全文获取类型
收费全文 | 13676篇 |
免费 | 1829篇 |
国内免费 | 3345篇 |
专业分类
测绘学 | 1745篇 |
大气科学 | 2058篇 |
地球物理 | 2898篇 |
地质学 | 6060篇 |
海洋学 | 1960篇 |
天文学 | 1630篇 |
综合类 | 1011篇 |
自然地理 | 1488篇 |
出版年
2024年 | 65篇 |
2023年 | 169篇 |
2022年 | 339篇 |
2021年 | 388篇 |
2020年 | 447篇 |
2019年 | 543篇 |
2018年 | 406篇 |
2017年 | 519篇 |
2016年 | 562篇 |
2015年 | 666篇 |
2014年 | 702篇 |
2013年 | 817篇 |
2012年 | 795篇 |
2011年 | 690篇 |
2010年 | 658篇 |
2009年 | 804篇 |
2008年 | 971篇 |
2007年 | 1019篇 |
2006年 | 1078篇 |
2005年 | 931篇 |
2004年 | 850篇 |
2003年 | 726篇 |
2002年 | 648篇 |
2001年 | 498篇 |
2000年 | 650篇 |
1999年 | 614篇 |
1998年 | 486篇 |
1997年 | 334篇 |
1996年 | 254篇 |
1995年 | 232篇 |
1994年 | 214篇 |
1993年 | 190篇 |
1992年 | 139篇 |
1991年 | 94篇 |
1990年 | 75篇 |
1989年 | 77篇 |
1988年 | 50篇 |
1987年 | 37篇 |
1986年 | 38篇 |
1985年 | 29篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
WANG Yachun 《东北亚地学研究》2002,(1)
The paper deals with the methods of formation pressure evaluation for a single well by using the very common ac-cepted parameters, such as drilling exponent , and flowline temperature , etc. which is part of compiling the end well report. 相似文献
22.
23.
Based on the Germany Koldwey Station's 1994-2003 conventional observation hourly data, this paper conducts a statistical analysis on the short-term climate characteristics for an arctic tundra region (Ny-(A)lesund island) where our first arctic expedition station (Huanghe Station) was located. Affected by the North Atlantic warming current, this area has a humid temperate climate, and the air temperature at Ny-(A)lesund rose above 0 ℃ even during deep winter season during our research period. The wind speed in this area was low and appeared most at southeast direction. We find that the temperature at Ny-(A)lesund rose in the faster rate (0.68 ℃/10 a) than those at the whole Arctic area. Compared with the floating ices where our expedition conducted in the Arctic, Ny-(A)lesund was warmer and more humid and had lower wind speed. Comparison of the near surface air temperature derived by NCEP/NCAR reanalysis to the conventional measurements conducted at the Koldwey site in Ny-(A)lesund area shows a good agreement for winter season and a significant difference for summer season. 相似文献
24.
Mineral assemblages in Al2O3‐rich, SiO2‐ and K2O‐poor metapelitic rocks from the western Odenwald Crystalline Complex (Variscan Mid‐German Crystalline Rise, southern Germany) include corundum, spinel, cordierite, sillimanite, garnet and staurolite. Quartz is absent from almost all samples. Therefore, the applicability of conventional geothermobarometry is very limited or even impossible. Detailed petrographic investigation on selected samples permits inference of the sequence of appearance and disappearance of several mineral assemblages. The recognition of such partial re‐equilibration stages and their associated mineral assemblages, together with mineral stabilities predicted from KFMASH pseudosections, enables the determination of the pressure‐temperature (P–T) trajectories experienced by these rocks during the Variscan metamorphism. The rocks were metamorphosed under low‐P/high‐T conditions and underwent an anti‐clockwise P–T evolution. A pressure increase from about 2 kbar to 4 ± 0.5 kbar was accompanied by heating. Peak metamorphic conditions were reached at pressures of 4 ± 0.5 kbar and temperatures of at least 640 °C, probably even higher. The retrograde evolution is characterised by near‐isobaric cooling from ≥ 640 °C to approximately 550 °C. The rocks underwent the anti‐clockwise evolution in a subduction‐related magmatic arc setting. The close spatial association of the low‐P/high‐T rocks with recently discovered metabasic eclogites in the eastern part of the Odenwald Crystalline Complex may indicate a fossil paired metamorphic belt in the Central European Variscides. 相似文献
25.
