全文获取类型
收费全文 | 2180篇 |
免费 | 55篇 |
国内免费 | 6篇 |
专业分类
化学 | 1562篇 |
晶体学 | 112篇 |
力学 | 55篇 |
数学 | 91篇 |
物理学 | 421篇 |
出版年
2023年 | 16篇 |
2022年 | 50篇 |
2021年 | 40篇 |
2020年 | 39篇 |
2019年 | 46篇 |
2018年 | 35篇 |
2017年 | 59篇 |
2016年 | 84篇 |
2015年 | 41篇 |
2014年 | 58篇 |
2013年 | 197篇 |
2012年 | 111篇 |
2011年 | 135篇 |
2010年 | 88篇 |
2009年 | 74篇 |
2008年 | 117篇 |
2007年 | 96篇 |
2006年 | 96篇 |
2005年 | 74篇 |
2004年 | 59篇 |
2003年 | 50篇 |
2002年 | 50篇 |
2001年 | 29篇 |
2000年 | 31篇 |
1999年 | 24篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 19篇 |
1995年 | 21篇 |
1994年 | 24篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 24篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 19篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1984年 | 27篇 |
1983年 | 21篇 |
1982年 | 29篇 |
1981年 | 30篇 |
1980年 | 22篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 18篇 |
1973年 | 16篇 |
排序方式: 共有2241条查询结果,搜索用时 62 毫秒
31.
Influence of electron‐beam (e‐beam) irradiation on multi‐walled (MW) and single‐walled (SW) carbon nanotube films grown by microwave chemical vapor deposition technique is investigated. These films were subjected to an e‐beam energy of 50 keV from a scanning electron microscope for 2.5, 5.5, 8.0, and 15 h, and to 100 and 200 keV from a transmission electron microscope for a few minutes to ∼2 h continuously. Such conditions resemble an increased temperature and pressure regime enabling a degree of structural fluidity. To assess structural modifications, they were analyzed prior to and after irradiation using resonance Raman spectroscopy (RRS) in addition to in situ monitoring by electron microscopy. The experiments showed that with extended exposures, both types of nanotubes displayed various local structural instabilities including pinching, graphitization/amorphization, and formation of an intramolecular junction (IMJ) within the area of electron beam focus possibly through amorphous carbon aggregates. RRS revealed that irradiation generated defects in the lattice as quantified through (1) variation of the intensity of radial breathing mode (RBM), (2) intensity ratio of D to G band (ID/IG), and (3) positions of the D and G bands and their harmonics (D* and G*) and combination bands (D + G). The increase in the defect‐induced D band intensity, quenching of RBM intensity, and only a slight increase in G band intensity are some of the implications. The MW nanotubes tend to reach a state of saturation for prolonged exposures, while the SW ones transform from a semiconducting to a quasi‐metallic character. Softening of the q = 0 selection rule is suggested as a possible reason to explain these results. Furthermore, these studies provide a contrasting comparison between MW and SW nanotubes. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
32.
S.K. Arora Vipul Patel R.G. Patel Brijesh Amin Anjana Kothari 《Journal of Physics and Chemistry of Solids》2004,65(5):965-973
The a.c. and d.c. conductivity of SrC4H4O6·3H2O are measured and are found to lie between usual conductivities of semiconductor and insulator. Temperature dependence of d.c. conductivity shows intrinsic conduction, which is confirmed by the slope of versus data. Due to application of thermal energy, noticeable conductivity peaks imply liberation of water molecules during dehydration and the formation of strontium oxalate. The conductivity plot has a nature similar to the intrinsic-to-extrinsic transition found in normal semiconductors. There occurs Efros hopping conduction in our samples. 相似文献
33.
Nayan Patel Mehmet Krta Vaidya Sankaran Suresh Menon 《Proceedings of the Combustion Institute》2007,31(2):2327-2334
Large-eddy simulation (LES) of a liquid-fueled lean-direct injection (LDI) combustor is carried out by resolving the entire inlet flow path through the swirl vanes and the combustor. A localized dynamic subgrid closure is combined with a subgrid mixing and combustion model so that no adjustable parameters are required for both non-reacting and reacting LES. Time-averaged velocity predictions compare well with the measured data. The unsteady flow features that play a major role in spray dispersion, fuel–air mixing and flame stabilization are identified from the simulation data. It is shown that the vortex breakdown bubble (VBB) is smaller with more intense reverse flow when there is heat release. The swirling shear layer plays a major role in spray dispersion and the VBB provides an efficient flameholding mechanism to stabilize the flame. 相似文献
34.
Charge density calculations and electronic band structures for Ga
x
Al1 − x
Sb with x = 1.0, 0.5 and 0.0 are presented in this work. The calculations are performed using the empirical pseudopotential method.
The charge density is computed for a number of planes, i.e. z = 0.0, 0.125 and 0.25 A
0 by generating the potential through a number of potential parameters available in the literature. The virtual crystal approximation
was applied for the semiconducting alloy. The characteristics of the band structure and charge density are observed to be
affected by the potential parameters. Calculated band gaps and the nature of gaps are in good agreement with the experimental
data reported. The ionicity is also reasonably in good agreement with other scales proposed in the literature; however the
formulation needs to be improved. The present work also demands indirect experimental band gap for the alloy.
相似文献
35.
The di-gamma and di-gluon decay widths of P-wave cc mesons are computed in nonrelativistic phenomenological quark-antiquark potential of the type V (r) =-4 3 α s r+ Ar ν with different choices of ν using spectroscopic parameters.The numerically obtained radial solutions are employed to obtain the di-gamma and di-gluon decay widths.The computed decay widths are consistent with other model predictions as well as with the known experimental values in the range of potential index 0.7 ≤ν≤ 1.1. 相似文献
36.
Patel Chirag N. Kumar Sivakumar Prasanth Pandya Himanshu A. Rawal Rakesh M. 《Molecular diversity》2021,25(1):421-433
Molecular Diversity - The pandemic outbreak of the Corona viral infection has become a critical global health issue. Biophysical and structural evidence shows that spike protein possesses a high... 相似文献
37.
Albrecht H Binder U Harder G Lembke-Koppitz I Philipp A Schmidt-Parzefall W Schröder H Schulz HD Wurth R Donker JP Drescher A Matthiesen U Scheck H Spaan B Spengler J Wegener aD Gabriel JC Schubert KR Stiewe J Waldi R Weseler S Brown NN Edwards KW Frisken WR Fukunaga C Gilkinson DJ Gingrich DM Goddard M Kapitza H Kim PC Kutschke R MacFarlane DB McKenna JA McLean KW Nilsson AW Orr RS Padley P Patel PM Prentice JD Seywerd HC Stacey BJ Yoon T Yun JC Ammar R Coppage D Davis R Kanekal S Kwak N 《Physical review letters》1986,56(6):549-552
38.
39.
40.