全文获取类型
收费全文 | 22162篇 |
免费 | 3405篇 |
国内免费 | 2424篇 |
专业分类
化学 | 15704篇 |
晶体学 | 270篇 |
力学 | 1319篇 |
综合类 | 188篇 |
数学 | 2300篇 |
物理学 | 8210篇 |
出版年
2024年 | 14篇 |
2023年 | 406篇 |
2022年 | 451篇 |
2021年 | 716篇 |
2020年 | 836篇 |
2019年 | 818篇 |
2018年 | 698篇 |
2017年 | 713篇 |
2016年 | 1003篇 |
2015年 | 1001篇 |
2014年 | 1137篇 |
2013年 | 1573篇 |
2012年 | 1856篇 |
2011年 | 1992篇 |
2010年 | 1296篇 |
2009年 | 1269篇 |
2008年 | 1469篇 |
2007年 | 1352篇 |
2006年 | 1217篇 |
2005年 | 970篇 |
2004年 | 774篇 |
2003年 | 657篇 |
2002年 | 632篇 |
2001年 | 462篇 |
2000年 | 454篇 |
1999年 | 481篇 |
1998年 | 422篇 |
1997年 | 414篇 |
1996年 | 452篇 |
1995年 | 362篇 |
1994年 | 374篇 |
1993年 | 269篇 |
1992年 | 252篇 |
1991年 | 231篇 |
1990年 | 165篇 |
1989年 | 129篇 |
1988年 | 116篇 |
1987年 | 97篇 |
1986年 | 95篇 |
1985年 | 85篇 |
1984年 | 58篇 |
1983年 | 49篇 |
1982年 | 38篇 |
1981年 | 28篇 |
1980年 | 31篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
961.
Shengli Niu Mengqi Liu Chunmei Lu Hui Li Mengjia Huo 《Journal of Thermal Analysis and Calorimetry》2014,115(1):73-79
Potential of carbide slag as transesterification catalyst is validated. Combined with X-ray fluorescence for ingredient determination, X-ray diffraction for textural phase analysis, scanning electron microscope for surface morphology observation and Hammett indicator for basic strength mensuration, thermal event of carbide slag is investigated through thermogravimetric analysis to estimate the potential of this calcium-based industrial waste as transesterification catalyst. Further, kinetic parameters are calculated through model-free method, where the experiments are conducted at temperature heating rates of 5, 10, 15, and 20 K min?1. As for activation energy and reaction order, Vyazovkin method and Avrami theory are respectively mentioned. Meanwhile, catalytic performance of carbide slag is labeled by transesterification efficiency and calcium hydroxide is conditionally mentioned for comparison. In conclusion, potential of carbide slag as transesterification catalyst is adequately validated. 相似文献
962.
Chen Chen Weng Xinliang Xu Xiao Xia Xiong Xiu Lian Lu Yi Feng Zhou 《Russian Journal of General Chemistry》2013,83(12):2447-2452
We have demonstrated that the fragments of Telaprevir can act as organocatalysts for asymmetric aldol reactions between aromatic aldehydes and acetone under mild conditions. The reaction conditions have been optimized in terms of the catalyst nature, choice of temperature, solvent, additive, and the catalyst loading. Under proper conditions, fairly good yield and enantioselectivity have been achieved. 相似文献
963.
Triterpenoids from the Roots and Stems of Rubus alceaefolius 总被引:1,自引:0,他引:1
964.
965.
H. M. Srivastava Shy-Der Lin Shuoh-Jung Liu Han-Chun Lu 《Russian Journal of Mathematical Physics》2012,19(1):121-130
Motivated essentially by their potential for applications in the mathematical, physical, and statistical sciences, the object
of this paper is to investigate several general families of hypergeometric polynomials and their associated multiple integral
representations. By suitably specializing the main results presented here, the corresponding integral representations are
derived for familiar simpler classes of hypergeometric polynomials such as (for example) the Lagrange polynomials, Shively’s
pseudo-Laguerre polynomials, and generalized Bessel polynomials. Each of the integral representations derived in this paper
may be also viewed as a linearization relationship for the product of two different members of the associated family of hypergeometric
polynomials. 相似文献
966.
By taking the coupling effect into consideration, we study the resonance condition of a photonic wire microring resonator (PWRR) sensor and compare our results with the previous work. Simulation results show that the resonant wavelength and sensitivity strongly depend on the coupling strength. The difference caused by the coupling effect can be up to tens of nanometers for the resonant peak position and tens of nm/RIU for the sensitivity in a silicon-on-insulator (SOI) PWRR. Such a giant influence from coupling effect cannot be disregarded and should be considered seriously for the design and application of PWRRs. It also shows an alternative tuning technique by controlling the coupling strength. 相似文献
967.
Dongsheng Cheng Chunyuan Lu Taishan Zeng 《Journal of Mathematical Analysis and Applications》2012,388(2):1080-1089
In this paper, we develop a fast block Jacobi method for linear systems based on discrete wavelet transform (DWT). Traditional wavelet-based methods for linear systems do not fully utilize the sparsity and the multi-level block structure of the transformed matrix after DWT. For the sake of numerical efficiency, we truncate the transformed matrix to be a sparse matrix by letting the small values be zero. To combine the advantages of the direct method and the iterative method, we solve the sub-systems appropriately based on the multi-level block structure of the transformed matrix after DWT. Numerical examples show that the proposed method is very numerically effective. 相似文献
968.
969.
Zhuangzhuang Liu Aimin Sha Liqun Hu Yongwei Lu Wenxiu Jiao Zheng Tong Jie Gao 《Chemical Papers》2017,71(4):741-751
Portland cement have to hydrate in cold climates in some particular conditions. Therefore, a better understanding of cement hydration under low temperatures would benefit the cement-based composites application. In this study, Portland cement was, therefore, kinetically and thermodynamically simulated based on a simple kinetics model and minimization of Gibbs free energy. The results of an evaluation indicate that Portland cement hydration impact factors include the water–cement ratio (w/c), temperature, and specific surface area, with the latter being an especially remarkable factor. Therefore, increasing the specific surface area to an appropriate level may be a solution to speed the delayed hydration due to low temperatures. Meanwhile, the w/c ratio is believed to be controlled under cold climates with consideration of durability. The thermodynamic calculation results suggest that low-temperature influences can be divided into three levels: irrevocable effects (<0 °C), recoverable effects (0–10 °C), and insignificant effects (10–20 °C). Portland cement was additionally measured via X-ray diffraction, thermal gravity analysis, and low-temperature nitrogen adsorption test in a laboratory and comparisons were drawn that validate the simulation result. 相似文献
970.