全文获取类型
收费全文 | 6951篇 |
免费 | 630篇 |
国内免费 | 926篇 |
专业分类
化学 | 6306篇 |
晶体学 | 22篇 |
力学 | 390篇 |
综合类 | 51篇 |
数学 | 382篇 |
物理学 | 1356篇 |
出版年
2024年 | 19篇 |
2023年 | 79篇 |
2022年 | 166篇 |
2021年 | 208篇 |
2020年 | 309篇 |
2019年 | 208篇 |
2018年 | 203篇 |
2017年 | 251篇 |
2016年 | 306篇 |
2015年 | 242篇 |
2014年 | 306篇 |
2013年 | 532篇 |
2012年 | 323篇 |
2011年 | 355篇 |
2010年 | 321篇 |
2009年 | 416篇 |
2008年 | 366篇 |
2007年 | 374篇 |
2006年 | 388篇 |
2005年 | 365篇 |
2004年 | 358篇 |
2003年 | 295篇 |
2002年 | 223篇 |
2001年 | 195篇 |
2000年 | 204篇 |
1999年 | 172篇 |
1998年 | 177篇 |
1997年 | 149篇 |
1996年 | 135篇 |
1995年 | 130篇 |
1994年 | 106篇 |
1993年 | 95篇 |
1992年 | 83篇 |
1991年 | 87篇 |
1990年 | 67篇 |
1989年 | 49篇 |
1988年 | 51篇 |
1987年 | 31篇 |
1986年 | 26篇 |
1985年 | 19篇 |
1984年 | 19篇 |
1983年 | 6篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 20篇 |
1978年 | 9篇 |
1971年 | 1篇 |
1966年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有8507条查询结果,搜索用时 843 毫秒
101.
Jerald S. Bradshaw Reed M. Izatt James J. Christensen Krzystof E. Krakowiak Bryon J. Tarbet Ronald L. Bruening S. Lifson 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(2):127-136
Silica gel-bound crown ethers and aza macrocycles have been synthesized with the attaching arm connected to the carbon framework of the macrocycles. The interactions of these bound macrocycles with cations are almost identical to those involving the analogous free macrocycles. This has allowed for predictable cation separation, concentration, and removal processes to be performed on a small scale. Quantum mechanical calculations and NMR measurements indicate that similarly bound chiral macrocycles will be capable of use in separating chiral organic amines.Dedicated to the memory of Professor James J. Christensen who died on 5 September 1987. 相似文献
102.
Q. Zhong L. He T. E. Beesley W. S. Trahanovsky P. Sun C. Wang D. W. Armstrong 《Chromatographia》2006,64(3-4):147-155
The comparisons of five different chiral stationary phases (CSPs) based on 2,6-dinitro-4-trifluoromethylphenyl (DNP-TFM) ether substituted β-cyclodextrin are presented. The five CSPs differ from each other in the linkage/spacer chemistry, or on the position of the substituents on β-cyclodextrin, or in the sequence of the synthetic procedure. The results show that there are two optimum combinations: (1) DNP-TFM randomly substituted on the β-cyclodextrin as the chiral selector along with a carbamate linkage chain bonding it to the silica support; and (2) β-cyclodextrin derivatized by DNP-TFM substituents only on the C-2 and C-3 positions of the cyclodextrin with an ether linkage chain anchoring it to the silica gel. These two combinations show complementary separations for some enantiomers. The spacer chain effect is much more pronounced for the CSP based on the β-cyclodextrin derivatives with DNP-TFM substituents only on C-2 and C-3 positions than its randomly substituted counterpart. The sequence of derivatizing the cyclodextrin and attaching it to silica gel also affects its selectivity and efficiency. The β-cyclodextrin should be derivatized before it is linked to the silica gel. 相似文献
103.
Gonzalo Cerruela García Irene Luque Ruiz Miguel Ángel Gómez-Nieto 《Journal of mathematical chemistry》2006,40(3):213-231
In this paper, we propose a new method for clustering of chemical databases based on the representation of measurements of structural similarity onto multidimensional spaces. The proposed method permits the tuning of the clustering process through the selection of the dimension of the projection space, the normal vectors and the sensibility of the projection process. The structural similarity of each element regarding to the database elements is projected onto the defined spaces generating clusters that represent the characteristics and diversity of the database and whose size and characteristics can be easily adjusted. 相似文献
104.
Lämmerhofer M 《Journal of chromatography. A》2005,1068(1):31-57
A review on the advantages, peculiarities, and the potential of enantioselective capillary electrochromatography (CEC) in nonaqueous media is presented. Some fundamentals on CEC with particular focus on enantioselective CEC are discussed. The strategies, concepts, preferentially utilized chiral selectors and column technologies that have been utilized to succeed in highly efficient enantiomer separations by nonaqueous CEC are described thoroughly. 相似文献
105.
106.
Summary A simple and rapid systematic optimization scheme was described for the micellar electrokinetic chromatographic separation of a group of flavonoids. The scheme employed an interpretative optimization approach to predict the optimum conditions for the separation of a group of flavonoids by micellar electrokinetic chromatography. By performing a set of nine pre-planned experiments conducted over the maximum working range for the system, global optimum separation conditions could be determined. To validate the optimization procedure, additional experiments were performed using the optimum experimental conditions derived from the optimization scheme. The results showed that satisfactory separation of all the peaks could be obtained. In addition, the application of the method in micropreparative micellar electrokinetic chromatography of the flavonoids was demonstrated. 相似文献
107.
In this study porous glass fiber membranes were modified by reaction with octadecyl-trichlorosilane to form C18 hydrophobic membranes. The contact angle and the CH2 vibration bands at 2855 and 2920 cm(-1) found by FTIR measurements verified the successful immobilization of C18 groups on the glass fiber membranes. The resulting C18 hydrophobic membranes were used to adsorb terpene lactones from crude Ginkgo biloba L. extracts. In batch adsorption processes, the modified C18 membranes exhibited a better adsorption performance than commercial C18 solid phase extraction adsorbents. Different desorption solvents were tested and ethyl acetate was found to preferentially desorb terpene lactones from the modified C18 membranes. In flow adsorption experiments at 1 mL/min, terpene lactone contents higher than 6 wt% (the standardized content) could be achieved in the elution step using ethyl acetate. 相似文献
108.
109.
聚对苯二甲酸乙二酯(PET)结晶速度很慢,通常加入成核剂来提高结晶速度。从专利文献来看,以离子聚合物为成核剂的例子也是很多的。离子聚合物与小分子成核剂的显著差别是:离子聚合物有一个很长的碳氢主链,其侧基为酸基,酸基被部分或全部地中和成盐。很明显,离子聚合物不象小分子成核剂那样能很好地分散在PET基体中,而是以独立的相存在。作为PET体系系列研究的继续,本文报道了离子聚合物Surlyn在PET中的相分离行为。 相似文献
110.