全文获取类型
收费全文 | 4371篇 |
免费 | 705篇 |
国内免费 | 657篇 |
专业分类
化学 | 4707篇 |
晶体学 | 53篇 |
力学 | 21篇 |
综合类 | 49篇 |
数学 | 87篇 |
物理学 | 816篇 |
出版年
2024年 | 13篇 |
2023年 | 94篇 |
2022年 | 189篇 |
2021年 | 269篇 |
2020年 | 282篇 |
2019年 | 234篇 |
2018年 | 214篇 |
2017年 | 201篇 |
2016年 | 286篇 |
2015年 | 229篇 |
2014年 | 276篇 |
2013年 | 506篇 |
2012年 | 299篇 |
2011年 | 205篇 |
2010年 | 214篇 |
2009年 | 204篇 |
2008年 | 226篇 |
2007年 | 231篇 |
2006年 | 220篇 |
2005年 | 244篇 |
2004年 | 169篇 |
2003年 | 159篇 |
2002年 | 140篇 |
2001年 | 79篇 |
2000年 | 69篇 |
1999年 | 50篇 |
1998年 | 62篇 |
1997年 | 65篇 |
1996年 | 59篇 |
1995年 | 40篇 |
1994年 | 28篇 |
1993年 | 37篇 |
1992年 | 30篇 |
1991年 | 29篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有5733条查询结果,搜索用时 31 毫秒
201.
Fe3O4@SiO2@propyltriethoxysilane@o‐phenylendiamine as an environmentally‐benign functionalized silica‐coated magnetic organometallic nanomaterial has been synthesized and characterized by Fourier transforms infrared (FT‐IR) spectroscopy, scanning electron microscopy (SEM) images and energy dispersive X‐ray (EDX) and vibrating sample magnetometer (VSM) analyses. Then, its catalytic activity was investigated for the one‐pot three‐component condensation reaction between dimedone, malononitrile and various substituted aromatic aldehydes to afford the corresponding 2‐amino‐4H‐chromene derivatives under mild reaction conditions. This nanocatalyst can be easily recovered from the reaction mixture by using a magnet and reused for at least five times without significant decrease in catalytic activity. 相似文献
202.
《化学:亚洲杂志》2017,12(6):643-647
A fully conjugated system 4 consisting of two 2‐aza‐21‐carbaporphyrin (NCP) subunits bridged by dipyrrin was synthesized by a highly selective condensation of 3‐pyrrole‐NCP 2 with aryl aldehydes. The free base 4 as well as its silver(III) complex 5 exhibited flexibility of the bridge allowing synergetic binding of AgI, thus leading to a mixed‐valence tetraporphyrinic assembly consisting of eight silver atoms which was characterized both in the solid state and in solution. Binding of chiral acid by 4 and 5 was shown by observation of an induced optical activity of the adducts. 相似文献
203.
Dr. Yong Wu Dr. Shanshan Cao Dr. Iskander Douair Prof. Laurent Maron Prof. Xihe Bi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(19):5999-6006
The [2+1] cycloaddition reaction of a metal carbene with an alkene can produce important cyclopropane products for synthetic intermediates, materials, and pharmaceutical applications. However, this reaction is often accompanied by side reactions, such as coupling and self-coupling, so that the yield of the cyclopropanation product of non-silver transition-metal carbenes and hindered alkenes is generally lower than 50 %. To solve this problem, the addition of a low concentration of diazo compound (decomposition of sulfonyl hydrazones) to alkenes catalyzed by either CuOAc or PdCl2 was studied, but side reactions could still not be avoided. Interestingly, however, the yield of cyclopropanation products for such hindered alkenes were as high as 99 % with AgOTf as a catalyst. To explain this unexpected phenomenon, reaction pathways have been computed for four different catalysts by using DFT. By combining the results of these calculations with those obtained experimentally, it can be concluded that the efficiency of the silver catalyst is due to the barrierless concerted cycloaddition step and the kinetic inhibition of side reactions by a high concentration of alkene. 相似文献
204.
Abstract An overview of results on microscopic properties, implantation features and dynamics of Fe ions implanted into Si, Ge and ZnS as investigated with in beam Mößbauer spectroscopy(IBMS) is given. Potential and limitations of the method are discussed. 相似文献
205.
