全文获取类型
收费全文 | 8767篇 |
免费 | 1165篇 |
国内免费 | 773篇 |
专业分类
化学 | 5359篇 |
晶体学 | 164篇 |
力学 | 160篇 |
综合类 | 51篇 |
数学 | 106篇 |
物理学 | 4865篇 |
出版年
2024年 | 19篇 |
2023年 | 68篇 |
2022年 | 207篇 |
2021年 | 228篇 |
2020年 | 241篇 |
2019年 | 201篇 |
2018年 | 219篇 |
2017年 | 293篇 |
2016年 | 313篇 |
2015年 | 306篇 |
2014年 | 404篇 |
2013年 | 708篇 |
2012年 | 645篇 |
2011年 | 499篇 |
2010年 | 395篇 |
2009年 | 530篇 |
2008年 | 511篇 |
2007年 | 648篇 |
2006年 | 493篇 |
2005年 | 478篇 |
2004年 | 434篇 |
2003年 | 385篇 |
2002年 | 338篇 |
2001年 | 254篇 |
2000年 | 230篇 |
1999年 | 254篇 |
1998年 | 201篇 |
1997年 | 208篇 |
1996年 | 168篇 |
1995年 | 137篇 |
1994年 | 126篇 |
1993年 | 115篇 |
1992年 | 92篇 |
1991年 | 90篇 |
1990年 | 51篇 |
1989年 | 51篇 |
1988年 | 28篇 |
1987年 | 20篇 |
1986年 | 21篇 |
1985年 | 10篇 |
1984年 | 22篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
I. V. Avilov I. V. Filatov É. I. Zen'kevich A. M. Shul'ga 《Journal of Applied Spectroscopy》2001,68(1):14-25
We have made a theoretical analysis of the factors influencing the electronic absorption spectra of monomers of porphyrins and chlorins as well as of their chemically bound dimers in which the monomeric subunits are bound through the CH2–CH2 group. On the basis of quantum–chemical calculations by the semiempirical method CNDO/S it is shown that the addition of extra–ligands causes a change in the conformation of the dimers. 相似文献
992.
Hongmin Chen Mei‐Ling Cheng Y. C. Jean L. James Lee Jintao Yang 《Journal of Polymer Science.Polymer Physics》2008,46(4):388-405
Free‐volume properties, size and distribution, in amorphous polystyrene exposed to CO2 gases have been measured as a function of pressure to 800 psi (5.5 MPa), of time, and of temperature using positron annihilation lifetime spectroscopy. The free volume increases significantly and its distribution broadens as a function of pressure. The free volume relaxes as a function of time with a characteristic time of 15 h, and 5.7 h for 400, and 800 psi, respectively, after depressurizing under vacuum. A portion of free volume created by CO2 exposure remains permanently in the polymer after CO2 exposure. The glass transition temperature decreases significantly as a function of CO2 pressure from the free‐volume data and is compared with the differential scanning calorimeter results. The observed free‐volume variations as a function of pressure, time, and temperature are discussed in terms of hole expansion, creation, free‐volume relaxation, plasticization, and hole filling in amorphous polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 388–405, 2008 相似文献
993.
R. Valenzuela G. Alvarez H. Montiel M.P. Gutirrez M.E. Mata-Zamora F. Barrn A.Y. Snchez I. Betancourt R. Zamorano 《Journal of magnetism and magnetic materials》2008,320(14):1961-1965
A low-field non-resonant microwave absorption has recently been observed in a variety of magnetically ordered materials at low DC fields (−1000 Oe HDC+1000 Oe), which is known as low-field microwave absorption (LFA). It has been shown that LFA is essentially similar to giant magnetoimpedance (GMI), and clearly different from ferromagnetic resonance (FMR). LFA strongly depends on the anisotropy field of the sample. In contrast with FMR (which can be described as the homogeneous precession of spins in the saturated state), LFA can be thought as a spin rotation process occurring during the magnetic saturation. In this work, we present a detailed study of the basic features of LFA in several types of materials: ferrites and amorphous microwires and ribbons; in particular the effects sample shape, temperature up to the Curie transition, the influence of easy axis and the effects of annealings. These examples show that once LFA is fully understood, it can become a powerful characterization tool. 相似文献
994.
995.
James N. OShea J. Ben Taylor Louise C. Mayor Janine C. Swarbrick Joachim Schnadt 《Surface science》2008,602(9):1693-1698
Here we present the characteristic signatures in X-ray absorption and photoemission spectroscopy for molecular damage in adsorbed monolayers of bi-isonicotinic acid on a rutile TiO2(1 1 0) surface. Bi-isonicotinic acid is the anchor ligand through which many important inorganic complexes are bound to the surface of TiO2 in dye-sensitized solar cells. The nature of the damage caused by excessive heating of the adsorbed monolayer is consistent with splitting the molecule into two adsorbed isonicotinic acid molecular fragments. The effect on the lowest unoccupied molecular orbitals (involved in electron transfer in the molecule) can be understood in terms of the adsorption geometry of the reaction products and their nearest neighbor interactions. 相似文献
996.
S. L. Khursan A. M. Nazarov E. M. Chainikova V. D. Komissarov 《Russian Chemical Bulletin》2001,50(5):793-797
The absorption spectra and rate constants of diphenylcarbonyl oxide recombination in a series of solvents and their binary mixtures were determined by flash photolysis. An increase in the solvent polarity causes hypsochromic shift of the maximum in the absorption spectrum of Ph2COO. The analysis of the solvent effect on the recombination rate constant in terms of the four-parameter Koppel—Palm equation shows that the reactivity of carbonyl oxide depends on both specific and non-specific solvations. Quantum chemical B3LYP/6-31G(d) calculations of H2COO and PhHCOO carbonyl oxides as well as the complexes of H2COO with acetonitrile and ethylene in different media were performed using a polarized continuum model. 相似文献
997.
E. Janata 《Journal of Chemical Sciences》2002,114(6):731-737
The kinetics of the reactions of hydroxyl radicals and hydrogen atoms with some aliphatic alcohols in aqueous solutions were
studied using pulse radiolysis. Based on the increase in optical absorption in the UV region, the rate constants for the reaction
of hydroxyl radicals and hydrogen atoms with methanol, ethanol, 2-propanol ort-butyl alcohol were determined to be 9.0 × 108, 2.2 × 109, 2.0 × 109,6.2×l08 and 1.1 × 106, 1.8 × 107, 5.3 × 107, 2.3 × 105 dm3 mol−1 s−1 respectively. The bimolecular decay rate constants for the alcohol radicals produced in methanol and ethanol were evaluated
to be 2.4 × 109 and 1.5 × 109 dm3 mol−1s−1. The values observed are in fairly good agreement with those reported earlier. 相似文献
998.
Construction of a spatial light modulator (SLM) using reverse saturable absorber molecules is suggested. The SLM characteristics
are derived using a recently proposed steady-state kinetic analysis. Results are presented for the rhodamine 6G dye molecules. 相似文献
999.
本文介绍空腔靶设计的物理思想、及能量吸收特性、X光转换特性和堵腔特性的实验研究方法,给出了实验观察到的一系列物理现象,通过对现象的分析而得出空腔靶的能量吸收和X光转换明显优于平面靶;利用相对孔径较大的聚焦透镜打空腔靶有利于改善靶的能量吸收和转换特性的结论。 相似文献
1000.