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971.
972.
Marcelle K. BouDagher-Fadel 《Cretaceous Research》1996,17(6):767-771
Tunisia, Ukraine, Russia, the North Sea area and elsewhere have yielded knowledge that the Early Cretaceous planktonic foraminifera are predominantly members of the Praehedbergellidae. The taxonomy and phylogeny of this family have been revised and refined. New generic and specific taxa have been proposed, new phylogenetic lineages have been described, and many type specimens have been imaged by scanning electron microscopy for the first time.Gorbachikella(Hauterivian–Early Aptian) gave rise toPraehedbergella(Late Hauterivian–Late Aptian), evolvingBlefuscuiana,Lilliputianella, and the planospiralBlowiellain the Barremian. The last gave rise toGlobigerinelloidesin the Aptian, from which the macroperforateAlanlordella(and its descendantPlanomalina) evolved in the Albian.Blowiellawas ancestral to taxa with radially elongated chambers (Claviblowiella, Leupoldina, Schackoina). 相似文献
973.
Cretaceous episodic growth of the Japanese Islands 总被引:1,自引:0,他引:1
G. Kimura 《Island Arc》1997,6(1):52-68
Abstract The Japanese Islands formed rapidly in situ along the eastern Asian continental margin in the Cretaceous due to both tectonic and magmatic processes. In the Early Cretaceous, huge oceanic plateaus created by the mid-Panthalassa super plume accreted with the continental margin. This tectonic interaction of oceanic plateau with continental crust is one of the significant tectonic processes responsible for continental growth in subduction zones. In the Japanese Islands, Late Cretaceous-Early Paleogene continental growth is much more episodic and drastic. At this time the continental margin uplifted regionally, and intra-continent collision tectonics took place in the northern part of the Asian continent. The uplifting event appears to have been caused by the subduction of very young oceanic crust (i.e. the Izanagi-Kula Plate) along the continental margin. Magmatism was also very active, and melting of the young oceanic slab appears to have resulted in ubiquitous plutons in the continental margin. Regional uplift of the continental margin and intra-continent collision tectonics promoted erosion of the uplifted area, and a large amount of terrigenous sediment was abruptly supplied to the trench. As a result of the rapid supply of terrigenous detritus, the accretionary complexes (the Hidaka Belt in Hokkaido and the Shimanto Belt in Southwest Japan) grew rapidly in the subduction zone. The rapid growth of the accretionary complexes and the subduction of very young, buoyant oceanic crust caused the extrusion of a high-P/T metamorphic wedge from the deep levels of the subduction zone. Episodic growth of the Late Cretaceous Japanese Islands suggests that subduction of very young oceanic crust and/or ridge subduction are very significant for the formation of new continental crust in subduction zones. 相似文献
974.
Anil Kumar Y J Bhaskar Rao V M Padma Kumari A M Dayal K Gopalan 《Journal of Earth System Science》1988,97(1):107-114
Palaeomagnetic, geochemical and geochronological studies have been conducted on a set of dolerite dykes intruding the Peninsular
gneisses near Huliyurdurga town, Karnataka, as a reconnaissance survey indicated a Cretaceous age for them. The dykes are
mainly tholeiitic in composition with their 87Sr/86Sr ratios tightly clustered around 0·7045. Their palaeomagnetic data (D
m
=329°,I
m
=−55°) and the corresponding palaeopole coordinates (λ
p
= 34°S,L
p
=108°E) are strikingly close to those of the Deccan Traps to the north. Whole rock K-Ar ages of these dykes ranging between
69 and 84 Ma are also similar to the range of K-Ar ages of the Deccan basalts. The chemical, palaeomagnetic and temporal coherence
between the dykes and the Deccan basalts indicate that they may indeed be tectonically related events. 相似文献
975.
对水压致裂法测得的应力结果之重新估价 总被引:1,自引:0,他引:1
本文讨论了水压致裂进行的绝对应力测量结果的可靠性,指出目前水压致裂法是深部绝对应力测量的较好方法。但应用现在通用的资料处理方法时,它可能给出偏小的最大水平主应力SH和偏大的最小水平主应力Shi特别是两个水平主应力差别较大的地区,这个偏差更加显著。以这样的数据,按照库伦强度准则和Byerlee定律去估价地区稳定性,易于得出与事实不符的结论。本文指出了造成上述测量误差的可能原因,并提出了降低测量误差,改进计算结果的办法。 相似文献
976.
