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121.
关于生命起源研究的问题及其主攻方向的探讨 总被引:1,自引:0,他引:1
本文综述和分析了近几十年来国内外关于生命起源的研究的问题及各种假说和见解,提出物质的起源是生命起源问题研究的核心,生命起源问题应是研究原始地球的非生命物质如何演变成为生命物质的,地球上分子手性的起源是生命起源问题研究的主攻方向,有机分子光学活性百发生在由化学进化转入生物进化这一过渡阶段。 相似文献
122.
E. O. Frind E. A. Sudicky S. L. Schellenberg 《Stochastic Environmental Research and Risk Assessment (SERRA)》1987,1(4):263-279
The migration of contaminants in heterogeneous aquifers involves dispersive processes that act at different scales. The interaction of these processes as a plume evolves can be studied by micro-scale modelling whereby two scales, a local- or micro-scale and an aquifer- or macro-scale, are covered simultaneously. Local-scale dispersive processes are represented through the local dispersion coefficient in the transport equation, while large-scale dispersion due to heterogeneities is represented through the resolution of the flow field and the diffusive exchange between streamtubes. The micro-scale model provides both the high degree of resolution compatible with local-scale processes, and the extent required for the approach to asymptotic conditions, using grids of up to a million nodal points. The model is based on the dual potential-streamfunction formulation for flow, and the transport problem is formulated in a natural coordinate system provided by the flownet. Simulations can be used to verify stochastic theories of dispersion, without the restrictive assumptions inherent in the theory. For the two-dimensional case, results indicate convergence of the effective dispersivity to the theoretical macrodispersivity value. Convergence takes place within a travel distance of about 50 correlation lengths of the hydraulic conductivity field. However, the approach taken to asymptotic conditions, as well as the macrodispersivity value, may differ for different realizations of the same medium. The influence of early-time events such as plume splitting on the asymptotic convergence remains to be investigated. 相似文献
123.
论浙江火山岩区金银矿床的成矿物质来源 总被引:2,自引:0,他引:2
稳定同位素和地质特征的研究,结果表明浙江火山岩区金银矿床的成矿物质系多元来源。金属和挥发性组分来源于岩石圈深部(下地壳或上地幔)和上地壳,成矿流体是大量大气水和少量岩浆水的混合溶液.金银矿化与板块运动及地热流体对流体系有关. 相似文献
124.
苏北箕状断陷形成的动力学机制 总被引:34,自引:1,他引:33
苏北盆地由多个小型箕状盆地组成,过去一直用“拉线作用”和“裂谷盆地”理论解释其成因,但大量地震资料显示,新生界地层“楔状实体”的形成除沉积因素外,更主要的是因为多次不均衡抬升削蚀所造成,实际是一个早第三纪残留盆地。新生代构造现象既是中生代时期构造作用的延续,也是始新世以来复杂应力环境作用的结果。印支-燕山中期,中国东部只受到太平洋-库拉板块一种力源作用,地层形变强烈,受力方向单一,以NW,NWW向挤压或左行剪切为主,发育了大量逆冲推覆构造,始新世,由印度板块向欧亚大陆冲撞引发的NE向挤压力加入到本区,使苏北盆地从此处在因两大板块非均速推进而产生的二元交变动力环境:印度板块力源占主导时,产生“右旋扭动”力偶,使燕山早-中期逆断层复活反转的同时,由于中国西部大陆的不断抬升,本区总的以沉积作用为主,而太洋板块力源占主导时又产生“左行剪切挤压”,在整体抬升基础上,斜坡-凸起处的过多蚀进一步加强了箕状盆地结构。两种力源的时空交替实际形成了一个完整的“断-坳-隆”沉降-抬升构造旋回,利用裂变途径迹资料探讨了不同方向构的形成年代。 相似文献
125.
新型随机地震动模型 总被引:2,自引:0,他引:2
在研究结构的随机地震反应时,要用大量的符合场地条件的地震记录作为输入数据。但强震历史记录却不是每个地区都有的,因此根据符合场地条件的现有地震记录建立随机地震动模型具有重要意义。本文利用中国抗震规范2001版修正选取的样本波作为目标波,考虑了幅值和频率的双重非平稳性,建立了新型随机地震动模型——改进的时变ARMA模型随机地震动模型。通过使用残差的卡方检验法,对多种非平稳ARMA模型生成的模拟波进行检验;同时又比较丁模拟波与目标波的功率谱密度图和反应谱图。结果证明:此法能够更精确地反映不同场地条件地震动的频谱和幅值的真实内容,从而建立符合目标场地条件的更为有效的模拟地震动,为相关研究与工程设计架起一座桥梁。 相似文献
126.
