全文获取类型
收费全文 | 1487篇 |
免费 | 53篇 |
国内免费 | 91篇 |
专业分类
化学 | 909篇 |
晶体学 | 2篇 |
力学 | 87篇 |
综合类 | 5篇 |
数学 | 402篇 |
物理学 | 226篇 |
出版年
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 24篇 |
2020年 | 27篇 |
2019年 | 21篇 |
2018年 | 18篇 |
2017年 | 24篇 |
2016年 | 28篇 |
2015年 | 39篇 |
2014年 | 66篇 |
2013年 | 90篇 |
2012年 | 74篇 |
2011年 | 57篇 |
2010年 | 69篇 |
2009年 | 99篇 |
2008年 | 84篇 |
2007年 | 114篇 |
2006年 | 96篇 |
2005年 | 66篇 |
2004年 | 70篇 |
2003年 | 50篇 |
2002年 | 56篇 |
2001年 | 31篇 |
2000年 | 43篇 |
1999年 | 46篇 |
1998年 | 35篇 |
1997年 | 35篇 |
1996年 | 25篇 |
1995年 | 19篇 |
1994年 | 26篇 |
1993年 | 27篇 |
1992年 | 12篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1631条查询结果,搜索用时 15 毫秒
61.
《Arabian Journal of Chemistry》2014,7(5):811-816
A simple, specific and accurate isocratic RP-HPLC-DAD method was developed for the simultaneous determination of phenylephrine, paracetamol, caffeine and chlorpheniramine in bulk and tablet dosage form. The four contents are present in variable concentrations and have variable chromatographic behavior making the process of analysis very difficult. For present studies a reversed-phase C-18 column (150 mm × 4.5 mm i.d., particle size 5 μm) with mobile phase consisting of acetonitrile, methanol and 10 Mm phosphate buffer 16:22:62 (v/v) (pH of buffer 2.5 ± 0.02, adjusted with ortho phosphoric acid) was used. The flow rate was 1.0 ml/min and eluents were monitored at 280 nm. The mean retention times of phenylephrine, paracetamol, caffeine and chlorpheniramine were found to be 1.8, 3.1, 5.2 and 10.9 min, respectively. The method was validated in terms of linearity, range, specificity, accuracy, precision and robustness. The proposed method was successfully applied to the estimation of phenylephrine, paracetamol, caffeine and chlorpheniramine in combined tablet dosage form. 相似文献
62.
Efficient cross polarization with simultaneous adiabatic frequency sweep on the source and target channels 总被引:2,自引:2,他引:0
In this work, we propose a new and efficient heteronuclear cross polarization scheme, in which adiabatic frequency sweeps from far off-resonance toward on-resonance are applied simultaneously on both the source and target spins. This technique, which we call as Simultaneous ADIabatic Spin-locking Cross Polarization (SADIS CP), is capable of efficiently locking both the source and target spins with moderate power even in the presence of large spectral distribution and fast relaxation. It is shown that by keeping the time-dependent Hartmann-Hahn mismatch minimal throughout the mixing period, polarization transfer can be accelerated. Experiments are demonstrated in a powder sample of L-alanine. 相似文献
63.
64.
Development of a Simple and Fast Electrochemical Method for Screening and Stoichiometric Determination of Dimenhydrinate 下载免费PDF全文
Jhonys Machado Freitas Thiago da Costa Oliveira Polyana Luiza Silva Denise Tofanello Gimenes Rodrigo Alejandro Abarza Munoz Eduardo Mathias Richter 《Electroanalysis》2014,26(9):1905-1911
Dimenhydrinate (DIM) is a salt composed by the combination of two active pharmaceutical ingredients: diphenhydramine (DIP) and 8‐chlorotheophylline (CTP). In this work, the use of batch injection analysis with multiple pulse amperometric detection (BIA‐MPA) was proposed for the first time for fast stoichiometric determination of DIM. DIP (cation) and CTP (anion) were determined simultaneously in pharmaceutical samples with a simple and fast injection procedure (70 injections h?1). Additional strategies were also proposed for rapid screening of samples containing the DIM salt. By a simple injection of a sample into the BIA system (without using of calibration curve), reliable information about stoichiometry of the DIM salt (1 : 1; DIP:CTP) and presence or absence of interfering species (electroactive) can be achieved. 相似文献
65.
Mycotoxins: Simultaneous Detection of Zearalenone and Citrinin by Voltammetry on Edge Plane Pyrolytic Graphite Electrode 下载免费PDF全文
Mycotoxins are highly toxic compounds often found in the food. It is of paramount importance to have analytical technique for point‐of‐care on‐spot detection for authorised personnel to immediately take the action required. Electrochemistry offers the portability for miniaturized sensor of mycotoxins. Here we show that edge‐plane pyrolytic electrode offers excellent selectivity and sensitivity towards simultaneous detection of zearalenone and citrinin. This will have a great impact for point‐of‐care mycotoxin detection. 相似文献
66.
《Journal of Saudi Chemical Society》2020,24(8):636-641
A catalyst-free and solvent-free synthetic route for convenient one-pot synthesizing pyrano[2,3-d] pyrimidine scaffolds through Knoevenagel-Michael cyclocondensation is reported using visible light irradiation as a green promoter at room temperature based on green chemistry principles. Completing the reactions takes thoroughly less time while obtaining the products in outstanding yields. This green method includes the application of non-hazardous reaction circumstances, direct work-up without column chromatographic separation, catalyst-free, solvent-free, cost effective, simple synthesis, one-pot procedure, and high atom-economy. 相似文献
67.
提出了用神经网络方法测定无机铬的形态。在Back Propagation(BP)算法的基础上,吸取了模拟退火算法的优点,解决了BP算法容易陷入局部极小点的问题。经实际样品分析,结果满意。 相似文献
68.
张淑芳 《光谱学与光谱分析》2006,26(3):535-538
提出了运用吸光度比值-导数光谱法同时测定Cr(Ⅲ)与Cu(Ⅱ)含量的新方法。在pH 5.7的HAc-NaAc的缓冲溶液中,Cr3+,Cu2+与铬天青S(CAS)和溴化十六烷基三甲胺(CTMAB)可分别形成蓝色三元络合物。其摩尔吸光系数分别为2.52×105 L·mol-1·cm-1和1.01×105 L·mol-1·cm-1。Cu2+和Cr3+的浓度分别在0.08~1.2 μg·mL-1和0.05~0.52 μg·mL-1范围内符合比尔定律,其检测限分别为0.014和0.013 μg·mL-1。此方法应用于环境水中Cr(Ⅲ),Cu(Ⅱ)的同时测定,取得了满意的结果。 相似文献
69.
偏最小二乘法用于同步荧光法同时测定维生素B1,维生素B2和维生素B6 总被引:5,自引:0,他引:5
本文将偏最小二乘法结合同步荧光扫描技术对含维生素B1,B2和B6的混合物进行了同时测定。对同步荧光法的测定条件及△λ的选择进行了试验和讨论,比较了△λ分别为65nm和30nm时的计算结果。所建立的方法用于复合维生素B片等药片叶B1,B2和B6孤同时测定,获较满意的结果。 相似文献
70.