全文获取类型
收费全文 | 3503篇 |
免费 | 481篇 |
国内免费 | 459篇 |
专业分类
化学 | 2723篇 |
晶体学 | 35篇 |
力学 | 201篇 |
综合类 | 43篇 |
数学 | 375篇 |
物理学 | 1066篇 |
出版年
2024年 | 17篇 |
2023年 | 74篇 |
2022年 | 136篇 |
2021年 | 149篇 |
2020年 | 155篇 |
2019年 | 140篇 |
2018年 | 108篇 |
2017年 | 116篇 |
2016年 | 160篇 |
2015年 | 155篇 |
2014年 | 210篇 |
2013年 | 255篇 |
2012年 | 267篇 |
2011年 | 304篇 |
2010年 | 206篇 |
2009年 | 180篇 |
2008年 | 189篇 |
2007年 | 176篇 |
2006年 | 158篇 |
2005年 | 152篇 |
2004年 | 125篇 |
2003年 | 100篇 |
2002年 | 116篇 |
2001年 | 100篇 |
2000年 | 86篇 |
1999年 | 92篇 |
1998年 | 81篇 |
1997年 | 61篇 |
1996年 | 63篇 |
1995年 | 49篇 |
1994年 | 51篇 |
1993年 | 34篇 |
1992年 | 43篇 |
1991年 | 24篇 |
1990年 | 30篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有4443条查询结果,搜索用时 10 毫秒
171.
报道了一种用于偏氟乙烯-三氟氯乙烯共聚物(VDF/CTFE共聚物)制备偏氟乙烯/三氟乙烯/三氟氯乙烯共聚物(VDF/TrFE/CTFE共聚物)的新方法,该方法以CuCl与2′,2-Bpy的配合物为催化剂,N-甲基吡咯烷酮(NMP)为溶剂,异丙苯(丙酮、2,6-二叔丁基-4-甲基苯酚)为链转移剂,通过原子转移法在VDF/CTFE共聚物上产生自由基,进而利用自由基链转移反应将VDF/CTFE共聚物上部分Cl原子用H原子取代以制备VDF/TrFE/CTFE三元共聚物.对该体系的反应机理及其影响因素进行研究发现,随着实验温度的升高(80~140℃),反应时间的延长,氢化量增加,产物中TrFE含量增加;反应温度越高,初始反应速度越快,完全氢化时间越短;催化剂与氢化量的比例基本为1:1,通过控制催化剂的量可以定量控制氢化率;新的反应体系不会对产物的分子量产生大的影响. 相似文献
172.
173.
Sen Hou Xin-Xin Li Xiao-Yu Li Xi-Zeng Feng Li Guan Yan-Lian Yang Chen Wang 《Analytical and bioanalytical chemistry》2009,394(8):2111-2117
Controllable cell growth on the defined areas of surfaces is important for potential applications in biosensor fabrication
and tissue engineering. In this study, controllable cell growth was achieved by culturing 293 T fibroblast cells on a mica
surface which had been patterned with collagen strips by a microcontact printing (μCP) technique. The collagen area was designed
to support cell adhesion and the native mica surface was designed to repel cell adhesion. Consequently, the resulting cell
patterns should follow the micro-patterns of the collagen. X-ray photoelectron spectroscopy (XPS), water contact angle (WCA)
measurement, atomic-force microscope (AFM) observation, and force-curve measurement were used to monitor property changes
before and after the collagen adsorption process. Further data showed that the patterned cells were of good viability and
able to perform a gene-transfection experiment in vitro. This technique should be of potential applications in the fields
of biosensor fabrication and tissue engineering.
Figure Controllable cells growth has been achieved by culturing 293T fibroblast cells on the mica surface which had been patterned
with collagen strips by microcontact printing (μCP) technique 相似文献
174.
