全文获取类型
收费全文 | 313256篇 |
免费 | 18665篇 |
国内免费 | 9791篇 |
专业分类
化学 | 172743篇 |
晶体学 | 3723篇 |
力学 | 16200篇 |
综合类 | 513篇 |
数学 | 35361篇 |
物理学 | 113172篇 |
出版年
2022年 | 2830篇 |
2021年 | 4334篇 |
2020年 | 5624篇 |
2019年 | 5466篇 |
2018年 | 5774篇 |
2017年 | 5379篇 |
2016年 | 8293篇 |
2015年 | 6488篇 |
2014年 | 9001篇 |
2013年 | 16545篇 |
2012年 | 15410篇 |
2011年 | 17619篇 |
2010年 | 12128篇 |
2009年 | 11898篇 |
2008年 | 14349篇 |
2007年 | 13702篇 |
2006年 | 12913篇 |
2005年 | 11192篇 |
2004年 | 9761篇 |
2003年 | 8342篇 |
2002年 | 7685篇 |
2001年 | 8503篇 |
2000年 | 6585篇 |
1999年 | 5664篇 |
1998年 | 4780篇 |
1997年 | 4743篇 |
1996年 | 4536篇 |
1995年 | 4207篇 |
1994年 | 3989篇 |
1993年 | 3899篇 |
1992年 | 3886篇 |
1991年 | 3989篇 |
1990年 | 3605篇 |
1989年 | 3427篇 |
1988年 | 3327篇 |
1987年 | 3175篇 |
1986年 | 3038篇 |
1985年 | 3995篇 |
1984年 | 4072篇 |
1983年 | 3226篇 |
1982年 | 3433篇 |
1981年 | 3327篇 |
1980年 | 3212篇 |
1979年 | 3301篇 |
1978年 | 3384篇 |
1977年 | 3318篇 |
1976年 | 3427篇 |
1975年 | 3108篇 |
1974年 | 3123篇 |
1973年 | 3166篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Xinyu Zhang Linxuan Li Prof. Giuseppe Zanoni Xinyue Han Prof. Xihe Bi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(22):e202200280
The direct gem-difluoroalkenylation of X−H bonds represents the most straightforward approach to access heteroatomic gem-difluoroalkenes that, as the isostere of the carbonyl group, have great potency in drug discovery. However, the construction of tetrasubstituted heteroatomic gem-difluoroalkenes by this strategy is still an unsolved problem. Here, we report the first direct X−H bond gem-difluoroalkenylation of amines and alcohols with trifluoromethyl ketone N-triftosylhydrazones under silver (for (hetero)aryl hydrazones) or rhodium (for alkyl hydrazones), thereby providing a most powerful method for the synthesis of tetrasubstituted heteroatomic gem-difluoroalkenes. This method features a broad substrate scope, high product yield, excellent functional group tolerance, and operational simplicity (open air conditions). Moreover, the site-specific replacement of the carbonyl group with a gem-difluorovinyl ether bioisostere in drug Trimebutine and the post-modification of bioactive molecules demonstrates potential use in medicinal research. Finally, the reaction mechanism was investigated by combining experiments and DFT calculations, and disclosed that the key step of HF elimination occurred via five-membered ring transition state, and the difference in the electrophilicity of Ag- and Rh-carbenes as well as the multiple intermolecular interactions rendered the effectiveness of Rh catalyst selectively for alkyl hydrazones. 相似文献
72.
Li Quanxin Li Zheng He Cheng Sun Huilin Tan Shengheng Zhang Hua 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(5):2105-2115
Journal of Radioanalytical and Nuclear Chemistry - The simplified 8-oxide system (SiO2-B2O3-Na2O-Al2O3-CaO-TiO2-MoO3-La2O3) has been prepared under two types of cooling methods, and analyzed with... 相似文献
73.
