全文获取类型
收费全文 | 1751篇 |
免费 | 117篇 |
国内免费 | 34篇 |
专业分类
化学 | 1395篇 |
晶体学 | 11篇 |
力学 | 55篇 |
数学 | 167篇 |
物理学 | 274篇 |
出版年
2024年 | 2篇 |
2023年 | 17篇 |
2022年 | 64篇 |
2021年 | 65篇 |
2020年 | 105篇 |
2019年 | 103篇 |
2018年 | 150篇 |
2017年 | 98篇 |
2016年 | 134篇 |
2015年 | 87篇 |
2014年 | 136篇 |
2013年 | 209篇 |
2012年 | 148篇 |
2011年 | 121篇 |
2010年 | 88篇 |
2009年 | 75篇 |
2008年 | 81篇 |
2007年 | 61篇 |
2006年 | 34篇 |
2005年 | 31篇 |
2004年 | 20篇 |
2003年 | 19篇 |
2002年 | 12篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有1902条查询结果,搜索用时 15 毫秒
981.
Karamoozian Najmeh Dehestani Maryam Behjatmanesh-Ardakani Reza 《Structural chemistry》2020,31(6):2543-2543
Structural Chemistry - Corrections are needed to the original publication of this article. The author’s affiliations were incorrectly assigned during submission. The authors apologize for the... 相似文献
982.
Hojjatollah Nazari Asieh Heirani‐Tabasi Maryam Hajiabbas Masoud Khalili Mohammadhossein Shahsavari Alavijeh Shadie Hatamie Armita Mahdavi Gorabi Elaheh Esmaeili Seyed Hossein Ahmadi Tafti 《先进技术聚合物》2020,31(2):248-259
Mimicking the extracellular matrix to have a similar nanofibrous structure regarding electrical conductivity and mechanical properties would be highly beneficial for cardiac tissue engineering. The molybdenum disulfide, MoS2, and reduced graphene oxide, rGO, nanosheets are two‐dimensional nanomaterials which can be considered as great candidates for enhancing the electrical and mechanical properties of biological scaffolds for cardiac tissue engineering applications. In this study, MoS2 and rGO nanosheets were synthesized and incorporated into silk fibroin nanofibers, SF, via electrospinning method. Then, the human iPSCs transfected with TBX‐18 gene, TBX18‐hiPSCs, were seeded on these scaffolds for in vitro studies. The MoS2 and rGO nanosheets were studied by Raman spectroscopy. After incorporation of the nanosheets into SF nanofibers, the associated characterizations were carried out including scanning electron microscopy, transmission electron microscopy, water contact angle, and mechanical test. Furthermore, SF, SF/MoS2, and SF/rGO scaffolds were used for in vitro studies. Herein, the scaffolds exhibited acceptable biocompatibility and considerable attachment to TBX18‐hiPSCs confirmed by 3‐(4, 5‐dimethylthiazol‐2‐yl)‐2, 5‐diphenyl tetrazolium bromide, MTT, assay, and scanning electron microscopy. Also, the real‐time PCR and immunostaining studies confirmed the maturity and upregulation of cardiac functional genes, including GATA‐4, c‐TnT, and α‐MHC in the SF/MoS2 and SF/rGO scaffolds compared with the bare SF one. Therefore, the reinforcement of these SF‐based scaffolds with MoS2 and rGO endues them as a suitable candidate for cardiac tissue engineering. 相似文献
983.
Hojati Seyedeh Fatemeh Amiri Amirhassan Mahamed Maryam 《Research on Chemical Intermediates》2020,46(2):1091-1107
Research on Chemical Intermediates - Polystyrene (PS)-coated magnetic graphene oxide (GO-Fe3O4) nanocomposite has been prepared and characterized by FT-IR, TEM and VSM techniques, and its catalytic... 相似文献
984.
基于纳米结构的电化学传感器用于伏安法测定苄丝肼、尿酸和叶酸(英文) 总被引:1,自引:0,他引:1
Sakineh Esfandiari Baghbamidi Hadi Beitollahi Seyed Zia Mohammadi Somayeh Tajik Somayeh Soltani-Nejad Vahhab Soltani-Nejad 《催化学报》2013,34(10):1869-1875
A carbon paste electrode modified with carbon nanotubes and ferrocene was fabricated.An electrochemical study of the modified electrode and an investigation into its efficiency for the electrocatalytic oxidation of benserazide,uric acid and folic acid were undertaken.The electrode was also used to study the electrocatalytic oxidation of benserazide using cyclic voltammetry,chronoamperometry,and square wave voltammetry(SWV).We found that the oxidation of benserazide at the surface of the modified electrode occurs at a potential about 285 mV lower than that of unmodified carbon paste electrode.SWV gave a linear dynamic range from 8.0×10-7 to 7.0×10 4 mol/L.The detection limit was 1.0×10-7 mol/L for benserazide.This modified electrode was used for the determination of benserazide,uric acid,and folic acid in an urine sample. 相似文献
985.
