全文获取类型
收费全文 | 294474篇 |
免费 | 2808篇 |
国内免费 | 1130篇 |
专业分类
化学 | 135692篇 |
晶体学 | 4342篇 |
力学 | 17200篇 |
综合类 | 54篇 |
数学 | 45738篇 |
物理学 | 95386篇 |
出版年
2021年 | 2210篇 |
2020年 | 2350篇 |
2019年 | 2817篇 |
2018年 | 11333篇 |
2017年 | 11976篇 |
2016年 | 8693篇 |
2015年 | 3372篇 |
2014年 | 4773篇 |
2013年 | 9168篇 |
2012年 | 11271篇 |
2011年 | 19656篇 |
2010年 | 13032篇 |
2009年 | 13344篇 |
2008年 | 17403篇 |
2007年 | 20495篇 |
2006年 | 7248篇 |
2005年 | 11749篇 |
2004年 | 8709篇 |
2003年 | 8392篇 |
2002年 | 6668篇 |
2001年 | 5872篇 |
2000年 | 4582篇 |
1999年 | 3317篇 |
1998年 | 2862篇 |
1997年 | 2916篇 |
1996年 | 2839篇 |
1995年 | 2427篇 |
1994年 | 2510篇 |
1993年 | 2404篇 |
1992年 | 2658篇 |
1991年 | 2781篇 |
1990年 | 2683篇 |
1989年 | 2734篇 |
1988年 | 2654篇 |
1987年 | 2674篇 |
1986年 | 2503篇 |
1985年 | 3149篇 |
1984年 | 3224篇 |
1983年 | 2699篇 |
1982年 | 2659篇 |
1981年 | 2600篇 |
1980年 | 2389篇 |
1979年 | 2798篇 |
1978年 | 2768篇 |
1977年 | 2885篇 |
1976年 | 2916篇 |
1975年 | 2701篇 |
1974年 | 2636篇 |
1973年 | 2787篇 |
1972年 | 2113篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
A. Lashgari S. Ghammamy R. Ramirez-Tagle G. Salgado-Moran 《Journal of Structural Chemistry》2015,56(8):1505-1513
Two new compounds of fluorine: (C2H5)4N[I2F] and (C2H5)4N[Br2F], have been easily synthesized in a nearly quantitative by a direct reaction of (C2H5)4NF, I2 and Br2. The products were isolated and characterized by elemental analysis and spectroscopic methods such as: Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). These compounds have been studied computationally with the Scalar ZORA relativistic level of theory using the ADF program package. The molecular parameters, and vibrational spectra were calculated. The excitation energies were found by timedependent perturbation density functional theory (TD-DFT). Molecule optimization, frequencies and excitation energies were calculated with standard Slatertype-orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all atoms. The FTIR, UV-Vis spectra and assignment of principal transitions and total density of state (TDOS) were extracted using the GaussSum 2.2 program. The comparison between experimental and calculated values showes that the experimental results correlate well with the predicted data. 相似文献
63.
Khusnutdinov R. I. Shchadneva N. A. Mayakova Yu. Yu. Aminov R. I. 《Russian Journal of Organic Chemistry》2021,57(6):950-953
Russian Journal of Organic Chemistry - Binder-free iron- and nickel-containing micro-, meso-, and macroporous zeolites FeHY and NiHY were found to effectively catalyze Knoevenagel condensation of... 相似文献
64.
Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been deemed as clean and sustainable strategies to solve the energy crisis and environmental problems. Various catalysts have been developed to promote the process of HER and OER. Among them, two-dimensional covalent organic frameworks (2D COFs) have received great attention due to their diverse and designable structure. In this minireview, we mainly summarize the diverse linkages of 2D COFs and strategies for enhancing the catalytic performance of 2D COFs for HER and OER, such as introducing active building blocks, metal ions and tailored linkages. Furthermore, a brief outlook for the development directions of COFs in the field of HER and OER is provided, expecting to stimulate new opportunities in future research. 相似文献
65.
Elasasy M. E. A. Elnaggar D. H. Hafez N. A. Abdel Azab M. E. Amr A. E. Omran M. M. Mohamed A. M. 《Russian Journal of General Chemistry》2021,91(5):915-925
Russian Journal of General Chemistry - Some new fluoro-heterocyclic compounds containing thiazole and pyridine moities have been synthesized and studied for their antiproliferative activity.... 相似文献
66.
67.
68.
Journal of Applied and Industrial Mathematics - We consider the optimization of the short wave phased antenna arrays as a quadratic programming problem. The penalty function method and the gradient... 相似文献
69.
Ahmed Waqar Chowdhury Z. Z. Kazi S. N. Johan MR. Akram Naveed Oon C. S. Abdelrazek Ali H. 《Journal of Thermal Analysis and Calorimetry》2021,144(4):1517-1534
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers... 相似文献
70.
M. Kroon E. Andreasson E. Persson Jutemar V. Petersson L. Persson M. Dorn P.A.T. Olsson 《Experimental Mechanics》2018,58(1):75-86
Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters. 相似文献