全文获取类型
收费全文 | 29658篇 |
免费 | 403篇 |
国内免费 | 225篇 |
专业分类
测绘学 | 735篇 |
大气科学 | 2261篇 |
地球物理 | 5766篇 |
地质学 | 10859篇 |
海洋学 | 2556篇 |
天文学 | 6291篇 |
综合类 | 65篇 |
自然地理 | 1753篇 |
出版年
2021年 | 275篇 |
2020年 | 298篇 |
2019年 | 302篇 |
2018年 | 727篇 |
2017年 | 725篇 |
2016年 | 839篇 |
2015年 | 468篇 |
2014年 | 802篇 |
2013年 | 1558篇 |
2012年 | 925篇 |
2011年 | 1222篇 |
2010年 | 1052篇 |
2009年 | 1364篇 |
2008年 | 1184篇 |
2007年 | 1173篇 |
2006年 | 1160篇 |
2005年 | 840篇 |
2004年 | 839篇 |
2003年 | 766篇 |
2002年 | 768篇 |
2001年 | 713篇 |
2000年 | 702篇 |
1999年 | 550篇 |
1998年 | 520篇 |
1997年 | 600篇 |
1996年 | 468篇 |
1995年 | 474篇 |
1994年 | 471篇 |
1993年 | 381篇 |
1992年 | 387篇 |
1991年 | 358篇 |
1990年 | 373篇 |
1989年 | 342篇 |
1988年 | 344篇 |
1987年 | 368篇 |
1986年 | 325篇 |
1985年 | 425篇 |
1984年 | 414篇 |
1983年 | 446篇 |
1982年 | 415篇 |
1981年 | 365篇 |
1980年 | 402篇 |
1979年 | 324篇 |
1978年 | 302篇 |
1977年 | 294篇 |
1976年 | 266篇 |
1975年 | 264篇 |
1974年 | 269篇 |
1973年 | 254篇 |
1971年 | 173篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
At the request of the International Maritime Organization (IMO), our laboratory has performed acute toxicity testing with 43 substances, for which insufficient or no data had been available for hazard rating concerning damage to marine living resources. 相似文献
132.
The abundances of light elements (deuterium, helium and lithium) are calculated in unconventional cosmologies in which these elements are produced by interaction of fast -particles ejected by massive pregalactic stars with a purely hydrogenous cosmological substrate. The number density and energetics of such stars needed for suitable production of light elements are estimated. It is shown that the models always lead to overproduction of lithium. The intensity of ultraviolet, X-ray, and -ray emission caused by explosions of pregalactic massive stars is calculated. The distortions of cosmic background radiation by Compton losses of electrons heated by explosive stars are also calculated. 相似文献
133.
C. E. Puente O. Robayo B. Sivakumar 《Stochastic Environmental Research and Risk Assessment (SERRA)》2001,15(5):372-383
In a companion paper (Puente et al., this issue), the capability of a deterministic fractal-multifractal (FM) approach to
faithfully and compactly describe the geometry of chloride and bromide tracers gathered at the Borden site was illustrated.
As trends in surrogate parameter space were found for successive plume contours (i.e. linear growth in coordinates by which
fractal interpolating functions pass, nearly constant rotations and fairly high scalings), this article reports usage of a
variety of prediction schemes, based on linear regressions and the aforementioned trends, in order to study the evolving plumes.
It is shown that the FM representation leads to plausible non-Gaussian plume evolutions and yields predictions that closely
approximate records for a period of time that extends even beyond one year. It is illustrated that such predicted geometries
are also consistent with predictions made via stochastic theories (i.e. Dagan, 1984). 相似文献
134.
The impact of rural land management changes on soil hydraulic properties and runoff processes: results from experimental plots in upland UK 下载免费PDF全文
M. R. Marshall C. E. Ballard Z. L. Frogbrook I. Solloway B. Reynolds H. S. Wheater 《水文研究》2014,28(4):2617-2629
To develop an evidence base to help predict the impacts of land management change on flood generation, four experimental sites were established on improved grassland used for sheep grazing at the Pontbren catchment in upland Wales, UK. At each site, three plots were established where surface runoff was measured, supplemented by measurements of soil infiltration rates and soil and vegetation physical properties. Following baseline monitoring, treatments were applied to two of the plots: exclusion of sheep (ungrazed) and exclusion of sheep and planting with native broadleaf tree species (tree planted), with the third plot acting as a control (grazed pasture). Due to a particularly dry summer that occurred pre‐treatment, the soil hydrological responses were initially impacted by the effects of the climate on soil structure. Nevertheless, treatments did have a clear influence on soil hydrological response. On average, post‐treatment runoff volumes were reduced by 48% and 78% in ungrazed and tree‐planted plots relative to the control, although all results varied greatly over the sites. Five years following treatment application, near‐surface soil bulk density was reduced and median soil infiltration rates were 67 times greater in plots planted with trees compared to grazed pasture. The results illustrate the potential use of upland land management for ameliorating local‐scale flood generation but emphasise the need for long‐term monitoring to more clearly separate the effects of land management from those of climatic variability. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
135.
