全文获取类型
收费全文 | 5444篇 |
免费 | 534篇 |
国内免费 | 795篇 |
专业分类
化学 | 1832篇 |
晶体学 | 46篇 |
力学 | 173篇 |
综合类 | 60篇 |
数学 | 297篇 |
物理学 | 1078篇 |
综合类 | 3287篇 |
出版年
2024年 | 12篇 |
2023年 | 60篇 |
2022年 | 117篇 |
2021年 | 150篇 |
2020年 | 148篇 |
2019年 | 113篇 |
2018年 | 114篇 |
2017年 | 240篇 |
2016年 | 243篇 |
2015年 | 319篇 |
2014年 | 386篇 |
2013年 | 335篇 |
2012年 | 378篇 |
2011年 | 367篇 |
2010年 | 373篇 |
2009年 | 386篇 |
2008年 | 375篇 |
2007年 | 426篇 |
2006年 | 391篇 |
2005年 | 335篇 |
2004年 | 264篇 |
2003年 | 217篇 |
2002年 | 215篇 |
2001年 | 182篇 |
2000年 | 152篇 |
1999年 | 152篇 |
1998年 | 53篇 |
1997年 | 28篇 |
1996年 | 39篇 |
1995年 | 27篇 |
1994年 | 33篇 |
1993年 | 22篇 |
1992年 | 22篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 9篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有6773条查询结果,搜索用时 15 毫秒
41.
Yu K Singh S Patrito N Chu V 《Langmuir : the ACS journal of surfaces and colloids》2004,20(25):11161-11168
Using cadium oxide (CdO) as the Cd precursor and tri-n-octylphosphine selenide (TOPSe) as the Se source, TOP-capped and TOP/tri-n-octylphosphine oxide (TOPO)-capped CdSe nanocrystals were synthesized without the use of an acid. The synthetic approach involved the addition of a TOPSe/TOP solution into a CdO/TOP solution with or without TOPO at one temperature and subsequent growth at a lower temperature. The temporal evolution of the optical properties, namely, absorption and luminescence, of the growing nanocrystals was monitored in detail. A comprehensive examination on the control of the photoluminescence (PL) properties was performed by systematically varying the TOP/TOPO weight ratio of the reaction media. Surprisingly, a rational choice of 100% TOP or 80% TOP was found to produce "quality" nanocrystals when monitored under the present experimental conditions and growth-time scale. The term "quality" is mainly based on the sharp features and rich substructure exhibited in the absorption spectra of the growing nanocrystals, as well as the sharp features in the emission spectra with narrow full width at half-maximum (fwhm). There are two distinguishable stages of growth: an early stage (<5 min) and a later stage. TOP plays a major role in the control of a slow growth rate in the early stage, while TOPO controls slow growth in the later stage. The optical sensitivity of the growing nanocrystals when dispersed in nonpolar or polar solvents was studied, including two size-dependent parameters, namely, the solvent sensitivity (PL intensity) and nonresonant Stokes shift (NRSS). The insights gained from the present study enable a synthetic approach in which high-quality CdSe nanocrystals are achieved with high synthetic reproducibility. 相似文献
42.
The ESR signals of bilirubin-IXα were studied including the samples treated with free radical generating and inhibiting systems, i.e.X-X0., Fe/EDTA, SOD, mannitol/ascorbate, DTPA, KCN et al.These stable signals all comprise those originated from a semiquinone radical(g=2.0012)and superoxide radical(g11=2.041, g⊥=2.0040).The latter is shown to be bound with metal ionsespecially iron, chelated by bilirubin.The iron probably comes from bilirubin precursor---hemootobin.Active oxygen free radical scavengers may destroy these radicals.Kinetic curves of regeneration of the bilirubin radicals have been determined.Bilirubin is discussed as"active oxygen trap"in mammatians. 相似文献
43.
