全文获取类型
收费全文 | 95299篇 |
免费 | 1051篇 |
国内免费 | 1399篇 |
专业分类
测绘学 | 2991篇 |
大气科学 | 6067篇 |
地球物理 | 18699篇 |
地质学 | 37063篇 |
海洋学 | 7419篇 |
天文学 | 18946篇 |
综合类 | 2316篇 |
自然地理 | 4248篇 |
出版年
2022年 | 603篇 |
2021年 | 924篇 |
2020年 | 1018篇 |
2019年 | 1080篇 |
2018年 | 6813篇 |
2017年 | 5940篇 |
2016年 | 4837篇 |
2015年 | 1343篇 |
2014年 | 2293篇 |
2013年 | 3766篇 |
2012年 | 3414篇 |
2011年 | 5688篇 |
2010年 | 4793篇 |
2009年 | 5777篇 |
2008年 | 4925篇 |
2007年 | 5498篇 |
2006年 | 3039篇 |
2005年 | 2146篇 |
2004年 | 2272篇 |
2003年 | 2184篇 |
2002年 | 1954篇 |
2001年 | 1656篇 |
2000年 | 1497篇 |
1999年 | 1160篇 |
1998年 | 1219篇 |
1997年 | 1190篇 |
1996年 | 970篇 |
1995年 | 986篇 |
1994年 | 889篇 |
1993年 | 770篇 |
1992年 | 734篇 |
1991年 | 742篇 |
1990年 | 838篇 |
1989年 | 723篇 |
1988年 | 661篇 |
1987年 | 794篇 |
1986年 | 636篇 |
1985年 | 862篇 |
1984年 | 941篇 |
1983年 | 884篇 |
1982年 | 805篇 |
1981年 | 827篇 |
1980年 | 724篇 |
1979年 | 643篇 |
1978年 | 679篇 |
1977年 | 600篇 |
1976年 | 568篇 |
1975年 | 571篇 |
1974年 | 540篇 |
1973年 | 606篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
491.
H. Flanquart C. Meur-Férec Ph. Deboudt V. Morel A.-P. Hellequin et al. 《GeoJournal》1991,24(2):223-223
Reports
Littoral '92 相似文献492.
Periodic Hartree-Fock STO-3G calculations have been performed on several tetracoordinated silica polymorphs: low and high quartz, low and idealized high cristobalite and prototype tridymite. The optimized structural parameters are in overall good agreement with experimental data. In the particular case of -quartz, the SiO4 tetrahedra are found to be irregular. The optimized values of the two different SiO bond lengths are respectively 1.608 Å and 1.613 Å. The potential energy versus tilt angle curves suggest a picture of the high temperature phases in terms of delocalized oxygen atoms which is consistent with a disordered structure. Finally, the bonding in silica polymorphs is discussed from electron density maps and Mulliken population analysis. 相似文献
493.
A layered basic intrusion has been found in the Central Granulite Belt of the Sri Lanka continental basement. It intruded parallel to bedding, before all or early during deformation of neighbouring metasediments. Deformation, affecting metasediments and the intrusion alike, includes flattening to c. 1/20 of the original thickness and NNW-stretching to c. 20 times the original length. The intrusion is now 170–300 m thick. Most of the deformation was acquired under granulite facies metamorphism. The intrusion was then folded, still at high T, by a large F4-synform with an axis parallel to str1 and a steep axial plane. A steep axial plane cleavage and minor folds are related to this big fold. Stretching continued along its axis. Late during formation of this fold a granite intruded, mainly following S4 cleavage planes. The intrusion shows a homogeneous gabbroic series at the bottom, followed upwards by a differentiated and layered series. A thin sequence of ultramafic rocks occurs near the middle. This indicates multiple melt-injection. More homogeneous partly biotite-bearing amphibolites form the top of the succession. Magmatic layering is well preserved, but no magmatic minerals or grain fabrics have escaped deformation or metamorphism. Static annealing under granulite facies conditions outlasted all deformation and was accompanied and followed by the beginning of cooling. Hornblende-Plagioclase coronas formed round garnets at this stage. Geochemical work, carried out by STOSCH (1991) on our samples, confirms the cumulate nature of the rocks.
