全文获取类型
收费全文 | 20616篇 |
免费 | 3612篇 |
国内免费 | 2578篇 |
专业分类
化学 | 14588篇 |
晶体学 | 209篇 |
力学 | 1252篇 |
综合类 | 136篇 |
数学 | 2959篇 |
物理学 | 7662篇 |
出版年
2024年 | 59篇 |
2023年 | 448篇 |
2022年 | 450篇 |
2021年 | 687篇 |
2020年 | 922篇 |
2019年 | 849篇 |
2018年 | 729篇 |
2017年 | 678篇 |
2016年 | 1051篇 |
2015年 | 1016篇 |
2014年 | 1150篇 |
2013年 | 1561篇 |
2012年 | 1791篇 |
2011年 | 1868篇 |
2010年 | 1339篇 |
2009年 | 1209篇 |
2008年 | 1376篇 |
2007年 | 1219篇 |
2006年 | 1069篇 |
2005年 | 965篇 |
2004年 | 770篇 |
2003年 | 670篇 |
2002年 | 722篇 |
2001年 | 590篇 |
2000年 | 485篇 |
1999年 | 458篇 |
1998年 | 363篇 |
1997年 | 328篇 |
1996年 | 346篇 |
1995年 | 305篇 |
1994年 | 239篇 |
1993年 | 175篇 |
1992年 | 166篇 |
1991年 | 167篇 |
1990年 | 129篇 |
1989年 | 106篇 |
1988年 | 58篇 |
1987年 | 58篇 |
1986年 | 76篇 |
1985年 | 53篇 |
1984年 | 32篇 |
1983年 | 27篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1975年 | 3篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
Covalent organic frameworks(COFs), as a class of crystalline porous materials with periodic lattices and porous structures, have received extensive attention in the fields of gas storage and separation, energy storage, catalysis and optoelectronics and so on. However, COFs are still in their infancy in the field of nuclear waste treatment, especially for sequestration of long-live problematic radionuclides, such as 99Tc. Battle of decontamination of pertechnetate(TcO4–), a main existence of 99Tc under aerobic environments, is far from finished. In this review, recent progresses of COFs and some relative materials in the sequestration of pertechnetate, and perspective on surmounting the unmet issues are elucidated. 相似文献
992.
A Hexagonal Covalent Porphyrin Framework as an Efficient Support for Gold Nanoparticles toward Catalytic Reduction of 4‐Nitrophenol 下载免费PDF全文
Zheng‐Dong Ding Yu‐Xia Wang Sai‐Fei Xi Prof. Dr. Yunxing Li Prof. Dr. Zaijun Li Prof. Dr. Xuehong Ren Prof. Dr. Zhi‐Guo Gu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):17029-17036
A hexagonal porphyrin‐based porous organic polymer, namely, CPF‐1, was constructed by 3+2 ketoenamine condensation of the C2‐symmetric porphyrin diamine 5,15‐bis(4‐aminophenyl)‐10,20‐diphenylporphyrin and 1,3,5‐triformylphloroglucinol. This material exhibits permanent porosity and excellent thermal and chemical stability. CPF‐1 can be employed as a superior supporting substrate to immobilize Au nanoparticles (NPs) as a result of the strong interactions between Au NPs and the CPF support. An Au@CPF‐1 hybrid was synthesized by an interfacial solution infiltration method with NaBH4 as reducing agent. Au NPs (5 nm) grew on CPF‐1 and were distributed without aggregation. Moreover, Au@CPF‐1 exhibits superior catalytic activity compared to many other reported Au‐based catalysts for the reduction of 4‐nitrophenol in the presence of NaBH4. In addition, Au@CPF‐1 has excellent stability and recyclability, and it can be reused for three successive reaction cycles without loss of activity. The dense distribution of phenyl rings on the channel walls of the CPF support can reasonably be regarded as the active sites that adsorb the 4‐nitrophenol molecule through hydrogen‐bonding and C?H ??? π interactions, as was confirmed by the X‐ray structure of model compound DAPP‐Benz. 相似文献
993.
