温特征的初步分析 总被引:5,自引:0,他引:5
本文以低纬高原城市昆明城区为研究对象,利用城内外屋顶面附近的风·温实测资料,分析了研究较少的,做为城市第二热力面的城市内外屋顶附近的风·温特征、变化规律及其差异,得到了一些有益的结果,可为探讨城市区域内屋顶面对城市气候形成的作用和机制、城市气候的深入研究,以及城市建筑的规划、设计提供依据。 相似文献
273.
分析1950年以来中等强度以上的ElNiño和LaNina当年和次年夏季(7月)低纬度风场和500hPa高度距平场,发现有不同的特征。其中中-西太平洋近赤道地区850、200hPa上风场异常变化十分明显,这种异常变化与南北半球大气相互作用有密切关系。在500hPa高度距平场上,北半球中、高和低纬地区表现出不同的正、负距平分布型式。上述特点对气候短期预测有一定参考意义。 相似文献
274.
Neutrino energy spectra have been calculated based on the recently measured energy spectra of Galactic very high energy γ-ray
sources. Based on these neutrino spectra the expected event rates in the ANTARES neutrino telescope and KM3NeT, a future neutrino
telescope in the Mediterranean Sea with an instrumented volume of one km3, have been calculated. For the brightest γ-ray sources we find event rates of the order of one neutrino per year. Although
the neutrino event rates are comparable to the background from atmospheric neutrinos the detection of individual sources seems
possible. 相似文献
275.
Quantitative estimation of helium-3 spatial distribution in the lunar regolith layer 总被引:2,自引:0,他引:2
3He (helium-3) in the lunar regolith implanted by the solar wind is one of the most valuable resources because of its potential as a fusion fuel. The abundance of 3He in the lunar regolith is related to solar wind flux, lunar surface maturity and TiO2 content, etc. A model of solar wind flux, which takes account of variations due to shielding of the nearside when the Moon is in the Earth's magnetotail, is used to present a global distribution of relative solar wind flux over the lunar surface. Using Clementine UV/VIS multispectral data, the global distribution of lunar surface optical maturity (OMAT) and the TiO2 content in the lunar regolith are calculated. Based on Apollo regolith samples, a linear relation between 3He abundance and normalized solar wind flux, optical maturity, and TiO2 content is presented. To simulate the brightness temperature of the lunar surface, which is the mission of the Chinese Chang-E project's multichannel radiometers, a global distribution of regolith layer thickness is first empirically constructed from lunar digital elevation mapping (DEM). Then an inversion approach is presented to retrieve the global regolith layer thickness. It finally yields the total amount of 3He per unit area in the lunar regolith layer, which is related to the regolith layer thickness, solar wind flux, optical maturity and TiO2 content, etc. The global inventory of 3He is estimated as 6.50×108 kg, where 3.72×108 kg is for the lunar nearside and 2.78×108 kg is for the lunar farside. 相似文献
276.
The solar wind conditions at one astronomical unit (AU) can be strongly disturbed by interplanetary coronal mass ejections
(ICMEs). A subset, called magnetic clouds (MCs), is formed by twisted flux ropes that transport an important amount of magnetic
flux and helicity, which is released in CMEs. At 1 AU from the Sun, the magnetic structure of MCs is generally modeled by
neglecting their expansion during the spacecraft crossing. However, in some cases, MCs present a significant expansion. We
present here an analysis of the huge and significantly expanding MC observed by the Wind spacecraft during 9 – 10 November 2004. This MC was embedded in an ICME. After determining an approximate orientation for
the flux rope using the minimum variance method, we obtain a precise orientation of the cloud axis by relating its front and
rear magnetic discontinuities using a direct method. This method takes into account the conservation of the azimuthal magnetic
flux between the inbound and outbound branches and is valid for a finite impact parameter (i.e., not necessarily a small distance between the spacecraft trajectory and the cloud axis). The MC is also studied using dynamic
models with isotropic expansion. We have found (6.2±1.5)×1020 Mx for the axial flux and (78±18)×1020 Mx for the azimuthal flux. Moreover, using the direct method, we find that the ICME is formed by a flux rope (MC) followed
by an extended coherent magnetic region. These observations are interpreted by considering the existence of a previously larger
flux rope, which partially reconnected with its environment in the front. We estimate that the reconnection process started
close to the Sun. These findings imply that the ejected flux rope is progressively peeled by reconnection and transformed
to the observed ICME (with a remnant flux rope in the front part). 相似文献
277.
利用大容山自动观测站2004年8月~2006年7月气象观测资料和容县气象站1958~2006年7月测风资料,对大容山的风能资源各参数进行了详细计算和分析,并结合预选风电场的地形地貌、交通运输、联网条件、环境保护等状况对大容山风能资源开发利用进行了可行性分析评价.结果表明:大容山年平均风速为7.2m/s,年平均风功率密度为390.8W/m^2,其风能资源丰富,且交通运输、联网、工程地质等条件较好,可选择在坡度较小的山头或山腰建设风电场,预选风电场可布置750kW的风机45台,总装机容量约为34MW. 相似文献
278.
《海洋技术学报》2024,(1)
为提高基础利用率增加海上风电设施的可行性,对楔形单桩基础竖向承载力特性进行研究分析。采用PLAXIS 3D 有限元软件建立楔形单桩基础模型,从桩侧摩阻力、桩侧法应力及土体位移对比分析楔形单桩基础与等截面单桩竖向承载特性差异,并探讨内摩擦角、楔角及楔高对承载力的影响。研究表明:楔形单桩基础竖向承载力高于等截面单桩基础,且承载力随着楔角、楔高的增大而增大,提高率最大达24.786%。倾斜侧壁的引入改变了桩侧摩阻力的传递规律;倾斜侧壁挤密桩周土体,桩侧摩阻力与法向应力增大,从而有效提高单桩基础的竖向承载力。研究成果可为今后海上风电单桩基础截面型式的设计提供参考。 相似文献
279.
280.
With the launch of SARAL/AltiKa altimeter, efforts have been made to develop wind speed retrieval algorithms. Here we present two algorithms for estimating and validating wind speed from AltiKa. The first method is based on a theoretical Geophysical Model Function (GMF) using forward model simulations for Ka band specifications. The second is the model function developed using the matched database of input and output vectors of Normalized Radar Cross Section (NRCS) from AltiKa and wind speed measurements from concurrent Jason-2 altimeters. Since the NRCS depends on both the surface roughness due to surface wind speed and on mean square slope of the surfaces, the significant wave height is used along with wind speed for model development as an proxy variable. Both the theoretical and empirical GMFs are evaluated for retrieval of wind speed from AltiKa and validated with NDBC buoys data. The empirical model provide wind speed retrieval accuracy of 1.4 m/s. The accuracy of wind retrievals from theoretical model is also in the similar range (1.6 m/s), indicating the sound physical basis applicable for the future altimeters with various incidence angles. The retrieved wind speed is applied for various case studies, bringing out all the regional and global features quite well. 相似文献