全文获取类型
收费全文 | 13041篇 |
免费 | 2515篇 |
国内免费 | 3179篇 |
专业分类
测绘学 | 1010篇 |
大气科学 | 2449篇 |
地球物理 | 3301篇 |
地质学 | 6692篇 |
海洋学 | 1849篇 |
天文学 | 504篇 |
综合类 | 1378篇 |
自然地理 | 1552篇 |
出版年
2024年 | 62篇 |
2023年 | 243篇 |
2022年 | 600篇 |
2021年 | 708篇 |
2020年 | 603篇 |
2019年 | 645篇 |
2018年 | 734篇 |
2017年 | 714篇 |
2016年 | 787篇 |
2015年 | 634篇 |
2014年 | 759篇 |
2013年 | 756篇 |
2012年 | 718篇 |
2011年 | 766篇 |
2010年 | 836篇 |
2009年 | 746篇 |
2008年 | 676篇 |
2007年 | 617篇 |
2006年 | 548篇 |
2005年 | 470篇 |
2004年 | 417篇 |
2003年 | 439篇 |
2002年 | 448篇 |
2001年 | 432篇 |
2000年 | 424篇 |
1999年 | 564篇 |
1998年 | 504篇 |
1997年 | 463篇 |
1996年 | 386篇 |
1995年 | 355篇 |
1994年 | 325篇 |
1993年 | 289篇 |
1992年 | 239篇 |
1991年 | 163篇 |
1990年 | 143篇 |
1989年 | 114篇 |
1988年 | 86篇 |
1987年 | 69篇 |
1986年 | 43篇 |
1985年 | 45篇 |
1984年 | 39篇 |
1983年 | 23篇 |
1982年 | 26篇 |
1981年 | 24篇 |
1980年 | 14篇 |
1979年 | 13篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1958年 | 7篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
A possible method for the determination of the magnitude and inclination of a sunspot magnetic-field
Jie-hai Jin 《Chinese Astronomy and Astrophysics》1985,9(1):15-19
A method is presented in this paper for the determination of both the H and the γ of a sunspot magnetic field by means of two polarizers with transmission axes inclined at ± 45° to the fast axis of a quarter-wave plate. Previously, this arrangement was used to determine H only.It is shown that the profiles of the Stokes parameters are sensitive to the sunspot atmosphere model used whereas the results given by the present method are not. It is shown, more ever, that the formula for determining H from the wave length shift, Δλ = 4.67 × 10?5gHλ2, cannot be used in many cases. 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.
An elastoplastic model for sands is presented in this paper, which can describe stress–strain behaviour dependent on mean effective stress level and void ratio. The main features of the proposed model are: (a) a new state parameter, which is dependent on the initial void ratio and initial mean stress, is proposed and applied to the yield function in order to predict the plastic deformation for very loose sands; and (b) another new state parameter, which is used to determine the peak strength and describe the critical state behaviour of sands during shearing, is proposed in order to predict simply negative/positive dilatancy and the hardening/softening behaviour of medium or dense sands. In addition, the proposed model can also predict the stress–strain behaviour of sands under three-dimensional stress conditions by using a transformed stress tensor instead of ordinary stress tensor. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
4.
Kunde Yang Yuanliang Ma Chao Sun Miller J.H. Potty G.R. 《Oceanic Engineering, IEEE Journal of》2004,29(4):964-972
This paper discusses the results of geoacoustic inversion carried out using explosive charge data from the Asian Seas International Acoustic Experiment (ASIAEX) East China Sea (ECS) Experiment. A multifrequency incoherent matched-field inversion processor and a genetic algorithm (GA) are used for the inversion. A multistep matched field inversion approach is presented, which makes use of the varying sensitivities of wave fields at various frequencies to reduce the inversion problem into a sequence of smaller inversions with fewer unknowns to estimate at each stage. Different parameters are estimated using data at different frequencies according to their sensitivities. Inversion results for different areas in the ECS region are summarized and compared with core data. 相似文献
5.
The accuracy of the AE index as a measure of the joule heat production rate is examined for a typical substorm event on 18 March 1978 by estimating the global joule heat production rate, as a function of time, using data obtained from the IMS six meridian chains. In spite of the fact that the AE index had had an initial slow growth which was followed by a rapid growth, the joule heat production rate attained a high level during the slow growth and thus their variations were considerably different from those of the AE index. Therefore, although the AE index is statistically linearly related to the global joule heat production rate, one should be cautious in assuming that details of time variations of the AE index during individual events represent those of the joule heat production rate. 相似文献
6.
本文对徐州地震台JB—72水平摆倾斜仪1988年11月至1989年5月间所记录到的24次同震阶变进行了深入分析,认为:a.造成同震阶变的原因是多方面的,而反应了地球应变场准静态调整的同震阶变才是有价值的价变异常;b.多观测手段的地震台站,同震阶变应该在不止一台仪器上得到响应。 相似文献
7.
Yi-Sui Sun 《Celestial Mechanics and Dynamical Astronomy》1983,30(1):7-19
In this paper, using two methods: LCN'S (Lyapunov characteristic numbers) method and slice cutting method, we study numerically two mappings with odd dimension: $$T_1 :\left\{ {\begin{array}{*{20}c} {x_{n + 1} = x_n + z_n ,} \\ {y_{n + 1} = y_n + x_{n + 1} , (\bmod 2\pi )} \\ {z_{n + 1} = z_n + A\sin y_{n + 1} ,} \\ \end{array} } \right. T_2 :\left\{ {\begin{array}{*{20}c} {x_{n + 1} = x_n + y_n + B \sin z_n ,} \\ {y_{n + 1} = y_n + A \sin x_{n + 1} , (\bmod 2\pi ),} \\ {z_{n + 1} = z_n + B \sin y_{n + 1} ,} \\ \end{array} } \right.$$ whereA, B are parameters. For the mappingT 1 the whole region is stochastic; however, we find two-dimensional invariant manifolds for the mappingT 2. 相似文献
8.
Aquasi-three-dimensionalnumericalpredictionmodelofsalinitystructureinBohaiSeaandHuanghaiSea¥SunWeiyangandWangZongshan(Receive... 相似文献
9.
10.
东营城区高精度三维地震采集方法研究 总被引:3,自引:0,他引:3
根据东营城区内建筑物较多,环境干扰较大,地下构造复杂,断裂非常发育,目的层埋藏深,资料信噪比较低的特点,以地震老资料和钻井资料为基础,建立地震地质模型,利用射线追踪技术选取合适的观测系统参数。充分利用卫星数字地图,没计了灵活多变的观测系统,采用可控震源与炸药震源配合使用方法,及时对城区内地下面元的覆盖次数、方位角和炮检距的分布进行质量监控,利用现场处理系统对资料进行及时分析,提高了地震资料品质。所获得的东营城区高精度三维地震采集资料显示,其浅中层分辨率和中深层信噪比都有了明显改善,取得了良好的地质效果。 相似文献