全文获取类型
收费全文 | 3404篇 |
免费 | 453篇 |
国内免费 | 412篇 |
专业分类
测绘学 | 340篇 |
大气科学 | 345篇 |
地球物理 | 1210篇 |
地质学 | 1110篇 |
海洋学 | 476篇 |
天文学 | 116篇 |
综合类 | 118篇 |
自然地理 | 554篇 |
出版年
2024年 | 14篇 |
2023年 | 18篇 |
2022年 | 58篇 |
2021年 | 79篇 |
2020年 | 107篇 |
2019年 | 103篇 |
2018年 | 92篇 |
2017年 | 132篇 |
2016年 | 135篇 |
2015年 | 144篇 |
2014年 | 173篇 |
2013年 | 289篇 |
2012年 | 142篇 |
2011年 | 164篇 |
2010年 | 109篇 |
2009年 | 166篇 |
2008年 | 202篇 |
2007年 | 233篇 |
2006年 | 179篇 |
2005年 | 196篇 |
2004年 | 157篇 |
2003年 | 151篇 |
2002年 | 139篇 |
2001年 | 114篇 |
2000年 | 127篇 |
1999年 | 122篇 |
1998年 | 96篇 |
1997年 | 111篇 |
1996年 | 79篇 |
1995年 | 61篇 |
1994年 | 46篇 |
1993年 | 62篇 |
1992年 | 39篇 |
1991年 | 31篇 |
1990年 | 31篇 |
1989年 | 28篇 |
1988年 | 30篇 |
1987年 | 23篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1971年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有4269条查询结果,搜索用时 15 毫秒
131.
132.
Xavier Emery 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(5):348-360
This work deals with the geostatistical simulation of a family of stationary random field models with bivariate isofactorial
distributions. Such models are defined as the sum of independent random fields with mosaic-type bivariate distributions and
infinitely divisible univariate distributions. For practical applications, dead leaf tessellations are used since they provide
a wide range of models and allow conditioning the realizations to a set of data via an iterative procedure (simulated annealing).
The model parameters can be determined by comparing the data variogram and madogram, and enable to control the spatial connectivity
of the extreme values in the realizations. An illustration to a forest dataset is presented, for which a negative binomial
model is used to characterize the distribution of coniferous trees over a wooded area. 相似文献
133.
Thorsten Wagener Hoshin V. Gupta 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(6):378-387
Methods for the identification of models for hydrological forecasting have to consider the specific nature of these models
and the uncertainties present in the modeling process. Current approaches fail to fully incorporate these two aspects. In
this paper we review the nature of hydrological models and the consequences of this nature for the task of model identification.
We then continue to discuss the history (“The need for more POWER‘’), the current state (“Learning from other fields”) and
the future (“Towards a general framework”) of model identification. The discussion closes with a list of desirable features
for an identification framework under uncertainty and open research questions in need of answers before such a framework can
be implemented. 相似文献
134.
Concentrated plasticity (CP) models are frequently used in static and dynamic building analysis and have been implemented in available commercial software. This investigation deals with three different CP‐models, a simplified macroelement model (SEM) for a complete building story, a frame element with elasto‐plastic interaction hinges (PH), and a frame element with fiber hinges (FB). The objectives of this work are to evaluate the quality of the earthquake responses predicted by these models and to identify important aspects of their implementation and limitations for their use in dynamic analysis. The three elements are tested in a single‐story asymmetric plan building and in a three‐story steel building. Results show that base shear and global response values are usually computed with better accuracy than interstory deformations and local responses. Besides, the main limitation of elasto‐plastic CP models is to control the displacement offsets that result from perfect elasto‐plastic behavior. On the other hand, calibration of the SEM‐model shows that global responses in steel structures may be computed within 20% error in the mean at a computational cost two orders of magnitude smaller than that of the other CP elements considered. However, the three element models considered lead to increasing levels of accuracy in the dynamic response and their use depends on the refinement of the analysis performed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
135.
Naohiro Nakamura 《地震工程与结构动力学》2005,34(11):1391-1406
It is important to estimate the influence of layered soil in soil–structure interaction analyses. Although a great number of investigations have been carried out on this subject, there are very few practical methods that do not require complex calculations. In this paper, a simple and practical method for estimating the horizontal dynamic stiffness of a rigid foundation on the surface of multi‐layered soil is proposed. In this method, waves propagating in the soil are traced using the conception of the cone model, and the impulse response function can be calculated directly and easily in the time domain with a good degree of accuracy. The characteristics of the impedance, that is the transformed value to the frequency domain of the obtained impulse response, are studied using two‐ to four‐layered soil models. The cause of the fluctuation of impedance is expressed clearly from its relation to reflected waves from the lower layer boundary in the model. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
136.
137.
Jennifer Miller 《The Professional geographer》2005,57(2):169-184
Predictive vegetation modeling can be used statistically to relate the distribution of vegetation across a landscape as a function of important environmental variables. Often these models are developed without considering the spatial pattern that is inherent in biogeographical data, resulting from either biotic processes or missing or misspecified environmental variables. Including spatial dependence explicitly in a predictive model can be an efficient way to improve model accuracy with the available data. In this study, model residuals were interpolated and added to model predictions, and the resulting prediction accuracies were assessed. Adding kriged residuals improved model accuracy more often than adding simulated residuals, although some alliances showed no improvement or worse accuracy when residuals were added. In general, the prediction accuracies that were not increased by adding kriged residuals were either rare in the sample or had high nonspatial model accuracy. Regression interpolation methods can be an important addition to current tools used in predictive vegetation models as they allow observations that are predicted well by environmental variables to be left alone, while adjusting over‐ and underpredicted observations based on local factors. 相似文献
138.
139.
140.