全文获取类型
收费全文 | 15253篇 |
免费 | 1519篇 |
国内免费 | 766篇 |
专业分类
化学 | 10923篇 |
晶体学 | 202篇 |
力学 | 567篇 |
综合类 | 49篇 |
数学 | 1293篇 |
物理学 | 4504篇 |
出版年
2024年 | 25篇 |
2023年 | 199篇 |
2022年 | 319篇 |
2021年 | 454篇 |
2020年 | 466篇 |
2019年 | 434篇 |
2018年 | 346篇 |
2017年 | 325篇 |
2016年 | 582篇 |
2015年 | 532篇 |
2014年 | 680篇 |
2013年 | 1046篇 |
2012年 | 1295篇 |
2011年 | 1351篇 |
2010年 | 836篇 |
2009年 | 779篇 |
2008年 | 1053篇 |
2007年 | 965篇 |
2006年 | 883篇 |
2005年 | 778篇 |
2004年 | 594篇 |
2003年 | 453篇 |
2002年 | 477篇 |
2001年 | 358篇 |
2000年 | 292篇 |
1999年 | 254篇 |
1998年 | 202篇 |
1997年 | 142篇 |
1996年 | 154篇 |
1995年 | 192篇 |
1994年 | 153篇 |
1993年 | 128篇 |
1992年 | 111篇 |
1991年 | 86篇 |
1990年 | 98篇 |
1989年 | 64篇 |
1988年 | 59篇 |
1987年 | 50篇 |
1986年 | 37篇 |
1985年 | 53篇 |
1984年 | 33篇 |
1983年 | 20篇 |
1982年 | 34篇 |
1981年 | 27篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1975年 | 10篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Abstract The enhanced osteoblast differentiation is beneficial to the prevention of osteoporosis. In this study, a homogeneous polysaccharide (LRP-S2A) with the potential of promoting osteoblast differentiation was obtained from the fruits of Lycium ruthenicum, a traditional herb for treatment of postmenopausal metabolic disorders. Structural identification indicated that LRP-S2A, with a relative molecular weight of 2.65 × 106 Da and an uronic acid content of 41.8%, contained Rha, Ara, Gal, Glc and GlcA in a molar ratio of 1.00 : 2.07 : 0.57 : 2.59 : 4.33 and was composed of a backbone consisting of 6-O-Me-α-(1→4)-D-GlcpA, 2-O-acetyl-α-(1→4)-D-Glcp, α-(1→2,4)-L-Rhap, β-(1→3)-D-Galp andα-(1→3,5)-L-Araf, and some branches consisting of 6-O-Me-α-(1→4)-D-GlcpA and terminal α-L-Araf. These results suggested that LRP-S2A with the potential of promoting osteoblast differentiation was a new acidic polysaccharide. 相似文献
932.
Wei Li Zhuang‐Fei Jiang Ling Tan Shu‐Xian Wang Chong‐Zhi Wang Jia‐Wei Zhang Lian‐Di Zhou Qi‐Hui Zhang Chun‐Su Yuan 《Journal of separation science》2020,43(6):1173-1182
Curcumin widely exists in food, and rapid selective and accurate detection of curcumin have great significance in chemical industry. In this experiment, a new magnetic biocompatibility molecularly imprinted polymer was prepared with nontoxic and biocompatible Zein to adsorb curcumin selectively. The polymer has high biocompatibility, good adsorption capacity, and specific adsorption for curcumin. Combined with portable electrochemical workstations, the polymer can be used to detect curcumin rapidly and cost‐effectively. Using curcumin as a template and Zein as the crosslinking agent, the polymers were synthesized on the surface of Fe3O4 particles for solid phase extraction. The experimental results showed that the polymer reached large adsorption capacity (32.12 mg/g) with fast kinetics (20 min). The adsorption characteristic of the polymer followed the Langmuir isotherm and pseudo‐second‐order kinetic models. Hexacyanoferrate was used as electrochemical probe to generate signals, and the linear range was 5–200 µg/mL for measuring curcumin. The experimental analysis showed that the polymer was an ideal material for selective accumulation of curcumin from complex samples. This approach has been successfully applied to the determination of curcumin in food samples with electrochemical detection, indicating that this is a feasible and practical technique. 相似文献
933.
