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   2039篇
  免费   277篇
  国内免费   182篇
化学   1353篇
晶体学   42篇
力学   111篇
综合类   26篇
数学   256篇
物理学   710篇
  2023年   35篇
  2022年   57篇
  2021年   81篇
  2020年   78篇
  2019年   86篇
  2018年   73篇
  2017年   67篇
  2016年   99篇
  2015年   93篇
  2014年   123篇
  2013年   152篇
  2012年   172篇
  2011年   174篇
  2010年   112篇
  2009年   109篇
  2008年   144篇
  2007年   102篇
  2006年   105篇
  2005年   84篇
  2004年   78篇
  2003年   66篇
  2002年   79篇
  2001年   50篇
  2000年   51篇
  1999年   26篇
  1998年   17篇
  1997年   16篇
  1996年   19篇
  1995年   13篇
  1994年   10篇
  1993年   5篇
  1992年   5篇
  1991年   7篇
  1990年   4篇
  1987年   9篇
  1986年   7篇
  1985年   6篇
  1984年   6篇
  1983年   10篇
  1982年   9篇
  1981年   5篇
  1980年   4篇
  1979年   4篇
  1978年   8篇
  1976年   4篇
  1975年   4篇
  1974年   5篇
  1973年   4篇
  1970年   3篇
  1968年   6篇
排序方式: 共有2498条查询结果,搜索用时 15 毫秒
111.
本文通过乳液聚合法制备磁性离子印迹材料Fe3O4@SiO2@IIM,并运用多种技术手段对其进行了表征。所制备的Fe3O4@SiO2@IIM磁材料颗粒较均一,粒径约为20nm,单分散性好,具有超顺磁性(饱和磁化强度为8.66emu·g-1)。基于此,建立了离子印迹磁固相萃取(IIMSPE)-石墨炉原子吸收光谱法(GFAAS)联用技术分析环境水样中Ni(Ⅱ)的新方法。对影响MSPE的因素进行了详细的考察。在最优实验条件下,方法对Ni(Ⅱ)的检出限为0.015ng·mL-1,相对标准偏差(RSDs)为7.3%(n=7,c=0.1ng·mL-1),富集倍数为24.8,所制备的磁性离子印迹材料不同批次间RSDs为10.9%(n=5,c=0.1ng·mL-1),所合成的材料可以重复使用5次以上。采用该方法分析了标准水样(GSBZ50009-88)中的Ni(Ⅱ)含量,验证方法的准确性,测定值和标准值吻合良好。将该方法应用于东湖水和长江水中Ni(Ⅱ)的测定,加标回收率为90.6%~107.2%。  相似文献   
112.
Triazole-based deubiquitylase (DUB)-resistant ubiquitin (Ub) probes have recently emerged as effective tools for the discovery of Ub chain-specific interactors in proteomic studies, but their structural diversity is limited. A new family of DUB-resistant Ub probes is reported based on isopeptide-N-ethylated dimeric or polymeric Ub chains, which can be efficiently prepared by a one-pot, ubiquitin-activating enzyme (E1)-catalyzed condensation reaction of recombinant Ub precursors to give various homotypic and even branched Ub probes at multi-milligram scale. Proteomic studies using label-free quantitative (LFQ) MS indicated that the isopeptide-N-ethylated Ub probes may complement the triazole-based probes in the study of Ub interactome. Our study highlights the utility of modern protein synthetic chemistry to develop structurally and new families of tool molecules needed for proteomic studies.  相似文献   
113.
Volume expansion and poor conductivity are two major obstacles that hinder the pursuit of the lithium-ion batteries with long cycling life and high power density. Herein, we highlight a misfit compound PbNbS3 with a soft/rigid superlattice structure, confirmed by scanning tunneling microscopy and electrochemical characterization, as a promising anode material for high performance lithium-ion batteries with optimized capacity, stability, and conductivity. The soft PbS sublayers primarily react with lithium, endowing capacity and preventing decomposition of the superlattice structure, while the rigid NbS2 sublayers support the skeleton and enhance the migration of electrons and lithium ions, as a result leading to a specific capacity of 710 mAh g−1 at 100 mA g−1, which is 1.6 times of NbS2 and 3.9 times of PbS. Our finding reveals the competitive strategy of soft/rigid structure in lithium-ion batteries and broadens the horizons of single-phase anode material design.  相似文献   
114.
In this study, surface modification of coal gangue (CG) was performed with titanate coupling agent 201 (isopropyl tri(dioctylpyrophosphate) titanate), and the effects of surface modifier on mechanical properties and thermal stability of high-density polyethylene filled with CG (HDPE/CG) and high-density polyethylene filled with modified CG (HDPE/mCG) composites were investigated. The coupling agent was successfully grafted on CG surface through chemical reaction according to the analyses of Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), and the coupling agent can effectively enhance the hydrophobicity of surface that was verified by water contact angle beyond 90° of modified CG sample. With the introduction of coupling agent, some enhancements of tensile strength, flexural strength, and impact strength were observed in HDPE/mCG compared with HDPE/CG, due to the improved compatibility between mCG fillers and matrix. The increased storage modulus and decreased loss factor of HDPE/mCG composite further confirm the stronger interface adhesion after modification. Moreover, it is found that titanate coupling agent 201 can improve the thermal stability of HDPE/mCG composite to some extent.  相似文献   
115.
