全文获取类型
收费全文 | 17606篇 |
免费 | 2323篇 |
国内免费 | 843篇 |
专业分类
化学 | 19816篇 |
晶体学 | 59篇 |
力学 | 32篇 |
综合类 | 25篇 |
数学 | 65篇 |
物理学 | 775篇 |
出版年
2024年 | 32篇 |
2023年 | 248篇 |
2022年 | 618篇 |
2021年 | 676篇 |
2020年 | 1249篇 |
2019年 | 944篇 |
2018年 | 762篇 |
2017年 | 629篇 |
2016年 | 1230篇 |
2015年 | 1070篇 |
2014年 | 1082篇 |
2013年 | 1262篇 |
2012年 | 961篇 |
2011年 | 1035篇 |
2010年 | 886篇 |
2009年 | 920篇 |
2008年 | 872篇 |
2007年 | 795篇 |
2006年 | 738篇 |
2005年 | 669篇 |
2004年 | 679篇 |
2003年 | 543篇 |
2002年 | 1206篇 |
2001年 | 249篇 |
2000年 | 158篇 |
1999年 | 198篇 |
1998年 | 221篇 |
1997年 | 157篇 |
1996年 | 107篇 |
1995年 | 112篇 |
1994年 | 56篇 |
1993年 | 38篇 |
1992年 | 33篇 |
1991年 | 33篇 |
1990年 | 33篇 |
1989年 | 20篇 |
1988年 | 27篇 |
1987年 | 21篇 |
1986年 | 68篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1972年 | 11篇 |
1970年 | 7篇 |
1966年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Stokes–Einstein (SE) and Stokes–Einstein–Debye (SED) relations in the neat ionic liquid (IL) [C2mim][NTf2] and IL/chloroform mixtures are studied by means of molecular dynamics (MD) simulations. For this purpose, we simulate the translational diffusion coefficients of the cations and anions, the rotational correlation times of the C(2)? H bond in the cation C2mim+, and the viscosities of the whole system. We find that the SE and SED relations are not valid for the pure ionic liquid, nor for IL/chloroform mixtures down to the miscibility gap (at 50 wt % IL). The deviations from both relations could be related to dynamical heterogeneities described by the non‐Gaussian parameter α(t). If α(t) is close to zero, at a concentration of 1 wt % IL in chloroform, both relations become valid. Then, the effective radii and volumes calculated from the SE and SED equations can be related to the structures found in the MD simulations, such as aggregates of ion pairs. Overall, similarities are observed between the dynamical properties of supercooled water and those of ionic liquids. 相似文献
972.
Sterically bulky pyrazines have been successfully utilized for the preparation of discrete oligo-nuclear TBP (trigonal bipyramidal), SqP (square pyramidal), and Oh (octahedral) copper(II) complexes. We have synthesized a unique linear pentanuclear complex [{Cu(hfac)2}5(μ-2-butyl-3-methylpyrazine)4]. The two terminal copper(II) ions have a SqP structure while the three inner ions have an Oh one. The solvent molecule was incorporated in the clearance of the lattice. From another reaction under harsh conditions, we separated [{Cu(hfac)2}3(μ-2-butyl-3-methylpyrazine)2], which can be regarded as the central moiety of the pentanuclear one. We also prepared a dinuclear complex [{Cu(hfac)2}2(μ-tetramethylpyrazine)], in which the pyrazine nitrogen atoms were located at TBP equatorial positions. Single-crystal EPR measurements supported its compressed TBP structure. The exchange coupling was antiferromagnetic with JTBP–TBP/kB = −3.6 K. The linear trinuclear [{Cu(hfac)2}3(μ-2,3,5-trimethylpyrazine)2], having two TBP Cu ions with an intervening Oh Cu ion, showed very weak antiferromagnetic coupling. DFT calculations on these compounds indicated that the σ-type orbital overlap between the Cu and N atoms is essential for superexchange interactions. 相似文献
973.
Yan Song Xiao-Qing Yu Su Chen 《Journal of polymer science. Part A, Polymer chemistry》2024,62(3):447-462
Fiber-spinning chemistry (FSC) has emerged as a promising micro-reaction platform due to its high-specific surface area, efficient heat and mass transfer, and enhanced reaction rate. The FSC strategy employs spinning fibers as microreactors, lessening the emissions of volatile organic compounds (VOCs), and realizing the design of micro/nanoscale fibers and the synthesis of nanomaterials. In this review, we highlight the latest advancements in FSC in respect of preparation mechanisms and technical advantages. Various FSC strategies, including microfluidic spinning, electro-microfluidic spinning (EMS), and microfluidic blow spinning (MBS) are emphasized. In particular, the regulation of microfluidic chips in the FSC process is introduced. Additionally, the application of the FSC strategy is summarized in the synthesis of fluorescent nanomaterials, nonweaving for multidimensional fibers, and all-weather smart textiles. Finally, the advanced progress and future perspectives are discussed. Overall, this review will provide theoretical guidance for the design of well-defined micro/nanoscale fibers based on the FSC platforms. 相似文献
974.
Large amounts of volatile organic compounds (VOCs) are emitted into the atmosphere from both human and natural sources. A significant portion of VOCs would be oxidized via their reactions with atmospheric oxidants like OH, NO3, ozone, etc. The products of the oxidation reactions are often of low volatility and may condense to form secondary organic aerosols (SOA). To study the effect of VOC oxidation in aerosol formation, we are building an oxidation flow reactor system, which consists of (1) a 22-l aluminum chamber, (2) an ozone source with an ozone detector, (3) a UV-C (254 nm) lamp, (4) a photoionization detector to measure the effective VOC concentration, (5) various flow/concentration controlling apparatuses, and (6) a scanning mobility particle sizer to monitor the generated particles. Under the conditions of high UV and ozone levels, the oxidation process can be speeded up by orders of magnitude in this reactor. We hope to use this reactor: (i) to learn the “potential” mass of SOA that can be formed from a given VOC source like a traffic or industry site; (ii) to trace back the SOA source by utilizing the shortened reaction times; (iii) to learn the trends from VOC to SOA. 相似文献
975.
Ahmad Bachir Fabiana Ciocchetti Daniel P. Couto Dr. Simone Di Noja Dr. Cristian Pezzato Dr. Giulio Ragazzon 《European journal of organic chemistry》2023,26(29):e202300498
Cyclobis(paraquat-p-phenylene), also known as “blue box”, is a highly electron-deficient macrocycle, widely used as a molecular receptor for small electron-rich molecules. Inserting a reactive functional group onto the molecular structure of this cyclophane is paramount for its inclusion into complex architectures. To this aim, including an alkyne moiety would be ideal, because it can participate in click reactions. However, the synthesis of such alkyne-functionalized cyclophane suffers from several drawbacks: the use of toxic and expensive CCl4, the need for high-pressure reactors, and overall low yield. We have revised the existing synthesis of this cyclophane derivative bearing an alkyne moiety, to overcome all these limitations. In particular, photochemical radical bromination is adopted to obtain a sensitive intermediate. We demonstrated that the synthesized host molecule can be functionalized via click reactions and take part in radical-radical interactions. Our work makes a key functionalized paraquat macrocycle more accessible, facilitating the development of novel redox-responsive systems. 相似文献
976.
977.
978.
979.
980.