全文获取类型
收费全文 | 6719篇 |
免费 | 1445篇 |
国内免费 | 1807篇 |
专业分类
测绘学 | 816篇 |
大气科学 | 1094篇 |
地球物理 | 1477篇 |
地质学 | 3587篇 |
海洋学 | 1016篇 |
天文学 | 299篇 |
综合类 | 764篇 |
自然地理 | 918篇 |
出版年
2024年 | 31篇 |
2023年 | 134篇 |
2022年 | 315篇 |
2021年 | 408篇 |
2020年 | 337篇 |
2019年 | 369篇 |
2018年 | 401篇 |
2017年 | 386篇 |
2016年 | 437篇 |
2015年 | 361篇 |
2014年 | 505篇 |
2013年 | 496篇 |
2012年 | 479篇 |
2011年 | 474篇 |
2010年 | 484篇 |
2009年 | 474篇 |
2008年 | 386篇 |
2007年 | 388篇 |
2006年 | 341篇 |
2005年 | 265篇 |
2004年 | 198篇 |
2003年 | 185篇 |
2002年 | 224篇 |
2001年 | 247篇 |
2000年 | 246篇 |
1999年 | 254篇 |
1998年 | 158篇 |
1997年 | 158篇 |
1996年 | 133篇 |
1995年 | 109篇 |
1994年 | 127篇 |
1993年 | 101篇 |
1992年 | 74篇 |
1991年 | 65篇 |
1990年 | 29篇 |
1989年 | 22篇 |
1988年 | 35篇 |
1987年 | 29篇 |
1986年 | 26篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1976年 | 5篇 |
1974年 | 2篇 |
1958年 | 6篇 |
1954年 | 2篇 |
排序方式: 共有9971条查询结果,搜索用时 15 毫秒
111.
112.
“Tripoli”的含义及译名的讨论 总被引:1,自引:0,他引:1
“Tripoli”是一种新型的石英质工业矿物原料,在我国长期被误译为硅藻土,影响地质部门对这一新矿种的认识和寻找。本文追溯了“Tripoli”一名的由来,正确地阐述了“Tripoli”的本质特征,分析了在国内文献中长期被误译的根源,指明了其正确含义,并建议废除各种不正确的中译名,译为“粉石英”。 相似文献
113.
磷石膏中的磷在雨水淋滤作用下浸出,将污染堆场附近水体。本研究采用生物炭固化磷石膏中的磷,以减少其对周遭水体的污染。主要通过模拟固化实验和对照浸出实验,分析生物炭用量、反应时间和温度、初始pH值对固化效果的影响,通过XRD、SEM-EDS分析固化后的生成物。实验结果显示,在生物炭用量为25 mg时,单位固化量达到最大值13.20 mg/g;在反应温度T=293 K、初始pH=7条件下,反应平衡时间72 h时浸出液的磷平衡浓度Ce= 1.40 mg/L;温度提升有助于提高生物炭的固化效果,当T=308 K时,浸出液的磷平衡浓度Ce=0.167 mg/L;碱性条件有利于固化反应持续进行,在pH=11条件下,浸出液的磷平衡浓度Ce=0.153 mg/L。实验结果表明生物炭对磷石膏中的磷具有明显的固化效果。磷石膏中的二水硫酸钙溶解后,Ca2+与表面带负电的生物炭结合,在生物炭显微结构的凹陷处,化学吸附溶液中的磷酸根生成了絮状、团簇状的羟基磷灰石(HAP)沉淀,从而使浸出磷得到有效控制。 相似文献
114.
115.
116.
本文总结了“青藏高原大地形及西太平洋暖池势力强迫对东亚及全球气候变化的影响”专题五年来的主要研究工作。其中包括青世故高原东部大气热源的时间演变特征,夏半年高原热源异常对我国降水和北半球环流的影响;西沙海温变化特征及其与我南方降水的关系,北太平洋海温主因子特征及其与华南前汛期降水的变化。 相似文献
117.
