全文获取类型
收费全文 | 15424篇 |
免费 | 2687篇 |
国内免费 | 2074篇 |
专业分类
化学 | 11025篇 |
晶体学 | 269篇 |
力学 | 794篇 |
综合类 | 198篇 |
数学 | 1713篇 |
物理学 | 6186篇 |
出版年
2024年 | 37篇 |
2023年 | 309篇 |
2022年 | 603篇 |
2021年 | 588篇 |
2020年 | 697篇 |
2019年 | 716篇 |
2018年 | 597篇 |
2017年 | 625篇 |
2016年 | 828篇 |
2015年 | 843篇 |
2014年 | 1005篇 |
2013年 | 1251篇 |
2012年 | 1497篇 |
2011年 | 1407篇 |
2010年 | 1006篇 |
2009年 | 951篇 |
2008年 | 1074篇 |
2007年 | 958篇 |
2006年 | 780篇 |
2005年 | 706篇 |
2004年 | 507篇 |
2003年 | 398篇 |
2002年 | 368篇 |
2001年 | 316篇 |
2000年 | 287篇 |
1999年 | 262篇 |
1998年 | 206篇 |
1997年 | 189篇 |
1996年 | 206篇 |
1995年 | 191篇 |
1994年 | 128篇 |
1993年 | 120篇 |
1992年 | 92篇 |
1991年 | 75篇 |
1990年 | 74篇 |
1989年 | 49篇 |
1988年 | 39篇 |
1987年 | 34篇 |
1986年 | 29篇 |
1985年 | 42篇 |
1984年 | 17篇 |
1983年 | 19篇 |
1982年 | 17篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
61.
In solid immersion lens (SIL) microscopy systems with high numerical aperture (NA), there always exists the aberration produced by Fresnel effects at the interface between SIL and the sample. This aberration may cause the degradation of the image of sample. We design a continuous phase filter and optimize the optical field distribution of SIL system. The numerical results show that when the continuous phase filter is used, the field distribution of SIL system can be optimized, and the focal depth and intensity of transmitted light can be increased. At the same time, the intensity of side-lobe and the resolution are kept almost unchanged. 相似文献
62.
63.
64.
A PICARD TYPE THEOREM AND BLOCH LAW 总被引:9,自引:0,他引:9
Ye Yasheng 《数学年刊B辑(英文版)》1994,15(1):75-80
A PICARD TYPE THEOREM AND BLOCH LAW ¥YEYASHENGAbstract:Apicardtypetheoremisproved,andacounterexampleisgiventoshowthattheBolch... 相似文献
65.
本文报道了一种测角单晶NMR探头。该探头采用单线圃双调谐电路,工作频率在90MHz-110 MHz连续可调,可进行交叉极化大功率去耦实验。文中提出了一种简单而有效的测角装置,可使单晶绕三个互相垂直轴转动实现单晶的NMR测量。作为典型的应用例子,本文利用该探头实现了单晶DGO(2NH2CH2COOH·H2C2O4)屏蔽张量的测量。 相似文献
66.
讨论了横向位移双曝光散斑图维纳谱的信息分布,并由此导出杨氏纹图的一般表达式。讨论了条纹可见度与应变,面内转动,照明光束直径与条纹图图空间坐标的关系,指出了在条纹可见度影响下最大可见条纹数目。还讨论了散斑衬比与衍射晕的关系。 相似文献
67.
Bai-suo JIN~ 《中国科学A辑(英文版)》2007,50(9):1303-1315
In the factor analysis model with large cross-section and time-series dimensions,we pro- pose a new method to estimate the number of factors.Specially if the idiosyncratic terms satisfy a linear time series model,the estimators of the parameters can be obtained in the time series model. The theoretical properties of the estimators are also explored.A simulation study and an empirical analysis are conducted. 相似文献
68.
The dendrite growth process of transparent NaBi(WO4)2 with small prandtl and high melting point was studied by using the in-situ observation system. According to the dynamic images and detailed information, there are two kinds of restriction effect on
the dendrite growth, the competition between arms and branches and the convection in the melt. The dendrite growth rate was
time dependent, and the rate of arm growth reached the maximum 5.8 mm/s in the diffusive-advective region and rapidly decreased
in the diffusive-convective region. The growth rate of branch had the same change trends as the arm’s. Based on the EPMA-EDS
data of solidification structure of quenched NaBi(WO4)2 melt, it was found that there were component differences from stoichiometric concentration in the melt near the interface
during the growth process.
Supported by the National Natural Science Foundation of China (Grant No. 50331040) and the Innovation Funds from Shanghai
Institute of Ceramics, Chinese Academy of Sciences (Grant No. SCX0623) 相似文献
69.
Crosslinking behaviors of acrylonitrile butadiene rubber (NBR)/poly (vinyl chloride) (PVC) alloy, filled with anhydrous copper sulfate (CuSO4) particles, were investigated for the first time by dynamic mechanical analysis (DMA) under hetero and isothermal modes, respectively. In the heterothermal testing, (NBR/PVC)/CuSO4 compound showed two marked increases in the storage modulus (E′), corresponding to coordination crosslinking of NBR-CuSO4 and self-crosslinking of NBR and PVC respectively. During the isothermal testing, a dramatic increase in E′ was found at the initial stage while that of original NBR/PVC alloy was not detected. The marked increase in E′ of (NBR/PVC)/CuSO4 compound was mainly due to the crosslinking induced by coordination between CN and Cu2+. The increasing extent of E′ increased with the rise of CuSO4 content, suggesting the formation of a greater number of crosslinks. Moreover, the activation energy (Ea) of crosslinking process was about 139 kJ/mol. In this work, fourier transform infrared spectrum (FT-IR) and equilibrium swelling method were also performed for the characterization of the compound. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 41–51, 2007 相似文献
70.
Stimulated Raman adiabatic passage (STIRAP) has been successfully extended to multilevel system. During the STIRAP process, the intermediate levels have notable population which is detrimental if these levels could decay to other levels through spontaneous emission. This paper proposes a novel method to reduce the intermediate level population during the STIRAP process. A complete population transfer can be achieved in this modified STIRAP even if the intermediate level decays to other levels. 相似文献