全文获取类型
收费全文 | 25463篇 |
免费 | 384篇 |
国内免费 | 263篇 |
专业分类
测绘学 | 624篇 |
大气科学 | 1945篇 |
地球物理 | 5420篇 |
地质学 | 8968篇 |
海洋学 | 2043篇 |
天文学 | 5373篇 |
综合类 | 39篇 |
自然地理 | 1698篇 |
出版年
2020年 | 136篇 |
2019年 | 127篇 |
2018年 | 290篇 |
2017年 | 266篇 |
2016年 | 414篇 |
2015年 | 299篇 |
2014年 | 423篇 |
2013年 | 1189篇 |
2012年 | 506篇 |
2011年 | 789篇 |
2010年 | 644篇 |
2009年 | 912篇 |
2008年 | 840篇 |
2007年 | 801篇 |
2006年 | 831篇 |
2005年 | 716篇 |
2004年 | 756篇 |
2003年 | 712篇 |
2002年 | 724篇 |
2001年 | 592篇 |
2000年 | 604篇 |
1999年 | 580篇 |
1998年 | 550篇 |
1997年 | 567篇 |
1996年 | 473篇 |
1995年 | 460篇 |
1994年 | 444篇 |
1993年 | 415篇 |
1992年 | 388篇 |
1991年 | 341篇 |
1990年 | 387篇 |
1989年 | 299篇 |
1988年 | 345篇 |
1987年 | 379篇 |
1986年 | 329篇 |
1985年 | 487篇 |
1984年 | 527篇 |
1983年 | 531篇 |
1982年 | 427篇 |
1981年 | 419篇 |
1980年 | 437篇 |
1979年 | 383篇 |
1978年 | 398篇 |
1977年 | 346篇 |
1976年 | 378篇 |
1975年 | 341篇 |
1974年 | 380篇 |
1973年 | 367篇 |
1972年 | 234篇 |
1971年 | 186篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Robert W. Luth 《Contributions to Mineralogy and Petrology》1995,122(1-2):152-158
The carbonation reaction CaMg(CO3)2 (dolomite)+2SiO2 (coesite)=CaMgSi2O6 (diopside)+2 CO2 (vapor) has been determined experimentally between 3.5 and 6 GPa in a multiple-anvil, solid-media apparatus. This reaction,
a candidate for carbonation of eclogites (garnet+clinopyroxene) in the Earth’s mantle, lies at higher pressure for a given
temperature than do the carbonation reactions for peridotites (olivine+orthopyroxene±clinopyroxene). A depth interval may
exist within the Earth’s mantle under either ‘normal’ or ‘subduction’ thermal regimes where carbonated peridotite could coexist
with carbonate-free, CO2-bearing eclogite.
Received: 25 May 1994/Accepted: 13 June 1995 相似文献
72.
M.?B.?BellEmail author L.?W.?Avery J.?M.?MacLeod J.?P.?Vallée 《Astrophysics and Space Science》2011,333(2):377-388
Sensitive spectral observations made in two frequency bands near 6.0 and 17.6 GHz are described for Orion and W51. Using frequency
switching we were able to achieve a dynamic range in excess of 10,000 without fitting sinusoidal or polynomial baselines.
This enabled us to detect lines as weak as T
A
∼1 mK in these strong continuum sources. Hydrogen recombination lines with Δn as high as 25 have been detected in Orion. In the Orion data, where the lines are stronger, we have also detected a systematic
shift in the line center frequencies proportional to linewidth that cannot be explained by normal optical depth effects. 相似文献
73.
74.
K. W. Helen Lau Keith E. Louden Sharon Deemer Jeremy Hall John R. Hopper Brian E. Tucholke W. Steven Holbrook Hans Christian Larsen † 《Geophysical Journal International》2006,167(1):157-170
New multichannel seismic reflection data were collected over a 565 km transect covering the non-volcanic rifted margin of the central eastern Grand Banks and the Newfoundland Basin in the northwestern Atlantic. Three major crustal zones are interpreted from west to east over the seaward 350 km of the profile: (1) continental crust; (2) transitional basement and (3) oceanic crust. Continental crust thins over a wide zone (∼160 km) by forming a large rift basin (Carson Basin) and seaward fault block, together with a series of smaller fault blocks eastwards beneath the Salar and Newfoundland basins. Analysis of selected previous reflection profiles (Lithoprobe 85-4, 85-2 and Conrad NB-1) indicates that prominent landward-dipping reflections observed under the continental slope are a regional phenomenon. They define the landward edge of a deep serpentinized mantle layer, which underlies both extended continental crust and transitional basement. The 80-km-wide transitional basement is defined landwards by a basement high that may consist of serpentinized peridotite and seawards by a pair of basement highs of unknown crustal origin. Flat and unreflective transitional basement most likely is exhumed, serpentinized mantle, although our results do not exclude the possibility of anomalously thinned oceanic crust. A Moho reflection below interpreted oceanic crust is first observed landwards of magnetic anomaly M4, 230 km from the shelf break. Extrapolation of ages from chron M0 to the edge of interpreted oceanic crust suggests that the onset of seafloor spreading was ∼138 Ma (Valanginian) in the south (southern Newfoundland Basin) to ∼125 Ma (Barremian–Aptian boundary) in the north (Flemish Cap), comparable to those proposed for the conjugate margins. 相似文献
75.