Summary The Indian summer monsoon, one of the earth's most vigorous and energetic seasonally occurring weather events, influences the global atmospheric circulation. Its onset, duration, and intensity are governed by large- and meso-scale geophysical processes, such as surface solar heating and air-sea interactions. In this paper, using innovative combinations of satellite sensor data, we investigate some of these fundamental processes which are closely tied to clouds and control the monsoon system's evolution. The study, which focuses on the monsoon period of June, 1979, examines the low-frequency variability of clouds and their effects on air-sea processes through an analysis of the complex influence clouds play on the surface heat and water budgets. First, the effects of clouds on both the solar and longwave components of the surface radiation budget are assessed using a cloud radiative forcing parameter. While the effects of clouds on the long-wave irradiance act in a manner opposite to their effects on the shortwave irradiance, only a partial compensation is found to take place and the net effect results in a maximum cloud forcing of 60 Wm–2 in the southwestern Arabian Sea. Second, employing satellite-derived precipitation and evaporation estimates, the paper analyzes the net surface fresh water budget variability around the monsoon onset. This budget is important in that fresh water affects the upper ocean density distribution and, consequently, the thermohaline circulation. Two regions are found to dominate the analysis: the western Arabian Sea, where evaporation is dominant by more than 10 mm day–1, and the eastern Arabian Sea, where precipitation is dominant by more than 10 mm day–1. Thus, a strong zonal gradient of fresh water at the surface is established during the monsoon. The last topic investigated is the intraseasonal variability of convection as analyzed using a cloud parameter indicative of deep convection. Cloud oscillations of 30–50 days, associated with the different phases of the monsoon, are found to propagate northward in the eastern Indian Ocean and eastward in the Bay of Bengal. Our analysis not only supports the hypothesis that the 30–50-day oscillation is driven by deep convection but also, and more importantly, suggests that the ocean thermal forcing is modulated by 30–50-day oscillations through cloud-induced surface radiative forcing. Although the results presented are limited in scope and preliminary because of the diffculty in quantifying the accuracy of the parameters examined, they do demonstrate: 1) the role of clouds in modulating the surface heat and water budgets, 2) the advantage of using combinations of multi-sensor and multi-platform satellite observations to quantify interrelated surface heat/water budget processes, and 3) the potential to examine the intraseasonal variability of air-sea interaction processes associated with the monsoon, even though these processes are not directly measurable from space.With 6 FiguresB. DiJulio passed away in September 1990. 相似文献
136.
P. Descamps T. Michalowski J. Berthier J.-P. Teng-Chuen-Yu B. Payet Y. Léonie H. Berrouachdi F. Benard 《Icarus》2007,189(2):362-369
We present a set of rotational lightcurve measurements of the small main belt Asteroid 3169 Ostro. Our observations reveal an unambiguous, double-peaked rotational lightcurve with a peak-to-peak variation up to 1.2±0.05 mag and a synodic period of 6.509±0.001 h. From the large flux variation and the overall shape of the lightcurves, we suggest that 3169 Ostro could be a tightly bound binary or a contact binary, similar to the Trojan Asteroid 624 Hektor. A shape model of this system is proposed on the assumption that 3169 Ostro is a Roche binary described by a pair of homogeneous elongated bodies, with a size ratio of 0.87, in hydrostatic equilibrium and in circular synchronous motion around each other. The direction of the spin axis is determined modulo 180° by its J2000 ecliptic coordinates λ0=50±10°, β0=±54±5°. The binary interpretation and the pole solution adequately fit the earlier photometric observations made in 1986 and 1988. However, additional supporting lightcurves are highly desirable especially in the next mutual events occurrence of 2008 and 2009 in order to remove the pole ambiguity and to confirm unambiguously the binary nature of 3169 Ostro. 相似文献
137.
