全文获取类型
收费全文 | 67755篇 |
免费 | 2291篇 |
国内免费 | 1395篇 |
专业分类
化学 | 33809篇 |
晶体学 | 1108篇 |
力学 | 3606篇 |
综合类 | 110篇 |
数学 | 5663篇 |
物理学 | 27145篇 |
出版年
2022年 | 869篇 |
2021年 | 802篇 |
2020年 | 836篇 |
2019年 | 798篇 |
2018年 | 885篇 |
2017年 | 805篇 |
2016年 | 1330篇 |
2015年 | 1061篇 |
2014年 | 1524篇 |
2013年 | 3141篇 |
2012年 | 3147篇 |
2011年 | 3784篇 |
2010年 | 2639篇 |
2009年 | 2641篇 |
2008年 | 3339篇 |
2007年 | 3157篇 |
2006年 | 2916篇 |
2005年 | 2595篇 |
2004年 | 2270篇 |
2003年 | 1987篇 |
2002年 | 1872篇 |
2001年 | 3197篇 |
2000年 | 2348篇 |
1999年 | 1723篇 |
1998年 | 1245篇 |
1997年 | 1195篇 |
1996年 | 1036篇 |
1995年 | 925篇 |
1994年 | 811篇 |
1993年 | 716篇 |
1992年 | 1029篇 |
1991年 | 1005篇 |
1990年 | 910篇 |
1989年 | 784篇 |
1988年 | 768篇 |
1987年 | 825篇 |
1986年 | 679篇 |
1985年 | 916篇 |
1984年 | 843篇 |
1983年 | 582篇 |
1982年 | 577篇 |
1981年 | 538篇 |
1980年 | 503篇 |
1979年 | 626篇 |
1978年 | 652篇 |
1977年 | 664篇 |
1976年 | 581篇 |
1975年 | 481篇 |
1974年 | 521篇 |
1973年 | 451篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
25.
Experimental Mechanics - There have been relatively few studies on mechanical properties of nanomaterials under high strain rates, mainly due to the lack of capable nanomechanical testing devices.... 相似文献
26.
27.
Yu Wang Xin-jing Zhao Rong-Jing Wei Gui-jie Liang Kang Wang Yuan-zhi Tan Ye Yang 《化学物理学报(中文版)》2021,34(5):591-597
The intermolecular interaction determines the photophysical properties of the organic aggregates, which are critical to the performance of organic photovoltaics. Here, excitonic coupling, an important intermolecular interaction in organic aggregates, between the π-stacking graphene quantum dots is studied by using transient absorption spectroscopy. We find that the spectral evolution of the ground state bleach arises from the dynamic variation of the excitonic coupling in the excited π-stacks. According to the spectral simulations, we demonstrate that the kinetics of the vibronic peak can be exploited as a probe to measure the dynamics of excitonic coupling in the excited π-stacks. 相似文献
28.
29.
Uhm H.S. Lee P.H. Kim Y.I. Kim J.H. Chang H.Y. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(4):628-635
A theory is developed for the density profile of low temperature plasmas confined by applied magnetic field and an experiment of the electron-cyclotron-resonance (ECR) plasma is conducted to compare the theoretical prediction and experimental measurements. Due to a large electron mobility along the magnetic field, electrons move quickly out of the system, leaving ions behind and building a space charge potential, which leads to the ambipolar diffusion of ions. In a steady-state condition, the plasma generation by ionization of neutral molecules is in balance with plasma loss due to the diffusion, leading to the electron temperature equation, which is expressed in terms of the plasma size, chamber pressure, and the ionization energy and cross section of neutrals. The power balance condition leads to the plasma density equation, which is also expressed in terms of the electron temperature, the input microwave power and the chamber pressure. It is shown that the plasma density increases, reaches its peak and decreases, as the chamber pressure increases from a small value (0.1 mTorr). These simple expressions of electron temperature and density provide a scaling law of ECR plasma in terms of system parameters. After carrying out an experimental observation, it is concluded that the theoretical predictions of the electron temperature and plasma density agree remarkably well with experimental data 相似文献
30.
In a previous paper (Ref. 1), an exact solution of the optimal planar interception with fixed end conditions was derived in closed form. The optimal control was expressed as an explicit function of the state variables and two fixed parameters, obtained by solving a set of nonlinear algebraic equations involving elliptic integrals. In order to facilitate the optimal control implementation, the present paper derives a highly accurate simplified solution assuming that the ratio of the pursuer turning radius to the initial range is small. An asymptotic expansion further reduces the computational workload. Construction of a near-optimal open-loop control, based on the approximations, completes the present paper. 相似文献