全文获取类型
收费全文 | 11258篇 |
免费 | 614篇 |
国内免费 | 382篇 |
专业分类
化学 | 7089篇 |
晶体学 | 77篇 |
力学 | 453篇 |
综合类 | 40篇 |
数学 | 1492篇 |
物理学 | 3103篇 |
出版年
2023年 | 105篇 |
2022年 | 334篇 |
2021年 | 329篇 |
2020年 | 331篇 |
2019年 | 296篇 |
2018年 | 235篇 |
2017年 | 237篇 |
2016年 | 447篇 |
2015年 | 383篇 |
2014年 | 408篇 |
2013年 | 694篇 |
2012年 | 730篇 |
2011年 | 853篇 |
2010年 | 535篇 |
2009年 | 525篇 |
2008年 | 667篇 |
2007年 | 664篇 |
2006年 | 579篇 |
2005年 | 543篇 |
2004年 | 439篇 |
2003年 | 388篇 |
2002年 | 322篇 |
2001年 | 196篇 |
2000年 | 145篇 |
1999年 | 145篇 |
1998年 | 99篇 |
1997年 | 97篇 |
1996年 | 136篇 |
1995年 | 110篇 |
1994年 | 125篇 |
1993年 | 87篇 |
1992年 | 71篇 |
1991年 | 68篇 |
1990年 | 73篇 |
1989年 | 63篇 |
1988年 | 50篇 |
1987年 | 46篇 |
1986年 | 36篇 |
1985年 | 55篇 |
1984年 | 79篇 |
1983年 | 37篇 |
1982年 | 61篇 |
1981年 | 50篇 |
1980年 | 45篇 |
1979年 | 56篇 |
1978年 | 47篇 |
1977年 | 28篇 |
1976年 | 29篇 |
1975年 | 29篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Hammad Ullah Alessandro Di Minno Cristina Santarcangelo Haroon Khan Jianbo Xiao Carla Renata Arciola Maria Daglia 《Molecules (Basel, Switzerland)》2021,26(8)
Helicobacter pylori (H. pylori) infections affect almost half of the world’s population, with gradually increasing incidence in developed countries. Eradication of H. pylori may provide significant benefits to the affected individual by healing a number of gastrointestinal and extra-digestive disorders. But due to increased microbial resistance and lack of patient adherence to the therapy, the eradication rate of H. pylori is below 80% with current pharmacological therapies. The usage of botanicals for their therapeutic purposes and medicinal properties have been increased in last decades. They can be use as alternative H. pylori treatments, especially against drug-resistant strains. Epidemiological studies have revealed that people with lower vegetable and micronutrient intake may be at increased risk of H. pylori infection. We have undertaken a review of clinical trials to evaluate the efficacy of vegetable extracts and micronutrients in patients with H. pylori. Various databases, such as Google Scholar, PubMed, Scopus, Web of Science, and the Cochrane Library, were searched for the articles published in English. A total of 24 clinical studies (15 for vegetable extracts and 9 for micronutrients) were selected to be reviewed and summarized in this article. Vegetable extracts (Broccoli sprouts, curcumin, Burdock complex, and Nigella sativa) and micronutrients (vitamin C and E) were not found to be as effective as single agents in H. pylori eradication, rather their efficacy synergized with conventional pharmacological therapies. Conversely, GutGard was found to be significantly effective as a single agent when compared to placebo control. 相似文献
992.
José W. D. Coutinho André M. B. S. Sampaio Iranaldo S. da Silva Flávio Colmati Roberto B. de Lima 《Journal of Solid State Electrochemistry》2018,22(10):3147-3159
The electrooxidation of ethylene glycol was studied using platinum–cadmium electrocatalysts supported on high surface area carbon Vulcan XC-72. This is the first instance of Cd being used as an electrocatalyst for glycol oxidation reaction. The catalysts were prepared with various Pt:Cd atomic ratios of 90:10, 80:20, and 70:30. All the catalysts prepared were synthesized by the alcohol reduction method with 20 wt.% metal on carbon. These materials were characterized morphologically by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) and electrochemically by cyclic voltammetry and chronoamperometry. The electrochemical measurements were carried out at 25, 35, 45, and 55 °C, and the products of the electrochemical reaction were monitored by high-performance liquid chromatography (HPLC). The XRD patterns of all the PtCd catalysts presented cubic face-centered structures, and TEM revealed a homogeneous particle distribution on the carbon support with low agglomeration. The average particle size was assumed to be the maximum of the Gaussian distribution curve of particle size, at close to 2.5 nm. The presence of Cd results in an improvement in the glycol oxidation reaction, as observed by cyclic voltammetry; linear sweep voltammetry shows a lower onset potential compared to that of pure platinum. At a constant potential of 0.50 V (vs. RHE) at ambient temperature, HPLC showed glycolaldehyde to be the main byproduct formed from ethylene glycol oxidation at potential constant of 0.50 V. 相似文献
993.
994.
A Biodegradable Polydopamine‐Derived Electrode Material for High‐Capacity and Long‐Life Lithium‐Ion and Sodium‐Ion Batteries 下载免费PDF全文
Tao Sun Zong‐jun Li Heng‐guo Wang Di Bao Fan‐lu Meng Prof. Xin‐bo Zhang 《Angewandte Chemie (International ed. in English)》2016,55(36):10662-10666
Polydopamine (PDA), which is biodegradable and is derived from naturally occurring products, can be employed as an electrode material, wherein controllable partial oxidization plays a key role in balancing the proportion of redox‐active carbonyl groups and the structural stability and conductivity. Unexpectedly, the optimized PDA derivative endows lithium‐ion batteries (LIBs) or sodium‐ion batteries (SIBs) with superior electrochemical performances, including high capacities (1818 mAh g?1 for LIBs and 500 mAh g?1 for SIBs) and good stable cyclabilities (93 % capacity retention after 580 cycles for LIBs; 100 % capacity retention after 1024 cycles for SIBs), which are much better than those of their counterparts with conventional binders. 相似文献
995.
