全文获取类型
收费全文 | 24950篇 |
免费 | 3997篇 |
国内免费 | 2883篇 |
专业分类
化学 | 18104篇 |
晶体学 | 288篇 |
力学 | 1498篇 |
综合类 | 247篇 |
数学 | 2645篇 |
物理学 | 9048篇 |
出版年
2024年 | 79篇 |
2023年 | 528篇 |
2022年 | 775篇 |
2021年 | 862篇 |
2020年 | 951篇 |
2019年 | 922篇 |
2018年 | 787篇 |
2017年 | 738篇 |
2016年 | 1173篇 |
2015年 | 1160篇 |
2014年 | 1358篇 |
2013年 | 1775篇 |
2012年 | 2217篇 |
2011年 | 2209篇 |
2010年 | 1542篇 |
2009年 | 1357篇 |
2008年 | 1551篇 |
2007年 | 1513篇 |
2006年 | 1368篇 |
2005年 | 1194篇 |
2004年 | 895篇 |
2003年 | 810篇 |
2002年 | 854篇 |
2001年 | 677篇 |
2000年 | 541篇 |
1999年 | 584篇 |
1998年 | 438篇 |
1997年 | 415篇 |
1996年 | 354篇 |
1995年 | 334篇 |
1994年 | 346篇 |
1993年 | 256篇 |
1992年 | 213篇 |
1991年 | 227篇 |
1990年 | 200篇 |
1989年 | 129篇 |
1988年 | 101篇 |
1987年 | 104篇 |
1986年 | 72篇 |
1985年 | 55篇 |
1984年 | 52篇 |
1983年 | 25篇 |
1982年 | 30篇 |
1981年 | 22篇 |
1980年 | 19篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1972年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
Wen Shao He Li Chuan Liu Prof. Dr. Chen‐Jiang Liu Prof. Dr. Shu‐Li You 《Angewandte Chemie (International ed. in English)》2015,54(26):7684-7687
The first copper‐catalyzed intermolecular dearomatization of indoles by an asymmetric propargylic substitution reaction was developed. This method provides a highly efficient synthesis of versatile furoindoline and pyrroloindoline derivatives containing a quaternary carbon stereogenic center and a terminal alkyne moiety with up to 86 % yield and 98 % ee. 相似文献
952.
Tianrong Yu Yang Gao Bo Wang Xing Dai Wanrun Jiang Ruixia Song Prof. Zhanwen Zhang Prof. Mingxing Jin Prof. Yongjian Tang Prof. Zhigang Wang 《Chemphyschem》2015,16(15):3308-3312
The mechanism of depolymerization is one of the most essential issues in chemical engineering and materials science. In this work, we investigate the depolymerization reactions of three typical free‐radical poly(alpha‐methylstyrene) tetramers by using first‐principles density functional theory. The calculated results show that these reactions all need to overcome the energy barriers in the range of 0.58 to 0.77 eV, and that breaking the C?C bond at the chain end leads to the dissociation of alpha‐methylstyrene monomers from the polymers. Electronic‐structure analysis indicates that the reactions occur easily at the CR3 unsaturated end, and that the frontier molecular orbitals that participate in the reactions are mainly localized at the unsaturated ends. Meanwhile, spin population analysis presents the unique net spin‐transfer process in free‐radical depolymerization reactions. We hope the current findings can contribute to understanding the free‐radical depolymerization mechanism and help guide future experiments. 相似文献
953.
Zhengjin Jiang Zhuohong Yang Roderich D. Süssmuth Norman Williams Smith Shuting Lai 《Journal of chromatography. A》2010,1217(7):1149-1156
It is believed that the enantiorecognition mechanism based on macrocyclic antibiotics involves multimodal interactions via hydrogen bonding, π–π interaction, steric hindrance, hydrophobic interaction and so on. A variety of enantiomeric N-benzoylated amino acids were separated using balhimycin (A) or its analogues bromobalhimycin (B) and dechlorobalhimycin (C) as chiral mobile phase additive using a CE method, which combined the partial filling technique with the dynamic coating technique and the co-EOF electrophoresis technique. The enantioresolution and the migration time were highly relevant to the structure of analytes, especially to the substitutions on the N-tagged benzoyl moiety of the amino acids. A steric effect and π–π interaction based mechanism is proposed in order to explain some observed enantioresolution differences between positional isomers. Notably dechlorobalhimycin exhibited the best enantioresolution for several N-benzoylated derivatives of leucine, which was rarely observed for N-dansylated amino acid derivatives. The hydrophobicity difference of the aglycone pocket among three chiral selectors was assumed to account for this behaviour. 相似文献
954.
955.
Hong Xia Dr. Jie Yang Hong‐Hua Fang Qi‐Dai Chen Dr. Hai‐Yu Wang Prof. Xiao‐Qiang Yu Prof. Yu‐Guang Ma Prof. Min‐Hua Jiang Prof. Hong‐Bo Sun Prof. 《Chemphyschem》2010,11(9):1871-1875
E, E‐1, 4‐bis[4′‐(N,N‐dibutylamino)styryl]‐2,5‐dimethoxy‐benzene (DBASDMB) organic crystals with high crystalline quality, large size and excellent optical properties are prepared. The linear and nonlinear properties in the crystal are comparatively studied. The relaxation dynamics pumped by two‐photon are very similar with that pumped by one‐photon. The crystal exhibits very strong two‐photon excited fluorescence and amplified spontaneous emission. Efficient two‐photon absorption, reasonably high fluorescent quantum efficiency, and high crystal quality together with stimulated emission make organic crystals ideal for the application in frequency upconversion and other optoelectronic fields. 相似文献
956.
