全文获取类型
收费全文 | 25371篇 |
免费 | 4388篇 |
国内免费 | 3598篇 |
专业分类
化学 | 18482篇 |
晶体学 | 296篇 |
力学 | 1848篇 |
综合类 | 253篇 |
数学 | 2926篇 |
物理学 | 9552篇 |
出版年
2024年 | 49篇 |
2023年 | 515篇 |
2022年 | 697篇 |
2021年 | 827篇 |
2020年 | 1030篇 |
2019年 | 923篇 |
2018年 | 779篇 |
2017年 | 730篇 |
2016年 | 1191篇 |
2015年 | 1106篇 |
2014年 | 1375篇 |
2013年 | 1730篇 |
2012年 | 2269篇 |
2011年 | 2301篇 |
2010年 | 1637篇 |
2009年 | 1478篇 |
2008年 | 1692篇 |
2007年 | 1443篇 |
2006年 | 1469篇 |
2005年 | 1268篇 |
2004年 | 1026篇 |
2003年 | 885篇 |
2002年 | 937篇 |
2001年 | 809篇 |
2000年 | 626篇 |
1999年 | 689篇 |
1998年 | 493篇 |
1997年 | 450篇 |
1996年 | 512篇 |
1995年 | 418篇 |
1994年 | 396篇 |
1993年 | 292篇 |
1992年 | 255篇 |
1991年 | 222篇 |
1990年 | 172篇 |
1989年 | 138篇 |
1988年 | 138篇 |
1987年 | 84篇 |
1986年 | 88篇 |
1985年 | 63篇 |
1984年 | 40篇 |
1983年 | 40篇 |
1982年 | 22篇 |
1981年 | 27篇 |
1980年 | 11篇 |
1979年 | 3篇 |
1974年 | 1篇 |
1966年 | 1篇 |
1957年 | 7篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Laser-induced breakdown spectroscopy(LIBS) is used to determine the total nitrogen(TN) and total phosphorus(TP) in soil.Quantitative determinations are conducted using the line intensity of the analyte element and element concentration.Calibration models are obtained using ten samples for TN and seven samples for TP.The rest samples are used to validate the results.Strong linear correlations are obtained from the determined TN and TP concentrations.LIBS is a powerful tool for analyzing soil samples to determine nutrient elements by selecting calibration and validation samples with similar matrix composition. 相似文献
932.
Qingxiang Zhou Zhenwen Zheng Junping Xiao Huili Fan Xiuyi Yan 《Analytical and bioanalytical chemistry》2016,408(19):5211-5220
933.
Fengyang Deng Bin Xu Yong Gao Zheng Liu Duanguang Yang Huaming Li 《Journal of polymer science. Part A, Polymer chemistry》2012,50(18):3767-3774
In this study, a series of linear poly(triazole)s (PTAs) were successfully synthesized by the metal‐ and solvent‐free, thermal click polymerization of diazide and dialkyne (A2 + B2) monomers. All click polymerizations proceeded smoothly at 80 °C in an open atmosphere without protection from oxygen and moisture. After being polymerized for 36 h, the crude polymer was further fractionated into three fractions using a multistep precipitation method. By selectively choosing precipitating agents, this process produced poly(triazole) fractions with low polydispersity index (<1.30). The resulting PTAs are soluble in common organic solvents and stable at a temperature up to 320 °C. Furthermore, the methyl benzoate moieties in the main chain can serve as useful building blocks for further postpolymerization functionalization, yielding 1,2,4‐triazole derivatives. This functionalization strategy offers potential for the development of novel triazole‐based materials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
934.
Zhong Lvling Li Baolin Zhang Liang Ma Xinjie Chai Shouning 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2018,92(4):785-792
Russian Journal of Physical Chemistry A - A new mesoporous carbon containing nitrogen and copper was prepared by carbonizing a polymer obtained by blending p-phenylenediamine, copper(II) sulfate,... 相似文献
935.
936.
Xiao‐Jie Liu Zhen‐Yu Li Zhong‐Feng Li Xiao‐Xia Gao Yu‐Zhi Zhou Hai‐Feng Sun Li‐Zeng Zhang Xiao‐Qing Guo Guan‐Hua Du Xue‐Mei Qin 《Magnetic resonance in chemistry : MRC》2012,50(3):187-192
Chronic unpredictable mild stress (CUMS) is a well‐validated model of depression. In this study, a urinary metabonomics method based on the NMR spectrometry was used to study the metabolic perturbation in CUMS‐induced rat depression model. With pattern recognition analysis, a clear separation of CUMS rats and healthy controls was achieved, and nine endogenous metabolites contributing to the separation were identified. CUMS‐treated rats were characterized by the increase of glycine, pyruvate, glutamine, and asparagines, as well as the decrease of 2‐oxoglutarate, dimethylglycine, citrate, succinate, and acetate. The urinary biochemical changes related to the metabolic disturbance in CUMS induced depression, and the possible correlations with live qi stagnation in traditional Chinese medicine are discussed. The work shows that CUMS is a reliable model for studying depression, and the noninvasive urinary metabolomic method is a valuable tool to investigate the biochemical pertubations in depression as an early diagnostic means. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
937.
Zhong‐Fu An Chao Zheng Dr. Run‐Feng Chen Jun Yin Jian‐Jian Xiao Hui‐Fang Shi Ye Tao Dr. Yan Qian Prof. Wei Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(49):15655-15661
A novel conjugated asymmetric donor–acceptor (CADA) strategy for preventing the redshift in photoluminescence, as well as preserving the merits of donor–acceptor architectures, was proposed and demonstrated for two triazine derivatives, which showed highly efficient, narrow, and blueshifted ultraviolet light emission in solid films along with special aggregation‐induced emission behavior. A mechanism of aggregation‐induced locally excited‐state emission by suppressing the twisted intramolecular charge‐transfer emission for the spectacular optoelectronic phenomena of these CADA molecules was suggested on the basis of both experimental measurements and theoretical calculations. By taking advantage of this special CADA architecture, fluorescent probes based on aggregates of conjugated asymmetric triazines in THF/water for the detection of explosives show superamplified detection of picric acid with high quenching constants (>1.0×107 M ?1) and a low detection limit of 15 ppb. 相似文献
938.
939.
940.
Jian Wang Yu Xu Yunfeng Zhang Hong Wang Weihui Zhong 《Rapid communications in mass spectrometry : RCM》2017,31(18):1541-1550