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71.
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73.
对山西省小灌区农田土壤水分在时空分布及其影响因素进行了分析.结果表明:大气降水、农田灌溉、作物蒸腾和田间土壤蒸发是影响土壤水分变化的主要因素.农田土壤水分分布随着作物的种类而变化. 相似文献
74.
Brendon A. Bradley Rajesh P. Dhakal Misko Cubrinovski John B. Mander Greg A. MacRae 《地震工程与结构动力学》2007,36(14):2211-2225
An improved seismic hazard model for use in performance‐based earthquake engineering is presented. The model is an improved approximation from the so‐called ‘power law’ model, which is linear in log–log space. The mathematics of the model and uncertainty incorporation is briefly discussed. Various means of fitting the approximation to hazard data derived from probabilistic seismic hazard analysis are discussed, including the limitations of the model. Based on these ‘exact’ hazard data for major centres in New Zealand, the parameters for the proposed model are calibrated. To illustrate the significance of the proposed model, a performance‐based assessment is conducted on a typical bridge, via probabilistic seismic demand analysis. The new hazard model is compared to the current power law relationship to illustrate its effects on the risk assessment. The propagation of epistemic uncertainty in the seismic hazard is also considered. To allow further use of the model in conceptual calculations, a semi‐analytical method is proposed to calculate the demand hazard in closed form. For the case study shown, the resulting semi‐analytical closed form solution is shown to be significantly more accurate than the analytical closed‐form solution using the power law hazard model, capturing the ‘exact’ numerical integration solution to within 7% accuracy over the entire range of exceedance rate. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
75.
Non-linear seismic behavior of structures with limited hysteretic energy dissipation capacity 总被引:1,自引:0,他引:1
Pierino Lestuzzi Youssef Belmouden Martin Trueb 《Bulletin of Earthquake Engineering》2007,5(4):549-569
This paper investigates the non-linear seismic behavior of structures such as slender unreinforced masonry shear walls or
precast post-tensioned reinforced concrete elements, which have little hysteretic energy dissipation capacity. Even if this
type of seismic response may be associated with significant deformation capacity, it is usually not considered as an efficient
mechanism to withstand strong earthquakes. The objective of the investigations is to propose values of strength reduction
factors for seismic analysis of such structures. The first part of the study is focused on non-linear single-degree-of-freedom
(SDOF) systems. A parametric study is performed by computing the displacement ductility demand of non-linear SDOF systems
for a set of 164 recorded ground motions selected from the European Strong Motion Database. The parameters investigated are
the natural frequency, the strength reduction factor, the post-yield stiffness ratio, the hysteretic energy dissipation capacity
and the hysteretic behavior model (four different hysteretic models: bilinear self-centring, with limited or without energy
dissipation capacity, modified Takeda and Elastoplastic). Results confirm that the natural frequency has little influence
on the displacement ductility demand if it is below a frequency limit and vice versa. The frequency limit is found to be around
2 Hz for all hysteretic models. Moreover, they show that the other parameters, especially the hysteretic behavior model, have
little influence on the displacement ductility demand. New relationships between the displacement ductility demand and the
strength reduction factor for structures having little hysteretic energy dissipation capacity are proposed. These relationships
are an improvement of the equal displacement rule for the considered hysteretic models. In the second part of the investigation,
the parametric study is extended to multi-degree-of-freedom (MDOF) systems. The investigation shows that the results obtained
for SDOF systems are also valid for MDOF systems. However, the SDOF system overestimates the displacement ductility demand
in comparison to the corresponding MDOF system by approximately 15%. 相似文献
76.
IP网络技术的现状及其多媒体应用研究 总被引:1,自引:0,他引:1
介绍了IP网络的现状、实现方式以及发展趋势,并分析了基于IP网络的多媒体通信若干技术和应用。 相似文献
77.
塔里木灌区近40年来气候变化特征 总被引:6,自引:1,他引:6
根据塔里木灌区阿拉尔气象站1961年1月-1999年12月的气温及降水资料,分析了塔里木灌区近40年的气候变化,得出近40年来塔里木灌区降水量呈上升趋势(4.60mm/10年),秋季降水量却呈下降趋势(-3.45mm/10年);年平均气温呈上升趋势(0.065℃/10年),冬季变暖的趋势(0.849℃/10年);年平均气温呈上升趋势(-0.171℃/10年);年极端低温的上升趋势(0.569℃/10年)大于年极端高温的下降趋势(-0.095℃/10年)。可以70年代末为界将近40年塔里木塔区气候分为冷、暖两个阶段,前为冷期,后为暖期。 相似文献
78.
79.
北疆棉区棉花膜下滴灌蒸散规律研究 总被引:6,自引:0,他引:6
通过对膜下灌溉技术下蒸散观测数据的分析,初步确定了棉花在整个生育期的蒸散量为500-600mm。在此基础上,分析了膜下灌溉技术对棉花产质量的影响。 相似文献
80.
不同灌溉对阜康地区冬小麦产量及土壤水分动态变化的影响 总被引:2,自引:0,他引:2
根据阜康生态试验站试验小区1999-2000年冬小麦不同灌溉量控制试验,验证了冬小麦水分敏感期为拔节-灌浆期,探讨了该区冬小麦产量与灌水量之间的关系。提出了阜康地区冬小麦返青水应采用“小水”灌溉的方式。同时通过对小区冬小麦成熟期灌水过程不同深度土壤水分含量的动态观测分析,提出冬小麦在成熟期对灌溉水分的消耗利用集中在0-30cm土壤层内的观点。 相似文献