全文获取类型
收费全文 | 1374篇 |
免费 | 72篇 |
国内免费 | 26篇 |
专业分类
化学 | 1022篇 |
晶体学 | 5篇 |
力学 | 72篇 |
数学 | 154篇 |
物理学 | 219篇 |
出版年
2024年 | 4篇 |
2023年 | 9篇 |
2022年 | 34篇 |
2021年 | 61篇 |
2020年 | 83篇 |
2019年 | 69篇 |
2018年 | 113篇 |
2017年 | 63篇 |
2016年 | 111篇 |
2015年 | 83篇 |
2014年 | 92篇 |
2013年 | 187篇 |
2012年 | 103篇 |
2011年 | 116篇 |
2010年 | 72篇 |
2009年 | 74篇 |
2008年 | 61篇 |
2007年 | 41篇 |
2006年 | 20篇 |
2005年 | 22篇 |
2004年 | 7篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 4篇 |
1999年 | 4篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有1472条查询结果,搜索用时 93 毫秒
181.
182.
Syntheses and photoisomerization of the new sulfone derivatives, 4,4‐di (p‐trifluoromethylphenyl)‐2,6‐diphenyl‐4H‐thiopyran‐1, 1‐dioxide and 4‐(p‐trifluoromethylphenyl)‐2,4,6‐triphenyl‐4H‐thiopyran‐1,1‐dioxide, have been investigated. The relative molar ratios of the photoproducts are compared with those of 2,4,4,6‐tetraphenyl‐4H‐thiopyran‐1,1‐dioxide as well as electron‐donating substituted 4‐methyl‐2,4,6‐triaryl‐4H‐thiopyran‐1,1‐dioxides as model compounds under identical experimental conditions using 1H NMR spectroscopy. The results observed are discussed on the basis of a triplet excited state di‐π‐methane rearrangement. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:557–561, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20455 相似文献
183.
Khezri Behrooz Maskanati Maryam Zohrevand Bahareh Liyaghati-Delshad Mozhdeh Soltanali Fatemeh 《Structural chemistry》2022,33(2):315-322
Structural Chemistry - This is an analysis report on the use of density functional theory (DFT) to investigate the potentials of pristine and amino acid–functionalized C4B32 borospherenes in... 相似文献
184.
Mahmoud Roushani Zahra Saedi Fatemeh Hamdi Hamid Reza Rajabi 《Journal of the Iranian Chemical Society》2018,15(10):2241-2249
In this study, a new Cr(III)-imprinted polymer (Cr(III)-IIP) is prepared from CrCl3·6H2O, methacrylic acid functional monomer, ethyleneglycoldimethacrylate cross-linking agent, 2,2?-azobisisobutyronitrile radical initiator and 2,2-(azanediylbis (ethane-2,1-diyl))bis(isoindoline-1,3-dione) ligand. To obtain the maximum adsorption capacity, the optimum condition was studied through pH, type and concentration of eluent, IIP weight, sample volume as well as the adsorption and desorption times. The Cr(III) ion content was determined via flame atomic absorption spectrometer. In optimum conditions, the adsorption capacity of the IIP for Cr(III) was obtained to be 74.65 mg g?1, using 50 mg of IIP and the initial pH solution of 3.0. Both the adsorption and desorption times for quantitative analyses of Cr(III) ions were 15 and 5 min; respectively. After elution of the adsorbed ions by 3 mL of 4 mol L?1 HNO3 aqueous solution, the established IIP-based SPE procedure provides a reasonable pre-concentration factor of 100. The IIP-based pre-concentration method provides a low detection limit of 1.7 µg L?1 with good repeatability (RSD?=?3.22%). Reusability studies confirmed that synthesis IIP is reusable and recoverable up to six cycles. According to the selectivity experiments, it was concluded that the prepared sorbent possesses more affinity toward Cr(III) ions than other ions such as Al3+, Pb2+, Cu2+, Mn2+, Fe2+, Zn2+, and Ni2+ ions. To evaluate the potential applicability of the proposed separation method, the pre-concentration and determination of trace amounts of Cr(III) were performed successfully in food samples with complex matrices, a bestial sample (i.e. cow liver) and an herbal product (i.e., broccoli) as real samples. 相似文献
185.
