全文获取类型
收费全文 | 25332篇 |
免费 | 600篇 |
国内免费 | 156篇 |
专业分类
化学 | 16856篇 |
晶体学 | 191篇 |
力学 | 644篇 |
综合类 | 1篇 |
数学 | 4373篇 |
物理学 | 4023篇 |
出版年
2021年 | 153篇 |
2020年 | 213篇 |
2019年 | 285篇 |
2018年 | 232篇 |
2017年 | 207篇 |
2016年 | 442篇 |
2015年 | 345篇 |
2014年 | 455篇 |
2013年 | 1324篇 |
2012年 | 1192篇 |
2011年 | 1508篇 |
2010年 | 780篇 |
2009年 | 624篇 |
2008年 | 1365篇 |
2007年 | 1417篇 |
2006年 | 1409篇 |
2005年 | 1411篇 |
2004年 | 1240篇 |
2003年 | 994篇 |
2002年 | 881篇 |
2001年 | 293篇 |
2000年 | 248篇 |
1999年 | 196篇 |
1998年 | 207篇 |
1997年 | 258篇 |
1996年 | 332篇 |
1995年 | 285篇 |
1994年 | 270篇 |
1993年 | 279篇 |
1992年 | 265篇 |
1991年 | 232篇 |
1990年 | 223篇 |
1989年 | 236篇 |
1988年 | 259篇 |
1987年 | 246篇 |
1986年 | 240篇 |
1985年 | 383篇 |
1984年 | 435篇 |
1983年 | 320篇 |
1982年 | 425篇 |
1981年 | 401篇 |
1980年 | 337篇 |
1979年 | 325篇 |
1978年 | 346篇 |
1977年 | 330篇 |
1976年 | 274篇 |
1975年 | 270篇 |
1974年 | 260篇 |
1973年 | 240篇 |
1972年 | 143篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
41.
Marie-Claire Giel Dr. Christopher J. Smedley Emily R. R. Mackie Taijie Guo Prof. Dr. Jiajia Dong Dr. Tatiana P. Soares da Costa Prof. Dr. John E. Moses 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(3):1197-1202
The boom in growth of 1,4-disubstituted triazole products, in particular, since the early 2000’s, can be largely attributed to the birth of click chemistry and the discovery of the CuI-catalyzed azide–alkyne cycloaddition (CuAAC). Yet the synthesis of relatively simple, albeit important, 1-substituted-1,2,3-triazoles has been surprisingly more challenging. Reported here is a straightforward and scalable click-inspired protocol for the synthesis of 1-substituted-1,2,3-triazoles from organic azides and the bench stable acetylene surrogate ethenesulfonyl fluoride (ESF). The new transformation tolerates a wide selection of substrates and proceeds smoothly under metal-free conditions to give the products in excellent yield. Under controlled acidic conditions, the 1-substituted-1,2,3-triazole products undergo a Michael addition reaction with a second equivalent of ESF to give the unprecedented 1-substituted triazolium sulfonyl fluoride salts. 相似文献
42.
Messenger RNA (mRNA)-based vaccines are advantageous because they can be relatively quicker and more cost efficient to manufacture compared to other traditional vaccine products. Lipid nanoparticles have three common purposes: delivery, self-adjuvanting properties, and mRNA protection. Faster vaccine development requires an efficient and fast assay to monitor mRNA purity and integrity. Microchip CE is known to be a robust technology that is capable of rapid separation. Here, we describe the development and optimization of a purity and integrity assay for mRNA-based vaccines encapsulated in lipid nanoparticles using commercial microchip-based separation. The analytical parameters of the optimized assay were assessed and the method is a stability indicating assay. 相似文献
43.
44.
Meccanica - The advancement of manufacturing techniques has led to a rapid increase in the design and fabrication of periodic and architectured materials for a variety of dynamics and wave... 相似文献
45.
Kmak Kelly N. Despotopulos John D. 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(7):3175-3181
Journal of Radioanalytical and Nuclear Chemistry - The extraction of 224Ra and 228Ac with dibenzo-21-crown-7 resin was studied in solutions with Rose Bengal and identical solutions without Rose... 相似文献
46.
Distinguishing and quantification of the human visual pathways using high-spatial-resolution diffusion tensor tractography 总被引:1,自引:0,他引:1
Arash Kamali Khader M. Hasan Pavani Adapa Azadeh Razmandi Zafer Keser John Lincoln Larry A. Kramer 《Magnetic resonance imaging》2014
Quantification of the living human visual system using MRI methods has been challenging, but several applications demand a reliable and time-efficient data acquisition protocol. In this study, we demonstrate the utility of high-spatial-resolution diffusion tensor fiber tractography (DTT) in reconstructing and quantifying the human visual pathways. Five healthy males, age range 24–37 years, were studied after approval of the institutional review board (IRB) at The University of Texas Health Science Center at Houston. We acquired diffusion tensor imaging (DTI) data with 1-mm slice thickness on a 3.0-Tesla clinical MRI scanner and analyzed the data using DTT with the fiber assignment by continuous tractography (FACT) algorithm. By utilizing the high-spatial-resolution DTI protocol with FACT algorithm, we were able to reconstruct and quantify bilateral optic pathways including the optic chiasm, optic tract, optic radiations free of contamination from neighboring white matter tracts. 相似文献
47.
Inside Back Cover: Alkaline Earth Metal Zirconate Perovskites MZrO3 (M=Ba2+, Sr2+, Ca2+) Derived from Molecular Precursors and Doped with Eu3+ Ions (Chem. Eur. J. 14/2016) 下载免费PDF全文
48.
Bob Boyd Gareth Brenton Eddie Clayton Jonathan Curtis R. M. Elliott G. A. Errock B. N. Green R. H. Bateman Simon J. Gaskell Iwan Griffiths Zdenek Herman Philip Jonathan Rich Kondrat Mila Laušević Chris Lock Deepak Mathur John F. J. Todd Károly Vékey 《Rapid communications in mass spectrometry : RCM》2016,30(11):1253-1264
49.
Discovery,Characterization, and Analogue Synthesis of Bohemamine Dimers Generated by Non‐enzymatic Biosynthesis 下载免费PDF全文
Dr. Peng Fu Aaron Legako Scott La Prof. Dr. John B. MacMillan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3491-3495
Dibohemamines A–C ( 5 – 7 ), three new dimeric bohemamine analogues dimerized through a methylene group, were isolated from a marine‐derived Streptomyces spinoverrucosus. The structures determined by spectroscopic analysis were confirmed through the semi‐synthetic derivatization of monomeric bohemamines and formaldehyde. These reactions, which could occur under mild conditions, together with the detection of formaldehyde in the culture, revealed that this dimerization is a non‐enzymatic process. In addition to the unique dimerization of the dibohemamines, dibohemamines B and C were found to have nm cytotoxicity against the non‐small cell‐lung cancer cell line A549. In view of the potent cytotoxicity of compounds 6 and 7 , a small library of bohemamine analogues was generated for biological evaluation by utilizing a series of aryl and alkyl aldehydes. 相似文献