全文获取类型
收费全文 | 13878篇 |
免费 | 1970篇 |
国内免费 | 2447篇 |
专业分类
化学 | 11222篇 |
晶体学 | 337篇 |
力学 | 587篇 |
综合类 | 195篇 |
数学 | 1492篇 |
物理学 | 4462篇 |
出版年
2024年 | 40篇 |
2023年 | 187篇 |
2022年 | 472篇 |
2021年 | 476篇 |
2020年 | 507篇 |
2019年 | 532篇 |
2018年 | 419篇 |
2017年 | 503篇 |
2016年 | 612篇 |
2015年 | 694篇 |
2014年 | 857篇 |
2013年 | 1088篇 |
2012年 | 1224篇 |
2011年 | 1305篇 |
2010年 | 1048篇 |
2009年 | 952篇 |
2008年 | 1162篇 |
2007年 | 935篇 |
2006年 | 912篇 |
2005年 | 753篇 |
2004年 | 602篇 |
2003年 | 489篇 |
2002年 | 566篇 |
2001年 | 408篇 |
2000年 | 314篇 |
1999年 | 234篇 |
1998年 | 170篇 |
1997年 | 110篇 |
1996年 | 117篇 |
1995年 | 83篇 |
1994年 | 67篇 |
1993年 | 71篇 |
1992年 | 56篇 |
1991年 | 69篇 |
1990年 | 37篇 |
1989年 | 44篇 |
1988年 | 22篇 |
1987年 | 35篇 |
1986年 | 20篇 |
1985年 | 26篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
以互通多孔碳(IPC)为载体,水热条件下在碳表面原位反应生成纳米结构的二氧化锰(MnO2),制备互通多孔碳/二氧化锰纳米(IPC/MnO2)复合电极材料. 采用扫描电镜(SEM),透射电镜(TEM),X射线衍射(XRD),热重分析(TGA)对其结构进行表征;采用循环伏安法、恒流充放电和交流阻抗对其电化学性能进行研究. 结果表明:生成的MnO2均匀地负载在碳的表面,形成多层次结构,并且随着温度的升高IPC表面负载的MnO2由纳米颗粒变为纳米片状结构;MnO2纳米片具有典型的K-Birnessite 型晶体结构;复合物中MnO2的含量约为34%(w). 在100 ℃制备的IPC/MnO2复合材料在三电极系统中最高比电容达到了411 F·g-1;随着反应温度的升高,比容量先增长后基本保持不变. 以IPC/MnO2为正极,活性炭(AC)为负极,1 mol·L-1 Na2SO4溶液为电解液组装成IPC/MnO2//AC 混合超级电容器,发现IPC/MnO2电极的电容器其电位窗口从1 V扩展到1.8 V,容量可达86F·g-1,且表现出良好的电容特性和大电流放电性能. 相似文献
92.
Shu Ping XU* Huan Wen CHEN Ai Min YU Qin Han JIN Hua Ying LIAO Changchun R&D Center for Analytical Instruments Department of Chemistry Jilin University Changchun Key Laboratory for Supramolecular Structure Spectroscopy of Ministr 《中国化学快报》2002,13(7):660-661
In recent years, the determination of Cr (VI) has attracted great attention because of its toxicity to human, plants and animals1-5. Usually, in the industrial waste water, the concentration of Cr (VI) is relatively high and should be determined frequently. So, an accurate, quick, and convenient method for the measurement of Cr (VI) in environmental water, as well as in river, lake, sea and tap water, is of great importance. The method for determination of Cr (VI) by diphenylcarbazine … 相似文献
93.
用密度泛函理论(DFT)在B3LYP/6鄄31G(d,p)的计算水平上研究了离子液中1鄄乙基鄄3鄄甲基咪唑阳离子(EMIM )的4鄄H和5鄄H原子催化丁烯双键异构反应的可能途径,优化了反应体系的平衡态和过渡态的几何构型,分析了反应过程中键参数的变化,通过振动分析对平衡态和过渡态进行了验证.计算结果表明,离子液中的EMIM 首先通过4鄄H和5鄄H原子吸附丁烯,进而催化丁烯的双键异构反应,EMIM 的4鄄H和5鄄H催化1鄄丁烯异构为2鄄丁烯的正反应活化能分别为204.2和207.3kJ·mol-1,逆反应活化能约为220.9和223.8kJ·mol-1,反应为基元反应. 相似文献
94.
