全文获取类型
收费全文 | 2541篇 |
免费 | 148篇 |
国内免费 | 16篇 |
专业分类
测绘学 | 57篇 |
大气科学 | 189篇 |
地球物理 | 680篇 |
地质学 | 1017篇 |
海洋学 | 295篇 |
天文学 | 259篇 |
综合类 | 24篇 |
自然地理 | 184篇 |
出版年
2023年 | 11篇 |
2022年 | 33篇 |
2021年 | 64篇 |
2020年 | 60篇 |
2019年 | 66篇 |
2018年 | 106篇 |
2017年 | 110篇 |
2016年 | 147篇 |
2015年 | 130篇 |
2014年 | 137篇 |
2013年 | 163篇 |
2012年 | 134篇 |
2011年 | 193篇 |
2010年 | 139篇 |
2009年 | 191篇 |
2008年 | 149篇 |
2007年 | 126篇 |
2006年 | 101篇 |
2005年 | 73篇 |
2004年 | 89篇 |
2003年 | 65篇 |
2002年 | 52篇 |
2001年 | 36篇 |
2000年 | 29篇 |
1999年 | 20篇 |
1998年 | 27篇 |
1997年 | 22篇 |
1996年 | 16篇 |
1995年 | 16篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1965年 | 3篇 |
排序方式: 共有2705条查询结果,搜索用时 196 毫秒
991.
Magdalena Kądziałko-Hofmokl Maria Jeleńska Katarzyna Delura Paweł Bylina 《Acta Geophysica》2010,58(2):269-299
Complex paleomagnetic, rock-magnetic and mineralogical studies were performed on serpentinized utramafic rocks from Braszowice-Brze?nica massif (BB) situated at the southern extremity of the Niemcza Shear Zone, close to the Sudetic Marginal Fault. Studies of magnetic minerals revealed presence of several varieties of magnetite grains, and partly altered Cr-spinels. Paleomagnetic studies revealed stable component HS of natural remanence carried by magnetite formed probably during the initial serpentinization. The directions of HS have good grouping within each locality, but differ between localities. Studies of anisotropy of magnetic susceptibility (AMS) have shown that directions of anisotropy axes are steep instead of horizontal as is common within the Niemcza Shear Zone. Taking advantage of the directions of AMS we rotated the directions of HS and brought them to the reference direction for the Sudetes for 372 Ma. We suggest that after acquiring AMS and HS during the Upper Devonian, the BB became divided into multiple units due to tectonic activity in the region. 相似文献
992.
Anna Belehaki Ivan Kutiev Bodo Reinisch Norbert Jakowski Pencho Marinov Ivan Galkin Chris Mayer Ioanna Tsagouri Themistocles Herekakis 《Acta Geophysica》2010,58(3):432-452
The purpose of this paper is to evaluate the performance of the TSMP-assisted Digisonde (TaD) topside profiling technique.
We present systematic comparisons between electron density profiles and TEC parameters extracted from TaD model with (a) CHAMP-derived TEC parameters, (b) CHAMP reconstructed profiles, (c) ground based GPSderived TEC parameters, and (d) profiles reconstructed from RPI/IMAGE plasmagrams. In all cases, TaD follows the general trend of plasmaspheric
observations derived from the above datasets. Especially during storm cases, TaD shows remarkable agreement with the variations
of the ground based GPS-derived TEC parameters. Overall, the comparison results shows that TaD method can be adopted by EURIPOS to provide the electron density
distribution up to plasmaspheric heights in real-time. 相似文献
993.
Some observations on the prediction of the dynamic parameters of debris flows in pyroclastic deposits in the Campania region of Italy 总被引:1,自引:0,他引:1
Over the last 20 years, many tools have been developed for the prediction of the post-failure behaviour of rapid landslides.
However, as pointed out by several researchers, knowledge may be improved by the performance of back-analyses using different
models and the evaluation of their reliability. This paper reports the back-analysis, conducted using numerical models, of
57 rapid landslides that have occurred in the Campania region. The back-analysis has been performed using the 2-D DAN_W code
(version 2003) with two different rheological models: the Voellmy and the frictional models. The latter has been immediately
discarded because it did not match the observed data. Instead, using the Voellmy model, the best-fit values of the parameters
(friction μ and turbulence ξ) for different types of flow (channelled, un-channelled and mixed flows) have been researched.
