全文获取类型
收费全文 | 2810篇 |
免费 | 474篇 |
国内免费 | 622篇 |
专业分类
测绘学 | 594篇 |
大气科学 | 305篇 |
地球物理 | 759篇 |
地质学 | 1400篇 |
海洋学 | 273篇 |
天文学 | 71篇 |
综合类 | 298篇 |
自然地理 | 206篇 |
出版年
2024年 | 24篇 |
2023年 | 44篇 |
2022年 | 90篇 |
2021年 | 109篇 |
2020年 | 99篇 |
2019年 | 143篇 |
2018年 | 111篇 |
2017年 | 129篇 |
2016年 | 152篇 |
2015年 | 162篇 |
2014年 | 190篇 |
2013年 | 158篇 |
2012年 | 200篇 |
2011年 | 185篇 |
2010年 | 171篇 |
2009年 | 181篇 |
2008年 | 157篇 |
2007年 | 178篇 |
2006年 | 160篇 |
2005年 | 141篇 |
2004年 | 128篇 |
2003年 | 104篇 |
2002年 | 108篇 |
2001年 | 76篇 |
2000年 | 97篇 |
1999年 | 95篇 |
1998年 | 55篇 |
1997年 | 54篇 |
1996年 | 61篇 |
1995年 | 60篇 |
1994年 | 58篇 |
1993年 | 47篇 |
1992年 | 40篇 |
1991年 | 34篇 |
1990年 | 20篇 |
1989年 | 20篇 |
1988年 | 22篇 |
1987年 | 20篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有3906条查询结果,搜索用时 15 毫秒
951.
论述了东北晚中生代断陷盆了J3-K1储层的孔隙组合特征及砂岩储层的孔隙结构类型,砂岩储层的孔隙组合为5种类型,正常粒间孔及缩小粒间孔组合;正常粒间孔及粒间扩大溶孔组合;粒间扩大溶孔及铸模孔组合;粒内溶孔及胶结物内溶孔组合,微孔和裂缝与少量原生粒间孔及残余缩小溶孔组合;特殊储层的孔隙组合因储层类型的不同而异,砾岩储层以砾间孔隙+砾间填隙物孔隙为主,安山岩储层为气孔+裂缝或气孔+裂缝+砾(粒)间空隙。 相似文献
952.
P. M. Bakker 《Geophysical Journal International》1998,134(2):515-518
In isotropic ray tracing, the ray approximation to the wavefield undergoes a phase shift when the ray crosses a caustic. The cumulative number of such phase shifts along a ray is usually called the KMAH index. The sign of these phase shifts is prescribed by the sign of the angular frequency in combination with the sign convention used for the Fourier transformation. In isotropic media the KMAH index always increases by one or by two, depending on the type of caustic crossed. For (quasi-)shear waves in anisotropic media the KMAH index may decrease. This is the case if the associated slowness sheet is locally concave in one or two of its principal directions of curvature. 相似文献
953.
非地震找油是对除地震勘探方法以外的物化探找油方法的总称。本文主要综述并探讨了在地质条件比较特殊的地区,通过对多种方法实现最佳组合,提高找油效果等问题。 相似文献
954.
太原市东山矿区岩溶地下水排供结合研究 总被引:1,自引:0,他引:1
太原市为华北地区严重缺水城市之一,而与此紧紧相连的太原市东山煤矿,丰富的岩溶地下水造成750下山煤层无法开采。为了解决东山煤矿12873万t煤炭资源带压开采问题及缓解太原市供水紧张的局面。笔者从分析东山岩溶水系统水文地质条件入手,对井田内水文地质条件进行了定量研究,认为将东山煤矿的疏干降压与太原市的供水结合起来其利大于弊。 相似文献
955.
矿井水的资源化与环境保护——以焦作矿区典型地段为例 总被引:1,自引:0,他引:1
针对我国煤矿区目前普遍存在的排、供矛盾和环境地质问题,本文首次提出了矿区排水、供水、环境保护三位一体优化结合的经济-水力管理模型。该模型通过布设地面矿坑抽水孔和奥灰(奥陶系灰岩)浅排孔等地上应急取水建筑物,增强了结合系统整体抗御突发性水害的能力,较好地解决了供水水源安全、稳定问题。同时,三位一体结合模型较为圆满地处理了长期以来从地质勘探到评价管理各个不同阶段,排、供和环保3个不同部门各立门户的封闭局面,避免了大量的重复投资,提高了评价、管理、决策的整体水平。本文以焦作矿区典型地段为研究实例。 相似文献
956.
