全文获取类型
收费全文 | 40003篇 |
免费 | 5718篇 |
国内免费 | 6817篇 |
专业分类
化学 | 20385篇 |
晶体学 | 664篇 |
力学 | 1444篇 |
综合类 | 543篇 |
数学 | 3296篇 |
物理学 | 9878篇 |
无线电 | 16328篇 |
出版年
2024年 | 149篇 |
2023年 | 585篇 |
2022年 | 1124篇 |
2021年 | 1212篇 |
2020年 | 1096篇 |
2019年 | 1145篇 |
2018年 | 1030篇 |
2017年 | 1193篇 |
2016年 | 1399篇 |
2015年 | 1761篇 |
2014年 | 2182篇 |
2013年 | 2778篇 |
2012年 | 3169篇 |
2011年 | 3238篇 |
2010年 | 2848篇 |
2009年 | 2895篇 |
2008年 | 3280篇 |
2007年 | 2991篇 |
2006年 | 2823篇 |
2005年 | 2423篇 |
2004年 | 2066篇 |
2003年 | 1701篇 |
2002年 | 1803篇 |
2001年 | 1621篇 |
2000年 | 1337篇 |
1999年 | 880篇 |
1998年 | 486篇 |
1997年 | 483篇 |
1996年 | 433篇 |
1995年 | 371篇 |
1994年 | 317篇 |
1993年 | 320篇 |
1992年 | 270篇 |
1991年 | 187篇 |
1990年 | 177篇 |
1989年 | 150篇 |
1988年 | 113篇 |
1987年 | 90篇 |
1986年 | 65篇 |
1985年 | 58篇 |
1984年 | 50篇 |
1983年 | 40篇 |
1982年 | 36篇 |
1981年 | 31篇 |
1980年 | 27篇 |
1979年 | 13篇 |
1978年 | 23篇 |
1977年 | 14篇 |
1976年 | 10篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Hong Wang 《Graphs and Combinatorics》1994,10(2-4):271-281
Letk and s be two positive integers with s≥3. LetG be a graph of ordern ≥sk. Writen =qk + r, 0 ≤r ≤k - 1. Suppose thatG has minimum degree at least (s - l)k. Then G containsk independent cyclesC 1,C 2,...,C k such thats ≤l(C i ) ≤q for 1 ≤i ≤r arnds ≤l(C i ) ≤q + 1 fork -r <i ≤k, where l(Ci) denotes the length ofC i . 相似文献
72.
高璟 《数学的实践与认识》2007,37(7):125-128
利用矩阵A的带W权Drazin逆的一个性质特征,对任意的矩阵A∈Cm×n,W∈Cn×m,建立了带W权的Drazin逆Ad,w的一种新的表示式,给出了具体的算法步骤,并且在文末给出了算例. 相似文献
73.
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
74.
A new estimation based on the Shannon entropy for the power-law distribution parameter is presented, The maximum likelihood estimation (MLE) of the parameter is discussed and the relation between the MLE and the moment estimation of the parameter is given out. It is shown that the minimum Shannon entropy estimation is equivalent to the MLE giving the log expectation. 相似文献
75.
This work reports a new synthetic approach for single‐phase TiO2 nanomaterials by solvothermal treatment of titanium tetrachloride in acetone at 80–110 °C. Small, uniform, and yet size‐tunable (5–10 nm) anatase titania nanocrystallites were obtained using a low concentration of TiCl4 in acetone (i.e., at molar ratios of TiCl4/acetone ≤ 1:15) in the temperature range of 80–110 °C, while rutile nanofibers were synthesized using a high concentration of TiCl4 (e.g., TiCl4/acetone = 1:10) at 110 °C. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
76.
In this talk, the interaction of a single photon injected to a single atom is studied, for which initially the photon is uncorrelated with the atom. The spontaneous emitted photon will then evolve to be entangled with the atom on their continuous kinetic variables (momentum) in the process of resonant scattering. We find the relations between the entanglement and their physical control parameters (such as the linewidth of the injected photon wave packet, and that of the atomic wave packet, etc. ), which indicates that high entanglement can be reached by broadening the scale of the atomic wave or squeezing the linewidth of the incident single-photon pulse. 相似文献
77.
沿直线的垂直方向匀速直线运动的带电直线的电场 总被引:1,自引:1,他引:0
本文利用相对论变换关系计算了沿直线的垂直方向匀速运动的带电直线的电场. 相似文献
78.
Kyung Hwa Hong Jong Lyoul Park In Hwan Sul Ji Ho Youk Tae Jin Kang 《Journal of Polymer Science.Polymer Physics》2006,44(17):2468-2474
Polyvinyl alcohol (PVA) nanofibers containing Ag nanoparticles were prepared by electrospinning PVA/silver nitrate (AgNO3) aqueous solutions, followed by short heat treatment, and their antimicrobial activity was investigated for wound dressing applications. Since PVA is a water soluble and biocompatible polymer, it is one of the best materials for the preparation of wound dressing nanofibers. After heat treatment at 155 °C for 3 min, the PVA/AgNO3 nanofibers became insoluble, while the Ag+ ions therein were reduced so as to produce a large number of Ag nanoparticles situated preferentially on their surface. The residual Ag+ ions were reduced by subsequent UV irradiation for 3 h. The average diameter of the Ag nanoparticles after the heat treatment was 5.9 nm and this value increased slightly to 6.3 nm after UV irradiation. It was found that most of the Ag+ ions were reduced by the simple heat treatment. The PVA nanofibers containing Ag nanoparticles showed very strong antimicrobial activity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2468–2474, 2006 相似文献
79.
80.
We have performed total-energy calculations to study theoretical scanning tunneling microscopy (STM) images of the Si(1 1 1)3 × 2 surfaces induced by the adsorption of alkaline-earth metals (AEMs). Previously, in a series of works on Ba/Si(1 1 1) system, we have found that the observed Si(1 1 1)3 × 1-Ba LEED phase indeed has a 3 × 2 periodicity with a Ba coverage of 1/6 ML and the HCC substrate structure. Based on results of the Ba case, we proposed that the HCC structure is also adopted for other AEM atoms, which was confirmed by our recent work. In this paper, we mainly report the STM simulations for different AEM systems to compare with existing experimental data. We discuss the difference in the detailed STM images for different AEM adsorbates. Especially, the difference in filled-state images between Mg and other AEM atoms is attributed to the strong Mg-Si interaction. 相似文献