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991.
Rajendra Singh P. K. Mandal A. K. Singh R. Kumar A. Sinha 《Rock Mechanics and Rock Engineering》2008,41(3):421-444
Summary Considering ground instability problems of underground coal mines at shallow covers, this paper reviews and describes problems
of optimal extraction of coal stuck below surface/subsurface constraints at Indian coal fields. Importance of thickness and
quality of inter-burden between the working horizon and surface/subsurface constraints is discussed from a ground movement
point of view during optimisation of coal recovery by underground mining beneath the constraints. A CIMFR, formerly CMRI idea,
known as Wide Stall Method, was found suitable to overcome the limitations of non-effective-width based optimisation of recovery
of coal, trapped in pillars below surface/subsurface objects, at shallow cover. The involved rock mechanics concept and three
successful field trials of the Wide Stall Method under three different geo-mining conditions of the country are also briefly
given in this paper.
Author’s address: Rajendra Singh, Central Institute of Mining and Fuel Research (CIMFR, formerly CMRI), Barwa Road, Dhanbad,
826001 Jharkhand, India 相似文献
992.
Cut Slopes in Clayey Soils: Consolidation and Overall Stability by Finite Element Method 总被引:1,自引:1,他引:0
José Leitão Borges 《Geotechnical and Geological Engineering》2008,26(5):479-491
When a cut slope in a saturated clay is undertaken, a transient water flow occurs and stress transferences from the water
to the soil skeleton take place in time (consolidation). Mainly in strongly overconsolidated clays, these stress transferences
may determine swelling of soil and therefore reduction of its shear strength in time. However, the lowering of the water level
associated to the cut increases effective mean stress, which may therefore counterbalance the above-mentioned effect. In the
paper, the behaviour of a cut slope in an overconsolidated clay is analysed by a finite element program that incorporates
the Biot consolidation theory (coupled analysis), with constitutive relations simulated by the p–q–θ critical state model. In addition, the variation in time of the overall stability is assessed with a computer program that
uses the finite element results and formulations of the critical state soil mechanics. In order to achieve a more complex
geotechnical interpretation of the problem, the analysis in time of the excess pore pressures, effective stresses, displacements
and stress levels is also presented. Finally, comparisons of stability results are analysed by changing some parameters, namely
the problem geometry (weight of excavated soil) and the over-consolidation ratio of the clay. 相似文献
993.
994.
Trophic states and nutrient storage of reservoirs in Chongqing 总被引:1,自引:0,他引:1
The trophic states of 35 reservoirs were investigated in the region of Chongqing, Southwest China. The results showed that the concentrations of nutrients and chlorophyll a were high and organic pollution and transparence (SD) were low in the water body. The concentrations of total nitrogen (TN) range from 0.52 mg/L to 5.94 mg/L and those of total phosphorus (TP) range from 0.002 mg/L to 0.598 mg/L. Chemical oxygen demand (COD) ranges from 0.75 mg/L to 9.3 mg/L and SD ranges from 0.48 m to 3.2 m. There was a significant positive correlation between COD and chlorophyll a, but a significant negative correlation between SD and chlorophyll a. In terms of the integrated nutrition state index, the eutrophication states of the reservoirs were assessed. Of the investigated reservoirs, about 22 reached the grade of eutrophication. Only one reservoir was in the state of oligotropher, the rest were in the state of mestropher. Integrated nutrition state indices range from 25.4 to 74.5. The storage capacity of nutrients in the reservoirs was calculated. The stored TN, TP and COD were about 4731, 206 and 10259 t, respectively. The main pollution sources are industrial and domestic wastes. With the development of aquaculture, the contamination level increases gradually. 相似文献
995.
The paper pertains to the study of steady state or residual strength of sandy soils (Yamuna sand lying in the Indo-Gangetic
alluvial plains) by consolidated rebounded drained triaxial test with volume change measurements and strain-controlled consolidated
undrained test as well. The observed behavior obtained from these two tests is then compared to check their comparative merit.
The same was also compared with those of Ganga and Toyoura sand, and with the predicted behavior obtained by using a semi
empirical model. The results obtained from rebounded drained and undrained tests are found to be in good agreement. The curvature
of ultimate steady state line of Yamuna sand is similar in trend to Ganga and Toyoura sand in the initial mean effective principle
stress range; but the experimental observations with reference to Yamuna sand is not in good agreement with the model predictions
in the region of higher mean normal stress. A semi empirical general model has been developed fitting the data for better
prediction of the steady state behavior. 相似文献
996.
