全文获取类型
收费全文 | 189214篇 |
免费 | 39099篇 |
国内免费 | 26906篇 |
专业分类
化学 | 125136篇 |
晶体学 | 2278篇 |
力学 | 12741篇 |
综合类 | 720篇 |
数学 | 22726篇 |
物理学 | 91618篇 |
出版年
2024年 | 759篇 |
2023年 | 2963篇 |
2022年 | 4600篇 |
2021年 | 4763篇 |
2020年 | 5465篇 |
2019年 | 5805篇 |
2018年 | 5151篇 |
2017年 | 5361篇 |
2016年 | 7613篇 |
2015年 | 7644篇 |
2014年 | 8650篇 |
2013年 | 12363篇 |
2012年 | 14211篇 |
2011年 | 15929篇 |
2010年 | 15708篇 |
2009年 | 15485篇 |
2008年 | 10171篇 |
2007年 | 9261篇 |
2006年 | 8379篇 |
2005年 | 7793篇 |
2004年 | 7166篇 |
2003年 | 5767篇 |
2002年 | 5290篇 |
2001年 | 5179篇 |
2000年 | 4170篇 |
1999年 | 4761篇 |
1998年 | 4050篇 |
1997年 | 3768篇 |
1996年 | 4186篇 |
1995年 | 4242篇 |
1994年 | 4254篇 |
1993年 | 3977篇 |
1992年 | 3481篇 |
1991年 | 3064篇 |
1990年 | 2550篇 |
1989年 | 2420篇 |
1988年 | 2288篇 |
1987年 | 1537篇 |
1986年 | 1565篇 |
1985年 | 1181篇 |
1984年 | 1238篇 |
1983年 | 512篇 |
1982年 | 1030篇 |
1981年 | 847篇 |
1980年 | 852篇 |
1979年 | 568篇 |
1978年 | 564篇 |
1977年 | 660篇 |
1976年 | 1077篇 |
1972年 | 549篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
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
32.
Wenpin Wang Qing Yao Jianhui Song Binbin Yao Hui Wang Zhibo Li 《Journal of Polymer Science.Polymer Physics》2019,57(11):662-669
The PeakForce Quantitative Nanomechanical Mapping based on atomic force microscope (AFM) is employed to first visualize and then quantify the elastic properties of a model nitrile rubber/poly(vinyl chloride) (NBR/PVC) blend at the nanoscale. This method allows us to consistently observe the changes in mechanical properties of each phase in polymer blends. Beyond measuring and discriminating elastic modulus and adhesion forces of each phase, we tune the AFM tips and the peak force parameters in order to reliably image samples. In view of viscoelastic difference in each phase, a three‐phase coexistence of an unmixed NBR phase, the mixed phase, and PVC microcrystallites is directly visualized in NBR/PVC blends. The nanomechanical investigation is also capable of recognizing the crosslinked rubber phase in cured rubber. The contribution of the mixed phase was quantified and it was found that the mechanical properties of blends are mainly determined by the homogeneity and stiffness of the mixed phase. This study furthers our understanding the structure–mechanical property relationship of thermoplastic elastomers, which is important for their potential design and applications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 662–669 相似文献
33.
Annals of the Institute of Statistical Mathematics - To obtain M-estimators of a response variable when the data are missing at random, we can construct three bias-corrected nonparametric... 相似文献
34.
Hongling Yu Heyong Wang Galia Pozina Chunyang Yin Xiao-Ke Liu Feng Gao 《Chemical science》2020,11(41):11338
Metal halide perovskites have demonstrated impressive properties for achieving efficient monochromatic light-emitting diodes. However, the development of white perovskite light-emitting diodes (PeLEDs) remains a big challenge. Here, we demonstrate a single-emissive-layer all-perovskite white PeLED using a mixed halide perovskite film as the emissive layer. The perovskite film consists of separated mixed halide perovskite phases with blue and red emissions, which are beneficial for suppressing halide anion exchange and preventing charge transfer. As a result, the white PeLED shows balanced white light emission with Commission Internationale de L''Eclairage coordinates of (0.33, 0.33). In addition, we find that the achievement of white light emission from mixed halide perovskites strongly depends on effective modulation of the halide salt precursors, especially lead bromide and benzamidine hydrochloride in our case. Our work provides very useful guidelines for realizing single-emissive-layer all-perovskite white PeLEDs based on mixed halide perovskites, which will spur the development of high-performance white PeLEDs.We demonstrated a single-emissive-layer all-perovskite white light-emitting diode based on a mixed halide perovskite film. 相似文献
35.
Cavitation erosion is caused in solids exposed to strong pressure waves developing in an adjacent fluid field. The knowledge of the transient distribution of stresses in the solid is important to understand the cause of damaging by comparisons with breaking points of the material. The modeling of this problem requires the coupling of the models for the fluid and the solid. For this purpose, we use a strategy based on the solution of coupled Riemann problems that has been originally developed for the coupling of 2 fluids. This concept is exemplified for the coupling of a linear elastic structure with an ideal gas. The coupling procedure relies on the solution of a nonlinear equation. Existence and uniqueness of the solution is proven. The coupling conditions are validated by means of quasi‐1D problems for which an explicit solution can be determined. For a more realistic scenario, a 2D application is considered where in a compressible single fluid, a hot gas bubble at low pressure collapses in a cold gas at high pressure near an adjacent structure. 相似文献
36.
37.
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
38.
Simultaneous determination of cinnamaldehyde and its metabolite in rat tissues by gas chromatography–mass spectrometry
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
39.
40.
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