全文获取类型
收费全文 | 30833篇 |
免费 | 5223篇 |
国内免费 | 4348篇 |
专业分类
化学 | 23469篇 |
晶体学 | 422篇 |
力学 | 1512篇 |
综合类 | 277篇 |
数学 | 3342篇 |
物理学 | 11382篇 |
出版年
2024年 | 30篇 |
2023年 | 582篇 |
2022年 | 715篇 |
2021年 | 1010篇 |
2020年 | 1200篇 |
2019年 | 1242篇 |
2018年 | 1121篇 |
2017年 | 1022篇 |
2016年 | 1534篇 |
2015年 | 1465篇 |
2014年 | 1843篇 |
2013年 | 2468篇 |
2012年 | 2869篇 |
2011年 | 3008篇 |
2010年 | 2138篇 |
2009年 | 1984篇 |
2008年 | 2236篇 |
2007年 | 1997篇 |
2006年 | 1814篇 |
2005年 | 1472篇 |
2004年 | 1188篇 |
2003年 | 900篇 |
2002年 | 888篇 |
2001年 | 721篇 |
2000年 | 574篇 |
1999年 | 616篇 |
1998年 | 449篇 |
1997年 | 412篇 |
1996年 | 398篇 |
1995年 | 358篇 |
1994年 | 313篇 |
1993年 | 289篇 |
1992年 | 202篇 |
1991年 | 216篇 |
1990年 | 189篇 |
1989年 | 125篇 |
1988年 | 126篇 |
1987年 | 87篇 |
1986年 | 92篇 |
1985年 | 77篇 |
1984年 | 75篇 |
1983年 | 46篇 |
1982年 | 39篇 |
1981年 | 29篇 |
1980年 | 31篇 |
1976年 | 19篇 |
1975年 | 17篇 |
1974年 | 14篇 |
1973年 | 18篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Pharmacokinetics and metabolism study of veratramine in mice after oral administration using LC‐MS/MS 下载免费PDF全文
Yue Cong Jun‐Li Zhang Sha‐Sha Li Shan Shen Jiang‐Ying Wang Zongwei Cai 《Biomedical chromatography : BMC》2016,30(9):1515-1522
A simple and sensitive high‐performance liquid chromatography coupled with hybrid triple quadrupole–linear ion trap mass spectrometry (Q‐trap‐MS) method was developed and validated for the determination of veratramine, the major bioactive and neurotoxic component in Veratrum nigrum L. Veratramine and the internal standard (IS) were separated with a Waters Symmetry C18 column and eluted with a gradient mobile phase system containing acetonitrile and 0.1% aqueous formic acid. The analysis was performed by using positive electrospray ionization mode with multiple reaction monitoring (MRM). Transition ions of m/z 410.2 → 295.2 for veratramine and m/z 426.1 → 113.8 for the IS were monitored. The method was validated with a good linearity in the range of 1–1000 ng/mL and lower limit of quantification of 1 ng/mL. The precision (CV) of intra‐ and inter‐day ranged from 3.92 to 7.29%, while the accuracy (bias) intra‐ and inter‐day were between ?4.78 and 1.65%. The recovery, stability and matrix effect were within the acceptable ranges. Five metabolites of veratramine, including four hydroxylated and one sulfated metabolites, were tentatively identified using predictive MRM–information dependent acquisition–enhanced product ion mode (predictive MRM‐IDA‐EPI). The developed method was successfully applied to the pharmacokinetic and metabolic study of veratramine in mice after oral administration of veratramine. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
993.
A blue-phase liquid crystal display (BPLCD) with low operating voltage and high transmittance is demonstrated by using a high dielectric material, which is used as an insulation layer or protrusion fixed on the pixel and common electrodes in in-plane switching (IPS) mode. The operating voltage is reduced to about 14 V and the transmittance is improved for the BPLCD with high dielectric constant protrusion. Compared with the conventional protrusion electrode structure, the proposed protrusion can make manufacturing process simple and easy because the electrode has no complex shape. The results will be significant in designing optimal BPLCDs. 相似文献
994.
This paper presents an efficient procedure for overcoming the deficiency of weighted essentially non‐oscillatory schemes near discontinuities. Through a thorough incorporation of smoothness indicators into the weights definition, up to ninth‐order accurate multistep methods are devised, providing weighted essentially non‐oscillatory schemes with enhanced order of convergence at transition points from smooth regions to a discontinuity, while maintaining stability and the essentially non‐oscillatory behavior. We also provide a detailed analysis of the resolution power and show that the solution enhancements of the new method at smooth regions come from their ability to render smoothness indicators closer to uniformity. The new scheme exhibits similar fidelity as other multistep schemes; however, with superior characteristics in terms of robustness and efficiency, as no logical statements or mapping function is needed. Extensions to higher orders of accuracy present no extra complexity. Numerical solutions of linear advection problems and nonlinear hyperbolic conservation laws are used to demonstrate the scheme's improved behavior for shock‐capturing problems. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
995.
借助于伪补和矩阵的幂序列研究了完全完备分配格上矩阵相对于特征值的特征向量的计算方法,利用特征向量的性质证明了最大特征向量的计算公式,并给出了一般特征向量的计算方法. 相似文献
996.
