全文获取类型
收费全文 | 59958篇 |
免费 | 696篇 |
国内免费 | 416篇 |
专业分类
测绘学 | 1213篇 |
大气科学 | 3499篇 |
地球物理 | 11685篇 |
地质学 | 22553篇 |
海洋学 | 5338篇 |
天文学 | 13946篇 |
综合类 | 142篇 |
自然地理 | 2694篇 |
出版年
2022年 | 556篇 |
2021年 | 809篇 |
2020年 | 906篇 |
2019年 | 990篇 |
2018年 | 2064篇 |
2017年 | 1884篇 |
2016年 | 2102篇 |
2015年 | 995篇 |
2014年 | 1918篇 |
2013年 | 3091篇 |
2012年 | 2218篇 |
2011年 | 2754篇 |
2010年 | 2510篇 |
2009年 | 3019篇 |
2008年 | 2645篇 |
2007年 | 2884篇 |
2006年 | 2556篇 |
2005年 | 1625篇 |
2004年 | 1569篇 |
2003年 | 1521篇 |
2002年 | 1395篇 |
2001年 | 1373篇 |
2000年 | 1209篇 |
1999年 | 944篇 |
1998年 | 962篇 |
1997年 | 991篇 |
1996年 | 750篇 |
1995年 | 743篇 |
1994年 | 685篇 |
1993年 | 589篇 |
1992年 | 571篇 |
1991年 | 549篇 |
1990年 | 606篇 |
1989年 | 530篇 |
1988年 | 478篇 |
1987年 | 561篇 |
1986年 | 432篇 |
1985年 | 633篇 |
1984年 | 668篇 |
1983年 | 643篇 |
1982年 | 596篇 |
1981年 | 549篇 |
1980年 | 548篇 |
1979年 | 472篇 |
1978年 | 544篇 |
1977年 | 453篇 |
1976年 | 420篇 |
1975年 | 443篇 |
1974年 | 396篇 |
1973年 | 426篇 |
排序方式: 共有10000条查询结果,搜索用时 797 毫秒
631.
The paper reports computed data on the seasonal variability of the Atlantic Ocean currents which were obtained through numerical integration (using conservative difference schemes) of non-linear equations of hydrothermodynamics taking into account an upper quasi-homogeneous layer and the bottom topography. The seasonal variability of the meridional heat transfer is discussed. The results were obtained using an adaptation approach.Translated by Vladimir A. Puchkin. 相似文献
632.
633.
Juvenile coho salmon, Onchorynchus kisutch, were exposed to 95mTc in both saltwater and freshwater to study the biokinetic behavior of this element in an anadromous fish. In freshwater, equilibrium whole-body concentration factors (CF5) ranged from 28 to 32 in two separate experiments, in sharp contrast to an equilibriumCF of < 5 in saltwater. While the uptake kinetics were unimodal in saltwater, in freshwater, biomodal uptake kinetics were observed.Technetium-95m retention was biphasic in freshwater depuration experiments, an initial rapid loss of 21% to 26% of the steady-state activity with an elimination half-life of 3 to 5 days was followed by a slower loss rate, with a whole-body elimination half-life ranging from 23 to 33 days. In saltwater, retention was monophasic with an elimination half-life of 5–16 days. Dramatic decreases in 95mTc body burdens when freshwater-labeled fish are transferred to Tc-labeled saltwater indicate that the changes in physiology accompanying saltwater acclimation lead to the loss of 95mTc. 相似文献
634.
635.
K. N. Visheratin N. E. Kamenogradskii F. V. Kashin V. K. Semenov V. P. Sinyakov L. I. Sorokina 《Izvestiya Atmospheric and Oceanic Physics》2006,42(2):184-202
The results of long-term (1980–2003) systematic measurements of the total ozone content at the Issyk Kul station (42.6° N, 77.0° E; 1650 m above sea level) are presented. The statistical characteristics and spectral structure of variations in the total ozone and the main tendencies of its temporal variability are determined. It is found that the total ozone content decreased in 1980–2003 at an average rate of (?1.29±0.08) DU/yr. The results of Fourier and wavelet analyses have shown that only oscillations with periods of 12, 27–29, and 102–105 months are rather stable and can be represented as harmonic oscillations. Oscillations with periods shorter than six months have the character of periodically arising pulsations. Among these, oscillations with periods of 27–29 and 34–37 days can be distinguished. It is noted that the spectral-temporal structure of variations in the total ozone content obtained from ground-based measurements at the Issyk Kul station is in good agreement with the corresponding structure obtained from TOMS satellite measurements. 相似文献
636.