With these values a parametric study has been carried out on four representative slope profiles of the Campania region, enabling
the prediction of runout, velocity and depth of flow (dynamic parameters) of potential debris flows.
相似文献
Anna Scotto di SantoloEmail: |
994.
C. P. C. David Y. Y. Sta. Maria F. P. Siringan J. M. Reotita P. B. Zamora C. L. Villanoy E. Z. Sombrito R. V. Azanza 《Environmental Geology》2009,58(2):447-454
The supply of nitrogen and phosphorus in coastal zones through time is reflected in the nutrients’ concentration in the sediment
record. Five aquaculture sites in the Philippines were investigated in an effort to establish how long-term changes in land
and coastal water use could have led to biogeochemical modifications affecting the coastal ecosystem. Samples from study sites
show a narrow concentration range for nitrogen and did not reveal any significant trend through time. In contrast, phosphorus
concentrations in most sites start at less than 20 ppm in sediments 30 years and older. The phosphorus value continuously
increase in younger sediments, with each site having a different magnitude change as well as timing of when the major increase
happened. The uppermost 10 cm, representing the last 15 years in sites with age control, typically show a 2- to 3-fold increase
in P load values. Historical increase in nutrient load also coincides with harmful algal bloom events in each area; when effective
P input exceeded 130 kg/km2 per year. Lastly, the observed increase may be attributed to several factors including physical attributes of the area, urbanization
of coastal zones, but most importantly in the proliferation of aquaculture activities. 相似文献
995.
借助光学显微镜和扫描电镜(SEM)揭示了淮南四个井田8煤层中黄铁矿的显微和亚微结构特征。煤层中黄铁矿的形态主要有莓球状、团块状、结核状及解理裂隙充填状。通过此次研究发现在属低硫煤的淮南煤田中,顾桥井田的黄铁矿含量偏高。结合酸碱指数(AAI)、盐度指数(SI)和滞留指数(RI)三个灰成分指相参数判定,顾桥井田中黄铁矿含量相对较高,原因是其沼泽水体的还原性较强、盐度大及水动力条件差。莓球状和结核状黄铁矿形成的原因是粘土矿物的晶格上铁与H:S反应发育而成,而充填胞腔或者沉积裂隙的黄铁矿,大多是因局部强还原微环境所致。 相似文献
996.
Carlos J. Archanjo Patrick Launeau Maria Helena B. M. Hollanda José Wilson P. Macedo Dunyi Liu 《International Journal of Earth Sciences》2009,98(8):1793-1807
Anisotropy of magnetic susceptibility (AMS) applied to an alkaline granite from Meruoca (NE Brazil) recorded weak anisotropies,
typically below 4%, and a considerable dispersion of the AMS axes. Red-clouded feldspars and clots of metasomatic minerals
enclosed in magmatic crystals indicate that hydrothermal fluids altered the granite. U–Pb isotopic data show high-common Pb
on zircons but allowed the calculation of a mean SHRIMP age of 523 ± 9 Ma attributed to the magmatic crystallization. Growth
of fine oxides by late fluid–rock interactions was responsible for the scattering of AMS. Rock magnetic data indicate they
consist mainly of an oxidized magnetite and (titano)hematite. Shape preferred orientation of mafic aggregates measured in
granite quarries shows that the pluton preserves a gently dipping magmatic foliation. AMS in some quarries with a well-defined
magmatic fabric, however, remains highly dispersed. When AMS mimics the mafic shape fabric, only magnetic foliations share
a common orientation. Locally, AMS grounded in coarse Ti-poor magnetite associated with titanite develops a consistent subhorizontal
oblate fabric that agrees with tectonic models suggesting that the cupola of the pluton has been exposed by erosion. 相似文献
997.
Hydrogen cyanide is an excellent organic reagent and is central to most of the reaction pathways leading to abiotic formation
of simple organic compounds containing nitrogen, such as amino acids, purines and pyrimidines. Reduced carbon and nitrogen
precursor compounds for the synthesis of HCN may be formed under off-axis hydrothermal conditions in oceanic lithosphere in
the presence of native Fe and Ni and are adsorbed on authigenic layer silicates and zeolites. The native metals as well as
the molecular hydrogen reducing CO2 to CO/CH4 and NO3
-/NO2
- to NH3/NH4
+ are a result of serpentinization of mafic rocks. Oceanic plates are conveyor belts of reduced carbon and nitrogen compounds
from the off-axis hydrothermal environments to the subduction zones, where compaction, dehydration, desiccation and diagenetic
reactions affect the organic precursors. CO/CH4 and NH3/NH4
+ in fluids distilled out of layer silicates and zeolites in the subducting plate at an early stage of subduction will react
upon heating and form HCN, which is then available for further organic reactions to, for instance, carbohydrates, nucleosides
or even nucleotides, under alkaline conditions in hydrated mantle rocks of the overriding plate. Convergent margins in the
initial phase of subduction must, therefore, be considered the most potent sites for prebiotic reactions on Earth. This means
that origin of life processes are, perhaps, only possible on planets where some kind of plate tectonics occur. 相似文献
998.
