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321.
采用方向交会法可以确定出点位的平面坐标。由于观测方向值、大地方位角、高斯平面坐标方位角所参考的基准面不同,在计算方位角时应考虑标高差改正、曲率改正等因素。通过试验数据,将采用方向交会法计算得出方位角与严密导线平差后的计算结果相比较,分析了一定条件下方向交会法计算方位角所能达到的实际精度水平。 相似文献
322.
323.
结合沪杭高速铁路,从满足投影长度小于10mm/km的要求出发,探讨了高速铁路控制网投影的选取方法,得出了一些有益的结论。 相似文献
324.
借助复变函数理论讨论了拉格朗日投影与常用等角投影间的解析变换问题,导出了拉格朗日投影正反解的复变函数表达式,在此基础上系统地建立了该投影与高斯投影、墨卡托投影和等角圆锥投影间解析变换的复变函数表示模型。这些复数变换公式是含参考椭球第一偏心率的符号形式,可解决不同参考椭球下的投影变换问题,与传统的实数变换公式相比,其结构更为简单,理论更为严密,便于实际使用。 相似文献
325.
326.
采用不同参数化方案对沪宁高速公路浓雾过程的模拟试验 总被引:1,自引:0,他引:1
以2006年12月24—27日沪宁高速公路及其周边地区出现的一次罕见持续性大雾为例,采用模式验证方法,研究了采用不同微物理过程和陆面过程参数化方案对浓雾模拟效果的影响。结果表明,对相对湿度等常规气象要素的模拟,各个参数化方案的模拟效果都较好,与实况都有很好的一致性。对直接表征能见度的变量———液态水含量的模拟,各个参数化方案中以微物理过程采用Lin方案,陆面过程采用SLAB方案模拟效果最好,其他方案的模拟效果与实况相比偏差较大。 相似文献
327.
Because glacial melting provides a significant amount of surface water resources, especially in cold arid regions, it is critical
that effective methods be developed for predicting their behavior. Glacier runoff differs from other types of stream flows,
being characterized by large diurnal fluctuations, with maximum discharge during the summer months. Moreover, the size and
remoteness of glaciers makes them difficult to study directly. Hence, developing effective modeling techniques is our best
hope for understanding and predicting glacial melting phenomena. In the past, physics-based models have been used with some
success. In this study, conducted in 2003 and 2004 on the Keqikaer Glacier on the south slope of Mt. Tuomuer, however, we
used the newer artificial neural networks (ANNs) modeling technique. As the input nerve cell, we used the hourly wind speed,
precipitation, air temperature, radiation balance, and ground temperature; the output nerve cell was the diurnal runoff at
the glacial terminus. We then analyzed the simulated results under different scenarios by varying the input-nerve-cell parameters.
It was found that ANN can simulate the process of glacier meltwater runoff successfully when basic parameters such as air
temperature, precipitation and radiation balance are few. The results indicate that ANN can simulate the process of glacial
meltwater runoff quite well, and that meteorological variables could in fact be used successfully to simulate glacier meltwater
runoff using the ANN method. 相似文献
328.
从合成孔径雷达干涉测量的原理出发,针对月基InSAR观测地球宏观物理现象的大尺度、连续性、长期性、动态观测等特点,首次以固体地球垂向潮汐形变为例对月基InSAR观测地球大尺度形变现象进行了仿真模拟,分析了该技术的远程大范围观测能力。根据固体地球垂向潮汐形变的大尺度分布特征和月基雷达的超大幅宽的观测特点,采用简化月基雷达观测几何模型,选定经纬跨度均为50°的中低纬区域为模拟测区,并计算了月基雷达重访周期与雷达波束扫过选定模拟测区内各点时的垂向潮汐形变,将形变计算结果进行时间差分,得到差分相对垂向潮汐形变,即是月基InSAR可观测到的垂向潮汐形变。模拟数值结果表明,月基雷达的重访周期约为24.8 h,在30天内各点的差分垂向潮汐形变可达30 cm。鉴于目前月基InSAR的理论形变观测精度达到厘米级,因此理论上用月基InSAR技术能够观测到模拟测区固体地球大范围垂向潮汐整体形变,也能利用观测数据研究地球潮汐大范围时间和空间变化特征;另一方面模拟结果也可为月基SAR观测其他地球宏观物理现象的参数设计与模拟提供参考。 相似文献
329.
Soil hydraulic functions can be obtained with methods that range from complex and costly to simple and cheap. Decisions as to which is the most appropriate method for a specific application have to be based on a comparison of generated hydraulic functions. This comparison should preferably be based on a statistical comparison of practical applications calculated with the different hydraulic functions rather than on a statistical comparison of the functions themselves. In this study four different methods were used to generate hydraulic functions: (A) direct on-site measurement, (B) measurement in soil horizons in the area, (C) use of a national data set, and (D) use of Van Genuchten parameters correlated with soil texture and organic matter content. The four methods were compared by their effect on two practical aspects of soil behaviour: (1) evapotranspiration deficit and (2) flux through a plane at 30 cm below soil surface. These two aspects are highly relevant for agricultural and environmental use. However, direct measurement is not feasible. A validated simulation model was used for the calculations and results obtained with method A were taken as a reference. Calculations were performed for three soil profiles for a period of seven years. Deficits and fluxes, calculated with the four methods to generate hydraulic functions, were not significantly different using the data of the seven-year period. However, methods were significantly different when rainfall deficits were used as a covariable. This is true with the exception of downward fluxes in the period October until March which are most important for leaching of pollutants. The user has to decide whether differences between methods are sufficiently large to justify repeated, expensive on-site measurements (method A) or whether an investment will be made to make standard series of curves to be used everywhere (methods C and D). 相似文献
330.