全文获取类型
收费全文 | 19450篇 |
免费 | 4022篇 |
国内免费 | 5075篇 |
专业分类
测绘学 | 1836篇 |
大气科学 | 2096篇 |
地球物理 | 4732篇 |
地质学 | 12848篇 |
海洋学 | 2159篇 |
天文学 | 246篇 |
综合类 | 1575篇 |
自然地理 | 3055篇 |
出版年
2024年 | 63篇 |
2023年 | 253篇 |
2022年 | 574篇 |
2021年 | 765篇 |
2020年 | 763篇 |
2019年 | 1061篇 |
2018年 | 780篇 |
2017年 | 904篇 |
2016年 | 985篇 |
2015年 | 1067篇 |
2014年 | 1431篇 |
2013年 | 1288篇 |
2012年 | 1345篇 |
2011年 | 1464篇 |
2010年 | 1291篇 |
2009年 | 1321篇 |
2008年 | 1261篇 |
2007年 | 1410篇 |
2006年 | 1371篇 |
2005年 | 1153篇 |
2004年 | 1077篇 |
2003年 | 939篇 |
2002年 | 782篇 |
2001年 | 671篇 |
2000年 | 668篇 |
1999年 | 618篇 |
1998年 | 571篇 |
1997年 | 493篇 |
1996年 | 398篇 |
1995年 | 347篇 |
1994年 | 324篇 |
1993年 | 241篇 |
1992年 | 232篇 |
1991年 | 140篇 |
1990年 | 115篇 |
1989年 | 132篇 |
1988年 | 76篇 |
1987年 | 61篇 |
1986年 | 38篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1954年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
31.
本文简介海南省1:5万坝王岭、猴狝岭幅区域地质调查的地球化学简单分段法在地层划分中的应用。根据对下古生界变质岩与白垩系红层两条地层实测剖面的地球化学资料整理,用简单分段法进行划分、其效果较好。它的地球化学组分基本能反映原始沉积物的特点和其沉积环境,且与岩石地层的划分相互印证。 相似文献
32.
张赤军 《大地测量与地球动力学》2002,22(4):31-34
介绍当今确定天文大地垂偏差的新仪器-CCD自动天体测量仪和确定两点间高程异常差的新方法,该方法用单极坐标代替繁琐的双极坐标进行计算,讨论了天文重力水准的误差及垂线偏差非线性影响等问题,估计在不久的将来,用这一手段施测山区似大地水准面的精度可望达到厘米级。 相似文献
33.
张晓晖 《成都信息工程学院学报》2002,17(3):166-169
通过对影响能见度的因素的分析,提出了一种能见度预报方法-综合分析法,极大地提高了能见度的预报准确率。 相似文献
34.
N. H. S. OLIVER I. CARTWRIGHT V. J. WALL S. D. GOLDING 《Journal of Metamorphic Geology》1993,11(5):705-720
Abstract Large calcite veins and pods in the Proterozoic Corella Formation of the Mount Isa Inlier provide evidence for kilometre-scale fluid transport during amphibolite facies metamorphism. These 10- to 100-m-scale podiform veins and their surrounding alteration zones have similar oxygen and carbon isotopic ratios throughout the 200 × 10-km Mary Kathleen Fold Belt, despite the isotopic heterogeneity of the surrounding wallrocks. The fluids that formed the pods and veins were not in isotopic equilibrium with the immediately adjacent rocks. The pods have δ13Ccalcite values of –2 to –7% and δ18Ocalcite values of 10.5 to 12.5%. Away from the pods, metadolerite wallrocks have δ18Owhole-rock values of 3.5 to 7%. and unaltered banded calc-silicate and marble wallrocks have δ13Ccalcite of –1.6 to –0.6%, and δ18Ocalcite of 18 to 21%. In the alteration zones adjacent to the pods, the δ18O values of both metadolerite and calc-silicate rocks approach those of the pods. Large calcite pods hosted entirely in calc-silicates show little difference in isotopic composition from pods hosted entirely in metadolerite. Thus, 100- to 500-m-scale isotopic exchange with the surrounding metadolerites and calc-silicates does not explain the observation that the δ18O values of the pods are intermediate between these two rock types. Pods hosted in felsic metavolcanics and metasiltstones are also isotopically indistinguishable from those hosted in the dominant metadolerites and calc-silicates. These data suggest the veins are the product of infiltration of isotopically homogeneous fluids that were not derived from within the Corella Formation at the presently exposed crustal level, although some of the spread in the data may be due to a relatively small contribution from devolatilization reactions in the calc-silicates, or thermal fluctuations attending deformation