全文获取类型
收费全文 | 1581篇 |
免费 | 304篇 |
国内免费 | 143篇 |
专业分类
化学 | 996篇 |
晶体学 | 9篇 |
力学 | 84篇 |
综合类 | 28篇 |
数学 | 214篇 |
物理学 | 697篇 |
出版年
2024年 | 3篇 |
2023年 | 29篇 |
2022年 | 23篇 |
2021年 | 39篇 |
2020年 | 60篇 |
2019年 | 65篇 |
2018年 | 54篇 |
2017年 | 35篇 |
2016年 | 69篇 |
2015年 | 63篇 |
2014年 | 79篇 |
2013年 | 106篇 |
2012年 | 127篇 |
2011年 | 144篇 |
2010年 | 81篇 |
2009年 | 88篇 |
2008年 | 83篇 |
2007年 | 92篇 |
2006年 | 93篇 |
2005年 | 78篇 |
2004年 | 76篇 |
2003年 | 49篇 |
2002年 | 49篇 |
2001年 | 27篇 |
2000年 | 27篇 |
1999年 | 40篇 |
1998年 | 35篇 |
1997年 | 25篇 |
1996年 | 36篇 |
1995年 | 29篇 |
1994年 | 27篇 |
1993年 | 26篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1973年 | 4篇 |
1930年 | 1篇 |
排序方式: 共有2028条查询结果,搜索用时 15 毫秒
961.
A dispersive liquid–liquid microextraction procedure coupled with GC‐MS is described for preconcentration and determination of banned aromatic amines from textile samples. Experimental conditions affecting the microextraction procedure were optimized. A mixture of 30 μL chlorobenzene (extraction solvent) and 800 μL ACN (disperser solvent), 5 min extraction time, and 5 mL aqueous sample volume were chosen for the best extraction efficiency by the proposed procedure. Satisfactory linearity (with correlation coefficients >0.9962) and repeatability (<9.78%) were obtained for all 20 aromatic amines; detection limits attained were much lower than the standardized liquid–liquid method. The proposed method has advantages of being quicker and easier to operate, and lower consumption of organic solvent. 相似文献
962.
Fengliu Lou Haitao Zhou Fride Vullum-Bruer Trung Dung Tran De Chen 《Journal of Energy Chemistry》2013,22(1):78-86
A 3D structured composite of carbon nanofibers@MnO2 on copper foil is reported here as a binder free anode of lithium ion batteries, with high capacity, fast charge/discharge rate and good stability. Carbon nanofiber yarns were synthesized directly over copper foil through a floating catalyst method. The growth of carbon nanofiber yarns was significantly enhanced by mechanical polishing of the copper foils, which can be attributed to the increased surface roughness and surface area of the copper foils. MnO2 was then grown over carbon nanofibers through spontaneous reduction of potassium permanganate by the carbon nanofibers. The obtained composites of carbon nanofibers@MnO2 over copper foil were tested as an anode in lithium ion batteries and they show superior electrochemical performance. The initial reversible capacity of carbon nanofibers@MnO2 reaches up to around 998 mAh·g?1 at a rate of 60 mmA·g?1 based on the mass of carbon nanofibers and MnO2. The carbon nanofibers@MnO2 electrodes could deliver a capacity of 630 mAh·g?1 at the beginning and maintain a capacity of 440 mmAh·g?1 after 105 cycles at a rate of 600 mA·g?1. The high initial capacity can be attributed to the presence of porous carbon nanofiber yarns which have good electrical conductivity and the MnO2 thin film which makes the entire materials electrochemically active. The high cyclic stability of carbon nanofibers@MnO2 can be ascribed to the MnO2 thin film which can accommodate the volume expansion and shrinking during charge and discharge and the good contact of carbon nanofibers with MnO2 and copper foil. 相似文献
963.
Weiren Cheng Xue Feng Lu Deyan Luan Xiong Wen Lou 《Angewandte Chemie (International ed. in English)》2020,59(41):18234-18239
Developing noble‐metal‐free bifunctional oxygen electrocatalysts is of great significance for energy conversion and storage systems. Herein, we have developed a transformation method for growing NiMn‐based bimetal–organic framework (NiMn‐MOF) nanosheets on multi‐channel carbon fibers (MCCF) as a bifunctional oxygen electrocatalyst. Owing to the desired components and architecture, the MCCF/NiMn‐MOFs manifest comparable electrocatalytic performance towards oxygen reduction reaction (ORR) with the commercial Pt/C electrocatalyst and superior performance towards oxygen evolution reaction (OER) to the benchmark RuO2 electrocatalyst. X‐ray absorption fine structure (XAFS) spectroscopy and density functional theory (DFT) calculations reveal that the strong synergetic effect of adjacent Ni and Mn nodes within MCCF/NiMn‐MOFs effectively promotes the thermodynamic formation of key *O and *OOH intermediates over active NiO6 centers towards fast ORR and OER kinetics. 相似文献
964.
Xiao-Yu Liu Xiao-Ling Wang Tao Shen Dong-Mei Ren Hong-Xiang Lou 《Natural product research》2020,34(15):2179-2185
AbstractOne new pentanortriterpenoid, 23,24,25,26,27-pentanorlanost-7,9(11)-dien-3β,22-diol (1), one new triterpenoid, lanost-8-en-3β,22S,23S-triol (2), together with the known triterpenoid, 23,24,25,26,27-pentanorlanost-8-en-3β,22-diol (3), were obtained from culture of the fungus Diplodia cupressi associated with the moss Polytrichum commune. The structures of the new compounds were elucidated by extensive spectroscopic techniques including HR-ESIMS and 1?D and 2?D NMR experiments. The cytotoxicity of these compounds against human cancer cell lines (A549, Hep G2, Hepa 1c1c7, and Hela) was evaluated and compound 2 exhibited weak inhibitory activity with IC50 value of 35.0?±?2.3?μM against the proliferation of the Hepa 1c1c7 cells. 相似文献
965.
