全文获取类型
收费全文 | 7599篇 |
免费 | 817篇 |
国内免费 | 522篇 |
专业分类
化学 | 5332篇 |
晶体学 | 96篇 |
力学 | 406篇 |
综合类 | 46篇 |
数学 | 685篇 |
物理学 | 2373篇 |
出版年
2024年 | 3篇 |
2023年 | 109篇 |
2022年 | 117篇 |
2021年 | 246篇 |
2020年 | 271篇 |
2019年 | 265篇 |
2018年 | 193篇 |
2017年 | 208篇 |
2016年 | 307篇 |
2015年 | 279篇 |
2014年 | 360篇 |
2013年 | 552篇 |
2012年 | 698篇 |
2011年 | 696篇 |
2010年 | 491篇 |
2009年 | 433篇 |
2008年 | 545篇 |
2007年 | 459篇 |
2006年 | 433篇 |
2005年 | 371篇 |
2004年 | 319篇 |
2003年 | 258篇 |
2002年 | 220篇 |
2001年 | 154篇 |
2000年 | 110篇 |
1999年 | 113篇 |
1998年 | 96篇 |
1997年 | 80篇 |
1996年 | 80篇 |
1995年 | 73篇 |
1994年 | 48篇 |
1993年 | 54篇 |
1992年 | 49篇 |
1991年 | 52篇 |
1990年 | 26篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1973年 | 3篇 |
1971年 | 6篇 |
1970年 | 6篇 |
排序方式: 共有8938条查询结果,搜索用时 31 毫秒
21.
A New Concept for Obtaining SnO2 Fiber‐in‐Tube Nanostructures with Superior Electrochemical Properties 下载免费PDF全文
Young Jun Hong Ji‐Wook Yoon Prof. Jong‐Heun Lee Prof. Yun Chan Kang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):371-376
Tin oxide (SnO2) nanotubes with a fiber‐in‐tube structure have been prepared by electrospinning and the mechanism of their formation has been investigated. Tin oxide‐carbon composite nanofibers with a filled structure were formed as an intermediate product, which were then transformed into SnO2 nanotubes with a fiber‐in‐tube structure during heat treatment at 500 °C. Nanofibers with a diameter of 85 nm were found to be located inside hollow nanotubes with an outer diameter of 260 nm. The prepared SnO2 nanotubes had well‐developed mesopores. The discharge capacities of the SnO2 nanotubes at the 2nd and 300th cycles at a current density of 1 A g?1 were measured as 720 and 640 mA h g?1, respectively, and the corresponding capacity retention measured from the 2nd cycle was 88 %. The discharge capacities of the SnO2 nanotubes at incrementally increased current densities of 0.5, 1.5, 3, and 5 A g?1 were 774, 711, 652, and 591 mA h g?1, respectively. The SnO2 nanotubes with a fiber‐in‐tube structure showed superior cycling and rate performances compared to those of SnO2 nanopowder. The unique structure of the SnO2 nanotubes with a fiber@void@tube configuration improves their electrochemical properties by reducing the diffusion length of the lithium ions, and also imparts greater stability during electrochemical cycling. 相似文献
22.
23.
Inside Cover: Selective Transformation of Syngas into Gasoline‐Range Hydrocarbons over Mesoporous H‐ZSM‐5‐Supported Cobalt Nanoparticles (Chem. Eur. J. 5/2015) 下载免费PDF全文
24.
Jongeun Kang Eunha Hwang Hyunseung Lee Mi Young Cho Sanu Karan Hak Nam Kim Jong Seung Kim Jonathan L. Sessler Sankarprasad Bhuniya Kwan Soo Hong 《Molecules (Basel, Switzerland)》2021,26(7)
We have synthesized new magnetic resonance imaging (MRI) T1 contrast agents (CA1 and CA2) that permit the activatable recognition of the cellular vicinal thiol motifs of the protein thioredoxin. The contrast agents showed MR relaxivities typical of gadolinium complexes with a single water molecule coordinated to a Gd3+ center (i.e., ~4.54 mM−1s−1) for both CA1 and CA2 at 60 MHz. The contrast agent CA1 showed a ~140% relaxivity enhancement in the presence of thioredoxin, a finding attributed to a reduction in the flexibility of the molecule after binding to thioredoxin. Support for this rationale, as opposed to one based on preferential binding, came from 1H-15N-HSQC NMR spectral studies; these revealed that the binding affinities toward thioredoxin were almost the same for both CA1 and CA2. In the case of CA1, T1-weighted phantom images of cancer cells (MCF-7, A549) could be generated based on the expression of thioredoxin. We further confirmed thioredoxin expression-dependent changes in the T1-weighted contrast via knockdown of the expression of the thioredoxin using siRNA-transfected MCF-7 cells. The nontoxic nature of CA1, coupled with its relaxivity features, leads us to suggest that it constitutes a first-in-class MRI T1 contrast agent that allows for the facile and noninvasive monitoring of vicinal thiol protein motif expression in live cells. 相似文献
25.
