全文获取类型
收费全文 | 108049篇 |
免费 | 5544篇 |
国内免费 | 4288篇 |
专业分类
化学 | 45351篇 |
晶体学 | 1157篇 |
力学 | 8794篇 |
综合类 | 342篇 |
数学 | 35369篇 |
物理学 | 26868篇 |
出版年
2024年 | 102篇 |
2023年 | 596篇 |
2022年 | 1061篇 |
2021年 | 1153篇 |
2020年 | 1297篇 |
2019年 | 1242篇 |
2018年 | 11287篇 |
2017年 | 11014篇 |
2016年 | 7393篇 |
2015年 | 2465篇 |
2014年 | 2093篇 |
2013年 | 2707篇 |
2012年 | 6515篇 |
2011年 | 13291篇 |
2010年 | 7543篇 |
2009年 | 7867篇 |
2008年 | 8535篇 |
2007年 | 10472篇 |
2006年 | 1942篇 |
2005年 | 2749篇 |
2004年 | 2721篇 |
2003年 | 2869篇 |
2002年 | 1865篇 |
2001年 | 957篇 |
2000年 | 948篇 |
1999年 | 731篇 |
1998年 | 649篇 |
1997年 | 547篇 |
1996年 | 600篇 |
1995年 | 510篇 |
1994年 | 427篇 |
1993年 | 383篇 |
1992年 | 336篇 |
1991年 | 304篇 |
1990年 | 260篇 |
1989年 | 235篇 |
1988年 | 188篇 |
1987年 | 156篇 |
1986年 | 152篇 |
1985年 | 134篇 |
1984年 | 95篇 |
1983年 | 93篇 |
1982年 | 92篇 |
1981年 | 68篇 |
1980年 | 76篇 |
1979年 | 68篇 |
1978年 | 56篇 |
1914年 | 45篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
The dielectric elastomer (DE) has attracted significant attention due to its desired features, including large deformation, fast response, and high energy density. However, for a DE actuator (DEA) utilizing a snap-through deformation mode, most existing theoretical models fail to predict its deformation path. This paper develops a new finite element method (FEM) based on the three-parameter Gent-Gent model suitable for capturing strain-stiffening behaviors. The simulation results are verified by experiments, indicating that the FEM can accurately characterize the snap-through path of a DE. The method proposed in this paper provides theoretical guidance and inspiration for designing and applying DEs and bistable electroactive actuators. 相似文献
982.
Nonlinear Dynamics - A time-delayed proportional–derivative controller is applied to suppress the nonlinear vibration of a rigid rotor suspended by the active magnetic bearing (AMB) subjected... 相似文献
983.
The relative stability of the 3A2, 1A2, and 1A1 states of phenylnitrene is evaluated by means of ab initio calculations followed by difference-dedicated configuration interaction (DDCI). This approach is based on effective Hamiltonian theory at a low order of perturbation to select rationally the determinants which contribute to the energy difference. The CI space built on this criterion is then treated variationally. The method allows a considerable reduction of the CI space compared with a complete CAS*SDCI calculation (where CAS stands for complete active space). Depending on the concerned energy difference, different model spaces may be chosen, as illustrated in the 3A2 → 1A2 and the 3A2 → 1A1 transitions in phenylnitrene. Since the CI space may reach considerable dimensions, a direct CI algorithm for selected CI spaces, the SCIEL algorithm, has been used to perform the calculations. The results are in excellent agreement with previous calculations and with available experimental data. © 1996 by John Wiley & Sons, Inc. 相似文献
984.
985.
986.
Hu Yinlong Hua Tianyang Chen Michael Z. Q. Shi Shang Sun Yonghui 《Nonlinear dynamics》2021,105(1):99-112
Nonlinear Dynamics - In this paper, the instability of semi-active control systems caused by the utilization of semi-active inerters is analyzed. The purpose of this study is to demonstrate the... 相似文献
987.
具有聚集诱导发光行为的环状多烯类分子 总被引:1,自引:1,他引:0
研究了ΔH-pyrans,fulvenes,siloles等环状多烯结构的小分子荧光染料在溶液,固态及薄层层析板上的荧光发射行为.与大多数传统的荧光染料小分子不同,这些多烯类荧光染料分子在稀溶液中基本没有荧光,而在聚集态下呈现非常明亮的荧光发射,同时伴随着荧光量子效率的大幅提高(聚集诱导发光).它们在薄层层析板上也具有很强的荧光发射.但当薄层层析板暴露于有机溶剂气氛下,荧光消失,离开有机溶剂气氛,荧光恢复,这一可逆过程并可多次重复.在固体状态,它们的荧光发射与聚集态结构密切相关.通过从无定型态到结晶态以及从一种结晶态到另一种结晶态的变化,可以有效的调节它们的固体荧光发射. 相似文献
988.
周富军 《高校应用数学学报(英文版)》2006,21(2):143-151
§1Introduction Avarietyofpartialdifferentialequationmodelsfortumorgrowthortherapyhave beendevelopedinthelastthreedecades[see2,3,16-18,21-26].Mostofthosemodelsare informoffreeboundaryproblems,andareverydiversified.Rigorousmathematical analysisofsuchfreeboundaryproblemshasdrawngreatinterest,andmanyinteresting resultshavebeenestablished[4-15].Inthispaperwedealwithamathematicalmodeldescribingtumorchemotherapy.In thismodelthetumorisviewedasdenselypacked,radially-symmetricsphereofradiusR(t)contain… 相似文献
989.
Can Liao Wei Wang Junling Wang Longfei Han Shuilai Qiu Lei Song Zhou Gui Yongchun Kan Yuan Hu 《Journal of Energy Chemistry》2021,(5):1-10
To date,lithium-ion batteries are becoming increasingly significant in the application of portable devices and electrical vehicles,and revolutionary progress in theoretical research and industrial application has been achieved.However,the commercial polyolefin separators with unsatisfying electrolytes affinity and poor thermal stability have extremely restricted the further application of lithium-ion batteries,especially in the high-temperature fields.In this work,magnetron sputtering deposition technique is employed to modify the commercial polyimide separator by coating silicon nitride on both sides.Magnetron sputtering deposition modified polyimide(MSD-PI)composite separator shows high thermal stability and ionic conductivity.More importantly,compared with the cells using Celgard separator,the cells with MSD-PI separator exhibit superior electrochemical performance,especially long-term cycle performance under high temperature environment,owing to the high thermal conductivity of surface Si3 N4 particles.Hence,lithium-ion batteries with MSD-PI separator are capable of improving thermal safety and capacity retention,which demonstrates that magnetron sputtering deposition technique could be regarded as a promising strategy to develop advanced organic/inorganic composite separators for high-temperature lithium-ion batteries. 相似文献
990.
平行排列液晶器件的波前调制特性 总被引:18,自引:17,他引:1
设计了一种新型的平行排列液晶相位调制器(LC PM),可在纯相位的模式下进行相位调制,研究了液晶相位调制器的光学特性,理论上给予了分析.对畸变波前进行了调制,在1 cm2的校正面积上,调制后的准确度PV(peak to valley)值接近λ/15(λ=0.6328 μm),RMS(Root Means Square)可达到λ/100,斯特列尔比SR (Strehl Ratio)达到0.989.改变了传统的扭曲向列液晶器件难于进行纯相位调制和得到高准确度调制的缺点,达到了理想的效果. 相似文献