全文获取类型
收费全文 | 16965篇 |
免费 | 3291篇 |
国内免费 | 4715篇 |
专业分类
测绘学 | 1569篇 |
大气科学 | 3558篇 |
地球物理 | 4011篇 |
地质学 | 9015篇 |
海洋学 | 2382篇 |
天文学 | 870篇 |
综合类 | 1629篇 |
自然地理 | 1937篇 |
出版年
2024年 | 142篇 |
2023年 | 439篇 |
2022年 | 940篇 |
2021年 | 1076篇 |
2020年 | 838篇 |
2019年 | 1056篇 |
2018年 | 983篇 |
2017年 | 964篇 |
2016年 | 1113篇 |
2015年 | 1000篇 |
2014年 | 1137篇 |
2013年 | 1104篇 |
2012年 | 1168篇 |
2011年 | 1090篇 |
2010年 | 1184篇 |
2009年 | 995篇 |
2008年 | 925篇 |
2007年 | 856篇 |
2006年 | 653篇 |
2005年 | 589篇 |
2004年 | 429篇 |
2003年 | 399篇 |
2002年 | 358篇 |
2001年 | 426篇 |
2000年 | 430篇 |
1999年 | 622篇 |
1998年 | 542篇 |
1997年 | 488篇 |
1996年 | 481篇 |
1995年 | 433篇 |
1994年 | 353篇 |
1993年 | 345篇 |
1992年 | 291篇 |
1991年 | 226篇 |
1990年 | 176篇 |
1989年 | 141篇 |
1988年 | 146篇 |
1987年 | 72篇 |
1986年 | 64篇 |
1985年 | 52篇 |
1984年 | 34篇 |
1983年 | 26篇 |
1982年 | 38篇 |
1981年 | 34篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1978年 | 7篇 |
1976年 | 9篇 |
1973年 | 5篇 |
1958年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
In this study, the differences in annual rainstorm changes in the Second Songhua River Basin and the Nenjiang River basin and their causes were compared from the perspective of mountain effects. The following results were drawn: (1) Altitude effect is the primary factor leading to increased rainstorms in the southern source; (2) Slope effect primarily leads to differences of the weather systems in the two sources, and thus cause the difference of the rainstorms; (3) Slope effect is responsible for the greater fluctuation in the observed floods in the southern source. These landform differences eventually lead to the differences in the characteristics of floods in the southern and northern sources. Commensurability method was used to identify the period of rainstorms in the southern and northern sources. The results showed that although rainstorms do not appear at the same time in the two sources they are characteristic of a 10 years’ period in both areas. These results can serve as hydrological references for flood control and long-term flood disaster predictions. 相似文献
942.
Yu Guangyuan Zhang Qiangyong Li Fan Cheng Lei Guo Xin 《Geotechnical and Geological Engineering》2021,39(6):4545-4562
Geotechnical and Geological Engineering - A set of splitting cracks often occur in the high side wall of the deep underground hydropower station due to the excavation-induced unloading during the... 相似文献
943.
Due to their particular physiology and life history traits, bryophytes are critical in regulating biogeochemical cycles and functions in alpine ecosystem. Hence, it is crucial to investigate their nutrient utilization strategies in comparison with vascular plants and understand their responses to the variation of growing season caused by climate change. Firstly, this study testified whether or not bryophytes can absorb nitrogen(N) directly from soil through spiking three chemical forms of 15N stable isotope tracer. Secondly, with stronger ability of carbohydrates assimilation and photosynthesis, it is supposed that N utilization efficiency of vascular plants is significantly higher than that of bryophytes. However, the recovery of soil N by bryophytes can still compete with vascular plants due to their greater phytomass. Thirdly, resource acquisition may be varied from the change of growing season, during which N pulse can be manipulated with 15N tracer addition at different time. Both of bryophytes and vascular plants contain more N in a longer growing season, and prefer inorganic over organic N. Bryophytes assimilate more NH4+ than NO3– and amino acid, which can be indicated from the greater shoot excess 15N of bryophytes. However, vascular plants prefer to absorb NO3– for their developed root systems and vascular tissue. Concerning the uptake of three forms N by bryophytes, there is significant difference between two manipulated lengths of growing season. Furthermore, the capacity of bryophytes to tolerate N-pollution may be lower than currently appreciated, which indicates the effect of climate change on asynchronous variation of soil N pools with plant requirements. 相似文献
944.
