全文获取类型
收费全文 | 2004篇 |
免费 | 262篇 |
国内免费 | 240篇 |
专业分类
化学 | 1402篇 |
晶体学 | 20篇 |
力学 | 88篇 |
综合类 | 4篇 |
数学 | 331篇 |
物理学 | 661篇 |
出版年
2024年 | 3篇 |
2023年 | 47篇 |
2022年 | 52篇 |
2021年 | 80篇 |
2020年 | 101篇 |
2019年 | 71篇 |
2018年 | 61篇 |
2017年 | 66篇 |
2016年 | 95篇 |
2015年 | 88篇 |
2014年 | 92篇 |
2013年 | 139篇 |
2012年 | 158篇 |
2011年 | 172篇 |
2010年 | 92篇 |
2009年 | 113篇 |
2008年 | 125篇 |
2007年 | 119篇 |
2006年 | 92篇 |
2005年 | 95篇 |
2004年 | 54篇 |
2003年 | 42篇 |
2002年 | 40篇 |
2001年 | 44篇 |
2000年 | 46篇 |
1999年 | 37篇 |
1998年 | 26篇 |
1997年 | 27篇 |
1996年 | 42篇 |
1995年 | 35篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 24篇 |
1991年 | 33篇 |
1990年 | 25篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1968年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2506条查询结果,搜索用时 765 毫秒
121.
Jochen C. Lauer Ziwei Pang Paul Janßen Dr. Frank Rominger Tobias Kirschbaum Prof. Dr. Marcus Elstner Prof. Dr. Michael Mastalerz 《ChemistryOpen》2020,9(2):183-190
Three shape-persistent [4+4] imine cages with truncated tetrahedral geometry with different window sizes were studied as hosts for the encapsulation of tetra-n-alkylammonium salts of various bulkiness. In various solvents the cages behave differently. For instance, in dichloromethane the cage with smallest window size takes up NEt4+ but not NMe4 + , which is in contrast to the two cages with larger windows hosting both ions. To find out the reason for this, kinetic experiments were carried out to determine the velocity of uptake but also to deduce the activation barriers for these processes. To support the experimental results, calculations for the guest uptakes have been performed by molecular mechanics’ simulations. Finally, the complexation of pharmaceutical interested compounds, such as acetylcholine, muscarine or denatonium have been determined by NMR experiments. 相似文献
122.
The flame‐retardant microcapsules were successfully fabricated with an aluminum hypophosphite (AHP) core. Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS) were used to verify that AHP was encapsulated in the microcapsules, and thermogravimetry analysis showed that microencapsulated AHP (MAHP) possessed higher thermal stability than that of AHP. Then, a flame‐retardant and smoke suppression system for silicone foams (SiFs) was obtained through a synergistic effect of MAHP and zinc borate (2ZnO·3B2O3·3.5H2O). The mechanical properties, flame retardance, and smoke suppression of SiFs with MAHP and zinc borate were tested using the tensile test, limiting oxygen index (LOI) test, UL‐94 test, and cone calorimeter test. The mechanical properties indicated that the tensile strength and elongation at break of SiFs could evidently improve with the incorporation of MAHP. Compared with pure SiF, SiF8 with 4.5‐wt% MAHP and 1.5‐wt% zinc borate could achieve an LOI value of 30.7 vol% and an UL‐94 V‐0 rating, the time to ignition amplified almost six times, the peak heat release rate and total heat release were 51.10% and 46.00% less than that of pure SiF, respectively, the fire performance index increased nearly 13 times, and the fire growth index value was only 13.18% of pure SiF. Moreover, the partial substitution of zinc borate imparted a substantial improvement in both flame retardancy and smoke suppression. Especially, the peak smoke production rate and total smoke production of SiF8 were merely 38.46% and 38.84% of pure SiF. 相似文献
123.
Yantao Pang Anoop Thomas Kalaivanan Nagarajan Robrecht M. A. Vergauwe Kripa Joseph Bianca Patrahau Kuidong Wang Cyriaque Genet Thomas W. Ebbesen 《Angewandte Chemie (International ed. in English)》2020,59(26):10436-10440
It is well known that symmetry plays a key role in chemical reactivity. Here we explore its role in vibrational strong coupling (VSC) for a charge‐transfer (CT) complexation reaction. By studying the trimethylated‐benzene–I2 CT complex, we find that VSC induces large changes in the equilibrium constant KDA of the CT complex, reflecting modifications in the ΔG° value of the reaction. Furthermore, by tuning the microfluidic cavity modes to the different IR vibrations of the trimethylated benzene, ΔG° either increases or decreases depending only on the symmetry of the normal mode that is coupled. This result reveals the critical role of symmetry in VSC and, in turn, provides an explanation for why the magnitude of chemical changes induced by VSC are much greater than the Rabi splitting, that is, the energy perturbation caused by VSC. These findings further confirm that VSC is powerful and versatile tool for the molecular sciences. 相似文献
124.
