全文获取类型
收费全文 | 611篇 |
免费 | 18篇 |
国内免费 | 28篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 53篇 |
地球物理 | 183篇 |
地质学 | 172篇 |
海洋学 | 38篇 |
天文学 | 144篇 |
综合类 | 10篇 |
自然地理 | 50篇 |
出版年
2024年 | 2篇 |
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 29篇 |
2017年 | 22篇 |
2016年 | 30篇 |
2015年 | 28篇 |
2014年 | 36篇 |
2013年 | 30篇 |
2012年 | 26篇 |
2011年 | 33篇 |
2010年 | 39篇 |
2009年 | 39篇 |
2008年 | 37篇 |
2007年 | 28篇 |
2006年 | 26篇 |
2005年 | 23篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 13篇 |
2001年 | 19篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有657条查询结果,搜索用时 15 毫秒
651.
Using formula to describe the average spectrum of the extragalactic far infrared background (FIRB) radiation measured by the COBE FIRAS instrument in the 0.15–2.4 THz frequency interval at mean temperature T=18.5 K, the radiative and thermodynamic properties, such as the total emissivity, total radiation power per unit area, total energy density, number density of photons, Helmholtz free energy density, entropy density, heat capacity at constant volume, and pressure are calculated. The value for the total intensity received in the 0.15–2.4 THz frequency interval is equal to 13.6 nW?m?2?sr?1. This value is about 19.4 % of the total intensity expected from the energy released by stellar nucleosynthesis over cosmic history. The radiative and thermodynamic functions of the extragalactic far infrared background (FIRB) radiation are calculated at redshift z=1.5. 相似文献
652.
Maria Gritsevich Vladimir Vinnikov Tomáš Kohout Juraj Tóth Jouni Peltoniemi Leonid Turchak Jenni Virtanen 《Meteoritics & planetary science》2014,49(3):328-345
In this study, we conduct a detailed analysis of the Ko?ice meteorite fall (February 28, 2010), to derive a reliable law describing the mass distribution among the recovered fragments. In total, 218 fragments of the Ko?ice meteorite, with a total mass of 11.285 kg, were analyzed. Bimodal Weibull, bimodal Grady, and bimodal lognormal distributions are found to be the most appropriate for describing the Ko?ice fragmentation process. Based on the assumption of bimodal lognormal, bimodal Grady, bimodal sequential, and bimodal Weibull fragmentation distributions, we suggest that, prior to further extensive fragmentation in the lower atmosphere, the Ko?ice meteoroid was initially represented by two independent pieces with cumulative residual masses of approximately 2 and 9 kg, respectively. The smaller piece produced about 2 kg of multiple lightweight meteorite fragments with the mean around 12 g. The larger one resulted in 9 kg of meteorite fragments, recovered on the ground, including the two heaviest pieces of 2.374 kg and 2.167 kg with the mean around 140 g. Based on our investigations, we conclude that two to three larger fragments of 500–1000 g each should exist, but were either not recovered or not reported by illegal meteorite hunters. 相似文献
653.
654.
Vladimir A. Krasnopolsky 《Icarus》2006,182(1):80-91
High-resolution spectra of Venus and Mars at the NO fundamental band at 5.3 μm with resolving power ν/δν=76,000 were acquired using the TEXES spectrograph at NASA IRTF on Mauna Kea, Hawaii. The observed spectrum of Venus covered three NO lines of the P-branch. One of the lines is strongly contaminated, and the other two lines reveal NO in the lower atmosphere at a detection level of 9 sigma. A simple photochemical model for NO and N at 50-112 km was coupled with a radiative transfer code to simulate the observed equivalent widths of the NO and some CO2 lines. The derived NO mixing ratio is 5.5±1.5 ppb below 60 km and its flux is . Predissociation of NO at the (0-0) 191 nm and (1-0) 183 nm bands of the δ-system and the reaction with N are the only important loss processes for NO in the lower atmosphere of Venus. The photochemical impact of the measured NO abundance is significant and should be taken into account in photochemical modeling of the Venus atmosphere. Lightning is the only known source of NO in the lower atmosphere of Venus, and the detection of NO is a convincing and independent proof of lightning on Venus. The required flux of NO is corrected for the production of NO and N by the cosmic ray ionization and corresponds to the lightning energy deposition of . For a flash energy on Venus similar to that on the Earth (∼109 J), the global flashing rate is ∼90 s−1 and ∼6 km−2 y−1 which is in reasonable agreement with the existing optical observations. The observed spectrum of Mars covered three NO lines of the R-branch. Two of these lines are contaminated by CO2 lines, and the line at 1900.076 cm−1 is clean and shows some excess over the continuum. Some photochemical reactions may result in a significant excitation of NO (v=1) in the lowest 20 km on Mars. However, quenching of NO (v=1) by CO2 is very effective below 40 km. Excitation of NO (v=1) in the collisions with atomic oxygen is weak because of the low temperature in the martian atmosphere, and we do not see any explanation of a possible emission of NO at 5.3 μm. Therefore the data are treated as the lack of absorption with a 2 sigma upper limit of 1.7 ppb to the NO abundance in the lower atmosphere of Mars. This limit is above the predictions of photochemical models by a factor of 3. 相似文献
655.
