全文获取类型
收费全文 | 2014篇 |
免费 | 311篇 |
国内免费 | 232篇 |
专业分类
化学 | 1443篇 |
晶体学 | 25篇 |
力学 | 109篇 |
综合类 | 13篇 |
数学 | 202篇 |
物理学 | 765篇 |
出版年
2024年 | 3篇 |
2023年 | 48篇 |
2022年 | 51篇 |
2021年 | 73篇 |
2020年 | 92篇 |
2019年 | 92篇 |
2018年 | 64篇 |
2017年 | 53篇 |
2016年 | 86篇 |
2015年 | 117篇 |
2014年 | 129篇 |
2013年 | 135篇 |
2012年 | 180篇 |
2011年 | 182篇 |
2010年 | 136篇 |
2009年 | 126篇 |
2008年 | 131篇 |
2007年 | 124篇 |
2006年 | 94篇 |
2005年 | 82篇 |
2004年 | 63篇 |
2003年 | 56篇 |
2002年 | 48篇 |
2001年 | 32篇 |
2000年 | 26篇 |
1999年 | 52篇 |
1998年 | 42篇 |
1997年 | 41篇 |
1996年 | 38篇 |
1995年 | 29篇 |
1994年 | 22篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有2557条查询结果,搜索用时 46 毫秒
81.
Shamsa Kanwal Qiang Ma Wenchao Dou Guannan Wang 《International journal of environmental analytical chemistry》2013,93(2):210-221
A new sensitive chemiluminescence (CL) method combined with continuous flow injection analysis is described for the determination of Cr(VI). Strong CL signals were generated by Cr(VI)-catalysed oxidation of gallic acid in the presence of potassium permanganate and hydrogen peroxide. Effects of reagent concentrations, temperature, pH, flow rates, mixing coil length and mixing flow sequences on the chemiluminescence intensity were studied. Under the optimised experimental conditions, the relationship between the logarithm of concentration (log?C) of Cr(VI) and the logarithm of intensity (log?I) is linear over the range of 2?×?10?11 – 5?×?10?4?mol?L?1, with the detection limit (3σ) of 4?×?10?12?mol?L?1. Relative standard deviation of ten measurements of 1?×?10?9?mol?L?1 Cr(VI) is 1.7%. This flow injection analysis (FIA) system proved to be able to analyse up to 40 samples h?1. Effects of various interferences possibly present in the water samples were investigated. Most cations and anions, as well as organic compounds, did not interfere with the determination of Cr(VI) in water samples. The experimental results obtained for chromium in reference materials were also in good agreement with the certified values. 相似文献
82.
Two concise routes toward betulin-3-yl-β-D-glucopyranoside, being different in the protection of primary alcohol of betulin, were developed. The synthesis adopted a stepwise glycosidation method employing glycosyl trichloroacetimidate as donor. 相似文献
83.
对基于MFCAV(Multi Fluid Channel on Averaged Volume)近似Riemann解法器的相容拉氏方法的熵条件进行了分析. 结果表明与满足声学形式Riemann解法器的熵不同, 前者只能在每个网格边界左、右两侧网格的熵随时间变化的和保证大于零, 即能保证整体熵增, 但不保证传统意义上的在每个网格中的熵增;而后者不仅保证整体熵增, 而且还满足传统意义上的熵增. 因此MFCAV的熵增相对声学形式解法器而言要弱一些, 由此表明其熵增可能要小些, 使得格式的耗散可能要小些.数值算例也验证了分析的正确性. 相似文献
84.
Hu Yuan Kaijian Bi Wanlin Chang Rongcai Yue Bo Li Ji Ye Qingyan Sun Huizi Jin Lei Shan Weidong Zhang 《Tetrahedron》2014
A total synthesis of Daphnodorin A, a member of the Daphnodorins, was accomplished. Key features of the synthetic strategy include construction of 2-substituted-3-functionalized benzofuran via intramolecular Heck reaction and a mild Barton–McCombie deoxygenation process mediated by triethylborane. The total synthesis provided Daphnodorin A in 19.7% or 5.6% overall yield over 7 or 15 steps. 相似文献
85.
86.
Retention behavior of a homologous series and positional isomers of aliphatic amino acids in hydrophilic interaction chromatography
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Michal Douša Jan Srbek Zdeněk Stránský Petr Gibala Lucie Nováková 《Journal of separation science》2014,37(7):739-747
The retention behavior of several series of free α‐ and ω‐amino acids and positional isomers of amino pentanoic acid in the hydrophilic interaction chromatography mode (HILIC) was studied. The study was carried out on three stationary phases followed by post‐column derivatization with fluorescence detection in order to describe the retention mechanism of the tested amino acids. The effect of chromatographic conditions including acetonitrile content in the mobile phase, mobile phase pH (ranging from 3.5 to 6.5) and concentration of buffer in the mobile phase was investigated. The effect of the number of carbon atoms (nC) in aliphatic chains of the individual homologue of α‐ and ω‐amino acids and the logarithm of the partition coefficient (logD) on retention was also a part of the presented study. A good correlation (r > 0.98) between the logk and logD values of amino acids or nC, respectively, was observed. The described linear relationships were subsequently applied to predict the retention behavior of individual members of the homologous series of amino acids and to optimize the mobile phase composition in HILIC. The obtained results confirmed that the retention mechanism of α‐amino acids, ω‐amino acids and positional isomers of amino acids was based on the logD values and the number of carbon atoms in the aliphatic chains of amino acids. The elution order of ω‐amino acids and positional isomers of amino pentanoic acid was strongly dependent on the mobile phase pH in the investigated range whereas the retention factors of all α‐amino acids remained essentially unchanged on all tested stationary phases. 相似文献
87.