List of abbreviations ss sedimentary bedding - s1 first cleavage, plane of first flattening - str1 Direction of first stretching; although L is usually used for lineations of different kind, including stretching, we use this term to point out that extension is proved in each case - F2 second folds = first folds folding s1 - s2 second cleavage or plane of flattening - F3 third folds - s3 third cleavage or plane of flattening - F4 fourth folds, folding s1,2,3 and F1,2,3 - s4 fourth cleavage or plane of flattening - str4 direction of fourth stretching - F5,6 fifth and sixth folds - gf(m) granulite facies (metamorphism) - af(m) amphibolite facies (metamorphism) - KNa-f KNa-feldspar - pg plagioclase - f feldspar - opx orthopyroxene - cpx clinopyroxene - px pyroxene - hb hornblende - bi biotite - cc calcite - do dolomite - qz quartz - mt magnetite 相似文献
Zusammenfassung Eine geschichtete Basische Intrusion wurde im Central Granulite Belt der tiefen, kontinentalen Kruste Sri Lankas entdeckt. Sie intrudierte parallel zur Schichtung in benachbarte Sedimente, vor aller oder sehr früh in deren Deformation. Die Deformation, die Sedimente und die Intrusion in gleicher Weise betraf, führte zu Plättung auf das ca. 1/20 der Ausgangsdicke und zu NNW-Streckung auf das ca. 20fache der Ausgangslänge. Heute ist die Intrusion 170–300 m dick. Der Hauptteil der Deformation wurde unter Granulit-Fazies-Bedingungen erworben. Noch bei hoher T wurde die Intrusion durch eine große F4-Falte gefaltet. Deren Achse liegt parallel der Streckungsrichtung, stri, ihre Achsenebene ist steil. Eine steile, Achsenebenen-parallele S4-Schieferung und kleinere Falten entstanden mit ihr. Während der Bildung dieser Falte hielt die Streckung parallel ihrer Achse an. Spät während ihrer Bildung intrudierte ein Granit. Er folgt im wesentlichen S4. Die Intrusion beginnt unten mit einer homogenen, gabbroiden Serie. Nach oben folgt eine differenzierte, geschichtete. Ein dünnes Paket ultramafischer Lagen erscheint nahe der Mitte. Es weist auf multiple Schmelz-Zufuhr hin. Homogenere Amphibolite, teils mit Biotit, bilden den obersten Teil. Magmatischer Lagenbau ist gut erhalten, lokal mit Gradierung. Magmatische Minerale oder Korngefüge haben Deformation und Metamorphose nicht überlebt. Statische Temperung unter Granulit-Fazies-Bedingungen überdauerte alle Deformation. Sie beginnt und dauert an bei bereits sinkender T. Hornblende-Plagioklas-Koronas bilden sich in diesem statischen Endstadium. STOSCH (1991) untersuchte unsere Proben von der Intrusion geochemisch. Er bestätigte die Kumulatnatur der Gesteine.
Résumé Une intrusion basique litée a été découverte dans la ceinture centrale granulitique du socle continental du Sri Lanka. L'intrusion s'est effectuée parallèlement à la stratification, avant la déformation des métasédiments encaissants ou tout au début de celleci. La déformation, qui affecte à la fois les métasédiments et l'intrusion, comporte un aplatissement jusqu'à ± 1/20 de l'épaisseur d'origine, et un allongement de ± 20 fois en direction NNW. L'intrusion présente actuellement une épaisseur de 170 à 300 m. La plus grande part de la déformation a été acquise dans les conditions du faciès des granulites. L'intrusion a ensuite été plissée, toujours à haute T, en un large synforme F4 dont l'axe est parallèle à l'allongement stri et dont le plan axial est vertical. Ce grand pli est accompagné d'une schistosité S4 plan-axiale redressée et de plis secondaires. L'allongement s'est poursuivi parallèlement à son axe. A la fin de la formation de ce pli, un granite s'est intrudé, qui suit en gros S4. L'intrusion comporte à sa base une série gabbroïque homogène, suivie vers le haut par une série litée et différenciée. Elle contient, vers son milieu, une intercalation mince de roches ultramafiques. Ceci implique des injections répétées de magma. Le sommet est formé d'amphibolites homogènes partiellement biotitiques. Le litage magmatique est bien conservé, mais aucun minéral ou fabrique magmatique n'a échappé à la déformation et au métamorphisme. Un recuit statique dans les conditions granulitiques a suivi la déformation; il a été accompagné et suivi par le début du refroidissement. A ce stade, des couronnes à hornblende-plagioclase se sont formées autour des grenats. Une étude géochimique, effectuée en 1991 par Stosch sur nos échantillons confirme le caractère de cumulat des roches.
