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991.
992.
Stefan?R?sel Anna?Rych?a Christian?Wurzbacher Hans-Peter?GrossartEmail author 《Aquatic Sciences - Research Across Boundaries》2012,74(1):87-99
Nutrient fluxes across terrestrial-aquatic boundaries and their subsequent integration into lake nutrient cycles are currently
a major topic of aquatic research. Although pollen represents a good substrate for microorganisms, it has been neglected as
a terrestrial source of organic matter in lakes. In laboratory experiments, we incubated pollen grains of Pinus sylvestris in water of lakes with different trophy and pH to estimate effects of pollen input and its subsequent microbial degradation
on nutrient dynamics. In this ex situ experiment, we measured concentrations of organic carbon, phosphorus and nitrogen in the surrounding water as well as microbial
dynamics (bacteria and fungal sporangia) at well-controlled conditions. Besides leaching, chemical and microbial decomposition
of pollen was strongest within the first week of incubation. This led to a marked increase of soluble reactive phosphorus
and total dissolved nitrogen (up to 0.04 and 1.5 mg L−1, respectively, after 5 days of incubation) in the ambient water. In parallel, pollen grains were rapidly colonized by heterotrophic
bacteria and aquatic fungi. Leaching and microbial degradation of pollen accounted for ≥80, ≥40, ≥50% for organic C, N and
P, respectively, and did not significantly differ among water samples from the studied lakes. Thus, pollen introduces high
amounts of bio-available terrestrial organic matter and nutrients into surface waters within a short time. A rough calculation
on P input into oligotrophic Lake Stechlin indicates that pollen plays an important ecological role in nutrient cycling of
temperate lakes. This requires further attention in aquatic ecology. 相似文献
993.
Alexandre A. Costa António Arêde Aníbal Costa Jo?o Guedes Bruno Silva 《Bulletin of Earthquake Engineering》2012,10(1):135-159
Stone masonry is one of the oldest building techniques used worldwide and it is known to exhibit poor behaviour under seismic
excitations. In this context, this work aims at assessing the in-plane behaviour of an existing double-leaf stone masonry
pier by experimental testing. Additionally, a detailed 3D finite element numerical analysis based on micro-modelling of the
original pier is presented (fully describing the geometry and division of each individual elements, namely infill, blocks
and joints) aiming at simulating the experimental test results. This numerical strategy can be seen as an alternative way
of analysing this type of constructions, particularly useful for laboratory studies, and suitable for the calibration of simplified
numerical models. As part of a wider research activity, this work is further complemented with the presentation of an effective
retrofit/strengthening technique (reinforced connected plaster) to achieve a significant improvement of its in-plane cyclic
response which is experimentally verified in the results presented herein. 相似文献
994.
本文对2011年1月至2014年4月间全球发生的80次MS≥7.0级地震前,二张营台和天堂河台Sacks体应变临震异常现象进行了研究,针对复杂震例提出了异常识别的前提条件。统计结果显示,体应变观测对震中距为8000km范围内的MS≥7.0级地震映震和前兆异常反映较好。同时,对异常现象进行了分类和描述,划分了三种异常类型:即固体潮畸变型、突变型和慢地震型,并对各种类型作了统计分析,进行了力学性质初步探讨。从研究结果来看,体应变异常信息对未来全球强震的发生具有一定的预示意义。 相似文献
995.
巨灾保险机制研究——新西兰、土耳其、美国加州、中国台湾、日本案例分析 总被引:1,自引:0,他引:1
分析总结了新西兰、土耳其、美国加州、中国台湾地区和日本等国家和地区地震保险制度的特点,依据分析提出:中国需要建立巨灾保险制度,政府要在其中承担主导性职责,同时,巨灾保险需要民营保险公司和政府的分工合作。 相似文献
996.
