全文获取类型
收费全文 | 25559篇 |
免费 | 4118篇 |
国内免费 | 2409篇 |
专业分类
化学 | 17900篇 |
晶体学 | 309篇 |
力学 | 1532篇 |
综合类 | 109篇 |
数学 | 2912篇 |
物理学 | 9324篇 |
出版年
2024年 | 70篇 |
2023年 | 524篇 |
2022年 | 947篇 |
2021年 | 909篇 |
2020年 | 1007篇 |
2019年 | 992篇 |
2018年 | 828篇 |
2017年 | 727篇 |
2016年 | 1202篇 |
2015年 | 1154篇 |
2014年 | 1344篇 |
2013年 | 1791篇 |
2012年 | 2399篇 |
2011年 | 2408篇 |
2010年 | 1580篇 |
2009年 | 1501篇 |
2008年 | 1645篇 |
2007年 | 1508篇 |
2006年 | 1357篇 |
2005年 | 1157篇 |
2004年 | 842篇 |
2003年 | 643篇 |
2002年 | 608篇 |
2001年 | 445篇 |
2000年 | 434篇 |
1999年 | 516篇 |
1998年 | 425篇 |
1997年 | 436篇 |
1996年 | 451篇 |
1995年 | 359篇 |
1994年 | 306篇 |
1993年 | 235篇 |
1992年 | 235篇 |
1991年 | 198篇 |
1990年 | 169篇 |
1989年 | 144篇 |
1988年 | 97篇 |
1987年 | 111篇 |
1986年 | 87篇 |
1985年 | 82篇 |
1984年 | 47篇 |
1983年 | 43篇 |
1982年 | 35篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Huiyun Wu Xin Li Shen Sheng Zhisong Huang Shuhai Huang Siqing Zhao Hua Wang Zhenhai Sun Xiegu Xu Rui Xiao 《Optik》2013
Model of an optical system with coherent laser array source and the piston phase optimized by the stochastic parallel gradient descent algorithm is established. With this model, theory of beam propagation through the optical system in turbulent atmosphere is analyzed, and the analytical formulas of the beam average intensity along the propagation path are derived. Strehl ratio of the received beam induced by intensity disorderly distribution and power efficiency of the received beam are introduced to evaluate performance of the optical system. Under the H-V 5/7 atmospheric turbulent model, performance of an optical system with determinate parameters was calculated, and the influences of the propagation distance and the laser wavelength were numerically analyzed, respectively. 相似文献
993.
Bo Wang Limin Qiu Kai Wang Daming Sun Xuejun Zhang Weijuan Yang Junhu Zhou 《Applied Acoustics》2012,73(5):508-513
A Helmholtz resonator can be used as a transmission part to connect the thermoacoustic engine (TE) with its load. However, the resonator can significantly influence the performance of the TE. In order to investigate the impact of a Helmholtz resonator on the onset process of a TE, infrared (IR) imaging is firstly used as a visualization method to characterize the onset mechanism. The influence of dimensions of the Helmholtz resonator on the onset process are analyzed experimentally and theoretically. Results show that the Helmholtz resonator reduces the pressure amplitude at the onset moment and increases the onset temperature of the TE, both of which depend on the acoustic power absorbed from the TE. Onset without a sudden increase of pressure amplitude is observed with the Helmholtz resonator at resonance length. This paper shows that IR imaging is an effective way to characterize the temperature distribution in a TE study. 相似文献
994.
995.
Ya-Song Sun Ben-Wen Li 《Journal of Quantitative Spectroscopy & Radiative Transfer》2012,113(17):2205-2212
Recently, an efficient numerical method, which is called the collocation spectral method (CSM), for radiative heat transfer problems, has been proposed by the present authors. In this numerical method there exists the exponential convergence rate, which can obtain a very high accuracy even using a small number of grids. In this article, the CSM based on body-fitted coordinates (BFC) is extended to simulate radiative heat transfer problems in participating medium confined in 2D complex geometries. This numerical method makes simultaneously the use of the merits of both the CSM and BFC. In this numerical approach, the radiative transfer equation (RTE) in orthogonal Cartesian coordinates should be transformed into the equation in body-fitted nonorthogonal curvilinear coordinates. In order to test the efficiency of the developed method, several 2D complex irregular enclosures with curved boundaries and containing an absorbing, emitting and scattering medium are examined. The results obtained by the CSM are assessed by comparing the predictions with those in references. These comparisons indicate that the CSM based on BFC can be recommended as a good option to solve radiative heat transfer problems in complex geometries. 相似文献
996.
Based on a recursive Green's function method, we investigate the conductance of mesoscopic graphene rings in the presence of disorder, in the limit of phase coherent transport. Two models of disorder are considered: edge disorder and surface disorder. Our simulations show that the conductance decreases exponentially with the edge disorder and the surface disorder. In the presence of flux, a clear Aharonov-Bohm conductance oscillation with the period Φ0 (Φ0=h/e) is observed. The edge disorder and the surface disorder have no effect on the period of AB oscillation. The amplitudes of AB oscillations vary with gate voltage and flux, which is consistent with the previous results. Additionally, ballistic rectification and negative differential resistance are observed in I-V curves, with on/off characteristic. 相似文献
997.
A continuous wave Er:YAP laser pumped by Mgo:PPLN laser locked at 1535 nm was reported. 170 mW of 1609 nm output was achieved
under total incident pump power of 7 W at 77 K. The slope efficiency were 5.0 and 3.1% with the cavity length 75 and 140 mm. 相似文献
998.
Frontispiece: Irreversible Denaturation of Proteins through Aluminum‐Induced Formation of Backbone Ring Structures
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
999.
1000.