全文获取类型
收费全文 | 2021篇 |
免费 | 93篇 |
国内免费 | 125篇 |
专业分类
化学 | 794篇 |
晶体学 | 30篇 |
力学 | 111篇 |
综合类 | 11篇 |
数学 | 984篇 |
物理学 | 309篇 |
出版年
2024年 | 5篇 |
2023年 | 32篇 |
2022年 | 44篇 |
2021年 | 36篇 |
2020年 | 55篇 |
2019年 | 64篇 |
2018年 | 47篇 |
2017年 | 68篇 |
2016年 | 69篇 |
2015年 | 55篇 |
2014年 | 100篇 |
2013年 | 142篇 |
2012年 | 84篇 |
2011年 | 101篇 |
2010年 | 95篇 |
2009年 | 172篇 |
2008年 | 133篇 |
2007年 | 133篇 |
2006年 | 92篇 |
2005年 | 75篇 |
2004年 | 69篇 |
2003年 | 60篇 |
2002年 | 56篇 |
2001年 | 59篇 |
2000年 | 50篇 |
1999年 | 36篇 |
1998年 | 41篇 |
1997年 | 46篇 |
1996年 | 24篇 |
1995年 | 29篇 |
1994年 | 22篇 |
1993年 | 11篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有2239条查询结果,搜索用时 15 毫秒
91.
Ray Jones 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(1):60-66
The structures of 6‐nitro‐1,3λ4δ2,5,2,4‐trithiadiazepine [C2HN3O2S3, ( 1 )], 6,7‐dinitro‐1,3λ4δ2,5,2,4‐trithiadiazepine [C2N4O4S3, ( 2 )], 1,3λ4δ2,5,2,4‐trithiadiazepine‐6,7‐dicarbonitrile [C4N4S3, ( 3 )] and 7‐acetyl‐1,3λ4δ2,5,2,4,6‐trithiatriazepine [C3H3N3OS3, ( 4 )] presented here include the most precise determinations of these seven‐membered 10 π‐electron aromatic ring systems published to date. Both ( 2 ) and ( 3 ) are sited around crystallographic twofold axes with half a molecule per asymmetric unit. Comparison with other published derivatives of these rings reveals the effect of substituents on bonding, conformations and intermolecular interactions, including π‐stacking. The deformation density analysis of ( 2 ) is consistent with the expected bonding electron density from other theoretical and experimental studies. 相似文献
92.
Thomas Wiesner Dr. Zhu Wu Dr. Jie Han Prof. Dr. Lei Ji Dr. Alexandra Friedrich Dr. Ivo Krummenacher Michael Moos Prof. Dr. Christoph Lambert Prof. Dr. Holger Braunschweig Benjamin Rudin Dr. Hilmar Reiss Olena Tverskoy Dr. Frank Rominger Prof. Dr. Andreas Dreuw Prof. Dr. Todd B. Marder Dr. Jan Freudenberg Prof. Dr. Uwe H. F. Bunz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(69):e202201919
Tetraiodotetraazapentacene I4TAP , the last missing derivative in the series of halogenated silylated tetraazapentacenes, was synthesized via condensation chemistry from a TIPS-ethynylated diaminobenzothiadiazol in three steps. Single and double reduction furnished its air-stable monoanion and relatively air-stable dianion, both of which were characterized by crystallography. All three species are structurally and spectroscopically compared to non-halogenated TAP and Br4TAP . I4TAP is an n-channel material in thin-film transistors with average electron mobilities exceeding 1 cm2 (Vs)−1. 相似文献
93.
堵塞行为是颗粒体系中一种常见的现象,其力学性质与堆积结构的关联非常复杂.本文采用离散元法研究了由两种不同半径颗粒组成的二维双分散无摩擦球形颗粒体系在临界堵塞态所呈现的结构特征,讨论了大小颗粒粒径比与大颗粒百分比对临界堵塞态的影响.数值模拟结果表明,当粒径比小于1.4时,临界平均接触数与大颗粒百分比关系不大,当粒径比大于1.4时随着大颗粒百分比的增大临界平均接触数先减小再增大.而临界体积分数在粒径比小于1.8时随着大颗粒百分比的增加先减小后增大,大于1.8时又基本不随大颗粒百分比而变化.大颗粒百分比在接近0或1时,系统近似为单分散体系,临界平均接触数与体积分数基本不随半径比的增大而变化;在接近0.5时,临界平均接触数随着半径比的增大逐渐减小,而临界体积分数则是先减小后增大.文中对大-小颗粒这一接触类型的百分比也进行了探讨,其值随着大颗粒百分比的增大呈二次函数的变化趋势,粒径比对这一变化趋势只有较小的影响. 相似文献
94.
Precision and sensitivity optimization of quantitative measurements in solid state NMR 总被引:2,自引:1,他引:1
Ziarelli F Viel S Sanchez S Cross D Caldarelli S 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,188(2):260-266
This work presents a methodology for optimizing the precision, accuracy and sensitivity of quantitative solid state NMR measurements based on the external reference method. It is shown that the sample must be exclusively located within and completely span the coil region where the NMR response is directly proportional to the sample amount. We describe two methods to determine this "quantitative" coil volume, based on whether the probe is equipped or not with a gradient coil. In addition, to improve the sensitivity and the accuracy, an optimum rotor packing design is described, which allows the sample volume of the rotor to be matched to the quantitative coil volume. Experiments conducted on adamantane and NaCl, which are representative of a soft and hard material, respectively, show that one order of magnitude increase in experimental precision can be achieved with this methodology. Interestingly, the precision can be further improved by using the ERETIC method in order to compensate for most instrumental instabilities. 相似文献
95.
