全文获取类型
收费全文 | 13048篇 |
免费 | 822篇 |
国内免费 | 575篇 |
专业分类
测绘学 | 679篇 |
大气科学 | 1181篇 |
地球物理 | 3675篇 |
地质学 | 4546篇 |
海洋学 | 1137篇 |
天文学 | 2163篇 |
综合类 | 193篇 |
自然地理 | 871篇 |
出版年
2023年 | 74篇 |
2022年 | 160篇 |
2021年 | 295篇 |
2020年 | 305篇 |
2019年 | 286篇 |
2018年 | 535篇 |
2017年 | 523篇 |
2016年 | 683篇 |
2015年 | 559篇 |
2014年 | 634篇 |
2013年 | 811篇 |
2012年 | 678篇 |
2011年 | 802篇 |
2010年 | 682篇 |
2009年 | 726篇 |
2008年 | 679篇 |
2007年 | 519篇 |
2006年 | 521篇 |
2005年 | 457篇 |
2004年 | 419篇 |
2003年 | 364篇 |
2002年 | 386篇 |
2001年 | 337篇 |
2000年 | 253篇 |
1999年 | 193篇 |
1998年 | 208篇 |
1997年 | 166篇 |
1996年 | 123篇 |
1995年 | 120篇 |
1994年 | 135篇 |
1993年 | 87篇 |
1992年 | 99篇 |
1991年 | 93篇 |
1990年 | 115篇 |
1989年 | 76篇 |
1988年 | 56篇 |
1987年 | 62篇 |
1986年 | 64篇 |
1985年 | 76篇 |
1984年 | 73篇 |
1983年 | 77篇 |
1982年 | 60篇 |
1981年 | 57篇 |
1980年 | 57篇 |
1979年 | 54篇 |
1978年 | 60篇 |
1975年 | 52篇 |
1974年 | 60篇 |
1972年 | 53篇 |
1971年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Micron-scale iron-distribution patterns in sphalerite grains derived from two contrasting mineral assemblages of the Nagybörzsöny hydrothermal ore deposits (high temperature stockwork and low temperature veins), were determined with electron microprobe, pointcounter and continuous chart-recorder measurements along radial profiles. A significant oscillation of iron-content ranging from 8.1 to 18 per cent for stockwork and 4.3 to 15.8 per cent for veins took place during crystal growth. Homogeneous crystal cores are characteristic for vein-filling, while replacement occurring in deeper levels of the stockwork results in mosaic cores. Frequent oscillation of iron content is relevant to top-sections of the ore bodies, copious supply being recorded in recurring shells, whereas scanty, unilateral ones produce crescents arranged in onion-like structure.
Zusammenfassung Bestimmungen der Eisenverteilung wurden an Zinkblendekörnern aus zwei verschiedenen Mineralparagenesen (Hochtemperatur-Stockwerk und Gangfüllungen niederiger Bildungstemperatur) der hydrothermalen Erzlagerstätte Nagybörzsöny im Mikronbereich durch Elektronen-Mikrosonde-Messungen (Punktzählung und kontinuierliche Band-Registrierung) entlang radialer Profile vorgenommen. Bedeutende Schwankungen des Eisengehaltes (8,1–18% für das Stockwerk und 4,3–15,8% für die Gänge) wurden registriert. Homogene Kristallkerne kennzeichnen die Gangfüllungen, wogegen in tieferen Horizonten des Stockwerks Verdrängungen zur Bildung von Kristallen mit Mosaik-Kernen führen. Allgemein ist in den Gipfel-Partien der Erzkörper Fluktuation des Eisengehaltes häufig. Gleichmäßiger Nachschub während des Kristallwachstums führte zu ringförmigen Zonen gleicher Eisengehalte, spärlicher oder einseitiger dagegen zu halbmondförmigen Hüllen mit Zwiebelstruktur.相似文献
992.
Summary The dielectric tensor of a time-varying anisotropic electron-plasma has been studied with the consideration of the effect of collision. The tripple splitting of the electromagnetic waves is obtained from the dispersion relation which gives the two usual magnetoionic modes in the limiting case. The randomness of electron number density has been evaluated by the help of field variables and also by the nature of fluctuation of dielectric tensor. 相似文献
993.
Krishna De 《Pure and Applied Geophysics》1970,80(1):114-123
Summary The propagation of Love waves is discussed on the basis of finite strain theory. The primary Love wave is found to be associated with a secondary Rayleigh wave and a tertiary Love wave. Numerical calculations are presented for two values of the wave-velocity; the results show that the theory of Love waves based on infinitesimal strain, is not applicable to short period waves. 相似文献
994.
