全文获取类型
收费全文 | 115570篇 |
免费 | 1318篇 |
国内免费 | 1456篇 |
专业分类
测绘学 | 3304篇 |
大气科学 | 7922篇 |
地球物理 | 21804篇 |
地质学 | 44730篇 |
海洋学 | 9329篇 |
天文学 | 22895篇 |
综合类 | 2362篇 |
自然地理 | 5998篇 |
出版年
2022年 | 620篇 |
2021年 | 1058篇 |
2020年 | 1121篇 |
2019年 | 1256篇 |
2018年 | 7817篇 |
2017年 | 6924篇 |
2016年 | 5591篇 |
2015年 | 1590篇 |
2014年 | 2698篇 |
2013年 | 4507篇 |
2012年 | 4104篇 |
2011年 | 7072篇 |
2010年 | 6105篇 |
2009年 | 7288篇 |
2008年 | 6169篇 |
2007年 | 6959篇 |
2006年 | 3628篇 |
2005年 | 2932篇 |
2004年 | 2984篇 |
2003年 | 2869篇 |
2002年 | 2635篇 |
2001年 | 2026篇 |
2000年 | 2029篇 |
1999年 | 1548篇 |
1998年 | 1616篇 |
1997年 | 1466篇 |
1996年 | 1244篇 |
1995年 | 1242篇 |
1994年 | 1042篇 |
1993年 | 1008篇 |
1992年 | 934篇 |
1991年 | 967篇 |
1990年 | 936篇 |
1989年 | 817篇 |
1988年 | 751篇 |
1987年 | 883篇 |
1986年 | 773篇 |
1985年 | 946篇 |
1984年 | 1070篇 |
1983年 | 1031篇 |
1982年 | 950篇 |
1981年 | 906篇 |
1980年 | 812篇 |
1979年 | 748篇 |
1978年 | 726篇 |
1977年 | 618篇 |
1976年 | 632篇 |
1975年 | 613篇 |
1974年 | 589篇 |
1973年 | 656篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Researches on breaking-induced currents by waves are summarized firstly in this paper. Then, a combined numerical model in orthogonal curvilinear coordinates is presented to simulate wave-induced current in areas with curved boundary or irregular coastline. The proposed wave-induced current model includes a nearshore current module established through orthogonal curvilinear transformation form of shallow water equations and a wave module based on the curvilinear parabolic approximation wave equation. The wave module actually serves as the driving force to provide the current module with required radiation stresses. The Crank-Nicolson finite difference scheme and the alternating directions implicit method are used to solve the wave and current module, respectively. The established surf zone currents model is validated by two numerical experiments about longshore currents and rip currents in basins with rip channel and breakwater. The numerical results are compared with the measured data and published numerical results. 相似文献
952.
Determination of Stellar Parameters with GAIA 总被引:1,自引:0,他引:1
C.A.L. Bailer-Jones 《Astrophysics and Space Science》2002,280(1-2):21-29
The GAIA Galactic survey satellite will obtain photometry in 15 filters of over 109 stars in our Galaxy across a very wide range of stellar types. No other planned survey will provide so much photometric information
on so many stars. I examine the problem of how to determine fundamental physical parameters (T
eff, log g, [Fe/H] etc.) from these data. Given the size, multidimensionality and diversity of this dataset, this is a challenging task
beyond any encountered so far in large-scale stellar parametrization. I describe the problems faced (initial object identification,
interstellar extinction, multiplicity, missing data etc.) and present a framework in which they can be addressed. A probabilistic
approach is advocated on the grounds that it can take advantage of additional information (e.g. priors and data uncertainties)
in a consistent and useful manner, as well as give meaningful results in the presence of poor or degenerate data. Furthermore,
I suggest an approach to parametrization which can use the other information GAIA will acquire, in particular the parallax,
which has not previously been available for large-scale multidimensional parametrization. Several of the problems identified
and ideas suggested will be relevant to other large surveys, such as SDSS, DIVA,FAME, VISTA and LSST, as well as stellar parametrization
in a virtual observatory.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
953.
954.
