全文获取类型
收费全文 | 3850篇 |
免费 | 110篇 |
国内免费 | 15篇 |
专业分类
化学 | 3111篇 |
晶体学 | 32篇 |
力学 | 38篇 |
数学 | 383篇 |
物理学 | 411篇 |
出版年
2023年 | 14篇 |
2022年 | 60篇 |
2021年 | 96篇 |
2020年 | 58篇 |
2019年 | 58篇 |
2018年 | 44篇 |
2017年 | 46篇 |
2016年 | 111篇 |
2015年 | 97篇 |
2014年 | 117篇 |
2013年 | 214篇 |
2012年 | 214篇 |
2011年 | 251篇 |
2010年 | 144篇 |
2009年 | 143篇 |
2008年 | 263篇 |
2007年 | 212篇 |
2006年 | 218篇 |
2005年 | 207篇 |
2004年 | 168篇 |
2003年 | 137篇 |
2002年 | 137篇 |
2001年 | 62篇 |
2000年 | 41篇 |
1999年 | 51篇 |
1998年 | 37篇 |
1997年 | 43篇 |
1996年 | 50篇 |
1995年 | 47篇 |
1994年 | 42篇 |
1993年 | 30篇 |
1992年 | 34篇 |
1991年 | 27篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 22篇 |
1984年 | 21篇 |
1983年 | 19篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 31篇 |
1979年 | 22篇 |
1978年 | 18篇 |
1977年 | 17篇 |
1975年 | 13篇 |
1956年 | 19篇 |
1955年 | 37篇 |
1954年 | 57篇 |
排序方式: 共有3975条查询结果,搜索用时 0 毫秒
161.
A number of reporter molecules of the structure R-(CH2)n-N+(CH3)2(CH2)mN+(CH3)3·2Br?, where R is a chromophore absorbing in the 300–500 mp region, have been synthesized. The effect of DNA and RNA on the absorption, induced circular dichroism, and proton magnetic resonance spectra is reported. A red shift and a hypochromic effect on the absorption spectra of the bound chromophore is observed. In all cases where R is an “unsymmetrical” 4-nitroaniline chromophore, it is found that DNA and RNA induce an opposite CD in the absorption band of the bound reporter molecules. These results together with PMR studies are interpreted in terms of the structure of the nucleic acid systems in solutions. 相似文献
162.
163.
The biaxial symmetry of the low temperature smectic phase of N-(4-n-hexyloxybenzylidene)-4-n-hexylaniline is demonstrated through observation of the deuterium NMR resonance of CDCl3 probe molecules dissolved in this phase. The biaxial ordering is revealed in the observed powder spectrum as well as in a complete rotation study of a uniformly aligned sample. 相似文献
164.
165.
Expedient and Diastereodivergent Assembly of Terpenoid Decalin Subunits having Quaternary Stereocenters through Organocatalytic Robinson Annulation of Nazarov Reagent
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)
Barbara Berkes Kristóf Ozsváth Laura Molnár Tamás Gáti Tamás Holczbauer György Kardos Tibor Soós 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(50):18101-18106
We report an expedient approach to highly functionalized cis‐ and trans‐decalines that could function as key structural subunits toward the synthesis of various classes of terpenoids. Key to the strategy is an organocatalyzed Robinson annulation reaction of the Nazarov reagent that affords chiral enone building blocks with high enantioselectivities. The quaternary carbon stereogenic center can direct the subsequent reactions and allow the rapid and diastereoconvergent assembly of complex decalines with contiguous stereocenters. 相似文献
166.
167.
Jelena Vasiljević Samira Hadžić Ivan Jerman Lidija Černe Brigita Tomšič Jožef Medved Matjaž Godec Boris Orel Barbara Simončič 《Polymer Degradation and Stability》2013
The aim of this study was to introduce a non-formaldehyde inorganic–organic hybrid sol–gel flame-retardant precursor (SiOP) containing phosphorous, nitrogen, and silicon and to compare its functional properties with those of the conventional formaldehyde-containing organic flame-retardant agent, organophosphonate (OP). SiOP was used at concentrations of 2%, 4%, and 8%, and OP was used at a concentration of 200 g/dm3. Both agents were applied to 100% cotton (CO) woven fabric by the pad-dry-cure method under the appropriate conditions. The presence of the SiOP and OP coatings on the CO fabric was confirmed by scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. The results of the vertical tests of flammability and the thermogravimetric analyses showed that the presence of the SiOP coating changed the thermal degradation pathway of the CO fabric and resulted in an increase in the thermo-oxidative stability of the cellulose fibres. The thermo-oxidative stability was enhanced by the addition of higher amount of dry solids. At comparable dry solids contents, OP preserved significantly greater flame retardancy and thermo-oxidative stability than did SiOP. These results indicated that the SiOP precursor could not act as an effective alternative to the OP agent in the flame-retardant protection of CO fabric. 相似文献
168.
169.
Jóźwiak Grzegorz Majer-Dziedzic Barbara Kwiecińska Justyna Waksmundzka-Hajnos Monika 《平面色谱法杂志一现代薄层色谱法》2017,30(2):126-130
JPC – Journal of Planar Chromatography – Modern TLC - Commercially available hop pellets of different origins were extracted by use of ethanol and water, chromatographed on silica... 相似文献