Jaroslav Střeštík 《Studia Geophysica et Geodaetica》1970,14(3):344-349
Zusammenfassung Es wird eine einfache auf der Symmetrie der Grundformeln der Fourierschen Transformation gegründete Methode, wie von den Spektralfunktionen
zur ursprünglichen Pulsationsform zu gelangen, beschrieben. Mit dieser Methode wird die durchschnittliche Form der Pi2-Pulsationen
konstruiert. Diese idealisierte Pulsation hat dieselben Eigenschaften wie ein statistisches Ensemble von Pulsationen. Der
wirkliche Verlauf der Intensit?t des magnetischen Feldes bei Pi2-Pulsationen wird durch die Methode aus den Induktionsregistrierungen
abgeleitet. Die berechnete Kurve zeigt starke Korrelation mit der direkten Registrierung der Intensit?t des magnetischen Feldes.
Address: Boční II, Praha 4-Spořilov. 相似文献
Address: Boční II, Praha 4-Spořilov. 相似文献
995.
Milan Rieder Miroslav Huka Dagmar Kučerová Luděk Minařík Jiří Obermajer Pavel Povondra 《Contributions to Mineralogy and Petrology》1970,27(2):131-158
Compositions of natural lithium-iron micas are approximated best by the sidero-phyllite-polylithionite join. These micas contain little or no magnesium and manganese. Their octahedral sheets contain close to two trivalent cations (mainly aluminum) in small crystallographic sites and a variable quantity of lithium and R+2 (mainly iron) in large sites. Octahedral vacancies are situated mostly in large sites. Lithium and R+2 approach a 44 replacement relationship in micas with octahedral occupancy close to six. Lithium and fluorine show a good positive correlation (small excess of fluorine over lithium), which indicates a crystallochemical association between them. There is a less distinct positive correlation between lithium and R+4.Based on simplifications, a calculation shows that about two-thirds of octahedral vacancies are caused by substitutions within the octahedral sheet, one-third, by tetrahedral substitutions. Different methods of calculating the crystallochemical formula yield slightly different numbers of octahedral vacancies, but do not affect the mica's position in plots of physical parameters against composition. If a crystallochemical formula is calculated from analysis of a mica contaminated with quartz, topaz, or feldspar, the apparent number of octahedral vacancies increases; such a formula exhibits unusual behavior in composition plots. 相似文献
996.
S. S. De 《Pure and Applied Geophysics》1972,98(1):173-177
Summary Wave propagation through the ionospheric plasma containing irregularities has been studied. The excess electron number density due to the presence of irregularities has been calculated in a way which may be suitably used for practical purposes. 相似文献
997.
998.
Summary The core waves recorded at four seismograph stations in Central Europe were investigated with the aim to find the most suitable set of travel-time curves and a fitting model of the core structure. Another travel-time curve was constructed by means of time differences between the core phases. The differences in the features of the travel-time curves were studied using records of shallow, intermediate and deep shocks from the same focal region (Tonga). 相似文献
999.
Résumé On donne les résultats de l'analyse de la dérive des pendules horizontaux de la station Píbram-Bezové Hory au cours des années 1927–1938. Différemment aux résultats publiés déjà antérieurement[2], on a tout d'abord séparé par la méthode des moindres carrés la dérive linéaire et le terme à période de durée d'un an exactement et ce n'est que le reste qu'on a analysé par la méthode de l'analyse spectrale spéciale[4, 6]. On a trouvé dans les deux éléments une période de 222, respectivement 223 jours, non considérée jusqu'alors et ne pouvant pas être interprétée jusqu'à présent du point de vue physique. Les autres résultats sont en bon accord avec ceux reçus à l'origine. On peut conclure de la comparaison des phases des composantes annuelles des pendules horizontaux et du mouvement du pôle[5] que les deux événements sont du même origine. 相似文献
1000.
Vladimír Kropáček Miroslav Krs Reviewer F. Janák 《Studia Geophysica et Geodaetica》1971,15(2):161-172
Summary The paper deals with the magnetic properties of the natural minerals haematite, ilmenite and pyrrhotite. The natural remanent magnetization Jn, the volume susceptibility , the specific magnetization of saturation so, the Curie temperature , the A.C. demagnetization of natural remanent magnetization, the thermal demagnetization Jn, the temperature dependence of the specific magnetization of saturation, and several other parameters were determined for the individual sets of minerals. Since natural minerals can and do contain various heterogeneous and isomorphic admixtures, their magnetic properties may change depending on the content and type of these admixtures. Therefore, all the investigations of the magnetic properties described in this paper were carried out with extensive sets of minerals, representing various Czechoslovak and world localities. A number of interesting results were obtained from the executed experiments, e.g., the different stability of the natural remanent magnetization of haematite with respect to A.C. demagnetization, the presence and type of heterogeneous inclusions in ilmenite, the phase changes connected with the -transition in natural pyrrhotites, etc. The types of distributions of the investigated values of the magnetic properties were also determined. 相似文献