全文获取类型
收费全文 | 281篇 |
免费 | 35篇 |
国内免费 | 75篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 9篇 |
地球物理 | 39篇 |
地质学 | 168篇 |
海洋学 | 15篇 |
天文学 | 138篇 |
综合类 | 8篇 |
自然地理 | 5篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 5篇 |
2014年 | 24篇 |
2013年 | 16篇 |
2012年 | 19篇 |
2011年 | 17篇 |
2010年 | 13篇 |
2009年 | 15篇 |
2008年 | 22篇 |
2007年 | 13篇 |
2006年 | 10篇 |
2005年 | 21篇 |
2004年 | 24篇 |
2003年 | 25篇 |
2002年 | 15篇 |
2001年 | 7篇 |
2000年 | 13篇 |
1999年 | 8篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 14篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
排序方式: 共有391条查询结果,搜索用时 15 毫秒
91.
在考虑径向对流和不同光学厚度的基础上,我们采用一般的辐射致冷假设;在统一的框架内考察了吸积盘的整体结构.对α模型,我们发现在不同的盘区存在不同的整体结构.在吸积率较低时,存在三种类型解:光学厚的局部辐射致冷解;光学薄的局部致冷解;光学薄的对流致冷解.这些解在盘内较大范围内都存在且互不交叉.但在吸积率较高和粘滞系数较大时,两种局部致冷解会相互交叉,而对流为主的解在所有盘区都稳定存在.另一方面,在吸积率较高和粘滞系数较小时,两种光学薄解会相互交叉,而光学厚和局部致冷为主的解在所有盘区都存在. 相似文献
92.
93.
掺铝氧化锌厚膜制备及其对三甲胺和海产品鲜度的敏感性 总被引:2,自引:0,他引:2
用烧结法制备掺铝氧化锌厚膜,把氧化锌粉末分别同0%,1%,3%,5%的Al2O3粉末机械研磨混合均匀,在1100℃下烧3h,再同粘合剂,有机溶剂混合制成浆料,用刮刀法在氧化铝基片上浆料制成膜,在100℃下烘干后再经1100℃烧结2h。膜的灵敏度的测量方法是将膜放在玻璃管内加热到测量温度,测量膜暴露在一定浓度TMA气体或由牡蛎放出的气体时电阻值的变化。测量温度为200,250,300℃和400℃,T 相似文献
94.
本文评述了星云和星子假说、太阳星云的崩塌、星盘的形成和演化、颗粒生长、星子增生、类地行星和类木行星的形成、行星迁移,以及太阳和行星的演化。 相似文献
95.
The instability of axisymmetric flows of ideal incompressible fluid with respect to infinitesimal perturbations with the nonconservation of angular momentum is investigated by numerically integrating the differential equations of hydrodynamics. The problem has been solved for two types of rotation profiles of an unperturbed flow: with zero and nonzero pressure gradients at the flow boundaries. Both rigid and free boundary conditions have been considered. The stability of axisymmetric flows with free boundaries is of great importance in disk accretion problems. Our calculations have revealed a crucial role of the flow pattern near the boundaries in the instability of the entire main flow. When the pressure gradient at the boundaries is zero, there is such a limiting scale of perturbations in azimuthal coordinate that longer-wavelength perturbations grow, while growing shorter-wavelength perturbations do not exit. In addition, for a fixed radial flow extent, there exists a nonzero minimum amplitude of the deviation of the angular velocity from the Keplerian one at which the instability vanishes. For a nonzero pressure gradient at the boundaries, the flow is unstable with respect to perturbations of any scale and at any small deviation of the angular velocity from the Keplerian one. 相似文献
96.
97.
98.
分析了影响深表土立井井壁可靠性的因素,并对主要因素进行合理量化,建立了指标体系。在此基础上,利用模糊评价理论,建立了深表土复杂条件下的井壁可靠性模糊评价方法。通过工程实例验证,表明该方法具有较高的实用性和准确性。 相似文献
99.
浅埋深、薄基岩、厚松散含水层下煤层综合机械化开采防治水技术应用 总被引:1,自引:0,他引:1
神东煤炭公司大柳塔矿12404工作面煤层埋深浅,上覆基岩薄、松散含水层厚,且地表有河流横过(工作面长度240m,推进度3900m,其中薄基岩富水段150m),为了减少工作面搬家次数提高生产效益,采取了地面抽排水、井下泄放水及地面注浆固沙等有效的防治水措施,工作面安全通过了母河沟,该防治水方法的应用改变了以往类似情况进行留煤柱跳采的方法,取得了浅埋深薄基岩厚含水层下煤层综合机械化安全开采经验,比停产跳采节省搬家费用2400万元,获得了显著的经济效益。 相似文献
100.
An important element of evaluating a large wildfire is to assess its effects on the soil in order to predict the potential watershed response. After the 55 000 ha Hayman Fire on the Colorado Front Range, 24 soil and vegetation variables were measured to determine the key variables that could be used for a rapid field assessment of burn severity. The percentage of exposed mineral soil and litter cover proved to be the best predictors of burn severity in this environment. Two burn severity classifications, one from a statistical classification tree and the other a Burned Area Emergency Response (BAER) burn severity map, were compared with measured ‘ground truth’ burn severity at 183 plots and were 56% and 69% accurate, respectively. This study also compared water repellency measurements made with the water drop penetration time (WDPT) test and a mini‐disk infiltrometer (MDI) test. At the soil surface, the moderate and highly burned sites had the strongest water repellency, yet were not significantly different from each other. Areas burned at moderate severity had 1·5 times more plots that were strongly water repellent at the surface than the areas burned at high severity. However, the high severity plots most likely had a deeper water repellent layer that was not detected with our surface tests. The WDPT and MDI values had an overall correlation of r = ?0·64(p < 0·0001) and appeared to be compatible methods for assessing soil water repellency in the field. Both tests represent point measurements of a soil characteristic that has large spatial variability; hence, results from both tests reflect that variability, accounting for much of the remaining variance. The MDI is easier to use, takes about 1 min to assess a strongly water repellent soil and provides two indicators of water repellency: the time to start of infiltration and a relative infiltration rate. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献