本文探究了多个影响因素对大豆脲酶诱导碳酸钙沉淀(SICP)的影响,以优选出主要影响因素并提供其最佳范围。首先分析了脲酶浓度和温度对脲酶活性的影响;之后通过正交实验设计,进行25种工况的SICP水溶液实验,研究不同因素组合下Ca2+利用率的变化规律;最后借助扫描电子显微镜观测不同工况下生成碳酸钙的形态。结果表明:低温有利于脲酶的保存及活性发挥,5 ℃时脲酶活性能保持21 d以上;同一温度下,脲酶浓度越大,脲酶初始活性越高,脲酶完全失活所需时间越短。pH值、脲酶与胶结液体积比是影响Ca2+利用率的主要因素。为达到较高的Ca2+利用率,脲酶和胶结液最佳体积比为1,氯化钙与尿素最佳浓度比为1.5,Ca2+最佳浓度为1 mol/L。当脲酶浓度较低时生成的六面体状碳酸钙较多;随着脲酶浓度的增大,所沉淀的碳酸钙向球形转变。大豆中富含的天冬氨酸是控制碳酸钙形态的重要因素。 相似文献
26.
Bioanalysis assays that reliably quantify biotherapeutics and biomarkers in biological samples play pivotal roles in drug discovery and development. Liquid chromatography coupled with mass spectrometry (LC–MS), owing to its superior specificity, faster method development and multiplex capability, has evolved as one of the most important platforms for bioanalysis of biotherapeutics, particularly new scaffolds such as half-life extension platforms for proteins and peptides, as well as antibody drug conjugates. Intact LC–MS analysis is orthogonal to bottom-up surrogate peptide approach by providing whole molecule quantitation and high-level sequence and structure information. Here we review the latest development in LC–MS bioanalysis of intact proteins and peptides by summarizing recent publications and discussing the important topics such as the comparison between top-down intact analysis and bottom-up surrogate peptide approach, as well as simultaneous quantitation and catabolite identification. Key bioanalytical issues around intact protein bioanalysis such as sensitivity, data processing strategies, specificity, sample preparation and LC condition are elaborated. For peptides, topics including quantitation of intact peptide vs. digested surrogate peptide, metabolites, sensitivity, LC condition, assay performance, internal standard and sample preparation are discussed. 相似文献
27.
Kyoungmin Kang Kosuke Sakamoto Dr. Yoshihiro Nishimoto Prof. Dr. Makoto Yasuda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(22):4930-4934
The regioselective anti-carboindation of ynamides by using InBr3 and silylated nucleophiles was developed to synthesize (Z)-β-(carbonylamino)alkenylindiums. The X-ray crystallographic analysis of an alkenylindium suggested that the reaction proceeded in an anti-addition fashion. In contrast to reported syn-carbometalations of ynamides by using organometallics, a cooperation of InBr3 and silylated nucleophiles to ynamides achieved an anti-addition, which was supported by DFT calculations. The scope of substrates included various ynamides and silylated nucleophiles, such as silyl ketene acetals and silyl ketene imines. The transformation of synthesized alkenylindiums by iodination, radical coupling, and Pd-catalyzed cross-coupling successfully afforded trisubstituted enamines with high regio- and stereoselectivities. 相似文献
28.
