全文获取类型
收费全文 | 1248篇 |
免费 | 115篇 |
国内免费 | 230篇 |
专业分类
测绘学 | 201篇 |
大气科学 | 70篇 |
地球物理 | 130篇 |
地质学 | 782篇 |
海洋学 | 134篇 |
天文学 | 190篇 |
综合类 | 31篇 |
自然地理 | 55篇 |
出版年
2024年 | 5篇 |
2023年 | 18篇 |
2022年 | 28篇 |
2021年 | 37篇 |
2020年 | 38篇 |
2019年 | 46篇 |
2018年 | 25篇 |
2017年 | 39篇 |
2016年 | 48篇 |
2015年 | 55篇 |
2014年 | 63篇 |
2013年 | 65篇 |
2012年 | 51篇 |
2011年 | 56篇 |
2010年 | 56篇 |
2009年 | 84篇 |
2008年 | 82篇 |
2007年 | 102篇 |
2006年 | 89篇 |
2005年 | 81篇 |
2004年 | 82篇 |
2003年 | 59篇 |
2002年 | 62篇 |
2001年 | 41篇 |
2000年 | 46篇 |
1999年 | 31篇 |
1998年 | 24篇 |
1997年 | 38篇 |
1996年 | 21篇 |
1995年 | 16篇 |
1994年 | 8篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1593条查询结果,搜索用时 31 毫秒
31.
David J. A. Williams Beda A. Hofmann Ian G. Glasspool 《Swiss Journal of Geoscience》2008,101(3):651-658
Vitrinite reflectance (Rr), proximate analysis and carbon isotope composition (δ13C) have been used to characterise coal samples from two zones of Late Carboniferous sediments (Gastern and Ferden) in the Aar massif where they are penetrated by the Lötschberg base tunnel (constructed between 1999 and 2005). Samples are characterised by variable ash yields (21.7–93.9%; dry basis); those with ash yields of less than ~50% and with volatile matter content (V;dry ash-free basis) within the limits 2 < V% ≤ 8 are anthracite. Values of Rr range from 3.89% to 5.17% and indicate coalification to the rank of anthracite and meta-anthracite in both Gastern and Ferden Carboniferous zones. Samples of anthracite and shale from the Gastern Carboniferous exhibit a relatively small range in δ13C values (–24.52‰ to –23.38‰; mean: –23.86‰) and are lighter than anthracite samples from the Ferden Carboniferous (mean: –22.20‰). The degree of coalification in the Gastern and Ferden Carboniferous zones primarily depends on the maximum rock temperature (T) attained as a result of burial heating. Vitrinite reflectance based estimates of T range from ~290° –360 °C. For a proposed palaeogeothemal gradient of 25 ° C/km at the time of maximum coalification the required overburden is attributable to relatively thin autochtonous Mesozoic/Cenozoic sedimentary cover of the Aar massif and Gastern granite and deep tectonic burial beneath advancing Helvetic, Ultrahelvetic and Prealpine (Penninic) nappes in Early Oligocene to Miocene. 相似文献
32.
D. Rouan N. Epchtein M. De Muizon F. Lacombe P. Puget D. Tiphene F. Boulanger X. Desert G. Guyot L. D'Hendecourt J -M. Lamarre A. Leger F. Pajot J -L. Puget E. Caux M. Giard G. Serra C. Cesarsky L. Vigroux A. Omont 《Astrophysics and Space Science》1994,217(1-2):41-44
Proposed to both the French and the European Space Agency as one possible small mission, SPICE is a project for a dedicated small satellite for a near-IR spectroscopic all-sky survey. The instrument would cover the spectral range 1.8 - 3.6µm, possibly extended to 1.8 - 7µm, at a resolution of 100, with pixels of 1 arc-min. The excellent sensitivity (0.02 MJy sr-1) results from: i) the quasi-zero level of background due to the efficient passive cooling of the whole experiment; ii) the use of large format arrays; iii) the non-stop observing mode (drift-scanning). The spectral domain, complementing the one of ISO, partially opaque from the ground, is specially rich in spectral features tracing stars and all components of the Interstellar Medium (molecular, atomic and ionized gas, dust). With a cooling below 80 K of the focal instrument, then it becomes possible to consider doubling the spectral domain and to cover the whole 1.8 - 7µm range. 相似文献
33.
