全文获取类型
收费全文 | 2969篇 |
免费 | 552篇 |
国内免费 | 606篇 |
专业分类
化学 | 2515篇 |
晶体学 | 60篇 |
力学 | 162篇 |
综合类 | 14篇 |
数学 | 363篇 |
物理学 | 1013篇 |
出版年
2024年 | 13篇 |
2023年 | 51篇 |
2022年 | 96篇 |
2021年 | 101篇 |
2020年 | 147篇 |
2019年 | 138篇 |
2018年 | 112篇 |
2017年 | 93篇 |
2016年 | 147篇 |
2015年 | 158篇 |
2014年 | 144篇 |
2013年 | 228篇 |
2012年 | 221篇 |
2011年 | 242篇 |
2010年 | 222篇 |
2009年 | 249篇 |
2008年 | 252篇 |
2007年 | 232篇 |
2006年 | 178篇 |
2005年 | 179篇 |
2004年 | 133篇 |
2003年 | 123篇 |
2002年 | 150篇 |
2001年 | 137篇 |
2000年 | 59篇 |
1999年 | 65篇 |
1998年 | 39篇 |
1997年 | 15篇 |
1996年 | 24篇 |
1995年 | 28篇 |
1994年 | 21篇 |
1993年 | 23篇 |
1992年 | 22篇 |
1991年 | 26篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1982年 | 1篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1974年 | 1篇 |
1957年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有4127条查询结果,搜索用时 31 毫秒
121.
122.
123.
Chunhui Dai Yuxiang Wang Yiwu Quan Qingmin Chen Yixiang Cheng Chengjian Zhu 《Journal of polymer science. Part A, Polymer chemistry》2014,52(21):3080-3086
The β‐diketonate‐based achiral polymer P‐1 could be synthesized by the polymerization of 3,7‐dibromo‐2,8‐dimethoxy‐5,5‐dioctyl‐5H‐dibenzo[b,d]silole ( M1 ) with (Z)?1,3‐bis(4‐ethynylphenyl)?3‐hydroxyprop‐en‐1‐one ( M2 ) via typical Sonogashira coupling reaction. The β‐diketonate unit in the main chain backbone of P‐1 can further coordinate with Eu(TTA)x [TTA? = 4,4,4‐trifluoro‐1‐(thiophen‐2‐yl)butane‐1,3‐dionate anion, X = 1, 2, 3] to afford corresponding Eu(III)‐containing polymer complexes. The resulting achiral polymer complex P‐2 (X = 2) can exhibit strong circular dichroism (CD) response toward both N‐Boc‐l and d‐ proline enantiomers. The CD signal was preliminarily attributed to coordination induction between chiral N‐Boc‐proline and the Eu(III) complex moiety. The linear regression analysis of CD sensing shows a good agreement between the magnitude of molar ellipticity and concentration of chiral N‐Boc‐l or d‐ proline, which indicates this kind Eu(III)‐containing achiral polymer complex can be used as a chiral probe for enantioselective recognition of N‐Boc‐l or d‐ proline enantiomers based on Cotton effect of CD spectra. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3080–3086 相似文献
124.
Simulation of near-infrared photodiode detectors based on β-FeSi_2/4H-SiC heterojunctions 总被引:1,自引:0,他引:1 下载免费PDF全文
In this paper,we propose a near-infrared p-type β-FeSi2/n-type 4H-SiC heterojunction photodetector with semiconducting silicide(β-FeSi2) as the active region for the first time.The optoelectronic characteristics of the photodetector are simulated using a commercial simulator at room temperature.The results show that the photodetector has a good rectifying character and a good response to near-infrared light.Interface states should be minimized to obtain a lower reverse leakage current.The response spectrum of the β-FeSi2/4H-SiC detector,which consists of a p-type β-FeSi2 absorption layer with a doping concentration of 1×1015cm-3 and a thickness of 2.5 μm,has a peak of 755 mA/W at 1.42 μm.The illumination of the SiC side obtains a higher responsivity than that of the β-FeSi2 side.The results illustrate that the β-FeSi2/4H-SiC heterojunction can be used as a near-infrared photodetector compatible with near-infrared optically-activated SiC-based power switching devices. 相似文献
125.
Quan Manh Phung Kristine Pierloot 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(54):12491-12496
Density functional theory (DFT) and an advanced ab initio technique based on density matrix renormalization group (DMRG-CASPT2) were employed to investigate a reactive N-bridged high-valent diiron-oxo species involved in H-abstraction reactions. We studied in detail two important doublet states, the ground state with two iron(IV) centers and a mixed valence FeV-FeIV excited state. We found that the latter state is low-lying. Furthermore, its electronic structure and spin density imply that it has significantly higher H-abstraction reactivity than the ground state. This low-lying excited state might be the reason behind the high oxidation reactivity of this diiron-oxo species towards methane. 相似文献
126.
