全文获取类型
收费全文 | 5457篇 |
免费 | 551篇 |
国内免费 | 195篇 |
专业分类
化学 | 4132篇 |
晶体学 | 91篇 |
力学 | 133篇 |
综合类 | 20篇 |
数学 | 628篇 |
物理学 | 1199篇 |
出版年
2023年 | 76篇 |
2022年 | 87篇 |
2021年 | 125篇 |
2020年 | 170篇 |
2019年 | 179篇 |
2018年 | 127篇 |
2017年 | 100篇 |
2016年 | 191篇 |
2015年 | 212篇 |
2014年 | 219篇 |
2013年 | 324篇 |
2012年 | 376篇 |
2011年 | 424篇 |
2010年 | 262篇 |
2009年 | 224篇 |
2008年 | 341篇 |
2007年 | 271篇 |
2006年 | 296篇 |
2005年 | 290篇 |
2004年 | 229篇 |
2003年 | 213篇 |
2002年 | 205篇 |
2001年 | 98篇 |
2000年 | 83篇 |
1999年 | 91篇 |
1998年 | 68篇 |
1997年 | 71篇 |
1996年 | 84篇 |
1995年 | 61篇 |
1994年 | 66篇 |
1993年 | 39篇 |
1992年 | 48篇 |
1991年 | 37篇 |
1990年 | 36篇 |
1989年 | 31篇 |
1988年 | 29篇 |
1987年 | 28篇 |
1986年 | 23篇 |
1985年 | 30篇 |
1984年 | 40篇 |
1983年 | 23篇 |
1982年 | 28篇 |
1981年 | 24篇 |
1980年 | 29篇 |
1979年 | 24篇 |
1978年 | 22篇 |
1977年 | 27篇 |
1976年 | 17篇 |
1975年 | 16篇 |
1974年 | 24篇 |
排序方式: 共有6203条查询结果,搜索用时 46 毫秒
991.
Lee J. Silverberg Tapas K. Mal Carlos N. Pacheco Megan L. Povelones Madeline F. Malfara Anthony F. Lagalante Mark A. Olsen Hemant P. Yennawar Hany F. Sobhi Kayla R. Baney Robin L. Bozeman Craig S. Eroh Michael J. Fleming Tracy L. Garcia Casey L. Gregory Julia E. Hahn Alyssa M. Hatter Lexi L. Johns Tianna L. Klinger Jennie J. Li Andrew J. Menig Grace C. Muench Melissa E. Ramirez Jordyn Reilly Nicole Sacco Alexandra M. Sheidy Marla M. Stoner Eric N. Thompson Soroush F. Yazdani 《Molecules (Basel, Switzerland)》2021,26(20)
A series of fourteen 2-aryl-3-phenyl-2,3-dihydro-4H-pyrido[3,2-e][1,3]thiazin-4-ones was prepared at room temperature by T3P-mediated cyclization of N-phenyl-C-aryl imines with thionicotinic acid, two difficult substrates. The reactions were operationally simple, did not require specialized equipment or anhydrous solvents, could be performed as either two or three component reactions, and gave moderate–good yields as high as 63%. This provides ready access to N-phenyl compounds in this family, which have been generally difficult to prepare. As part of the study, the first crystal structure of neutral thionicotinic acid is also reported, and showed the molecule to be in the form of the thione tautomer. Additionally, the synthesized compounds were tested against T. brucei, the causative agent of Human African Sleeping Sickness. Screening at 50 µM concentration showed that five of the compounds strongly inhibited growth and killed parasites. 相似文献
992.
Chi Wu Aizhen Niu Yue Zhao Chengming Li Yuliang Yang 《Macromolecular rapid communications》2001,22(9):704-707
The thermal decomposition of polystyrene clusters prepared by using 4‐methacryloyloxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl as a branching agent was studied. The weight‐average molar mass (M̄w) and the radius of gyration (Rg) of the resultant clusters can be scaled as M̄w ∝︁ Rg3.0 ± 0.1, revealing that these clusters have a uniform chain density. Moreover, the dynamic properties of such clusters converge unexpectedly faster than the static properties as the molar mass decreases. 相似文献
993.
994.
995.
