首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   16190篇
  免费   2608篇
  国内免费   1721篇
化学   8164篇
晶体学   162篇
力学   853篇
综合类   106篇
数学   1290篇
物理学   4965篇
无线电   4979篇
  2024年   68篇
  2023年   464篇
  2022年   579篇
  2021年   775篇
  2020年   658篇
  2019年   630篇
  2018年   542篇
  2017年   527篇
  2016年   756篇
  2015年   778篇
  2014年   910篇
  2013年   1132篇
  2012年   1374篇
  2011年   1330篇
  2010年   1012篇
  2009年   1007篇
  2008年   977篇
  2007年   896篇
  2006年   890篇
  2005年   768篇
  2004年   496篇
  2003年   431篇
  2002年   427篇
  2001年   318篇
  2000年   300篇
  1999年   323篇
  1998年   287篇
  1997年   269篇
  1996年   272篇
  1995年   231篇
  1994年   197篇
  1993年   132篇
  1992年   130篇
  1991年   112篇
  1990年   105篇
  1989年   85篇
  1988年   69篇
  1987年   33篇
  1986年   48篇
  1985年   32篇
  1984年   22篇
  1983年   21篇
  1982年   17篇
  1981年   8篇
  1980年   11篇
  1975年   8篇
  1973年   5篇
  1972年   7篇
  1965年   6篇
  1964年   5篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
261.
In the present study, a specific and sensitive approach using ultra-high-performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry was developed and validated for the quantitative analysis of 14 constituents in rat plasma, liver, and heart. The method was fully validated and successfully applied to pharmacokinetic, hepatic disposition, and heart tissue distribution studies of 14 compounds after the oral administration of Qi-Li-Qiang-Xin capsule. Ginsenoside Rb1, alisol A, astragaloside IV, and periplocymarin were found to be highly exposed in rat plasma, while toxic components such as hypaconitine, mesaconitine, and periplocin had low circulation levels in vivo. Moreover, sinapine thiocyanate, neoline, formononetin, calycosin, and alisol A exhibited significant liver first-pass effects. Notably, high levels of alisol A, periplocymarin, benzoylmesaconine, and benzoylhypaconine were observed in the heart. Based on high exposure and appropriate pharmacokinetic features in the systemic plasma and heart, astragaloside IV, ginsenoside Rb1, periplocymarin, benzoylmesaconine, benzoylhypaconine, and alisol A can be considered as the main potentially effective components. Ultimately, the results provide relevant information for discovery of effective substances, as well as further anti-heart failure action mechanism investigations of Qi-Li-Qiang-Xin capsule.  相似文献   
262.
双金属有机骨架及其衍生物一方面具有单金属有机骨架孔道丰富、比表面积大、结构可调、活性位点丰富等特点,另一方面具有双组分与多孔结构之间的协同效应,因而受到了研究人员的密切关注,在储能、催化、分离、传感器、医药、气体存储等领域广泛应用。和单金属MOFs类似,双金属MOFs的导电性不佳、结构易坍塌,这极大地限制了其在电化学储能中的应用。通过对双金属MOFs进行热处理,易得到分布均匀的多孔碳@双金属氧化物/硫化物/磷化物/硒化物等衍生物,不仅保持了独特的多孔结构,而且提高了材料的导电性和结构稳定性,有利于在电化学储能中的应用。因此,本文从双金属MOFs中的主要金属离子入手,综述了双金属MOFs及其衍生物用于超级电容器、锂离子电池、钠离子电池、金属空气电池等电化学储能器件的最新应用进展。在此基础上,总结了双金属MOFs在电化学储能应用中的优势,并对其制备、作用机理和后处理研究提出了建议。  相似文献   
263.
Polymyxin-based combination therapy is commonly used to treat carbapenem-resistant Acinetobacter baumannii (CRAB) infections. In the present study, the bactericidal effect of polymyxin B and minocycline combination was tested in three CRAB strains containing blaOXA-23 by the checkerboard assay and in vitro dynamic pharmacokinetics/pharmacodynamics (PK/PD) model. The combination showed synergistic or partial synergistic effect (fractional inhibitory concentration index ≤0.56) on the tested strains in checkboard assays. The antibacterial activity was enhanced in the combination group compared with either monotherapy in in vitro PK/PD model. The combination regimen (simultaneous infusion of 0.75 mg/kg polymyxin B and 100 mg minocycline via 2 h infusion) reduced bacterial colony counts by 0.9–3.5 log10 colony forming units per milliliter (CFU/mL) compared with either drug alone at 24 h. In conclusion, 0.75 mg/kg polymyxin B combined with 100 mg minocycline via 2 h infusion could be a promising treatment option for CRAB bloodstream infections.  相似文献   
264.
