全文获取类型
收费全文 | 33888篇 |
免费 | 1982篇 |
国内免费 | 3159篇 |
专业分类
测绘学 | 1936篇 |
大气科学 | 4257篇 |
地球物理 | 6980篇 |
地质学 | 16100篇 |
海洋学 | 2198篇 |
天文学 | 2272篇 |
综合类 | 3031篇 |
自然地理 | 2255篇 |
出版年
2024年 | 22篇 |
2023年 | 126篇 |
2022年 | 372篇 |
2021年 | 402篇 |
2020年 | 350篇 |
2019年 | 425篇 |
2018年 | 5075篇 |
2017年 | 4342篇 |
2016年 | 3018篇 |
2015年 | 676篇 |
2014年 | 648篇 |
2013年 | 576篇 |
2012年 | 1491篇 |
2011年 | 3189篇 |
2010年 | 2591篇 |
2009年 | 2789篇 |
2008年 | 2347篇 |
2007年 | 2781篇 |
2006年 | 423篇 |
2005年 | 560篇 |
2004年 | 670篇 |
2003年 | 692篇 |
2002年 | 513篇 |
2001年 | 378篇 |
2000年 | 389篇 |
1999年 | 548篇 |
1998年 | 491篇 |
1997年 | 428篇 |
1996年 | 441篇 |
1995年 | 372篇 |
1994年 | 314篇 |
1993年 | 303篇 |
1992年 | 249篇 |
1991年 | 197篇 |
1990年 | 152篇 |
1989年 | 128篇 |
1988年 | 129篇 |
1987年 | 66篇 |
1986年 | 58篇 |
1985年 | 44篇 |
1984年 | 31篇 |
1983年 | 23篇 |
1982年 | 37篇 |
1981年 | 52篇 |
1980年 | 39篇 |
1979年 | 17篇 |
1978年 | 7篇 |
1976年 | 14篇 |
1973年 | 5篇 |
1958年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
内蒙古敖汉旗七家金矿构造位置上处于兴蒙造山带与华北克拉通北缘的结合部位, 靠近兴蒙造山带一侧, 是近年来新发现的石英脉型金矿床.区内岩脉以闪长玢岩为主, 且与石英脉型矿体空间关系密切.根据岩脉与矿体的穿插关系, 将其分为成矿前闪长玢岩和成矿后闪长玢岩.LA-ICP-MS锆石U-Pb年代学表明, 成矿前闪长玢岩加权平均年龄为166.3±3.4 Ma, 成矿后闪长玢岩加权平均年龄为128.6±4.5 Ma, 与区域上两期构造-岩浆活动时间(分别为160 Ma左右和128 Ma左右)近似吻合.主量元素特征显示: 二者均属于准铝质, 高钾钙碱性系列; 微量元素特征显示: 二者均富集轻稀土元素、大离子亲石元素(Rb、K)和活泼的不相容元素(U、Pb), 相对亏损重稀土元素和高场强元素(Nb、Ta、Ti), 反映出岩浆来源具壳源特征.主微量元素特征均显示出二者具有岛弧岩浆岩的地球化学属性.另外, 成矿后闪长玢岩有较高的Nb/Ta(18.66~20.27)和Zr/Hf(37.16~39.23)比值, 暗示其岩浆来源具明显的幔源特征.岩石地球化学特征表明, 成矿前闪长玢岩可能起源于太平洋板块俯冲导致的下地壳部分熔融岩浆; 成矿后闪长玢岩可能起源于俯冲流体交代的地幔楔熔融岩浆, 并在其演化侵位过程中伴有地壳物质的混染.结合闪长玢岩成岩时代、岩石成因及区域构造演化, 反映出七家金矿的形成与太平洋板块的西向俯冲密切相关, 矿床在地壳由挤压增厚向伸展减薄的转换过程中形成. 相似文献
972.
973.
974.
975.
The impact of boreal autumn SST anomalies over the South Pacific on boreal winter precipitation over East Asia 总被引:1,自引:0,他引:1
The possible mechanism behind the variability in the dipole pattern of boreal winter precipitation over East Asia is analyzed in this study. The results show that the SST anomalies(SSTAs) over the South Pacific Ocean(SPO) in boreal autumn are closely related to the variability in the dipole pattern of boreal winter precipitation over East Asia. The physical link between the boreal autumn SPO SSTAs and the boreal winter East Asian precipitation dipole pattern is shown to mainly be the seasonal persistence of the SPO SSTAs themselves. The seasonal persistence of the SPO SSTAs can memorize and transport the signal of the boreal autumn SSTAs to the following winter, and then stimulates a meridional teleconnection pattern from the SH to the NH, resulting in a meridional dipole pattern of atmospheric circulation over East Asia in boreal winter. As a major influencing factor, this dipole pattern of the atmospheric circulation can finally lead to the anomalous precipitation dipole pattern over East Asia in boreal winter. These observed physical processes are further confirmed in this study through numerical simulation. The evidence from this study, showing the impact of the SPO SSTAs in boreal autumn,not only deepens our understanding of the variability in East Asian boreal winter precipitation, but also provides a potentially useful predictor for precipitation in the region. 相似文献
976.
