全文获取类型
收费全文 | 3489篇 |
免费 | 518篇 |
国内免费 | 209篇 |
专业分类
化学 | 2818篇 |
晶体学 | 29篇 |
力学 | 120篇 |
综合类 | 22篇 |
数学 | 273篇 |
物理学 | 954篇 |
出版年
2024年 | 17篇 |
2023年 | 62篇 |
2022年 | 98篇 |
2021年 | 100篇 |
2020年 | 153篇 |
2019年 | 144篇 |
2018年 | 108篇 |
2017年 | 96篇 |
2016年 | 160篇 |
2015年 | 166篇 |
2014年 | 188篇 |
2013年 | 223篇 |
2012年 | 269篇 |
2011年 | 290篇 |
2010年 | 201篇 |
2009年 | 178篇 |
2008年 | 215篇 |
2007年 | 164篇 |
2006年 | 174篇 |
2005年 | 152篇 |
2004年 | 138篇 |
2003年 | 133篇 |
2002年 | 116篇 |
2001年 | 71篇 |
2000年 | 69篇 |
1999年 | 67篇 |
1998年 | 46篇 |
1997年 | 46篇 |
1996年 | 47篇 |
1995年 | 45篇 |
1994年 | 39篇 |
1993年 | 18篇 |
1992年 | 21篇 |
1991年 | 24篇 |
1990年 | 16篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1974年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有4216条查询结果,搜索用时 15 毫秒
151.
A General Method for Preparing Bridged Organosilanes with Pendant Functional Groups and Functional Mesoporous Organosilicas 下载免费PDF全文
Prof. Jana Hodačová Dr. Guillaume Toquer Dr. Xavier Cattoën Dr. Michel Wong Chi Man 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(33):10371-10382
New organosilica precursors containing two triethoxysilyl groups suitable for the organosilica material formation through the sol‐gel process were designed and synthesised. These precursors display alkyne or azide groups for attaching targeted functional groups by copper‐catalysed azide–alkyne cycloaddition (CuAAC) and can be used for the preparation of functional organosilicas following two strategies: 1) the functional group is first appended by CuAAC under anhydrous conditions, then the functional material is prepared by the sol‐gel process; 2) the precursor is first subjected to the sol‐gel process, producing porous, clickable bridged silsesquioxanes or periodic mesoporous organosilicas (PMOs), then the desired functional groups are attached by means of CuAAC. Herein, we show the feasibility of both approaches. A series of bridged bis(triethoxysilane)s with different pending organic moieties was prepared, demonstrating the compatibility of the first approach with many functional groups. In particular, we demonstrate that organic functional molecules bearing only one derivatisation site can be used to produce bridged organosilanes and bridged silsesquioxanes. In the second approach, clickable PMOs and porous bridged silsesquioxanes were prepared from the alkyne‐ or azide‐containing precursors, and thereafter, functionalised with complementary model azide‐ or alkyne‐containing molecules. These results confirmed the potential of this approach as a general methodology for preparing functional organosilicas with high loadings of functional groups. Both approaches give rise to a wide range of new functional organosilica materials. 相似文献
152.
Dr. Tao Xu Dr. Chi Wai Cheung Prof. Dr. Xile Hu 《Angewandte Chemie (International ed. in English)》2014,53(19):4910-4914
Iron catalysis has been developed for the intermolecular 1,2‐addition of perfluoroalkyl iodides to alkynes and alkenes. The catalysis has a wide substrate scope and high functional‐group tolerance. A variety of perfluoroalkyl iodides including CF3I can be employed. The resulting perfluoroalkylated alkyl and alkenyl iodides can be further functionalized by cross‐coupling reactions. This methodology provides a straightforward and streamlined access to perfluoroalkylated organic molecules. 相似文献
153.
β‐Functionalization of Carboxylic Anhydrides with β‐Alkyl Substituents through Carbene Organocatalysis 下载免费PDF全文
Zhichao Jin Shaojin Chen Yuhuang Wang Pengcheng Zheng Prof. Dr. Song Yang Prof. Dr. Yonggui Robin Chi 《Angewandte Chemie (International ed. in English)》2014,53(49):13506-13509
The first NHC‐catalyzed functionalization of carboxylic anhydrides is described. In this reaction, the β carbon behaves as a nucleophilic carbon and undergoes asymmetric reactions with electrophiles. Anhydrides with challenging β‐alkyl substituents work effectively. 相似文献
154.