An LC‐MS/MS method for simultaneous determination of cefprozil diastereomers in human plasma and its application for the bioequivalence study of two cefprozil tablets in healthy Chinese volunteers 下载免费PDF全文
Min Liu Jing‐Yi Ma Yanan Zhang Xiaolin Wang Hongna Zhao Aihua Du Man Yang Lingjie Meng Ming Deng Huichen Liu 《Biomedical chromatography : BMC》2016,30(3):288-293
A rapid and sensitive liquid chromatography–tandem mass spectrometric method was developed for the first time and validated for the determination of cefprozil diastereomers in human plasma. The plasma samples were prepared by protein precipitation using acetonitrile. Detection was performed using an electronic spray ion source in the negative ion mode, operating in the multiple reaction monitoring of the transitions m/z 388.0 to m/z 205.0 for cefprozil diastereomers and m/z 346.1 to m/z 268.1 for cephalexin (the internal standard). The calibration curves of cis‐cefprozil and trans‐cefprozil were linear in the ranges 0.125–16.0 µg/mL and 0.0403–1.72 µg/mL, respectively. The lower limits of quantification of cis‐ and trans‐cefprozil were 0.125 and 0.0403 µg/mL in human plasma, respectively. The intra‐ and inter‐day precisions of cis‐ and trans‐cefprozil were all <9.7%, and the accuracy ranged from 99.2 to 104.7% and from 100.6 to 102.2%, respectively. The validated method was successfully applied to a bioequivalence study of two cefprozil formulations in 24 healthy Chinese volunteers. The two cefprozil tablets were bioequivalent by measurement of cis‐, trans‐ and total cefprozil. We suggest that the bioequivalence of cefprozil formulations can be evaluated only using cis‐cefprozil as the analyte in future studies. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
997.
998.
Yao Zhang Jie Li Guoyu Ren Baofu Qin Haixia Ma 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(6):485-490
Azole compounds have attracted commercial interest due to their high bactericidal and plant‐growth‐regulating activities. Uniconazole [or 1‐(4‐chlorophenyl)‐4,4‐dimethyl‐2‐(1H‐1,2,4‐triazol‐1‐yl)pent‐1‐en‐3‐ol] is a highly active 1,2,4‐triazole fungicide and plant‐growth regulator with low toxicity. The pharmacological and toxicological properties of many drugs are modified by the formation of their metal complexes. Therefore, there is much interest in exploiting the coordination chemistry of triazole pesticides and their potential application in agriculture. However, reports of complexes of uniconazole are rare. A new cobalt(II) complex of uniconazole, namely dichloridotetrakis[1‐(4‐chlorophenyl)‐4,4‐dimethyl‐2‐(1H‐1,2,4‐triazol‐1‐yl‐κN4)pent‐1‐en‐3‐ol]cobalt(II), [CoCl2(C15H18ClN3O)4], was synthesized and structurally characterized by element analysis, IR spectrometry and X‐ray single‐crystal diffraction. The crystal structural analysis shows that the CoII atom is located on the inversion centre and is coordinated by four uniconazole and two chloride ligands, forming a distorted octahedral geometry. The hydroxy groups of an uniconazole ligands of adjacent molecules form hydrogen bonds with the axial chloride ligands, resulting in one‐dimensional chains parallel to the a axis. The complex was analysed for its antifungal activity by the mycelial growth rate method. It was revealed that the antifungal effect of the title complex is more pronounced than the effect of fungicide uniconazole for Botryosphaeria ribis, Wheat gibberellic and Grape anthracnose. 相似文献
999.
1000.
Screening and identification of Caulis Sinomenii bioactive ingredients with dual‐target NF‐κB inhibition and β2‐AR agonizing activities 下载免费PDF全文
Dan Sun Yanqi Han Weiya Wang Zengyong Wang Xiaoyao Ma Yuanyuan Hou Gang Bai 《Biomedical chromatography : BMC》2016,30(11):1843-1853
Caulis Sinomenii (CS) is a valuable traditional medicine in China. Its extract can act as an anti‐inflammatory agent and a vascular smooth muscle relaxant. However, the underlying mechanisms remain unknown. In this study, we developed a simple dual‐target method based on ultra‐performance liquid chromatography/quadrupole time‐of‐flight mass spectrometry combined with a dual‐target bioactive screening assay for anti‐inflammatory and antispasmodic activities to characterize the chemical structure of various bioactive compounds of CS rapidly. Seven potential NF‐κB inhibitors were identified, including laudanosoline‐1‐O‐xylopyranose, 6‐O‐methyl‐laudanosoline‐1‐O‐glucopyranoside, menisperine, sinomenine, laurifoline, magnoflorine and norsinoacutin. Furthermore, IL‐6 and IL‐8 assays confirmed the anti‐inflammatory effects of these potential NF‐κB inhibitors, in which laudanosoline‐1‐O‐d ‐xylopyranose and menisperine were revealed as novel NF‐κB inhibitors. Among the seven identified alkaloids, three potential β2‐adrenergic receptor agonists, including sinomenine, magnoflorine and laurifoline, were characterized using a luciferase reporter system to measure for the activity of β2‐adrenergic receptor agonists. Finally, sinomenine, magnoflorine and laurifoline were identified not only as potential NF‐κB inhibitors but also as potential β2‐adrenegic receptor agonists, which is the first time this has been reported. Molecular dynamic simulation and docking results suggest that the three dual‐bioactive constituents could not only inhibit Pseudomonas aeruginosa PAK strain‐induced inflammatory responses via a negative regulation of the Braf protein that participates in MAPK signaling pathway but also activate the β2‐adrenegic receptor. These results suggest that CS extract has dual signaling activities with potential clinical application as a novel drug for asthma. 相似文献