全文获取类型
收费全文 | 28470篇 |
免费 | 5136篇 |
国内免费 | 3696篇 |
专业分类
化学 | 20188篇 |
晶体学 | 360篇 |
力学 | 2042篇 |
综合类 | 263篇 |
数学 | 3059篇 |
物理学 | 11390篇 |
出版年
2024年 | 51篇 |
2023年 | 610篇 |
2022年 | 919篇 |
2021年 | 1054篇 |
2020年 | 1188篇 |
2019年 | 1115篇 |
2018年 | 960篇 |
2017年 | 855篇 |
2016年 | 1374篇 |
2015年 | 1312篇 |
2014年 | 1605篇 |
2013年 | 1963篇 |
2012年 | 2582篇 |
2011年 | 2622篇 |
2010年 | 1861篇 |
2009年 | 1733篇 |
2008年 | 1869篇 |
2007年 | 1631篇 |
2006年 | 1672篇 |
2005年 | 1413篇 |
2004年 | 1041篇 |
2003年 | 865篇 |
2002年 | 867篇 |
2001年 | 696篇 |
2000年 | 600篇 |
1999年 | 659篇 |
1998年 | 484篇 |
1997年 | 481篇 |
1996年 | 510篇 |
1995年 | 447篇 |
1994年 | 406篇 |
1993年 | 294篇 |
1992年 | 276篇 |
1991年 | 233篇 |
1990年 | 210篇 |
1989年 | 180篇 |
1988年 | 160篇 |
1987年 | 95篇 |
1986年 | 104篇 |
1985年 | 75篇 |
1984年 | 49篇 |
1983年 | 40篇 |
1982年 | 28篇 |
1981年 | 25篇 |
1980年 | 16篇 |
1975年 | 7篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The metal-catalyzed Baeyer-Villiger oxidation of cyclohexanone with molecular oxygen (latm) in the presence of benzaldehyde gives δ -caprolactone in high yield. The same oxidation in the absence of metal catalysts is also studied. Additives to the system can improve the reaction highly efficiently. 相似文献
992.
A Pronounced Halogen Effect on the Organogelation Properties of Peripherally Halogen Functionalized Poly(benzyl ether) Dendrons 下载免费PDF全文
Prof. Dr. Yu Feng Hui Chen Zhi‐Xiong Liu Yan‐Mei He Prof. Dr. Qing‐Hua Fan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(14):4980-4990
An interesting halogen‐substituent effect on the organogelation properties of poly(benzyl ether) dendrons is reported. A new class of poly(benzyl ether) dendrons with halo substituents decorating their periphery was synthesized and fully characterized. A systematic study on the gelation abilities, thermotropic behaviors, aggregated microstructures, and mechanical properties of self‐assembled organogels was performed to elucidate the halogen‐substituent effects on their organogelation propensity. It was found that the exact halogen substitutions on the periphery of dendrons exert a profound effect on the organogelation propensity, and dendrons G n ‐Cl (n=2, 3) and G2‐I proved to be highly efficient organogelators. The cooperation of multiple π–π, dispersive halogen, CH–π, and weak C?H ??? X hydrogen‐bonding interactions were found to be the key contributor to forming the self‐assembled gels. Dendritic organogels formed from G n ‐Cl (n=2, 3) in 1,2‐dichloroethane exhibited thixotropic‐responsive properties, and such thixotropic organogels are promising materials for future research and applications. 相似文献
993.
