全文获取类型
收费全文 | 7538篇 |
免费 | 1592篇 |
国内免费 | 3074篇 |
专业分类
测绘学 | 448篇 |
大气科学 | 924篇 |
地球物理 | 2178篇 |
地质学 | 6091篇 |
海洋学 | 900篇 |
天文学 | 257篇 |
综合类 | 929篇 |
自然地理 | 477篇 |
出版年
2024年 | 20篇 |
2023年 | 52篇 |
2022年 | 129篇 |
2021年 | 158篇 |
2020年 | 111篇 |
2019年 | 123篇 |
2018年 | 160篇 |
2017年 | 137篇 |
2016年 | 157篇 |
2015年 | 171篇 |
2014年 | 135篇 |
2013年 | 190篇 |
2012年 | 154篇 |
2011年 | 668篇 |
2010年 | 454篇 |
2009年 | 588篇 |
2008年 | 258篇 |
2007年 | 421篇 |
2006年 | 605篇 |
2005年 | 684篇 |
2004年 | 1331篇 |
2003年 | 837篇 |
2002年 | 582篇 |
2001年 | 477篇 |
2000年 | 352篇 |
1999年 | 381篇 |
1998年 | 382篇 |
1997年 | 396篇 |
1996年 | 269篇 |
1995年 | 204篇 |
1994年 | 181篇 |
1993年 | 402篇 |
1992年 | 339篇 |
1991年 | 175篇 |
1990年 | 66篇 |
1989年 | 108篇 |
1988年 | 36篇 |
1987年 | 73篇 |
1986年 | 41篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1978年 | 9篇 |
1977年 | 16篇 |
1976年 | 10篇 |
1950年 | 8篇 |
1940年 | 9篇 |
1937年 | 15篇 |
1933年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
101.
102.
The large cylinder is a new-type structure that has been applied to harbor and offshore engineering. An analytic method of the relationship between loads and the structure displacement is developed based on the failure mode of deep embedded large cylinder structures. It can be used to calculate directly the soil resistance and the ultirnate bearing capacity of the structure under usage. A new criterion of the large cylinder structure, which discriminates the deep embedded cylinder from the shallow embedded cylinder, is defined. Model tests prove that the proposed method is feasible for the analysis of deep embedded large cylinder structures. 相似文献
103.
This paper proposes a nonlinear robust adaptive control strategy to force a six degrees of freedom underactuated underwater vehicle with only four actuators to follow a predefined path at a desired speed despite of the presence of environmental disturbances and vehicle’s unknown physical parameters. The proposed controller is designed using Lyapunov’s direct method, the popular backstepping and parameter projection techniques. The closed loop path following errors can be made arbitrarily small. Interestingly, it is shown that our developed control strategy is easily extendible to situations of practical importance such as parking and point-to-point navigation. Numerical simulations are provided to illustrate the effectiveness of the proposed methodology. 相似文献
104.
对海水中Zn(Ⅱ),Ca(Ⅱ),Cd(Ⅱ)与高岭石、伊利石和蒙脱石等粘土矿物;无定形水合氧化铁、α-FeOOH等铁的水合氧化物;δ-MaO_2,γ-MnOOH,水锰矿等锰的水合氧化物等30个左右实验体系的液-固界面台阶型动力学曲线进行了系统的实验测定和全面的条件研究。在实验测定上提出两种方法、互为校核。对动力学曲线之台阶的消长和变化规律作了系统研究,确定主要影响因素是:金属离子初始浓度、固体交换剂量、体系的pH值和温度,以及搅拌速度等。 相似文献
105.
A Unified Variational Principle of Fluid Mechanics and Application on Solitary Subdomain or Point 总被引:1,自引:0,他引:1
-According to basic equations of fluid mechanics, this paper presents a unified variational principle of fluid mechanics (UVPFM) by using the optimization method of weighted residuals (OMWR). The advantages are as follows, the establishment of the functional and the variational principle is easy, it can change various problems of fluid mechanics derived by basic equations into a unified optimization problem, and the solution is the optimum one in some sense. According to the OMWR for the solitary subdomain, this paper uses UVPFM onto any solitary subdomain and gives the solution of the hydrodynamics equation which is suitable only for that solitary subdomain. According to the OMWR for solitary point, this paper uses UVPFM to any solitary point and gives the solution of the hydrodynamics equation (point solution) which is suitable only for that solitary point. As the solution for the solitary subdomain or solitary point is developed independently, the compatibility with other subdomain or other points, do 相似文献
106.
107.
对于含多资料三维分潮波模型建立了一种岸边资料运动学外推的潮波第一边值方法,并对渤海的四大原湖波进行试算。结果证实本方法可行,该方法使潮波方程既满足第一边值问题,充分利用岸边测站资料,又保证岸界法向流速为零条件,符合物理意义。并对复型病态矩阵的收敛问题提出了一种可行性处理。 相似文献
108.
Circulations east of Taiwan and in East China Sea and east of Ryukyu Islands during early summer 1985YuanYaochu;Cho-tengLiu;P... 相似文献
109.
A novel method for prediction of the load carrying capacity of a corroded reinforced concrete beam (CRCB) is presented in the paper. Nine reinforced concrete beams, which had been working in an aggressive environment for more than 10 years, were tested in the laboratory. Comprehensive tests, including flexural test, strength test for corroded concrete and rusty rebar, and pullout test for bond strength between concrete and rebar, were condueted. The flexural test results of CRCBs reveal that the distribution of surface cracks on the beams shows a fractal behavior. The relationship between the fractal dimensions and mechanical properties of CRCBs is then studied. A prediction model based on artificial neural network (ANN) is established by the use of the fractal dimension as the corrosion index, together with the basic intbrmation of the beam. The validity of the prediction model is demonstrated through the experimental data, and satisfactory resuits are achieved. 相似文献
110.
1 INTsoDUcrIONTemperature is one of the most impoFtant essential factors of ocean, and its verticalstructure, especially the phenomenon ofthermocline, is concerned by military and manufacturepractices at all times. There are two classes of research methods for thermocIine, statisticmethod and numerical method. In recent years, more attention has been paid to the latterwhich becomes the primary development direction. Since Munk et al (1948) pot forward1-D model of thermocline at steady sta… 相似文献