全文获取类型
收费全文 | 5062篇 |
免费 | 699篇 |
国内免费 | 733篇 |
专业分类
化学 | 3909篇 |
晶体学 | 54篇 |
力学 | 405篇 |
综合类 | 29篇 |
数学 | 514篇 |
物理学 | 1583篇 |
出版年
2024年 | 10篇 |
2023年 | 96篇 |
2022年 | 188篇 |
2021年 | 209篇 |
2020年 | 224篇 |
2019年 | 223篇 |
2018年 | 172篇 |
2017年 | 180篇 |
2016年 | 213篇 |
2015年 | 209篇 |
2014年 | 241篇 |
2013年 | 352篇 |
2012年 | 422篇 |
2011年 | 444篇 |
2010年 | 303篇 |
2009年 | 262篇 |
2008年 | 319篇 |
2007年 | 246篇 |
2006年 | 253篇 |
2005年 | 231篇 |
2004年 | 175篇 |
2003年 | 176篇 |
2002年 | 166篇 |
2001年 | 140篇 |
2000年 | 119篇 |
1999年 | 132篇 |
1998年 | 88篇 |
1997年 | 88篇 |
1996年 | 86篇 |
1995年 | 73篇 |
1994年 | 51篇 |
1993年 | 63篇 |
1992年 | 47篇 |
1991年 | 48篇 |
1990年 | 39篇 |
1989年 | 35篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 12篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1973年 | 7篇 |
1972年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有6494条查询结果,搜索用时 343 毫秒
61.
62.
Steric/hyperlayer field-flow fractionation (FFF) is an established analytical technique for separating and characterizing particles in the 1-100 microns diameter range. The separation can be based on differences in size, density, shape and mechanical properties of the particles. In the course of an analysis of the water transporter system of Chinese hamster ovary (CHO) cells and one of their high permeability mutants, the first successful attempt was made to use the steric/hyperlayer FFF system for the purpose of separating particles based on a time-dependent property, namely, the differential swelling of the two cell types. The present study was undertaken to simulate numerically the separation and suggest selection of operating conditions to minimize repetitive experiments. The computer simulation was developed using Maple V, a symbolic computing environment. It is shown that the model is able to predict an optimal velocity of carrier buffer that maximizes resolution. Predicted velocity/resolution pairs are in good agreement with available experimental data. Empirical models for the lift forces encountered in such FFF experiments, and for the zone broadening observed in work with cell sized particles, form the basis for this model. 相似文献
63.
64.
SYNERGISTIC MODIFICATION OF EPDM AND CROSSLINKING AGENT IN IMMISCIBLE BLENDS OF POLYVINYL CHLORIDE WITH LOW DENSITY POLYETHYLENE 总被引:1,自引:0,他引:1
Zheng-ping Fang Guo-wei Ma Yu-zheng Xu Li-fang Tong 《高分子科学》2006,(2):147-154
The synergism of ethylene-propylene-diene monomer copolymer (EPDM) and dicumyl peroxide (DCP, a crosslinking agent) in low density polyethylene (LDPE)/poly(vinyl chloride) (PVC) blends was investigated. When EDPM and DCP are added to the blends simultaneously, the tensile properties could be improved significantly, especially for the blends with LDPE matrix. For example, incorporation of 10/1 (mass ratio) EPDM/DCP improves the tensile strength of the LDPE/PVC (mass ratio 80/20) blend from 7.9 MPa to 8.5 MPa and the elongation at break from 25% to 503%. Results from selective extraction, phase-contrast microscopy and thermal analysis reveal that the improvement in the tensile properties of the blends with LDPE matrix is principally due to the formation of a fine crosslinking network of the LDPE and EPDM phase. The outstanding modification effect of EPDM is explained by its dual functions: molecular entanglement with LDPE and the enhanced efficiency of DCP in the blends. 相似文献
65.
Efficient aerobic oxidation of benzylic compounds has been achieved under no irradiation using a new organocatalytic system in the presence of acridine yellow and N-hydroxyphthalimide with assistance of a catalytic amount of molecular bromine. Various substrates, especially alkylaromatics, were effectively oxygenated to the corresponding carbonyl compounds with molecular oxygen as oxidant under mild conditions. For instance, indan was oxidized with 92% conversion and 79% selectivity for 1-indanone under 0.3 MPa of O2 at 75 °C. 相似文献
66.
Jie Chen Rong Ji Dai Bin Tong Sheng Yuan Xiao Wei Wei Meng 《中国化学快报》2007,18(1):10-12
The reduction of 4-nitrophenol catalyzed by nitroreductase in the presence of NADH was investigated in this paper.4-Amino- phenol and 4-bydroxylamino-phenol were found in the reductive products.The relationship between reaction time and the reductive ratio were studied.The similar reducing ratios of 4-nitrophenol were obtained under aerobic and anaerobic conditions.The results indicated that an oxygen-insensitive reaction was proceeded in the reduction of 4-nitrophenol and nitroreductase was an oxygen- insensitive enzyme.The reductive products of 4-nitrophenol were determined by HPLC and MS. 相似文献
67.
68.
A palldium(0)-catalyzed tandem cyclization/Suzuki coupling reaction of various 1,6-enyne substrates was developed. This Pd-catalyzed enyne cyclization reaction represents a new process for the synthesis of stereodefined alpha-arylmethylene-gamma-butyrolactones, lactams, multifunctional tetrahydrofurans, pyrrolidines, and cyclopentanes. The mechanism of the reaction was studied by the employment of different enyne isomers and boronic acids; a pi-allyl palladium intermediate was suggested to explain the formation of the cyclic products. The stereochemistry of this reaction can be well explained by a chairlike transition state. 相似文献
69.
70.
Introduction Ionchromatography (IC)hasbeenrecognizedasausefulmethodfortheseparationofinorganicanionsandcationssinceitsintroductionbySmalletal .in 1975 .1AsignificanttrendinthedevelopmentofICmethodissearchforsensitiveanduniversaldetectionmethods .Themaindet… 相似文献