全文获取类型
收费全文 | 17623篇 |
免费 | 2845篇 |
国内免费 | 3101篇 |
专业分类
化学 | 9197篇 |
晶体学 | 184篇 |
力学 | 792篇 |
综合类 | 283篇 |
数学 | 1553篇 |
物理学 | 4735篇 |
无线电 | 6825篇 |
出版年
2024年 | 71篇 |
2023年 | 425篇 |
2022年 | 669篇 |
2021年 | 771篇 |
2020年 | 736篇 |
2019年 | 716篇 |
2018年 | 572篇 |
2017年 | 714篇 |
2016年 | 830篇 |
2015年 | 952篇 |
2014年 | 1068篇 |
2013年 | 1303篇 |
2012年 | 1296篇 |
2011年 | 1398篇 |
2010年 | 1101篇 |
2009年 | 1154篇 |
2008年 | 1276篇 |
2007年 | 1097篇 |
2006年 | 1019篇 |
2005年 | 984篇 |
2004年 | 728篇 |
2003年 | 638篇 |
2002年 | 662篇 |
2001年 | 586篇 |
2000年 | 541篇 |
1999年 | 366篇 |
1998年 | 277篇 |
1997年 | 200篇 |
1996年 | 221篇 |
1995年 | 172篇 |
1994年 | 171篇 |
1993年 | 142篇 |
1992年 | 117篇 |
1991年 | 128篇 |
1990年 | 108篇 |
1989年 | 64篇 |
1988年 | 64篇 |
1987年 | 42篇 |
1986年 | 44篇 |
1985年 | 50篇 |
1984年 | 25篇 |
1983年 | 23篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1968年 | 2篇 |
1961年 | 3篇 |
1957年 | 3篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
71.
空中制导-攻击匹配(GAM)旨在确定武器单元、制导单元以及目标三者之间的最优匹配关系,以使多作战智能体任务联盟整体作战效能最大。分析了基于混合通信方式的多作战智能体制导-攻击匹配过程,建立制导攻击匹配约束优化问题模型,设计了一种禁忌策略的嵌套遗传算法(TS-NGA)对模型进行求解,算法的外层循环寻求武器单元和制导单元的最优配对,内层循环寻求武器单元和目标的最优配对。针对GAM问题特点,制定了编码与解码策略、交叉、变异规则以及选择、禁忌策略。仿真实验结果表明所设计求解算法能较好地解决三维变量的GAM问题模型。 相似文献
72.
73.
Yue Jia Tingji Yao Guangcai Ma Qi Xu Xianglong Zhao Hui Ding Xiaoxuan Wei Haiying Yu Zhiguo Wang 《Molecules (Basel, Switzerland)》2022,27(9)
Biotransformation of organophosphorus flame retardants (OPFRs) mediated by cytochrome P450 enzymes (CYPs) has a potential correlation with their toxicological effects on humans. In this work, we employed five typical OPFRs including tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), tris(1-chloro-2-propyl) phosphate (TCIPP), tri(2-chloroethyl) phosphate (TCEP), triethyl phosphate (TEP), and 2-ethylhexyl diphenyl phosphate (EHDPHP), and performed density functional theory (DFT) calculations to clarify the CYP-catalyzed biotransformation of five OPFRs to their diester metabolites. The DFT results show that the reaction mechanism consists of Cα-hydroxylation and O-dealkylation steps, and the biotransformation activities of five OPFRs may follow the order of TCEP ≈ TEP ≈ EHDPHP > TCIPP > TDCIPP. We further performed molecular dynamics (MD) simulations to unravel the binding interactions of five OPFRs in the CYP3A4 isoform. Binding mode analyses demonstrate that CYP3A4-mediated metabolism of TDCIPP, TCIPP, TCEP, and TEP can produce the diester metabolites, while EHDPHP metabolism may generate para-hydroxyEHDPHP as the primary metabolite. Moreover, the EHDPHP and TDCIPP have higher binding potential to CYP3A4 than TCIPP, TCEP, and TEP. This work reports the biotransformation profiles and binding features of five OPFRs in CYP, which can provide meaningful clues for the further studies of the metabolic fates of OPFRs and toxicological effects associated with the relevant metabolites. 相似文献
74.
Xi Jiang Qi Liao Jianjun Zhou Zhaohui Wang Chiming Chan Lin Li 《Journal of Polymer Science.Polymer Physics》2013,51(11):907-914
We have developed a morphologic method to investigate the relaxation processing of the stretched polymer chains in melts, in which an atomic force microscope probe was used to shear the surface of an isotactic polypropylene melt to obtain the isolated shish‐kebab structure. We present the results of the time dependence of length of the isolated shish‐kebab structure and the stress dependence of the kebab density along the direction of shish in this paper. Our results demonstrate that the shear‐oriented polymer melts show the relaxation dynamics of worm‐like chain where the length deficit of the isolated shish‐kebab structure is scaled with the relaxation time as a power of 1/3. The melting behavior of shish‐kebab structure was also investigated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 907–914 相似文献
75.
Chunxia Miao Shihan Qi Kang Liang Yanli Qi Junda Huang Mingguang Wu Hongshun Zhao Jiandong Liu Yurong Ren Jianmin Ma 《Journal of Energy Chemistry》2021,(12):566-573
Lithium metal batteries have obtained increasing interest due to their high specific capacity.Nonetheless,the growth of lithium dendrites brings safety risks to... 相似文献
76.
Isovaleroyl oxokadsurane, a novel dibenzocyclooctadiene lignan pos-sessing a spirobenzofuranoid skeleton was isolated from the stems of Kadsura coccinea.Its structure and relative configuration were determined by X-ray diffraction analysis. 相似文献
77.
Yanpei Luo Xin Zhou Jiangwei Zhang Yu Qi Zheng Li Fuxiang Zhang Can Li 《Journal of Energy Chemistry》2021,(12):385-390
The hybridization between the outmost s orbitals of metal (Bi3+,Sn2+,Pb2+,Ag+) and O 2p orbitals has been widely employed to develop innovative semiconductors w... 相似文献
78.
Yi-Si Feng Hong-Xia Qi Wei-Cheng Wang Yu-Feng Liang Hua-Jian Xu 《Tetrahedron letters》2012,53(23):2914-2917
A novel synthetic protocol for 2-aminophenyl sulfide derivatives via the reactions of benzothiazole with aryl iodides was reported for the first time. The reactions were catalyzed by CuCl with tetrabutylammonium hydroxide as the base and water as the solvent without ligand at 50 °C or room temperature. A variety of aryl iodides underwent the C–S cross-coupling reaction with benzothiazole to afford smoothly the corresponding products in excellent yield. 相似文献
79.
80.
本文讨论了非晶态NdxT1-x(T=Fe,Co,Ni)薄膜为滋结构,以及在低温下磁化强度随温度变化的反常特性,在20K附近观测到磁化强度有陡降现象,并且在较大的成份范围内所对应的温度基本不变,我们认为,在这类非晶态合金中,当Nd含量超过一定值后,其磁中性态(通称基态)可能同时是散反铁磁性和散铁磁性的共存态,在20K附近的磁化强度发生陡降,是散反铁磁性←→顺磁性相转变的反映,这两种磁结构共存的临界成份相应约为:Nd-Fe情况x≥0.45;Nd-Co,x≥0.20;Nd-Ni,x≥0.08。
关键词: 相似文献