全文获取类型
收费全文 | 7224篇 |
免费 | 331篇 |
国内免费 | 76篇 |
专业分类
化学 | 5156篇 |
晶体学 | 85篇 |
力学 | 306篇 |
综合类 | 1篇 |
数学 | 803篇 |
物理学 | 1280篇 |
出版年
2024年 | 16篇 |
2023年 | 60篇 |
2022年 | 506篇 |
2021年 | 385篇 |
2020年 | 297篇 |
2019年 | 295篇 |
2018年 | 259篇 |
2017年 | 213篇 |
2016年 | 379篇 |
2015年 | 207篇 |
2014年 | 270篇 |
2013年 | 626篇 |
2012年 | 449篇 |
2011年 | 438篇 |
2010年 | 295篇 |
2009年 | 233篇 |
2008年 | 291篇 |
2007年 | 295篇 |
2006年 | 244篇 |
2005年 | 194篇 |
2004年 | 185篇 |
2003年 | 163篇 |
2002年 | 182篇 |
2001年 | 82篇 |
2000年 | 65篇 |
1999年 | 55篇 |
1998年 | 52篇 |
1997年 | 34篇 |
1996年 | 45篇 |
1995年 | 40篇 |
1994年 | 51篇 |
1993年 | 42篇 |
1992年 | 44篇 |
1991年 | 45篇 |
1990年 | 31篇 |
1989年 | 58篇 |
1988年 | 44篇 |
1987年 | 36篇 |
1986年 | 38篇 |
1985年 | 43篇 |
1984年 | 47篇 |
1983年 | 40篇 |
1982年 | 28篇 |
1981年 | 25篇 |
1980年 | 31篇 |
1979年 | 24篇 |
1978年 | 31篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1975年 | 17篇 |
排序方式: 共有7631条查询结果,搜索用时 17 毫秒
991.
Sarah A. Richardson Thomas M. Rawlings Joanne Muter Marc Walker Jan J. Brosens Neil R. Cameron Ahmed M. Eissa 《Macromolecular bioscience》2019,19(2)
A novel strategy for the surface functionalization of emulsion‐templated highly porous (polyHIPE) materials as well as its application to in vitro 3D cell culture is presented. A heterobifunctional linker that consists of an amine‐reactive N‐hydroxysuccinimide ester and a photoactivatable nitrophenyl azide, N‐sulfosuccinimidyl‐6‐(4′‐azido‐2′‐nitrophenylamino)hexanoate (sulfo‐SANPAH), is utilized to functionalize polyHIPE surfaces. The ability to conjugate a range of compounds (6‐aminofluorescein, heptafluorobutylamine, poly(ethylene glycol) bis‐amine, and fibronectin) to the polyHIPE surface is demonstrated using fluorescence imaging, FTIR spectroscopy, and X‐ray photoelectron spectroscopy. Compared to other existing surface functionalization methods for polyHIPE materials, this approach is facile, efficient, versatile, and benign. It can also be used to attach biomolecules to polyHIPE surfaces including cell adhesion‐promoting extracellular matrix proteins. Cell culture experiments demonstrated that the fibronectin‐conjugated polyHIPE scaffolds improve the adhesion and function of primary human endometrial stromal cells. It is believed that this approach can be employed to produce the next generation of polyHIPE scaffolds with tailored surface functionality, enhancing their application in 3D cell culture and tissue engineering whilst broadening the scope of applications to a wider range of cell types. 相似文献
992.
We present the results from investigations of the nonlinear refractive index and nonlinear absorption coefficient of tris(acetylacetonato)manganese(III) solution, using Z-scan technique with a low-power continuous-wave laser at 514 nm. We demonstrate that the light-induced nonlinear refractive index variation leads to strong self-focusing and self-defocusing. A pump and probe technique was used to investigate the cause of nonlinearity. Furthermore, the nonlinear absorption effect was utilized to demonstrate all optical switching. 相似文献
993.
El Sayed Moustafa Yasser B. Saddeek Essam R. Shaaban 《Journal of Physics and Chemistry of Solids》2008,69(9):2281-2287
Glasses with compositions 25Li2O-(75−x)Bi2O3-x B2O3, with 0?x?30 mol%, have been prepared using the melt quenching technique. The density and the molar volume have been determined. IR spectroscopy is used as a structural probe of the nearest neighbor environment in the glass network. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400-1100 nm. The values of the optical band gap Egopt for indirect transition and refractive index have been determined for 0?x?30 mol%. The average electronic polarizability of the oxide ion αo2− and the optical basicity have been estimated from the calculated values of the refractive indices. Variations in the different physical parameters such as the density, molar volume, optical band gap, refractive index, average electronic polarizability of the oxide ion and optical basicity with B2O3 content have been analyzed and discussed in terms of the changes in the glass structure. 相似文献
994.