Kang Yang Chang-Shan Yang Xing-Xian Dong Dr. Yu-Hui Tan Prof. Yun-Zhi Tang Dr. Wen-Juan Wei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(26):5887-5892
Smart multifunctional molecular ferroelectrics bearing high Curie temperatures and diverse excellent physical properties, such as second harmonic generation (SHG) responses, luminescence, and semiconductivity, among others, have significant applications but have seldom been documented. Herein, the rare-earth metals Nd and Pr are introduced into a simple molecular system (nBu4N )3[M(NO3)x(SCN)y] (nBu4N=tetrabutyl ammonium, M=rare-earth metal, nBu=CH3CH2CH2CH2), and two new multifunctional molecular ferroelectrics are obtained: (nBu4N )3[Nd(NO3)4(SCN)2] ( 1 ) and (nBu4N )3[Pr(NO3)4(SCN)2] ( 2 ). Their distinct heat and dielectric anomaly dependence on temperature verifies that compounds 1 and 2 experience high-temperature para-ferroelectric phase transitions at 408 and 413 K, respectively. Strikingly, both molecular ferroelectrics possess large spontaneous polarization with Ps values of 9.05 and 8.50 μC cm−2, respectively, and are further characterized by the appearance of multiple intersecting non-180° domains and polarization switching behavior. In particular, compounds 1 and 2 show good stability with only a small decrease in SHG intensity after switching cycles, suggesting that they have great potential for application in nonlinear optical (NLO) switches. Simultaneously, the rare-earth compounds 1 and 2 present bright yellow–red and bright green fluorescence, respectively, at room temperature. 相似文献
29.
Dr. Saud Asif Ahmed Qiao-Bo Liao Qi Shen Dr. Mirza Muhammad Faran Ashraf Baig Juan Zhou Cai-Feng Shi Dr. Pir Muhammad Dr. Sumaira Hanif Prof. Kai Xi Prof. Xing-Hua Xia Prof. Kang Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(57):12996-13001
Layered/two-dimensional covalent organic frameworks (2D COF) are crystalline porous materials composed of light elements linked by strong covalent bonds. Interlayer force is one of the main factors directing the formation of a stacked layer structure, which plays a vital role in the stability, crystallinity, and porosity of layered COFs. The as-developed new way to modulate the interlayer force of imine-linked 2D TAPB-PDA-COF (TAPB = 1,3,5-tris(4-aminophenyl)benzene, PDA = terephthaldehyde) by only adjusting the pH of the solution. At alkaline and neutral pH, the pore size of the COF decreases from 34 Å due to the turbostratic effect. Under highly acidic conditions (pH 1), TAPB-PDA-COF shows a faster and stronger turbostratic effect, thus causing the 2D structure to exfoliate. This yields bulk quantities of an exfoliated few/single-layer 2D COF, which was well dispersed and displayed a clear Tyndall effect (TE). Furthermore, nanopipette-based electrochemical testing also confirms the slipping of layers with increase towards acidic pH. A model of pH-dependent layer slipping of TAPB-PDA-COF was proposed. This controllable pH-dependent change in the layer structure may open a new door for potential applications in controlled gas adsorption/desorption and drug loading/releasing. 相似文献
30.
Chenxia Kang Dr. Ju Fang Likang Fu Shuxian Li Prof. Qiming Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(69):16392-16401
A 3D hierarchical carbon cloth/nitrogen-doped carbon nanowires/Ni@MnO2 (CC/N-CNWs/Ni@MnO2) nanocomposite electrode was rationally designed and prepared by electrodeposition. The N-CNWs derived from polypyrrole (PPy) nanowires on the carbon cloth have an open framework structure, which greatly increases the contact area between the electrode and electrolyte and provides short diffusion paths. The incorporation of the Ni layer between the N-CNWs and MnO2 is beneficial for significantly enhancing the electrical conductivity and boosting fast charge transfer as well as improving the charge-collection capacity. Thus, the as-prepared 3D hierarchical CC/N-CNWs/Ni@MnO2 electrode exhibits a higher specific capacitance of 571.4 F g−1 compared with those of CC/N-CNWs@MnO2 (311 F g−1), CC/Ni@MnO2 (196.6 F g−1), and CC@MnO2 (186.1 F g−1) at 1 A g−1 and remarkable rate capability (367.5 F g−1 at 10 A g−1). Moreover, asymmetric supercapacitors constructed with CC/N-CNWs/Ni@MnO2 as cathode material and activated carbon as anode material deliver an impressive energy density of 36.4 W h kg−1 at a power density of 900 W kg−1 and a good cycling life (72.8 % capacitance retention after 3500 cycles). This study paves a low-cost and simple way to design a hierarchical nanocomposite electrode with large surface area and superior electrical conductivity, which has wide application prospects in high-performance supercapacitors. 相似文献