Snežana S. Nenadović Ljiljana M. Kljajević Maja A. Nešić Marijana Ž. Petković Katarina V. Trivunac Vladimir B. Pavlović 《Environmental Earth Sciences》2017,76(2):79
The paper presents chemical and structural analysis of geopolymer materials which are obtained by alkali-activated calcined clay (metakaolin) originated from Serbia under strictly defined conditions. Characterization of the metakaolin and geopolymers molecular structure has been done using X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The paper presents the possibility of obtaining geopolymer structure and differences in chemical and structural characterization of these materials taking into account the concentration of NaOH as a variable parameter. The results of MALDI analysis of metakaolin and synthesized geopolymer structures using various matrix system: 2,4,6 trihydroxyacetophenone (THAP), α-cyano-4-hydroxycinnamic, 2,6 dihydroxyacetophenone and laser desorption/ionization, have shown that THAP matrix is the most appropriate for analysing these aluminosilicate materials. 相似文献
656.
This paper presents a review of the genetic types and geochemical processes that have formed ‘metalliferous’ coals around the world. Primary attention is given to elements in coal that are currently being extracted from coal as raw material (Ge and U) or have, in our opinion, the best chance for such use (REE, Ag, Au, and PGE). Coals with anomalously high concentrations of other metals having potential for economic by-product recovery (Be, Sc, V, Ga, Sb, Cs, Mo, W, and Re) are briefly considered. Original data and a survey of the literature indicate that metalliferous coals are in many coal basins. Ore formation in coal-bearing structures may occur during peat accumulation, during diagenesis of the organic matter, or by epigenesis. Various metals are supplied to sedimentary basins as minerals that are transported by water and wind or as ionic species in surface water and descending and ascending underground water and may be incorporated into peat or coals. The modes of occurrence of metals in the enriched coals are diverse. The data presented in this review indicates that metalliferous coals should be regarded as promising for economic recovery for by-products in the course of coal mining and combustion. 相似文献
657.
Aleksandra AJNOV Vladimir SIMI Branimir JOVANIEVI Olga CVETKOVI Radovan DIMITRIJEVI Nenad GRUBIN 《《地质学报》英文版》2008,82(6)
Sediments of the western part of the Valjevo-Mionica basin (Serbia) were examined both geochemically and mineralogically to explain, on the basis of their sedimentological characteristics, the causes of changes in their qualitative and quantitative composition. A total of 62 samples obtained from the drillhole at depths up to 400 m was investigated. Using correlation of the obtained data, six geochemical zones were defined, two of which being specially distinguished by their mineralogical, geochemical and sedimentological characteristics. The first one, upper zone A, consists of banded marlstones interbedded with clay and oil shales and is characterized by presence of analcite and searlesite. These minerals and very high contents of Na2O indicate sedimentation in alkaline conditions with increased salinity in arid climate. That provided pronounced water stratification, as well as higher bioproductivity in the basin and sedimentary organic matter preservation. Therefore, the zone A sediments are characterized by high organic matter contents of the type which provides good potential for production of liquid hydrocarbons. Another specific zone, zone F, contains sediments with very high MgO, K2O and Li concentrations. Their geochemical correlation, as well as almost complete absence of illite in this zone, indicates the presence of interstratified clay mineral type illite-saponite (lithium-bearing Mg-smectite). 相似文献