Hongjin Wang Tengfei Long Hao Zhang Meng Li Qi Sun Xin Zhai Lixin Sun 《Biomedical chromatography : BMC》2022,36(4):e5301
3,4-Difluorobenzyl(1-ethyl-5-(4-((4-hydroxypiperidin-1-yl)-methyl)thiazol-2-yl)-1H-indol-3-yl)carbamate (NAI59), a small molecule with outstanding therapeutic effectiveness to anti-pulmonary fibrosis, was developed as an autotaxin inhibitor candidate compound. To evaluate the pharmacokinetics and plasma protein binding of NAI59, a UPLC–MS/MS method was developed to quantify NAI59 in plasma and phosphate-buffered saline. The calibration curve linearity ranged from 9.95 to 1990.00 ng/mL in plasma. The accuracy was −6.8 to 5.9%, and the intra- and inter-day precision was within 15%. The matrix effect and recovery, as well as dilution integrity, were within the criteria. The chromatographic and mass spectrometric conditions were also feasible to determine phosphate-buffered saline samples, and it has been proved that this method exhibits good precision and accuracy in the range of 9.95–497.50 ng/mL in phosphate-buffered saline. This study is the first to determine the pharmacokinetics, absolute bioavailability, and plasma protein binding of NAI59 in rats using this established method. Therefore, the pharmacokinetic profiles of NAI59 showed a dose-dependent relationship after oral administration, and the absolute bioavailability in rats was 6.3%. In addition, the results of protein binding showed that the combining capacity of NAI59 with plasma protein attained 90% and increased with the increase in drug concentration. 相似文献
74.
Zhihong Zhao Bin Wang Rui Tan Wenjing Liu Minghui Zhang 《Magnetic resonance in chemistry : MRC》2022,60(4):427-433
In this study, the transverse relaxation time (T2) of activated carbon (AC) in different relative environment humidity was detected firstly by low-field nuclear magnetic resonance (LFNMR). The pore size (diameter) of AC distributions was calculated by the relationship between T2 and surface relaxation rate (ρ), where ρ was obtained by the detection of nine porous materials with known pore size. The results showed that the pore size distributions of AC calculated by ρ < 0.19 nm/ms were in good agreement with that obtained by nitrogen adsorption method and proved that LFNMR as a new detection method was feasible for characterizing AC pore size distribution. 相似文献
75.
76.
77.
Chumakov Yu. M. Graur V. O. Ulchina Ya. I. Smaglii V. A. Gulea A. P. Garbuz O. S. Tsapkov V. I. 《Journal of Structural Chemistry》2022,63(6):905-913
Journal of Structural Chemistry - The crystal structures and biological properties of [N′-(2-oxidobenzylidene)-N-(prop-2-en-1-yl)-carbamohydrazonothioato(2-)](1,10-phenanthroline)copper... 相似文献
78.
Zhongxian Fan Jiaen Xie Dr. Tumpa Sadhukhan Chao Liang Can Huang Wenqing Li Tingxuan Li Dr. Pingyu Zhang Dr. Samya Banerjee Dr. Krishnan Raghavachari Dr. Huaiyi Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(3):e202103346
Four photo-catalysts of the general formula [Ir(CO6/ppy)2(L)]Cl where CO6=coumarin 6 ( Ir1 – Ir3 ), ppy=2-phenylpyridine ( Ir4 ), L=4′-(3,5-di-tert-butylphenyl)-2,2′ : 6′,2′′-terpyridine ( Ir1 ), 4′-(3,5-bis(trifluoromethyl)phenyl)-2,2′ : 6′,2′′-terpyridine ( Ir2 and Ir4 ), and 4-([2,2′ : 6′,2′′-terpyridin]-4′-yl)-N,N-dimethylaniline ( Ir3 ) were synthesized and characterized. These photostable photo-catalysts ( Ir1 – Ir3 ) showed strong visible light absorption between 400–550 nm. Upon light irradiation (465 and 525 nm), Ir1 – Ir3 generated singlet oxygen and induced rapidly photo-catalytic oxidation of cellular coenzymes NAD(P)H. Ir1 – Ir3 showed time-dependent cellular uptake with excellent intracellular retention efficiency. Upon green light irradiation (525 nm), Ir2 provided a much higher photo-index (PI=793) than the clinically used photosensitizer, 5-aminolevulinicacid (5-ALA, PI>30) against HeLa cancer cells. The observed necro-apoptotic anticancer activity of Ir2 was due to the Ir2 triggered photo-induced intracellular redox imbalance (by NAD(P)H oxidation and ROS generation) and change in the mitochondrial membrane potential. Remarkably, Ir2 showed in vivo photo-induced catalytic anticancer activity in mouse models. 相似文献
79.
80.
Zhang Bing Yang Jie-qin Liu Ying Hu Bin Yang Yang Zhao Li Lu Qiang 《Cellulose (London, England)》2022,29(12):6565-6578
Cellulose - Heating is essential in various biomass pre-treatments and thermal conversion processes. It is of practical significance to study the characteristics of cellulose-lignin and... 相似文献