全文获取类型
收费全文 | 31251篇 |
免费 | 5509篇 |
国内免费 | 7336篇 |
专业分类
测绘学 | 4371篇 |
大气科学 | 4723篇 |
地球物理 | 5826篇 |
地质学 | 15337篇 |
海洋学 | 3842篇 |
天文学 | 4121篇 |
综合类 | 2170篇 |
自然地理 | 3706篇 |
出版年
2024年 | 122篇 |
2023年 | 353篇 |
2022年 | 950篇 |
2021年 | 1164篇 |
2020年 | 1288篇 |
2019年 | 1512篇 |
2018年 | 1269篇 |
2017年 | 1406篇 |
2016年 | 1525篇 |
2015年 | 1729篇 |
2014年 | 1873篇 |
2013年 | 2018篇 |
2012年 | 1946篇 |
2011年 | 2029篇 |
2010年 | 1649篇 |
2009年 | 2087篇 |
2008年 | 2047篇 |
2007年 | 2167篇 |
2006年 | 2078篇 |
2005年 | 1916篇 |
2004年 | 1753篇 |
2003年 | 1546篇 |
2002年 | 1347篇 |
2001年 | 1216篇 |
2000年 | 1168篇 |
1999年 | 1067篇 |
1998年 | 1051篇 |
1997年 | 655篇 |
1996年 | 584篇 |
1995年 | 543篇 |
1994年 | 484篇 |
1993年 | 416篇 |
1992年 | 274篇 |
1991年 | 226篇 |
1990年 | 154篇 |
1989年 | 112篇 |
1988年 | 109篇 |
1987年 | 69篇 |
1986年 | 45篇 |
1985年 | 34篇 |
1984年 | 25篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1973年 | 7篇 |
1954年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
K. A. van der Hucht 《Astronomy and Astrophysics Review》1992,4(2):123-159
Summary Recent literature on Population I Wolf-Rayet star research extending from the Milky Way to blue compact dwarf galaxies is reviewed, broken down into inventory, basic parameters and galactic distribution, atmospheres, binaries, intrinsic variability, mass loss, enrichment and evolution. Also the incidence of Wolf-Rayet stars with variable non-thermal radio emission, excess X-ray fluxes, and episodic/periodic IR excesses is reviewed. These phenomena appear to be associated with wind-wind interaction in wide long-period WR+OB binaries and with wind-compact object interaction in WR+c binaries, with orbit sizes of the order of magnitude of the WR radio photosphere sizes or larger. 相似文献
74.
本文应用了最新取得的“五统一”区域重力成果,并经过对浅表松散槽(如下辽河断陷,大岩体等)的密度亏损进行补偿改正后,求取了全省的区域重力场及其垂向二次导数,计算了莫氏面等深度图。在分析区域重力场及其垂向二次导数异常特征和莫氏面起伏特征的基础上,划分出辽宁深部构造的基本格局。从平面上探讨了深部构造与地形地势、地质构造及矿产分布的关系,从剖面上剖析了辽宁省地壳分层的宏观特征 相似文献
75.
The Waterman Metamorphic Complex of the central Mojave Desert was exposed as a consequence of early Miocene detachment-dominated extension. However, it has evidence consistent with a more extensive geological history that involves collision of a crustal fragment(s), tectonic thickening by overthrusting and two periods of extension. The metamorphic complex contains granitoid intrusives and felsic mylonitic gneisses as well as polymetamorphic rocks that include marble, calc-silicate, quartzite. mafic granulite, pyribolite, amphibolite, migmatite and biotite schist. The latter group of rocks was affected by an initial series of high-grade metamorphic events (M1 and M2) and a localized lower grade overprint (M3). The initial metamorphism (M1) can be separated into two stages along its high-grade P–T path: M1a, a granulite facies metamorphism at 800–850° C and 7.5–9 kbar and Mlb, an upper amphibolite facies overprint at 750–800° C and 10–12 kbar. M1a developed mineral assemblages and textures consistent with granulite facies conditions at a reduced activity of H2O and is associated with intense ductile deformation (D1) and minor local partial melting. M1b overprinted the granulite assemblages with a series of hydrous phases under conditions of increasing pressure and H2O activity and is accompanied by little or no deformation. M2 developed at lower pressures and temperatures (650–750° C, 4.5–5.5 kbar) and is distinguished by a second local overprint of hydrous phases that reflects an input of aqueous fluids probably associated with the intrusion of a series of granitic dykes and veins. Effects of M3 are confined to the Mitchel detachment zone, an anastomosing early Miocene detachment fault, and are characterized by local ductile/brittle deformation (D2) of the pre-existing high-grade rocks and granitoid intrusives and by the production of mylonites and mylonitic gneisses under greenschist facies conditions (300–350° C, 3–5 kbar). The initial overprint (M1a) represents metamorphism, devolatilization and minor partial melting of supracrustal rocks under granulite facies conditions as a consequence of tectonic and, possibly, magmatic thickening. The increasing pressure transition of M1a to M1b reflects a period of continued compressional tectonism, thrusting and influx of H2O, in part, locally related to crystallization of partial melts. The near isothermal decompression between M1b and M2 probably represents a pre-112-Ma extensional episode that may have been the result of a decompressional readjustment of a thickened crust. Following the initial extensional event, the metamorphic complex remained at depths of 10–17 km for at least 90 Ma until it was uplifted following Miocene extension. M3 develops locally in response to this second extensional period resulting from the early Miocene detachment faulting. 相似文献
76.
探讨用遗传算法对数学模型进行优化。考虑到控制系统稳健性的要求 ,用遗传算法寻找出控制系统最佳稳定域 ,实现控制系统数学模型的寻优。阐述了用遗传算法求解问题的步骤和参数的取值 ,并用仿真实验对优化结果进行了检验。结果表明 :在控制系统数学模型的优化中 ,遗传算法具有其他算法无可比拟的优越性。 相似文献
77.
当前,由于缺乏对气象服务投入量与产出量准确而完整的统计,要对气象服务的各种经济效益作出总体评价是困难的。然而,在专项气象服务中,却不乏原始、完整而准确的资料。作者从此出发,讨论了专项气象服务经济效益评价的理论。并通过实地调查,以彭州市气象局几项专项气象服务为例探讨了评价技术。 相似文献
78.
79.
G. Machabeli D. Khechinashvili G. Melikidze D. Shapakidze 《Monthly notices of the Royal Astronomical Society》2001,327(3):984-988
We present a model for microstructure in pulsar radio emission. We propose that micropulses result from alteration of the radio wave generation region by nearly transverse drift waves propagating across the pulsar magnetic field and encircling the bundle of the open magnetic field lines. It is demonstrated that such waves can modify the curvature of the field lines significantly. This, in turn, affects strongly fulfilment of the resonance conditions necessary for the excitation of radio waves. The time-scale of micropulses is therefore determined by the wavelength of the drift waves. The main features of the microstructure are naturally explained within the framework of this model. 相似文献
80.
M. V. Sazhin V. E. Zharov T. A. Kalinina 《Monthly notices of the Royal Astronomical Society》2001,323(4):952-964
Parallax measurements allow distances to celestial objects to be determined. Together with measurements of their position on the celestial sphere, they give a full three-dimensional picture of the location of the objects relative to the observer. The distortion of the parallax value of a distant source affected by weak microlensing is considered. This means that the weak microlensing leads to distortion of the distance scale. The gravitational deflection causes a retrograde apparent motion of the image, which is revealed as a negative parallax. It is shown that the distortions may significantly change the parallax values when they amount to several microseconds of arc. In particular, at this level many measured values of parallaxes should be negative. 相似文献