Bo Xiao Xiaoyan Chi Li Zhang Huige Qu Yujing Liu Xiaojie Wang Juhua Zhou 《Applied biochemistry and biotechnology》2014,173(8):2129-2139
Efficient expression of target protein is one of strategies for gene therapy or vaccine design. Many studies showed that codon optimization could enhance the expression of target proteins. In this paper, a target sequence of about 1.26 kb encoding the major capsid protein VP6 of grass carp reovirus (GCRV) and an optimized counterpart were synthesized and inserted into vectors for expressing VP6. The final constructs (named as pcDV6G and pcDV6YG) were transfected in Ctenopharyngodon idellus kidney (CIK) cells. The fluorescence analysis and the Western blot results showed that the gene fragment was transfected and expressed in CIK cells successfully. Although the qRT-PCR results showed no difference at the messenger RNA (mRNA) levels between the different versions of vp6 in the indicated stages, the enzyme-linked immunosorbent assay (ELISA) results showed that the protein level of VP6 expressed by pcDV6YG was higher than that by pcDV6G in the indicated hours. Taken together, these results suggest that the enhanced expression of GCRV VP6 in CIK cells by relative sequence optimization may be a good choice for making DNA vaccine against GCRV. 相似文献
155.
Won-Jae Chi Jae-Seon Park Dae-Kyung Kang Soon-Kwang Hong 《Applied biochemistry and biotechnology》2014,173(7):1703-1716
A Gram-negative, aerobic, motile, rod-shaped, agarolytic bacterium, designated as H7, was isolated from a coastal seawater sample. This strain grows at pH 6.0–8.0, temperature of 15–40 °C, and at an NaCl concentration of 1–7 % (w/v). Ubiquinone-8 was the predominant respiratory quinone, and the DNA G+C content was 45.82 mol%. Analysis of the 16S rRNA sequence suggests that strain H7 belongs to the genus Pseudoalteromonas. DNA-DNA hybridization analysis showed DNA relatedness of as low as 55.42 and 40.27 % with its nearest phylogenetic neighbors Pseudoalteromonas atlantica IAM12927T and Pseudoalteromonas espejiana NCIMB2127T, respectively, which led us to name H7 Pseudoalteromonas hodoensis sp. nov. The type strain is H7T (=DSM25967T = KCTC23887T). An agarase (AgaA7) was purified to homogeneity from the cell-free culture broth of H7 through many steps of chromatography. Purified AgaA7 had an apparent molecular weight of 35 kDa, with a distinct NH2-terminal sequence of Ala-Asp-Ala-Thr-X-Pro (X, any amino acid) from the reported proteins, implying that it is a novel enzyme. The optimum pH and temperature for agarase activity were 7.0 and 45 °C, respectively. Thin-layer chromatography analysis, mass spectrometry, and enzyme assay using p-nitrophenyl-α/β-D-galactopyranoside revealed that AgaA7 is both an exo- and endo-type β-agarase that degrades agarose into neoagarotetraose, neoagarohexaose, and neoagarooctaose (minor). 相似文献
156.
Kai Li Xiaolong Tang Honghong Yi Ping Ning Ying Xiang Chi Wang Xianmang Xu 《Research on Chemical Intermediates》2014,40(1):169-177
Manganese–cobalt–cerium oxide (Mn–Co–Ce–Ox) catalysts were synthesized by the co-precipitation method and tested for activity in low-temperature catalytic oxidation of NO in the presence of excess O2. With the best Mn–Co–Ce mixed-oxide catalyst, approximately 80 % NO conversion was achieved at 150 °C and a space velocity of 35,000 h?1. The effect of reaction conditions (reaction temperature, volume fractions of NO and O2, gas hourly space velocity (GHSV), and catalyst stability) was investigated. The optimum reaction temperature was 150 °C. Increasing the O2 content above 3 % results in almost no improvement of NO oxidation. This catalyst enables highly effective removal of NO within a wide range of GHSV. Furthermore, the stability of the Me–Co–Ce–Ox catalyst was excellent; no noticeable decrease of NO conversion was observed in 40 h. 相似文献
157.