In this article, the effect of ionization on the energy spectrum of electrons within the interaction of a laser pulse with hydrogen atoms is investigated using particle-in-cell simulation codes. The results show that the behaviour of electrons' energy distribution function in the field-ionized plasma, which occurred due to the field ionization, compared with that in the pre-plasma strongly depends on the pulse shape. For short rise-time pulses (here 30 fs), due to the rapid enhancement of laser electric field, ionization occurs quickly, and as a result, there is not much difference in the electron energy in both the media. However, for pulses with rise time of 40 fs, in the pre-plasma state, the electron population reaches higher energies compared with the field-ionized plasma state. The main reason for this difference is the nonlinear wave breaking that happens earlier due to density inhomogeneity in the field-ionized plasma. On the other hand, at longer rise-time pulses (here 60 and 70 fs), electrons achieve higher energies in the field-ionized plasma than those in the case of pre-plasma. In this case, because of density fluctuations in the field-ionized plasma, the Raman backscattered radiations are seeded by a strong initial noise at the earlier times and the Mendonca condition for chaos threshold is met sooner. Therefore, the electrons gain more energy through the stochastic mechanism that is in agreement with chaotic nature of the motion. 相似文献
186.
A mixed CuI/CuIIcatalyst based on magnetic cysteine functionalized graphene oxide (CuI/II@Cys-MGO) was prepared and used for the azidonation reaction of aryl boronic acids and one-pot synthesis of 1,4-diaryl −1,2,3-triazoles. Aryl azides were obtained in good yields and short reaction times via cross-coupling of aryl boronic acids with sodium azide in the presence of CuII catalytic species in this catalytic system. The azide-alkyne cycloaddition reaction was catalyzed by CuI catalytic species in CuI/II@Cys-MGO nanocomposite. 相似文献
187.
The European Physical Journal Special Topics - This topical issue collects contributions related to recent achievements and scientific progress in special chaotic systems. The individual papers... 相似文献
188.
Fatemeh Jafari Mehmandoost-Khajeh-Dad Ali Akbar Mohammadi-Dadkan Maysam Ghal-Eh Nima Yazdandoust Hamideh 《Physics of Particles and Nuclei Letters》2019,16(6):761-767
Physics of Particles and Nuclei Letters - Plastic scintillators are widely used in detecting nuclear radiation due to their low construction cost, the ability to be produced in nearly any shape and... 相似文献
189.
190.
Neshat Askarzadeh Masoumeh Haghbin Nazarpak Korosh Mansoori Mehdi Farokhi Mahdi Gholami Javad Mohammadi Fatemeh Mottaghitalab 《Macromolecular bioscience》2020,20(9)
Herein, a bilayer cylindrical conduit (P‐CA) is presented consisting of electrospun polycaprolactone (PCL) nanofibers and sodium alginate hydrogel covalently cross‐linked with N,N′‐disuccinimidyl carbonate (DSC). The bilayer P‐CA conduit is developed by combining the electrospinning and outer–inner layer methods. Using DSC, as a covalent crosslinker, increases the degradation time of the sodium alginate hydrogel up to 2 months. The swelling ratio of the hydrogel is also 503% during the first 8 h. The DSC cross‐linked sodium alginate in the inner layer of the conduit promotes the adhesion and proliferation of nerve cells, while the electrospun PCL nanofibers in the outer layer provide maximum tensile strength of the conduit during surgery. P‐CA conduit promotes the migration of Schwann cells along the axon in a rat model based on functional and histological evidences. In conclusion, P‐CA conduit will be a promising construct for repairing sciatic nerves in a rat model. 相似文献