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931.
We studied high-grade metamorphic rocks of the El Cristo hill area of the Tandilia belt. Mineral analyses and thermodynamic calculations were carried out for two adjacent rock samples: an amphibole–biotite gneiss and a garnet–biotite-bearing migmatite. Peritectic garnets in the migmatite show core compositions of pyr4.5(gro + andr)10spes6alm79.5 changing to pyr3.5(gro + andr)17spes6alm73.5 at their thin rims. Garnet compositions in the gneiss are pyr6.5(gro + andr)26spes12alm55.5 and pyr4.5(gro + andr)34spes12alm49.5 for core and rim, respectively. A P–T path was constructed by calculating pseudosections in the 11-component system Si–Ti–Al–Fe–Mn–Mg–Ca–Na–K–O–H and contouring them by isopleths for garnet components using the PERPLE_X software package. Supra-solidus crystallization of garnet cores in the migmatite began at 5.8 kbar and 660 °C. Garnet rims equilibrated at 7.0 kbar and 640 °C compatible with garnet cores in the amphibole–biotite gneiss (7.6 kbar and 660 °C). The further chemical development of garnet in this rock points to P–T conditions of 11.6 kbar and 620 °C and 12.2 kbar and 595 °C (outermost garnet rim). At this high-pressure stage Ca-amphibole was not stable. Most biotite formed during exhumation whereas the high-pressure accessory minerals, titanite and epidote, persisted. According to the obtained anti-clockwise P–T path the originally partly melted material was tectonically transported from ∼22 km (middle crust) to ∼40 km (lower crust) depths reaching a geothermal gradient as low as 15 °C km−1. This transport probably occurred along a major suture zone, which was active during the Paleoproterozoic (2.25–2.10 Ga), before a terminating collision of terranes near the SW boundary of the Rio de la Plata craton. 相似文献
932.
利用北京延庆站风廓线雷达水平风廓线资料进行大气温度平流的反演,详细分析2014年11月15日夜间冷空气入侵过程,并统计分析2015年9—11月6次冷空气入侵过程,同T639L60模式的预报风场及温度平流预报产品进行对比。结果表明:在一定预报时效内 (约6~12 h),风廓线雷达获取的水平风廓线与模式给出的预报风场有较好的一致性;由风廓线雷达反演的温度平流与模式给出的温度平流量级相同,温度平流属性一致;风廓线雷达6 min完成1次垂直高度分辨率为120 m的探测,高时空分辨率使风廓线雷达获取的温度平流较T639L60模式更能反映大气温度平流的细节。 相似文献
933.
2016年6—8月T639、ECMWF及日本模式中期预报性能检验 总被引:1,自引:1,他引:0
对2016年6—8月T639、ECMWF及日本(文中简称JP)数值模式的中期预报产品进行了分析和检验。结果表明:3个模式对亚洲中高纬环流形势的调整和演变均具有较好的预报性能,其中ECMWF模式预报效果最好。对于副热带高压,ECMWF和T639模式均能较好地预报副热带高压移动趋势,但具体过程存在不同偏差,ECMWF模式偏差较小;3个模式中期时效均能报出四川盆地的持续高温过程,且对北方850 hPa温度的转折性变化趋势均有较好的预报能力,ECMWF和JP模式对南方地区温度变化的预报能力明显优于北方地区,T639模式对南方温度预报偏差较大,ECMWF模式综合预报效果最好。对台风妮妲,ECMWF模式预报与零场较为接近,T639模式误差较大。 相似文献
934.
Grote Reber 《Astrophysics and Space Science》1995,224(1-2):93-96
The study of star forming regions (SFR) allows us to observe many young stellar objects with both the same metallicities and distances but with different masses. Because of its close distance ( 140pc) Taurus-Auriga is one of the best studied SFR with more than 100 well-studied, low-mass, pre-main sequence stars, T Tauri stars (TTS). A motivation for studying X-ray emission of T associations is to understand the origin of X-rays and coronal activity. The large sample observed with the ROSAT All-Sky Survey (RASS) also enables us to compare different types of young stars. Other primary goals include star formation efficiency and the interaction of young stars with their intermediate environment (probed by absorption of X-rays). RASS detection rates are comparable withEinstein Observatory results: 43 out of 65 (66%) weak-lined TTS (WTTS) and 9 out of 79 (11%) classical TTS (CTTS) exhibit X-ray emission above RASS detection limit. A strong correlation between X-ray surface flux and stellar rotation indicates that WTTS are intrinsically more X-ray active than CTTS, because WTTS rotate faster. However, rotation is not the only parameter that determines X-ray activity. Also, we compare Taurus-Auriga TTS with TTS of southern SFR like ScoCen, Lupus, Chamaeleon, and CrA. A new result is that CTTS and WTTS can be discriminated reliably by their X-ray spectral hardness ratios. X-ray emission of CTTS appears to be harder, partly because of circumstellar absorption. Spectral fits give results consistent with Raymond-Smith spectra and emission temperatures of 1.0 keV for both WTTS and CTTS. However, we find that CTTS and WTTS have significantly different X-ray luminosity functions. Medians of absorption corrected X-ray luminosities (logL
X
in cgs units) are 29.701 ± 0.045 for WTTS and 29.091 ± 0.032 for CTTS. WTTS are intrinsically more luminous than CTTS, most likely because WTTS rotate on average faster than CTTS and are less absorbed. This paper concentrates on differences between CTTS and WTTS and indirect clues to be drawn from X-ray absorption and hardness ratios about circumstellar material around TTS. 相似文献
935.
936.
李杰 《CT理论与应用研究》1998,7(2):20-21
目的:对T2加权低信号产生机理及临床诊断价值进行探讨。方法:应用philips 1.0T磁共振成像仪,采用TR1800-2000ms/TE80-150ms获取T2加权像。结果:30例急性出血;60例慢性出血;2例黑色素瘤;10例肝硬化结节;视网膜母细胞瘤5例,其它15例,结论:T2加权低信号对疾病的诊断及鉴别诊断具有重要意义。 相似文献
937.
938.
939.
Rädler K.-H. Apstein E. Rheinhardt M. Schüler M. 《Studia Geophysica et Geodaetica》1998,42(3):224-231
At the Forschungszentrum Karlsruhe an experiment is in preparation which it is hoped, in view of the geodynamo and other cosmic dynamos, that a homogeneous dynamo will be demonstrated and investigated. This experiment is discussed within the framework of mean-field dynamo theory. Results are presented concerning kinematic cylindrical mean-field dynamo models reflecting some features of the experimental device, as well as results of detailed calculations of the -effect that apply to arbitrarily high magnetic Reynolds numbers. On this basis estimates of the excitation conditions of the dynamo are given and predictions concerning the geometrical structure of the generated magnetic fields are made. 相似文献
940.