全文获取类型
收费全文 | 149199篇 |
免费 | 19142篇 |
国内免费 | 11875篇 |
专业分类
化学 | 71270篇 |
晶体学 | 1218篇 |
力学 | 6920篇 |
综合类 | 533篇 |
数学 | 11910篇 |
物理学 | 41738篇 |
综合类 | 46627篇 |
出版年
2024年 | 661篇 |
2023年 | 2771篇 |
2022年 | 4384篇 |
2021年 | 4960篇 |
2020年 | 4751篇 |
2019年 | 4325篇 |
2018年 | 3885篇 |
2017年 | 3762篇 |
2016年 | 5621篇 |
2015年 | 5814篇 |
2014年 | 7476篇 |
2013年 | 9060篇 |
2012年 | 10766篇 |
2011年 | 11131篇 |
2010年 | 7751篇 |
2009年 | 7757篇 |
2008年 | 8370篇 |
2007年 | 7789篇 |
2006年 | 6934篇 |
2005年 | 6112篇 |
2004年 | 4593篇 |
2003年 | 3635篇 |
2002年 | 3373篇 |
2001年 | 3113篇 |
2000年 | 2993篇 |
1999年 | 4473篇 |
1998年 | 4150篇 |
1997年 | 4100篇 |
1996年 | 4090篇 |
1995年 | 3438篇 |
1994年 | 3271篇 |
1993年 | 2727篇 |
1992年 | 2385篇 |
1991年 | 2130篇 |
1990年 | 1796篇 |
1989年 | 1485篇 |
1988年 | 1221篇 |
1987年 | 873篇 |
1986年 | 650篇 |
1985年 | 419篇 |
1984年 | 271篇 |
1983年 | 162篇 |
1982年 | 147篇 |
1981年 | 108篇 |
1980年 | 76篇 |
1979年 | 47篇 |
1978年 | 34篇 |
1976年 | 38篇 |
1975年 | 33篇 |
1974年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
A liquid dewetting method for the determination of the viscoelastic properties of ultrathin polymer films has been extended to study thickness effects on the properties of ultrathin polycarbonate (PC) films. PC films with film thicknesses ranging from 4 to 299 nm were placed on glycerol at temperatures from below the macroscopic glass transition temperature (Tg) to above it with the dewetting responses being monitored. It is found that the isothermal creep results for films of the same thickness, but dewetted at different temperatures can be superposed into one master curve, which is consistent with the fact of PC being a thermorheologically simple material. Furthermore, the results show that the Tg of PC thin films is thickness dependent, but the dependence is weaker than the results for freely standing films and similar to literature data for PC films supported on rigid substrates. It was also found that the rubbery plateau region for the PC films stiffens dramatically, but still less than what has been observed for freely standing polycarbonate films. The rubbery stiffening is discussed in terms of a recently reported model that relates macroscopic segmental dynamics with the stiffening. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1559–1566 相似文献
2.
3.
We consider concentrated vorticities for the Euler equation on a smooth domain in the form of supported on well-separated vortical domains , , of small diameters . A conformal mapping framework is set up to study this free boundary problem with being part of unknowns. For any given vorticities and small , through a perturbation approach, we obtain such piecewise constant steady vortex patches as well as piecewise smooth Lipschitz steady vorticities, both concentrated near non-degenerate critical configurations of the Kirchhoff–Routh Hamiltonian function. When vortex patch evolution is considered as the boundary dynamics of , through an invariant subspace decomposition, it is also proved that the spectral/linear stability of such steady vortex patches is largely determined by that of the 2N-dimensional linearized point vortex dynamics, while the motion is highly oscillatory in the 2N-codim directions corresponding to the vortical domain shapes. 相似文献
4.
5.
We study the full counting statistics of transport electrons through a semiconductor two-level quantum dot with Rashba spin–orbit (SO) coupling, which acts as a nonabelian gauge field and thus induces the electron transition between two levels along with the spin flip. By means of the quantum master equation approach, shot noise and skewness are obtained at finite temperature with two-body Coulomb interaction. We particularly demonstrate the crucial effect of SO coupling on the super-Poissonian fluctuation of transport electrons, in terms of which the SO coupling can be probed by the zero-frequency cumulants. While the charge currents are not sensitive to the SO coupling. 相似文献
6.
Simultaneous determination of cinnamaldehyde and its metabolite in rat tissues by gas chromatography–mass spectrometry 下载免费PDF全文
Hang Zhao Qian Yang Yanhua Xie Jiyuan Sun Honghai Tu Wei Cao Siwang Wang 《Biomedical chromatography : BMC》2015,29(2):182-187
Cinnamaldehyde (CA), an active ingredient isolated from the traditional Chinese medicine Cortex Cinnamomi, has a wide range of bioactivities. To clarify the distribution characteristics of CA, a selective and sensitive method utilizing gas chromatography–mass spetrometry was initially developed for simultaneously determining the concentration of CA and its metabolite cinnamyl alcohol in rat tissues. Selected ion masses of m/z 131, 105 and 92 were chosen, and separation of the analytes was performed on a DB‐5 ms (30 m × 0.25 mm, 0.25 µm, thickness) capillary column by gas chromatography–mass spectrometry. The calibration curves demonstrated good linearity and reproducibility over the range of 20–2000 and 20–4000 ng/mL for various tissue samples. Recoveries ranged from 86.8 to 107.5%, while intra‐ and interday relative standard deviations were all <11.3%. The analysis method was successfully applied in tissue distribution studies for CA and cinnamyl alcohol. As CA and cinnamyl alcohol may inter‐convert to one another, simultaneous determination of both analytes provides a comparative and accurate data for tissue study. The concentrations of CA and cinnamyl alcohol remaining in spleen were the highest among the main organs, including heart, liver, spleen, lung, kidney and brain. In addition, there was no long‐term accumulation of CA in rat tissues. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
7.
8.
9.
Qin Yin Shou-Guo Wang Xiao-Wei Liang De-Wei Gao Jun Zheng Shu-Li You 《Chemical science》2015,6(7):4179-4183
An organocatalytic asymmetric chlorinative dearomatization of naphthols was realized for the first time, providing chiral naphthalenones with a Cl-containing all-substituted stereocenter in excellent yields and enantioselectivity (up to 97% yield and 96% ee). The reaction features mild reaction conditions, good tolerance of diverse functional groups and simple reaction operation. 相似文献
10.
深水铺管船的动力定位能力评估系统 总被引:1,自引:0,他引:1
为解决评估铺管船作业能力的难题,提出一种适用于评估铺管船动力定位能力的方法,开发了动力定位能力评估程序系统,并针对高海况环境条件设计了优化的辅助作业方案.采用数值计算方法对铺管船作业期间的平均二阶力、风载荷以及流载荷进行仿真计算,建立了环境载荷与动力定位系统提供的推力之间的平衡关系,给出了用于评估铺管船动力定位能力的系统模块,采用动力定位能力包络线的方式表达动力评估结果.在高海况作业中给出安全建议,即采用辅助拖轮作用于船舶适当位置以增强动力定位能力,从而降低工程作业风险. 相似文献