P. A. Lozovik A. K. Morozov M. B. Zobkov T. A. Dukhovicheva L. A. Osipova 《Water Resources》2007,34(2):204-216
A relationship between indirect chemical indices of organic matter content of surface waters and light absorption in the visible and ultraviolet ranges is discussed. The allochthonous and autochthonous types of organic matter are found to essentially differ in the rate of light absorption. Techniques are proposed for the calculation of the concentrations of allochthonous and autochthonous organic matter by the integral rate of light consumption in the visible region and the bichromate oxidability of water, as well as by three indirect indices: chemical oxygen demand, permanganate oxidability, and water color index. The mean concentrations of allochthonous and autochthonous organic matter in large lakes (Ladoga, Onega, and Baikal) and in rivers and smaller water bodies in Karelia (>300 water objects) are analyzed. Allochthonous organic matter was found to predominate in most surface waters of Karelia (>80%), while allochthonous organic matter predominates only in lakes with a small specific catchment area (supposedly, <5) and in highly eutrophic lakes. 相似文献
138.
Binh Thai Pham Dieu Tien Bui Indra Prakash Long Hoang Nguyen M. B. Dholakia 《Environmental Earth Sciences》2017,76(10):371
Landslide susceptibility assessment using GIS has been done for part of Uttarakhand region of Himalaya (India) with the objective of comparing the predictive capability of three different machine learning methods, namely sequential minimal optimization-based support vector machines (SMOSVM), vote feature intervals (VFI), and logistic regression (LR) for spatial prediction of landslide occurrence. Out of these three methods, the SMOSVM and VFI are state-of-the-art methods for binary classification problems but have not been applied for landslide prediction, whereas the LR is known as a popular method for landslide susceptibility assessment. In the study, a total of 430 historical landslide polygons and 11 landslide affecting factors such as slope angle, slope aspect, elevation, curvature, lithology, soil, land cover, distance to roads, distance to rivers, distance to lineaments, and rainfall were selected for landslide analysis. For validation and comparison, statistical index-based methods and the receiver operating characteristic curve have been used. Analysis results show that all these models have good performance for landslide spatial prediction but the SMOSVM model has the highest predictive capability, followed by the VFI model, and the LR model, respectively. Thus, SMOSVM is a better model for landslide prediction and can be used for landslide susceptibility mapping of landslide-prone areas. 相似文献
139.
A. Mascle R. Vially E. Deville B. Biju-Duval J.P. Roy 《Marine and Petroleum Geology》1996,13(8):941-961
The Southeast Basin of France is the thickest onshore French sedimentary basin which contains locally as much as 10 km of Mesozoic-Cenozoic sediment. Basin development occurred in several stages between late Carboniferous and late Cretaceous times. Partial tectonic inversion took place during two compressive events, the so-called ‘Pyrenean’ and ‘Alpine’ phases of late Cretaceous-early Tertiary and late Tertiary ages respectively. They are separated by an intervening stretching event of Oligocene age, which further south resulted in the opening of the western Mediterranean oceanic basin. As a result of this complex tectonic history, structural traps were difficult to image on the seismic data shot during the first phase of exploration prior to 1980. Oil and gas natural seeps, and shows in several wells, indicate that some petroleum systems are, or have been active, at least in some places.The present erosional western margin of the basin is more or less superimposed on the initial Triassic-Jurassic margin. Margin subsidence and Tertiary inversion are discussed using regional sections on which the polyphase history of the entire basin is well shown. These sections are located on three major segments where the Mesozoic margin is either partly preserved (Ardèche), or has been partly inverted in late Tertiary times (Vercors-Chartreuse), or has been completely inverted in early Tertiary times (Corbières-eastern Pyrenees). 1-D ‘Genex’ basin modelling on the Ardèche segment, and 2-D ‘Thrustpack’ structural-maturity modelling in the Vercors-Chartreuse segment are used to further assess the remaining petroleum plays. 相似文献
140.
In this work, we consider the formation of electrostatic, dust-acoustic solitary structure in a unmagnetized plasma with Lorentzian electrons (kappa-distributed) and more than one species of thermal ions (Maxwellian). The work is inspired by results of different space-based observations of electrostatic solitary waves (ESW) in the near-earth and magnetospheric plasmas and recent experimental realization of existence of superthermal electron component in various space plasmas. We have, in this work, shown that existence of compressive potential structure is possible only with more than one species of thermal ions. Besides, formation of compressive double layers is also possible which depends on the amount of deviation of the electron thermal velocities from a Maxwellian distribution. We show that both dust-temperature and super-thermal electrons lead to a decrease in the soliton amplitude. 相似文献