Md Sabir Alam Md Noushad Javed Faheem Hyder Pottoo Aafrin Waziri Faisal A. Almalki Md Saquib Hasnain Arun Garg Md Khalid Saifullah 《应用有机金属化学》2019,33(9)
Microwave irradiation (MI) process characteristically enables extremely rapid “in‐core” heating of dipoles and ions, in comparison to conventional thermal (conductance) process of heat transfer. During the process of nanoparticles synthesis, MI both modulates functionality behaviors as well as dynamic of reaction in favorable direction. So, MI providing a facile, favorable and alternative approach during nanoparticles synthesis nanoparticles with enhanced catalytic performances. Although, conventionally used reducing and capping reagents of synthetic origin, are usually environmentally hazardous and toxic for living organism. But, in absence of suitable capping agent; stability, shelf life and catalytic activity of metallic nanoparticles adversely affected. However, polymeric templates which emerged as suitable choice of agent for both reducing and capping purposes; bearing additional advantages in terms of catalyst free one step green synthesis process with high degree of biosafety and efficiency. Another aspect of current works was to understand role of process variables in growth mechanism and catalytic performances of microwave processed metallic nanoparticles, as well as comparison of these parameters with conventional heating method. However, due to poor prediction ability with previously published architect OFAT (One factor at a time) design with these nanoparticles as well as random selection of process variables with their different levels, such comparison couldn't be possible. Hence, using gum Ghatti (Anogeissus latifolia) as a model bio‐template and under simulated reaction conditions; architect of QbD design systems were integrated in microwave processed nanoparticles to establish mechanistic role these variables. Furthermore, in comparison to conventional heating; we reported well validated mathematical modeling of process variables on characteristic of nanoparticles as well as synthesized gold nanoparticles of desired and identical dimensions, in both thermal and microwave‐based processes. Interestingly, despite of identical dimension, MI processed gold nanoparticles bearing higher efficiency (kinetic rate) against remediation of hazardous nitro dye (4‐nitrophenol), into safer amino (4‐aminophenol) analogues. 相似文献
206.
207.
Dr. Gregory Chatel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(44):9665-9673
Based on recent examples and initiatives reported in the literature, this concept article discusses how chemistry can contribute to the circular economy approach in order to improve our current and future economical, societal, and environmental system. Through five proposed levels of contribution, chemists can take a significant part in this global approach via the consideration of green chemistry principles, the simplification of syntheses, the limitation of complex products preparation, the efficient utilization of resources but also the novel ways of waste valorization. A more systematic and generalized environmental and economic assessment from the lab-scale is also recommended. At last, chemists have to work even more collaboratively and in a multidisciplinary way, within chemistry and beyond. 相似文献
208.
One of the commonly used methods to synthesize furans is the three-component reaction among aromatic aldehyde, arylamine, and acetylenedicarboxylate. The main advantages of this work are easy reaction work-up, short reaction time, high yield and easy recyclability, reusability of the catalyst. And also basalt fiber applications are surely innovative in many industrial and economic fields, because of its good mechanical, chemical and thermal performances. 相似文献
209.
Dr. Ritesh Haldar Kamal Batra Stefan Michael Marschner Dr. Agnieszka B. Kuc Dr. Stefan Zahn Prof. Dr. Roland A. Fischer Prof. Dr. Stefan Bräse Prof. Dr. Thomas Heine Prof. Dr. Christof Wöll 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(33):7847-7851
In organic photovoltaics, porphyrins (PPs) are among the most promising compounds owing to their large absorption cross-section, wide spectral range, and stability. Nevertheless, a precise adjustment of absorption band positions to reach a full coverage of the so-called green gap has not been achieved yet. We demonstrate that a tuning of the PP Q- and Soret bands can be carried out by using a computational approach for which substitution patterns are optimized in silico. The most promising candidate structures were then synthesized. The experimental UV/Vis data for the solvated compounds were in excellent agreement with the theoretical predictions. By attaching further functionalities, which allow the use of PP chromophores as linkers for the assembly of metal-organic frameworks (MOFs), we were able to exploit packing effects resulting in pronounced redshifts, which allowed further optimization of the photophysical properties of PP assemblies. Finally, we use a layer-by-layer method to assemble the PP linkers into surface-mounted MOFs (SURMOFs), thus obtaining high optical quality, homogeneous and crystalline multilayer films. Experimental results are in full accord with the calculations, demonstrating the huge potential of computational screening methods in tailoring MOF and SURMOF photophysical properties. 相似文献
210.
Georgia Englezou Kristoffer Kortsen Ana A. C. Pacheco Robert Cavanagh Joachim C. Lentz Eduards Krumins Carlos Sanders-Velez Steven M. Howdle Alisyn J. Nedoma Vincenzo Taresco 《Journal of polymer science. Part A, Polymer chemistry》2020,58(11):1571-1581
2-methyltetrahydrofuran (2-MeTHF) is a readily available, inexpensive, neoteric, bio-based solvent. It has been adopted across a wide range of chemical processes including the batch manufacture of fine chemicals, enzymatic polycondensations and ring opening polymerizations. To reduce the environmental burden related to the synthesis of pharmaceutical-grade polymers based on lactide and caprolactone, we envisaged the use of 2-MeTHF. For the first time, we combined a series of metal-free and enzymatic ROPs with free radical and controlled RAFT polymerizations (carried out separately and in tandem) in 2-MeTHF, in order to easily tune the chemistry and the architecture of the final polymers. After a simple purification, the amphiphilic polymers were formulated into nanoparticles and tested for their cytocompatibility in three model cell lines, to assess their application as potential polymeric excipients for nanomedicines. 相似文献