全文获取类型
收费全文 | 1924篇 |
免费 | 496篇 |
国内免费 | 292篇 |
专业分类
化学 | 814篇 |
晶体学 | 26篇 |
力学 | 83篇 |
综合类 | 42篇 |
数学 | 283篇 |
物理学 | 601篇 |
无线电 | 863篇 |
出版年
2024年 | 20篇 |
2023年 | 72篇 |
2022年 | 100篇 |
2021年 | 104篇 |
2020年 | 103篇 |
2019年 | 88篇 |
2018年 | 64篇 |
2017年 | 73篇 |
2016年 | 80篇 |
2015年 | 98篇 |
2014年 | 94篇 |
2013年 | 121篇 |
2012年 | 139篇 |
2011年 | 128篇 |
2010年 | 97篇 |
2009年 | 128篇 |
2008年 | 119篇 |
2007年 | 98篇 |
2006年 | 130篇 |
2005年 | 119篇 |
2004年 | 102篇 |
2003年 | 69篇 |
2002年 | 61篇 |
2001年 | 87篇 |
2000年 | 78篇 |
1999年 | 51篇 |
1998年 | 30篇 |
1997年 | 28篇 |
1996年 | 25篇 |
1995年 | 32篇 |
1994年 | 24篇 |
1993年 | 28篇 |
1992年 | 15篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 21篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有2712条查询结果,搜索用时 15 毫秒
31.
Introduction As an important type of fungicides, triazole compounds are highly efficient, low poisonous and inward absorbent.1-3 At present, the studies on triazole derivatives are mainly concentrated on compounds with triazole as the only active group. The report of triazole compounds that contain both triazole group and other active group in a single molecule has rarely been found. Dialkyl-substituted dithiocarbamate salts have also shown interesting biological effects.4 N,N-Dialkyldithio-… 相似文献
32.
IntroductionTheincreasingcommercialvalueoftransitionmetalcomplexesofxanthateshasarousedconsiderableinterestintheirchemistry .Whiletheiranalyticalapplicationsarewellknown ,1theyarenowfindingextensiveuseinvulcan izationofrubber ,frothfloatationprocessforconcentrationofsulphideores ,asantioxidants ,lubricants ,2 ,3andhavebeenfoundtopossessfungicidalandinsecticidalactivi ties .4 Recently ,molecularrecognitionbetweenhostandguestmolecules ,inclusionphenomenaandnoncovalentmolecularinteractionarefunda… 相似文献
33.
The influence of cetyltrimethyl ammonium bromide on electrochemical properties of thyroxine reduction at carbon nanotubes modified electrode 总被引:2,自引:0,他引:2
The effect of cetyltrimethyl ammonium bromide (CTAB) on the electrochemical behaviors of thyroxine at a glassy carbon electrode (GCE) modified with single-walled carbon nanotubes (SWNTs) was investigated. At the SWNTs film-coated GCE, a well-defined oxidation peak of thyroxine at 0.78 V was obtained, but the reduction peak of thyroxine was indiscernible. When trace CTAB was added to the working solution, the reduction current could be greatly enhanced and the oxidation current remained stable. The reaction mechanisms for the reduction of thyroxine were explored by chronocoulometry. Thyroxine might form particular ion complex with CTAB via the interaction between iodine atoms on thyroxine and bromide ions in CTAB, which made the concentration of thyroxine at the surface of the modified electrode increased and the electron transfer rate enhanced. The proper mechanisms for the enhanced reduction of thyroxine in the present of CTAB were explored by several electrochemical techniques including cycle voltammetry linear sweep voltammetry and others. It was concluded that the special interactions between the thyroxine CTAB and SWNTs resulted in the increase of the reduction peak current. All results indicated that two iodine atoms on the thyroxine and four electrons were involved the reduction process which was irreversible and two iodine ions produced. In this system, the sensitive reduction peak of thyroxine at 0.3 V was employed to determine thyroxine and a low detection limit of 2x10(-8) mol/L was obtained for 2 min accumulation at 0.9 V. The SWNTs coated GCE had good stability and reproducibility. 相似文献
34.
1 INTRODUCTION Benzimidazole is an interesting heterocyclic compound because it is found in various naturally occurring drugs, such as omeprazole, astemizole and emedastine difumarate[1]. The efficacy of sub- stituted benzimidazoles in the treatment of parasitic infections is well known[2~4]. Substituted benzimid- azole moieties are established pharmacophores in parasitic chemotherapy. Bis(2-benzimidazole) and some substituted bis(benzimidazol-2-yl)alkanes have attracted much interest … 相似文献
35.
High molecular weight copoly(ether ketone)s (PEK) based on 4-(4-hydroxyphenyl)-1-phthalazinone (DHPZ)/4,4′-thiobisphenol (TBP)/4,4′-diflourodiphenylketone (DFK) were prepared by nucleophilic substitution polycondensation. The copolymers were characterized by FT- and ^1H-NMR. Thermal properties and solubility of copolymers were studied. 相似文献
36.
建立了单信道40Gbit/s归零-差分相移键控码(RZ-DPSK)传输系统模型,详细地分析并比较了线性相位噪声和非线性相位噪声对系统性能的影响。结果表明,由放大器自发辐射(ASE)噪声带来的线性相位噪声对传输系统的性能影响最大,ASE与自相位调制(SPM)相互作用引起的Gordon-Mollenauer(G-M)相移次之,带内四波混频(IFWM)的影响最小。在最优输入功率的条件下,由ASE带来的线性相位噪声引起的系统差分相位Q值代价大于204dB,由G-M相移引起的系统差分相位Q值代价小于7.5dB。仿真结果表明,对于采用掺铒光纤放大器(EDFA)级联放大的单信道40Gbit/s RZ-DPSK传输系统,ASE噪声是限制系统无中继传输距离的最主要因素。 相似文献
37.
38.
39.
40.