全文获取类型
收费全文 | 1968篇 |
免费 | 74篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 86篇 |
大气科学 | 152篇 |
地球物理 | 706篇 |
地质学 | 681篇 |
海洋学 | 154篇 |
天文学 | 137篇 |
综合类 | 11篇 |
自然地理 | 138篇 |
出版年
2022年 | 12篇 |
2021年 | 25篇 |
2020年 | 49篇 |
2019年 | 34篇 |
2018年 | 61篇 |
2017年 | 51篇 |
2016年 | 80篇 |
2015年 | 71篇 |
2014年 | 69篇 |
2013年 | 115篇 |
2012年 | 89篇 |
2011年 | 117篇 |
2010年 | 101篇 |
2009年 | 123篇 |
2008年 | 100篇 |
2007年 | 71篇 |
2006年 | 68篇 |
2005年 | 45篇 |
2004年 | 42篇 |
2003年 | 51篇 |
2002年 | 31篇 |
2001年 | 51篇 |
2000年 | 31篇 |
1999年 | 36篇 |
1998年 | 30篇 |
1997年 | 29篇 |
1996年 | 23篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 18篇 |
1990年 | 18篇 |
1989年 | 16篇 |
1988年 | 19篇 |
1987年 | 12篇 |
1986年 | 21篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 26篇 |
1982年 | 21篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 13篇 |
1975年 | 17篇 |
1973年 | 14篇 |
1972年 | 10篇 |
1969年 | 9篇 |
排序方式: 共有2065条查询结果,搜索用时 15 毫秒
21.
22.
Identification of Greigite in the Pliocene Sediments of Qinghai Lake and Its Geological Significance
正Objective The Qinghai Lake in North China is the largest interior plateau lake in Central Asia,and is sensitive to climate change and the environmental effects of Tibetan Plateau uplift.An almost continuous 626 m long sediment core was drilled in an in-filled part of the southern lake basin in the Scientific Drilling at Qinghai Lake.Previous 相似文献
23.
24.
Rene PUTISKA Marian MARSCHALKO Isik YILMAZ Dominik NIEMIEC CHENG Xianfeng Ivan DOSTAL Jan KUBAC 《《地质学报》英文版》2021,95(5):1763-1770
This article presents a research study of complex limestone karst engineering-geological conditions in the municipality Valaská near Banská Bystrica in Slovakia. The aim of the study is to demonstrate the impossibility of spatial identification of cave spaces using surface geophysical methods due to the specific engineering-geological conditions of a thick surface layer of anthropogenic fill containing highly heterogeneous anthropogenic material. Its maximum thickness is 3 m. Another specificific condition of the study area is its location in the built-up area, due to which the applicability of geophysical methods was limited. The article contains methodological recommendations to be used in analogous geological conditions with karst structures topped with anthropogenic fill, which complicates the identification of cave spaces. The recommended solution herein is the identification of the cave system using underground mapping of the karst and its projection onto the surface for which surface geophysical methods have been combined. 相似文献
25.
Enteromorpha prolifera (Scheldt Estuary) and E. linza (Thermaikos Gulf) were incubated at three salinities with 100 and 200microgL(-1)Cd and Zn. The objective was to measure effects of Cd, Zn and nitrogen (N) status on the pools of metal-binding non-protein thiols: glutathione and phytochelatins, (gamma-glutamyl-cysteinyl)(n)-glycine (PC). In E. linza, ammonium pools were higher, but amino acid pools, total N and protein contents were lower than in E. prolifera. Reduced glutathione (GSH) pools were positively correlated with free glutamate and protein contents. In E. linza GSH pools increased and the ratio of reduced to oxidized glutathione (GSH:(GSH+0.5GSSG)), an indicator of oxidative stress, decreased with Cd contents, indicating Cd-induced glutathione oxidation. Total glutathione pools (reduced plus oxidized) ranged from 16nmolSgdwt(-1) in controls (at 0.5micromolCdgdwt(-1)) to 179nmolSgdwt(-1) (at 1.9micromolCdgdwt(-1)) at the highest cadmium dosage. Cadmium stimulated PC synthesis in E. prolifera which suggests that in N-rich algae, glutathione pools were high enough for PC synthesis. In both species GSH and protein increased with Zn contents, whereas GSH:(GSH+0.5GSSG) decreased, which would indicate Zn-induced oxidative stress; in E. linza, at the highest salinity the glutathione redox ratio decreased from 0.61 (at 2.9micromolZngdwt(-1)) to 0.26 (at 4.9nmolSgdwt(-1)) (at 0.5molCdgdwt(-1)). PCs were not synthesized in response to Zn, which may have resulted in Zn-induced GSH oxidation. The presence of both oxidative effects (Cd, Zn) and detoxification (Cd) could be identified by observing the responses of glutathione and PC pools to metal stress. 相似文献
26.
Natural Resources Research - Catastrophic cases of methane explosion during exploratory drilling within the Be?chatów ortholignite deposit have led to testing for methane in other Polish... 相似文献
27.
