全文获取类型
收费全文 | 9790篇 |
免费 | 1787篇 |
国内免费 | 2251篇 |
专业分类
测绘学 | 721篇 |
大气科学 | 1880篇 |
地球物理 | 2422篇 |
地质学 | 4799篇 |
海洋学 | 1269篇 |
天文学 | 480篇 |
综合类 | 1108篇 |
自然地理 | 1149篇 |
出版年
2024年 | 52篇 |
2023年 | 219篇 |
2022年 | 479篇 |
2021年 | 552篇 |
2020年 | 423篇 |
2019年 | 418篇 |
2018年 | 542篇 |
2017年 | 475篇 |
2016年 | 568篇 |
2015年 | 484篇 |
2014年 | 619篇 |
2013年 | 565篇 |
2012年 | 536篇 |
2011年 | 542篇 |
2010年 | 574篇 |
2009年 | 522篇 |
2008年 | 492篇 |
2007年 | 444篇 |
2006年 | 367篇 |
2005年 | 285篇 |
2004年 | 269篇 |
2003年 | 281篇 |
2002年 | 341篇 |
2001年 | 340篇 |
2000年 | 300篇 |
1999年 | 418篇 |
1998年 | 397篇 |
1997年 | 354篇 |
1996年 | 339篇 |
1995年 | 280篇 |
1994年 | 257篇 |
1993年 | 199篇 |
1992年 | 170篇 |
1991年 | 131篇 |
1990年 | 138篇 |
1989年 | 96篇 |
1988年 | 78篇 |
1987年 | 77篇 |
1986年 | 60篇 |
1985年 | 33篇 |
1984年 | 25篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 6篇 |
1976年 | 4篇 |
1958年 | 3篇 |
1938年 | 2篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
A formula for the thickness of a shear band formed in saturated soils under a simple shear or a combined stress state has been proposed. It is shown that the shear band thickness is dependent on the pore pressure properties of the material and the dilatancy rate, but is independent of the details of the combined stress state. This is in accordance with some separate experimental observations. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
2.
Lu Sun 《国际地质力学数值与分析法杂志》2003,27(1):69-84
A closed‐form deflection response of a beam rest is presented in this paper using the integral transform method. The theory of linear partial differential equations is used to represent the deflection of beam subjected to a moving harmonic line load in integration form. The solution is finally carried out using the inverse Fourier transform. To evaluate the integration analytically, poles of the integrand are identified with the help of algebraic equation theory. Residue theorem is then utilized to represent the integration as a contour integral in the complex plane. Closed‐form deflections and numerical results are provided for different combinations of load frequency and velocity. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
3.
4.
I INTRODUCTIONWetland has very important effect on retainingwater and against drought, regUlating climate, controlling soil erosion and so on ac. Today men often attachimportance to economic effect of wetland reclamation,but neglect and destroy other functions and effectswhich result in blind wetland development, a lot ofwetland degeneration. The area of freshwater wetland inthe 1950s was 134 x 10'ha, but in the 1970s 70% hadchanged into farmland (MITSCH, 1993). The area ofwetland in d… 相似文献
5.
Yi-Zhong Fan Zi-Gao Dai Yong-Feng Huang Tan Lu Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2002,2(5):449-453
The optical flash accompanying GRB 990123 is believed to be powered by the reverse shock of a thin shell. With the best-fit physical parameters for GRB 990123 and the assumption that the parameters in the optical flash are the same as in the afterglow, we show that: 1) the shell is thick rather than thin, and we have provided the light curve for the thick shell case which coincides with the observation; 2) the theoretical peak flux of the optical flash accounts for only 3×10~-4 of the observed. In order to remove this discrepancy, the physical parameters, the electron energy and magnetic ratios, εe and εB, should be 0.61 and 0.39, which are very different from their values for the late afterglow. 相似文献
6.
Profiles of spectral lines emitted from an accretion ring around an object with strong gravitational field should be affected by Doppler shift, gravitational redshift, and deflection of light. Taking these effects into account, precise line profile of a Keplerian ring around a Kerr black hole for a distant observer is obtained by solving the kinetic equation of photons. 相似文献
7.
青藏块体东北缘地壳水平运动状态 总被引:10,自引:6,他引:4
应用青藏块体东北缘1999~2003年多期GPS观测资料,计算了不同时段GPS点水平运动速率。通过分析发现:甘青块体可分为东部块体和西部块体,东、西部块体的运动状态存在明显的差异;受2001年11月14日昆仑Ms8.1地震的影响,震后地壳运动状态发生了明显的改变。 相似文献
8.
5个新发现的X选BL Lac天体 总被引:1,自引:0,他引:1
利用ROSATVLA方法筛选,从ROSATX射线源中选出了一批新的BLLac天体和类星体的候选体.1996年12月8日至17日,利用北京天文台2.16m望远镜和新从美国引进的OMR摄谱仪,对这批新候选体进行了光谱认证.经SUN工作站处理,又发现了5个新的X选BLLac天体.此外,还对去年作者在OMR引进之前发现的BLLac天体进行了检验,结果发现,去年发现的7个BLLac天体中,2322+343的CaIIH&K“Breakstrength”为26.9%,稍大于判据25%,因此,2322+343到底是BLLac天体还是射电星系还有待于进一步测光及偏振观测的验证. 相似文献
9.
This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
10.
A new algorithm of order five is presented for the solution of the initial value problem where the system of ordinary differential equations is of second order and does not contain the first derivative. 相似文献