全文获取类型
收费全文 | 929篇 |
免费 | 77篇 |
国内免费 | 96篇 |
专业分类
化学 | 610篇 |
晶体学 | 14篇 |
力学 | 95篇 |
综合类 | 17篇 |
数学 | 172篇 |
物理学 | 194篇 |
出版年
2024年 | 5篇 |
2023年 | 31篇 |
2022年 | 30篇 |
2021年 | 32篇 |
2020年 | 62篇 |
2019年 | 43篇 |
2018年 | 32篇 |
2017年 | 28篇 |
2016年 | 47篇 |
2015年 | 42篇 |
2014年 | 37篇 |
2013年 | 60篇 |
2012年 | 75篇 |
2011年 | 57篇 |
2010年 | 45篇 |
2009年 | 52篇 |
2008年 | 44篇 |
2007年 | 41篇 |
2006年 | 36篇 |
2005年 | 37篇 |
2004年 | 24篇 |
2003年 | 26篇 |
2002年 | 40篇 |
2001年 | 19篇 |
2000年 | 12篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 16篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 7篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 18篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有1102条查询结果,搜索用时 0 毫秒
81.
The successive projections algorithm (SPA) is widely used to select variables for multiple linear regression (MLR) modeling. However, SPA used only once may not obtain all the useful information of the full spectra, because the number of selected variables cannot exceed the number of calibration samples in the SPA algorithm. Therefore, the SPA-MLR method risks the loss of useful information. To make a full use of the useful information in the spectra, a new method named “consensus SPA-MLR” (C-SPA-MLR) is proposed herein. This method is the combination of consensus strategy and SPA-MLR method. In the C-SPA-MLR method, SPA-MLR is used to construct member models with different subsets of variables, which are selected from the remaining variables iteratively. A consensus prediction is obtained by combining the predictions of the member models. The proposed method is evaluated by analyzing the near infrared (NIR) spectra of corn and diesel. The results of C-SPA-MLR method showed a better prediction performance compared with the SPA-MLR and full-spectra PLS methods. Moreover, these results could serve as a reference for combination the consensus strategy and other variable selection methods when analyzing NIR spectra and other spectroscopic techniques. 相似文献
82.
The Influencing Mechanism of Acidity on the Oxidation Peak Currents of Uric Acid and Ascorbic Acid at the PACPE by Cyclic Voltammetry 下载免费PDF全文
In this paper, a pre‐anodized carbon paste electrode (PACPE) is fabricated by a simple electrochemical pretreatment method, which can be used for the simultaneous determination of uric acid (UA) and ascorbic acid (AA). The influencing mechanism of the acidity on the size of oxidation peak current (ip,a) of UA and AA is discussed in detail. According to the results, in different pH conditions, the intensity of hydrogen bonding between UA, AA and the surface of PACPE, the degree of reduction reaction at the auxiliary electrode, and the structural configurations of UA and AA with different species in reaction system have evident influence on the size of oxidation peak current. In pH 7.00 phosphate buffer solution, the calibration curves for UA and AA are obtained in the range of 5.0 x 10‐7–5.0 x 10‐5 mol/L and 3.0 x 10‐5–5.0 x 10‐3 mol/L, respectively. The detection limits for UA and AA are found to be 2.0 x 10‐8 mol/L and 1.2 x 10‐6 mol/L, respectively. This proposed method has been successfully applied to determine UA and AA in human urine simultaneously with satisfactory results. 相似文献
83.
Daoke Yu Wenbin Chen Shichao Zhang Rakesh Chilivery Fuhai Li Xupeng Lu 《Phosphorus, sulfur, and silicon and the related elements》2020,195(6):464-473
AbstractThe synthesis conditions of HZSM-5 zeolite, including crystallization temperature, crystallization time and raw material ratio, were investigated by L32 (48) orthogonal test to specifically optimize its performance in dimethyl ether (DME) aromatization for the first time. Based on the total yield of aromatic products, the synthesis conditions of HZSM-5 zeolite with the best DME aromatization properties were obtained by comprehensive analysis and validation experiments. The relationship between the aromatization performance, crystalline structure, pore structure, and acidity of HZSM-5 zeolite were analyzed. The results showed that the HZSM-5 zeolite accompanied by hierarchical structure, an appropriate Brønsted and Lewis acid content and uniform crystal morphology, was successfully synthesized under optimized conditions. Over this unmodified and un-doped catalyst, the conversion of DME approached to 99.3% and the total yield of aromatics reached was 53.5%. 相似文献
84.