Xavier Cattoën Achraf Noureddine Jonas Croissant Nirmalya Moitra Kristýna Bürglová Jana Hodačová Olivia de los Cobos Martine Lejeune Fabrice Rossignol Delphine Toulemon Sylvie Bégin-Colin Benoît P. Pichon Laurence Raehm Jean-Olivier Durand Michel Wong Chi Man 《Journal of Sol-Gel Science and Technology》2014,70(2):245-253
The combination of the copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction with sol–gel processing enables the versatile preparation of sol–gel materials under different shapes with targeted functionalities through a diversity-oriented approach. In this account, the development of the CuAAC reaction under anhydrous conditions for the synthesis of sol–gel precursors and for the assembling of magnetic nanoparticles on self-assembled monolayers is related, as well as the use of the classical CuAAC methodologies for the functionalization of mesoporous silica nanoparticles and microdots arrays. Coupling CuAAC and Sol–Gel will result in simplified preparations of multifunctional materials with controlled morphologies. 相似文献
158.
Luocai Yi Dr. Junxiang Chen Ping Shao Dr. Junheng Huang Xinxin Peng Junwei Li Dr. Genxiang Wang Chi Zhang Prof. Zhenhai Wen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):20287-20294
Two-dimensional (2D) monometallic pnictogens (antimony or Sb, and bismuth or Bi) nanosheets demonstrate potential in a variety of fields, including quantum devices, catalysis, biomedicine and energy, because of their unique physical, chemical, electronic and optical properties. However, the development of general and high-efficiency preparative routes toward high-quality pnictogen nanosheets is challenging. A general method involving a molten-salt-assisted aluminothermic reduction process is reported for the synthesis of Sb and Bi nanosheets in high yields (>90 %). Electrocatalytic CO2 reduction was investigated on the Bi nanosheets, and high catalytic selectively to formate was demonstrated with a considerable current density at a low overpotential and an impressive stability. Bi nanosheets continuously convert CO2 into formate in a flow cell operating for one month, with a yield rate of 787.5 mmol cm−2 h−1. Theoretical results suggest that the edge sites of Bi are far more active than the terrace sites. 相似文献
159.
Dr. Dean Strotz Dr. Julien Orts Dr. Harindranath Kadavath Dr. Michael Friedmann Dhiman Ghosh Dr. Simon Olsson Dr. Celestine N. Chi Aditya Pokharna Prof. Dr. Peter Güntert Dr. Beat Vögeli Prof. Dr. Roland Riek 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(49):22316-22323
Protein allostery is a phenomenon involving the long range coupling between two distal sites in a protein. In order to elucidate allostery at atomic resoluion on the ligand-binding WW domain of the enzyme Pin1, multistate structures were calculated from exact nuclear Overhauser effect (eNOE). In its free form, the protein undergoes a microsecond exchange between two states, one of which is predisposed to interact with its parent catalytic domain. In presence of the positive allosteric ligand, the equilibrium between the two states is shifted towards domain–domain interaction, suggesting a population shift model. In contrast, the allostery-suppressing ligand decouples the side-chain arrangement at the inter-domain interface thereby reducing the inter-domain interaction. As such, this mechanism is an example of dynamic allostery. The presented distinct modes of action highlight the power of the interplay between dynamics and function in the biological activity of proteins. 相似文献
160.
由于抗生素的不当使用和细菌多药耐药的出现, 迫切需要开发新的抗菌剂. 本文制备了具有光热转换性能的正电荷半导体高分子材料及具有协同抗菌活性的半导体聚合物纳米粒子(SP-PPh3 NPs). SP-PPh3 NPs的光热转化效率为43.8%. 带正电荷的SP-PPh3 NPs可以附着在细菌上, 有助于将热量有效传递给细菌. 在热和正电荷的协同作用下, SP-PPh3 NPs对革兰氏阴性大肠杆菌(E. coli)和革兰氏阳性金黄色葡萄球菌(S. aureus)均具有抗菌活性, 其对二者的体外抑菌率分别为99.9%和98.6%. 此外, SP-PPh3 NPs具有良好的生物相容性, 对小鼠的主要器官几乎无副作用. 对细菌感染的小鼠皮肤伤口用SP-PPh3 NPs治疗12 d后, 伤口可以很好地愈合. 相似文献