全文获取类型
收费全文 | 12865篇 |
免费 | 2360篇 |
国内免费 | 3046篇 |
专业分类
化学 | 10052篇 |
晶体学 | 270篇 |
力学 | 695篇 |
综合类 | 356篇 |
数学 | 1721篇 |
物理学 | 5177篇 |
出版年
2024年 | 17篇 |
2023年 | 125篇 |
2022年 | 298篇 |
2021年 | 312篇 |
2020年 | 372篇 |
2019年 | 454篇 |
2018年 | 357篇 |
2017年 | 417篇 |
2016年 | 520篇 |
2015年 | 606篇 |
2014年 | 735篇 |
2013年 | 970篇 |
2012年 | 1084篇 |
2011年 | 1157篇 |
2010年 | 1028篇 |
2009年 | 1034篇 |
2008年 | 1167篇 |
2007年 | 1112篇 |
2006年 | 1080篇 |
2005年 | 898篇 |
2004年 | 690篇 |
2003年 | 633篇 |
2002年 | 599篇 |
2001年 | 508篇 |
2000年 | 419篇 |
1999年 | 296篇 |
1998年 | 201篇 |
1997年 | 148篇 |
1996年 | 140篇 |
1995年 | 116篇 |
1994年 | 106篇 |
1993年 | 110篇 |
1992年 | 99篇 |
1991年 | 79篇 |
1990年 | 81篇 |
1989年 | 59篇 |
1988年 | 54篇 |
1987年 | 42篇 |
1986年 | 36篇 |
1985年 | 26篇 |
1984年 | 17篇 |
1983年 | 21篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1973年 | 3篇 |
1970年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Delong Liu Jing Ma Hou Chen Ping Yin Naiyi Ji Guangxi Zong 《Journal of polymer science. Part A, Polymer chemistry》2011,49(23):5109-5115
Zerovalent ytterbium (Yb) powder is firstly used as a catalyst in single electron transfer‐living radical polymerization of methyl methacrylate initiated by carbon tetrachloride in N, N‐dimethylformamide (DMF) and dimethyl sulfoxide, respectively. Polymerization proceeds in a “living”/controlled way as evidenced by kinetic studies and chain extension results, producing well‐defined polymers with controlled degree of polymerization and narrow molecular weight distribution. The apparent activation energy of polymerization in DMF is accounted to be 36.2 kJ/mol, and the energy of equilibrium state is calculated to be 13.9 kJ/mol. An increase in the concentration of Yb(0) yields a higher monomer conversion. It is observed that polymerization rate experiments a rapid increase in the presence of more polar solvent water, and increasing in the content of H2O results in an increase in the apparent rate constant of polymerization, and a decrease in the molecular weight distribution. The reaction rate and molecular weight increase along with the decrease of DMF content. The effect of Yb(0) powder content, different ligands and concentration of initiator on the polymerization is also investigated. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
912.
Xiao‐Hua Ma Li‐Min Fu Yunfeng Zhao Xi‐Cheng Ai Jian‐Ping Zhang Yu Han Zhi‐Xin Guo 《Journal of Polymer Science.Polymer Physics》2011,49(9):649-656
Achiral nonlinear optical (NLO) chromophores 1,3‐diazaazulene derivatives, 2‐(4′‐aminophenyl)‐6‐nitro‐1,3‐diazaazulene (APNA) and 2‐(4′‐N,N‐diphenylaminophenyl)‐6‐nitro‐1,3‐diazaazulene (DPAPNA), were synthesized with high yield. Despite the moderate static first hyperpolarizabilities (β0) for both APNA [(136 ± 5) × 10?30 esu] and DPAPNA [(263 ± 20) × 10?30 esu], only APNA crystal shows a powder efficiency of second harmonic generation (SHG) of 23 times that of urea. It is shown that the APNA crystallization driven cooperatively by the strong H‐bonding network and the dipolar electrostatic interactions falls into the noncentrosymmetric P212121 space group, and that the helical supramolecular assembly is solely responsible for the efficient SHG response. To the contrary, the DPAPNA crystal with centrosymmetric P‐1 space group is packed with antiparalleling dimmers, and is therefore completely SHG‐inactive. 1,3‐Diazaazulene derivatives are suggested to be potent building blocks for SHG‐active chiral crystals, which are advantageous in high thermal stability, excellent near‐infrared transparency and high degree of designing flexibility. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
913.
复模糊数是模糊复分析中的基本概念,在模糊复分析中,它的运算是基于扩张原理的形式给出的,是对元素遍历某个条件所对应的结果进行运算,这种遍历过程给实际操作带来了很多的不便,因此,在一定程度上也阻碍了模糊复分析理论的应用.对此,本文基于模糊结构元的理论基础,探讨了复模糊数运算的另一种新的途径,这种方法简化了复模糊数的运算,也... 相似文献
914.
Keith D. Barnes Ping Chen Yingyan Chang Robert M. Lewis Christopher M. Manley Nicholas J. Mayhew 《合成通讯》2013,43(1):67-72
A convergent synthesis of indoprofen via a Buchwald coupling approach is reported. Using this methodology, indoprofen and a set of analogs of indoprofen were readily prepared. 相似文献
915.
916.
917.
We reported an interfacial self-assembly of regularly layered porous poly(4-vinylpyridine)(P4VP) films at the interfaces of water-chloroform or -dichloroethane.The porous diameters were in the range from hundred nanometers to several micrometers.It was revealed that formation of such kind of porous materials was solvent dependent.Moreover,cyclic Ag nanoparticles could be grown in the porous P4VP films to form Ag-P4VP nanohybrids under radiation. 相似文献
918.
Yao Yun Hu Jing Mei Yin Da Bin Gao Ying Ping Jia Guang Yun Zhou Ying Na Cui Shen Min Li 《中国化学快报》2008,19(5):529-532
Photopromoted carbonylation of 1-bromo-6-chlorohexane with CO catalyzed by CuBr2 and CdI2 has been carried out under ambient conditions. The results indicate that the carbonylation proceeds with the major product of chloroester ClCH2(CH2)5COOCH3 under catalysis of CuBr2. Furthermore, the activity of the carbonylation can be improved by addition of basic additives (NaOAc, Na3PO4 or (n-C4H9)3N). Among these additives, (n-C4H9)3N is the most efficient in terms of the yield of ClCH2(CH2)5COOCH3. However, the methoxycarbonyl substituting chlorine product of BrCH2(CH2)5COOCH3 is not obtained in the presence of CdI2. This is quite different from the carbonylation of monochloroalkane. 相似文献
919.
Tian Ping ZHANG Wen Peng ZHANG 《数学学报(英文版)》2008,24(2):215-222
The main purpose of this paper is to use the properties of the Gauss sums, primitive characters and the mean value of Dirichlet L-functions to study the hybrid mean value of the error term E(n, l, c, q) and the hyper-Kloosterman sums K(h,n+1,q), the asymptotic property of the mean square value ∑^p c=1 E^2(n, 1, c, p), and give two interesting mean value formulae. 相似文献
920.