全文获取类型
收费全文 | 7995篇 |
免费 | 264篇 |
国内免费 | 61篇 |
专业分类
化学 | 5318篇 |
晶体学 | 41篇 |
力学 | 277篇 |
数学 | 1593篇 |
物理学 | 1091篇 |
出版年
2023年 | 48篇 |
2022年 | 111篇 |
2021年 | 191篇 |
2020年 | 155篇 |
2019年 | 163篇 |
2018年 | 140篇 |
2017年 | 114篇 |
2016年 | 282篇 |
2015年 | 236篇 |
2014年 | 240篇 |
2013年 | 444篇 |
2012年 | 532篇 |
2011年 | 597篇 |
2010年 | 364篇 |
2009年 | 356篇 |
2008年 | 520篇 |
2007年 | 485篇 |
2006年 | 487篇 |
2005年 | 412篇 |
2004年 | 352篇 |
2003年 | 279篇 |
2002年 | 293篇 |
2001年 | 99篇 |
2000年 | 73篇 |
1999年 | 67篇 |
1998年 | 79篇 |
1997年 | 88篇 |
1996年 | 99篇 |
1995年 | 58篇 |
1994年 | 79篇 |
1993年 | 59篇 |
1992年 | 56篇 |
1991年 | 43篇 |
1990年 | 53篇 |
1989年 | 48篇 |
1988年 | 39篇 |
1987年 | 44篇 |
1986年 | 32篇 |
1985年 | 44篇 |
1984年 | 63篇 |
1983年 | 40篇 |
1982年 | 45篇 |
1981年 | 31篇 |
1980年 | 40篇 |
1979年 | 29篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1976年 | 14篇 |
1974年 | 16篇 |
1973年 | 14篇 |
排序方式: 共有8320条查询结果,搜索用时 109 毫秒
941.
942.
Luis A. Toledo-Matos Maximo Antonio Pech-Canul 《Journal of Solid State Electrochemistry》2011,15(9):1927-1934
The evolution under open-circuit conditions of iron passive films formed at 0.8 VSCE in a borate buffer solution at pH 8.4 was investigated with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry.
The composition of the freshly formed passive film as determined by X-ray photoelectron spectroscopy (XPS) was found to be
in agreement with a bilayer model, where the inner layer is composed mainly of iron oxide and the outer layer consists of
a hydrated material. Results of XPS measurements also showed that the open-circuit breakdown of passive films was consistent
with a reductive dissolution mechanism. When the iron electrode reached an intermediate stage in the open-circuit potential
decay (approximately −0.3 VSCE), the oxide film, containing both Fe(II) and Fe(III), was still protective. The impedance response in this stage exhibited
a mixed control by charge transfer at the metal/film and film/solution interfaces and diffusion of point defects through the
film. At the final stage of the open-circuit potential decay (approximately −0.7 VSCE), the oxide film was very thin, and the ratio of Fe3+/Fe2+ and O2−/OH− had decreased significantly. The impedance response also exhibited a mixed charge-transfer–diffusion control, but the diffusion
process was related to transport of species in the electrolyte solution resulting from dissolution of the oxide film. 相似文献
943.
Jaime-Vasconcelos MÁ Frontana-Uribe BA Morales-Serna JA Salmón M Cárdenas J 《Molecules (Basel, Switzerland)》2011,16(11):9109-9115
From the aerial parts of Salvia occidentalis (Labiatae) a new diterpenoid with a rearranged neo-clerodane skeleton was isolated. This new compound was named salvioccidentalin and its structure was established by spectroscopic means. A probable biogenetic relationship with salvigenolide from S. fulgens and salvileucalin A and spiroleucantholide from Salvia leucantha is proposed. 相似文献
944.
945.
946.
947.
Dr. Antonio A. Ceacero‐Vega Dr. Bernabé Ballesteros Dr. Iustinian Bejan Dr. Ian Barnes Prof. José Albaladejo 《Chemphyschem》2011,12(11):2145-2154
Relative rate coefficients for the gas‐phase reaction of chlorine atoms (Cl) and hydroxyl radicals (OH) with 1,8‐cineole were determined by Fourier‐transform infrared (FTIR) spectroscopy between 285 and 313 K at atmospheric pressure. The temperature dependence of both reactions shows simple Arrhenius behaviour which can be represented by the following expressions (in units of cm3 molecule?1s?1): k(1,8‐cineole+OH)=(6.28±6.53)×10?8exp[(?2549.3±155.7)/T] and k(1,8‐cineole+Cl)=(1.35±1.07)×10?10exp[(?151.6±237.7)/T]. Major products of the titled reactions were identified by solid‐phase microextraction (SPME) coupled to a GC‐MS. Additionally, the first step of the reaction was theoretically studied by ab initio calculations and a reaction mechanism is proposed. 相似文献
948.
949.
Carolina Estarellas Prof. Antonio Frontera Dr. David Quiñonero Prof. Dr. Pere M. Deyà 《Chemphyschem》2011,12(15):2742-2750
This article analyzes the interplay between lone pair–π (lp–π) or anion–π interactions and halogen‐bonding interactions. Interesting cooperativity effects are observed when lp/anion–π and halogen‐bonding interactions coexist in the same complex, and they are found even in systems in which the distance between the anion and halogen‐bond donor molecule is longer than 9 Å. These effects are studied theoretically in terms of energetic and geometric features of the complexes, which are computed by ab initio methods. Bader′s theory of “atoms in molecules” is used to characterize the interactions and to analyze their strengthening or weakening depending upon the variation of charge density at critical points. The physical nature of the interactions and cooperativity effects are studied by means of molecular interaction potential with polarization partition scheme. By taking advantage of all aforementioned computational methods, the present study examines how these interactions mutually influence each other. Additionally, experimental evidence for such interactions is obtained from the Cambridge Structural Database (CSD). 相似文献
950.
Prestianni A Joubert L Chagnes A Cote G Adamo C 《Physical chemistry chemical physics : PCCP》2011,13(43):19371-19377
Density functional theory calculations were performed on uranyl complexed with nitrate and monoamide ligands (L) [UO(2)(NO(3))(2)·2L]. The obtained results show that the complex stability is mainly governed by two factors: (i) the maximization of the polarizability of the coordinating ligand and (ii) the minimization of the steric hindrance effects. Furthermore, the electrostatic interaction between ligands and uranium(vi) was found to be a crucial parameter for the complex stability. These results pave the way to the definition of (quantitative) property/structure relationships for the in silico screening of monoamide ligands with improved extraction efficiency of uranium(vi) in nitrate acidic solution. 相似文献