UWAN-MAC: An Energy-Efficient MAC Protocol for Underwater Acoustic Wireless Sensor Networks 总被引:2,自引:0,他引:2
In this paper, we propose a distributed, scalable, energy-efficient media access control (MAC) protocol that works despite long, unknown propagation delays of the underwater acoustic medium. This protocol can be used for delay-tolerant applications such as underwater ecological sensor networks between energy-limited nodes. Our protocol differs significantly from ALOHA, multiple access with collision avoidance (MACA), and the media access protocol for wireless LANs (MACAW) in that energy is the main performance metric in our case rather than bandwidth utilization. We show that under a realistic underwater sensor network scenario, our MAC protocol wastes only 4% of the transmit energy and only 1.5% of the receive energy due to collisions, when the average number of neighbors is four, and the duty cycle is 0.004. This distributed, scalable MAC protocol has the potential to serve as a primer for the development of energy-efficient MAC protocols for future underwater sensor networks. 相似文献
637.
Akcha F Tanguy A Leday G Pelluhet L Budzinski H Chiffoleau JF 《Marine environmental research》2004,58(2-5):753-756
DNA single-strand breaks were measured by the comet assay in both gill and hemolymph cells of mussels collected in 3 sampling areas of the French coast (Pointe du Castelli, Pen Bron and Saint-Nazaire Harbour). Whole mussel tissue samples were also collected for the chemical determination of PAH, PCB and heavy metal concentrations. In mussel, a higher level of DNA strand breaks was measured in gill than in hemolymph cells (p < 0.01). Despite a factor of contamination from 2 to 3 between sites, no difference in the extent of mussel DNA strand breaks was shown between sampling locations (p > 0.05), questioning the sensitivity of the assays used in biomonitoring studies. 相似文献
638.
The Kimmeridge Clay is considered a major oil source rock for the North Sea hydrocarbon province. The formation is also developed onshore in an organic-rich mudstone facies. This paper examines the possibility of onshore oil generation from the Kimmeridge Clay. Geochemically, onshore basin margin sediments contain rich, potential source horizons with mainly Type l/Type ll oil-prone kerogen, but are immature. Some deeper Cleveland Basin sediments have reached marginal maturity. Burial history reconstruction suggests significant formation palaeoburial depths in central areas of the Cleveland and Wessex Basins. Computed vitrinite isoreflectance contours show the Wealden and Isle of Wight Kimmeridge Clay to be thermally mature. Basin modelling suggests an early Palaeogene onset of oil generation in parts of the Cleveland Basin, while maximum oil generation could have been reached by the formation base in the Isle of Wight area during the late Cretaceous. Although basin subsidence ceased in the Neogene, in the Weald and Isle of Wight, where the formation is still deeply buried, oil generation probably continued for some time during uplift. Thus significant quantities of oil could have been generated. Whether or not this oil is present today however, would depend on the correct timing of suitable migration and trap structures. 相似文献
639.
The wadic project: A comprehensive field evaluation of directional wave instrumentation 总被引:1,自引:0,他引:1
J. Allender T. Audunson S. F. Barstow S. Bjerken H. E. Krogstad P. Steinbakke L. Vartdal L. E. Borgman C. Graham 《Ocean Engineering》1989,16(5-6)
The results of a comprehensive field trial of nearly all commercially available directional wave measurement systems at the Edda field in the North Sea during winter 1985-86 are presented. The results summarize the accuracy of the principal engineering wave parameters from each system and the dependence on sea state. Limiting factors on system performance and operational problems are also included in the assessment. Overall experience has been good with systems utilizing widely different measurement principles returning consistent results. 相似文献
640.
Sedimentary facies of cores from the eastern side of the Rockall Bank and the Feni Drift (55°–58°N) have been studied. They confirm the existence of slumping which contributes only in small part to drift build-up.
These slumps occurred at different episodes during last Glacial and early Post-Glacial periods. They are sandwiched in between more important turbidites, and are found in places where the drift lies against the slope and so is acted upon by continental-rise sedimentary processes. The sea level rise periods with ice melting seems to favour gravity flow release. 相似文献