997.
基于传递系数法的滑坡滑带土强度参数反分析研究 总被引:4,自引:0,他引:4
基于对滑坡强度参数反分析基本原理的分析,利用工程实践应用最为广泛的传递系数法建立了滑坡反分析计算模型,进而得出反分析理论基础,从数学意义上揭示了滑坡反分析本质为求解由滑坡状态条件确定了的系数项和常数项的二元多次方程。通过滑坡反分析状态分析,根据滑坡变形特征确定了稳定性评估指标。利用至少两个反分析剖面,采用试算法和插值法求解了一系列当Fsi′=Fs时的c、φ组合,然后用图解法求解滑坡滑带土强度参数。该方法在某滑坡中得到成功的应用,其计算精度基本满足工程要求,为反分析在滑坡稳定性分析及预测中的应用进行了有益的探讨。 相似文献
998.
Evolution of the composition of seawater through geologic time, and its influence on the evolution of life 总被引:2,自引:2,他引:0
Tsuyoshi Komiya Takafumi Hirata Kouki Kitajima Shinji Yamamoto Takazo Shibuya Yusuke Sawaki Tomoko Ishikawa Degan Shu Yong Li Jian Han 《Gondwana Research》2008,14(1-2):159
The redox state of the surface environment of the early Earth is still controversial, and a detailed and quantitative estimate is still lacking. We carried out in-situ analyses of major, trace, and rare-earth elements of carbonate minerals in rocks with primary sedimentary structures in shallow and deep sea-deposits, in order to eliminate secondary carbonate and contamination of detrital materials, and to estimate the redox condition of seawater through time. Based on the Ce content and anomalies of the carbonate minerals at given parameters of atmospheric CO2 content (pCO2) and Ca content of seawater, we calculated the oxygen contents of shallow and deep seawater, respectively. The results show that the oxygen content of the deep sea was low and constant until at least 1.9 Ga. The oxygen content of shallow seawater increased after 2.7 Ga, but fluctuated. It became quite high at 2.5 and 2.3 Ga, but eventually increased after the Phanerozoic. In addition, the calculation of a high pCO2 condition shows that seawater was more oxic even in the Archean than at present, suggesting a relatively low pCO2 through geologic time.Our detailed calculations from compositions of carbonate minerals in Three Gorge area, south China show a low oxygen content of seawater after the Snowball Earth until the late Ediacaran, an increase in the late Ediacaran, and a significant decrease around the Precambrian–Cambrian and Nemakit/Daldynian–Tommotian boundaries. These variations were possibly caused by global regression and dissolution of methane hydrates. 相似文献
999.
Frank J. Millero Abzar Mirzaliyev Javid Safarov Fen Huang Mareva Chanson Astan Shahverdiyev Egon Hassel 《Aquatic Geochemistry》2008,14(4):289-299
The density ρ of Caspian Sea waters was measured as a function of temperature (273.15–343.15) K at conductivity salinities
of 7.8 and 11.3 using the Anton-Paar Densitometer. Measurements were also made on one of the samples (S = 11.38) diluted with water as a function of temperature (T = 273.15–338.15 K) and salinity (2.5–11.3). These latter results have been used to develop an equation of state for the Caspian
Sea (σ = ±0.007 kg m−3)
where ρ0 is the density of water and the parameters A, B and C are given by
Measurements of the density of artificial Caspian Sea water at 298.15 K agree to ± 0.012 kg m−3 with the real samples. These results indicate that the composition of Caspian Sea waters must be close to earlier measurements
of the major components. Model calculations based on this composition yield densities that agree with the measured values
to ± 0.012 kg m−3. The new density measurements are higher than earlier measurements. This may be related to a higher concentration of dissolved
organic carbon found in the present samples (500 μM) which is much higher than the values in ocean waters (~65 μM). 相似文献
1000.
介绍了实际工作中经常遇到的地形图时空数据建库方法:保持现状式和数据追加式。分析对比了两种方法的优缺点:保持现状式实时维护了时空数据的现势性,方便现状数据的使用,但其数据库和表个数多,数据维护、历史数据恢复以及增量数据计算较复杂。数据追加式数据库个数少,数据维护、历史数据恢复以及增量数据计算较简单,但在使用现状数据时需做一定的数据查询、输出操作。作者建议使用后者,并将其中一个工作库固定为现状库,历史数据恢复时再建其他工作库以方便使用。 相似文献