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271.
全球贸易自由化对中国和世界经济的影响 总被引:6,自引:0,他引:6
全球贸易自由化是当前和未来世界经济发展不可避免的趋势,2001年开始的多哈回合贸易自由化多边谈判和最近刚刚取消的“多种纤维协定”(MFA)将在全球贸易自由化进程中发挥重要的作用。本研究的目的是通过一些案例分析,揭示贸易自由化对中国和世界经济的影响。采用全球贸易模型,我们分析了MFA和在多哈回合初期欧盟、美国和凯恩斯集团分别提出的贸易自由化提案。研究结果表明,虽然取消MFA对一些国家纺织部门带来冲击,但它极大地促进了大多数国家经济的发展,改善了全球福利;多哈谈判过程中提出的各种贸易自由化提案都在不同程度上促进世界经济的发展,但其影响大小依次为凯恩斯提案、美国提案和欧盟提案;贸易自由化对经济的影响在不同部门和不同国家间存在显著差别;更大程度的贸易自由化不但符合全球共同利益,也符合中国国家利益;中国在推动全球贸易自由化过程中应发挥更积极和更大的作用。 相似文献
272.
273.
Hans -Georg Grothues 《Astrophysics and Space Science》1995,229(1):1-22
The interrelations between the physical parameters of a cometary nucleus, and the morphology of the dust tail and its streamers are systematically investigated by means of a model developed by Beißer (1990a), involving a rotating nucleus. The analysis of streamers in the tail, using direct modeling and synchrone grids, provides a suitable tool to deduce substantial informations on the nucleus' state of rotation. Opportunities and limitations of this analysis are discussed. Dust emission parameters like the distribution of active regions on the nucleus, or the emission characteristics can only be determined if certain other physical properties of the nucleus have been independently measured before. 相似文献
274.
Filamentary objects of submicron size isolated from an extraterrestrial particle and from the Gunflint cherts are compared and shown to have similarities of size, shape and interior structure. 相似文献
275.
We present radial velocity measurements proving the binary nature of all the known extremely Fe-deficient Post-ABG stars including HD 44179, the central star of the well known but poorly understood Red-Rectangle nebula. With the observed orbital parameters, it is more likely that the stars represent a particular stage in binary evolution, rather than a typical post-AGB evolutionary stage. 相似文献
276.
277.
Hans Rickman Marc Fouchard Giovanni B. Valsecchi Christiane Froeschlé 《Earth, Moon, and Planets》2005,97(3-4):411-434
We investigate different approximate methods of computing the perturbations on the orbits of Oort cloud comets caused by passing stars, by checking them against an accurate numerical integration using Everhart’s RA15 code. The scenario under study is the one relevant for long-term simulations of the cloud’s response to a predefined set of stellar passages. Our sample of stellar encounters simulates those experienced by the Solar System currently, but extrapolated over a time of 1010 years. We measure the errors of perihelion distance perturbations for high-eccentricity orbits introduced by several estimators – including the classical impulse approximation and Dybczyński’s (1994, Celest. Mech. Dynam. Astron. 58, 1330–1338) method – and we study how they depend on the encounter parameters (approach distance and relative velocity). We introduce a sequential variant of Dybczyński’s approach, cutting the encounter into several steps whereby the heliocentric motion of the comet is taken into account. For the scenario at hand this is found to offer an efficient means to obtain accurate results for practically any domain of the parameter space. 相似文献
278.