966.
Xue Feng Lu Bao Yu Xia Shuang‐Quan Zang Xiong Wen Lou 《Angewandte Chemie (International ed. in English)》2020,59(12):4634-4650
In view of the clean and sustainable energy, metal–organic frameworks (MOFs) based materials, including pristine MOFs, MOF composites, and their derivatives are emerging as unique electrocatalysts for oxygen reduction reaction (ORR). Thanks to their tunable compositions and diverse structures, efficient MOF‐based materials provide new opportunities to accelerate the sluggish ORR at the cathode in fuel cells and metal–air batteries. This Minireview first provides some introduction of ORR and MOFs, followed by the classification of MOF‐based electrocatalysts towards ORR. Recent breakthroughs in engineering MOF‐based ORR electrocatalysts are highlighted with an emphasis on synthesis strategy, component, morphology, structure, electrocatalytic performance, and reaction mechanism. Finally, some current challenges and future perspectives for MOF‐based ORR electrocatalysts are also discussed. 相似文献
967.
Dr. Yi Huang Dr. Yongjin Fang Dr. Xue Feng Lu Dr. Deyan Luan Prof. Xiong Wen Lou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):20086-20090
Confining nanostructured electrode materials in porous carbon represents an effective strategy for improving the electrochemical performance of lithium-ion batteries. Herein, we report the design and synthesis of hybrid hollow nanostructures composed of highly dispersed Co3O4 hollow nanoparticles (sub-20 nm) embedded in the mesoporous walls of carbon nanoboxes (denoted as H-Co3O4@MCNBs) as an anode material for lithium-ion batteries. The facile metal–organic framework (MOF)-engaged strategy for the synthesis of H-Co3O4@MCNBs involves chemical etching-coordination and subsequent two-step annealing treatments. Owing to the unique structural merits including more active interfacial sites, effectively alleviated volume variation, good and stable electrical contact, and easy access of Li+ ions, the H-Co3O4@MCNBs exhibit excellent lithium-storage performance in terms of high specific capacity, excellent rate capability, and cycling stability. 相似文献
968.
Louíse Jank Rodrigo Barcellos Hoff Flávia Justina da Costa Tânia Mara Pizzolato 《International journal of environmental analytical chemistry》2013,93(10):1013-1037
A reliable multiclass method has been developed and validated for the determination of eight antibiotics from distinct classes (sulfonamides, macrolides, fluoroquinolones, tetracyclines, cephalosporins and dihydrofolate reductase inhibitors) in wastewater – influent and effluent – and surface water from Porto Alegre, Brazil. The pre-concentration and clean-up was conducted with a simple and fast protocol using solid-phase extraction allowing a 100-fold concentration factor. The proposed method was validated by using spiked blank wastewater samples in terms of linearity, repeatability, reproducibility, recovery, matrix effects and limits of detection and quantification. Recovery was obtained in the range of 66–149%. Method limit of quantification ranged between 1.6 and 61.7 ng L?1. Samples (n = 16) were taken from January to August 2011 in one wastewater treatment plant, which uses conventional biological treatment. Sulfamethoxazole and trimethoprim show higher concentration, ranging from >10 to <6500 ng L?1, whereas erythromycin presented the lower amount. Differences between influent and effluent profiles were discussed. Surface water samples (n = 8) were collected in Arroio Diluvio, in four sampling points, in February 2012. From the eight antibiotics analysed, five were detected: sulfamethoxazole, trimethoprim, azythromicyn, ciprofloxacin and norfloxacin, in a concentration range of 376–572 ng L?1, 27–94 ng L?1, 24–40 ng L?1, 16–66ng L?1 and 30–54 ng L?1, respectively. 相似文献
969.
Dr. Anqiang Pan Ting Zhu Hao Bin Wu Prof. Xiong Wen Lou 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(2):494-500
Nanosheet‐assembled hierarchical V2O5 hollow microspheres are successfully obtained from V‐glycolate precursor hollow microspheres, which in turn are synthesized by a simple template‐free solvothermal method. The structural evolution of the V‐glycolate hollow microspheres has been studied and explained by the inside‐out Ostwald‐ripening mechanism. The surface morphologies of the hollow microspheres can be controlled by varying the mixture solution and the solvothermal reaction time. After calcination in air, hierarchical V2O5 hollow microspheres with a high surface area of 70 m2 g?1 can be obtained and the structure is well preserved. When evaluated as cathode materials for lithium‐ion batteries, the as‐prepared hierarchical V2O5 hollow spheres deliver a specific discharge capacity of 144 mA h g?1 at a current density of 100 mA g?1, which is very close to the theoretical capacity (147 mA h g?1) for one Li+ insertion per V2O5. In addition, excellent rate capability and cycling stability are observed, suggesting their promising use in lithium‐ion batteries. 相似文献
970.
光子器件激光封装中热致角度偏移的降低 总被引:1,自引:0,他引:1
对光电子器件激光封装中光纤准直器的热致角度偏移进行了实验研究和理论分析.设计了一种新型的拱形焊接支承架,并对其热稳定性进行了测试.测试结果表明,在加载十个连续的温度循环周期后,其角度偏移为0.01°,而在同样的测试条件下,传统的鞍形支承架的角度偏移达到0.023°.采用非线性热—应力耦合有限元模型对封装结构中热应力的变化、残余应力的分布以及准直器角度偏移进行分析.理论分析结果与实验结果极好地吻合.进一步的理论计算得到新型拱形支承架的饱和热致角度偏移为0.043°,与传统鞍形支承架的0.065°相比得到了较大的降低. 相似文献