全文获取类型
收费全文 | 481篇 |
免费 | 26篇 |
国内免费 | 2篇 |
专业分类
化学 | 359篇 |
晶体学 | 12篇 |
力学 | 14篇 |
数学 | 50篇 |
物理学 | 74篇 |
出版年
2024年 | 1篇 |
2022年 | 16篇 |
2021年 | 20篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2018年 | 17篇 |
2017年 | 18篇 |
2016年 | 15篇 |
2015年 | 18篇 |
2014年 | 23篇 |
2013年 | 34篇 |
2012年 | 15篇 |
2011年 | 39篇 |
2010年 | 17篇 |
2009年 | 21篇 |
2008年 | 19篇 |
2007年 | 32篇 |
2006年 | 20篇 |
2005年 | 30篇 |
2004年 | 14篇 |
2003年 | 22篇 |
2002年 | 16篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有509条查询结果,搜索用时 5 毫秒
101.
Mohammad Wasim Muhammad Daud Mohammad Arif Rameez ul-Islam Sajid Iqbal Yasir Anwar 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(2):653-659
In the under developed countries, the people of far-flung rural areas still depend to a large extent upon herbal medicines.
At the foundation of usage of herbal medicine is the experience of thousands of years. The present paper deals with the characterisation
of exotic fruits for essential and toxic elements. The samples include Morus nigra, Morus alba, Salvadora persica and Carissa opaca (from low and high altitude). Two standardizations of neutron activation analysis, that is, semi-absolute k
0-instrumental neutron activation analysis (k
0-INAA) and epithermal neutron activation analysis (ENAA) were employed for the quantification of elements. The analysis methodologies
were validated by analyzing the IAEA-336 (lichen) and NIST-SRM-1572 (citrus leaves). Sixteen elements including Br, Ca, Cl,
Co, Cr, Fe, I, K, Mg, Mn, Na, Rb, Sb, Sc Sr, and Zn were determined in all samples. Daily intakes of various elements from
the samples were measured and compared with the dietary reference intakes. Additionally, principal component analysis was
performed to extract information regarding samples and elements. 相似文献
102.
Homotopy perturbation method is used to solve specific second order ordinary differential equations and tested for different examples. The results obtained demonstrate efficiency of the proposed method. 相似文献
103.
Arif Kivrak 《Journal of organometallic chemistry》2007,692(11):2346-2349
A new and efficient one-pot synthesis of cyanoferrocene from ferrocenecarboxaldehyde is described by employing the NH2OH · HCl/KI/ZnO/CH3CN system. 相似文献
104.
105.
We present herein a new nanocatalyst, namely binary CuPt alloy nanoparticles (NPs) supported on reduced graphene oxide (CuPt‐rGO), as a highly active heterogeneous catalyst for the transfer hydrogenation (TH) protocol that is demonstrated to be applicable over the reduction of various unsaturated organic compounds (olefins, aldehydes/ketones and nitroarenes) in aqueous solutions at room temperature. CuPt alloy NPs were synthesized by the co‐reduction of metal (II) acetylacetonates by borane‐tert‐butylamine (BTB) complex in hot oleylamine (OAm) solution and then assembled on reduced graphene oxide (rGO) via ultrasonic‐assisted liquid phase self‐assembly method. The structure of yielded CuPt NPs and CuPt‐rGO nanocatalyst were characterized by TEM, XRD and ICP‐MS. The activity of Cu7Pt3‐rGO nanocatalysts were then tested for the THs that were conducted in a commercially available high‐pressure tube using water as sole solvent and ammonia borane as a hydrogen donor at room temperature. The presented catalytic TH protocol was successfully applied over nitroarenes, olefines and aldehydes/ketones, and all the tested compounds were converted to corresponding reduction products with the yields reaching up to 99% under ambient conditions. Moreover, the Cu7Pt3‐rGO nanocatalyst was also reusable in the TH by providing 99% yield after five consecutive runs in TH of nitrobenzene as an example. 相似文献
106.
Arif SALIMOV 《数学年刊B辑(英文版)》2022,43(2):223-232
The main purpose of this paper is to study the differential geometrical objects on tangent bundle corresponding to dual-holomorphic objects of dual-holomorphic manifold.As a result of this approach, the authors find a new class of lifts(deformed complete lifts)in the tangent bundle. 相似文献
107.
James K. Harper Atta M. Arif J. Y. Li Gary Strobel David M. Grant 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(12):e570-e571
The fungal metabolite terrein (alternative name: trans‐2,3‐dihydroxy‐4‐propenylcyclopent‐4‐enone), C8H10O3, forms monoclinic (P21) crystals. The molecules form hydrogen‐bonded chains, with O?O distances of 2.7115 (16) and 2.8155 (15) Å. 相似文献
108.
The main purpose of this paper is to study the deformed Riemannian extension▽g +VG··in the cotangent bundle, where G is a twin Norden metric on the base manifold. 相似文献
109.
110.
Laser cutting of sharp edge: Thermal stress analysis 总被引:1,自引:0,他引:1
Laser cutting of sharp edge and thermal stress development in the cutting section is examined. The finite element method is used to predict temperature and stress fields while the X-ray diffraction (XRD) technique is used to measure the residual stress around the cut edges. A mild steel sheet with 5 mm thickness is used in the simulations and the experiment. The morphological and metallurgical changes around the edges are examined using the optical microscopy and scanning electron microscopy (SEM). It is found that temperature remains high at the sharp edge when the laser beam is located in this region. This, in turn, lowers the cooling rate and reduces von Mises stress in this region. The magnitude of the residual stress is about 90 MPa at the sharp corner while the maximum von Mises stress is in the order of 280 MPa, which occurs away from sharp corner. In addition, the residual stress predicted agrees with the experimental data. 相似文献