全文获取类型
收费全文 | 6511篇 |
免费 | 1435篇 |
国内免费 | 2050篇 |
专业分类
测绘学 | 328篇 |
大气科学 | 680篇 |
地球物理 | 1952篇 |
地质学 | 4771篇 |
海洋学 | 563篇 |
天文学 | 130篇 |
综合类 | 479篇 |
自然地理 | 1093篇 |
出版年
2024年 | 42篇 |
2023年 | 139篇 |
2022年 | 325篇 |
2021年 | 321篇 |
2020年 | 289篇 |
2019年 | 351篇 |
2018年 | 313篇 |
2017年 | 254篇 |
2016年 | 326篇 |
2015年 | 391篇 |
2014年 | 395篇 |
2013年 | 395篇 |
2012年 | 458篇 |
2011年 | 436篇 |
2010年 | 424篇 |
2009年 | 436篇 |
2008年 | 403篇 |
2007年 | 453篇 |
2006年 | 453篇 |
2005年 | 405篇 |
2004年 | 370篇 |
2003年 | 316篇 |
2002年 | 299篇 |
2001年 | 265篇 |
2000年 | 253篇 |
1999年 | 248篇 |
1998年 | 214篇 |
1997年 | 194篇 |
1996年 | 154篇 |
1995年 | 114篇 |
1994年 | 133篇 |
1993年 | 108篇 |
1992年 | 102篇 |
1991年 | 49篇 |
1990年 | 37篇 |
1989年 | 42篇 |
1988年 | 26篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 7篇 |
1977年 | 1篇 |
1954年 | 7篇 |
排序方式: 共有9996条查询结果,搜索用时 15 毫秒
931.
һ���ɵ���ֱ�����굽��������ֱ��ת�� 总被引:2,自引:2,他引:2
?????????????????????????ι??????????????????????????????γ?????е?4?η???,???????????????γ??????????4?η?????????????????Ч?????????е???????????????????? 相似文献
932.
«ɽ�����ѧ����۲�������仯 总被引:1,自引:0,他引:1
??????????????????????????????????????????????????????????????????????????????????仯???????????????1????????????????仯????????????????????????????????????????????????????????????????????????л?????????????仯????????????????????仯???????|2??????????????仯??????????????????|3?????μ?????????????????????????-???ο???????????仯??????????????????????????????????????? 相似文献
933.
??????M8.0????????????????????С???????????????????о???????????λ????????????????????ν???ие???????????????????1??M8.0??????????????????????????????????????С????????????????????????????????????????????????42°????????????????????????????20 km??2?????????????????????????????????????10 km?????????????????С??????????????????????????????????????????????????????λ?????????7 km??3??2??14??
ML3.7?????????????????93°?????????????????????С??????????????????????????????????2???????£????????????????????????????????????????????????????????????????4??2??28??ML3.8?????????λ?????????????????????????????????????????????????????????£???????????? 相似文献
934.
This paper presents a three‐dimensional energy‐based solution for the time‐dependent response of a deeply embedded and unsupported semi‐infinite tunnel of circular cross‐section. The tunnel is taken to be excavated quasi‐instantaneously from an infinite rock body that initially exhibits an isotropic stress state and that is made up of a homogeneous, isotropic and viscoelastic material. The viscoelastic behaviour is modelled by means of Burger's model, and the rock is taken to behave volumetrically linear elastic and to exhibit exclusively deviatoric creep. This viscoelastic problem is transformed into the Laplace domain, where it represents a quasi‐elastic problem. The displacement fields in the new solution are taken to be the products of independent functions that vary in the radial and longitudinal directions. The differential equations governing the displacements of the system and appropriate boundary conditions are obtained using the principle of minimum potential energy. The solutions for these governing equations in the Laplace domain are then obtained analytically and numerically using a one‐dimensional finite difference technique. The results are then transformed back into the time domain using an efficient numerical scheme. The accuracy of the new solution is comparable with that of a finite element analysis but requires much less computation effort. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
935.
Two formulations for calculating dynamic response of a cylindrical cavity in cross‐anisotropic porous media based on complex functions theory are presented. The basis of the method is the solution of Biot's consolidation equations in the complex plane. Employing two groups of potential functions for solid skeleton and pore fluid (each group includes three functions), the u–w formulation of Biot's equations are solved. Difference of these two solutions refers to use of two various potential functions. Equations for calculating stress, displacement and pore pressure fields of the medium are mentioned based on each two formulations. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
936.
Kinematic pile–soil interaction under vertically impinging seismic P waves is revisited through a novel continuum elastodynamic solution of the Tajimi type. The proposed model simulates the steady‐state kinematic response of a cylindrical end‐bearing pile embedded in a homogeneous viscoelastic soil stratum over a rigid base, subjected to vertically propagating harmonic compressional waves. Closed‐form solutions are obtained for the following: (i) the displacement field in the soil and along the pile; (ii) the kinematic Winkler moduli (i.e., distributed springs and dashpots) along the pile; (iii) equivalent, depth‐independent, Winkler moduli to match the motion at the pile head. The solution for displacements is expressed in terms of dimensionless transfer functions relating the motion of the pile head to the free‐field surface motion and the rock motion. It is shown that (i) a pile foundation may significantly alter (possibly amplify) the vertical seismic excitation transmitted to the base of a structure and (ii) Winkler moduli pertaining to kinematic loading differ from those for inertial loading. Simple approximate expressions for kinematic Winkler moduli are derived for use in applications. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
937.
陈以良 《广东海洋大学学报》1991,(2)
溶胶的电动电位是溶胶发生电动现象的主要原因,它的大小直接影响溶胶的稳定性。本文采用界面移动法研究了溶胶的浓度,电极的种类以及不同的辅助液和硫化锑溶胶的电动电位之间的关系。 相似文献
938.
对高级数据加密标准(AES)和RSA两种数据加密算法进行了介绍和比较。通过横向混合,进行了编码设计的一种探索,分析新编码方式的特点和安全性并进行了软件实现。 相似文献
939.
浙江中生代主要浅成热液金银矿床在蚀变-矿化过程中的一些物理化学特征参数(如T、P、St和ρ等)呈非线性的变化关系,其控制变量是P、T和PH值.推断条带(或环带)状构造的矿脉(石)是由减压沸腾作用造成的.据Drummond等(1985)沸腾的模拟计算和研究表明,[H+]浓度是决定沸腾热液中的Au、Ag等成矿元素命运的主要因素.因此,可以[H+]浓度(状态变量)作为序参量来反映成矿溶液中Au、Ag浓度的变化趋势;并建立其自组织过程的动力学方程与开放沸腾热液系统Au、Ag沉淀的耗散结构模型. 相似文献
940.
杨进 《成都信息工程学院学报》2001,16(3):220-223
提出了导体系统电容问题求解的一种新方法,借助双球面坐标系和平行板电容公式,求出了异心球形电容器电容的解析式。此外,对另外几种类型异体系统的电容也作了讨论。 相似文献