全文获取类型
收费全文 | 3318篇 |
免费 | 314篇 |
国内免费 | 239篇 |
专业分类
化学 | 265篇 |
晶体学 | 25篇 |
力学 | 2038篇 |
综合类 | 24篇 |
数学 | 337篇 |
物理学 | 1182篇 |
出版年
2024年 | 11篇 |
2023年 | 34篇 |
2022年 | 87篇 |
2021年 | 60篇 |
2020年 | 110篇 |
2019年 | 88篇 |
2018年 | 72篇 |
2017年 | 129篇 |
2016年 | 138篇 |
2015年 | 110篇 |
2014年 | 163篇 |
2013年 | 168篇 |
2012年 | 144篇 |
2011年 | 200篇 |
2010年 | 130篇 |
2009年 | 147篇 |
2008年 | 141篇 |
2007年 | 178篇 |
2006年 | 176篇 |
2005年 | 166篇 |
2004年 | 182篇 |
2003年 | 165篇 |
2002年 | 121篇 |
2001年 | 113篇 |
2000年 | 95篇 |
1999年 | 100篇 |
1998年 | 118篇 |
1997年 | 68篇 |
1996年 | 62篇 |
1995年 | 46篇 |
1994年 | 53篇 |
1993年 | 41篇 |
1992年 | 41篇 |
1991年 | 48篇 |
1990年 | 36篇 |
1989年 | 32篇 |
1988年 | 21篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1971年 | 4篇 |
1957年 | 8篇 |
排序方式: 共有3871条查询结果,搜索用时 562 毫秒
131.
Feng Ruoqiang Wu Yue Shen Shizhao 《Acta Mechanica Solida Sinica》2006,19(3):248-254
The cable net supported glass curtain wallas the most advanced technique in dot point supported glass curtain wall, is widely used in China. Because of its large deflection and high nonlinearity under wind load, the dynamic performance of the cable net is greatly different from that of the conventional linear structures. The continuous membrane theory is used to construct the nonlinear vibration differential equation of the cable net, and the harmonic balance method is used to solve the analytic formula of the nonlinear frequency. In order to verify the accuracy of the above analytic formula, the results of the formula and the nonlinear FEM time-history method are compared and found to be in good agreement. Furthermore, the nonlinear vibration differential equation and the nonlinear frequency obtained in this paper are the basis for the wind-induced response analysis of a cable net under fluctuating wind load. 相似文献
132.
Appling Mindlin's theory of thick plates and Hamilton system to propagation of elastic waves under free boundary condition, a solution of the problem was given. Dispersion equations of propagation mode of strip plates were deduced from eigenfunction expansion method. It was compared with the dispersion relation that was gained through solution of thick plate theory proposed by Mindlin. Based on the two kinds of theories, the dispersion curves show great difference in the region of short waves, and the cutoff frequencies are higher in Hamiltonian systems. However, the dispersion curves are almost the same in the region of long waves. 相似文献
133.
134.
135.
136.
基于粗糙集模糊神经网络的爆破振动危害预测 总被引:2,自引:0,他引:2
为了探索一种能克服单因素预测的局限性、提高爆破振动危害预测精度的方法,基于粗糙集模糊神经网络理论,建立了综合考虑爆破振动幅值、主频率、主频率持续时间及结构动力特性等10个因素的民房破坏程度预测模型;用铜绿山矿爆破振动和民房破坏情况观测数据,对该模型进行了训练和测试,测试结果与现场观测结果具有良好的一致性。研究表明:粗糙集理论可将现场数据进行属性约简,简化输入变量,缩小神经网络的搜索空间,改善爆破振动的预测性能;基于粗糙集模糊神经网络理论的爆破振动危害预测模型,能更好地考虑各种因素对危害程度的综合影响,避免了单因素预测的局限性。 相似文献
137.
138.
Huaqing Peng Heng Li Yu Zhang Siyuan Wang Kai Gu Mifeng Ren 《Entropy (Basel, Switzerland)》2022,24(2)
In order to reduce maintenance costs and avoid safety accidents, it is of great significance to carry out fault prediction to reasonably arrange maintenance plans for rotating mechanical equipment. At present, the relevant research mainly focuses on fault diagnosis and remaining useful life (RUL) predictions, which cannot provide information on the specific health condition and fault types of rotating mechanical equipment in advance. In this paper, a novel three-stage fault prediction method is presented to realize the identification of the degradation period and the type of failure simultaneously. Firstly, based on the vibration signals from multiple sensors, a convolutional neural network (CNN) and long short-term memory (LSTM) network are combined to extract the spatiotemporal features of the degradation period and fault type by means of the cross-entropy loss function. Then, to predict the degradation trend and the type of failure, the attention-bidirectional (Bi)-LSTM network is used as the regression model to predict the future trend of features. Furthermore, the predicted features are given to the support vector classification (SVC) model to identify the specific degradation period and fault type, which can eventually realize a comprehensive fault prediction. Finally, the NSF I/UCR Center for Intelligent Maintenance Systems (IMS) dataset is used to verify the feasibility and efficiency of the proposed fault prediction method. 相似文献
139.
基于单幅数字散斑投影及图像相关的离面振动测量 总被引:1,自引:0,他引:1
采用单幅数字散斑图投影及高速数字图像采集技术,研究了动态离面位移的测量。采用商用液晶投影仪将计算机产生的模拟散斑图投影到待测动态变形物体表面,由高速数字图像采集设备摄取并保存变形散斑图,采用时间序列数字图像相关软件计算出物体表面各点随时间变化的离面位移。这种方法用于振动分析时不仅可以获得振型分布,而且还可以获得各点的振幅值。与现有的激光频闪照相测振及激光多普勒测振等方法相比,具有光学系统简单,可全场定量测量。悬臂梁振动实验结果证实了该方法的有效性。 相似文献
140.