全文获取类型
收费全文 | 69803篇 |
免费 | 11100篇 |
国内免费 | 14685篇 |
专业分类
测绘学 | 7016篇 |
大气科学 | 8481篇 |
地球物理 | 14989篇 |
地质学 | 36419篇 |
海洋学 | 7868篇 |
天文学 | 4926篇 |
综合类 | 4788篇 |
自然地理 | 11101篇 |
出版年
2024年 | 241篇 |
2023年 | 686篇 |
2022年 | 1791篇 |
2021年 | 2146篇 |
2020年 | 2343篇 |
2019年 | 2938篇 |
2018年 | 2138篇 |
2017年 | 2655篇 |
2016年 | 2767篇 |
2015年 | 3016篇 |
2014年 | 3779篇 |
2013年 | 4083篇 |
2012年 | 4058篇 |
2011年 | 4433篇 |
2010年 | 3639篇 |
2009年 | 4679篇 |
2008年 | 4585篇 |
2007年 | 5086篇 |
2006年 | 4888篇 |
2005年 | 4128篇 |
2004年 | 3880篇 |
2003年 | 3614篇 |
2002年 | 3045篇 |
2001年 | 2703篇 |
2000年 | 2495篇 |
1999年 | 2359篇 |
1998年 | 2123篇 |
1997年 | 1830篇 |
1996年 | 1638篇 |
1995年 | 1379篇 |
1994年 | 1354篇 |
1993年 | 1181篇 |
1992年 | 906篇 |
1991年 | 638篇 |
1990年 | 556篇 |
1989年 | 469篇 |
1988年 | 349篇 |
1987年 | 222篇 |
1986年 | 166篇 |
1985年 | 128篇 |
1984年 | 57篇 |
1983年 | 41篇 |
1982年 | 54篇 |
1981年 | 39篇 |
1980年 | 42篇 |
1979年 | 41篇 |
1978年 | 47篇 |
1977年 | 43篇 |
1976年 | 26篇 |
1954年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
91.
We explore the possibility of searching for groups of radio sources from the FIRST catalog on angular scales 1′–5′. We developed an efficient method of searching for such groups that takes into account the need for combining the components of extended sources represented in the catalog by separate objects. We found 31 groups of radio sources with angular sizes <5′ that contain no fewer than five sources with flux densities ≥3 mJy. This number is at least triple the expected number of such groups for a random Poisson distribution of radio sources in the sky. The prospects for using groups of radio sources to detect and study distant systems of galaxies are discussed. 相似文献
92.
YANGYong-liang SHITong-guang JLANGLU-guang LIYue 《中国地理科学(英文版)》2003,13(2):130-133
In recent years, many coal-producing countries have paid great attention to the land subsidence causedby coal cutting. In China, because of the dense population in coalfield areas, the land subsidence hazard is more seri-ous. After a brief analysis on the mechanism of land subsidence, this paper gives a comprehensive and systematical ac-count on all kinds of hazards caused by the land subsidence in China. The study shows that land subsidence has endan-gered land, buildings, traffic and communication lines, dykes and dams. It also causes damage to ecological and socialenvironment. In order to lessen the hazard of land subsidence, preventive measures should be taken to reduce the col-lapse amount, such as extraction with stowing, banded mining system, succession and coordination mining system, orhigh-pressure mudflow between rock strata. Measures of reinforcing or moving certain buildings should also be taken toreduce the destructive degree. In order to harness the subsidence land and bring them under control for fanning, mea-sures should be taken such as filling with spoil or fine breeze, excavating the deeper and covering the shallower land. 相似文献
93.