Richard Dallier Jean-Gabriel Cuby Jean Czarny Jacques Baudrand 《Experimental Astronomy》1994,3(1-4):183-184
ISIS IR is the first attempt to use fibre optics for near infrared spectroscopy (1.8m). It is a field spectrograph (2D spectroscopy), and can work at various resolving powers (up to 25000). It can be transported anywhere, and soon it will be used at CFHT with one NICMOS 3-based camera.Département d'Astrophysique Extragalactique et de Cosmologie 相似文献
34.
George D. Nicolson 《Astrophysics and Space Science》1995,230(1-2):315-327
The development of radio astronomy at the Hartebeesthoek Radio Astronomy Observatory in South Africa is described. The Hartebeesthoek site was established originally by NASA as one of three Deep Space Stations equipped with 26-m parabolic reflector antennas. It was first used for radio astronomy by South Africa in terms of the NASA host nation agreement which allowed for its use at times when the facility was not needed for its primary purpose of tracking space probes. After NASA withdrew from South Africa in 1975, the South African Council for Scientific and Industrial Research took over the site and the 26-m parabolic reflector antenna, which NASA had abandoned in position, and established it as a national observatory. The development of the facility to the stage where it could support a variety of observing programmes such as continuum observations and mapping, spectroscopy and pulsar timing is described as well as the role played by the Observatory in global programmes of very long baseline interferometry. 相似文献
35.
R. Mewe 《Astronomy and Astrophysics Review》1991,3(2):127-168
Summary From the early discovery in 1948 of X-rays from the Solar corona, X-ray spectroscopy has proven to be an invaluable tool in studying hot astrophysical and laboratory plasmas. Because the emission line spectra and continua from optically thin plasmas are fairly well known, high-resolution X-ray spectroscopy has its most obvious application in the measurement of optically thin sources such as the coronae of stars. In particular X-ray observations with theEINSTEIN observatory have demonstrated that soft X-ray emitting coronae are a common feature among stars on the cool side of the Hertzsprung-Russell diagram, with the probable exception of single very cool giant and supergiant stars and A-type dwarfs. Observations with the spectrometers aboardEINSTEIN andEXOSAT have shown that data of even modest spectral resolution (/ = 10–100) permit the identification of coronal material at different temperatures whose existence may relate to a range of possible magnetic loop structures in the hot outer atmospheres of these stars. The higher spectral resolution of the next generation of spectrometers aboard NASA'sAXAF and ESA'sXMM will allow to fully resolve the coronal temperature structure and to enable velocity diagnostics and the determination of coronal densities, from which the loop geometry (i.e. surface filling factors and loop lengths) can be derived. In this paper various diagnostic techniques are reviewed and the spectral results fromEINSTEIN andEXOSAT are discussed. A number of spectral simulations forAXAF andXMM, especially high-resolution iron K-shell, L-shell, and2s-2p spectra in the wavelength regions around 1.9 Å, 10 Å, and 100 Å, respectively, are shown to demonstrate the capabilities for temperature, density, and velocity diagnostics. Finally, iron K-shell spectra are simulated for various types of detectors such as microcalorimeter, Nb-junction, and CCD. 相似文献
36.
Geraldo Magela da Costa Gabriel de Oliveira Polli Márcio A. Kahwage Eddy de Grave Antônio Claret Soares Sabioni Júlio Cesar Mendes 《Physics and Chemistry of Minerals》2006,33(3):161-166
Mössbauer spectra (MS) of blue, green and yellow beryl (ideally Be3Al2Si6O18) containing approximately 1% of iron were obtained at 295 and 500 K. Room temperature (RT) spectra of both blue and green samples showed the presence of an asymmetric Fe2+ doublet (ΔE
Q~2.7 mm/s, δ~1.1 mm/s), with a very broad low-velocity peak. There is no clear evidence for the presence of a ferric component. The MS of the yellow sample at RT consists of an intense central absorption with parameters typical for Fe3+ (ΔE
Q~0.4 mm/s, δ~0.29 mm/s), plus an apparently symmetrical Fe2+ doublet. This sample acquires a light-blue shade upon heating in air at about 620 K. Thermal treatments at high temperatures caused no significant changes in the MS, but the green and yellow beryl acquire a blue colour. All these results are interpreted in relation to the existence of channel water and the distribution of iron among the available crystallographic sites. 相似文献
37.