In this study, a small set of ancestry informative SNPs was selected to differentiate African, European, East and South Asian samples, which was detected by the next-generation sequencing technology. A total of 127 Chinese Shaanxi Han individuals were collected as test samples. No statistically significant linkage disequilibrium of any pair of loci or departure from Hardy–Weinberg equilibrium of each locus was observed in the test population. To evaluate the performance of ancestry assignment using this panel, admixture analysis, principal component analysis, and likelihood ratio calculations were conducted based on the 1000 genome data and test samples. All populations were clustered into four groups, African, European, South and East Asian populations, which were consistent with their geographical origins. The pairwise fixation index (FST) between populations from different continental groups ranged from 0.140 to 0.621 with average 0.415, and the pairwise FST between populations from the same continent ranged from 0.000 to 0.056 with average 0.012. The likelihood ratio results of 125 test individuals indicated that their ancestry components were highly possible from East Asia. In conclusion, this small set of ancestry informative SNPs can be used as a reliable tool to identify and quantify ancestry components of unknown samples.  相似文献   
116.
The molecular mechanisms for the photoconversion of fluorescent proteins remain elusive owing to the challenges of monitoring chromophore structural dynamics during the light-induced processes. We implemented time-resolved electronic and stimulated Raman spectroscopies to reveal two hidden species of an engineered ancestral GFP-like protein LEA, involving semi-trapped protonated and trapped deprotonated chromophores en route to photoconversion in pH 7.9 buffer. A new dual-illumination approach was examined, using 400 and 505 nm light simultaneously to achieve faster conversion and higher color contrast. Substitution of UV irradiation with visible light benefits bioimaging, while the spectral benchmark of a trapped chromophore with characteristic ring twisting and bridge-H bending motions enables rational design of functional proteins. With the improved H-bonding network and structural motions, the photoexcited chromophore could increase the photoswitching-aided photoconversion while reducing trapped species.  相似文献   
117.
将SnO2负载在碳球上通过不完全烧结的方法得到含有大量碳的空心状C@SnO2,随后加入TAA(硫代乙酰胺),利用离子交换法在水热过程中制备了具有不同硫化程度的空心结构的C@SnO2@SnS2三元复合物。利用XRD、FESEM、TEM、XPS、UV-Vis DRS、PL等测试手段对合成样品进行表征,并测试了其光催化去除Cr(VI)的性能。结果表明,C、SnO2和SnS2三者之间的协同作用以及空心结构的形貌显著增强了SnO2的光催化性能,其中CSS-2样品对Cr(VI)具有最佳的去除能力,太阳光照射120 min后对Cr(VI)的去除率高达98.8%。  相似文献   
118.
陈钦  郭依洁  张冲  张淑华 《合成化学》2020,28(10):869-874
利用水热法合成了4-(N,N′-双(4-羧基苄基)氨基)苯磺酸(H3L)的两个离子型配合物:[Mn(phen)2(H2O)2]?(HL)?(H2O)4(1)和[Zn(phen)2(H2O)2]?(HL)?(H2O)6(2, phen =邻菲罗啉),其结构经FL、 IR、元素分析、X-射线单晶衍射、 X-射线粉末衍射和TG表征。结果表明:化合物1属于单斜晶体,P21/c空间群,晶胞参数a=11.997(1) Å, b=22.978(1) Å, c=18.093(1) Å, β=92.749(3)°, V=4981.8(3) Å3, Z=4。化合物2属于单斜晶体,P21/c空间群,晶胞参数a=11.861(1) Å, b=22.816(1) Å, c=18.251(1) Å, β=92.832(5)°, V=4932.8(5) Å3,Z=4。化合物2有较好的荧光性质;初始分解温度为80 ℃。   相似文献   
119.
Unprecedented dual aggregation‐induced emission (AIE) behavior based on a steric‐hindrance photochromic system is presented, with incorporation one or two bulky aryl groups, resulting in different flexibleness. The dual AIE behavior of open and closed isomers can be explained by restriction of intramolecular rotation (RIR), restriction of intramolecular vibration (RIV), and intermolecular stacking. The large bulky benzothiophene causes restricted rotation, enhancing the emission of open form in solution and weak π–π molecular packing, thereby efficiently enhancing the luminescence performance in the solid state. With incorporation of two large bulky benzothiophene groups, BBTE possesses the most outstanding AIE activity, undergoing highly efficient and reversible off‐to‐on fluorescence in film upon alternating UV and visible light irradiation along with excellent fatigue resistance. The off‐to‐on fluorescent photoswitch is successfully established in super resolution imaging.  相似文献   
120.
Asymmetric hydrogenation has evolved as one of the most powerful tools to construct stereocenters. However, the asymmetric hydrogenation of unfunctionalized tetrasubstituted acyclic olefins remains the pinnacle of asymmetric synthesis and an unsolved challenge. We report herein the discovery of an iridium catalyst for the first, generally applicable, highly enantio‐ and diastereoselective hydrogenation of such olefins and the mechanistic insights of the reaction. The power of this chemistry is demonstrated by the successful hydrogenation of a wide variety of electronically and sterically diverse olefins in excellent yield and high enantio‐ and diastereoselectivity.  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