We derive a time series of two-dimensional velocity fields for a flare region on 1992 December 16, based on the asymmetries of the H line. The H spectra were obtained by an imaging spectrograph at the Solar Tower Telescope of Nanjing University. Four sites with evident chromospheric downflows are found to appear and decay consecutively in the studied region. The value of maximum velocities is 30–40 km s–1 and the lifetime of downflows is 2–3 min at these sites. It is also shown that the asymmetries only exist at the line wing, while the line center has nearly no shifts for this flare. Finally, we make a discussion on the characteristics of the velocity distribution and its correlations with the intensity distribution, as well as with the hard X-ray emission. 相似文献
118.
By use of the dispersion equation given by Song, Wu, and Dryer (1987) for a cylinder plasma with mass motion and gravity included, we investigate the linear current instabilities developed in loop prominences. The results indicate that the mode of linear instability depends mainly on whetherv
s
2
> or not, wherev
s
is the sonic velocity at heightz, =GM/(R +z) is the gravity potential,G the gravitational constant,M andR the mass and the radius of the Sun respectively. Ifv
s
2
> , then the sausage instability will be dominant. Otherwise, the kink instability will be more important. A possible explanation of knot structure, which appears sometimes in solar loop prominences has been given. 相似文献
119.
Xiang Xu 《Geochimica et cosmochimica acta》2006,70(17):4319-4331
Interaction of dissolved aqueous species with natural organic matter (NOM) is thought to be important in sequestering some species and enhancing the transport of others, but little is known about these interactions on a molecular scale. This paper describes a combined experimental 133Cs and 35Cl nuclear magnetic resonance (NMR) and computational molecular dynamics (MD) modeling study of the interaction of Cs+ and Cl− with Suwannee River NOM. The results provide a detailed picture of the molecular-scale structure and dynamics of these interactions. Individual NOM molecules are typically hundreds to thousands of Daltons in weight, and on the molecular scale their interaction with small dissolved species can be investigated in ways similar to those used to study the interaction of dissolved aqueous species with mineral surfaces. As for such surface interactions, understanding both the structural environments and the dynamics over a wide range of frequencies is essential. The NMR results show that Cs+ is associated with NOM at pH values from 3.4 ± 0.5 (unbuffered Suwannee River NOM solution) to 9.0 ± 0.5. The extent of interaction increases with decreasing CsCl concentration at constant pH. It also decreases with increasing pH at constant CsCl concentration due to pH-dependent negative structural charge development on the NOM caused by progressive deprotonation of carboxylic and phenolic groups. The presence of NOM has little effect on the 133Cs chemical shifts, demonstrating that its local coordination environment does not change significantly due to interaction with the NOM. Narrow, solution-like line widths indicate rapid exchange of Cs+ between the NOM and bulk solution at frequencies of >102 Hz. The MD simulations support these results and show that Cs+ is associated with the NOM principally as outer sphere complexes and that this interaction does not reduce the Cs+ diffusion coefficient sufficiently to cause NMR line broadening. The 35Cl NMR data and the MD results are consistent in demonstrating that there is no significant complexation between Cl− and NOM in the pH range investigated, consistent with negative structural charge on the NOM. 相似文献
120.
The Xiangxi River is the first middling tributary of the Changjiang River near the Three Gorges Dam. The River is subject
to phosphorus pollution mainly from industrial wastewater. As the water quality of the Xiangxi River could directly influence
the water quality of the Three Gorges Reservoir, the research on phosphorus levels and its change in the sediment profile
of the Xiangxi River could provide useful information in the dynamic changes in the system, thereby offering options for mitigative
measures. Water and sediment samples from lower reaches of Xiangxi River were collected and the different forms of phosphorus
in sediments of the Xiangxi River were studied. The concentrations of total phosphorus in sediment ranged from 757.67 to 1438.54 mg/kg.
Inorganic phosphorus concentrations ranged from 684.63 to 1055.58 mg/kg. Phosphorus contamination was serious in some parts
of the Xiangxi River. With an average concentration of 635.17 mg/kg, calcium-bound phosphorus is the main form among different
inorganic phosphorus forms. Labile phosphorus and iron/aluminum-bound phosphorus measured 3.40, 0.05and 35.28 mg/kg, respectively.
The mobilization potential of phosphorus of sediments was studied through adsorption and release experiments. The equilibrium
concentration of phosphorus adsorption and release was around 0.1 mg/L. The initial concentrations of phosphorus in the overlying
water and the sediments have obvious effect on phosphorus mobilization potential. In addition, the release rate of phosphorus
in sediment increased with water depth. 相似文献