全文获取类型
收费全文 | 12010篇 |
免费 | 2374篇 |
国内免费 | 2008篇 |
专业分类
化学 | 8755篇 |
晶体学 | 210篇 |
力学 | 754篇 |
综合类 | 151篇 |
数学 | 1333篇 |
物理学 | 5189篇 |
出版年
2024年 | 32篇 |
2023年 | 227篇 |
2022年 | 381篇 |
2021年 | 440篇 |
2020年 | 577篇 |
2019年 | 551篇 |
2018年 | 498篇 |
2017年 | 458篇 |
2016年 | 652篇 |
2015年 | 645篇 |
2014年 | 759篇 |
2013年 | 955篇 |
2012年 | 1236篇 |
2011年 | 1219篇 |
2010年 | 903篇 |
2009年 | 880篇 |
2008年 | 975篇 |
2007年 | 827篇 |
2006年 | 687篇 |
2005年 | 572篇 |
2004年 | 446篇 |
2003年 | 348篇 |
2002年 | 349篇 |
2001年 | 298篇 |
2000年 | 242篇 |
1999年 | 215篇 |
1998年 | 148篇 |
1997年 | 119篇 |
1996年 | 114篇 |
1995年 | 88篇 |
1994年 | 94篇 |
1993年 | 66篇 |
1992年 | 68篇 |
1991年 | 58篇 |
1990年 | 57篇 |
1989年 | 39篇 |
1988年 | 29篇 |
1987年 | 17篇 |
1986年 | 21篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1974年 | 4篇 |
1972年 | 2篇 |
1966年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
341.
研究了不同淋洗液浓度对加速器质谱测量用NH4HfF5制样过程中阳离子交换产额的影响,用重量法对阳离子交换产额进行了测量。研究了多相法合成的NH4HfF5样品热稳定性,用XRD表征了不同温度处理下样品物相的变化情况。研究了三种(液相、固相和多相)合成方法对样品中180HfF5-离子束流和19F-/16O-比值的影响,用离子源进行了测量。结果表明:在阳离子交换过程选择60mL 1mol/L HCl为淋洗液时,阳离子交换产额可达97%。多相法合成的NH4HfF5样品在573K热处理1h后物相转变为NH4Hf2F9,在773 K、973 K、1173 K和1373 K热处理1h后物相则转变为HfO2,说明在热处理温度高于573 K后NH4HfF5热稳定较差。多相法合成的NH4HfF5样品中19F-/16O-比值能达到35,180HfF5-离子束流能达到560 nA,优于液相和固相法合成的样品。 相似文献
342.
We develop an anisotropic perfectly matched layer (PML) method for solving the time harmonic electromagnetic scattering problems in which the PML coordinate stretching is performed only in one direction outside a cuboid domain. The PML parameters such as the thickness of the layer and the absorbing medium property are determined through sharp a posteriori error estimates. Combined with the adaptive finite element method, the proposed adaptive anisotropic PML method provides a complete numerical strategy to solve the scattering problem in the framework of FEM which produces automatically a coarse mesh size away from the fixed domain and thus makes the total computational costs insensitive to the choice of the thickness of the PML layer. Numerical experiments are included to illustrate the competitive behavior of the proposed adaptive method. 相似文献
343.
344.
A series of Mannich base derivatives of 2-hydroxy-chalcones were obtained expediently in good to excellent yields by microwave-assisted Mannich reaction. The regioselectivity of the reaction occurred preferentially at the C-3 position of the 2-hydroxy-chalcone backbone. In comparison with conventional results, results from microwave possesses give better yields in shorter times. Further vasorelaxation assay showed that 2-hydroxy-3-((4-methylpiperazin-1-yl)methyl)-4,6-dimethoxymethoxy-3′-bromo-chalcone 8 significantly decreased maximal PE-induced contraction (Emax = 100 ± 5.97%, EC50 = 10.2 ± 0.51 µM). 相似文献
345.
Hui Qiang Tao Chen Zhuo Wang Wenqian Li Yunzhe Guo Jie Yang Xueshun Jia Hui Yang Weibo Hu Ke Wen 《中国化学快报》2021,31(12):3225-3229
The development of heterogeneous catalysts with substrate shape, size or electronic constitution selectivity is a huge challenge in photocatalysis. Reported herein is a host-guest interaction strategy to endow photocatalysts with special selectivity. By adjusting the precursors, conjugated macrocycle polymers (CMPs) with pillar[5]arene struts (CMP-1 and CMP-2) and a corresponding non-pillar[5]arene-contained conjugated organic polymer (COP-1) were prepared and the photocatalytic activities toward sulfide derivatives were investigated. The sulfides showed similar conversions when COP-1 was used as a photocatalyst, but exhibited significant differences when it turned to the CMPs. Remarkably, the conversion yield of S-1 achieved near 18 folds over the one of S-2 when CMP-2 was used as a catalyst. Mechanism studies confirmed that the “host-guest” effect of pillar[5]arene struts in CMPs was the main cause of the difference. The present work establishes CMPs as novel heterogeneous photocatalysts with substrate selectivity, and such a method will inspire the researchers concerning preparation of heterogeneous catalysts with excellent selectivity. 相似文献
346.
