全文获取类型
收费全文 | 36997篇 |
免费 | 9652篇 |
国内免费 | 1439篇 |
专业分类
化学 | 42082篇 |
晶体学 | 329篇 |
力学 | 510篇 |
综合类 | 1篇 |
数学 | 2524篇 |
物理学 | 2642篇 |
出版年
2023年 | 26篇 |
2022年 | 93篇 |
2021年 | 234篇 |
2020年 | 1283篇 |
2019年 | 2618篇 |
2018年 | 1072篇 |
2017年 | 690篇 |
2016年 | 3460篇 |
2015年 | 3592篇 |
2014年 | 3517篇 |
2013年 | 4176篇 |
2012年 | 3095篇 |
2011年 | 2314篇 |
2010年 | 2937篇 |
2009年 | 2901篇 |
2008年 | 2507篇 |
2007年 | 1865篇 |
2006年 | 1562篇 |
2005年 | 1696篇 |
2004年 | 1490篇 |
2003年 | 1368篇 |
2002年 | 2051篇 |
2001年 | 1371篇 |
2000年 | 1303篇 |
1999年 | 380篇 |
1998年 | 54篇 |
1997年 | 58篇 |
1996年 | 43篇 |
1995年 | 34篇 |
1994年 | 24篇 |
1993年 | 27篇 |
1992年 | 28篇 |
1991年 | 13篇 |
1990年 | 21篇 |
1989年 | 12篇 |
1988年 | 18篇 |
1987年 | 7篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 11篇 |
1970年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Beyond Stereoselectivity,Switchable Catalysis: Some of the Last Frontier Challenges in Ring‐Opening Polymerization of Cyclic Esters
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Sophie M. Guillaume Dr. Evgueni Kirillov Dr. Yann Sarazin Prof. Dr. Jean‐François Carpentier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):7988-8003
Metal‐based catalysts and initiators have played a pivotal role in the ring‐opening polymerization (ROP) of cyclic esters, thanks to their high activity and remarkable ability to control precisely the architectures of the resulting polyesters in terms of molar mass, dispersity, microstructure, or tacticity. Today, after two decades of extensive research, the field is slowly reaching maturity. However, several challenges remain, while original concepts have emerged around new types or new applications of catalysis. This Review is not intended to comprehensively cover all of these aspects. Rather, it provides a personal overview of the very recent progress achieved in some selected, important aspects of ROP catalysis—stereocontrol and switchable catalysis. Hence, the first part addresses the development of new metal‐based catalysts for the isoselective ROP of racemic lactide towards stereoblock copolymers, and the use of syndioselective ROP metal catalysts to control the monomer sequence in copolymers. A second part covers the development of ROP catalysts—primarily metal‐based catalysts, but also organocatalysts—that can be externally regulated by the use of chemical or photo stimuli to switch them between two states with different catalytic abilities. Current challenges and opportunities are highlighted. 相似文献
42.
43.
Brandão Pedro Francisco Ramos Rui Miguel Rodrigues José António 《Analytical and bioanalytical chemistry》2018,410(26):6873-6880
Analytical and Bioanalytical Chemistry - Formaldehyde is often applied in the industrial production of different products, such as textiles, insulation materials, or cosmetics, due to its... 相似文献
44.
45.
46.
47.
48.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
49.
Complementary regioselective esterification of non-reducing oligosaccharides catalyzed by different hydrolases 总被引:1,自引:0,他引:1
The enzymatic transesterification of several tri- and tetrasaccharides with vinyl laurate is described. The lipases from Candida antarctica B (Novozym 435) and Thermomyces lanuginosus (Lipozyme TL IM) and the alkaline protease from Bacillus licheniformis (subtilisin Carlsberg) have been used with each carbohydrate to obtain different regioisomers. By using the sugars in their amorphous form, complete solubility is achieved in the reaction media (tert-butanol/pyridine mixtures for the lipases and pyridine for the protease) and high isolated yields of the corresponding monoesters are obtained. Good to excellent regioselectivity is observed for all the enzymes, showing a final complementary picture respect to the primary hydroxyls of the oligosaccharides studied. 相似文献
50.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献