全文获取类型
收费全文 | 13455篇 |
免费 | 2272篇 |
国内免费 | 1810篇 |
专业分类
化学 | 10443篇 |
晶体学 | 196篇 |
力学 | 786篇 |
综合类 | 109篇 |
数学 | 1640篇 |
物理学 | 4363篇 |
出版年
2024年 | 28篇 |
2023年 | 199篇 |
2022年 | 377篇 |
2021年 | 443篇 |
2020年 | 470篇 |
2019年 | 554篇 |
2018年 | 451篇 |
2017年 | 390篇 |
2016年 | 664篇 |
2015年 | 764篇 |
2014年 | 802篇 |
2013年 | 1017篇 |
2012年 | 1194篇 |
2011年 | 1162篇 |
2010年 | 902篇 |
2009年 | 871篇 |
2008年 | 944篇 |
2007年 | 768篇 |
2006年 | 682篇 |
2005年 | 644篇 |
2004年 | 551篇 |
2003年 | 505篇 |
2002年 | 616篇 |
2001年 | 482篇 |
2000年 | 310篇 |
1999年 | 265篇 |
1998年 | 226篇 |
1997年 | 158篇 |
1996年 | 144篇 |
1995年 | 135篇 |
1994年 | 113篇 |
1993年 | 82篇 |
1992年 | 74篇 |
1991年 | 76篇 |
1990年 | 52篇 |
1989年 | 38篇 |
1988年 | 26篇 |
1987年 | 28篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1981年 | 15篇 |
1980年 | 31篇 |
1979年 | 11篇 |
1978年 | 27篇 |
1977年 | 49篇 |
1976年 | 21篇 |
1975年 | 20篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 795 毫秒
91.
93.
Guilin Wen Qing-Guo Wang Chong Lin Xu Han Guangyao Li 《Chaos, solitons, and fractals》2006,29(5):1142-1146
Synchronization under output feedback control with multiple random time delays is studied, using the paradigm in nonlinear physics—Chua’s circuit. Compared with other synchronization control methods, output feedback control with multiple random delay is superior for a realistic synchronization application to secure communications. Sufficient condition for global stability of delay-dependent synchronization is established based on the LMI technique. Numerical simulations fully support the analytical approach, in spite of the random delays. 相似文献
94.
95.
The existence and semiclassical limit of the solution to one-dimensional transient quantum drift-diffusion model in semiconductor
simulation are discussed. Besides the proof of existence of the weak solution, it is also obtained that the semiclassical
limit of this solution solves the classical drift-diffusion model. The key estimates rest on the entropy inequalities derived
from separation of quantum quasi-Fermi level. 相似文献
96.
Measurement of small-signal and large-signal responses of packaged laser modules at high temperature
Ning Hua Zhu Ji Min Wen Hai Peng Song Shang Jian Zhang Liang Xie 《Optical and Quantum Electronics》2006,38(15):1245-1257
In this paper, the pulsed injection method is extended to measure the chip temperature of various packaged laser modules,
such as the DFB laser modules, the FP laser modules, and the EML laser modules. An optimal injection condition is obtained
by investigating the dependence of the lasing wavelength on the width and period of the injection pulse in a relatively wide
temperature range. The small-signal frequency responses and large-signal performances of packaged laser modules at different
chip temperature are measured. The adiabatic small-signal modulation characteristics of packaged LD are first extracted. In
the large-signal measurement, the effects of chip temperature, bias current and driving signal on the performances of the
laser modules are discussed. It has been found that the large-signal performances of the EML modules depend on the different
red-shift speeds of the DFB and EAM sections as chip temperature varying, and the optimal characteristics may be achieved
at higher temperature. 相似文献
97.
Jin Kyu Park Dong Hun Lee Bok Ju Song Jae Buem Oh Hwan Kyu Kim 《Journal of polymer science. Part A, Polymer chemistry》2006,44(3):1326-1342
We have designed and synthesized novel perfluorinated polyimides with 3D controlled structure. At first, we successfully developed the new synthetic routes to diamines with pendant bulky perfluorinated aromatic units in a multi‐step synthetic procedure. Novel perfluorinated polyimides were prepared in a two‐step reaction in N‐methyl‐2‐pyrrolidinone (NMP) solution: The first step was for the synthesis of polyamic acids (PAAs) and the second reaction was for the imidization of PAA. The polymer yield was over 89% and the inherent viscosity of PAAs was in the range of 0.24–0.36 dL/g. The thin films were prepared by spin‐coating the PAA solution in NMP onto various substrates such as a Si wafer or a KBr pellet, dried at 80 °C and further cured at 230 °C. The resultant polyimides are thermally stable over 400 °C. The refractive index and birefringence of the resultant polyimides are 1.5858–1.6452 and 0.01–0.005, respectively. The refractive index of polyimide decreases with increasing the fluorine content. The copolymerization and the ether linkages into the backbone reduce the birefringence of polyimides. Surprisingly, the pendant ether linkage is not a crucial factor in reducing the polyimide birefringence. Their birefringence is comparatively very low, compared with that of previous polyimides. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1326–1342, 2006 相似文献
98.
Wen.-C. Chiang J.G. Lin K.H. Hsu D.S. Hussey D.V. Baxter 《Journal of magnetism and magnetic materials》2006
We investigate Co/Nb multilayers to explore the spontaneous π-phase shift between the superconducting (SC) layers, which is attributed for causing the non-monotonic change of the SC transition temperature (Tc) with the ferromagnetic (FM) layer thickness (tFM) in several FM/SC multilayered systems. The issue of interfacial roughness is also explored by growing Co/Nb multilayers at various sputtering pressures. Transport measurements show a non-monotonic dependence of Tc on tFM, and this dependence is insensitive to the structural variation present in the samples, as measured by X-ray scattering. 相似文献
99.
Positive Steady States of a Prey-predator Model with Diffusion and Non-monotone Conversion Rate 总被引:1,自引:0,他引:1
Rui PENG Ming Xin WANG Wen Van CHEN 《数学学报(英文版)》2007,23(4):749-760
In this paper, we study the positive steady states of a prey-predator model with diffusion throughout and a non-monotone conversion rate under the homogeneous Dirichlet boundary condition. We obtain some results of the existence and non-existence of positive steady states. The stability and uniqueness of positive steady states are also discussed. 相似文献
100.
This paper reviews our recent experimental and simulation results regarding the electromagnetic wave transmission through
three configurations of sandwiching structures of metamaterials: a metallic mesh sandwiched between two identical layers composed
of split rings, metallic fractals, and fractal slits, respectively. We observed the enhanced transmission of the waves through
these three types of sandwiching composites with respect to the opaque metallic mesh. The locations of the transmission peaks
in the spectrum are associated closely with the band characteristics of the sandwiching layer by appearing either on the left-
or the right-hand side of its band.
PACS 41.20.Jb; 42.70.Qs; 78.20.-e; 42.25.Bs; 47.53.+n 相似文献