Yunong Li Lei Wang Jingxiang Low Di Wu Canyu Hu Wenbin Jiang Jun Ma Chengming Wang Ran Long Li Song Hangxun Xu Yujie Xiong 《中国化学快报》2020,31(1):231-234
Efficient catalytic system with low energy consumption exhibits increasing importance due to the upcoming energy crisis.Given this situation,it should be an admirable strategy for reducing energy input by effectively utilizing incident solar energy as a heat source during catalytic reactions.Herein,aza-fused7 r-conjugated microporous polymer(aza-CMP)with broad light absorption and high photothermal conversion efficiency was synthesized and utilized as a support for bimetallic AuPd nanocatalysts in light-driven benzyl alcohol oxidation.The AuPd nanoparticles anchored on aza-CMP(aza-CM P/Au_xPdy)exhibited excellent catalytic performance for benzyl alcohol oxidation under 50 mW/cm^2 light irradiation.The improved catalytic performance by the aza-CMP/Au_xPdy is attributed to the unique photothermal effect induced by aza-CMP,which can promote the catalytic benzyl alcohol oxidation occurring at Au Pd.This work presents a novel approach to effectively utilize solar energy for conventional catalytic reactions through photothermal effect. 相似文献
85.
Wenbin Wang Yutang Wang Ruoou Yang Qunlei Wen Youwen Liu Zheng Jiang Huiqiao Li Tianyou Zhai 《Angewandte Chemie (International ed. in English)》2020,59(39):16974-16981
Electrochemical synthesis based on electrons as reagents provides a broad prospect for commodity chemical manufacturing. A direct one‐step route for the electrooxidation of amino C?N bonds to nitrile C≡N bonds offers an alternative pathway for nitrile production. However, this route has not been fully explored with respect to either the chemical bond reforming process or the performance optimization. Proposed here is a model of vacancy‐rich Ni(OH)2 atomic layers for studying the performance relationship with respect to structure. Theoretical calculations show the vacancy‐induced local electropositive sites chemisorb the N atom with a lone pair of electrons and then attack the corresponding N(sp3)?H, thus accelerating amino C?N bond activation for dehydrogenation directly into the C≡N bond. Vacancy‐rich nanosheets exhibit up to 96.5 % propionitrile selectivity at a moderate potential of 1.38 V. These findings can lead to a new pathway for facilitating catalytic reactions in the chemicals industry. 相似文献
86.
Wenbin Guo Dr. Nathalie Daro Dr. Sébastien Pillet Dr. Mathieu Marchivie Dr. El-Eulmi Bendeif Dr. Elodie Tailleur Dr. Kittipong Chainok Dominique Denux Dr. Guillaume Chastanet Prof. Philippe Guionneau 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(57):12927-12930
The current craze for research around the spin crossover phenomenon can be justified to some extent by the mechanical properties due to the decrease of volume associated with the transition of the metal ion from the HS state to the LS state. As demonstrated here, the molecular complex [Fe(PM-pBrA)2(NCS)2] exhibits, on the contrary, an increase of the unit-cell volume from HS to LS. This counter-intuitive and unprecedented behavior that concerns both the thermal and the photoexcited spin conversions is revealed by a combination of single-crystal and powder X-ray diffraction complemented by magnetic measurements. Interestingly, this abnormal volume change appears concomitant with the wide rotation of a phenyl ring which induces a drastic modification, though reversible, of the structural packing within the crystal. In addition, the light-induced HS state obtained through the Light-Induced Excited Spin-State Trapping shows a remarkably high relaxation temperature, namely T(LIESST), of 109 K, one of the highest so far reported. The above set of quite unusual characteristics opens up new fields of possibilities within the development of spin crossover materials. 相似文献
87.