and metamorphism. The overall L-shaped trend of the data on plots of δ13C vs. δ18O is most consistent with mixing of large volumes of externally derived fluids with small volumes of locally derived fluid produced by devolatilization of calc-silicate rocks. Localization of the vein systems in dilatant sites around metadolerite/calc-silicate boundaries indicates a strong structural control on fluid flow, and the stable isotope data suggest fluid migration must have occurred at scales greater than at least 1 km. The ultimate source for the external fluid is uncertain, but is probably fluid released from crystallizing melts derived from the lower crust or upper mantle. Intrusion of magmas below the exposed crustal level would also explain the high geothermal gradient calculated for the regional metamorphism. 相似文献
35.
In this paper a slightly different approach is proposed for the process of determining the functions S
m
and H
m
* of the algorithm of the canonical version of Hori method. This process will be referred to as integration theory of the mth order equation of the method. It will be shown that the ordinary differential equation with an auxiliary parameter t
* as independent variable, introduced through Hori auxiliary system, can be replaced by a partial differential equation in the time t. In this way, the mth order equation of the algorithm assumes a form very similar to the one of other perturbation methods. In virtue of this new approach of the integration theory for Hori method, Lagrange's variational equations introduced by Sessin are revised. As an example, the Duffing equation is solved through this new approach. 相似文献
36.
用电测深研究地电断面、寻找隐伏多金属矿体时,以往采用ρ_s(或η_s)等值线断面图进行地质推断解释,因受浅源信号的干扰,效果差。本文提出了采用ρ_s(或η_s)差值法,能排除浅源干扰信号,反映出地电断面的相对变化,突出了深部微弱信息,取得了较好的地质解释效果。 相似文献
37.
38.
Aimed at promoting regional coalitions and expanding the approach to economic links, this paper puts forward some new concepts
such as link intensity and receiving coefficient, expounds the indexes of quantitative analysis of economic links and establishes
the quantitative-analysis model of economic links. With help of the model, this paper calculates the values of the link intensities
between Su-Xi-Chang (Suzhou-Wuxi-Changzhou) region and Shanghai, and analyzes the regional difference of the economic links. 相似文献
39.
Geoff Kite 《水文研究》1993,7(2):227-233
Using current meters to estimate flows in fast mountain streams is difficult and inaccurate. The salt dilution method offers an easier and more accurate alternative. The method has been used for many years but is time consuming and messy because of the need to mix chemical solutions and measure chemical concentrations in the field. A computer program has been developed which uses a laptop computer to calculate the mixing length and the mass of salt needed. The program controls the conductivity measurements and calculates the streamflow directly in the field. The development of this program is described and examples are presented of the application of the method in the Rocky Mountains of Alberta and British Columbia. 相似文献
40.
为了给公路设计部门提供选线依据,运用瞬变电磁法在山西境内的某两条高速公路隧道工程设计线路段上进行探测,以查明下覆不良地质构造的发育情况.通过对瞬变电磁法的探测能力进行理论上的讨论,对不同地电断面情况下的异常体电磁响应的定性分析,得出用瞬变电磁法探测不良地质体的可行性结论.经过资料处理,查出不良地质构造赋存的位置,解释结果与钻探资料完全吻合. 相似文献