全文获取类型
收费全文 | 3691篇 |
免费 | 475篇 |
国内免费 | 374篇 |
专业分类
化学 | 2714篇 |
晶体学 | 33篇 |
力学 | 217篇 |
综合类 | 41篇 |
数学 | 349篇 |
物理学 | 1186篇 |
出版年
2024年 | 17篇 |
2023年 | 67篇 |
2022年 | 117篇 |
2021年 | 132篇 |
2020年 | 145篇 |
2019年 | 130篇 |
2018年 | 100篇 |
2017年 | 109篇 |
2016年 | 157篇 |
2015年 | 146篇 |
2014年 | 208篇 |
2013年 | 250篇 |
2012年 | 274篇 |
2011年 | 320篇 |
2010年 | 212篇 |
2009年 | 189篇 |
2008年 | 198篇 |
2007年 | 198篇 |
2006年 | 184篇 |
2005年 | 160篇 |
2004年 | 147篇 |
2003年 | 119篇 |
2002年 | 111篇 |
2001年 | 105篇 |
2000年 | 86篇 |
1999年 | 81篇 |
1998年 | 89篇 |
1997年 | 59篇 |
1996年 | 62篇 |
1995年 | 47篇 |
1994年 | 52篇 |
1993年 | 41篇 |
1992年 | 41篇 |
1991年 | 25篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 20篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1974年 | 4篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有4540条查询结果,搜索用时 15 毫秒
981.
982.
Daniel Guan 《Inventiones Mathematicae》1995,121(1):135-145
Oblatum 28-VII_1993 & 15-II-1995 相似文献
983.
湛江市鲜瘦猪肉营养价值的比较研究 总被引:1,自引:1,他引:0
首次报道湛江市鲜瘦猪肉的水分含量、干重及无机金属元素含量。与全国代表值比较实验测得水分含量高4.71%,干重均值低4.71%,两者经统计学处理均呈现极显著性差异,人体重要的无机金属营养元素Zn、Cu、Fe、Ca、Mg、Na、K均呈现极显著性的降低,上述结果提示,湛江市现市售鲜瘦猪肉的营养价值已显著下降。 相似文献
984.
985.
986.
A novel visible light-driven oxidative cascade reaction for the synthesis of β-thiocyanato alcohols via difunctionalization of alkenes is described for the first time. In this protocol inorganic ion thiocyanate was successfully converted into radical through photocatalysis by employing Rose Bengal as a photocatalyst to mediate the single-electron transfer. This hydroxylation process did not need extra reducing agent and the new CS and CO bonds could be constructed in one pot. Molecular oxygen not only was used as an excellent terminal oxidant, but also served as a green oxygen source, which is one of the most ideal processes to realize CH bond oxidation functionalization. Moreover, the reaction also proceeded very well under irradiation of sunlight. 相似文献
987.
Guangmiao Qu Qi Guan Haiyan Sun Musen Lin Yuan Cai Yong Pan 《Journal of Dispersion Science and Technology》2018,39(8):1172-1177
In this paper, molecular dynamics simulation methods were used to investigate salt effects on micellization of N-Dodecyl-N,N-Dimethyl-3-Ammonio-1-Propane-sulfonate (SB12-3) in aqueous solution. It is proved that micelle shapes transform from spherical to prolate spherical shape after 30.0?ns simulation with different NaCl and CaCl2 concentration. By comparison with the eccentricity value without salt addition, SB12-3 shows salt tolerance behaviors due to its unique “inner salt” structure of amphiphilic surfactant. Radial distribution function (RDF), hydrophobic groups solvent accessible surface area (SASA), hydrogen bond, and the deuterium order parameter (SCD) are to elucidate salt effects on SB12-3 micelle formation. The radius of micelle is achieved by the related RDF value and in accordance with other researches. The addition of NaCl and CaCl2 didn’t change the structure of micelle significantly and have little effects on the interactions between SB12-3 and water molecule. By comparison with the results without salt system, SASA of hydrophobic groups is almost the same, and SASA of hydrophilic groups and total molecule fluctuates only slightly. This further indicates that the surface of micelles is more hydrophilic due to the strong interactions between SB12-3 and water molecules. The existence of NaCl and CaCl2 will enhance the hydrophilic interactions. 相似文献
988.