76.
Models of surface energy balance and snow metamorphism are utilized to predict the energy and meltwater fluxes at an Arctic site in the forest–tundra transition zone of north-western Canada. The surface energy balance during the melt period is modelled using an hourly bulk aerodynamic approach. Once a snowcover becomes patchy, advection from the bare patches to the snow-covered areas results in a large spatial variation in basin snowmelt. In order to illustrate the importance of small-scale, horizontal advection, a simple parameterization scheme using sensible heat fluxes from snow free areas was tested. This scheme estimates the maximum horizontal advection of sensible heat from the bare patches to the snow-covered areas. Calculated melt was routed through the measured snowcover in each landscape type using a variable flow path, meltwater percolation model. This allowed the determination of the spatial variability in the timing and magnitude of meltwater release for runoff. Model results indicate that the initial release of meltwater first occurred on the shallow upland tundra sites, but meltwater release did not occur until nearly two weeks later on the deep drift snowcovers. During these early periods of melt, not all meltwater is available for runoff. Instead, there is a period when some snowpacks are only partially contributing to runoff, and the spatial variation of runoff contribution corresponds to landscape type. Comparisons of melt with and without advection suggests that advection is an important process controlling the timing of basin snowmelt. 相似文献
77.
H. Wöhl 《Solar physics》1971,16(2):362-372
Spectra of umbrae of several sunspots in the wavelength region 4000–8000 Å scanned photoelectrically at the Göttingen Locarno Observatory were used in order to search for absorption lines of molecules. Several thousands of lines of known molecules were reidentifled (see Table II and Table III). Newly identified molecules are CoH, NiH and H2O (see Table IV and Wöhl (1969a)). The Zeemann effect on molecular lines (of MgH and CaH; see Table V and Wöhl (1969b)) in spectra of umbrae was detected. 相似文献
78.
79.
Dacites form a relatively small proportion of lavas in the Taupo Volcanic Zone, New Zealand (5km3), and occur mainly on the eastern side. In this paper their origin is considered in terms of three processes: (a) partial melting of crustal rocks; (b) fractional crystallisation of basalt and andesite; and (c) sub-surface mixing of basic and acid magma. Modelling techniques are used to calculate the most acceptable degree of fractional crystallisation and magma mixing to fit major-element data, and these values are used to compare calculated and observed trace-element values. The success or failure of the model is determined by the closeness of the two sets of values. For partial-melt models, trace-element values alone are calculated by the batch-melting equation.Results indicate that White Island dacite can best be modelled by fractional crystallisation; Manawahe by fractional crystallisation plus limited crustal contamination; Maungaongaonga by partial melting of Western Basement greywacke, and Tauhara by partial melting of this greywacke together with minor mixing with a more basic magma. Results from Parekauau and Horohoro indicate that these lavas are unlikely to have formed by any of the processes examined. 相似文献
80.
THREE-WAY METHODS FOR THE CALIBRATION OF CHROMATOGRAPHIC SYSTEMS:COMPARING PARAFAC AND THREE-WAY PLS
For the calibration of chromatographic systems,different methods can be used.One class of methodsutilizes three-way approaches.The calibration problem is stated in such a way that the decompositionof a three-way array can serve for the prediction of retention on new stationary phases.Two three-way approaches are presented:the Unfold-PCA and PARAFAC models.The theory ofboth methods is presented and the differences are highlighted,the main difference being that PARAFACis a trilinear decomposition whereas Unfold-PCA is not.Both three-way methods are evaluated on asmall data set consisting of retention measurements of eight solutes at six mobile phase compositions onsix stationary phases.The differences in performance of the two models are minor,For calibration purposes,two variants of the methods are discussed:three-way PLS and an extensionof PARAFAC.Again the theory and differences between the two methods are explained.The predictiveperformance of the two methods is compared using the same data set as earlier.The differences inpredictive performance,however,are minor.Both methods are capable of predicting 98% of thevariation in the test sets.Yet,there are other considerations when comparing methods than predictiveperformance,e.g.the quality of the predictions. 相似文献