P. M. Hartshorne 《Cretaceous Research》1989,10(4)
The Lower Cretaceous Mural Limestone marks the maximum marine incursion into southeast Arizona during Aptian-Albian time and records the middle Cretaceous transition from coral-dominated to rudist-bivalve dominated reefs. Upper Mural Limestone facies are most often dominated by corals. However, rudists form significant frameworks at some localities, one of which is described in this paper. The paleoenvironmental distribution of three potential reef-builders (corals, rudists, and ‘oysters’) were studied at this patch reef locality. Corals built the framework of the inner reef core. The rudist Petalodontia initially gained a foothold in sheltered areas among corals and subsequently built a framework in the outer reef core. Caprinid rudists formed mounds in the outer reef to back reef areas. The rudists Toucasia and Monopleura and the oyster-like bivalve Chondrodonta formed beds or were scattered in the reef-flank and shelf lagoon sediments and did not contribute to the reef framework.Upper Mural Limestone reefs are important examples of the coexistence of corals and rudists during this middle Cretaceous faunal transition period. This study supports the idea that rudist-bivalves initially colonized protected back-reef areas early in the Cretaceous and only later in the Cretaceous did rudists dominate reef frameworks. 相似文献
977.
John A. OKeefe 《Cretaceous Research》1985,6(3):261-269
It is proposed to regard the terminal Cretaceous event as similar to the radiolarian extinction event in the late Eocene: the result of a volcanic eruption or series of eruptions on the moon. Some glassy ash, lapilli and blocks from these eruptions fell to the earth; some, in geocentric orbit, formed clouds around the earth. In accordance with current theory, it is found that the clouds in orbit would evolve into sets of rings, which would last a few hundred thousand to a few million years, and would perturb the climate of the earth. One such eruption apparently included iridium-bearing material, perhaps from the deep interior of the moon.The hypothesis permits a reconciliation between the evidence for the catastrophic intervention of extra-terrestrial masses in the earth environment, and the evidence for gradual (though rapid) change of flora and fauna at the Cretaceous/Tertiary boundary. The formation of the E-ring of Saturn by ejecta from the Saturnian satellite Enceladus may have been analogous. The theory might be tested by studies of diurnal layering in molluscan shells. 相似文献
978.
979.
辽宁西部九佛堂组昼蜓化石的新发现及其地质意义 总被引:1,自引:0,他引:1
发现于辽宁省义县早白垩世九佛堂组上段地层中的昼蜓化石(孟氏丽昼蜓Abrohemeroscopus mengi Ren,Liu et Chen,2003)与北京西山卢尚坟组的巴依萨昼蜓(Hemeroscopus baissicus Pritykina,1977)在形态上比较相似,但在演化程度上更为原始,主要体现在后翅臀套较小(仅有6~7个翅室),径增脉(Rspl)缺,后翅CuAa脉弯曲、带有5个明显的后分支,前翅MP脉短、终止于翅后缘近翅结处,翅痣下有一个明显的支脉,后翅CuAa和MP域基部较窄、在三角室下方仅有1排翅室。据此,九佛堂组上段的地质时代定为早白垩世早期(Berriasian-Hauterivian)较为合理。 相似文献
980.
WANG Xinshe ZHENG Yadong JIA Wen Department of Earth Space Science Peking University Beijing Institute of Geology Chinese Academy of Geological Science Beijing No. Institute of Geological Resource Exploration of Inner Mongoli Chifeng 《《地质学报》英文版》2004,78(1):237-245
The Louzidian metamorphic core complex (LMCC) in southern Chifeng is located on the northern margin of the North China craton. Structural analyses of the LMCC and its extensional detachment system indicate that the LMCC experienced two-stage extension. The ductile regime experienced top-to-northeast shearing extension and the brittle detachment fault underwent top-down-outwards slipping. Between these two stages, a semi-ductile regime recorded the transition from ductile to brittle. The hanging wall of the detachment fault is similar to those classic supradetachment basins in western North America. Analyses of provenance and paleocurrent directions in the basins show that there were two filling stages. In the early stage, materials came from the southwest margin of the basin and the hanging wall of the detachment system and were transported from southwest to northeast; while in the late stage, deposits were derived from the footwall of the detachment fault and transported outwards to the two sides of the 相似文献