The ultrasound-induced cleavage of covalent and non-covalent bonds to activate drugs (sonopharmacology) is a promising concept to gain control over the action of active pharmaceutical ingredients by an external trigger. Previously, linear polymer architectures bearing drug payloads were exploited for drug release by using the principles of polymer mechanochemistry. In this work, the carrier design is altered by the polymer topology to improve the ultrasound-triggered release of covalently anchored drugs from polymer scaffolds. We use microgels crosslinked by mechanoresponsive disulfides and copolymerized with Diels-Alder adducts of furylated payload molecules and acetylenedicarboxylate. Force-induced thiol formation induces a Michael-type addition liberating the payload from the microgels. The use of microgels significantly reduces sonication times compared to linear polymer chains and shields the cargo efficiently from non-triggered activation using ultrasound that produces inertial cavitation at a frequency of 20 kHz as model condition.  相似文献   
265.
The synthesis of hyper-branched ethene oligomers through catalytic insertion reactions with late transition metal catalysts is unique in its synthetic and practical scope. In this study, a series of iminopyridyl Ni(II) and Pd(II) complexes with electron-rich distal aryl motifs were synthesized and characterized. These complexes were very efficient in ethene oligomerization and co-oligomerization with methyl acrylate (MA). Hyperbranched ethene oligomers with different microstructures were generated using different metal species in ethene oligomerization. More importantly, hyperbranched ethene-MA co-oligomers with varying incorporation ratios were generated via ethene and MA co-oligomerization using the Pd(II) complexes. Most notably, weak neighboring group interactions of distal aryl motifs in the nickel system are more effective in influencing the microstructure of ethene oligomers than the corresponding palladium system.  相似文献   
266.
Natural fibers containing components with phenolic hydroxyl groups, such as jute, wool, and silk, can be directly modified by laccase-catalyzed grafting. However, cellulosic fibers like cotton cannot be functionalized in this manner. In this work, we developed a facile two-step method to graft polymers on cotton fabric via laccase catalysis. First, polydopamine (PDA) coating was deposited on the surface of the cotton fabrics via catalysis of laccase/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) system. Then, the newly formed PDA coating acted as the secondary reaction platform for subsequent laccase-mediated grafting of hydrophobic monomer dodecyl gallate (DG). The oxidation of dopamine (DA) catalyzed with the laccase/TEMPO system was investigated using UV–visible (UV–vis) spectroscopy. The scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) results verified that the PDA was coated on the surface of cotton fibers. Fourier transform infrared (FTIR) spectra indicated that the PDA-coated cotton was successfully grafted with DG (DG-PDA-cotton). According to the weighting method, the grafting percentage was about 1.06%. The hydrophobicity of the DG-PDA-cotton fabrics was greatly improved with a contact angle of 133°. Also, the grafted cotton fabrics show repellency of water-soluble stains like coffee, milk, and tea. This study provides a new strategy for surface modification of cotton by laccase-mediated grafting, which offers the references for the green fabrication of cotton fabrics with improved functionalization.  相似文献   
267.
Fan  Xuemei  Liu  Yandan  Fan  Xinhui  Nan  Yue  Su  Lingling  Wang  Shumin  Wang  Yimeng  Wang  Xiangting 《分析试验室》2022,(9):1029-1033
N and S co-doped graphene quantum dotsNS-GQDswith excellent fluorescence properties were synthesized by hydrothermal method using citrate and thiourea as ingredientsand were characterized. The fluorescence signal was notably reduced in the presence of single stranded DNAssDNAsince ssDNA can adsorb on the surface of NS-GQDs through p-p stacking interaction. Whereas a significantly restored fluorescence signal was observed in the presence of bleomycinowing to the irreversible cleavage of ssDNA by bleomycin with Fe2+ as cofactor. Thusa fluorescence sensor for bleomycin detection was developed. The linear range was from 1.8 to 1200 nmol/L and the detection limit was 0.25 nmol/L. The method was used to detect bleomycin content in human serum samples with satisfactory results. © 2022, Youke Publishing Co.,Ltd. All rights reserved.  相似文献   
268.
本文报导了X射线衍射法确定的三氯化钕异丙醇络合物[NdCl3·(CH3CHOHCH3)3]2的晶体结构。在晶体中每二个钕离子通过二个氯离子形成的氯桥相联,组成一个双核稀土络合物分子。其中每个Nd离子是七配位的。  相似文献   
269.
氢气(H2)具有能量密度高、环境友好等优点,是一种很有前景的清洁能源载体.目前,电催化水裂解大规模制氢被认为是一种理想可行的方法.析氢反应(HER)涉及多个步骤,首先形成吸附的氢(Volmer步骤),然后是脱附步骤(Heyrovsky步骤)或两个相邻的吸附氢形成H2(Tafel步骤).与酸性介质相比,碱性介质中的HER...  相似文献   
270.
析氢反应是电解水产制氢的关键反应之一.在碱性条件下,由于催化剂表面与反应过程中产生的氧物种、氢物种与催化剂的吸附未处于最佳状态,析氢反应动力学往往比较缓慢,比在酸性条件下慢2-3个数量级.目前,铂基纳米催化剂被认为是最优的析氢催化剂,但因价格昂贵、稳定性较差,限制了其在电解水器件上的大规模应用.因此,设计一种价格较为低...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号