全文获取类型
收费全文 | 6326篇 |
免费 | 586篇 |
国内免费 | 750篇 |
专业分类
化学 | 5168篇 |
晶体学 | 84篇 |
力学 | 30篇 |
综合类 | 35篇 |
数学 | 8篇 |
物理学 | 2337篇 |
出版年
2024年 | 10篇 |
2023年 | 45篇 |
2022年 | 154篇 |
2021年 | 135篇 |
2020年 | 133篇 |
2019年 | 146篇 |
2018年 | 187篇 |
2017年 | 219篇 |
2016年 | 239篇 |
2015年 | 199篇 |
2014年 | 289篇 |
2013年 | 960篇 |
2012年 | 372篇 |
2011年 | 380篇 |
2010年 | 299篇 |
2009年 | 375篇 |
2008年 | 382篇 |
2007年 | 485篇 |
2006年 | 370篇 |
2005年 | 363篇 |
2004年 | 285篇 |
2003年 | 280篇 |
2002年 | 244篇 |
2001年 | 152篇 |
2000年 | 159篇 |
1999年 | 133篇 |
1998年 | 136篇 |
1997年 | 77篇 |
1996年 | 50篇 |
1995年 | 59篇 |
1994年 | 49篇 |
1993年 | 64篇 |
1992年 | 39篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 22篇 |
1988年 | 25篇 |
1987年 | 11篇 |
1986年 | 13篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 6篇 |
排序方式: 共有7662条查询结果,搜索用时 15 毫秒
81.
微波辐射下三组分“一锅法”合成5-芳基-1,5,6,7,8,9-六氢化-2H-吡唑[5,4-b]并喹啉-6-酮 总被引:1,自引:0,他引:1
在微波辐射下以芳醛、1,3-环己二酮或达米酮和氨基吡唑为原料, 用乙二醇作能量转移剂, 三组分“一锅法”快速合成了一系列吡唑[5,4-b]并喹啉类化合物. 该方法速度快(30~90 s), 产率高(88%~98%), 环境友好. 产物结构通过红外光谱、核磁共振谱和元素分析证实, 化合物4e的单晶经X射线衍射分析, 进一步确证了产物结构. 相似文献
82.
利用微波辐射和固体碱性载体试剂催化绕丹宁及N-苯基绕丹宁和芳香醛的缩合反应合成了14个绕丹宁衍生物并研究了影响反应的因素。 相似文献
83.
Xiaoping Zhan 《European Polymer Journal》2007,43(4):1588-1594
Oral clonidine, used as an antihypertensive, can result in some side effects such as dry mouth, drowsiness, dizziness and sedation; thus, clonidine transdermal drug delivery (TDD) was considered. Use of the controlled release membrane was one of the methods in TDD systems to regulate the permeation properties. A new type of copolymer membrane that controlled clonidine linear release in TDD system was synthesized by UV radiation. This membrane consisted of three monomers: 2-hydroxy-3-phenoxypropylacrylate, 4-hydroxybutyl acrylate and diethyl maleate. The membrane had both fine permeation properties and perfect physical properties when three monomers were in the weight ratio of 4:4:2; this type of membrane was chosen as an optimized membrane. It was found that the membrane controlled clonidine zero-order release, the permeation rates decreased with the thicknesses of membranes increasing, and the permeation rates were linearly dependent on the square root of the concentration of clonidine. Furthermore, the optimized membranes were characterized by FTIR, DSC and SEM. 相似文献
84.
微波辐照增强原煤磁分离脱硫机理探讨 总被引:5,自引:0,他引:5
采用~(57)Fe穆斯堡尔谱学方法,研究微波-磁分离法脱硫机理及微波辐照深度对脱硫率的影响。结果表明,微波选择性介质加热,可以激励煤中顺磁性黄铁矿FeS_2热解,使其转化为非化学计量的磁黄铁矿Fe_(1-x)S(0相似文献
85.