Heqing Jiang Dr. Fangyi Liang Oliver Czuprat Konstantin Efimov Armin Feldhoff Dr. Steffen Schirrmeister Dr. Thomas Schiestel Dr. Haihui Wang Prof. Jürgen Caro Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(26):7898-7903
A porous perovskite BaCoxFeyZr0.9?x?yPd0.1O3?δ (BCFZ‐Pd) coating was deposited onto the outer surface of a BaCoxFeyZr1?x?yO3?δ (BCFZ) perovskite hollow‐fiber membrane. The surface morphology of the modified BCFZ fiber was characterized by scanning electron microscopy (SEM), indicating the formation of a BCFZ‐Pd porous layer on the outer surface of a dense BCFZ hollow‐fiber membrane. The oxygen permeation flux of the BCFZ membrane with a BCFZ‐Pd porous layer increased 3.5 times more than that of the blank BCFZ membrane when feeding reactive CH4 onto the permeation side of the membrane. The blank BCFZ membrane and surface‐modified BCFZ membrane were used as reactors to shift the equilibrium of thermal water dissociation for hydrogen production because they allow the selective removal of the produced oxygen from the water dissociation system. It was found that the hydrogen production rate increased from 0.7 to 2.1 mL H2 min?1 cm?2 at 950 °C after depositing a BCFZ‐Pd porous layer onto the BCFZ membrane. 相似文献
957.
Kun Jiang Zhi‐Jun Jia Shi Chen Li Wu Ying‐Chun Chen Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(9):2852-2856
An efficient tandem reaction for the asymmetric synthesis of six‐membered spirocyclic oxindoles has been successfully developed through a formal [2+2+2] annulation strategy. The amine‐catalysed stereoselective Michael addition of aliphatic aldehydes to electron‐deficient olefinic oxindole motifs gave chiral C3 components, which were further combined with diverse electrophiles (activated olefins or imines) to afford spirocyclic oxindoles with versatile molecular complexity (up to six contiguous stereogenic centres, high diastereo‐ and enantioselectivities). 相似文献
958.
A simple, rapid and sensitive method for the determination of pirimicarb in tomato and pear using polymer monolith microextraction (PMME) based on the molecularly imprinted polymer (MIP) monolith combined with high-performance liquid chromatography-photodiodes array detector (HPLC-PAD) was developed. By optimizing the polymerization conditions, such as the nature of porogenic solvent and functional monomer, the molar ratio of the monomer and cross-linker, an pirimicarb MIP monolith was synthesized in a micropipette tip using methacrylic acid (MAA) as the functional monomer, ethylene dimethacrylate (EGDMA) as the cross-linker and the mixture of toluene-dodecanol as the porogenic solvent. The MIP monolith showed highly specific recognition for the template pirimicarb. The monolith was applied for the selective extraction of pirimicarb in tomato and pear. Several parameters affecting MIP-PMME were investigated, including the nature and volume of extraction solvent, sample volume, flow rate and sample pH. Under the optimum PMME and HPLC conditions, the linear ranges were 2.0-1400 μg/kg for pirimicarb in tomato and pear with the correlation coefficient of above 0.999. The detection limits (s/n=3) were both 0.6 μg/kg. The proposed method was successfully applied for the selective extraction and determination of pirimicarb in tomato and pear. 相似文献
959.
This paper reports a lab-on-a-chip device that counts the number of bacteria flowing through a microchannel. The bacteria number counting is realized by a microfluidic differential Resistive Pulse Sensor (RPS). By using a single microfluidic channel with two detecting arm channels placed at the two ends of the sensing section, the microfluidic differential RPS can achieve a high signal-to-noise ratio. This method is applied to detect and count bacteria in aqueous solution. The detected RPS signals amplitude for Pseudomonas aeruginosa ranges from 0.05 V to 0.17 V and the signal-to-noise ratio is 5-17. The number rate of the bacteria flowing through the sensing gate per minute is a linear function of the sample concentration. Using this experimentally obtained correlation curve, the concentration of bacteria in the sample solution can be evaluated within several minutes by measuring the number rate of the bacteria flowing through the sensing gate of this microfluidic differential RPS chip. The method described in this paper is simple and automatic, and have wide applications in determining the bacteria and cell concentrations for microbiological and other biological applications. 相似文献
960.
Wang T Jiang J Liu Y Li Z Liu M 《Langmuir : the ACS journal of surfaces and colloids》2010,26(24):18694-18700
Bolaamphiphiles with L-glutamic acid headgroups and hybrid linkers, each composed of two rigid benzene rings and different polymethylene units, were designed, and morphological controls of the hierarchical self-assemblies were realized via changing solution pH and application to solid surfaces. At a low pH of 3, bolaamphiphiles formed hydrogels with water and molecules with short and long spacers formed nanofibers and helical nanoribbon-nanotubes, respectively. In a pH 12 aqueous solution, vesicles were observed from cryo-TEM measurements for amphiphiles with short spacers that could transfer to huge vesicles when cast onto a mica surface. Amphiphiles with longer spacers self-assembled into nanoparticles in a pH 12 aqueous solution while micellar fibers were formed on a mica surface. Those assemblies were characterized with UV-vis, CD, and FT-IR spectroscopy and AFM and TEM observations. With molecular structure modification and the fine tuning of conditions, morphology transitions between various nanostructures were obtained from the self-assembled bolaamphiphiles. The environmental pH can induce different interaction modes between the headgroups, and at high pH, there are strong interactions between molecular assemblies and the mica surface. It is suggested that the active headgroups, rigid necks, and flexible linkers with different lengths render molecules with diverse aggregation morphologies. 相似文献