125.
Shan-Shan Guo Xue Pang Yang Wang Zhu-Feng Geng Ju-Qin Cao Jun-Yu Liang 《Natural product research》2020,34(18):2595-2601
AbstractOne new sesquiterpene (α-iso-cubebenol acetate, 8), together with 9 known compounds (1-7, 9, 10) were isolated from the stems of Schisandra chinensis (Turcz.) Baill. by repeated silica gel column chromatography. Based on the results of MS, NMR spectra and comparing with literature data, the six dibenzocyclooctadiene lignans were identified as schizandrin A to C (1-3), schizandrin (4), schisantherin A (5) and gomisin J (6), the two sesquiterpenes were identified as α-iso-cubebenol (7) and α-iso-cubebenol acetate (8), while the two triterpenic acids were identified as ganwuweizic acid (9) and kadsuric acid (10). The antifeedant activity of the 10 compounds against Tribolium castaneum adults was tested. Gomisin J (6) exhibited activity at 1500?ppm concentration with 40.3% antifeeding index percentages. As for the dibenzocyclooctene lignans (compounds 1–3, 6), the number of methylenedioxies and the position of hydroxyl groups were the main factors to affect their antifeedant activities. 相似文献
126.
根据气体冷却服的特点,对不同进风型式下气体冷却服中空气流动与换热进行研究。建立了进气口加设挡板层、进气口带均流器型和直吹型3种型式气体冷却服(服装夹层)中冷却空气流动过程的数学模型。对气体的流动过程进行分析,结果表明:不同的进风型式对气体冷却服空气层的温度分布状况、平均气流流速、平均温度、对流散热量影响较大;其中进气口加设挡板层的服装空气夹层温度分布最均匀,进气直吹型的平均气流流速最大,对流散热效果最好。研究结果为气体冷却服进一步的布风优化设计提供了理论和应用依据。 相似文献
127.
With adjustable pulse durations, a semiconductor saturable absorber mirror (SESAM) passively mode-locked picosecond Nd:YVO4 laser was studied. The pulse duration was adjustable from 20 to 80 ps by using intracavity etalons of different thicknesses. 相似文献
128.
Enhanced Catalytic Activity in Liquid‐Exfoliated FeOCl Nanosheets as a Fenton‐Like Catalyst 下载免费PDF全文
Jian Zhang Prof. Xiu‐Ling Jiao Dr. Yu‐Guo Xia Fang‐Fang Liu Ying‐Ping Pang Xin‐Fu Zhao Prof. Dai‐Rong Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(27):9321-9329
A facile liquid‐phase exfoliation method to prepare few‐layer FeOCl nanosheets in acetonitrile by ultrasonication is reported. The detailed exfoliation mechanism and generated products were investigated by combining first‐principle calculations and experimental approaches. The similar cleavage energies of FeOCl (340 mJ m?2) and graphite (320 mJ m?2) confirm the experimental exfoliation feasibility. As a Fenton reagent, FeOCl nanosheets showed outstanding properties in the catalytic degradation of phenol in water at room temperature, under neutral pH conditions, and with sunlight irradiation. Apart from the increased surface area of the nanosheets, the surface state change of the nanosheets also plays a key role in improving the catalytic performance. The changes of charge density, density of states (DOS), and valence state of Fe atoms in the exfoliated FeOCl nanosheets versus plates illustrated that surface atomistic relationships made the few‐layer nanosheets higher activity, indicating the exfoliation process of the FeOCl nanosheets also brought about surface state changes. 相似文献
129.
C.H. Jeffrey Pang 《Journal of Differential Equations》2012,253(1):203-224
The framework of differential inclusions encompasses modern optimal control and the calculus of variations. Necessary optimality conditions in the literature identify potentially optimal paths, but do not show how to perturb paths to optimality. We first look at the corresponding discretized inclusions, estimating the subdifferential dependence of the optimal value in terms of the endpoints of the feasible paths. Our approach is to first estimate the coderivative of the reachable map. The discretized (nonsmooth) Euler–Lagrange and Transversality Conditions follow as a corollary. We obtain corresponding results for differential inclusions by passing discretized inclusions to the limit. 相似文献
130.
The ionization spectrum of sulfur dioxide has been successfully studied by using the symmetry-adapted-cluster configuration-interaction (SAC-CI) general-R and SD-R methods and the basis set correlation-consistent polarized valence triple-zeta (cc-pVTZ). The SAC-CI general-R method reproduces the experimental spectrum well for both the main peaks and the satellite peaks of ionization spectrum of SO2. The sequence of ionic states corresponding to main peaks of SO2 has been re-determined according to the SAC-CI conclusions and it is reordered as X^2A1, A^2B2, B2A2, C^2B1,D^2A1, E^2B2 and F^2A1. Besides, the equilibrium structures and adiabatic ionization potentials (AIPs) of ionic states of main peaks of SO2 are calculated by using the SAC-CI SD-R method. 相似文献