Yueting Li Jie Liu Rubin Su Qian Li Yijun Chen Jiao Yang Shujun Zhao Zhixin Jia Hongbin Xiao 《Journal of separation science》2020,43(6):1032-1042
Detection and determination of many known/unknown compounds in traditional Chinese medicines have always been challenging. To comprehensively identify compounds in Qishen granule, which is a widely prescribed herbal formula for treating chronic heart failure, a pseudotargeted screening method was proposed based on compound biosynthetic correlation using ultra high‐performance liquid chromatography coupled with high‐resolution mass spectrometry. Firstly, all possible compounds of Qishen granule were classified into nine types according to their core skeletons, and potential analogue molecular formulas were predicted according to core compound‐related biosynthetic correlations, such as methylation, hydroxylation, and glucosidation. Secondly, nine pseudocompound databases consisting of core compounds, deduced biosynthetic correlations, and predicted analogue molecular formulas were established. Then, compounds of interest were directly located by pseudotargeted screening of high resolution mass spectrometry data and further verified by target tandem mass spectrometry. As a result, 213 constituents were identified and 21 of them were determined as potential new compounds. This demonstrated that pseudotargeted screening based on compound biosynthetic correlations significantly facilitated the processing of extremely large information data and improved the efficiency of compound identification. This research provided essential data for exploration of effective substances in Qishen granule and enriched the methodology for comprehensive characterization of constituents in complex traditional Chinese medicines. 相似文献
934.
Nam Sook Kim Sun Hee Moon Hwan Seong Choi Ji Hyun Lee Seongsoo Park Hoil Kang 《Journal of separation science》2020,43(14):2750-2765
An analytical method for the simultaneous and reliable determination of 20 antigout and antiosteoporosis pharmaceutical compounds in adulterated health food products was developed using liquid chromatography with electrospray ionization tandem mass spectrometry and liquid chromatography with quadrupole‐time‐of‐flight mass spectrometry. The method was validated through the determination of specificity, linearity, limit of detection, and limit of quantification, method detection limit, method quantitation limit, precision, accuracy, recovery, and stability. The matrix effect was also determined. The validation results of the developed method are as follows: for solid and liquid blank samples, limits of detection ranged from 0.05 to 5.00 ng/mL and limits of quantification ranged from 0.15 to 15.00 ng/mL. Linearity was acceptable, and the correlation coefficients (R2) were ≥0.99 for all target compounds. Both intra and interday precision were less than 9.16% RSD, and accuracies ranged from 95.31 to 116.68%. Mean recoveries for different types of dietary supplements classified as powders, liquids, tablets, and capsules were found to be 80.81 to 117.62% with less than 15.00% relative standard deviation. The stability of the standard mixture solution was less than 11.72% relative standard deviation after 48 h. By the proposed method, the presence of dexamethasone was determined in seized herbal food products at concentrations that ranged from 126 to 215 µg/g. 相似文献
935.