阿尔金北缘大平沟金矿床成因 总被引:4,自引:1,他引:4
大平沟金矿是阿尔金北缘地区近年来新发现的一个中型金矿床。它受韧性剪切带构造的控制,矿化类型为蚀变糜棱岩型夹少量钾长石石英脉型。文章通过地质地球化学的研究,探讨了该矿床的成因。稀土元素、硫同位素、铅同位素和锶同位素地球化学特征反映成矿物质主要来源于变质岩;流体包裹体和氢氧同位素反映成矿流体主要来源于变质水,有少量重熔岩浆水和大气降水的混入,成矿温度198~2 90℃,成矿流体密度0 .791~0 .971g/cm3 ;盐度w(NaCleq) =2 .0 3%~5 .5 % ,成矿压力(42 0~72 0 )×10 5Pa ,成矿深度为1.6 1~2 .6 8km。石英流体包裹体Rb_Sr等时线年龄表明成矿时代为加里东期。大平沟金矿床属于中温动力变质热液成因矿床。 相似文献
127.
128.
以湖南宏厦桥花岗岩体作为研究区,对地下水化学分析资料进行了研究,发现区内地下水系超淡、极软的、弱-中性的重碳酸型水,其化学组成以Ca2 、Mg2 、K 、Na 、HCO3-为主。与株洲地区的地下水相比,可溶性S iO2、K 、Na 和游离CO2明显偏高,而且,在水中M g2 、K 、Na 、HCO3-所占比重更大,m eq%平均比值分别是株洲地区地下水的2.23、1.27、1.16倍,表现出典型的花岗岩地区地下水相应的化学组成。研究还发现,区内地下水化学的分布具有较强的水平分带性。研究认为:区内地下水化学的形成和迁移受岩性、大气降水及影响水交替强度的地形、地貌、地表水系、断裂构造的控制,同时受其他气候要素及植被、人类活动等生物作用的影响;区内地下水化学成分的形成以硅酸盐矿物的分解和水解等化学风化作用为主,风化过程中CO2的积极参与起作关键性的促进作用。同时水中CO2的减少和阴离子以HCO3-离子占绝对优势地位,进一步说明花岗岩的化学风化过程是一个净碳汇的过程。 相似文献
129.
Stochastic modelling of soil moisture dynamics in a grassland of Qilian Mountain at point scale 总被引:2,自引:0,他引:2
Stochastic modeling of soil moisture dynamics is crucial to the quantitative understanding of plant responses to water stresses,hydrological control of nutrient cycling processes,water competition among plants,and some other ecological dynamics,and thus has become a hotspot in ecohydrology at present.In this paper,we based on the continuously monitored data of soil moisture during 2002―2005 and daily precipitation date of 1992―2006,and tried to make a probabilistic analysis of soil moisture dynamics at point scale in a grassland of Qilian Mountain by integrating the stochastic model improved by Laio and the Monte Carlo method.The results show that the inter-annual variations for the soil moisture patterns at different depths are very significant,and that the coefficient of variance(CV) of surface soil moisture(20 cm) is almost continually kept at about 0.23 whether in the rich or poor rainy years.Interestingly,it has been found that the maximal CV of soil moisture has not always appeared at the surface layer.Comparison of the analytically derived soil moisture probability density function(PDF) with the statistical distribution of the observed soil moisture data suggests that the stochastic model can reasonably describe and predict the soil moisture dynamics of the grassland in Qilian Mountain at point scale.By extracting the statistical information of the historical precipitation data in 1994―2006,and inputting them into the stochastic model,we analytically derived the long-term soil moisture PDF without considering the inter-annual climate fluctuations,and then numerically derived the one when considering the inter-annual fluctuation effects in combination with a Monte-Carlo procedure.It was found that,though the peak position of the probability density distribution significantly moved towards drought when considering the disturbance forces,and its width was narrowed,accordingly its peak value was increased,no significant bimodality was observed in the soil moisture dynamics under the given intensity of random fluctuation disturbance. 相似文献
130.
We develop stochastic approaches to determine the potential for tsunami generation from earthquakes by combining two interrelated
time series, one for the earthquake events, and another for the tsunami events. Conditional probabilities for the occurrence
of tsunamis as a function of time are calculated by assuming that the inter-arrival times of the past events are lognormally
distributed and by taking into account the time of occurrence of the last event in the time series. An alternative approach
is based on the total probabilitiy theorem. Then, the probability for the tsunami occurrence equals the product of the ratio,
r (= tsunami generating earthquakes/total number of earthquakes) by the conditional probability for the occurrence of the next
earthquake in the zone. The probabilities obtained by the total probability theorem are bounded upwards by the ratio r and, therefore, they are not comparable with the conditional probabilities. The two methods were successfully tested in three
characteristic seismic zones of the Pacific Ocean: South America, Kuril-Kamchatka and Japan. For time intervals of about 20
years and over the probabilities exceed 0.50 in the three zones. It has been found that the results depend on the approach
applied. In fact, the conditional probabilities of tsunami occurrence in Japan are slightly higher than in the South America
region and in Kuril-Kamchatka they are clearly lower than in South America. Probabilities calculated by the total probability
theorem are systematically higher in South America than in Japan while in Kuril-Kamchatka they are significantly lower than
in Japan. The stochastic techniques tested in this paper are promising for the tsunami potential assessment in other tsunamigenic
regions of the world. 相似文献