Uniform nylon 6 nanofibers with diameters around 200 nm were prepared by electrospinning. Polymorphic phase transitions and crystal orientation of nylon 6 in unconfined (i.e., as-electrospun) and a high T(g) (340 degrees C) polyimide confined nanofibers were studied. Similar to melt-spun nylon 6 fibers, electrospun nylon 6 nanofibers also exhibited predominant, meta-stable gamma crystalline form, and the gamma-crystal (chain) axes preferentially oriented parallel to the fiber axis. Upon annealing above 150 degrees C, gamma-form crystals gradually melted and recrystallized into the thermodynamically stable alpha-form crystals, which ultimately melted at 220 degrees C. Release of surface tension accompanied this melt-recrystallization process, as revealed by differential scanning calorimetry. For confined nanofibers, both the melt-recrystallization and surface tension release processes were substantially depressed; gamma-form crystals did not melt and recrystallize into alpha-form crystals until 210 degrees C, only 10 degrees C below the T(m) at 220 degrees C. After complete melting of nano-confined crystals at 240 degrees C and recrystallization at 100 degrees C, only alpha-form crystals oriented perpendicular to the nanofiber axis were obtained. In the polyimide-confined nanofibers, the Brill transition (from the monoclinic alpha-form to a high temperature monoclinic form) was observed at 180-190 degrees C, which was at least 20 degrees C higher than that in unconfined nylon 6 at approximately 160 degrees C. This, again, was attributed to the confinement effect. 相似文献
175.
Preparation and surface properties of latexes with fluorine enriched in the shell by silicon monomer crosslinking 总被引:1,自引:0,他引:1
Ping ting Xiong Pei zhi Chen Hong zhi Huang Rong Guan 《European Polymer Journal》2007,43(5):2117-2126
A series of core-shell acrylic copolymer latexes containing fluorine enriched in the shell have been prepared by emulsion polymerization of a variety of hydrocarbon monomers with (perfluoroalkyl)methyl methacrylate and vinyltriethoxysilicone. In the presence of a reactive anionic and a long chain anionic-nonionic emulsifier, the core-shell latexes were prepared and characterized by transmission electron microscopy (TEM) and tapping-mode atomic force microscopy (AFM). From AFM and contact angle measurements, it was observed that the resulting fluorine and silicon-containing acrylic copolymers with surface energy as low as 15.5 mN/m formed a dense and gradient film containing a surface layer with high a fluorine content, and that the fluorinated particles can be fixed on the surface due to the crosslinking reaction of multi-functional silicon monomer even though the fluorinated carbon number was not enough to crystallize. 相似文献
176.
Catalytically Active Rh Sub‐Nanoclusters on TiO2 for CO Oxidation at Cryogenic Temperatures 下载免费PDF全文
Hongling Guan Dr. Jian Lin Dr. Botao Qiao Dr. Xiaofeng Yang Dr. Lin Li Dr. Shu Miao Prof. Jingyue Liu Prof. Aiqin Wang Prof. Xiaodong Wang Prof. Tao Zhang 《Angewandte Chemie (International ed. in English)》2016,55(8):2820-2824
The discovery that gold catalysts could be active for CO oxidation at cryogenic temperatures has ignited much excitement in nanocatalysis. Whether the alternative Pt group metal (PGM) catalysts can exhibit such high performance is an interesting research issue. So far, no PGM catalyst shows activity for CO oxidation at cryogenic temperatures. In this work, we report a sub‐nano Rh/TiO2 catalyst that can completely convert CO at 223 K. This catalyst exhibits at least three orders of magnitude higher turnover frequency (TOF) than the best Rh‐based catalysts and comparable to the well‐known Au/TiO2 for CO oxidation. The specific size range of 0.4–0.8 nm Rh clusters is critical to the facile activation of O2 over the Rh–TiO2 interface in a form of Rh?O?O?Ti (superoxide). This superoxide is ready to react with the CO adsorbed on TiO2 sites at cryogenic temperatures. 相似文献
177.
Unusual Formation of CoSe@carbon Nanoboxes,which have an Inhomogeneous Shell,for Efficient Lithium Storage 下载免费PDF全文
Dr. Han Hu Jintao Zhang Dr. Buyuan Guan Prof. Xiong Wen Lou 《Angewandte Chemie (International ed. in English)》2016,55(33):9514-9518
Hybrid hollow nanostructures with tailored shell architectures are attractive for electrochemical energy storage applications. Starting with metal–organic frameworks (MOFs), we demonstrate a facile formation of hybrid nanoboxes with complex shell architecture where a CoSe‐enriched inner shell is intimately confined within a carbon‐enriched outer shell (denoted as CoSe@carbon nanoboxes). The synthesis is realized through manipulation of the template‐engaged reaction between Co‐based zeolitic imidazolate framework (ZIF‐67) nanocubes and Se powder at elevated temperatures. By virtue of the structural and compositional features, these unique CoSe@carbon nanoboxes manifest excellent lithium‐storage performance in terms of high specific capacity, exceptional rate capability, excellent cycling stability, and high initial Coulombic efficiency. 相似文献
178.