本文报导的方法是在南京大学高鸿教授研究的K_3Fe(CN)_6示波极谱滴定法(在PH8的K_2HPO_4—KH_2PO_4—KBr底液中,用0.04660mol/LK_3Fe(CN)_6标准溶液对纯抗坏血酸测定)的基础上,考虑到L—抗坏血酸(以下简称V_e)在碱性、中性介质中稳定性差,如用于V_e含量很微的果蔬测定,对结果影响大。本文改为H_2C_2O_4—KBr的酸性介质作底液,用 相似文献
44.
电化学免疫分析法研究进展 总被引:27,自引:8,他引:27
电化学免疫分析法是将免疫分析与电化学分析技术相结合的一种免疫分析新方法,近十多年来,电化免疫分析的研究有了迅速的发展。本文对电化学的免疫分析法的标记物、免疫方法、电化学检测技术进行了概括总结,并展望了电化学免疫分析的发展前景。 相似文献
45.
许多三唑类化合物具有优良的杀菌和植物生长调节活性 ,如三唑酮、三唑醇、烯效唑、烯唑醇等 ,对常见真菌病害具有很好的防治效果 ,并具有增产、抗倒和生长调节作用 ,已成为重要的杀菌剂类型 [1] .为筛选新型高活性三唑类杀菌剂和探讨其活性与结构间的关系 ,我们利用生物等排体理论以常规三唑类杀菌剂三唑酮为先导物设计合成了 1 6个含芳硫基的新三唑类化合物 ,其合成路线如下 :RCCH2 BrO+HNNNB NRCCH2O NNHAC-Na ACBr2NRCCHOBrNN(1 ) (2 ) (3 )3 +SH R′B NRCCHOS R′NN (4 )RCCH2 CH2 NMe2 .HClO+HNNNH2 O… 相似文献
46.
47.
48.
碳纳米管电极超大容量离子电容器交流阻抗特性 总被引:18,自引:0,他引:18
采用碳纳米管作为超大容量离子电容器的电极材料,应用交流阻抗频谱法,研究了超大容量离子电容器的频率响应特性.结果表明,用碳纳米管块作电极,超大容量离子电容器在频率250 mHz以下出现“电荷饱和”;而用活性炭块作电极, 超大容量离子电容器在频率为100 mHz时仍未出现“电荷饱和”,这说明碳纳米管电极超大容量离子电容器的频率响应特性优于活性炭电极超大容量离子电容器的频率响应特性.上述两类超大容量离子电容器的阻抗谱中均出现倾角约为45°的直线段,其相位角均远小于理想电容器的相位角90°. 相似文献
49.
Synthesis and Characterization of Poly(butylene adipate-co-terephthalate) Catalyzed by Rare Earth Stearates 总被引:1,自引:0,他引:1
Rare earth (Nd, Y, La, Dy) stearates have been synthesized and used as single component catalysts for the polycondensation of dimethyl terephthalate, adipic acid and 1,4-butanediol for the first time preparing biodegradable poly(butylene adipate-co-terephthalate) (PBAT) with high molecular weight, The microstructures of PBAT were characterized by ^1H NMR spectra. The PBAT exhibits good mechanical properties such as high tensile strength (ca. 20 MPa) and long break elongation (〉700%). 相似文献
50.
Kui Wu Nathan A. Yee Sangeetha Srinivasan Amir Mahmoodi Michael Zakharian Jose M. Mejia Oneto Maksim Royzen 《Chemical science》2021,12(21):7583
Correction for ‘Click activated protodrugs against cancer increase the therapeutic potential of chemotherapy through local capture and activation’ by Kui Wu et al., Chem. Sci., 2021, 12, 1259–1271, DOI: 10.1039/D0SC06099B.The authors regret that the reference to the bond-breaking bioorthogonal chemistry, termed ‘click-to-release’ was omitted from the original article. In addition, we would like to include a reference describing the synthesis of compound 1, which is an intermediate to the protodrugs described in the original article. These references are listed below as ref. 1 and 2.The Royal Society of Chemistry apologizes for these errors and any consequent inconvenience to authors and readers. 相似文献