Yihan Zhang Cui Bo Yanhao Fan Rui An Long Chen Yifan Zhang Yiqun Jia Xinhong Wang 《Biomedical chromatography : BMC》2019,33(3)
A quick and effective workflow based on ultra‐performance liquid chromatography coupled with electron spray ionization and LTQ‐Orbitrap mass spectrometry (UPLC‐LTQ‐Orbitrap MS) was established for compositional analysis and screening of the characteristic compounds of three species of Atractylodes rhizome for quality evaluation. This technique was employed to determine the seven main components in Atractylodes rhizome samples. Ultimately, 78 constituents were identified; of these, seven characteristic compounds were selected for species discrimination, comprising atractylodin (63), atractylenolide I (43), atractylenolide II (49), atractylenolide III (53), atractylon (69), methyl‐atractylenolide II (54) and (4E,6E,12E)‐tetradecadecatriene‐8,10‐diyne‐1,3‐diacetate (59). The seven main compounds, including six characteristic compounds, were simultaneously determined in 29 batches of Atractylodes rhizome samples. Thus, the method validation showed acceptable results. Quantitative analysis showed significantly different contents of the seven main components among the three species of Atractylodes rhizome, which indicates possible distinctions in the pharmacological effects. This established method can simultaneously provide qualitative and quantitative results for compositional characterization of Atractylodes rhizomes and for quality control. 相似文献
994.
Li-Dan Lin Prof. Dr. Dan Zhao Prof. Dr. Xin-Xiong Li Prof. Dr. Shou-Tian Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(2):442-453
During the past decade, research on the design and synthesis of zeolite-like metal–organic frameworks (ZMOFs) has developed greatly. As an important subclass of ZMOFs, zeolite-like cluster organic frameworks (ZCOFs) built from 4-connected metal-cluster secondary building units (SBUs) and appropriate linear organic ligand bridges have attracted sustained interest, because such materials not only integrate the merits of inorganic zeolites, ZMOFs, and metal clusters, including interesting topologies, high surface areas, extra-large cavities and channels, structural tunability, and unique physicochemical properties from various metal clusters, but also open up a new avenue to design and fabricate hybrid zeolite-like materials that have many potential applications in material sciences. In this review, recent developments in ZCOFs are summarized by classifying the ZCOFs into four categories according to the composition of the SBUs: 1) ZCOFs based on metal–halide cluster SBUs, 2) ZCOFs based on metal–oxygen cluster SBUs, 3) ZCOFs based on metal–chalcogen cluster SBUs, and 4) ZCOFs based on mixed types of metal-cluster SBUs. Besides, challenges associated with the design and synthesis of ZCOFs and the vast potential of this area are also discussed. 相似文献
995.
Dawei Xu Li Zheng Xinhong Cheng Gang Wang Qian Wang Wenbo Xin Peiyi Ye Lingyan Shen Yuehui Yu 《Physics letters. A》2019,383(25):3134-3137
The efficient passivation of in situ NH3-plasma pre-treatment and its regulation of the band alignment between HfO2 and 4H-SiC have been investigated by XPS. With in situ NH3-plasma passivation by PEALD, a VBO of 0.72 eV and a CBO of 1.54 eV can be obtained across the HfO2/4H-SiC interface. The Si-O bonds components reduction in the passivated interface layers will lead to band bending or band shift at the interface and regulate the band alignments between HfO2 and 4H-SiC. The physical mechanism investigation of band alignments can be a cornerstone for the application of HfO2/4H-SiC heterojunctions in the high-power devices. 相似文献
996.
Yi Zheng Ziqing Wang Gabrielle Lui Dborah Hirt Jean‐Marc Treluyer Sihem Benaboud Radia Aboura Ins Gana 《Biomedical chromatography : BMC》2019,33(5)
Levofloxacin, pefloxacin, ciprofloxacin and moxifloxacin are four fluoroquinolones used in the treatment of serious bacterial infections. The antibacterial activity of fluoroquinolones is concentration dependent. Therefore, therapeutic drug monitoring in daily clinical practice is warranted to ensure the therapy's efficacy and prevent bacterial resistance. The purpose of the present study was to develop a method using high‐pressure liquid chromatography with an ultraviolet detector for simultaneous quantification of these four fluoroquinolones in human plasma. A 50 μL aliquot of plasma was precipitated by 200 μL of methanol using gatifloxacin as internal standard. The chromatographic separation was performed on a Kinetex XB‐C18 column using a mobile phase composed of a mixture of orthophosphoric acid 0.4% (v/v), acetonitrile and methanol at a flow rate of 1.2 mL/min. Dual UV wavelength mode was used, with levofloxacin and moxifloxacin monitored at 293 nm, and pefloxacin and ciprofloxacin monitored at 280 nm. The calibration was linear over the ranges of 0.125–25 mg/L for levofloxacin, 0.1–20mg/L for moxifloxacin and 0.05‐10 mg/L for both pefloxacin and ciprofloxacin. Inter‐ and intra‐day trueness and precision were <13% for all the compounds under study. The proposed method was simple, reliable, cost‐effective and suitable for therapeutic drug monitoring or pharmacokinetics studies. 相似文献
997.