Dr. Guijian Guan Dr. Yongqing Cai Dr. Shuhua Liu Dr. Haidong Yu Dr. Shiqiang Bai Dr. Yuan Cheng Dr. Tao Tang Dr. M. S. Bharathi Prof. Yong‐Wei Zhang Prof. Ming‐Yong Han 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(5):1675-1681
High‐level incorporation of Ag in Au nanoclusters (NCs) is conveniently achieved by controlling the concentration of Ag+ in the synthesis of bovine serum albumin (BSA)‐protected Au NCs, and the resulting structure is determined to be bimetallic Ag28Au10‐BSA NCs through a series of characterizations including energy‐dispersive X‐ray spectroscopy, mass spectroscopy, and X‐ray photoelectron spectroscopy, together with density functional theory simulations. Interestingly, the Ag28Au10 NCs exhibit a significant fluorescence redshift rather than quenching upon interaction with hydrogen peroxide, providing a new approach to the detection of hydrogen peroxide through direct comparison of their fluorescence peaks. Furthermore, the Ag28Au10 NCs are also used for the sensitive and selective detection of herbicide through fluorescence enhancement. The detection limit for herbicide (0.1 nm ) is far below the health value established by the U.S. Environmental Protection Agency; such sensitive detection was not achieved by using AuAg NCs with low‐level incorporation of Ag or by using the individual metal NCs. 相似文献
179.
Shougang Wang Xiaohui Guan Xiuhong Zhong Zhiping Yang Weili Huang Baoyang Jia Tao Cui 《Biomedical chromatography : BMC》2016,30(10):1632-1640
A selective and sensitive HPLC–MS/MS method was developed for the simultaneous determination of cucurbitacin IIa (cuIIa) and cucurbitacin IIb (cuIIb), the major bioactive cucurbitacins of Hemsleya amabilis, in rat plasma using euphadienol as internal standard (IS). After liquid–liquid extraction with dichloromethane, separation was achieved on a Syncronis HPLC C18 column (150 mm × 4.6 mm, 5 μm) using an isocratic mobile phase system consisting of acetonitrile–water (85:15, v/v) at a flow rate of 0.6 mL/min with a split ratio of 1:2. Detection was performed on a TSQ Quantum Ultra mass spectrometer equipped with an positive‐ion electrospray ionization source. The lower limits of quantification (LLOQs) were 0.25 and 0.15 ng/mL for cuIIa and cuIIb, respectively. The intra‐ and inter‐day precision was <11.5% for the LLOQs and each quality control level of the analytes, and accuracy was between ?9.1 and 7.6%. The extraction recoveries of the analytes and IS from rat plasma were all >87.1%. The method was fully validated and applied to compare the pharmacokinetic profiles of the two cucurbitacins in rat plasma after oral administration of H. amabilis extract between normal and indomethacin‐induced rats. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
180.
Dr. Zhen Lei Zong‐Jie Guan Dr. Xiao‐Li Pei Shang‐Fu Yuan Xian‐Kai Wan Jin‐Yuan Zhang Prof.Dr. Quan‐Ming Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(32):11156-11160
A red–near‐IR dual‐emissive nanocluster with the composition [Au10Ag2(2‐py?C≡C)3(dppy)6](BF4)5 ( 1 ; 2‐py?C≡C is 2‐pyridylethynyl, dppy=2‐pyridyldiphenylphosphine) has been synthesized. Single‐crystal X‐ray structural analysis reveals that 1 has a trigonal bipyramidal Au10Ag2 core that contains a planar Au4(2‐py?C≡C)3 unit sandwiched by two Au3Ag(dppy)3 motifs. Cluster 1 shows intense red–NIR dual emission in solution. The visible emission originates from metal‐to‐ligand charge transfer (MLCT) from silver atoms to phosphine ligands in the Au3Ag(dppy)3 motifs, and the intense NIR emission is associated with the participation of 2‐pyridylethynyl in the frontier orbitals of the cluster, which is confirmed by a time‐dependent density functional theory (TD‐DFT) calculation. 相似文献