Lu‐Ning Sun Ye Zhang Yu‐Qing Yang Ye Shen Yu‐Wen Ying Yu‐Wen Su Xue‐Hui Zhang Yun Liu Xu Huang Yong‐Qing Wang 《Journal of separation science》2020,43(16):3183-3196
Proton pump inhibitors, including omeprazole, rabeprazole, lansoprazole, and pantoprazole, achieved simultaneous enantioselective determination in the human plasma by chiral liquid chromatography–tandem mass spectrometry. The four corresponding stable isotope‐labeled proton pump inhibitors were adopted as the internal standards. Each enantiomer and the internal standards were extracted with acetonitrile containing 0.1% ammonia, then separated with a Chiralpak IC column (5 µm, 4.6 mm × 150 mm) within 10 min. The mobile phase was composed of acetonitrile–ammonium acetate (10 mM) containing 0.2% acetic acid (50:50, v/v). To quantify all enantiomers, an API 4000 tandem mass spectrometer was used, and multiple reaction monitoring transitions were performed on m/z 360.1→242.1, 384.1→200.1, 370.1→252.1, and 346.1→198.1, respectively. No significant matrix effect was observed for all analytes. The calibration curve for all enantiomers were linear from 1.25 to 2500 ng/mL. The precisions for intra‐ and inter‐run were < 14.2%, and the accuracy fell in the interval of –5.3 to 8.1%. Stability of samples was confirmed under the storage and processing conditions. The developed method was also suitable for separation and determination of ilaprazole enantiomers. The validated method combining the equilibrium dialysis method was applied to the protein binding ratio studies of four pairs proton pump inhibitor enantiomers in human plasma. 相似文献
936.
Shao-Dong Li Feng Su Miao-Li Zhu Li-Ping Lu 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(9):863-868
A new coordination polymer (CP), namely, poly[[diaquatris[μ2‐1,4‐bis(1H‐imidazol‐1‐yl)benzene]bis[μ6‐4‐(2,4‐dicarboxylatophenoxy)phthalato]tetracobalt(II)] hexahydrate], {[Co4(C16H6O9)2(C12H10N4)3(H2O)2]·6H2O}n, has been synthesized by solvothermal reaction. The CP was fully characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, and powder and single‐crystal X‐ray diffraction. It presents a three‐dimensional (3D) structure based on tetranuclear CoII secondary building units (SBUs) with a tfz‐d net and point symbol (43)2(46·618·84). The 4‐(2,4‐dicarboxyphenoxy)phthalic acid (H4dcppa) ligands are completely deprotonated and link {Co4(COO)4}4? SBUs into two‐dimensional (2D) layers. Furthermore, adjacent layers are connected by 1,4‐bis(1H‐imidazol‐1‐yl)benzene (bib) ligands, giving rise to a 3D supramolecular architecture. Interestingly, there are numerous elliptical cavities in the CP where isolated unique discrete hexameric water clusters have been observed. The results of thermogravimetric and magnetic analyses are described in detail. 相似文献
937.
Nonlinear Dynamics - Combining the complex factors of mechanical impact, Coulomb friction, harmonic excitation, and Gaussian white noise, an electromagnetic energy harvesting system is analytically... 相似文献
938.
Chun-Wei Chen Long Zhang Shi-Jian Su Mei-Yu Huang Su-Fen Mao Ying-Yan Jiang 《先进技术聚合物》1996,7(8):711-714
Silica-supported polysilazane (SiO2-Si-N), and its platinum complex (SiO2-Si-N-Pt) were prepared. It was found that SiO2-Si-N–Pt can catalyze hydrogenation of o-xylene under mild conditions (40–50°C, 1 atm). The products of the reaction were cis-and trans-1,2-dimethylcyclohexane. The formation of trans-1,2-dimethylcyclohexane may be adequately explained according to the ‘roll-over’ model. The stereoselectivity was influenced by temperature and catalyst concentration, the proportion of the cis isomer decreasing with an increase in each of the two factors. The effects of other reaction parameters, such as the N/Pt mole ratio in the complex, solvents and reaction time, etc. on the hydrogenation of o-xylene were also studied. The SiO2-Si-N–Pt catalyst is very stable in reaction and turnover numbers amount to 200 in 80 hr. 相似文献
939.
940.
通过引入电子性作用V_c,在弱耦合条件下导出了两带模型的T_c公式和同位素效应指数公式,计算了超导体MgB_2的超导转变温度和同位素效应,得到了与实验相符的结果。结果表明,带内电子性作用比带间电子性作用对同位素效应指数的影响要大。 相似文献