We report the synthesis and physical studies of a novel porphyrazine (pz) dimer [1[Ni,Cu]]2, which has Ni(II) ions incorporated into the pz cores and is linked by two Cu(II) ions coordinated to bis(picolinamide) chelates attached to the pz periphery. [1[Ni,Cu]]2 was prepared from precursor pz 2 with a selenodiazole ring fused to the pz core. This ring was deprotected to form the diamino-pz 3, which reacted with 2 mol of picolinoyl chloride hydrochloride to form pz 1[2H,2H], with peripheral bis(picolinamide) chelates; this was metalated to form [1[Ni,Cu]]2. The crystal structures of 1[2H,2H] and [1[Ni,Cu]]2 are presented. The latter is a dimer in which parallel, face-to-face pz's with an average separation of 3.30 angstroms are linked through the peripheral picolinamide ligands by a pair of peripheral Cu(II) ions. Each Cu(II) is coordinated with distorted square-planar geometry by a picolinamide from each pz. In this report, we focus on the interaction of these two peripheral Cu(II) ions. We discuss the preparation and magnetic properties of the pz dimer complex [1[Ni,Cu]]2 with two Cu(II) ions in the peripheral chelate but a diamagnetic metal ion Ni(II) in the pz core. Although [1[Ni,Cu]]2 contains two Cu(II) ions (S = 1/2), we could detect no electron paramagnetic resonance signal, which suggests very strong antiferromagnetic exchange between those two Cu(II) ions. Temperature-dependent magnetic susceptibility measurement gives an exchange splitting between the S = 0 ground state and the excited triplet state of delta = 660 cm(-1). 相似文献
95.
Three new alkaloids, longistylumphyllines A–C (1–3), together with the six known alkaloids deoxycalyciphylline B, deoxyisocalyciphylline B, methyl homosecodaphniphyllate, daphnicyclidin A, daphnicyclidin B, and daphnicyclidin F, were isolated from the stems and leaves of Daphniphyllum longistylum. Their structures and relative configuration were elucidated on the basis of spectroscopic data, especially 1D and 2D NMR techniques. 相似文献
96.
Min Zeng Ang Ren Wubin Wu Yongsheng Zhao Chuanlang Zhan Jiannian Yao 《Chemical science》2020,11(34):9154
We present herein an innovative host–guest method to achieve induced molecular chirality from an achiral stilbazolium dye (DSM). The host–guest system is exquisitely designed by encapsulating the dye molecule in the molecule-sized chiral channel of homochiral lanthanide metal–organic frameworks (P-(+)/M-(−)-TbBTC), in which the P- or M-configuration of the dye is unidirectionally generated via a spatial confinement effect of the MOF and solidified by the dangling water molecules in the channel. Induced chirality of DSM is characterized by solid-state circularly polarized luminescence (CPL) and micro-area polarized emission of DSM@TbTBC, both excited with 514 nm light. A luminescence dissymmetry factor of 10−3 is obtained and the photoluminescence quantum yield (PLQY) of the encapsulated DSM in DSM@TbTBC is ∼10%, which is close to the PLQY value of DSM in dilute dichloromethane. Color-tuning from green to red is achieved, owing to efficient energy transfer (up to 56%) from Ln3+ to the dye. Therefore, this study for the first time exhibits an elegant host–guest system that shows induced strong CPL emission and enables efficient energy transfer from the host chiral Ln-MOF to the achiral guest DSM with the emission color tuned from green to red.Homochiral Ln-MOFs are synthesized to encapsulate achiral dyes to induce strong circularly polarized luminescence with a luminescence dissymmetry factor of 10−3. 相似文献
97.
98.
综述了吸附理论的进展及其在吸附分离中的应用,并介绍了对气体分离过程至关重要的混合气的吸附模型或关联式。 相似文献
99.
在这篇文章中, 作者研究涉及凹凸非线性项的Kirchhoff型问题-(a + b ∫R3|▽u|2dx) Δu + λV (x)u = μf(x)|u|q?2u + |u|p?2u, x ∈ R3,u ∈ H1(R3),其中a,b > 0 是常数, λ, μ > 0 是参数, 1 < q < 2, 4 < p < 6 且 V 是一个非负连续位势. 在f(x) 和 V 的合适条件下,此问题正解的存在性和集中性能够通过Nehari 流形和Ekeland 变分原理得到. 相似文献