Pham Thi Tuyet Nhung Do Thi Hoai Pham Tuan-Anh Thibaut Le Bertre Pierre Darriulat Pham Ngoc Diep Nguyen Thi Phuong Nguyen Thi Thao Jan Martin Winters 《天文和天体物理学研究(英文版)》2019,(3):97-110
Atacama Large Millimetre/sub-millimetre Array(ALMA) observations of CO(1–0) and CO(2–1) emissions from the circumstellar envelope of the asymptotic giant branch(AGB) star EP Aqr have been made with four times better spatial resolution than previously available. They are analysed with emphasis on the de-projection in space of the effective emissivity and flux of matter using as input a prescribed configuration of the velocity field, assumed to be radial. The data are found to display an intrinsic axisymmetry with respect to an axis making a small angle with respect to the line of sight. A broad range of wind configurations, from prolate(bipolar) to oblate(equatorial) has been studied and found to be accompanied by significant equatorial emission. Qualitatively, the effective emissivity is enhanced near the equator to produce the central narrow component observed in the Doppler velocity spectra and its dependence on star latitude generally follows that of the wind velocity with the exception of an omni-present depression near the poles. In particular, large equatorial expansion velocities produce a flared disc or a ring of effective emissivity and mass loss. The effect on the determination of the orientation of the star axis of radial velocity gradients, and possibly competing rotation and expansion in the equatorial disc, is discussed. In general,the flux of matter is found to reach a broad maximum at distances of the order of 500 AU from the star.Arguments are given that may be used to favour one wind velocity distribution over another. As a result of the improved quality of the data, a deeper understanding of the constraints imposed on morphology and kinematics has been obtained. 相似文献
28.
The application of low-cost L1 GPS receivers integrated with micro-electro-mechanical system (MEMS) inertial measurement units
(IMU) allows the continuous observation of position, velocity and orientation which opens new possibilities for comparison
of athletes’ performance throughout a racecourse. In this paper, we compare loosely and closely coupled integration strategies
under realistic racing scenarios when GPS is partially or completely masked. The study reveals that both integration approaches
have a similar performance when the satellite constellation is completed or the outages are short. However, for less than
four satellites, the closely coupled strategy clearly outperforms the loosely coupled approach. The second part of the paper
is devoted to the important problem of system initialization, because the conventional GPS/IMU alignment methods are no longer
applicable when using MEMS-IMU. We introduce a modified coarse alignment method and a quaternion estimation method for the
computation of the initial orientation. Simulations and practical experiments reveal that both methods are numerically stable
for any initial orientation of the sensors with the error characteristics of MEMS-IMUs. Throughout the paper, our findings
are supported by racing experiments with references provided in both, the measurement and the navigation domains. 相似文献
29.
Osman Turan Zafer Ayaz Seref Aksu Jan Kanar Antoni Bednarek 《Ocean Engineering》2008,35(13):1339-1356
The study investigates the experimental and numerical analysis of the occurrence of auto-parametric rolling for large, high-speed pod-driven ships in waves. Considering unique design and performance targets, the aim here is to exploit susceptibility to auto-parametric rolling behaviour and to identify probable design and operational precautions. In order to achieve this aim, an existing non-linear time-domain software to simulate capsizing and other critical manoeuvring behaviours of slow- to medium-speed conventional and podded ships in waves is being enhanced for fast pod-driven vessels and then compared against the dedicated model test conducted in long-crested regular and random waves for a large, pod-driven containership model. This paper includes the presentation of current numerical modifications for pod-driven ships and the verification analysis. 相似文献
30.
Burrows of the thalassinidean shrimps Neaxius acanthus and Corallianassa coutierei are striking aspects in tropical seagrass beds of the Spermonde Archipelago, Indonesia. Burrow construction, behaviour, burrow type and associated commensal community were investigated to clarify the ecological role and food requirements of these shrimps and their commensals. Gut content analysis and stable-isotope data were used to unravel the food sources and the trophic interactions among the commensal community.Individuals of Neaxius acanthus were caught on Bone Batang Island. In narrow aquaria filled with sediment they constructed burrows resembling those found in the field. During burrow construction and maintenance only little sediment was brought to the surface, most was sorted and compacted to create a distinct lining. Maintenance work by single shrimps typically took about 5 min, after which the shrimp walked up to the entrance and rested for a similar period of time. There were no differences in behaviour between day and night. Intrasexual encounters inside the burrow were characterised by a high level of aggression and all resulted in one participant being driven out of the burrow. Intersexual encounters led to coexistence with both animals taking turns in burrow maintenance and guarding the entrance. Offered seagrass leaves were pulled underground, cut into pieces and eventually integrated into the lining. Burrows of Corallianassa coutierei resembled a deep U-shape. Chambers branching off halfway down and at the deepest point contained seagrass fragments. All steep parts of the burrow were lined similar to burrows of N. acanthus.No commensals were found associated with Corallianassa coutierei. However, burrows of Neaxius acanthus in the field typically contained a pair of shrimps, up to 8 individuals of the commensal bivalve Barrimysia cumingii and large numbers of gammarid amphipods. Other animals found associated with the burrow were the goby Austrolethops wardi, a palaemonid shrimp species and two species of tube-building polychaetes, one of which was also found as an epibiont on N. acanthus.Stable-isotope and gut content analyses indicate that the diet of Neaxius acanthus, its commensal Austrolethops wardi, and Corallianassa coutierei is mainly derived from detrital seagrass leaves, with a potential contribution of sediment organic matter and seagrass epiphytes. In contrast the isotopic signature of Barrimysia cumingii suggests the presence of symbiotic sulphide metabolism bacteria. This study underlines that, besides their interactions with the surrounding ecosystem, thalassinid shrimp burrows play an important role as a sub-habitat with a unique associated fauna. 相似文献