Tumor microenvironment is a multicomponent system consisting of tumor cells, noncancer cells, extracellular matrix, and signaling molecules, which hosts tumor cells with integrated biophysical and biochemical elements. Because of its critical involvement in tumor genesis, invasion, metastasis, and resistance, the tumor microenvironment is emerging as a hot topic of tumor biology and a prospective therapeutic target. Unfortunately, the complex of microenvironment modeling in vitro is technically challenging and does not effectively generalize the local tumor tissue milieu. Recently, significant advances in microfluidic technologies have provided us with an approach to imitate physiological systems that can be utilized to mimic the characterization of tumor responses with pathophysiological relevance in vitro. In this review, we highlight the recent progress and innovations in microfluidic technology that facilitates the tumor microenvironment study. We also discuss the progress and future perspective of microfluidic bionic approaches with high efficiency for the study of tumor microenvironment and the challenges encountered in cancer research, drug discovery, and personalized therapy. 相似文献
88.
Weidong Shang Sheng‐Nan Su Rong Shi Ze‐Dong Mou Guo‐Qiang Yu Xia Zhang Dawen Niu 《Angewandte Chemie (International ed. in English)》2021,60(1):385-390
We here report glycosyl sulfoxides appended with an aryl iodide moiety as readily available, air and moisture stable precursors to glycosyl radicals. These glycosyl sulfoxides could be converted to glycosyl radicals by way of a rapid and efficient intramolecular radical substitution event. The use of this type of precursors enabled the synthesis of various complex C‐linked glycoconjugates under mild conditions. This reaction could be performed in aqueous media and is amenable to the synthesis of glycopeptidomimetics and carbohydrate‐DNA conjugates. 相似文献
89.
Haotian Pei Wenyu Su Meng Gui Mingjie Dou Yingxin Zhang Cuizhu Wang Dan Lu 《Molecules (Basel, Switzerland)》2021,26(7)
Six parts of lotus (seeds, leaves, plumule, stamens, receptacles and rhizome nodes) are herbal medicines that are listed in the Chinese Pharmacopoeia. Their indications and functions have been confirmed by a long history of clinical practice. To fully understand the material basis of clinical applications, UPLC-QToF-MS combined with the UNIFI platform and multivariate statistical analysis was used in this study. As a result, a total of 171 compounds were detected and characterized from the six parts, and 23 robust biomarkers were discovered. The method can be used as a standard protocol for the direct identification and prediction of the six parts of lotus. Meanwhile, these discoveries are valuable for improving the quality control method of herbal medicines. Most importantly, this was the first time that alkaloids were detected in the stamen, and terpenoids were detected in the cored seed. The stamen is a noteworthy part because it contains the greatest diversity of flavonoids and terpenoids, but research on the stamen is rather limited. 相似文献
90.
San-E Zhu Jian-Hui Zhang Yu Gong Li-Feng Dou Li-Hua Mao Hong-Dian Lu Chun-Xiang Wei Hong Chen Xue-Fei Wang Wei Yang 《Molecules (Basel, Switzerland)》2021,26(5)
A broadband visible light-absorbing [70]fullerene-BODIPY-triphenylamine triad (C70-B-T) has been synthesized and applied as a heavy atom-free organic triplet photosensitizer for photooxidation. By attaching two triphenylmethyl amine units (TPAs) to the π-core of BODIPY via ethynyl linkers, the absorption range of the antenna is extended to 700 nm with a peak at 600 nm. Thus, the absorption spectrum of C70-B-T almost covers the entire UV–visible region (270–700 nm). The photophysical processes are investigated by means of steady-state and transient spectroscopies. Upon photoexcitation at 339 nm, an efficient energy transfer (ET) from TPA to BODIPY occurs both in C70-B-T and B-T, resulting in the appearance of the BODIPY emission at 664 nm. Direct or indirect (via ET) excitation of the BODIPY-part of C70-B-T is followed by photoinduced ET from the antenna to C70, thus the singlet excited state of C70 (1C70*) is populated. Subsequently, the triplet excited state of C70 (3C70*) is produced via the intrinsic intersystem crossing of C70. The photooxidation ability of C70-B-T was studied using 1,5-dihydroxy naphthalene (DHN) as a chemical sensor. The photooxidation efficiency of C70-B-T is higher than that of the individual components of C70-1 and B-T, and even higher than that of methylene blue (MB). The photooxidation rate constant of C70-B-T is 1.47 and 1.51 times as that of C70-1 and MB, respectively. The results indicate that the C70-antenna systems can be used as another structure motif for a heavy atom-free organic triplet photosensitizer. 相似文献