Dioritic and granodioritic rocks coexist in the Gęsiniec Intrusion in SW Poland showing typical relationships in many mafic–felsic
mingling zones worldwide, such as dioritic syn-putonic dykes and microgranular enclaves within granodioritic host. Plagioclase
zonation from granodioritic rocks suggests late stage mixing probably with dioritic magma, whereas no magma mixing is recorded
in plagioclase from dioritic rocks. The diorites seem to show effects of interaction with evolved, leucocratic melts derived
from granodiorite, not with the granodioritic melt itself. We conclude that the diorites’ compositions were modified after
their emplacement within the granodioritic host, when the diorites were essentially solidified and injection of evolved melt
from granodiorite did not involve marked modification of plagioclase composition. Compositional zoning patterns of plagioclase
in diorites can be modeled by closed system fractional crystallization interrupted by resorption induced probably by decompression.
Granodioritic plagioclase seems to be affected by the same resorption event. Plagioclase that crystallized in dioritic magma
before the resorption does not record interaction between dioritic and granodioritic magmas, suggesting that both magmas evolved
separately.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
999.
Sergio Archangelsky Viviana Barreda Mauro G. Passalia Maria Gandolfo Mercedes Prámparo Edgardo Romero Rubén Cúneo Alba Zamuner Ari Iglesias Magdalena Llorens Gabriela G. Puebla Mirta Quattrocchio Wolfgang Volkheimer 《Cretaceous Research》2009,30(5):1073-1082
In this report, we analyze the angiosperm fossil record (micro- and megafossil) from the central and southern basins of Argentina, southern South America, deposited between the late Barremian (128.3 Ma) to the end of the Coniacian (85.8 Ma). Based on this analysis, three major stages in the evolution of the angiosperms in the southernmost region of South America are established as follows: the late Barremian–Aptian, the latest Aptian-earliest Albian, and the middle Albian- Coniacian. The comparison between our fossil data set and those from Australia, North America, Asia and Europe suggest that the evolution and diversification of the angiosperms at mid and high latitudes in both hemispheres occurred roughly synchronously. 相似文献
1000.
NEAR-Shoemaker spacecraft images of the surface of the near-Earth Asteroid 433 Eros reveal that more than 200 craters on Eros are partially filled with smooth deposits, termed ponds [Veverka, J., and 32 colleagues, 2001a. Science 292, 484-488]. These ponds appear smooth even at a high resolution of 1.2 cm/pixel and spectral analysis suggests that they may be made up of particles ?50 μm in size [Robinson, M.S., Thomas, P.C., Veverka, J., Murchie, S., Carcish, B., 2001. Nature 413, 396-400; Riner, M.A., Eckart, J.M., Gigilio, J.G., Robinson, M.S., 2006. Lunar Planet. Sci. XXXVII. Abstract 2291]. Coupled with the concentration of ponds at low latitudes, the possible small particle size suggests that these deposits might be related to electrostatic transport of dust near the local terminator [Robinson, M.S., Thomas, P.C., Veverka, J., Murchie, S., Carcish, B., 2001. Nature 413, 396-400]. The work presented here incorporates the precise lighting geometry within a crater at a specified latitude into two models for electrostatic transport of dust grains in order to explore dust deposition and pond formation via this mechanism, particularly as a function of latitude. We find that micrometer-sized dust particles are preferentially transported into craters at latitudes where solar illumination angles are often low. In addition we find that if particles are electrostatically lifted off the surface they are preferentially transported into topographic depressions independent of whether the particles undergo stable levitation. The primary limiting factor for our model is uncertainty concerning the dust launching mechanism. Despite that, and though it does not match the observed north-south asymmetry in pond distribution, our model demonstrates potential for good general agreement between future predictions of pond formation via electrostatic transport of dust and observations of pond locations on the surface of Eros. 相似文献