Zhongqing Wu 《地震学报(英文版)》2015,(1):11-16
The thermodynamic properties of crystals can be routinely calculated by density functional theory calculations combining with quasi-harmonic approximation.Based on the method developed recently by Wu and Wentzcovitch(Phys Rev B 79:104304, 2009) and Wu(Phys Rev B 81:172301, 2010), we are able to further ab initio include anharmonic effect on thermodynamic properties of crystals by one additional canonical ensemble with numbers of particle, volume and temperature fixed(NVT) molecular dynamic simulations. Our study indicates that phonon–phonon interaction causes the renormalized phonon frequencies of wadsleyite decrease with temperature. This is consistent with the Raman experimental observation. The anharmonic free energy of wadsleyite is negative and its heat capacity at constant pressure can exceed the Dulong–Petit limit at high temperature. The anharmonicity still significantly affects thermodynamic properties of wadsleyite at pressure and temperature conditions correspond to the transition zone. 相似文献
945.
文中简要介绍了河南省岩石矿物测试中心从70年代后期开始的堆浸研究的几个阶段及其研究内容,主要成果,以及成果的经济效益及社会效益,并提出了堆浸研究的方向 相似文献
946.
We describe organogenesis at a histological level in American shad (Alosa sapidissima) larvae from 0 until 45 days after hatching (DAH). Larval development was divided into four stages based on the feeding mode, external morphological features, and structural changes in the organs: stage 1 (0–2 DAH), stage 2 (3–5 DAH), stage 3 (6–26 DAH) and stage 4 (27–45 DAH). At early stage 2 (3 DAH), American shad larvae developed the initial digestive and absorptive tissues, including the mouth and anal opening, buccopharyngeal cavity, oesophagus, incipient stomach, anterior and posterior intestine, differentiated hepatocytes, and exocrine pancreas. The digestive and absorptive capacity developed further in stages 2 to 3, at which time the pharyngeal teeth, taste buds, gut mucosa folds, differentiated stomach, and gastric glands could be observed. Four defined compartments were discernible in the heart at 4 DAH. From 3 to 13 DAH, the excretory systems started to develop, accompanied by urinary bladder opening, the appearance and development of primordial pronephros, and the proliferation and convolution of renal tubules. Primordial gills were detected at 2 DAH, the pseudobranch was visible at 6 DAH, and the filaments and lamellae proliferated rapidly during stage 3. The primordial swim bladder was first observed at 2 DAH and started to inflate at 9 DAH; from then on, it expanded constantly. The spleen was first observed at 8 DAH and the thymus was evident at 12 DAH. From stage 4 onwards, most organs essentially manifested an increase in size, number, and complexity of tissue structure. 相似文献
947.
948.
现代区域开发的矿产资源需求生命周期研究及意义 总被引:16,自引:1,他引:16
矿产资源是社会经济发展的重要物质基础,受社会经济和科学技术发展的限制,各类矿产资源的需求存在着从初始,增长,停滞和衰落的周期性变化以及明显的空间分嘏差异。 相似文献
950.
变质地质学的研究离不开变质反应动力学。元素扩散具有完备的数理基础和丰富的实验数据, 相对成熟地应用于变质地质学, 是目前变质反应动力学的研究热点。本文从变质岩石学的视角, 对扩散的基本数理原理、矿物元素扩散系数及其影响因素、扩散在变质地质学中的应用及其存在的问题做了系统的介绍和总结。本文强调, 元素扩散是变质岩中普遍存在的动力学过程, 一方面会改造矿物原始的生长环带, 给传统温压计和相平衡模拟确定温压条件造成困恼, 另一方面也给变质作用的研究带来动力学视角, 为限定变质-构造热事件的时间尺度和速率提供精准的标尺, 比如扩散速率计或者扩散年代学。扩散这种动力学方法在变质地质学中的应用和进一步发展仍需未来工作。
相似文献