E. M. Chamorro Pérez I. Daniel J.-C. Chervin P. Dumas J. D. Bass T. Inoue 《Physics and Chemistry of Minerals》2006,33(7):502-510
High-pressure synchrotron infrared (IR) absorption spectra were collected between 650 and 4,000 cm−1 at ambient temperature for hydrous Mg-ringwoodite (γ-Mg2SiO4) up to 30 GPa. The main feature in the OH− stretching region is an extremely broad band centred at 3,150 cm−1. The hydrogen bond is strong for most protons and the most probable site for protonation is the tetrahedral edge. With increasing pressure, this band shifts downward while decreasing its integrated intensity until disappearance at a pressure of 25 GPa. Only one band at 2,450 cm−1 and an absorption plateau persist with a maximum wavenumber of 3,800 cm−1. This behaviour is reversible upon pressure release. We interpret this as a second-order phase transition occurring in hydrated Mg-ringwoodite at high pressure (beyond ∼ 25 GPa). This result is compatible with the observation by Kleppe et al. (Phys Chem Miner 29:473–476, 2002a) who suggested the presence of Si–O–Si linkages and/or partial increase in the coordination of Si. Beyond the phase transition, the protons are delocalized and their environment on the ringwoodite structure is probably quite different from that at low pressure. Data obtained in situ at high pressures and temperatures are needed to better understand the effect of protonation on the structure and to better constrain this phase transition. 相似文献
38.
SUN Xiao-jie LI Chao-lin WANG Li-bin REN Ri-chun LI Hai-yan ZHUANG Yi-ming LIU Ying-xin SUN Ke .Daqing Petroleum Institute Daqing Heilongjiang China .Coalfield Geological Geophysical Exploration Company of Jilin Province Changchun China .Coal Field Geology Bureun of Jilin Province Changchun China 《吉林大学学报(地球科学版)》2006,(Z2)
已知勘查区深度范围前提下,最大炮检X和道间距ΔX,不可以太大也不可以太小,施工前能够计算出它的允许值范围。 相似文献
39.
大别山及苏鲁地区微粒金刚石分类及其大地构造意义 总被引:3,自引:1,他引:3
1992年发现大别山首例微粒金刚石之后,又于2003年和2004年在大别山和苏鲁地区的榴辉岩薄片中和榴辉岩的人工重砂中发现了微粒金刚石。本文报道其中尚未发表的7颗,并对2颗较大的薄片中的微粒金刚石和2颗自由晶体金刚石进行拉曼光谱和红外光谱测试。研究结果表明,本区所有微粒金刚石都为IaA和IaB型金刚石的混合体。缺少Ib型金刚石,表明没有人造金刚石的混入。薄片中的金刚石大部分为石榴子石的包裹体,少数产出于颗粒之间,直径为30-180μm。自由颗粒微粒金刚石直径为400-700μm。在大别山北部,不但又一次找到了微粒金刚石,还在石榴子石中发现有单斜辉石、磷灰石和金红石的出溶。这表明北大剐不但是超高压地质体,而且可能是本区俯冲最深的地质体。 相似文献
40.
T. Geisler 《Physics and Chemistry of Minerals》2002,29(6):420-429
Raman spectroscopy and the powder diffraction technique have been used to monitor the recovery process of two partially metamict
zircons (2.6 and 4.8 × 1018
α-decays g−1) from Sri Lanka during a series of isothermal annealing experiments in the temperature range from 870 to 1622 K. These experiments
show for the first time that structural recovery in partially metamict zircon proceeds via three distinct recovery stages,
each of which occurs within a distinct time-temperature regime. Whereas the first two stages have previously been recognized
(recovery of damaged crystalline remnants and epitaxial recrystallization), the third stage has not yet been identified as
a single activated process. It is suggested that anisotropic defect annealing during the first stage at low temperatures,
where the structure recovers preferentially along the a(b) plane, produces a geometrical situation where large structural rearrangements are necessary to remove the remaining defects
inside the crystalline material. This situation is approximately reached when the amorphous domains start to recrystallize.
The reason for anisotropic annealing can be found in a different connectivity between polyhedral linkages in both directions
of the zircon lattice. High apparent activation energies, in the range of 6.4 to 7.9 eV, were determined for the third recovery
stage from the Raman data, which are interpreted to reflect large structural rearrangements (i.e. polyhedral tilting) associated
with the final recovery of the c axis. This explains the occurrence of a distinct recrystallization stage without defect annealing. Finally, it should be
mentioned that the first recovery stage is not necessarily expected to occur in less damaged zircon crystals (<∼2 × 1018
α-decays g−1), since less stable defects along the basal plane might have already been self-annealed during radiation damage accumulation
under ambient temperatures.
Received: 6 September 2001 / Accepted: 25 February 2002 相似文献