Franco Gatta Maria Rosaria Del Giudice Luciano Di Simone Guido Settimj 《Journal of heterocyclic chemistry》1980,17(5):865-868
A new synthesis of 7-chloro-2,3-diamino-5-phenyl-3H-1,4-benzodiazepines is described, which allows for the preparation of compounds bearing the same or different substituents at the 2 and 3 positions, starting from 2-amino-7-chloro-3-hydroxy-5-phenyl-3H-1,4-benzodiazepines. 相似文献
996.
After the preparation of 1,4-bis(4,5-dihydro-1H-imidazol-2-yl)benzene(bdib),a nitrogen heterocycle with potential coordination manners of both cis-and tram-configuration forms,three complexes,including successfully self-assembled.Complexes 1 and 2 crystallized in the monoclinic system with P21/n space group and complex 3 in the triclinic system with P1 space group. 相似文献
997.
Meriem Mokhtar Sarah Bouamar Arianna Di Lorenzo Caterina Temporini Maria Daglia Ali Riazi 《Molecules (Basel, Switzerland)》2021,26(12)
Cucurbita moschata Duchesne (Cucurbitaceae) is a plant food highly appreciated for the content of nutrients and bioactive compounds, including polyphenols and carotenoids, which contribute to its antioxidant and antimicrobial capacities. The purpose of this study was to identify phenolic acids and flavonoids of Cucurbita moschata Duchesne using high-performance liquid chromatography–diode array detection–electrospray ionization tandem mass spectrometry (HPLC–DAD–ESI-MS) at different ripening stages (young, mature, ripened) and determine its antioxidant and antimicrobial activities. According to the results, phenolic acids and flavonoids were dependent on the maturity stage. The mature fruits contain the highest total phenolic and flavonoids contents (97.4 mg GAE. 100 g−1 and 28.6 mg QE. 100 g−1).A total of 33 compounds were identified. Syringic acid was the most abundant compound (37%), followed by cinnamic acid (12%) and protocatechuic acid (11%). Polyphenol extract of the mature fruits showed the highest antioxidant activity when measured by DPPH (0.065 μmol TE/g) and ABTS (0.074 μmol TE/g) assays. In the antimicrobial assay, the second stage of ripening had the highest antibacterial activity. Staphylococcus aureus was the most sensitive strain with an inhibition zone of 12 mm and a MIC of 0.75 mg L−1. The lowest inhibition zone was obtained with Salmonella typhimurium (5 mm), and the MIC value was 10 mg L−1. 相似文献
998.
An electrothermal atomic absorption (ETAAS) method for the determination of traces of iron (0.1-1.0 microgram g-1) in Fe-doped indium phosphide (InP) has been developed. In order to overcome the indium matrix-effect and to achieve a useful detection limit, a preliminary solvent-extraction of Fe(III) with acetylacetone (HAA) is necessary. After sample dissolution with hydrochloric acid (1 + 1) the digest is evaporated to dryness, Fe(II) is oxidized to Fe(III) with nitric acid, the residue is dissolved in 0.01 mol L-1 HCl and the iron is extracted at pH 2.0 with 0.5 mol L-1 HAA in toluene. The organic phase is injected into the graphite furnace and the iron is directly evaluated by external organic standard calibration. The limit of detection (3SB) resulting from further in-situ preconcentration is 0.03 microgram g-1. When the method was applied to the analysis of real samples containing 0.2-0.7 microgram g-1 Fe, the RSD was in the range 8-21%. Results were compared with those independently obtained on the decomposed sample solution with inductively coupled atomic emission spectrometry (ICP-AES). The detection limit of the ICP-AES method, that needs matrix-matched standards, is 0.20 microgram g-1. 相似文献
999.
Synthesis, characterization and hydrodesulfurization activity of silica-dispersed NiMoW trimetallic catalysts 下载免费PDF全文
Silica-dispersed NiMoW trimetallic hydrodesulfurization catalysts were prepared by deposition-precipitation method. For comparative purposes, bulk NiMoW trimetallic catalysts were obtained by co-precipitation. Silica was employed to disperse active metals for full utilization of active components and silica-dispersed NiMoW catalyst had high active metal content. BET analysis showed that silica-dispersed NiMoW trimetallic catalysts had a high surface area (165.1 m2/g) and pore volume (0.27 ml/g). Transmission electron microscopy results proved that active components were well dispersed. Hydrodesulfurization activity of silica-dispersed NiMoW catalysts was much higher than that of comparative catalysts and up to twice greater than those of commercial NiMo alumina-supported systems per gram of catalyst. 相似文献
1000.
研究了油/水界面电解的示差半微分循环伏安行为。在0.01mol/L LiCl(w)-0.01mol/L TBATCIPB(nb)体系“电位窗”比TBATPB(nb)向正方向扩展约50mV,残余电流基本消除,使“电位窗”内的平台向左右拓宽约50mV。算得界面电容约为16μF/cm~2。考察了琥珀酰胆碱离子在w/nb界面的传递伏安特性,结果与一般半微分循环伏安法相似。但峰形改善,检测限降低一个数量级(1×10~(-6)mol/L),相对标准偏差在5%以内,可用于定量测定琥珀酰胆碱。 相似文献