Nonlinear Dynamics - This paper studies the formation–containment control problem for networked nonlinear Euler–Lagrange systems with input saturation. To realize the concurrency of... 相似文献
994.
995.
An approach of analytical calculation for photonic band gap structure (PBGS) of one-dimensional periodic media, such as non-uniform distribution plasma photonic crystal (PPC), is given on the basis of the recently reported differential transfer matrix method. The dispersion equation of electromagnetic wave propagating in one dimensional non-uniform distribution PPC is derived and the PBGSs for several numerical cases, such as linear distribution, exponential distribution and Epstein distribution, are calculated and discussed. 相似文献
996.
Tungsten doped mesoporous SBA‐16 as novel heterogeneous catalysts for oxidation of cyclopentene to glutaric acid 下载免费PDF全文
Novel heterogeneous tungsten species in mesoporous silica SBA‐16 catalysts based on ship‐in‐a‐bottle methodology are originally reported for oxidizing cyclopentene (CPE) to glutaric acid (GAC) using hydrogen peroxide (H2O2). For all W‐SBA‐16 catalysts, isolated tungsten species and octahedrally coordinated tungsten oxide species are observed while WO3 crystallites are detected for the W‐SBA‐16 catalysts with Si/ W = 5, 10, and 20. The specific surface areas and the corresponding total pore volumes decrease significantly as increasing amounts of tungsten incorporated into the pores of SBA‐16. Using tungsten‐substituted mesoporous SBA‐16 heterogeneous catalysts, high yield of GAC (55%) is achieved with low tungsten loading (for Si/W = 30, ~13 wt%) for oxidation of CPE. The W‐SBA‐16 catalysts with Si/W = 30 can be reused five times without dramatic deactivation. In fact, low catalytic activity provided by bulk WO3 implies that the highly distributed tungsten species in SBA‐16 and the steric confinement effect of SBA‐16 are key elements for the outstanding catalytic performance. 相似文献
997.
998.
Pomponlike La2(MoO4)3 microstructures assembled with single-crystalline nanoflakes have been facilely fabricated via a surfactant-assisted ultrasound route for the first time. Various synthesis conditions were examined, such as the surfactant concentration, the molecular structure of surfactants, and the pH value. The obtained pomponlike microstructures were characterized by X-ray diffraction (XRD), (field-emission) scanning electron microscopy [(FE)SEM], transmission electron microscopy (TEM), and nitrogen adsorption/desorption isotherms. It has been revealed that a minimum concentration of sodium dodecylsulfate (SDS) was required for the formation of pomponlike La2(MoO4)3 microstructures. When the SDS concentration is above 0.02 mol L−1, the pomponlike microstructures become more perfect, and the size is also increased with the increasing SDS concentration. Under the same sonication, similar pomponlike microstructures were obtained when a cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), was used instead of the anionic surfactant SDS, indicating that the hydrophobic alkyl chains are an important factor for the formation of the pomponlike La2(MoO4)3 microstructures. It is also found that the pomponlike La2(MoO4)3 microstructures can only be obtained within an optimal pH range of 8.0–9.0 under sonication. Based on TEM, Fourier transform infrared spectroscopy (FT-IR) and solubilization experiment, a formation mechanism of pomponlike La2(MoO4)3 microstructures was proposed, in which the collaborative action of surfactants and sonication plays a key role. Furthermore, the porosity of the pomponlike La2(MoO4)3 microstructures were discussed. 相似文献
999.
<正>We present a novel method for realizing double-image encryption algorithm by combining the images in different transform domains.Two original images are encrypted into two interim images by fractional Fourier transform and gyrator transform,respectively.The two encrypted images can be obtained by means of the addition and subtraction of the two interim images.This is defined as a double-image sharing scheme,in which the original images are encrypted into two parts.The original images cannot be recovered only with any one of the two interim images.Numerical simulation experiments demonstrate the validity of the algorithm. 相似文献