全文获取类型
收费全文 | 59835篇 |
免费 | 9491篇 |
国内免费 | 6972篇 |
专业分类
化学 | 42825篇 |
晶体学 | 734篇 |
力学 | 3437篇 |
综合类 | 453篇 |
数学 | 6753篇 |
物理学 | 22096篇 |
出版年
2024年 | 200篇 |
2023年 | 1208篇 |
2022年 | 2237篇 |
2021年 | 2360篇 |
2020年 | 2535篇 |
2019年 | 2371篇 |
2018年 | 2075篇 |
2017年 | 1983篇 |
2016年 | 2908篇 |
2015年 | 2967篇 |
2014年 | 3525篇 |
2013年 | 4422篇 |
2012年 | 5387篇 |
2011年 | 5354篇 |
2010年 | 3820篇 |
2009年 | 3582篇 |
2008年 | 3837篇 |
2007年 | 3376篇 |
2006年 | 3061篇 |
2005年 | 2642篇 |
2004年 | 2103篇 |
2003年 | 1679篇 |
2002年 | 1633篇 |
2001年 | 1313篇 |
2000年 | 1139篇 |
1999年 | 1221篇 |
1998年 | 958篇 |
1997年 | 867篇 |
1996年 | 865篇 |
1995年 | 791篇 |
1994年 | 642篇 |
1993年 | 556篇 |
1992年 | 460篇 |
1991年 | 421篇 |
1990年 | 356篇 |
1989年 | 252篇 |
1988年 | 193篇 |
1987年 | 174篇 |
1986年 | 166篇 |
1985年 | 143篇 |
1984年 | 89篇 |
1983年 | 94篇 |
1982年 | 56篇 |
1981年 | 41篇 |
1980年 | 30篇 |
1979年 | 19篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1972年 | 19篇 |
1957年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
241.
Huang F Hou L Wu H Wang X Shen H Cao W Yang W Cao Y 《Journal of the American Chemical Society》2004,126(31):9845-9853
A series of aminoalkyl-substituted polyfluorene copolymers with benzothiadiazole (BTDZ) of different content were synthesized by Suzuki coupling reaction, and their quaternized ammonium polyelectrolyte derivatives were obtained through a postpolymerization treatment on the terminal amino groups. Copolymers are soluble in environmentally friendlier solvents, such as alcohols. It was found that the efficient energy transfer occurs by exciton trapping on the narrow band gap BTDZ site under UV illumination. Only 1% of BTDZ content is needed to completely quench a fluorene emission for both the neutral and the quaternized copolymers in the neat film. Absolute PL efficiencies of copolymer films were greatly enhanced as a result of the suppression of excimer formation. Light-emitting devices fabricated from these copolymers show high external quantum efficiencies over 3% and 1% for the neutral precursor and the quaternized copolymers, respectively, with high work function metals such as Al as a cathode. To the best of our knowledge, this is the first report on an electroluminescent polymer which bears the high EL efficiency, the electron-injection ability from high work function metals, and the solubility in environment-friendly solvents at the same time. These features make them a promising candidate for the next generation of light-emitting copolymers in PLED flat panel display application. 相似文献
242.
Ying Wang Pu Xiao Gang Qiang Wu Su Qing Shi Jun Nie 《中国化学快报》2007,18(8):977-980
A benzophenone derivative photoinitiator, HBP-TDI-HQ-TDI-HBP (HTCTH), was synthesized based on 4-hydroxy benzophenone (HBP), toluene-2,4-diisocyanate (TDI) and hydroquinone (HQ). HTCTH was a more effective photoinitiator which had longer wavelength absorption in the UV-vis absorption spectra than the low molecular counterpart benzophenone (BP). It showed that both rate of polymerization (Rp) and final conversion (P) increased with increase of amine and HTCTH concentration in photopolymerization. 相似文献
243.
Junfeng Zhou Xiaochen Dong Tao Chen Qiang Yang Qiaohua Tan Jianjun Wang 《European Polymer Journal》2007,43(5):2088-2095
A series of well-defined two-armed polymers containing a crown ether core, poly(stearyl methacrylate)-crown ether-poly(stearyl methacrylate) (PSMA-crown-PSMA), with different molecular weight were synthesized via atom transfer radical polymerization (ATRP). The resultant polymers were characterized by 1H NMR and GPC. The self-assembly behaviors of this kind of polymer in selective solvents were studied by TEM, and it was found that polymers with different molecular weight can directly self-assemble into hollow spheres, solid spheres and a monolayer film with regular pores by varying molecular weight and water content. The possible molecular packing motels for their self-assembly behaviors were proposed. 相似文献
244.
The enantiodifferentiating [4+4] photocyclodimerization of anthracenecarboxylic acid (AC) mediated by native, mono- and di-3,6-anhydro-γ-cyclodextrins was investigated in both aqueous solution and solid-state. The solid-state photolyses gave inherently disfavored head-to-head photodimers in much higher chemical and optical yields than in the aqueous solution. 相似文献
245.
246.
247.
248.
甲亚胺与姜黄素测定土壤有效硼方法的对比研究 总被引:9,自引:0,他引:9
土壤有效硼是决定土壤供硼能力的重要指标,目前中国多以沸水浸提土壤,并用姜黄素比色测硼值作为作物硼营养丰缺诊断指标.但在长期实践中,发现作物硼营养状况与热水溶性硼的相关性不稳定,同时测定值重现性不良。为提高作物硼营养诊断和预测的准确性,本研究通过0.01mol/LCaCl2在260℃、35min浸提土壤条件下,用甲亚胺比色与沸水浸提,姜黄素比色法测定土壤有效硼的对比研究,证明甲亚胺法测定结果稳定,操作方法简便,适用于低硼土壤的大批量试样的自动分析。为甲亚胺测硼方法的推广应用,本研究已研制甲亚胺粉状试剂获得成功,与进口甲亚胺比较,性能完全一致。 相似文献
249.
使用TPR和H2-TPD技术对镍铝系催化剂的还原和氢脱附性能进行了研究,并与其催化性能相关联。结果发现,镍铝系催化剂的氢脱附能力与其催化性能之间有一定联系,脱附氢能力越强,催化剂的甲烷部分氧化反应性能就越好,但催化性能与还原性能无直接关联。 相似文献
250.
大肠杆菌有限生长的微量热及非线性动力学研究 总被引:2,自引:0,他引:2
The finite growth of Escherichia coli was studied by using a LKB 2277 BioActivity Mollitor. We found that the finite growth is a nonliear dynamic process. The nonlinear dynamic behaviour in the finite growth process and the nonlinear dynamic models describing the process were discovered and established. The curve of logistic map corresponding to the finite growth thermogram of Escherichia coli was obtained and the nonlinear dynamic parameters were calculated by means of a computer. Moreover, we also discussed the nonlinear dynamic characters of Escherichia colt in its finite growth process. 相似文献