Xian Tao Ke‐Cheng Shen Qing‐Yun Tang Meng Feng Jiang‐Tao Fang Yu‐Long Wang Ying‐Zhong Shen 《应用有机金属化学》2012,26(7):323-329
New N‐silver(I) acetylbenzamide complexes of type Ln?AgNC9H8O2 (L = PPh3; n = 1, 2a; n = 2, 2b; n = 3, 2c; L = P(OEt)3; n = 1, 2d; n = 2, 2e; n = 3, 2f) were prepared. These complexes were obtained in high yields and characterized by elemental analysis, 1H NMR, 13C{H} NMR, 31P{H} NMR and IR spectroscopy, respectively. The molecular structure of 2b has been determined by X‐ray single‐crystal analysis in which the silver atom is in a distorted tetrahedral geometry and crystallizes as cis–trans. New N‐silver(I) acetylbenzamide complexes have a four‐membered ring, which could influence their chemical and physical properties and modulate volatility. Metal organic chemical vapor deposition experiments were carried out successfully at 400°C and 450°C using 2e as precursor for the deposition of silver films, respectively. The high‐purity silver film obtained at 400°C is dense and homogeneous. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
347.
An easily prepared tetraphosphine N,N,N′,N′‐tetra(diphenylphosphinomethyl)‐1,2‐ethylenediamine (1) combined with PdCl2 affords an efficient catalytic system for Suzuki cross‐coupling of aryl and heteroaryl bromides. A high turnover number of 750 000 is obtained with the catalyst loading as low as 1 ppm. This catalyst system exhibits good stability and longevity. In this study, a broad scope of substrates is investigated and satisfactory yields are obtained. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
348.
In this study, a novel task-specific ionic liquid functionalized gold nanoparticle (TSIL-GNP) was successfully prepared and applied in the recognition of amino acids. Particularly, the surface of GNP was modified with the ionic liquid containing carbamido and ester group via thiol, which was characterized by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The stability of this material in aqueous solution improves apparently and can remain unchanged for more than three months. The effect of pH was also discussed in this study. Attractive ionic interaction would effectively weaken intensity of the covalent coupling between the metal ion and the functional groups of amino acids. Thus, TSIL-GNP was successfully applied to recognizing serine, aspartic acid, lysine, arginine, and histidine in the presence of Cu2+ through distinctive color changes. Suspension would be generated once a spot of cysteine was added into the GNPs solution. Results indicated that it had a good linear relationship between extinction coefficients and concentration of amino acids in a wide range of 10−3–10−6 M. Moreover, the proposed strategy was successfully used to analyze the histidine in urinary samples. In brief, TSIL-GNP is a suitable substrate for discrimination of five amino acids in a rapid and simple way without sophisticated instruments. 相似文献
349.
Determination of ecliptasaponin A in rat plasma and tissues by liquid chromatography‐tandem mass spectrometry
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jing Zhao Erwei Liu Lifeng Han Linlin Wang Yi Zhang Tao Wang Shiming Fang Xiumei Gao 《Biomedical chromatography : BMC》2016,30(6):846-851
A sensitive, rapid and specific high‐performance liquid chromatography tandem mass spectrometry method (HPLC‐MS/MS) was developed to determine ecliptasaponin A in rat plasma and tissues after oral administration. Ginsenoside Rg1 was used as the internal standard (IS). The plasma and tissues samples were prepared by liquid‐liquid extraction with ethyl acetate and separated on an Eclipse Plus C18 column (2.1 mm × 150 mm, 5 µm) at a flow rate of 0.4 mL/min using acetonitrile and water (containing 0.05% acetic acid) as the mobile phase. The tandem mass detection was carried out with eletrospray ionization in negative mode. Quantification was performed by using multiple reaction monitoring (MRM), which monitored the fragmentation of m/z 633.4→587.2 for ecliptasaponin A and m/z 859.4→637.4 for the IS. The calibration curves obtained were linear in different matrices, and the lower limit of quantification (LLOQ) achieved was 0.5 ng/mL both for rat plasma and tissues. The intra‐ and inter‐day precisions were below 15%. This method was successfully applied to pharmacokinetic study of ecliptasaponin A in rat plasma and tissues after oral administration. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
350.