This paper describes the screening for metabolites of butoprozine, a new anti-anginal drug, in dog bile by means of reverse-phase HPLC. Although it does involve a simple clean-up step to remove a substantial amount of endogenous bile compounds, this screening method nevertheless avoids extraction of metabolites and thus allows all metabolites to be introduced into the chromatographic system. A single run of 100 minutes from 100% water to 100% methanol in a linear gradient effects adequate separation of the great majority of metabolites without interference from remaining endogenous compounds. Two methods of differentiating between metabolite peaks and endogenous peaks have been worked out. The first one makes use of 14C-labeled butoprozine by measuring the amount of radioactivity in the column effluent while simultaneously recording the UV absorbance. The second method compares continuous gradient chromatograms of bile recorded before and after butoprozine administration under very similar conditions. The latter method can be applied to both radioactive and non-radioactive materials. 相似文献
86.
Guihua Huang Yipeng Huang Wei Xu Qiuhong Yao Xiaofang Liu Caifeng Ding Xi Chen 《中国化学快报》2019,30(5):1021-1023
Using cesium lead halide perovskite nanocrystals, CsPb(Cl/Br)_3, as a light absorber, we report a highly effective UV and blue light blocking film. The CsPb(Cl/Br)_3 nanocrystals are well dispersed in the ethyl cellulose(EC) matrix to compose a UV and blue light shielding film, and the absorption edge of the film is tunable by adjusting Cl to Br ratio using anion exchange. The CsPbCl_2 Br-EC film exhibits a transmittance of 5% at 459 nm, 90% at 478 nm and 95% in the range of 500–800 nm, which makes it excellent for UV and blue light shielding. In addition, the as-prepared EC-CsPb(Cl/Br)_3 film shows excellent photostability under UV irradiation. Results demonstrate that this EC-CsPb(Cl/Br)_3 based materials with sharp absorbance edges, tunable blocking wavelength, and high photostability can be useful for the applications in UV and blue light blocking and optical filters 相似文献
87.
Xiong Wen Ye Yu Ping Zhang Ling Bo Qu Li Qun Fan Bo Li 《中国化学快报》2007,18(11):1399-1402
Microwave irradiation was firstly attempted for the preparation of organic-based monoliths of poly(styrene-divinylbenzene- methacrylic acid), which single step in situ polymerization was carried out during 15 min. The colunm permeability, electrophoretic and chromatographac behaviors were comparatively evaluated using pressure-assisted CEC, GEC and low pressure-driven separation modes. The largest theoretical plates for the preparing column could be close to 18,0000 plates/m for thiourea in the mode of p-CEC. It provided a viable alternative to traditional initiation means for the perparation of monolithic capillary columns. 相似文献
88.
89.
Frank?WendlerEmail author Gerhard?Grane? Thomas?Heinze 《Cellulose (London, England)》2005,12(4):411-422
The thermal stability of cellulose/N-methylmorpholine-N-oxide (NMMO) solutions were investigated using UV/VIS spectrometry with a temperature programming cuvette and caloric measurements
by means of the Systag calorimeter RADEX (mini-autoclave). Both analytical methods allow to characterize the influences of
stabilizers and additives. With the temporal course of the optical density, temperature and pressure thermal runaway reactions
with gas evolution and accumulation of chromophoric degradation products were recognized. Kinetic model calculations compared
with UV/VIS measurements demonstrate the existence of autocatalytic reactions in cellulose/NMMO solutions. Varying the heating
rate autocatalysis can be proved by dynamic caloric measurements as well. 相似文献
90.
Vivek Polshettiwar 《Tetrahedron letters》2007,48(41):7343-7346
An environmentally benign aqueous Biginelli protocol for the synthesis of substituted 3,4-dihydropyrimidin-2(1H)-ones using polystyrenesulfonic acid (PSSA) as a catalyst has been achieved. These microwave-assisted reactions proceed efficiently in water in the absence of organic solvent, with simple filtration as the product isolation step. 相似文献