Ju Wang Wei Yao Di Fan Zhenjun Qiu Jieqiong Song Kai Pan Taijun Hang 《Biomedical chromatography : BMC》2019,33(10)
HR011303 is a novel and highly selective urate transporter 1 (URAT1) inhibitor. In this study, a sensitive liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed and validated for quantification of HR011303 in beagle dog plasma. Plasma samples were pretreated with protein‐precipitation extraction by acetonitrile and added with a trifluoromethyl substituted analog of HR011303 as internal standard. The chromatographic separation was performed on a Shiseido C18 column (100 × 4.6 mm, i.d., 5 μm) by mobile phases consisting of 5 mm ammonium–formic acid (100:0.1) and acetonitrile–formic acid (100:0.1) solutions in gradient elution. The MS detection was conducted in electrospray positive ionization with multiple reactions monitoring at m/z 338 → 240 for HR011303 and m/z 328 → 230 for the internal standard using 25 eV argon gas collision induced dissociation. The established LC–MS/MS method showed good selectivity, sensitivity, precision and accuracy. The plasma pharmacokinetics of HR011303 in beagle dogs following both oral and intravenous administration were then successfully evaluated using this LC–MS/MS method. 相似文献
998.
Meng Liu Dr. Hao Fan Dr. Ou Zhuo Xiao Du Longqi Yang Prof. Peng Wang Lijun Yang Prof. Qiang Wu Prof. Xizhang Wang Prof. Zheng Hu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3843-3848
Molybdenum disulfide (MoS2) is an intensively studied anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity, but it is still confronted by severe challenges of unsatisfactory rate capability and cycle life. Herein, few-layer MoS2 nanosheets, vertically grown on hierarchical carbon nanocages (hCNC) by a facile hydrothermal method, introduce pseudocapacitive lithium storage owing to the highly exposed MoS2 basal planes, enhanced conductivity, and facilitated electrolyte access arising from good hybridization with hCNC. Thus, the optimized MoS2/hCNC exhibits reversible capacities of 1670 mAh g−1 at 0.1 A g−1 after 50 cycles, 621 mAh g−1 at 5.0 A g−1 after 500 cycles, and 196 mAh g−1 at 50 A g−1 after 2500 cycles, which are among the best for MoS2-based anode materials. The specific power and specific energy, which can reach 16.1 kW and 252.8 Wh after 3000 cycles, respectively, indicate great potential in high-power and long-life LIBs. These findings suggest a promising strategy for exploring advanced anode materials with high reversible capacity, high-rate capability, and long-term recyclability. 相似文献
999.
Applied Biochemistry and Biotechnology - Pectin, as one of the most widely used functional polysaccharide, can be abundantly extracted from apple pomace which is the main by-product of apple juice... 相似文献
1000.
We analytically obtained the Schmidt decomposition of the entangled state between the pseudo spin and the true spin in graphene with Rashba spin–orbit coupling. The entangled state has the standard form of the Bell state, where the SU(2) spin symmetry is broken. These states can be explicitly expressed as the superposition of two nonorthogonal, but mirror symmetrical spin states entangled with the pseudo spin states. Because of the closely locking between the pseudo spin and the true spin, it is found that the orbit curve in the spin-polarization parameter space for the fixed equi-energy contour around Dirac points has the same shape as the -contour. Due to the spin–orbit coupling that cause the topological transition in the local geometry of the dispersion relation, the new equi-energy contours around the new emergent Dirac Points can be obtained by squeezing the one around the original Dirac point. The spin texture in the momentum space around the Dirac points is analyzed under the Rashba spin–orbit interaction and it is found that the orientation of the spin polarization at each crystal momentum is independent of the Rashba coupling strength. 相似文献