全文获取类型
收费全文 | 33042篇 |
免费 | 6892篇 |
国内免费 | 7276篇 |
专业分类
测绘学 | 2273篇 |
大气科学 | 5652篇 |
地球物理 | 9066篇 |
地质学 | 17010篇 |
海洋学 | 4054篇 |
天文学 | 1883篇 |
综合类 | 3209篇 |
自然地理 | 4063篇 |
出版年
2024年 | 183篇 |
2023年 | 608篇 |
2022年 | 1459篇 |
2021年 | 1720篇 |
2020年 | 1480篇 |
2019年 | 1774篇 |
2018年 | 1936篇 |
2017年 | 1856篇 |
2016年 | 2116篇 |
2015年 | 1817篇 |
2014年 | 2183篇 |
2013年 | 2259篇 |
2012年 | 2023篇 |
2011年 | 2068篇 |
2010年 | 1973篇 |
2009年 | 1817篇 |
2008年 | 1775篇 |
2007年 | 1630篇 |
2006年 | 1279篇 |
2005年 | 1319篇 |
2004年 | 1020篇 |
2003年 | 1019篇 |
2002年 | 1077篇 |
2001年 | 1025篇 |
2000年 | 996篇 |
1999年 | 1272篇 |
1998年 | 979篇 |
1997年 | 1086篇 |
1996年 | 973篇 |
1995年 | 821篇 |
1994年 | 676篇 |
1993年 | 610篇 |
1992年 | 499篇 |
1991年 | 350篇 |
1990年 | 291篇 |
1989年 | 237篇 |
1988年 | 218篇 |
1987年 | 148篇 |
1986年 | 130篇 |
1985年 | 91篇 |
1984年 | 67篇 |
1983年 | 54篇 |
1982年 | 46篇 |
1981年 | 40篇 |
1980年 | 47篇 |
1979年 | 34篇 |
1978年 | 23篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1958年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
51.
With a new theory on the 1PN celestial mechanics recently developed by Damour, Soffel and Xu (1991,1992,1993,1994), definitions
and expressions of the 1PN spin angular momentum are investigated and analysed. The total spin angular momentum of a system
of extended bodies such as the solar system is calculated and expressed as the function of local parameters and observables
under reasonable assumptions, which would find its application in the evolution and dynamics of systems of celestial bodies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
52.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
53.
以N_(263)浸渍在DA_(201)大孔吸附树脂上制得了N_(263)浸渍树脂,测定了静态时树脂Pb(Ⅱ)的吸附容量。通过柱层析法,试验了酸度,流速和干扰离子等因素对N_(263)浸渍树脂吸附和洗脱Pb的影响。建立了N_(263)浸渍树脂分离─富集后衔接原子吸收和比色法测定Pb(Ⅱ)的方法,测定了地质样品中Pb(Ⅱ),测试结果理想。 相似文献
54.
Lin Liu 《Chinese Astronomy and Astrophysics》1997,21(4):488-500
With the aim of analyzing the errors in the radial position of satellites, we give in this paper the expressions for the radial perturbation which include the complete zeroth- and first-order terms in the orbital eccentricity. A simpler and faster method of calculating the perturbation is given. 相似文献
55.
THE SIMULATED STORAGE CAPACITY OF FLOOD AND WATERLOGGING IN THE TYPICAL AGRICULTURAL REGION IN JIANGHAN PLAIN 总被引:2,自引:0,他引:2
1INTRODUCTIONJianghanPlainisoneoftheimportantbasesofChina′sagriculturalproductivitylocatedinthemiddleChangjiangRivervalleyofcentralChina.TheJianghanplainapproximately6.6×104km2inareaandover30millioninpopulationistherenowned“countryoffishandrice"in… 相似文献
56.
57.
Abstract— Abundances and isotopic compositions of noble gases in metal and graphite of the Bohumilitz IAB iron meteorite were measured. The abundance ratios of spallogenic components in metal reveal a 3He deficiency which is due to the diffusive loss of parent isotopes, that is, tritium (Tilles, 1963; Schultz, 1967). The diffusive loss likely has been induced by thermal heating by the Sun during cosmic‐ray exposure (~160 Ma; Lavielle et al, 1999). Thermal process such as impact‐induced partial loss may have affected the isotopic composition of spallogenic Ne. The 129Xe/131Xe ratio of cosmogenic components in the metal indicates an enhanced production of epi‐thermal neutrons. The abundance ratios of spallogenic components in the graphite reveal that it contained small amounts of metal and silicates. The isotopic composition of heavy noble gases in graphite itself was obtained from graphite treated with HF/HCl. The isotopic composition of the etched graphite shows that it contains two types of primordial Xe (i.e., Q‐Xe and El Taco Xe). The isotopic heterogeneity preserved in the Bohumilitz graphite indicates that the Bohumilitz graphite did not experience any high‐temperature event and, consequently, must have been emplaced into the metal at subsolidus temperatures. This situation is incompatible with an igneous model as well as the impact melting models for the IAB‐IIICD iron meteorites as proposed by Choi et al. (1995) and Wasson et al (1980). 相似文献
58.
In this paper, we reconstruct the finite energy force-free magnetic field of the active region NOAA 8100 on 4 November 1997
above the photosphere. In particular, the 3-D magnetic field structures before and after a 2B/X2 flare at 05:58 UT in this
region are analyzed. The magnetic field lines were extrapolated in close coincidence with the Yohkoh soft X-ray (SXR) loops accordingly. It is found that the active region is composed of an emerging flux loop, a complex loop
system with differential magnetic field shear, and large-scale, or open field lines. Similar magnetic connectivity has been
obtained for both instants but apparent changes of the twisting situations of the calculated magnetic field lines can be observed
that properly align with the corresponding SXR coronal loops. We conclude that this flare was triggered by the interaction
of an emerging flux loop and a large loop system with differential magnetic field shear, as well as large-scale, or open field
lines. The onset of the flare was at the common footpoints of several interacting magnetic loops and confined near the footpoints
of the emerging flux loop. The sheared configuration remained even after the energetic flare, as demonstrated by calculated
values of the twist for the loop system, which means that the active region was relaxed to a lower energy state but not completely
to the minimum energy state (two days later another X-class flare occurred in this region). 相似文献
59.
成都及附近地区旅游气候资源研究 总被引:9,自引:0,他引:9
通过对成都及附近等7个地区多年气候资源及人体舒适指数进行分级比较,得出了7个地区的人体舒适指数的时间分布特征及对当地旅游的影响。 相似文献
60.
刘满全 《地球科学与环境学报》1994,(2)
本文介绍紫阳骨坡治理工程中有关抗滑桩的设计与施工。文中详细地论述了设计中设计人员应根据工程的具体情况去灵活处理的一些技术问题,如确定有关参数的选择原则,计算上的条件简化和一些具体技术细节的处理方法等. 相似文献