全文获取类型
收费全文 | 26588篇 |
免费 | 5020篇 |
国内免费 | 7441篇 |
专业分类
测绘学 | 4384篇 |
大气科学 | 5423篇 |
地球物理 | 5866篇 |
地质学 | 11191篇 |
海洋学 | 5907篇 |
天文学 | 242篇 |
综合类 | 2234篇 |
自然地理 | 3802篇 |
出版年
2024年 | 68篇 |
2023年 | 343篇 |
2022年 | 933篇 |
2021年 | 1121篇 |
2020年 | 1291篇 |
2019年 | 1345篇 |
2018年 | 1286篇 |
2017年 | 1427篇 |
2016年 | 1514篇 |
2015年 | 1698篇 |
2014年 | 1778篇 |
2013年 | 2066篇 |
2012年 | 1841篇 |
2011年 | 1879篇 |
2010年 | 1478篇 |
2009年 | 1710篇 |
2008年 | 1697篇 |
2007年 | 1825篇 |
2006年 | 1724篇 |
2005年 | 1547篇 |
2004年 | 1378篇 |
2003年 | 1202篇 |
2002年 | 1096篇 |
2001年 | 942篇 |
2000年 | 867篇 |
1999年 | 788篇 |
1998年 | 724篇 |
1997年 | 628篇 |
1996年 | 520篇 |
1995年 | 500篇 |
1994年 | 455篇 |
1993年 | 375篇 |
1992年 | 231篇 |
1991年 | 198篇 |
1990年 | 132篇 |
1989年 | 103篇 |
1988年 | 101篇 |
1987年 | 59篇 |
1986年 | 29篇 |
1985年 | 42篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1954年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The hydrocarbon generation mechanism and the three-stage type model of hydrocarbon generation for carbonate source rocks 总被引:1,自引:0,他引:1
The diagenetic mechanism and process of carbonate rocks, which is different to that of clastic rocks, decides the existence
of different existing state organic matters in carbonate rocks. This has been verified by both the microscopic observation
of organic petrology and the analysis of organic geochemistry of many samples. Based on the hydrous pyrolysis simulation experiment
of the low-mature carbonate rocks, the contrasting study on the yield and their geochemistry characteristics of different
existing state soluble organic matters of a series of various maturity samples shows that the different existing state organic
matters make different contributions to hydrocarbon generation during every evolution state. So that, the hydrocarbon generation
process of carbonate rocks can be summarized as the following three stages: the first is the direct degradation of biogenic
bitumen macromolecules during the immature stage, the second is the thermal degradation of a large amount of kerogen at the
mature stage, the last stage is the expulsion or release of inclusion organic matter owing to the increased thermal expansion
pressure during the high evolution stage.
Part of achievements of the Eighth Five-Year National Science-Technology Key-Task Project “85-102-02-07”. 相似文献
992.
A methodology for improving geopotential models has been developed. Theoretical relations have been derived converting coefficients in harmonic expansions for radial distortions due to geopotential models into geopotential Stokes coefficients. Terms of the order of 10
–10
in magnitude have been retained. 相似文献
993.
Based on characteristics and trap types of gas reservoirs in large and medium gas fields in China, 4 gas reservoir models
have been established:(i) structural trap gas reservoir model I, formed earlier than or simutaneously with generating of gases;
(ii) structural trap gas reservoir model II, formed later than generating of gases; (iii) fossil weathered residuum gas reservoir
model; and (iV) mud diapir abnormal temperature and pressure gas reservoir model. Distribution patterns of large-medium gas
fields are described with the concept of “sealed compartment”. It is concluded that the inner-compartment area, marginal area
of the compartment and the areas between two overlapped sealed compartments are the most favourable areas for discovering
large-medium gas fields.
Project supported by the “85–102” Chinese National Key Science and Technology Project. 相似文献
994.
Evolution model and formation mechanism of bio-thermocatalytic transitional zone gas 总被引:1,自引:0,他引:1
As a new genetic type of natural gas exploration area, the bio-thermocatalytic transitional zone gas (BTTZG) has been highly
stressed by geologists both at home and abroad. Systematic study on the generation mechanism of hydrocarbon at the transitional
zone is presented. Based on simulating experiments and geochemistry analysis of the source rock with lower evolution, a hydrocarbon-forming
model at the transitional zone has been established. The mechanism is proposed that under the condition of low temperature
and pressure combining with extremely active structural stress and clay mineral catalysis, BTTZG is formed by de-group of
soluble organic matter and polarized compositions through orthocarbon ion as well as by condensation polymerization of aromatic
ring-rich insoluble organic matter. This mechanism controls the formation of BTTZG, and furthermore, BTTZG is the product
of superimposition and interaction of all the factors mentioned above. 相似文献
995.
In this contribution we discuss the geometry-free GPS single baseline model and show how the least-squares ambiguities are affected by changes in the stochastic model. We particularly pay attention to the effect of time correlation, cross-correlation and satellite elevation dependence. We also differentiate between the impact on the location of the ambiguity search space and the impact on the size and shape of the search space. The analysis is carried out for both the model in which the ionospheric delays are assumed absent, and for the model in which they are assumed present. The former model is applicable to short baselines only. 相似文献
996.
Fluid inclusion leachates obtained from vug and vein quartz samples from an Archean (3.23 Ga) Fe-oxide hydrothermal deposit in the west-central part of the Barberton greenstone belt, South Africa, were analyzed by ion chromatography for chloride, bromide, and iodide. The deposit, known as the ironstone pods, formed by seafloor hydrothermal activity and fluid discharge. Quartz is dominated by type I liquid-vapor, aqueous inclusions with a bimodal salinity distribution (0–0.25 MCl− and 0.9–1.8 MCl−). Bulk analytical salinities range from 0.45 to 0.99 MCl− represent averages of type I inclusions. Bulk fluid inclusion bromide and iodide concentrations are 1.44–3.32 mM and 0.01–0.12 mM, respectively. For comparison, modern seawater has halogen contents of 590 mM chloride, 0.9 mM bromide, and 0.5 μM total iodine. In the fluids from the ironstone pods, bromide and iodide are enriched relative to chloride, when compared with modern seawater.Approximate Br−Cl− and I−Cl− ratios of 3.2 Ga Barberton seawater are 2.5 × 10−3 and 40 × 10−6, respectively. Dispersion to higher values was caused principally by reaction with organic sediments whose trends are similar to those seen for modern vent fluids at unsedimented and sedimented ridges, relative to modern seawater. These halide ratios are greater than those of modern seawater, suggesting a change in the halide ratios of seawater over geological time. The analytical data are consistent with a model in which marine organic sedimentation has fractionated bromine and iodine out of seawater relative to chloride, thereby causing the halide ratios of seawater to decrease from high early and mid-Archean values towards their present day values. 相似文献
997.
998.
999.
在计算覆盖整个黄晔裂谷200口人工井(包括少部分探井)沉降量的基础上,总结本区二种基本沉降曲线模式。统计出热沉降(St)与初始沉降(Si)之比为0.6,依此为约束条件与大陆岩石圈伸展的地球动力学正演模式进行对比,与简单剪切模式预测的热沉降与初始沉降之比值及几何效应更接近。进一步证实黄骅裂谷以简单剪切机制形成的地球动力学模式更合理,这与著名的以纯剪模式形成的北海伸展盆地不同 相似文献
1000.