全文获取类型
收费全文 | 11230篇 |
免费 | 1604篇 |
国内免费 | 1028篇 |
专业分类
化学 | 5910篇 |
晶体学 | 135篇 |
力学 | 522篇 |
综合类 | 83篇 |
数学 | 815篇 |
物理学 | 3121篇 |
无线电 | 3276篇 |
出版年
2024年 | 54篇 |
2023年 | 321篇 |
2022年 | 388篇 |
2021年 | 468篇 |
2020年 | 485篇 |
2019年 | 444篇 |
2018年 | 367篇 |
2017年 | 346篇 |
2016年 | 525篇 |
2015年 | 543篇 |
2014年 | 677篇 |
2013年 | 804篇 |
2012年 | 879篇 |
2011年 | 907篇 |
2010年 | 632篇 |
2009年 | 547篇 |
2008年 | 708篇 |
2007年 | 580篇 |
2006年 | 551篇 |
2005年 | 470篇 |
2004年 | 309篇 |
2003年 | 299篇 |
2002年 | 249篇 |
2001年 | 180篇 |
2000年 | 214篇 |
1999年 | 232篇 |
1998年 | 189篇 |
1997年 | 169篇 |
1996年 | 205篇 |
1995年 | 158篇 |
1994年 | 151篇 |
1993年 | 116篇 |
1992年 | 112篇 |
1991年 | 93篇 |
1990年 | 84篇 |
1989年 | 58篇 |
1988年 | 65篇 |
1987年 | 46篇 |
1986年 | 46篇 |
1985年 | 39篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1970年 | 12篇 |
1937年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
JunZhou Yong-zhiQiu Xiao-pengZang Chang-wangPan QiangChen JianShen Si-congLin 《高分子科学》2005,(1):93-102
N,N-dimethyl-N-methacryloyloxyethyl-N-carboxyethyl ammonium (DMMCA) was graft-copolymerized onto the surface of segmented poly(ether urethane) (SPEU) and PE film. The carboxybetaine structure on SPEU and PE film surfaces was confirmed by ATR-FTIR, XPS and water contact angle measurements. Through the experiments with platelet adhesion and protein adhesion assay in vitro, the two materials studied, including poly-DMMCA gel, all show excellent nonthrombogenicity. This confirms once again that the zwitterionic molecular structure on the surfaces of materials is essential for improving their nonthrombogenicity and biocompatibility. 相似文献
72.
73.
74.
通过对两间小学639名学生进行微量元素检测及体格检查,并进行中医辩证分型,发现广州市部份小学生体内微量元素缺乏较严重,占体检总人数的62.3%,同时也存在营养不良,贫血、佝偻病,急慢性上呼吸道炎等、按中医辩证分型有肝热、脾气虚弱、肝血不足、肾气虚等,本文试从微量元素缺乏与中医辩证中找出两者之间的联系,以便于指导治疗,提高小学生的健康水平,增强体质和智力。 相似文献
75.
The rates of photoinduced electron transfer (ET) reactions across two oligo-norbornyl spacer groups (S), that is, structure 1 fused by two norbornadiene (NBD) units and structure 2 fused by three NBD units, are examined. Substituted naphthalene acted as an electron donor (D), whilst ethylene-1,2-dicarboxylate as an electron acceptor (A). ET rates were measured by fluorescence quenching experiments on these D-S-A dyads, and the results were correlated with reaction free energies according to the Marcus relationship. It was found that naphthalene with phenyl substituents showed relatively slower ET rates. The conformational flexibility of phenyl substituents may cause a hindrance on the electronic coupling between D and A. Another salient feature was the abnormally high quenching rates observed in nonpolar solvents such as cyclohexane, the results of which may be ascribed to a competing energy transfer process. 相似文献
76.
采用SCF-X_α-MS方法, 对于C(2×2)S/Fe(001)吸附体系, 选择Fe_5S和Fe_9S两种原子簇模型, 研究了该吸附体系的电子结构、吸附成键特征及其相互作用图象。结果表明, S吸附于Fe(001)单晶表面具有较强的定域性质, S原子与底物Fe原子之间的吸附相互作用主要表现为S(3p)-Fe(4s,3d)之间的轨道相互作用。通过对表面吸附键长的优化, 其结果与X.S.Zhang等的ARPEFS的实验结果一致。 相似文献
77.
78.
The coordination of silver cation to diphosphene Mes*P=PMes* ( 1 , Mes* = tBu3C6H2) was investigated in detail. The reaction of 1 with Ag[Al(ORF)4] (ORF = OC(CF3)3) in the ratios of 2 : 1, 3 : 2 and 1 : 2 led to the formation of the first cationic silver linked diphosphene complexes 2 — 4 . Complexes 2 and 3 contain two and three diphosphene molecules linked by the linear Ag(I) cation, respectively, and they feature unusual zig‐zag topologies. Complex 4 is a dinuclear silver complex, and each Ag(I) center features a tetrahedral geometry, coordinated by one phosphorus atom of diphosphene 1 and three chloro atoms of two CH2Cl2 molecules. 相似文献
79.
纳米TiO2膜用于光催化氧化测定化学需氧量的研究 总被引:4,自引:0,他引:4
A photocatalytic oxidation method for determination of chemical oxygen demand (COD) using nano-TiO2 film, based on the use of a nano-TiO2-Ce(SO4)2 system and electrochemical detection, was proposed. The technique was originated from the direct determination of the Ce(Ⅲ) concentration change resulting from photocatalytic oxidation of organic compounds. Ce(Ⅲ), which was produced by photocatalytic reduction of Ce(SO4)2, could be measured at a multi-walled carbon nanotubes (MWNT) chemically modified electrode (CME). The COD values by this method were calculated from the differential pulse voltammetry (DPV) current of Ce(Ⅲ) at the CME. Under the optimal operation conditions, the detection limit of 0.5 mg·L^-1 COD with the linear range of 1-600 mg·L^-1 was achieved. This method was also applied to determination of various COD of ground water and wastewater samples. The resuits were in good agreement with those from the conventional COD methods, i.e., permanganate and dichromate ones. 相似文献
80.