In this article, we have described the asymmetric cyclization of L‐serinoates and N‐benzyl L‐serinoate with phosphoro(no‐)dichloridates or their thio‐analog, respectively, and we have investigated the asymmetric induction effect of the chiral carbon center on the forming of a chiral phosphorus center. The diastereomeric excess percentages (de%) of the desired products 2‐oxo‐ and 2‐thio‐1,3,2‐oxazaphospholidines, are obtained based on their 31P NMR data. In some cases, the cyclization products have been separated as pure diastereomers by column chromatography. Their configuration is preliminarily discussed. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:187–191, 2000 相似文献
996.
Chi‐Ming Chan Lin Li Kai‐Mo Ng Jianxiong Li Lu‐Tao Weng 《Macromolecular Symposia》2000,159(1):113-122
Two series of polyethers were synthesized by the polymerization of 1, n‐dibromoalkane (n = 4, 6, 8, 10, 12, 14 and 18) with bisphenol‐A (BA) and 4, 4'‐(hexafluoroisopropylidene) diphenol‐A. The length of the flexible aliphatic segment changes from 4 Å to 21 Å (corresponding to 4 to 18 CH2 groups). X‐ray photoelectron spectroscopy (XPS), time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and atomic force microscopy (AFM) were used to characterize the surfaces of the polyethers. The influence of the length of the flexible aliphatic segments on the surface composition of the BA and 6FBA polyethers was investigated. The intensity ratios of the characteristic SIMS peaks of the flexible segments to those of the rigid segments were related to the length of the flexible segments and the XPS results confirmed that the SIMS intensity ratios can be used to determine the surface compositions. AFM was utilized to investigate the crystallization process of the BA polymer with n = 8. The appearance of nuclei, the generation of primary lamellae and the formation of spherulites were observed dynamically. Nuclei appeared first as 10 nm dots, some disappeared and a few could grow into lamellae. The lamellae that developed from the nuclei bred more lamellae, which in turn induced secondary nucleation and branching of lamellae and finally led to a spherical appearance. 相似文献
997.
Zheling Feng Zhujun Fang Cheng Chen Chi Teng Vong Jiali Chen Ruohan Lou Maggie Pui Man Hoi Lishe Gan Ligen Lin 《Molecules (Basel, Switzerland)》2021,26(22)
To identify the chemical components responsible for the anti-hyperglycemic effect of Cyclocarya paliurus (Batal.) Iljinsk (Juglandaceae) leaves, an ethanol extract (CPE) and a water extract (CPW) of C. paliurus leaves, as well as their total flavonoids (CPF), triterpenoids (CPT) and crude polysaccharides (CPP), were prepared and assessed on streptozotocin (STZ)-induced diabetic mice. After being orally administrated once a day for 24 days, CPF (300 mg/kg), CPP (180 mg/kg), or CPF+CPP (300 mg/kg CPF + 180 mg/kg CPP) treatment reversed STZ-induced body weight and muscle mass losses. The glucose tolerance tests and insulin tolerance tests suggested that CPF, CPP, and CPF+CPP showed anti-hyperglycemic effect in STZ-induced diabetic mice. Furthermore, CPF enhances glucose-stimulated insulin secretion in MIN6 cells and insulin-stimulated glucose uptake in C2C12 myotubes. CPF and CPP suppressed inflammatory cytokine levels in STZ-induced diabetic mice. Additionally, CPF and CPP improved STZ-induced diabetic nephropathy assessed by H&E staining, blood urea nitrogen content, and urine creatinine level. The molecular networking and Emperor analysis results indicated that CPF showed potential anti-hyperglycemic effects, and HPLC–MS/MS analysis indicated that CPF contains 3 phenolic acids and 9 flavonoids. In contrast, CPT (650 mg/kg) and CPC (300 mg/kg CPF + 180 mg/kg CPP + 650 mg/kg CPT) did not show anti-hyperglycemic effect. Taken together, polysaccharides and flavonoids are responsible for the anti-hyperglycemic effect of C. paliurus leaves, and the clinical application of C. paliurus need to be refined. 相似文献
998.
Chi Ching Mak Nick Bampos Jeremy K. M. Sanders 《Angewandte Chemie (International ed. in English)》1998,37(21):3020-3023
Rigid and flexible linkers are combined in the new dendrimer shown schematically in the picture, which contains nine metalloporphyrin units (Porph). The construction is such that the four “arms” of the dendrimer can fold in a cooperative and predetermined manner in response to added 1,4-diazabicyclo[2.2.2]octane (DABCO). 相似文献
999.
1000.