Seyed Mohammad VAHDAT Fereshteh CHEKIN Mehdi HATAMI Maryam KHAVARPOUR Saeed BAGHERY Ziba ROSHAN‐KOUHI 《催化学报》2013,34(4):758-763
Tin dioxide (SnO2 ) nanoparticles efficiently catalyzed unsymmetrical four-component Hantzsch condensations of various aldehydes, dimedone, ethyl acetoacetate, and ammonium acetate to form polyhydroquinoline derivatives in excellent yields. This novel method offers several advantages over the traditional method of synthesizing these compounds, including safety, mild conditions, short reaction times, high yields, and an easy workup. 相似文献
986.
Mahmood Tajbaksh Maryam Farhang Hamid Reza Mardani Rahman Hosseinzadeh Yaghoub Sarrafi 《催化学报》2013,34(12):2217-2222
A one pot three‐component coupling reaction of phenylacetylene, aldehyde, and amine derivatives in the presence of Cu(II) Salen complex as an efficient heterogeneous catalyst under solvent‐free conditions is reported. The catalyst displayed high activity and afforded the corresponding propargylamines in good to excellent yields. This method provides a wide range of substrate applicability. The catalyst was reused several times without significant loss of its catalytic activity. 相似文献
987.
The hydrothermal synthesis of analcime (ANA) with N,N′‐dibenzyl‐N,N,N′,N′‐tetramethylethylenediamine (DBTMED) as template was systematically studied. The various parameters that affect the crystallization of analcime, such as temperature, time, Al source, and Si/Al ratio were investigated. Systematic variations of these parameters revealed that ANA was obtained from the reaction mixture with the optimized ratios of SiO2/Al2O3 = 5–9.5 in presence of DBTMED, whereas template‐free clear solution methods require SiO2/Al2O3 ratio of greater than 25. When experiments were conducted at 130 and 150 °C for 4 days, a mixture of analcime and zeolite P was present in the samples, and a pure analcime sample could be obtained with heating in the temperature range 160–180 °C. When microwave and conventional heating were used, analcime could be obtained after 2 days. The obtained products were characterized by XRD, SEM, and IR spectroscopy. 相似文献
988.
The application of a blister test for measuring the interfacial fracture energy, Ga, is demonstrated. In the designed apparatus a fluid is injected at a constant rate to the interface between a solid substrate and a deformable coating to create a blister. The necessary fluid pressure and blister diameter were measured automatically as a function of time. Based on the collected data, the adhesion energy is calculated via Gent's equation. 相似文献
989.
Adhesive and cohesive properties by indentation method of plasma-sprayed hydroxyapatite coatings 总被引:2,自引:0,他引:2
Z. Mohammadi A.A. Ziaei-Moayyed A. Sheikh-Mehdi Mesgar 《Applied Surface Science》2007,253(11):4960-4965
Adhesive and cohesive properties of the plasma-sprayed hydroxyapatite (HA) coatings, deposited on Ti-6Al-4V substrates by varying the plasma power level and spray distance (SD), were evaluated by an indentation method. The crystallinity and the porosity decreased with increasing both of these two parameters. The microhardness value, Young's modulus (E) and coating fracture toughness (KC) were found to increase with a combinational increase in spray power and SD. The Knoop and Vickers indentation methods were used to estimate E and KC, respectively. The critical point at which no crack appears at the interface was determined by the interface indentation test. This was used to define the apparent interfacial toughness (KCa) which is representative of the crack initiation resistance of the interface. It was found that KCa reaches to a maximum at a medium increase in both spray power and SD, while other mechanical properties of the coatings reaches to the highest value with further increase in these two plasma parameters. The tensile adhesion strength of the coatings, measure by the standard adhesion test, ISO 13779-4, was shown to alter in the same manner with KCa results. It was deduced that a combinational increase in spray power and SD which leads to a higher mechanical properties in the coatings, does not necessarily tends to a better mechanical properties at the interface. 相似文献
990.