全文获取类型
收费全文 | 31349篇 |
免费 | 4610篇 |
国内免费 | 6012篇 |
专业分类
化学 | 25526篇 |
晶体学 | 572篇 |
力学 | 1378篇 |
综合类 | 515篇 |
数学 | 3498篇 |
物理学 | 10482篇 |
出版年
2024年 | 22篇 |
2023年 | 370篇 |
2022年 | 604篇 |
2021年 | 884篇 |
2020年 | 987篇 |
2019年 | 1076篇 |
2018年 | 902篇 |
2017年 | 915篇 |
2016年 | 1317篇 |
2015年 | 1466篇 |
2014年 | 1787篇 |
2013年 | 2479篇 |
2012年 | 2712篇 |
2011年 | 2882篇 |
2010年 | 2247篇 |
2009年 | 2112篇 |
2008年 | 2551篇 |
2007年 | 2302篇 |
2006年 | 2112篇 |
2005年 | 1757篇 |
2004年 | 1543篇 |
2003年 | 1313篇 |
2002年 | 1409篇 |
2001年 | 1176篇 |
2000年 | 949篇 |
1999年 | 727篇 |
1998年 | 483篇 |
1997年 | 421篇 |
1996年 | 363篇 |
1995年 | 338篇 |
1994年 | 293篇 |
1993年 | 259篇 |
1992年 | 225篇 |
1991年 | 173篇 |
1990年 | 169篇 |
1989年 | 115篇 |
1988年 | 94篇 |
1987年 | 79篇 |
1986年 | 71篇 |
1985年 | 63篇 |
1984年 | 46篇 |
1983年 | 34篇 |
1982年 | 20篇 |
1981年 | 24篇 |
1980年 | 14篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Removal of Endotoxin from Human Serum Albumin Solutions by Hydrophobic and Cationic Charged Membrane 总被引:1,自引:0,他引:1
Removal of end6toxin from medicine injection is very important, becauseendotoxin withpotential biological activity causes pyrogenic and shock reactions in' mammals-'on...intravenous injection even as law as "an6gram amounts. Endotoxin, a constituent ofpotential contaminant of physiological fluids and aqueous solutions 'and very stable atextreme temperature and PH values. For removing endotoxin from solutions ofbiomolecules, such as HSA, adsorption techniques are usedl.' Many methods forendot… 相似文献
992.
993.
Spontaneous vesicle formation was observed in aqueous mixtures of partially hydrolyzed polyacrylamide and single-tailed cationic surfactants. The influences of pH, addition of long-chain alcohols, variation of hydrocarbon chain length, and head group size of the cationic surfactants were investigated systematically. It was found that 30-50% hydrolyzed degree of polyacrylamide and cationic surfactants with 10 or 12 methylene groups are suitable for vesicle formation in the mixed aqueous systems at pH 9.2. Addition of long-chain alcohols was found to be helpful for vesicle formation in some cases. The vesicle stability was also investigated at various temperatures and amounts of ethanol addition. Copyright 2001 Academic Press. 相似文献
994.
Jue Xiao CAI Zheng Hong ZHOU Kang Ying LI Chi Hung YEUNG Chu Chi TANG* State Key Laboratory of Elemento-Organic Chemistry Institute of Elemento-Organic Chemistry Nankai University Tianjin Open Laboratory of Chirotechnology D 《中国化学快报》2002,13(7)
Optically active 1,1-binaphthalene-2, 2-diol has become a quite important chiral source in different fields of chirotechnology, especially in asymmetric synthesis1. Its synthesis and resolution has been extensively studied and various resolution methods have been reported2. Among the reported resolution methods, the following three, namely, via the formation of phosphoric acid derivatives3, boric acid derivatives4 and inclusion complexes5, are the most important. OHOH+_( )-1(-)-(S)-1(+)-(R)… 相似文献
995.
TaoJIANG BuXingHAN GuoYingZHAO ZhongHaoLI YanHongCHANG HaiXiangGAO JunChunLI 《中国化学快报》2004,15(3):296-299
The oxidation of styrene with molecular oxygen catalyzed by PdCl2 CuCl2 has been investigated in supercritical CO2 with a batch reactor. The oxidative system of styrene contains four components at the beginning and seven components during the reaction. The critical temperature, critical pressure, and critical density at different conversions are determined by using a high-pressure view cell. The effect of phase behavior on the conversion and selectivity were studied. Experimental results showed that the critical parameters of the reaction mixture at fixed initial molar ratio changed with the conversion of reactant. The conversion of styrene reached maximum near the critical density of the reaction mixture. Product selectivity also varied with density of reaction mixture and could be tuned to some degree. 相似文献
996.
INTRODUCTIONInrecentyearsresearchprojectsonROMPofcycloolefinshavebeenattractingattentionofscientistsengagedinthesynthesisanddesignofnewpolyTneric'AprojectsupportedbytheNationalNaturalSCienceFoundationofChina(projectapprovalnumber:29474160).'-Correspondingauthormaterials,amongthemROMPsofnorbornene,norbornenederivativesandDCPDhavefoundgrowingfavourinthechemists,.y.,LI--4].Acrosslinkedpolarer(PDCPD),anewplastic,possessingexcellentmechanicalproperties(highNIS,TSetc)a-ndgoodthermal… 相似文献
997.
Two new type dicoumarins (dicoumaro-p-menthanes), named dibothrioclinins I (1) and II (2) were isolated from the roots and rhizomes of Gerbera piloselloides (L.) CASS., collected in Yunnan Province, China. Their structures were elucidated on the basis of MS, 1D ((1)H-NMR, (13)C-NMR, DEPT and NOE) and 2D ((1)H-(1)H COSY, HMQC, HMBC) NMR spectral analyses. The relative structures of the two compounds were established by NOE difference spectroscopy and further confirmed by single-crystal X-ray diffraction studies. 相似文献
998.
工业氨基三甲叉膦酸中副产物的核磁共振分析 总被引:1,自引:0,他引:1
采用多种核磁共振(NMR)技术测定了工业氨基三甲叉膦酸(ATMP)产品中副产物的分子结构,发现该物质为甲氨基二甲叉膦酸(MADMP),它是甲醛歧化反应导致的副产物;给出了可能的反应方程式;测出了MADMP的相对含量,MADMP与ATMP摩尔比约为2。 相似文献
999.
XinYingZHANG XueSenFAN JianJiWANG YanZhenLI 《中国化学快报》2004,15(10):1170-1172
Quinoline derivatives were efficiently prepared through acid-catalyzed Friedlander reaction in ionic liquid ([bmim] [BF4]). It is shown that the proposed method is operationally simple and environmentally benign in that the reaction media and the catalyst can be recovered and be reused effectively for at least four times. 相似文献
1000.