全文获取类型
收费全文 | 2784篇 |
免费 | 338篇 |
国内免费 | 324篇 |
专业分类
测绘学 | 159篇 |
大气科学 | 314篇 |
地球物理 | 786篇 |
地质学 | 1194篇 |
海洋学 | 307篇 |
天文学 | 365篇 |
综合类 | 97篇 |
自然地理 | 224篇 |
出版年
2024年 | 9篇 |
2023年 | 34篇 |
2022年 | 114篇 |
2021年 | 138篇 |
2020年 | 131篇 |
2019年 | 143篇 |
2018年 | 178篇 |
2017年 | 194篇 |
2016年 | 184篇 |
2015年 | 161篇 |
2014年 | 178篇 |
2013年 | 173篇 |
2012年 | 178篇 |
2011年 | 204篇 |
2010年 | 136篇 |
2009年 | 170篇 |
2008年 | 143篇 |
2007年 | 113篇 |
2006年 | 111篇 |
2005年 | 108篇 |
2004年 | 89篇 |
2003年 | 80篇 |
2002年 | 72篇 |
2001年 | 47篇 |
2000年 | 46篇 |
1999年 | 54篇 |
1998年 | 26篇 |
1997年 | 28篇 |
1996年 | 24篇 |
1995年 | 18篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1976年 | 5篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1967年 | 2篇 |
排序方式: 共有3446条查询结果,搜索用时 31 毫秒
151.
为缓解淡水资源短缺及化石能源过度使用问题,提出多点液压式波浪能海水淡化系统,该系统主要由采能装置、液压传递系统与反渗透膜海水淡化设备组成。系统的采能装置采用振荡浮子式,可将波浪能转换为浮子振荡从而被液压系统吸收达到采集波浪能的目的。为了提高液压式波浪能海水淡化系统的采能效率及淡水率,利用AMEsim软件对液压传递系统进行建模与仿真,分析了蓄能器、浮子个数及波高对液压传递系统输出响应的影响。结果表明:蓄能器能够使液压马达的输出响应更加稳定;当浮子的数量增加时,液压系统达到稳定的运行状态所需的时间更短,从而有利于提高系统的效率;波高在2 m左右时,本系统的产水量达到最大。 相似文献
152.
153.
154.
155.
Chemical and mineralogical characterization of the Mineo (Sicily,Italy) pallasite: A unique sample
下载免费PDF全文
![点击此处可从《Meteoritics & planetary science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A. Zucchini M. Petrelli F. Frondini C. M. Petrone P. Sassi A. Di Michele S. Palmerini O. Trippella M. Busso 《Meteoritics & planetary science》2018,53(2):268-283
The Mineo pallasite is characterized here for the first time. The only 42 g still available worldwide is part of the collection of the Department of Physics and Geology, University of Perugia. A multianalytical approach was used, joining field-emission scanning electron microscopy, Raman analysis, X-ray powder diffraction, electron-probe microanalysis, and laser ablation inductively coupled plasma mass spectrometry. Results highlighted that (1) the Mineo pallasite belongs to the Main Group pallasites; (2) the silicate component is essentially olivine, with no pyroxene component; (3) the olivine chemical composition varies in terms of both iron and trace elements; (4) the metal phase is essentially kamacite with the taenite mainly found in the plessite structure; (5) phosphide phases are present as schreibersite and barringerite. The observed compositional variability in olivines as well as their occurrence as both angular and rounded crystals suggest that the Mineo pallasite could have been derived from a large impact of a differentiated parent body with a larger solid body. The resulting pallasite conglomerate consists of the compositionally different olivines, likely coming from different areas of the same differentiated parent body, and the residual molten Fe-Ni. 相似文献
156.
Simone Lotti Teresa Mineo Christian Jacquey Silvano Molendi Matteo D’Andrea Claudio Macculi Luigi Piro 《Experimental Astronomy》2017,44(3):371-385
In this paper we are going to review the latest estimates for the particle background expected on the X-IFU instrument onboard of the ATHENA mission. The particle background is induced by two different particle populations: the so called “soft protons” and the Cosmic rays. The first component is composed of low energy particles (< 100s keV) that get funnelled by the mirrors towards the focal plane, losing part of their energy inside the filters and inducing background counts inside the instrument sensitivity band. The latter component is induced by high energy particles (> 100 MeV) that possess enough energy to cross the spacecraft and reach the detector from any direction, depositing a small fraction of their energy inside the instrument. Both these components are estimated using Monte Carlo simulations and the latest results are presented here. 相似文献
157.
Emanuele Perinati Marco Barbera Sebastian Diebold Alejandro Guzman Andrea Santangelo Chris Tenzer 《Experimental Astronomy》2017,44(3):387-399
We present a preliminary assessment of the non-X-ray background for the WFI on board ATHENA conducted at IAAT in the context of the collaborative background and radiation damage working group activities. Our main result is that in the baseline configuration originally assumed for the camera the requirement on the level of non-X-ray background could not be met. In light of the results of Geant4 simulations we propose and discuss a possible optimization of the camera design and pinpoint some open issues to be addressed in the next phase of investigation. One of these concerns the possible contribution to the non-X-ray background from soft protons and ions funneled to the focal plane through the optics. This is not quantified at this stage, here we just briefly report on our ongoing activities aimed at validating the mechanisms of proton scattering at grazing incidence. 相似文献
158.
M. D’Andrea S. Lotti C. Macculi L. Piro A. Argan F. Gatti 《Experimental Astronomy》2017,44(3):359-370
ATHENA is a large X-ray observatory, planned to be launched by ESA in 2028 towards an L2 orbit. One of the two instruments of the payload is the X-IFU: a cryogenic spectrometer based on a large array of TES microcalorimeters, able to perform integral field spectrography in the 0.2–12 keV band (2.5 eV FWHM at 6 keV). The X-IFU sensitivity is highly degraded by the particle background expected in the L2 orbit, which is induced by primary protons of both galactic and solar origin, and mostly by secondary electrons. To reduce the particle background level and enable the mission science goals, the instrument incorporates a Cryogenic AntiCoincidence detector (CryoAC). It is a 4 pixel TES based detector, placed < 1 mm below the main array. In this paper we report a scientific assessment of the CryoAC observational capabilities in the hard X-ray band (E > 10 keV). The aim of the study has been to understand if the present detector design can be improved in order to enlarge the X-IFU scientific capability on an energy band wider than the TES array. This is beyond the CryoAC baseline, being this instrument aimed to operate as anticoincidence particle detector and not conceived to perform X-ray observations. 相似文献
159.
The MoSE project (construction of mobile barrier to safeguard the Lagoon of Venice) entails changes to the structure of the lagoon's inlets. This could have consequences for the areas near the inlets and for the dynamics of the lagoon ecosystem as a whole. In order to predict the effects of the proposed alterations on the hydrodynamics of the lagoon, a well-tested hydrodynamic-dispersion model was applied. Simulations were carried out considering both idealised and realistic tide and wind scenarios. 相似文献
160.