- . , . , , 1/20 20- NNW . 170–300 . . F4, str1, . , S4, . . . S4. , , . . , , . coxpa . , .. . , . . . . STOSCH (1991) .
List of abbreviations ss sedimentary bedding - s1 first cleavage, plane of first flattening - str1 Direction of first stretching; although L is usually used for lineations of different kind, including stretching, we use this term to point out that extension is proved in each case - F2 second folds = first folds folding s1 - s2 second cleavage or plane of flattening - F3 third folds - s3 third cleavage or plane of flattening - F4 fourth folds, folding s1,2,3 and F1,2,3 - s4 fourth cleavage or plane of flattening - str4 direction of fourth stretching - F5,6 fifth and sixth folds - gf(m) granulite facies (metamorphism) - af(m) amphibolite facies (metamorphism) - KNa-f KNa-feldspar - pg plagioclase - f feldspar - opx orthopyroxene - cpx clinopyroxene - px pyroxene - hb hornblende - bi biotite - cc calcite - do dolomite - qz quartz - mt magnetite 相似文献
494.
G. M. Petrov 《Astrophysics and Space Science》1991,177(1-2):269-270
The classical method of determination of the absolute azimuth (or Bessel's parameter n) can secure sufficiently precision for RA from observations of stars at high geographical latitudes during polar night only. 相似文献
495.
A principally new, quantitative system of the classification of the spectra of planetary nebulae is proposed. Spectral class of excitation class of the nebulap is determined according to the relative intensities of emission lines (N
1+N
2) [OIII]/4686 HeII and (N
1+N
2) [OIII]/H (Table I, Figure 1). The excitation classes are obtained for 142 planetary nebulae of all classes—low (p=1–3), middle (p=4–8), and high (p=9–12+) (Tables II, III, and IV). An empirical relationship between excitation classp and mean radius of nebulae
is discovered (Figure 2). This relationship as well as excitation classp, as an independend parameter, admit an evolutionary interpretation. It is shown that after reaching the highest class of excitationp=12+ the nebulae decrease their class of excitation with the further increases of sizes. The diagram of this relationship
has two nearly-symmetric branches — rising and descending with the apogee onp=12+ (Figure 2). 相似文献
496.
A detailed list of line identifications of the far UV spectrum of the O4I(n)f star Puppis (HD 66811) in the wavelength range 1168–1984 Å recorded on 16 April, 1981 with the International Ultraviolet Explorer (IUE) is presented. The detailed analysis of the radial velocities measured in the same wavelength range is also presented. 相似文献
497.
The variations of the declinations of 36 Belgrade zenith stars from BZS170 Catalogue published in Astronomy and Astrophysics,177, 313–316 (1987) are examined by spectral analysis. The prospect is to evaluate multiples of the Chandler period of which the most prominent for all stars is the double one. 相似文献
498.
G. Z. Xie F. K. Liu Y. Y. Zhu J. H. Fan R. W. Lu 《Astrophysics and Space Science》1991,179(2):321-329
It has become clear in recent years that relativistic beaming is a good explanation for the BL Lac phenomenon. Of studies based on the relativistic beaming model of BL Lac objects, we note that the orientation of jet's axis to the line-of-sight is very small and, therefore, the observed flux emitted from a rapidly moving source is orders of magnitude higher than the flux in its rest-frame:F
obs = 3 +
F
intr, where is the bulk relativistic Doppler factor. Then the observed apparent magnitudem
v
must be corrected for this effect. For our 39 samples, the corrected apparent magnitudem
v
corr
and logZ have a good correlation. 相似文献
499.
V. G. Surdin 《Astrophysics and Space Science》1991,183(1):129-134
Four pairs of visual double star clusters with the lowest mass-to-luminosity ratio have been selected among globular clusters of our Galaxy. By taking into accounts the effects of dynamical friction and compressive gravitational shocks, we conclude that the probability for the pairs to be gravitationally bound is very low. 相似文献
500.
Quasi-steady high-temperature current sheets are an energy source during the main or hot phase of solar flares. Such sheets are shown to be stabilized with respect to the tearing instability by a small transverse component of magnetic field existing in the sheets. 相似文献