The remnant resulting from the merger of two neutron stars produces neutrinos in copious amounts. In this paper we present the neutrino emission results obtained via Newtonian, high-resolution simulations of the coalescence event. These simulations use three-dimensional smoothed particle hydrodynamics together with a nuclear, temperature-dependent equation of state and a multiflavour neutrino leakage scheme. We present the details of our scheme, discuss the neutrino emission results from a neutron star coalescence and compare them with the core-collapse supernova case where neutrino emission has been studied for several decades. The average neutrino energies are similar to those in the supernova case, but contrary to the latter, the luminosities are dominated by electron-type antineutrinos that are produced in the hot, neutron-rich, thick disc of the merger remnant. The cooler parts of this disc contain substantial fractions of heavy nuclei, which, however, do not influence the overall neutrino emission results significantly. Our total neutrino luminosities from the merger event are considerably lower than those found in previous investigations. This imposes constraints on the ability of neutron star mergers to produce a gamma-ray burst via neutrino annihilation. The neutrinos are emitted preferentially along the initial binary rotation axis, an event seen 'pole-on' would appear much brighter in neutrinos than a similar event seen 'edge-on'. 相似文献
94.
Makoto Ideta 《Astrophysics and Space Science》2003,284(2):531-534
Dynamical evolution of N-body bars embedded in spherical and prolate dark matter halos is investigated. In particular, the configuration such that
galactic disks are placed in the plane perpendicular to the equatorial plane of the prolate halos is considered. Such a configuration
is frequently found in cosmological simulations. N-body disks embedded in a fixed external halo potential were simulated, so that the barred structure was formed via dynamical
instability in initially cool disks. In the subsequent evolution, bars in prolate halos dissolved gradually with time, while
the bar pattern in spherical halos remained almost unchanged until the end of simulations. The e-folding time of bars suggest
that they could be destroyed in a time smaller than a Hubble time.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
95.
We demonstrate that the chaotic orbits of Prometheus and Pandora are due to interactions associated with the 121:118 mean motion resonance. Differential precession splits this resonance into a quartet of components equally spaced in frequency. Libration widths of the individual components exceed the splitting, resulting in resonance overlap which causes the chaos. Mean motions of Prometheus and Pandora wander chaotically in zones of width 1.8 and 3.1 deg yr−1, respectively. A model with 1.5 degrees of freedom captures the essential features of the chaotic dynamics. We use it to show that the Lyapunov exponent of 0.3 yr−1 arises because the critical argument of the dominant member of the resonant quartet makes approximately two separatrix crossings every 6.2 year precessional cycle. 相似文献
96.
Piero F. Spinnato Michael Fellhauer Simon F. Portegies Zwart 《Monthly notices of the Royal Astronomical Society》2003,344(1):22-32
We study the efficiency at which a black hole or dense star cluster spirals in to the Galactic Centre. This process takes place on a dynamical friction time-scale, which depends on the value of the Coulomb logarithm (ln Λ). We determine the accurate value of this parameter using the direct N -body method, a tree algorithm and a particle-mesh technique with up to two million plus one particles. The three different techniques are in excellent agreement. Our measurement for the Coulomb logarithm appears to be independent of the number of particles. We conclude that ln Λ= 6.6 ± 0.6 for a massive point particle in the inner few parsec of the Galactic bulge. For an extended object, such as a dense star cluster, ln Λ is smaller, with a value of the logarithm argument Λ inversely proportional to the object size. 相似文献
97.
茅排金矿床属中-低温硫化物金矿床,矿体的分布严格受断裂构造控制.通过应用不同的物探方法来寻找控矿断裂,从而达到间接地寻找矿体分布的目的,取得了较好的效果。 相似文献
98.
本文给出1993—1994年期间,用云南天文台1米望远镜折轴摄谱仪观测获得类太阳色球活动星。εEri的5个波段高分辨、高信噪比光谱,运用两种不同方法:谱线轮廓塞曼致宽分析和多重线统计分析法成功地测定了εEri的表面磁场强度和磁场的覆盖因子,并对这两种磁场测定方法作了简单的讨论. 相似文献
99.
从地形地貌特征、重磁地球物理场、深部构造与断裂构造以及地震活动、震源机制等多方面论述北东东向构造是南海北缘的主要活动构造。对于长期以来认为新华夏系北东向构造是该区主要活动构造的观点来说,这是一种新的学术思想。 相似文献
100.
DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHEHEXIREGION,CHINA肖洪浪,高前兆,李福兴DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHE... 相似文献