Wencan Jiang Gongwei Sun Wenbin Cui Shasha Men Miao Jing Danna Pu Sichun Zhang Xiaozhou Yuan Xinrong Zhang Chengbin Wang 《Molecules (Basel, Switzerland)》2020,25(22)
Background: Element-tagged immunoassay coupled with inductively coupled plasma mass spectrometry (ICP-MS) detection has the potential to revolutionize immunoassay analysis for multiplex detection. However, a further study referring to the standard evaluation and clinical sample verification is needed to ensure its reliability for simultaneous analysis in clinical laboratories. Methods: Carcinoembryonic antigen (CEA) and α-fetoprotein (AFP) were chosen for the duplex immunoassay. The performance of the assay was evaluated according to guidelines from the Clinical and Laboratory Standards Institute (CLSI). Moreover, reference intervals (RIs) of CEA and AFP were established. At last, 329 clinical samples were analyzed by the proposed method and results were compared with those obtained with electrochemiluminescent immunoassay (ECLIA) method. Results: The measurement range of the assay was 2–940 ng/mL for CEA and 1.5–1000 ng/mL for AFP, with a detection limit of 0.94 ng/mL and 0.34 ng/mL, respectively. The inter-assay and intra-assay imprecision were all less than 6.58% and 10.62%, respectively. The RI of CEA and AFP was 0–3.84 ng/mL and 0–9.94 ng/mL, respectively. Regarding to clinical sample detection, no significant difference was observed between the proposed duplex assay and the ECLIA method. Conclusions: The ICP-MS-based duplex immunoassay was successfully developed and the analytical performance fully proved clinical applicability. Well, this could be different with other analytes. 相似文献
88.
Ascorbic acid (AA) is one of the essential nutrients in bee pollen, however, it is unstable and likely to be oxidized. Generally, the oxidation form (dehydroascorbic acid (DHA)) is considered to have equivalent biological activity as the reduction form. Thus, determination of the total content of AA and DHA would be more accurate for the nutritional analysis of bee pollen. Here we present a simple, sensitive, and reliable method for the determination of AA, total ascorbic acids (TAA), and DHA in rape (Brassica campestris), lotus (Nelumbo nucifera), and camellia (Camellia japonica) bee pollen, which is based on ultrasonic extraction in metaphosphoric acid solution, and analysis using hydrophilic interaction liquid chromatography (HILIC)-ultraviolet detection. Analytical performance of the method was evaluated and validated, then the proposed method was successfully applied in twenty-one bee pollen samples. Results indicated that contents of AA were in the range of 17.54 to 94.01 µg/g, 66.01 to 111.66 µg/g, and 90.04 to 313.02 µg/g for rape, lotus, and camellia bee pollen, respectively. In addition, percentages of DHA in TAA showed good intra-species consistency, with values of 13.7%, 16.5%, and 7.6% in rape, lotus, and camellia bee pollen, respectively. This is the first report on the discriminative determination between AA and DHA in bee pollen matrices. The proposed method would be valuable for the nutritional analysis of bee pollen. 相似文献
89.
Hai Hu Wenjun Xiao Jian Yuan Jianwei Shi Dannong He Wenfeng Shangguan 《Journal of Sol-Gel Science and Technology》2008,45(1):1-8
A set of anatase titanium dioxide (TiO2) films coated on foam nickel that modified by Al2O3 films as transition layer (indicated as TiO2/Al2O3 films) were synthesized via sol-gel route. The bulk and surface properties of the TiO2/Al2O3 films were characterized by thermal gravimetric and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD),
field-emission scanning electron microscope (FE-SEM), and BET. The photocatalytic activities of TiO2/Al2O3 films were investigated based on the degradation of gaseous acetaldehyde under ultraviolet (UV) irradiation. The foam nickel
is a promising substrate material in practical applications because of its excellent hydrodynamic properties for gas passing.
The TiO2/Al2O3 composite films showed much higher photocatalytic activity and stability for degradation of gaseous acetaldehyde than the
onefold TiO2 films. The significant enhancement in photocatalytic activity and stability can be ascribed to the coating of Al2O3 transition layer, which concentrates the target substances around TiO2 particles and increases the specific surface area (SSA) of the substrate (the SSAs of bare foam nickel and Al2O3 modified foam nickel are 0.12 and 113.7 m2/g, respectively) to provide more sites for TiO2 loading. 相似文献
90.
Hongmin Liu Xiaojiang Ye Zhiwei Lian Yuangao Wen Wenfeng Shangguan 《Research on Chemical Intermediates》2006,32(1):9-16
Formaldehyde is one of the most harmful pollutants that endanger occupants' health and the way of its effective removal has
become a focus in the field of air quality. This paper studies the static photocatalytic removal of formaldehyde experimentally
and finds out that carbon monoxide, which is more harmful to occupants' health than the formaldehyde itself, is one of the
by-products in the process of photocatalytic oxidation of formaldehyde. The increase of carbon monoxide concentration should
be taken into consideration in the photocatalytic application. The photocatalyst surface at room temperature can weakly adsorb
CO and CO2, which can deactivate the photocatalysts. 相似文献