Aharmim B Ahmed SN Amsbaugh JF Anthony AE Banar J Barros N Beier EW Bellerive A Beltran B Bergevin M Biller SD Boudjemline K Boulay MG Bowles TJ Browne MC Bullard TV Burritt TH Cai B Chan YD Chauhan D Chen M Cleveland BT Cox-Mobrand GA Currat CA Dai X Deng H Detwiler J DiMarco M Doe PJ Doucas G Drouin PL Duba CA Duncan FA Dunford M Earle ED Elliott SR Evans HC Ewan GT Farine J Fergani H Fleurot F Ford RJ Formaggio JA Fowler MM Gagnon N Germani JV Goldschmidt A Goon JT Graham K Guillian E 《Physical review letters》2008,101(11):111301
The Sudbury Neutrino Observatory (SNO) used an array of 3He proportional counters to measure the rate of neutral-current interactions in heavy water and precisely determined the total active (nu_x) 8B solar neutrino flux. This technique is independent of previous methods employed by SNO. The total flux is found to be 5.54_-0.31;+0.33(stat)-0.34+0.36(syst)x10(6) cm(-2) s(-1), in agreement with previous measurements and standard solar models. A global analysis of solar and reactor neutrino results yields Deltam2=7.59_-0.21;+0.19x10(-5) eV2 and theta=34.4_-1.2;+1.3 degrees. The uncertainty on the mixing angle has been reduced from SNO's previous results. 相似文献
995.
Gholam Reza Gordani Reza ShojaRazavi Sayed Hamid Hashemi Ali Reza Nasr Isfahani 《Optics and Lasers in Engineering》2008,46(7):550-557
Laser surface alloying of an electroless plating Ni–P coatings on an Al-356 aluminium alloy was carried out using a 1-kW pulsed Nd:YAG laser. The microstructure, chemical composition and phase identification of the alloyed layer were determined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD), respectively. It was shown that laser surface treatment produced a relatively smooth, crack-free and hard surface layer. The hardness of the surface significantly increased due to the formation of the uniformly distributed fine Ni–Al intermetallic phases. The corrosion behaviour of the surface alloyed specimens in 3.5% NaCl solution at 23 °C was also determined by electrochemical techniques. The laser-alloyed surface showed an improved corrosion and pitting potential compared to the substrate as well as the plated Ni–P coating. 相似文献
996.
Total fragmentation cross section for the reaction 158A Pb ions + Cu target is measured using the most sensitive track detector CR-39. Measured values are compared with calculations. Exposures of target-detector stack with 158A P5 projectiles are made at CERN-SPS beam facility. Results of calibration of CR-39 detector in a charge region (63 ≤ Z ≤ 83) are also reported, which can be used for high energy particle identification using CR-39 and in determination of partial charge changing cross sections. The charge resolution δz achieved by this technique is about 0.2e. A systematic dependence of total fragmentation cross section on target properties is revealed and the corresponding results are presented. 相似文献
997.
998.
Glasses in the system TeO2/Nb2O5/ZnO/CdS were studied with respect to the density, molar volume, refractive index, polarizability, molar refraction, metallization and third order non-linear optical susceptibility. The third order non-linear optical susceptibilities, χ(3), were measured using degenerate four-wave mixing (DFWM). The addition of CdS to TeO2-based glasses leads to increasing refractive as well as the non-linear refractive indices. The largest measured value of the third order non-linear optical susceptibility was 7.8 × 10?13 esu and has been found in the 90TeO2 · 5Nb2O5 · 5ZnO · 0.4 CdS glass. The non-linear optical susceptibility increased with increasing CdS-concentration. In order to estimate the third order non-linear optical susceptibility, the theoretical model of Lines and the empirical equation of Miller were used. 相似文献
999.
Hafiz Ejaz Ahmed Yasir Iqbal Muhammad Hammad Aziz Muhammad Atif Zahida Batool Atif Hanif Nafeesah Yaqub W. A. Farooq Shafiq Ahmad Amanullah Fatehmulla Hijaz Ahmad 《Molecules (Basel, Switzerland)》2021,26(15)
Metal oxide nanoparticles synthesized by the biological method represent the most recent research in nanotechnology. This study reports the rapid and ecofriendly approach for the synthesis of CeO2 nanoparticles mediated using the Abelmoschus esculentus extract. The medicinal plant extract acts as both a reducing and stabilizing agent. The characterization of CeO2 NPs was performed by scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), and Fourier transform infrared spectroscopy (FTIR). The in vitro cytotoxicity of green synthesized CeO2 was assessed against cervical cancerous cells (HeLa). The exposure of CeO2 to HeLa cells at 10–125 µg/mL caused a loss in cellular viability against cervical cancerous cells in a dose-dependent manner. The antibacterial activity of the CeO2 was assessed against S. aureus and K. pneumonia. A significant improvement in wound-healing progression was observed when cerium oxide nanoparticles were incorporated into the chitosan hydrogel membrane as a wound dressing. 相似文献
1000.
Hussein Bassal Akram Hijazi Hussein Farhan Christine Trabolsi Bouchra Sayed Ahmad Alia Khalil Marc Maresca Fawaz El Omar 《Molecules (Basel, Switzerland)》2021,26(15)
Psophocarpus tetragonolobus has long been used in traditional medicine and cuisine. In this study, Psophocarpus tetragonolobus extracts were isolated by maceration and ultrasound-assisted extraction and were evaluated for their antioxidant and anti-inflammatory effects in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. The obtained results show that both extracts (maceration and ultrasound) were rich in bioactive molecules and exerted substantial antioxidant and anti-inflammatory effects. The P. tetragonolobus extracts’ treatment in LPS-stimulated RAW264.7 macrophages resulted in a significant downregulation of the expressions of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β mRNA. In addition, the P. tetragonolobus extracts’ treatment attenuated inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) protein expression. Our observations indicate that there is no significant difference between the two studied extracts of P. tetragonolobus in terms of biological properties (specifically, antioxidant and anti-inflammatory effects. Regardless of the extraction method, P. tetragonolobus could be used for treating diseases related to oxidative stress and inflammatory reactions. 相似文献