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991.
从理论N体模拟、射电辐射、红外辐射以及统计比较等几个方面,概述了棒在星系恒星形成中的作用,并讨论了在这一问题研究中出现的互相予盾的一些结果。 相似文献
992.
993.
对北大西洋由低纬度到高纬度的深海钻探和大洋钻探计划 664、 659、 60 8、 60 9、 61 0共5个站位中的上新世以来钙质超微化石组合演变历史进行了研究。该化石组合的主要分子为Reticulofenestra和 Gephyrocapsa属的一些种类 ,以及 Pseudoemiliania lacunosa和 Emiliania hux-leyi两种。通过对该化石组合的定量分析 ,识别出该化石组合自上新世至全新世的 8个演化阶段。每一阶段的超微化石组合都具有独自的特征优势分子以及相应的地理差异。老优势种不断被新兴的优势种所取代 ,上新世的 Reticulofenestra被第四纪的 Gephyrocapsa所替换 ,Emilianiahuxleyi是现代海洋超微浮游生物的优势种。第四纪超微化石组合演化的特点还在于 ,其优势种由 P.lacunosa与 Gephyrocapsa属中一些种的频繁交替取代 ,并显示出比上新世化石组合明显加快的演化速度。根据这些变化可推知该组合的演变过程 :在上新世期间 ,由中新世延续来的分子 (如 Reticulofenestra,Discoaster和 Sphenolithus属 )的逐渐衰退和上新世新生分子 (如 P.lacunosa种和 Gephyrocapsa属 )的逐渐兴起 ,以及第四纪 Gephyrocapsa属内的迅速演化。这些演化过程导致了该化石组合的主要成分随时间迁移而不断更新。由组合中不同优势种及常见分子生态习性的不同而 相似文献
994.
Shiliang Su Dan Li Xiang Yu Zhonghao Zhang Qi Zhang Rui Xiao Junjun Zhi Jiaping Wu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(6):737-746
Given the important role of land ecosystem in social-economic progress at regional, national, and international scale and
concurrent degradation of land ecosystems under rapid urbanization, a systematic diagnosis of land ecological security (eco-security)
for sustainable development is needed. A catastrophe model for land ecological security assessment was developed in order
to overcome the disadvantages in subjectivity and complexity of the currently used assessment methods. The catastrophe assessment
index system was divided into hierarchical sub-systems under the pressure-state-response framework. The catastrophe model
integrated multiple assessment indices of land eco-security according to the inherent contradictions and relative importance
of indices without calculating weights. Specifically, membership degree of higher level index was calculated based on the
membership degrees of lower level indices that were subjective to suitable model, such as cusp, fold, swallowtail and butterfly
model. This model was applied to evaluate the state of land eco-security in Shanghai. Mann–Kendall’s test was utilized to
characterize its temporal trend between 1999 and 2008. Significant downward trend was identified for land eco-security, in
terms of pressure sub-index, state sub-index, response sub-index and synthetic index. All these implied that land ecosystem
conditions were not optimistic for Shanghai and such situation should draw the attention of policy makers. The calculation
procedure presented in this paper does not require a high level of technical expertise to determine the membership degree,
making it simple and operational. Being applicable to similar land ecosystems, the catastrophe model is thus believed to provide
an alternative approach to land eco-security assessment. 相似文献
995.
商州蛇绿岩带与晋宁运动 总被引:1,自引:0,他引:1
商州蛇绿岩带具有完善的蛇绿岩套岩石组合;细碧岩与堆晶岩系渡型洋中脊玄武岩地球化化学特征。 相似文献
996.
Coalbed methane reservoir pressure is an important parameter used to assess the producibility of coalbed methane wells. Practices indicate that high production of coalbed methane well is partly related closely to abnormally high pressure. Permo-Carboniferous coalbed methane resources are very abundant in the Liulin–Wupu District, Eastern Ordos Basin, which has been the highlight of coalbed methane exploration in China in recent years. In this district, the abnormally high pressure is present locally in the Pennsylvanian No. 8 coalbed methane reservoir (the Taiyuan Formation). Based on the distribution of the abnormally high pressure, burial history, hydrocarbon generation, hydrodynamics, and sealing regimes, the authors suggest that the abnormal coalbed methane reservoir pressure is related closely to local hydrodynamic trapping. The gas generated during the qualification is preserved, owing to the confinement of lower permeable roof and floor rock layers, and water trapping in the updip direction (like the “fairway” in San Juan Basin). As a result of pressure reconstruction event, the abnormally high pressure is formed during the uplifting stage. The current coalbed methane wells with high production are always located in abnormally high pressure areas. Therefore, the areas with abnormally high pressure in Liulin–Wupu District can be the preferred areas for commercial coalbed methane development. 相似文献
997.
998.
By considering an area affected by a Ms 7.1 earthquake in Yushu Tibetan Autonomous Prefecture, Qinghai Province, in 2010 as an example, this paper analyzed the public response level after an earthquake disaster and discussed the principal factors influencing public response behaviors using a questionnaire survey. The results showed that the local public’s response level is low in the studied area. The average response scoring rate is only 0.50. Gender, family income, experience and religion are the most significant factors influencing the public response level. Females or individuals with low family income and little education tend to have lower response capability and are more vulnerable during an earthquake disaster. Furthermore, on the whole, participants who had experience coping with unexpected safety events appear to adopt more reasonable response behavior during an earthquake disaster. The relatively undeveloped economy and low education level are the basic limiting factors for improving the public response capability in the studied area. Certain policies and suggestions to improve the response capability and disaster reduction were discussed. 相似文献
999.
Crustal seismic anisotropy in Yunnan, Southwestern China 总被引:5,自引:0,他引:5
Using seismic data recorded by Yunnan Telemetry Seismic Network from January 1, 2000, to May 31, 2005, the polarization directions
of fast shear waves are obtained at 15 seismic stations by SAM technique, which is a systematic analysis method on shear-wave
splitting. The results show that predominant directions of polarizations of fast shear waves at most stations are mainly nearly
in the N–S or NNW directions in Yunnan. The predominant polarization directions of fast shear waves at stations located on
the active faults are consistent with the strike of active faults, directions of regional principal compressive strains from
GPS measurement, and directions of regional principal compressive stress. A few of the stations show that polarization patterns
of fast shear waves are more complicated or inconsistent with the strike of active faults and the directions of principal
GPS compressive strains; these stations are always located at the junction of several faults. We conclude that the predominant
polarization direction of fast shear waves indicates that the direction of the in situ maximum principal compressive stress
is controlled by multiple tectonic aspects, such as the regional stress field and faults. 相似文献
1000.
Using a two-dimensional semi-geostrophic model. the stability of fronts near shelf break (shelfbreak font, western boundary current front) and its mechanism are studied. We find that the stability of the front is related to the frontal structure. In general, the increase of the lower layer depth lowers the unstable growth rate (a1). (1) The shelfbreak front is baroclinically unstable and ai increases with the increase of the bottom slope, different from the conclusion of Flagg and Beardsley (1978). (2) A western boundary current front with uniform vorticity in the upper layer is barotropically unstable, due to the strong horizontal shear of the mean current. The unstable growth rate of this front for a realistic topography is only one seventh of that of the flat bottom case. (3) For a western boundary current front with hyperbolic tangent structure, we find its wave propagation speed to be about 0. 5 m/s, in agreement with the observed values. The front is baroclinically unstable. (4)The unstable growth 相似文献