Beilei Zhang Xiao Du Xiaogang Hao Fengfeng Gao Di Zhang Changlin Liu Guoqing Guan 《Journal of Solid State Electrochemistry》2018,22(8):2473-2483
In this study, a novel potential-triggered electroactive composite film consisting of mesoporous silica SBA-15, polyaniline (PANI), and polystyrenesulfonate (PSS) was fabricated in an aqueous electrolyte solution via a facile pulse potentiostatic method. The obtained composite film was characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric (TG) analysis, and scanning electron microscopy (SEM). The ion exchange properties were evaluated in a solution containing 0.1 M Pb(NO3)2 by using an electrochemical quartz crystal microbalance (EQCM) as well as cyclic voltammetry (CV) method. It was found that the uptake/release of Pb2+ ions in/from SBA-15/PANI/PSS composite film was successfully achieved by modulating the redox states of the electroactive composite film, and the composite film exhibited different ion exchange behaviors at different scan rates. Based on these results, the ion exchange mechanism was proposed. Compared with the PANI/PSS composite film, the SBA-15/PANI/PSS composite film had higher adsorption capacity as well as higher selectivity toward Pb2+ ions, which should be attributed to the 3D porous morphology of the composite film with more active sites in the mesoporous SBA-15. Remarkably, the film maintained a high stability over 97% even after 500 successive cycles. It is expected that this SBA-15/PANI/PSS composite film can serve as a promising electroactive material for the effective separation of Pb2+ ions from wastewater. 相似文献
989.
Oscillation for systems of nonlinear neutral type parabolic partial functional differential equations 总被引:14,自引:0,他引:14
YANGJUN GUANXINPING 《高校应用数学学报(英文版)》1997,12(2):165-178
This paper discusses the oscillation of solutions for systems of nonlinear neutral type parabolic partial fuctional differential equations of the form 相似文献
990.
Luo Y Uboh CE Soma LR Guan FY Rudy JA Tsang DS 《Rapid communications in mass spectrometry : RCM》2005,19(10):1245-1256
A method for the simultaneous separation, identification, quantification and confirmation of the presence of 21 glucocorticoids (GCC) in equine plasma by liquid chromatography coupled with triple stage quadrupole tandem mass spectrometry (LC/TSQ-MS/MS) is described. Plasma sample augmented with the 21 GCC was extracted with methyl tert-butyl ether (MTBE) and analyzed by positive electrospray ionization. Desoxymetasone or dichlorisone acetate was used as the internal standard (IS). Quantification was performed by IS calibration. For each drug, one major product ion was chosen and used for screening for that drug. Analyte confirmation was performed by using the three most intense product ions formed from the precursor ion and the corresponding mass ratios. The recovery of the 21 GCC when spiked into blank plasma at 5 ng/mL was 45-200% with coefficient of variation (CV) from 0.3-18%. The limit of detection (LOD) and that of quantification (LOQ) for most of the analytes were 50-100 pg/mL and 1 ng/mL, respectively, whereas that of confirmation (LOC) was 100-300 pg/mL depending on the analyte. Intra- and inter-day precisions expressed as CV for quantification of 1 and 10 ng/mL was 1.0-17%, and 0.51-19%, respectively, and the accuracy was from 84-110%. The linear concentration range for quantification was 0.1-100 ng/mL (r(2) > 0.997). Estimated measurement uncertainty was from 11-37%. This study was undertaken to develop a method for simultaneous screening, identification, quantification and confirmation of these agents in post-race equine plasma samples. The method has been successfully applied to screening of a large number of plasma samples obtained from racehorses in competition and in pharmacokinetic studies of dexamethasone in the horse and concurrent changes in endogenous GCC, hydrocortisone and cortisone. The method is simple, sensitive, selective and reliably reproducible. 相似文献