In view of rapid developments in iterative solvers, it is timely to re‐examine the merits of using mixed formulation for incompressible problems. This paper presents extensive numerical studies to compare the accuracy of undrained solutions resulting from the standard displacement formulation with a penalty term and the two‐field mixed formulation. The standard displacement and two‐field mixed formulations are solved using both direct and iterative approaches to assess if it is cost‐effective to achieve more accurate solutions. Numerical studies of a simple footing problem show that the mixed formulation is able to solve the incompressible problem ‘exactly’, does not create pressure and stress instabilities, and obviate the need for an ad hoc penalty number. In addition, for large‐scale problems where it is not possible to perform direct solutions entirely within available random access memory, it turns out that the larger system of equations from mixed formulation also can be solved much more efficiently than the smaller system of equations arising from standard formulation by using the symmetric quasi‐minimal residual (SQMR) method with the generalized Jacobi (GJ) preconditioner. Iterative solution by SQMR with GJ preconditioning also is more elegant, faster, and more accurate than the popular Uzawa method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
26.
27.
28.
利用上海天文台的照相底片资料,确定了疏散星团NGC6530天区364颗恒星的自行和成员概率,并对有关自行测定的方法、结果和精度等问题作了较为详细的介绍和讨论。使用的底片历元差为87年,全部恒星自行中误差的均方根值为1.09mas/a。 相似文献
29.
《Mathematical Geology》1997,29(5):653-668
Filtering either through the electronics of an instrument or through digital procedure is performed routinely on geophysical
data. When velocity fluctuations are measured in turbulent flows using electromagnetic current meters (ECMs), a builtin lowpass
Butterworth filter of order n usually attenuates fluctuations at high frequencies. However, the effects of this filter may
not be acknowledged in turbulence studies, thus impeding comparisons between data collected with different ECMs. This paper
explores the implications of the filters on the characteristics of velocity signals, mainly on variance, power spectra, and
correlation analyses. Variance losses resulting from filtering can be important but will vary with the order n of the Butterworth
filter, decreasing as n increases. Knowing the filter response, it is possible to reconstruct the original signal spectrum
to evaluate the effect of filtering on variance and to allow comparisons between data collected with different instruments.
The autocorrelation function also is affected by filtering which increases the value of the coefficients in the first lags,
resulting in an overestimation of the integral length scale of coherent structures. These important effects add to those related
to size and shape differences in ECM sensors and must be taken into account in comparative studies. 相似文献
30.
The Mordor Alkaline Igneous Complex (MAIC) is a composite intrusion comprising a body of syenite and a funnel-shaped layered
mafic–ultramafic intrusion of lamprophyric parentage, the Mordor Mafic–Ultramafic Intrusion or MMUI. The MMUI is highly unusual
among intrusions of lamprophyric or potassic parentage in containing primary magmatic platinum-group element (PGE)-enriched
sulfides. The MMUI sequence consists largely of phlogopite-rich pyroxenitic cumulates, with an inward dipping conformable
layer of olivine-bearing cumulates divisible into a number of cyclic units. Stratiform-disseminated sulfide accumulations
are of two types: disseminated layers at the base of cyclic units, with relatively high PGE tenors; and patchy PGE-poor disseminations
within magnetite-bearing upper parts of cyclic units. Sulfide-enriched layers at cycle bases contain anomalous platinum group
element contents with grades up to 1.5 g/t Pt+Pd+Au over 1-m intervals, returning to background values of low parts per billion
(ppb) on a meter scale. They correspond to reversals in normal fractionation trends and are interpreted as the result of new
magma influxes into a continuously replenished magma chamber. Basal layers have decoupled Cu and PGE peaks reflecting increasing
PGE tenors up-section, due to increasing R factors during the replenishment episode, or progressive mixing of between resident PGE-poor magma and more PGE-enriched
replenishing magma. The presence of PGE enriched sulfides in cumulates from a lamprophyric magma implies that low-degree partial
melts do not necessarily leave sulfides and PGEs in the mantle restite during partial melting.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献