全文获取类型
收费全文 | 42198篇 |
免费 | 727篇 |
国内免费 | 637篇 |
专业分类
测绘学 | 1049篇 |
大气科学 | 3511篇 |
地球物理 | 8582篇 |
地质学 | 13949篇 |
海洋学 | 3874篇 |
天文学 | 9504篇 |
综合类 | 133篇 |
自然地理 | 2960篇 |
出版年
2021年 | 238篇 |
2020年 | 315篇 |
2019年 | 320篇 |
2018年 | 710篇 |
2017年 | 670篇 |
2016年 | 1000篇 |
2015年 | 715篇 |
2014年 | 960篇 |
2013年 | 2161篇 |
2012年 | 1189篇 |
2011年 | 1672篇 |
2010年 | 1395篇 |
2009年 | 1969篇 |
2008年 | 1777篇 |
2007年 | 1672篇 |
2006年 | 1595篇 |
2005年 | 1441篇 |
2004年 | 1367篇 |
2003年 | 1316篇 |
2002年 | 1224篇 |
2001年 | 1079篇 |
2000年 | 1078篇 |
1999年 | 1015篇 |
1998年 | 912篇 |
1997年 | 919篇 |
1996年 | 786篇 |
1995年 | 726篇 |
1994年 | 635篇 |
1993年 | 574篇 |
1992年 | 588篇 |
1991年 | 535篇 |
1990年 | 560篇 |
1989年 | 493篇 |
1988年 | 471篇 |
1987年 | 539篇 |
1986年 | 500篇 |
1985年 | 609篇 |
1984年 | 692篇 |
1983年 | 657篇 |
1982年 | 607篇 |
1981年 | 551篇 |
1980年 | 510篇 |
1979年 | 485篇 |
1978年 | 477篇 |
1977年 | 435篇 |
1976年 | 383篇 |
1975年 | 398篇 |
1974年 | 386篇 |
1973年 | 393篇 |
1972年 | 230篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The summer monsoon season of the year 2006 was highlighted by an unprecedented number of monsoon lows over the central and
the western parts of India, particularly giving widespread rainfall over Gujarat and Rajasthan. Ahmedabad had received 540.2mm
of rainfall in the month of August 2006 against the climatological mean of 219.8mm. The two spells of very heavy rainfall
of 108.4mm and 97.7mm were recorded on 8 and 12 August 2006 respectively. Due to meteorological complexities involved in replicating
the rainfall occurrences over a region, the Weather Research and Forecast (WRF-ARW version) modeling system with two different
cumulus schemes in a nested configuration is chosen for simulating these events. The spatial distributions of large-scale
circulation and moisture fields have been simulated reasonably well in this model, though there are some spatial biases in
the simulated rainfall pattern. The rainfall amount over Ahmedabad has been underestimated by both the cumulus parameterization
schemes. The quantitative validation of the simulated rainfall is done by calculating the categorical skill scores like frequency
bias, threat scores (TS) and equitable threat scores (ETS). In this case the KF scheme has outperformed the GD scheme for
the low precipitation threshold. 相似文献
82.
G. Caro V.C. Bennett B. Bourdon T.M. Harrison A. von Quadt S.J. Mojzsis J.W. Harris 《Chemical Geology》2008,247(1-2):253-265
146Sm–142Nd and 147Sm–143Nd systematics were investigated in garnet inclusions in diamonds from Finsch (S. Africa) and Hadean zircons from Jack Hills (W. Australia) to assess the potential of these systems as recorders of early Earth evolution. The study of Finsch inclusions was conducted on a composite sample of 50 peridotitic pyropes with a Nd model age of 3.3 Ga. Analysis of the Jack Hills zircons was performed on 790 grains with ion microprobe 207Pb/206Pb spot ages from 3.95 to 4.19 Ga. Finsch pyropes yield 100 × ?142Nd = ? 6 ± 12 ppm, ?143Nd = ? 32.5, and 147Sm/144Nd = 0.1150. These results do not confirm previous claims for a 30 ppm 142Nd excess in South African cratonic mantle. The lack of a 142Nd anomaly in these inclusions suggests that isotopic heterogeneities created by early mantle differentiation were remixed at a very fine scale prior to isolation of the South African lithosphere. Alternatively, this result may indicate that only a fraction of the mantle experienced depletion during the first 400 Myr of its history. Analysis of the Jack Hills zircon composite yielded 100 × ?142Nd = 8 ± 10 ppm, ?143Nd = 45 ± 1, and 147Sm/144Nd = 0.5891. Back-calculation of this present-day ?143Nd yields an unrealistic estimate for the initial ?143Nd of ? 160 ?-units, clearly indicating post-crystallization disturbance of the 147Sm–143Nd system. Examination of 146,147Sm–142,143Nd data reveals that the Nd budget of the Jack Hills sample is dominated by non-radiogenic Nd, possibly contained in recrystallized zircon rims or secondary subsurface minerals. This secondary material is characterized by highly discordant U–Pb ages. Although the mass fraction of altered zircon is unlikely to exceed 5–10% of total sample, its high LREE content precludes a reliable evaluation of 146Sm–142Nd systematics in Jack Hills zircons. 相似文献
83.
84.
M. Mejías J. Garcia-Orellana J. L. Plata M. Marina E. Garcia-Solsona B. Ballesteros P. Masqué J. López C. Fernández-Arrojo 《Environmental Geology》2008,54(3):521-536
A methodology for the characterization of deep carbonate aquifers has been developed and applied to El Maestrazgo Jurassic
aquifer in Castellón, Spain. Characterization of these aquifer formations, located at more than 300 m deep, consisted of a
previous phase of compilation, analysis and synthesis of the existing information about the area, followed by a coordinated
combination of different speciality studies: geology, stratigraphy, structural analysis, hydrogeology, hydrochemistry, geophysics
and remote sensing. Geological studies included geological mapping, definition of stratigraphical units and facies and structural
analysis. The aim of the hydrogeology study was to define aquifer formations, recharge area, aquifer points inventory and
groundwater flow directions for the establishment of piezometric and water quality observation nets. Special techniques were
applied, like thermal infrared aerial images and the evaluation of submarine groundwater discharge by means of natural radium
isotopes. Hydrochemical techniques, including majority elements characterization and stable isotopes (18O, 2H and 3H) determination, allowed classifying hydrochemical facies and establishing a renewal pattern for water within the system.
Geophysics was useful in determining the aquifer geometry, the features of the basement and the petrophysical characteristics
of the geological formations. Preliminary results show an important tectonic complexity and the possibilities for groundwater
uses in the area of study. 相似文献
85.
86.
87.
88.
89.
90.
A suite of schistsone from the garnet zone, 19 from thestaurolite zone, 2 from the kyanite isograd, and one from thekyanite zonewere separated into their constituent minerals.Chemical analyses of one chlorite and of 23 sets of coexistingbiotites and garnets were carried out by photometric and titrametricprocedures. Plots of garnet-biotite tie-lines from divariantassemblages on appropriate phase diagrams result in intersectingtie-lines which cannot be ascribed to experimental error. Theoreticalconsiderations argue that at equilibrium, at the same pressureand temperature or at constant pressure and varying temperature,tie-lines of divariant assemblages should not intersect. Possibleexplanations require that diffusion equilibrium of Fe and Mgbe restricted to volumes smaller than that of a hand specimenor that P as well as T varies considerably. Emission spectrographicdeterminations of Fe and Mg in biotite indicate that the Fe/Mgratio varies among biotites little more than a centimeter apart.Such a variation would argue more in favor of a lack of diffusionequilibrium. 相似文献