麻粒岩相条件下石榴黑云斜长片麻岩实验结果表明,含水矿物黑云母(Bi)脱水熔融、长英质矿物部分熔融的性质主要受控于温度条件;而矿物相转变不仅受控于温压条件,而且与脱水熔融、部分熔融存在密切成因联系。依据Bi脱水熔融性质和石榴石(Gi)转变反应特征,可划分以下三个阶段:(1)当温度在700℃时,Bi转变为钛铁矿(Ilm)+磁铁矿(Mt)+H_2O,Gt转变为Mt,(2)当温度在730—760℃,Bi脱水熔融为富K_2O熔体(Melt)+Ilm+Mt,Gt转变为紫苏辉石(Hy)+堇青石(Crd);(3)当温度大于790℃时,Bi脱水熔融为Melt+Hy+Ilm+Mt+H_2O,Gt则转变为Hy+尖晶石(Sp)+Crd组合。熔体比例和熔体演化特征除受温压条件控制外,与长英质矿物部分熔融程度和脱水熔融性质关系密切。实验结果显示,在麻粒岩相变质作用以及与其相伴随的重熔作用(或区域性混合岩化作用)过程中,不仅存在传统的固相+固相(或流体相)的反应和脱水熔融反应,而且存在熔体参与的变质反应(即:未熔矿物与熔体之间的反应)。该项实验对深入探讨麻粒岩相矿物演化的成因机制及其动力学意义提供可靠的实验依据。 相似文献
957.
TherelationbetweentheresponsespectrumandthephasediferencespectrumFENG-XINZHAO(赵凤新)andYU-XIANHU(胡聿贤)InstituteofGeophysics,Sta... 相似文献
958.
S. Sørensen H. Falbe-Hansen M. Mangoni J. Hjorth N. R. Jensen 《Journal of Atmospheric Chemistry》1996,24(3):299-315
Products and mechanisms have been investigated for the reactions between dimethylsulfide (DMS) and dimethylsulfoxide (DMSO) and the hydroxyl radical (OH) in the presence of NOx. All of the experiments were performed in a 480 L reaction chamber, applying Fourier transform infrared spectroscopy (FT-IR) and ion chromatography as the analytical techniques.In addition to the sulfur containing products that are known to be produced from the gas phase reaction between DMS and OH (SO2, dimethylsulfone, methylsulfonyl peroxynitrate, methanesulfonic acid, H2SO4), DMSO and methanesulfinic acid (CH3S(O)OH) were also observed as products. Only SO2, DMSO2 and methylsulfonyl peroxynitrate were found as sulfur containing products in the reaction between DMSO and OH. Based on these new results we propose a mechanism for the atmospheric oxidation of DMS and DMSO by OH radical. 相似文献
959.
960.
We use a simple model of the formation, growth, coalescence and migration of veins of basaltic melt generated by partial melting in chondritic asteroids to deduce the sizes of, and pressures within, the fluid-filled dikes reaching the surfaces of such bodies. The gas contents ( 1000 ppm of mainly CO and N2) of the asteroids were high enough that bubbles of free gas trapped in the melt veins gave the basaltic melts significant buoyancy; expansion of these gases as a dike opened to the vacuum at the surface led to fragmentation of the melts into liquid droplets which were transported upwards by the accelerating gases to the surface. The sizes of these droplets and, hence, of the pyroclastic glass beads into which they cooled, are calculated to lie in the range 30 μm to 4 mm; this range is essentially independent of the size or gas content of the asteroid parent and only weakly dependent on the internal pressure of the erupting fluid. The fate of the pyroclasts, however, does depend on all of these factors. At very low internal pressures, significant separation of the gas and liquid in a rising dike may take place and not all of the liquid will be expelled from the dike when it opens to the surface. For relatively large ( 100 km radius) asteroids with relatively low ( 300 ppm) gas contents, the larger clasts are too heavy to be lifted from the level at which magma fragmentation takes place by the gas flow and so would also remain behind to form basaltic veins. The apparent absence of basaltic veins in meteorites then implies both that internal pressures in near-surface dikes were generally greater than 0.3 MPa and that low gas contents were not common. Finally, as long as pyroclasts are lofted from the magma fragmentation level, they will be accelerated to at least 90% of the final gas speed. If this speed exceeds the escape speed from the asteroid (as happens readily for high gas contents and small asteroids), the pyroclasts will be expelled into space and lost from the meteorite record. Otherwise (low gas contents or large asteroids), they will eventually fall back to be incorporated into the surface regolith, modifying the chemical and physical properties of meteorites subsequently derived from it. 相似文献