Multiplexed Determination of Amino‐Terminal Pro‐B‐Type Natriuretic Peptide and C‐Reactive Protein Cardiac Biomarkers in Human Serum at a Disposable Electrochemical Magnetoimmunosensor
下载免费PDF全文
![点击此处可从《Electroanalysis》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Berta Esteban‐Fernández de Ávila Vanessa Escamilla‐Gómez Valentina Lanzone Susana Campuzano María Pedrero Dario Compagnone José M. Pingarrón 《Electroanalysis》2014,26(2):254-261
A rapid magnetoimmunosensor for the simultaneous determination of two cardiac biomarkers, amino‐terminal pro‐B‐type natriuretic peptide (NT‐proBNP) and C‐reactive protein (CRP), in human serum is described. Specific capture antibodies were covalently immobilized onto carboxylic acid‐modified magnetic beads. The quantification of NT‐proBNP and CRP was performed by using indirect competitive and sandwich configurations, respectively, and horseradish peroxidase‐labeled tracers. The use of dual screen‐printed carbon electrodes allowed the achievement of simultaneous independent amperometric readout for each cardiac biomarker. The developed methodology showed very low limits of detection (0.47 ng mL?1). An international standard for CRP serum spiked with NT‐proBNP was analyzed to evaluate the usefulness of the magnetoimmunosensor. 相似文献
96.
Dr. Yuanyuan Li Dr. Shunjie Liu Huwei Ni Haoke Zhang Dr. Hequn Zhang Clarence Chuah Chao Ma Prof. Kam Sing Wong Prof. Jacky W. Y. Lam Prof. Ryan T. K. Kwok Prof. Jun Qian Prof. Xuefeng Lu Prof. Ben Zhong Tang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):12922-12926
The traditional design strategies for highly bright solid-state luminescent materials rely on weakening the intermolecular π–π interactions, which may limit diversity when developing new materials. Herein, we propose a strategy of tuning the molecular packing mode by regioisomerization to regulate the solid-state fluorescence. TBP-e-TPA with a molecular rotor in the end position of a planar core adopts a long-range cofacial packing mode, which in the solid state is almost non-emissive. By shifting molecular rotors to the bay position, the resultant TBP-b-TPA possesses a discrete cross packing mode, giving a quantum yield of 15.6±0.2 %. These results demonstrate the relationship between the solid-state fluorescence efficiency and the molecule's packing mode. Thanks to the good photophysical properties, TBP-b-TPA nanoparticles were used for two-photon deep brain imaging. This molecular design philosophy provides a new way of designing highly bright solid-state fluorophores. 相似文献
97.
Glycoproteins are produced by the post‐translational modification process of proteins and they play an important role in mediating various biological processes. Our understanding towards biochemical functions of individual glycoproteins has been seriously hampered due to the heterogeneous expression of carbohydrate parts in glycoproteins. Despite the advancement in recombinant expression and chromatographic techniques, the isolation of pure glycoforms remains nearly impossible. To obtain homogenous glycoproteins, tremendous efforts hves been spent in developing various ligation and glycosylation techniques. This minireview discusses selected methods for the preparation and ligation of glycopeptides. The importance of the development of new chemical synthesis method for glycoproteins has also been discussed, which would be one of the next directions in this field. 相似文献
98.
Mikhail V. Vener Andrei V. Churakov Alexander P. Voronin Olga D. Parashchuk Sergei V. Artobolevskii Oleg A. Alatortsev Denis E. Makhrov Alexander G. Medvedev Aleksander Filarowski 《Molecules (Basel, Switzerland)》2022,27(3)
Two new peroxosolvates of drug-like compounds were synthesized and studied by a combination of X-ray crystallographic, Raman spectroscopic methods, and periodic DFT computations. The enthalpies of H-bonds formed by hydrogen peroxide (H2O2) as a donor and an acceptor of protons were compared with the enthalpies of analogous H-bonds formed by water (H2O) in isomorphic (isostructural) hydrates. The enthalpies of H-bonds formed by H2O2 as a proton donor turned out to be higher than the values of the corresponding H-bonds formed by H2O. In the case of H2O2 as a proton acceptor in H-bonds, the ratio appeared reversed. The neutral O∙∙∙H-O/O∙∙∙H-N bonds formed by the lone electron pair of the oxygen atom of water were the strongest H-bonds in the considered crystals. In the paper, it was found out that the low-frequency Raman spectra of isomorphous crystalline hydrate and peroxosolvate of N-(5-Nitro-2-furfurylidene)-1-aminohydantoin are similar. As for the isostructural hydrate and peroxosolvate of the salt of protonated 2-amino-nicotinic acid and maleic acid monoanion, the Raman spectra are different. 相似文献
99.
以碱溶法制备的高孔隙度硅胶为基质,与γ-环氧丙基丙氧基三甲氧基硅烷配基进行共价键合,经过酸性水解,使其转化为二醇基,制成了高效亲水凝胶色谱填料。键合反应中采用70 ℃回流冷凝管,使生成的甲醇可顺利地排到体系外,促使反应向有利于键合的方向进行,以获得较高的配基密度。研究表明,水解反应条件与配基密度以及柱效密切相关。当配基密度为2.6~3.5 μmol/m2时,才能显示出较高的柱效。蛋白质分离实验结果显示,此填料的相对分子质量排阻极限为300000,牛血清白蛋白的回收率为99%。 相似文献
100.