全文获取类型
收费全文 | 2200篇 |
免费 | 95篇 |
国内免费 | 666篇 |
专业分类
化学 | 2725篇 |
晶体学 | 9篇 |
力学 | 7篇 |
综合类 | 15篇 |
数学 | 8篇 |
物理学 | 197篇 |
出版年
2024年 | 4篇 |
2023年 | 25篇 |
2022年 | 55篇 |
2021年 | 67篇 |
2020年 | 74篇 |
2019年 | 80篇 |
2018年 | 63篇 |
2017年 | 82篇 |
2016年 | 80篇 |
2015年 | 72篇 |
2014年 | 104篇 |
2013年 | 218篇 |
2012年 | 149篇 |
2011年 | 127篇 |
2010年 | 125篇 |
2009年 | 130篇 |
2008年 | 146篇 |
2007年 | 145篇 |
2006年 | 132篇 |
2005年 | 118篇 |
2004年 | 122篇 |
2003年 | 115篇 |
2002年 | 100篇 |
2001年 | 72篇 |
2000年 | 71篇 |
1999年 | 69篇 |
1998年 | 52篇 |
1997年 | 49篇 |
1996年 | 45篇 |
1995年 | 40篇 |
1994年 | 41篇 |
1993年 | 41篇 |
1992年 | 28篇 |
1991年 | 25篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 2篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有2961条查询结果,搜索用时 203 毫秒
161.
利用液相沉淀法可控合成了均匀的棒状CuFe4Ox催化剂。通过原位X射线粉末衍射(XRD)、高分辨透射电子显微镜(TEM)及程序升温还原(TPR)等手段表征其晶相结构、形貌和还原性能。通过还原棒状CuFe4Ox获得Cu0/Fe3O4 纳米棒,原位X射线光电子能谱(XPS)用于确定Cu0/Fe3O4 表面的相组成。通过液相沉淀法制备棒状CuFe4Ox,在120℃保持3 h后加入Na2CO3溶液至pH等于9时所得棒状形貌最为规整。以异戊醇脱氢反应作为探针反应,比较了Cu0/Fe3O4 纳米棒和Cu0/Fe3O4 纳米颗粒的催化反应性能,发现Cu0/Fe3O4 纳米棒比Cu0/Fe3O4 纳米粒子具有更好的活性和稳定性,表明棒状Fe3O4 担载的Cu纳米粒子具有更好的结构稳定性。 相似文献
162.
Yi Zhang Xiaolan Yang Xiaolei Hu Miaomiao Liu Chunyan ChenYanling Xie Jun PuJing Wu Gaobo LongFei Liao 《Analytica chimica acta》2013
A resonant-light-scattering (RLS) method was proposed to quantify phosphate for screening inhibitors of isozymes of cyclic nucleotide phosphodiesterase (PDE). In acidified mixtures of phosphate, papaverine and molybdate, there were aggregates exhibiting micrometre sizes, no absorbance peaks over 360 nm but strong RLS peaks at 392 nm; Mie scattering thus accounted for the RLS signals. When papaverine was added before molybdate to acidified samples of phosphate, RLS signals at 392 nm were stable from 5 to 25 min since the addition of molybdate; after optimization, phosphate from 0.40 to 3.60 μM was quantifiable. This RLS method tolerated 60 mg L−1 proteins besides common PDE inhibitors and dimethyl sulfoxide in acidified samples of phosphate; the integration of this RLS method with the coupled action of a phosphomonoesterase on PDE product was thus rational to measure PDE activities without the removal of proteins in samples. By quantifying activities of a truncated mutant of human PDE4B2 via this RLS method, Michaelis–Menten constant, inhibition constants of rolipram, papaverine and theophylline varied over three magnitudes and were consistent with those estimated by an improved malachite green assay of phosphate, respectively. Hence, this novel RLS method was promising for screening inhibitors of PDE isozymes. 相似文献
163.
We present the successful application of emulsion electrospinning for the encapsulation of a model for highly volatile fragrances, namely (R)-(+)-limonene in a poly(vinyl alcohol) (PVA) fibrous matrix. The influence of the emulsion formulation and of its colloidal properties on the fiber morphology, as well as on the limonene encapsulation efficiency, is described. The release profile of the fragrance from the electrospun nanofibers over a fifteen days range shows that this type of nanofibrous matrices with a high fragrance loading capacity is of great potential for applications in various fields, such as cosmetics or food packaging. 相似文献
164.
165.
A practical protocol was disclosed for the nickel-catalyzed C-alkylation of 9-fluorenone hydrazone with alcohols using t-BuOK as the base, and 9-monoalkylated fluorene derivatives were obtained in good yields under the benign conditions. 相似文献
166.
A simple methodology for the reduction of acid chlorides to their corresponding alcohols has been developed. Various carboxylic acids were converted to alcohols in excellent yields using NaBH4-K2CO3 in a mixed solvent system of dichloromethane and water (1:1) in the presence of a phase-transfer catalyst at low temperature. The importance of the work is its simplicity, selectivity, excellent yield, and very short reaction time. This new reduction condition has proved to be an excellent chemoselective method for a range of acid chlorides in the presence of various functional groups. 相似文献
167.
168.
General methods for the preparation of a variety of pyridone and oxypyridine derivatives are described. 2‐,3‐,4‐Hydroxy pyridine and 2‐pyridinemethanol were alkylated with ethylene‐, propylene‐, and stryrene‐oxide and epichlorohydrin in the presence of different Lewis acids as a catalyst. The best yield of 3a was achieved in the presence of CdI2/BF3 · OEt2. The corresponding pyridone derivatives (3a–d, 7a–d) were obtained from the reaction of 2‐and 4‐hydroxypyridine with oxiranes in good yields, whereas oxypyridine derivatives (5a–d, 9a,b) were obtained from reactions of 3‐hydroxypyridine and 2‐pyridinemethanol with oxiranes. Chlorohydrines (3d, 5d, 7d) were easily converted to corresponding epoxy derivatives (10, 11, 12) in basic medium; then amino alcohols (13–17) were obtained from the reaction of these epoxy derivatives with amines. 相似文献
169.
A series of β-amino alcohols derivatives were synthesized from (R)-2-amino-1-butanol and (S)-1,2-propanediol, and they have been used as organocatalaysts in the racemic ring opening of epoxide in good yields with high enantiomeric excess (up to 97%). 相似文献
170.
Herein we report that LiAlH4/AlCl3 is a very efficient reagent for the reductive dehydration of aryl propargylic alcohols in tetrahydrofuran solvent at reflux to give 1,3-dienes with good yields and high E selection. The reaction conditions are mild and easy to operate, and a variety of aryl functional groups, such as bromo, fluoro, butyl, and methoxyl groups, are tolerated. With our protocol, useful (E,E)-1,3-dienes can be synthesized. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献