全文获取类型
收费全文 | 14500篇 |
免费 | 1616篇 |
国内免费 | 1555篇 |
专业分类
测绘学 | 699篇 |
大气科学 | 2015篇 |
地球物理 | 4214篇 |
地质学 | 5921篇 |
海洋学 | 1356篇 |
天文学 | 1446篇 |
综合类 | 706篇 |
自然地理 | 1314篇 |
出版年
2024年 | 50篇 |
2023年 | 178篇 |
2022年 | 373篇 |
2021年 | 523篇 |
2020年 | 468篇 |
2019年 | 439篇 |
2018年 | 864篇 |
2017年 | 716篇 |
2016年 | 830篇 |
2015年 | 639篇 |
2014年 | 779篇 |
2013年 | 878篇 |
2012年 | 730篇 |
2011年 | 811篇 |
2010年 | 768篇 |
2009年 | 756篇 |
2008年 | 686篇 |
2007年 | 581篇 |
2006年 | 502篇 |
2005年 | 406篇 |
2004年 | 398篇 |
2003年 | 354篇 |
2002年 | 330篇 |
2001年 | 311篇 |
2000年 | 271篇 |
1999年 | 366篇 |
1998年 | 403篇 |
1997年 | 352篇 |
1996年 | 345篇 |
1995年 | 264篇 |
1994年 | 240篇 |
1993年 | 193篇 |
1992年 | 183篇 |
1991年 | 151篇 |
1990年 | 176篇 |
1989年 | 127篇 |
1988年 | 104篇 |
1987年 | 108篇 |
1986年 | 88篇 |
1985年 | 78篇 |
1984年 | 78篇 |
1983年 | 55篇 |
1982年 | 63篇 |
1981年 | 67篇 |
1980年 | 54篇 |
1979年 | 42篇 |
1977年 | 41篇 |
1976年 | 40篇 |
1974年 | 42篇 |
1971年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
TYSC-3Q与PSJ-2型数字测井仪是目前煤田测井中常用的二种测井仪器,在使用过程中难免发生诸如测井控制故障、声速探管故障、密度三侧向探管故障、井温、井液电阻率探管故障、电法面板故障、数字测井面板故障、电测井故障等常见故障类型。通过对各类故障因素进行剖析,指出了故障易发生的部位,并详细的介绍了检查的方法及故障的排除步骤。 相似文献
104.
Any calculation of seismic wave propagation comprising the seismic source, the travel path, and the receiver site in a single finite-difference (FD) model requires a considerable amount of computer time and memory. Moreover, the methods currently available for including point sources in the 2D FD calculations are far-field approximations only. Therefore we have developed a new hybrid method for treating the seismic wave fields at localized 2D near-surface structures embedded in a 1D background medium, and excited by a point source. The source radiation and propagation in the background model is solved by the discrete-wave number (DW) method, while the propagation in the local 2D structure is calculated by the FD method. The coupling between the two sets of calculations is performed on a rectangular excitation box surrounding the local structure. We show the usefulness of the method in ground-motion studies where both near-field source effects and local site effects are important. Technical problems connected with the inconsistency between the 3D source radiation and the 2D FD calculation are minor for the relatively distant in-plane point explosive sources, but are more serious for the in-plane dislocation sources. 相似文献
105.
Carbonyl products have been identified and their formation yields measured in experiments involving the gas phase reaction of ozone with 1,1-disubstituted alkenes at ambient T and p=1 atm. of air. Sufficient cyclohexane was added to scavenge the hydroxyl radical in order to minimize OH-alkene and OH-carbonyl reactions. Formation yields (carbonyl formed/ozone reacted) of primary carbonyls were close to the value of 1.0 that is consistent with the mechanism: O3+R1R2C=CH2 (HCHO+R1R2COO)+(1–)(R1COR2+H2COO) where formaldehyde and the ketone R1 COR2 are the primary carbonyls and R1R2COO and H2COO are the corresponding biradicals. Measured values of were 0.58–0.82 and indicate modest preferential formation of formaldehyde and the disubstituted biradical as compared to the ketone and the biradical H2COO. Carbonyls other than the primary carbonyls were identified. Their formation is discussed in terms of subsequent reactions of the disubstituted biradicals R1R2COO. Similarities and differences between disubstituted and monosubstituted biradicals are outlined. 相似文献
106.