Zhengjun Quan Zhang Zhang Xicun Wang Zheng Li 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6):1397-1402
Under grinding and solvent-free conditions via a one-pot procedure, the reaction of 2-benzofuroyl chloride with ammonium thiocyanate and aryloxyacetetic acid hydrazide afforded 1-aryloxyacetyl-4-(2-benzofuroyl)-thiosemicarbazide. Not isolating, the resulting thiosemicarbazides were further ground with HIO4·H2O to give a series of new 1-aryloxyacetyl-4-(2-benzofuroyl)-semicarbazides in high yields. Structures of compounds are confirmed by elemental analyses and IR and 1H NMR spectra. 相似文献
127.
128.
In response to aggravated fossil resources consuming and greenhouse effect, CO2 reduction has become a globally important scientific issue because this method can be used to produce value-added feedstock for application in alternative energy supply. Photoelectrocatalysis, achieved by combining optical energy and external electrical bias, is a feasible and promising system for CO2 reduction. In particular, applying graphene in tuning photoelectrochemical CO2 reduction has aroused considerable attention because graphene is advantageous for enhancing CO2 adsorption, facilitating electrons transfer, and thus optimizing the performance of graphene-based composite electrodes. In this review, we elaborate the fundamental principle, basic preparation methods, and recent progress in developing a variety of graphene-based composite electrodes for photoelectrochemical reduction of CO2 into solar fuels and chemicals. We also present a perspective on the opportunities and challenges for future research in this booming area and highlight the potential evolution strategies for advancing the research on photoelectrochemical CO2 reduction. 相似文献
129.
A coupled immersed boundary‐lattice Boltzmann method with smoothed point interpolation method for fluid‐structure interaction problems 下载免费PDF全文
Shuangqiang Wang Yunan Cai Guiyong Zhang Xiaobo Quan Jianhua Lu Sheng Li 《国际流体数值方法杂志》2018,88(8):363-384
The immersed boundary‐lattice Boltzmann method has been verified to be an effective tool for fluid‐structure interaction simulation associated with thin and flexible bodies. The newly developed smoothed point interpolation method (S‐PIM) can handle the largely deformable solids owing to its softened model stiffness and insensitivity to mesh distortion. In this work, a novel coupled method has been proposed by combining the immersed boundary‐lattice Boltzmann method with the S‐PIM for fluid‐structure interaction problems with large‐displacement solids. The proposed method preserves the simplicity of the lattice Boltzmann method for fluid solvers, utilizes the S‐PIM to establish the realistic constitutive laws for nonlinear solids, and avoids mesh regeneration based on the frame of the immersed boundary method. Both two‐ and three‐dimensional numerical examples have been carried out to validate the accuracy, convergence, and stability of the proposed method in consideration of comparative results with referenced solutions. 相似文献
130.
Preparation of core–shell structure Fe3O4@SiO2 superparamagnetic microspheres immoblized with iminodiacetic acid as immobilized metal ion affinity adsorbents for His‐tag protein purification 下载免费PDF全文
Qian Ni Bing Chen Shaohua Dong Lei Tian Quan Bai 《Biomedical chromatography : BMC》2016,30(4):566-573
The core–shell structure Fe3O4/SiO2 magnetic microspheres were prepared by a sol–gel method, and immobiled with iminodiacetic acid (IDA) as metal ion affinity ligands for protein adsorption. The size, morphology, magnetic properties and surface modification of magnetic silica nanospheres were characterized by various modern analytical instruments. It was shown that the magnetic silica nanospheres exhibited superparamagnetism with saturation magnetization values of up to 58.1 emu/g. Three divalent metal ions, Cu2+, Ni2+ and Zn2+, were chelated on the Fe3O4@SiO2–IDA magnetic microspheres to adsorb lysozyme. The results indicated that Ni2+‐chelating magnetic microspheres had the maximum adsorption capacity for lysozyme of 51.0 mg/g, adsorption equilibrium could be achieved within 60 min and the adsorbed protein could be easily eluted. Furthermore, the synthesized Fe3O4@SiO2–IDA–Ni2+ magnetic microspheres were successfully applied for selective enrichment lysozyme from egg white and His‐tag recombinant Homer 1a from the inclusion extraction expressed in Escherichia coli. The result indicated that the magnetic microspheres showed unique characteristics of high selective separation behavior of protein mixture, low nonspecific adsorption, and easy handling. This demonstrates that the magnetic silica microspheres can be used efficiently in protein separation or purification and show great potential in the pretreatment of the biological sample. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献