Principal oscillation pattern analysis of the 30- to 60-day oscillation in the tropical troposphere 总被引:1,自引:0,他引:1
The Principal Oscillation Pattern technique is used to derive an index of the 30- to 60-day oscillation in the tropical troposphere. In the 200-mb equatorial velocity potential field, one dominant pair of POPS is found. Its properties compare very well with the properties of the oscillation identified in previous studies. In particular, a good correlation between the time evolution of the POP coefficients and area-averaged outgoing long-wave radiation (ORL) is found. The POPS are derived from a 2-year subinterval of the whole 5-year data set. This leaves independent data for subsequent verification. The patterns and their characteristic numbers are almost unchanged if the whole data set is analysed. Also, the analysis is insensitive to changes of the analysis area: if the analysis is limited to 90°-longitude equatorial sectors, the signal is also identified and its patterns are consistent with the patterns derived from the full data set. Interestingly, the signal is best defined in the eastern hemisphere. The POPS may be used to derive associated correlation patterns of other quantities in winter and summer separately. The path of the oscillation has a marked annual cycle: in northern winter it migrates from the Indian Ocean across northern Australia into the region of the South Pacific Convergence Zone (SPCZ) and in northern summer it moves from the Indian Ocean across South Asia along the intertropical Convergence Zone (ITCZ) to South America. The POP coefficient may be seen as a bivariate index of the state (phase and strength) of the 30- to 60-day oscillation. Since the POP technique incorporates a prediction equation for the phase of the POP coefficients, the POP model allows for the prediction of the complex amplitude of the oscillation. In a sequence of forecast experiments, of which about two-thirds used independent data, the POP forecasts were found to be useful in about half of all cases for lead times of several days. The correlation and RMS skills were calculated for the POP forecast and for persistence. The POP forecast appears to be considerably better with respect to both measures. The correlation skill scores 60% after 7 days. The POP forecast is most skillful in northern winter and if strong signals are present with minima of velocity potential in the eastern hemisphere. 相似文献
279.
Various explanations of the bipolar-flow phenomenon in star-forming regions are compared and confronted with the observed facts. It is concluded that stellar-wind interpretations are inconsistent with the constraints. The exotic property of young stellar objects may be their extreme spin which implies strong magnetic fields and vacuum discharges above thee
± pair-formation threshold (of 1012 eV). Pair-plasma jets are thought to be centrifugally driven by young stars during their first 104±1 years of rapid rotation. 相似文献
280.
Estuarine Phytoplankton Responses to Hurricanes and Tropical Storms with Different Characteristics (Trajectory,Rainfall, Winds) 总被引:1,自引:0,他引:1
We examined the short-term (<1 month post-storm) impact of storms [Tropical Storm (TS) Helene in 2000, Hurricane (H) Isabel
in 2003, H Alex, Tropical Depression (TD) Bonnie and TS Charley in 2004] varying in their trajectory, wind and rainfall characteristics,
on water column structure, nutrients, and phytoplankton biomass in North Carolina’s Neuse R. Estuary (NRE). Data are presented
from two sampling programs, ModMon (biweekly) and FerryMon (measurements made every 3 min daily). Helene’s winds mixed the
previously stratified water column, delivering sediment-bound nutrients to the euphotic zone, and localized freshwater input
from Helene was also evident. Mean chlorophyll a concentrations in the mesohaline portion of the NRE, where N was strongly limiting before the storm (molar DIN:DIP < 1),
more than doubled after the storm. Unlike with Helene, the water column was well mixed before passage of Isabel, and nutrient
concentrations were high. As a result, minimal impact on phytoplankton biomass was detected despite Isabel’s high winds and
significant freshwater input. In fact, conditions became less favorable for phytoplankton growth after the storm. Alex was
fast moving and relatively small, but its winds were sufficient to mix the water column. Although data from ModMon suggest
that chlorophyll a was only slightly higher after passage of Alex, FerryMon detected an ephemeral bloom that was missed by ModMon. Overall,
these results suggest that relatively small tropical storms and hurricanes can lead to significant increases in phytoplankton
biomass. However, the phytoplankton response depends on both the characteristics of a particular storm and the physical–chemical
conditions of the water column before storm passage. Finally, the ephemeral bloom that developed as a result of Alex, the
strong response of phytoplankton in the mesohaline portion of the estuary to nutrient inputs, and their patchiness on several
other occasions suggests that storms may create “hot spots” for trophic transfer and biogeochemical dynamics in estuaries.
Adaptive sampling is necessary to capture these features and to fully understand the impact of perturbations such as storms
on estuarine ecosystem functioning. 相似文献