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101.
Errors in the kinematic wave and diffusion wave approximations for time-independent (or steady-state) cases of channel flow were derived for three types of boundary conditions: zero flow at the upstream end, and critical flow depth and zero depth gradient at the downstream end. The diffusion wave approximation was found to be in excellent agreement with the dynamic wave approximation, with errors in the range 1–2% for values of KF (? 7.5), where K is the kinematic wave number and F0 is the Froude number. Even for small values of KF (e.g. KF20 = 0.75), the errors were typically less than 15%. The accuracy of the diffusion wave approximation was greatly influenced by the downstream boundary condition. The error of the kinematic wave approximation was found to be less than 13% in the region 0.1 ? x ? 0.95 for KF = 7.5 and was greater than 30% for smaller values of KF (? 0.75). This error increased with strong downstream boundary control. 相似文献
102.
以边坡为研究对象,针对基于罗盘、免棱镜全站仪、激光测距仪、三维激光扫描仪和数字摄影测量工作站的5种产状测量方法,采用误差理论进行产状测量精度评定。研究表明,罗盘产状测量的倾向、倾角中误差分别为±4°和±3°,其精度评定既可以提高对罗盘产状测量精度的认识,也可为其他4种非接触类产状测量方法的精度评定提供验算数据。利用罗盘只能进行高陡边坡下部结构面的产状测量,测量范围有限且高耗低效;非接触类产状测量方法则可以解决人员难以到达的高陡边坡上部结构面的产状测量问题。其中,三维激光扫描和数字近景摄影测量方法可以获取边坡岩体大量随机结构面上的产状信息,为基于随机动力学的边坡稳定性评价提供重要的基础数据。 相似文献
103.
104.
基于均值漂移模型,重点讨论粗差估值的计算问题,给出了观测值统计相关时数据探测法(data snooping)的粗差估值公式。探讨数据探测法粗差估值与粗差的同时定位与定值法(LEGE)、拟准检定法(QUAD)、部分最小二乘法(PLS)的粗差估值之间的关系,证明当观测值统计相关时,部分最小二乘法和QUAD法在粗差估值的计算上具有等价性,与数据探测法和LEGE法都不一致。当观测值统计独立且不等权时,QUAD法、PLS法和数据探测法具有等价性,与LEGE法在粗差估值上不同;当观测值统计独立且等权时,4种方法在粗差估值计算上具有等价性。最后通过算例验证了结论。 相似文献
105.
106.
Airborne Gradiometry Error Analysis 总被引:3,自引:0,他引:3
Christopher Jekeli 《Surveys in Geophysics》2006,27(2):257-275
Gravity gradiometry is one of the older methods of determining the Earth’s local gravitational field, but lies in the shadow
of more conventional static and moving-base gravimeter-based systems. While the static torsion balance appears to have been
relegated to the museum, support for the airborne and space-borne differential accelerometer (gradiometer) continues so as
to overcome limitations in spatial resolution and accuracy inherent in ordinary moving-base gravimetry. One airborne system
exists, building on 30 year old technology concepts, and new technologies (e.g., cold-atom interferometry) promise significant
improvements. Concomitant advances are required to measure accurately the angular velocity and angular acceleration of the
platform, which inseparably combine (in an absolute sense) with the Earth’s gravitational gradients. A numerical analysis
of instrument errors, with simulated aircraft dynamics, shows that navigation-grade gyros are just sufficient to account for
these effects in gradiometers with 1E/
sensitivity. More accurate instruments, with 0.1 E/
sensitivity, require commensurate sensitivity in the gyros, of the order of 0.01°/h/
= 1.5\times10−4 ° \
for typical survey aircraft dynamics. On the other hand, typical orientation errors in the platform, which are problematic
for vector gravimetry, are much less of a concern in gradiometry. They couple to the gradient signals and affect only the
very low frequencies of the total gradient error. 相似文献
107.
In this study, the predictability of the El Nino-South Oscillation(ENSO) in an operational prediction model from the perspective of initial errors is diagnosed using the seasonal hindcasts of the Beijing Climate Center System Model,BCC;SM1.1(m). Forecast skills during the different ENSO phases are analyzed and it is shown that the ENSO forecasts appear to be more challenging during the developing phase, compared to the decay phase. During ENSO development, the SST prediction errors are significantly negative and cover a large area in the central and eastern tropical Pacific, thus limiting the model skill in predicting the intensity of El Nino. The large-scale SST errors, at their early stage, are generated gradually in terms of negative anomalies in the subsurface ocean temperature over the central-western equatorial Pacific,featuring an error evolutionary process similar to that of El Nino decay and the transition to the La Nina growth phase.Meanwhile, for short lead-time ENSO predictions, the initial wind errors begin to play an increasing role, particularly in linking with the subsurface heat content errors in the central-western Pacific. By comparing the multiple samples of initial fields in the model, it is clearly found that poor SST predictions of the Nino-3.4 region are largely due to contributions of the initial errors in certain specific locations in the tropical Pacific. This demonstrates that those sensitive areas for initial fields in ENSO prediction are fairly consistent in both previous ideal experiments and our operational predictions,indicating the need for targeted observations to further improve operational forecasts of ENSO. 相似文献
108.
介绍了卫星信号内部时延的定义以及在GPS导航电文NAV和CNAV中所给出的各种时延差参数,推导了采用不同的卫星信号测距时应采用的各种卫星钟差模型。 相似文献
109.
110.
Theoretical Basis and Application of an Analogue- Dynamical Model in the Lorenz System 总被引:2,自引:0,他引:2
The theoretical basis and application of an analogue-dynamical model (ADM) in the Lorenz system
is studied. The ADM can effectively combine statistical and dynamical methods in which the small disturbance
of the current initial value superimposed on the historical analogue reference state can be regarded as a
prediction objective. Primary analyses show that under the condition of appending disturbances in model
parameters, the model errors of ADM are much smaller than those of the pure dynamical model (PDM).
The characteristics of predictability on the ADM in the Lorenz system are analyzed in phase space by
conducting case studies and global experiments. The results show that the ADM can quite effectively
reduce prediction errors and prolong the valid time of the prediction in most situations in contrast
to the PDM, but when model errors are considerably small, the latter will be superior to the former.
To overcome such a problem, the multi-reference-state updating can be applied to introduce the
information of multi-analogue and update analogue and can exhibit exciting performance in the ADM. 相似文献