Wan Bo Wu Fuyuan Chen Ling Zhao Liang Liang Xiaofeng Xiao Wenjiao Zhu Rixiang 《中国科学:地球科学(英文版)》2019,62(12):2005-2016
Numerous continents have rifted and drifted away from Gondwana to repeatedly open ocean basins over the past-500 millionyears.These Gondwana-derived continents drifted towards and collided with components of the Eurasian continent to successively close the preexisting oceans between the two.Plate tectonics satisfactorily describes the continental drift from Gondwana to Eurasia but does not define the geodynamic mechanism of continuously rifting to collisions of continents in the Tethy an Realm.After reappraisal of geological records of the rift,collision and subduction initiation from the surface and various geophysical observations from depth,we propose that Eurasia-directed subducting oceanic slabs would have driven Tethyan system in the Phanerozoic.The Eurasia-directed subduction would have dragged the passive Gondwana margin to rift and drift northwards,giving birth to new oceans since the Paleozoic.The closure of preexisting oceans between the Gondwana-derived continents and Eurasia led to continental collisions,which would have induced the initiation of oceanic subduction in the Tethyan Realm.Multiple episodic switches between collision-subduction-rift repeatedly led to the separation of continental fragments from Gondwana and dragged them to drift towards Eurasia.The final disappearance of Neo-Tethy s would have induced collision of the Gondwana-derived continents with the Eurasian continent,giving rise to the Cenozoic Alpine-Zagros-Himalayan collisional system.Therefore,the Eurasia-directed oceanic subduction would have acted as a 'one-way train' that successively transferred the ruptured Gondwana continental fragments in the south,into the terminal in the north.In this regard,the engine of this "Tethyan one-way train" is the negative buoyancy of subducting oceanic slabs. 相似文献
997.
Rotation motion and its effects on strong-motion data, in most cases, are much smaller than that of translational motion and have been ignored in most analyses of strong-motion data. However, recent observations from near-fault and/or extreme large ground motions suggest that these effects might be underestimated and quantitative analyses seem to be necessary for improving our understating of these effects. Rotation motion-related effects include centrifugal acceleration, the effects of gravity and effects of the rotation frame. Detailed analyses of these effects based on the observed data are unavailable in the literature. In this study, we develop a numerical algorithm for estimating the effects of rotational motion on the strong-motion data using a set of six-component ground motions and apply it to a set of rotation rate-strong motion velocity data. The data were recorded during a magnitude 6.9 earthquake. The peak value of the derived acceleration and rotation rate of this dataset are about 186 cm/s/s and 0.0026 rad/s. Numerical analyses of data gives time histories of these rotational motion-related effects. Our results show that all the rotation angles are less than 0.01°. The maximum centrifugal acceleration, effect from gravity and effect of the rotation frame are about 0.03 and 0.14 cm/s/s, respectively. Both these two effects are much smaller than the peak acceleration 186 cm/s/s. This result might have been expected because our data are not near-field and wave motions are expected to be nearly plane waves. However, it is worth noticing that the centrifugal acceleration is underestimated and a small rotational effect can cause large waveform difference in acceleration data. The waveform difference before and after the correction for rotational motion can reach 16 cm/s/s (about 10 %). 相似文献
998.
999.
Jacek?StankiewiczEmail author Michael?H.?Weber Ayman?Mohsen Rami?Hofstetter 《Pure and Applied Geophysics》2012,169(4):615-623
In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region
of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007
to be used for ambient seismic noise analysis. Empirical Green’s functions are extracted from cross-correlations of long term
recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range
from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green’s functions makes it possible to identify
the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean
Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured
between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four
such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving
an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead
Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure
of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of
the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth
of ~5 km. The reliability of the results is confirmed by checkerboard recovery tests. 相似文献
1000.
Aquatic dance flies (Empididae; Clinocerinae and Hemerodromiinae) are important components of freshwater assemblages, especially in running waters. They are predators as larvae and adults and thus essential for understanding aquatic food webs. This study was conducted in Plitvice lakes National Park (Croatia) representing a wide variety of freshwater habitats (springs, streams, lakes and tufa barriers). Adults were collected monthly from March 2007 until March 2009 using pyramid-type emergence traps at 13 locations. A total of 3865 specimens comprising 18 species were collected. The dominant genus was Chelifera, while the most abundant species was Hemerodromia unilineata. All species were univoltine except Chelifera precabunda, Chelifera pyrenaica and Chelifera stigmatica that were bivoltine. Considerable differences in composition and structure of aquatic dance flies assemblages were recorded along a longitudinal gradient of studied sites, primarily related to differences in physical and chemical parameters of water. Water temperature was the main factor influencing the timing of emergence. Hemerodromia species preferred variable water temperature throughout the year while the majority of the Chelifera species preferred stable water temperature characteristic of spring sites. Furthermore, discharge affected assemblage composition of aquatic dance flies. The highest abundance of aquatic dance flies was recorded in lotic habitats with fast water current over substrates of moss, gravel and particulate tufa with detritus. These results give a new insight on microhabitat preference and their distribution on unique karstic habitats. 相似文献