全文获取类型
收费全文 | 24867篇 |
免费 | 4141篇 |
国内免费 | 3271篇 |
专业分类
化学 | 18968篇 |
晶体学 | 332篇 |
力学 | 1410篇 |
综合类 | 217篇 |
数学 | 2913篇 |
物理学 | 8439篇 |
出版年
2024年 | 68篇 |
2023年 | 443篇 |
2022年 | 805篇 |
2021年 | 840篇 |
2020年 | 1020篇 |
2019年 | 967篇 |
2018年 | 827篇 |
2017年 | 713篇 |
2016年 | 1231篇 |
2015年 | 1241篇 |
2014年 | 1415篇 |
2013年 | 1880篇 |
2012年 | 2094篇 |
2011年 | 2179篇 |
2010年 | 1561篇 |
2009年 | 1583篇 |
2008年 | 1853篇 |
2007年 | 1578篇 |
2006年 | 1415篇 |
2005年 | 1261篇 |
2004年 | 1021篇 |
2003年 | 828篇 |
2002年 | 960篇 |
2001年 | 755篇 |
2000年 | 650篇 |
1999年 | 506篇 |
1998年 | 346篇 |
1997年 | 262篇 |
1996年 | 312篇 |
1995年 | 255篇 |
1994年 | 220篇 |
1993年 | 205篇 |
1992年 | 147篇 |
1991年 | 132篇 |
1990年 | 116篇 |
1989年 | 90篇 |
1988年 | 86篇 |
1987年 | 68篇 |
1986年 | 53篇 |
1985年 | 56篇 |
1984年 | 46篇 |
1983年 | 29篇 |
1982年 | 19篇 |
1981年 | 28篇 |
1980年 | 14篇 |
1979年 | 17篇 |
1978年 | 9篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1971年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Musammir Khan Yakai Feng Dazhi Yang Wei Zhou Hong Tian Ying Han Li Zhang Wenjie Yuan Jin Zhang Jintang Guo Wencheng Zhang 《Journal of polymer science. Part A, Polymer chemistry》2013,51(15):3166-3176
The synthetic polycations are ideal candidates as antimicrobial agents, because they resemble natural antimicrobial peptides, but to render hemocompatibility to these materials is a great challenge. Herein, we used 2‐(tert‐butyl‐aminoethyl) methacrylate (TBAEMA), to synthesize its homopolymer and pegylated random and diblock copolymers with polyethyleneglycol methacrylate (PEGMA, Mn = 360 Da) by single‐electron transfer–living radical polymerization (SET‐LRP). In the second step, the secondary amino groups in the precursor polymers were quaternized with iodomethane and bromohexane, to obtain three series of quaternized polymers. The antimicrobial properties of these quaternized polymers were evaluated against Escherichia coli (E. coli), by studying the minimum inhibitory concentrations (MICs) which ranged between 32 and 200 mg L?1 and showed higher values for the quaternized random than the diblock copolymers. In addition to, we have also demonstrated the grafting of these polycations onto polycarbonate urethane film surfaces, which showed good killing efficacy against E. coli. Furthermore, the hemolysis of these materials was investigated against human red blood cells, which indicated that except the quaternized homopolymers that showed highest hemolysis, all other amphiphilic polycations exhibited very low hemolytic activity. Therefore, our designed materials with controlled structures and functionality, synthesized from cheaply available resources could serve as useful agents in the field of biomedicines and implantable materials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3166–3176 相似文献
992.
17β‐Estradiol (E2) surface molecularly imprinted polymers have been prepared using functionalized monodispersed poly(glycidyl methacrylate‐co‐ethylene dimethacrylate) beads as a support. The resulting polymers were found to be uniform in size (5 μm), and the surfaces of the microspheres possessed large pore‐like structures. A chromatographic experiment demonstrated that the resulting microspheres exhibited high levels of recognition and selectivity toward the target molecule. The particles were employed as a novel sorbent in a molecularly imprinted SPE protocol. A method was then developed involving the combination of the pretreatment with HPLC to determine the levels of estrogen secreted from Michigan Cancer Foundation‐7 cells. The obtained results revealed that the extraction recoveries of E2 from real samples were in the range of 73.0–97.5% with RSDs of < 7.5% (n = 3). Calibration curves were established with R values > 0.9996 for concentrations in the range of 0.50–100.00 ng/mL. The LOD of this new method was 0.14 ng/mL. Compared with traditional C18 SPE agents, the particles showed high selectivity and extraction efficiency for E2 in the pretreatment process. The particles could therefore be used to determine trace estrogen in biological samples with a UV detector only. 相似文献
993.
Liu Han Yu Aili Liu Huiqiang Chu Sheng Tan Shaozao 《Russian Journal of Applied Chemistry》2017,90(7):1171-1180
Russian Journal of Applied Chemistry - Based on the advantages of graphene and zeolite, respectively, the graphene/zeolite composites with core-shell structure were synthesized. The features of the... 相似文献
994.
995.
996.
Non-specular reflection of self-collimated beams in photonic-crystal-made prism and waveguide system
Fei Zhou Kui Han Yang Ge Faliang Ju Yifeng Shen Gang Tang 《Optics Communications》2012,285(12):2780-2784
We demonstrate a dual-beam-reflection phenomenon for a Gaussian beam illuminating at a Kretschmann configuration composed of a photonic-crystal-made prism and a dielectric waveguide. One reflection beam has a positive shift and the other has a negative shift. The finite-difference time-domain (FDTD) shows that the specific phenomenon takes place only when the corresponding quasi-guided mode supported in the Kretschmann configuration is excited. Field profile of the quasi-guided mode demonstrates a strong localized stationary field in the dielectric waveguide. We found that the maximum positive lateral shift (LS) is 14.27a (where a is the lattice constant), corresponding to 3.07 times of the incident wavelength, which is 0.7135 times of the beam waist and much larger than that in some previous reports. 相似文献
997.
First-principles study of structural stability and elastic property of pre-perovskite PbTiO3 下载免费PDF全文
The structural stability and the elastic properties of a novel structure of lead titanate,which is named preperovskite PbTiO3 (PP-PTO) and is constructed with TiO6 octahedral columns arranged in a one-dimensional manner,are investigated by using first-principles calculations.PP-PTO is energetically unstable compared with conventional perovskite phases,however it is mechanically stable.The equilibrium transition pressures for changing from preperovskite to cubic and tetragonal phases are 0.5 GPa and 1.4 GPa,respectively,with first-order characteristics.Further,the differences in elastic properties between pre-perovskite and conventional perovskite phases are discussed for the covalent bonding network,which shows a highly anisotropic character in PP-PTO.This study provides a crucial insight into the structural stabilities of PP-PTO and conventional perovskite. 相似文献
998.
Formation and dissociation of protonated cytosine–cytosine base pairs in i-motifs by ab initio quantum chemical calculations 下载免费PDF全文
Formation and dissociation mechanisms of C-C+ base pairs in acidic and alkaline environments are investigated, employing ab initio quantum chemical calculations. Our calculations suggest that, in an acidic environment, a cytosine monomer is first protonated and then dimerized with an unprotonated cytosine monomer to form a C-C+ base pair; in an alkaline environment, a protonated cytosine dimer is first unprotonated and then dissociated into two cytosine monomers. In addition, the force for detaching a C-C+ base pair was found to be inversely proportional to the distance between the two cytosine monomers. These results provide a microscopic mechanism to qualitatively explain the experimentally observed reversible formation and dissociation of i-motifs. 相似文献
999.
1000.