107.
Summary A coalification data set from the first seam of the Rosice-Oslavany coal district in the Boskovice furrow was used to estimate the temperature gradient prevailing within the furrow during Autunian sedimentation. An appreciable scatter of the data reflects the complicated history of the sedimentary region. The northern part of the district displays a higher degree of coalification. The results of the evaluation suggest that the region ceased to subside in the upper Autunian, and that the extent of the post-Autunian erosion does not exceed 500 metres. This version of the burial history, which is consistent with geological data, yields a temperature paleogradient of 76 mK/m for the northern part and of 72 mK/m for the southern part of the district. The gradients estimated are higher than those prevailing during the Carboniferous sedimentation in the Central Bohemian Basin (45 – 53 mK/m), lower than values found for the Ostrava Formation in the Upper Silesian Basin during its Namurian A sedimentation (about 95 mK/m), but comparable with values evaluated for the Karviná Formation of the same basin deposited during the Namurian B - C and Westphalian A (60 – 77 mK/m).Dedicated to the Memory of Professor Karel P 相似文献
108.
The behavioural approach in human geography accentuates the view of quality of the environment through man and his value orientations. The quality of environment from the point of view of human experience raises behavioural-geographical questions that are the core of the presented topic. Aspects of environmental imaginations and sensations as well as human value system are presented as variables affecting the structure of the perceived environment and human spatial behaviour. In this context, the authors present results of two behavioural studies that correspond to new models of man and environment from the viewpoint of a behavioural approach. The suggested humanistic approach in behavioural geography emphasizes above all the emotional aspect of the relationship between man and environment, which through environmental values, spatial sensations, and meanings, leads to human spatial behaviour. 相似文献
109.
Weak and strong ground motions were numerically predicted for three stations of the Ashigara Valley test site. The prediction was based on the records from a rock-outcrop station, one weak-motion record from a surface-sediments station, and the standard geotechnical model. The data were provided by the Japanese Working Group on the Effects of Surface Geology as a part of an international experiment. The finite-difference method for SH waves in a 2-D linear viscoelastic medium (a causalQ model) was employed.Comparison with the real records shows that at two stations the predictions fit better than at the third one. Strangely, the two better predictions were for stations situated at larger distances from the reference rock station (one station was on the surface, the other in a borehole). The strong ground motion (the peak acceleration of about 200 cm s–2) was not predicted qualitatively worse than the weak motion (8 cm s–2). A less sophisticated second prediction (not submitted during the experiment), in which we did not attempt to fit the available weak-motion record at the sedimentary station, agrees with the reality significantly better. 相似文献
110.
Stanislav Horník 《GeoJournal》1993,31(4):379-382
Some results of biogeographic research on meadows in the Dyje-Svratka basin in the Czech Republic. The paper shows one example of biogeographic inventory of natural ecosystems in an unflooded meadow in the Dyje-Svratka basin. It is part of the complex physio-geographic research of the Geographic Department of the Masaryk University in Brno aimed at gaining a basis for territorial interpretation of ecological regularities and territorial application of general ecological optimizing principles. A segment of biocenosis of Ulmi-fraxineta carpini has been analyzed (Zlatník 1956).The endeavour of Czech geographers to study geosystems of various dimensions completely gets in the limelight. In question is the understanding of mutual relationship of components of geosystems based on the exchange of mass and energy. There are two ways of studying them: spatial relations or approaches concentrated on processes. In contrast to the above unilateral concept, the endeavour to make the approaches compatible appears rarely. This complex view is made possible by geobiocenologically taken biogeography in papers of Zlatník and Rauer, their students and successors. This paper shows only one example of the results of biogeographic stock-taking of meadows in the Dyje-Svratka basin, indicating relations of eco- and geosystems which confirm the necessity of ecological orientation of the present biogeography and its potential contribution to ecology. 相似文献