Yu-Kun QIAN Chang-Xia LIANG Zhuojian YUAN Shiqiu PENG Junjie WU Sihua WANG 《大气科学进展》2016,33(5):614-631
Based on 25-year(1987–2011) tropical cyclone(TC) best track data, a statistical study was carried out to investigate the basic features of upper-tropospheric TC–environment interactions over the western North Pacific. Interaction was defined as the absolute value of eddy momentum flux convergence(EFC) exceeding 10 m s~(-1)d~(-1). Based on this definition, it was found that 18% of all six-hourly TC samples experienced interaction. Extreme interaction cases showed that EFC can reach~120 m s~(-1)d~(-1) during the extratropical-cyclone(EC) stage, an order of magnitude larger than reported in previous studies.Composite analysis showed that positive interactions are characterized by a double-jet flow pattern, rather than the traditional trough pattern, because it is the jets that bring in large EFC from the upper-level environment to the TC center. The role of the outflow jet is also enhanced by relatively low inertial stability, as compared to the inflow jet. Among several environmental factors, it was found that extremely large EFC is usually accompanied by high inertial stability, low SST and strong vertical wind shear(VWS). Thus, the positive effect of EFC is cancelled by their negative effects. Only those samples during the EC stage, whose intensities were less dependent on VWS and the underlying SST, could survive in extremely large EFC environments, or even re-intensify. For classical TCs(not in the EC stage), it was found that environments with a moderate EFC value generally below ~25 m s~(-1)d~(-1) are more favorable for a TC's intensification than those with extremely large EFC. 相似文献
977.
Shang-Ping Xie 《大气科学进展》2016,33(4):409-410
正Forty years ago,Klaus Wyrtki(1975)of University of Hawaii discovered that El Nino warming off South America is not a result of local wind change but a response to the relaxed equatorial trade winds some 10 000 km away near the international dateline.The Kelvin wave mechanism was quickly verified from wind-forced ocean model simulations.Consequent 相似文献
978.
The mechanisms behind the seasonal deepening of the mixed layer(ML) in the subtropical Southeast Pacific were investigated using the monthly Argo data from 2004 to 2012. The region with a deep ML(more than 175 m) was found in the region of(22?–30?S, 105?–90?W), reaching its maximum depth(~200 m) near(27?–28?S, 100?W) in September. The relative importance of horizontal density advection in determining the maximum ML location is discussed qualitatively. Downward Ekman pumping is key to determining the eastern boundary of the deep ML region. In addition, zonal density advection by the subtropical countercurrent(STCC) in the subtropical Southwest Pacific determines its western boundary, by carrying lighter water to strengthen the stratification and form a "shallow tongue" of ML depth to block the westward extension of the deep ML in the STCC region. The temperature advection by the STCC is the main source for large heat loss from the subtropical Southwest Pacific. Finally, the combined effect of net surface heat flux and meridional density advection by the subtropical gyre determines the northern and southern boundaries of the deep ML region: the ocean heat loss at the surface gradually increases from 22?S to 35?S, while the meridional density advection by the subtropical gyre strengthens the stratification south of the maximum ML depth and weakens the stratification to the north. The freshwater flux contribution to deepening the ML during austral winter is limited. The results are useful for understanding the role of ocean dynamics in the ML formation in the subtropical Southeast Pacific. 相似文献
979.
Tabish U. Ansari N. Ojha R. Chandrasekar C. Balaji Narendra Singh Sachin S. Gunthe 《Journal of Atmospheric Chemistry》2016,73(4):363-380
The spatial distribution of trace gases exhibit large spatial heterogeneity over the Indian region with an elevated pollution loading over densely populated Gangetic Plains (IGP). The contending role and importance of anthropogenic emissions and meteorology in deciding the trace gases level and distribution over Indian region, however, is poorly investigated. In this paper, we use an online regional chemistry transport model (WRF/Chem) to simulate the spatial distribution of trace gases over Indian region during one representative month of only three meteorological seasons namely winter, spring/summer and monsoon. The base simulation, using anthropogenic emissions from SEAC4RS inventory, is used to simulate the general meteorological conditions and the realistic spatial distribution of trace gases. A sensitivity simulation is conducted after removing the spatial heterogeneity in the anthropogenic emissions, i.e., with spatially uniform emissions to decouple the role of anthropogenic emissions and meteorology and their role in controlling the distribution of trace gases over India. The concentration levels of Ozone, CO, SO2 and NO2 were found to be lower over IGP when the emissions are uniform over India. A comparison of the base run with the sensitivity run highlights that meteorology plays a dominant role in controlling the spatial distribution of relatively longer-lived species like CO and secondary species like Ozone while short-lived species like NOX and SO2 are predominantly controlled by the spatial variability in anthropogenic emissions over the Indian region. 相似文献
980.
Based on the dynamic framework of WRF and Morrison 2-moment explicit cloud scheme, a salt-seeding scheme was developed and used to simulate the dissipation of a warm fog event during 6–7 November 2009 in the Beijing and Tianjin area. The seeding effect and its physical mechanism were studied. The results indicate that when seeding fog with salt particles sized 80 μm and at a quantity of 6 gm~(-2) at the fog top, the seeding effect near the ground surface layer is negative in the beginning period, and then a positive seeding effect begins to appear at 18 min, with the best effect appearing at 21 min after seeding operation. The positive effect can last about 35 min. The microphysical mechanism of the warm fog dissipation is because of the evaporation due to the water vapor condensation on the salt particles and coalescence with salt particles.The process of fog water coalescence with salt particles contributed mostly to this warm fog dissipation. Furthermore, two series of sensitivity experiments were performed to study the seeding effect under different seeding amounts and salt particles sizes. The results show that seeding fog with salt particles sized of 80 μm can have the best seeding effect, and the seeding effect is negative when the salt particle size is less than 10 μm. For salt particles sized 80 μm, the best seeding effect, with corresponding visibility of 380 m, can be achieved when the seeding amount is 30 g m~(-2). 相似文献