APPLICATION OF ANALYTIC HIERARCHY PROCESS TO ASSESSING THE ECOLOGICAL VULNERABILITY OF WETLANDS IN THE JIANGHAN PLAIN 总被引:4,自引:1,他引:4
WANGXue-lei NINGLong-mei HUWang-bin 《中国地理科学(英文版)》2003,13(3):272-276
Wetlands in the Jianghan Plain are important components of wetland types in lake area in the middle and lower reaches the Changjiang (Yangtze) River and they fulfill many uses and functions related to hydrology,waste assimilation, ecosystem productivity and biodiversity. Owing to natural factors and human activities, especially excessive reclamation from lakes, the shrinking process of the lakes has been accelerated. Wetland ecosystem has shown the characteristics of vulnerability. According to the analysis of wetland ecological function in the Jianghan Plain, this paper presented an index system related to productivity, stability and environmental capacity. By using the method of Analytic Hierarchy Process, we computed the values of the relative weights of the indexes, and evaluated the vulnerability level of the wetland ecosystem by the method of multi-indexes. The case study showed that the fragile extent of wetland ecosystem in the Jianghan Plain is 5.6. This means that the wetland ecosystem in the Jiang-han Plain is laid to the state of middle vulnerability. Therefore, the wetland conservation and eco-rehabilitation in the JiangJaan Plain should be paid attention to. 相似文献
955.
According to B.L. Berry’s “harmonic model,” any natural or social process is a superposition of several cosmic rhythms. The
author assumes that stability of these rhythms allows prediction of earth phenomena over an unlimited time. We show that the
statistical criteria supposedly substantiating the harmonic model were applied incorrectly. The initial data for the analysis
were biased and selected incompetently; the adequacy of the methods used was not verified. Predictions of natural catastrophes
(earthquakes, weather anomalies, etc.) and various social events according to Berry’s model are unsatisfactory. Statistics
do not confirm that these predictions are at least slightly better than random guessing. Berry’s model is unacceptable; it
is untenable both in detail and in general. 相似文献
956.
The metallogenic efficiency of the marginal sea lithosphere of Northeastern Asia is associated mainly with the ore formation
variety of the remaining cratons and microcratons that defined the structural peculiarity of the region; these are setoffs
of the Precambrian basement, brachyform, anticline highs, and genesis of rifts within TMA periods. These formations allowed
us to explain the reasons for the unique metal-bearing feature of the marginal sea lithosphere of the Pacific Ocean ore belt
in addition to phenomena of an inherited nature of mineralization and conditions of formation of polychronous ore deposits. 相似文献
957.
Analysis of paleolimnological data on a part of Lake Imandra (Kola Peninsula), polluted by wastewaters discharged from a copper-nickel plant, is used to calculate the vertical profile of toxicity of bottom sediments and determine the response of dominant species of diatomic complex to the growing toxicity. The species are aggregated by the similar responses to the load. The dependence between the population sizes of diatom groups and toxicity is established. The diatom complex is shown to change its structure twice—at the toxicity exceeding the background level by factors of 1.2 and 3.2, respectively. A model is developed to describe variations in the species composition of the community under growing toxicity; the model is shown to be applicable to the analysis of paleolimnological data. General analysis of the model is given, and typical scenarios of variation in the number of species under growing toxic load are described. 相似文献
958.
Marc W. Pound Jave O. Kane Bruce A. Remington Dmitri D. Ryutov Akira Mizuta Hideaki Takabe 《Astrophysics and Space Science》2005,298(1-2):177-181
Over the past few years, our group has been developing hydrodynamic models to simulate formation of the Eagle Nebula pillars.
The true test of any model is, of course, how well it can reproduce the observations. Here, we discuss how we go about testing
our models against observations. We describe the process by which we “observe” the model data to create synthetic maps. We
show an example of this technique using one of our model runs and compare the resultant synthetic map to the real one. 相似文献
959.
960.
Averaged many-year measurement data on the concentrations of mineral forms of biogenic elements are analyzed, and their total concentrations in the rivers of Selenga, Chikoi, Khilok, Uda, Dzhida, and Temnik are evaluated. The monthly variations of the concentrations of major biogenic substances are characterized, and their ratios within a year are determined. Characteristics of river water runoff and biogenic substance concentrations are used to evaluate their within-year discharge by rivers. Characteristic variations in the ratios between the total and mineral forms of biogenic elements discharged by rivers have been revealed. It is established that the share of mineral components in the total input into the Selenga delta Ntot and Ptot are 82 and 22%, respectively. 相似文献