全文获取类型
收费全文 | 8350篇 |
免费 | 707篇 |
国内免费 | 767篇 |
专业分类
化学 | 2452篇 |
晶体学 | 91篇 |
力学 | 466篇 |
综合类 | 141篇 |
数学 | 4561篇 |
物理学 | 2113篇 |
出版年
2023年 | 62篇 |
2022年 | 132篇 |
2021年 | 195篇 |
2020年 | 270篇 |
2019年 | 224篇 |
2018年 | 241篇 |
2017年 | 228篇 |
2016年 | 308篇 |
2015年 | 223篇 |
2014年 | 394篇 |
2013年 | 688篇 |
2012年 | 366篇 |
2011年 | 433篇 |
2010年 | 379篇 |
2009年 | 475篇 |
2008年 | 519篇 |
2007年 | 576篇 |
2006年 | 452篇 |
2005年 | 398篇 |
2004年 | 377篇 |
2003年 | 391篇 |
2002年 | 308篇 |
2001年 | 279篇 |
2000年 | 232篇 |
1999年 | 214篇 |
1998年 | 188篇 |
1997年 | 159篇 |
1996年 | 161篇 |
1995年 | 127篇 |
1994年 | 118篇 |
1993年 | 82篇 |
1992年 | 67篇 |
1991年 | 61篇 |
1990年 | 53篇 |
1989年 | 43篇 |
1988年 | 53篇 |
1987年 | 37篇 |
1986年 | 28篇 |
1985年 | 46篇 |
1984年 | 35篇 |
1983年 | 21篇 |
1982年 | 35篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1979年 | 28篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 6篇 |
1973年 | 9篇 |
排序方式: 共有9824条查询结果,搜索用时 171 毫秒
41.
42.
The interaction between biomolecules with their target ligands plays a great role in regulating biological functions. Aptamers are short oligonucleotide sequences that can specifically recognize target biomolecules via structural complementarity and thus regulate related biological functions. In the past ten years, aptamers have made great progress in target biomolecule recognition, becoming a powerful tool to regulate biological functions. At present, there are many reviews on aptamers applied in biomolecular recognition, but few reviews pay attention to aptamer-based regulation of biological functions. Here, we summarize the approaches to enhancing aptamer affinity and the advancements of aptamers in regulating enzymatic activity, cellular immunity and cellular behaviors. Furthermore, this review discusses the challenges and future perspectives of aptamers in target recognition and biological functions regulation, aiming to provide some promising ideas for future regulation of biomolecular functions in a complex biological environment. 相似文献
43.
热激活延迟荧光(Thermally activated delayed fluorescence, TADF)材料由于三线态激子可通过反系间窜越(Reverse intersystem crossing, RISC)转换为单线态激子,在有机发光二极管(Organic light-emitting diodes, OLEDs)中理论上可达到100%的激子利用率而被广泛关注。但实验上开发设计高性能TADF材料较为复杂且研究周期较长,理论研究可以从本质上建立材料结构-性能的关系,预测材料的性质并提供一定的分子设计策略。本文围绕高性能TADF材料的开发,从发光原理出发,系统阐述了分子的设计策略及光物理参数如材料单-三线态能级差(Single-triplet energy gap, ΔEST)、系间/反系间窜越速率、吸收/发射光谱、辐射/非辐射速率等的计算原理、计算方法和研究进展。最后我们探讨了TADF材料理论研究面临的机遇和挑战,通过对TADF材料的理论研究综述和研究前景的展望,期待吸引更多的研究工作者,推动该领域的发展和突破。 相似文献
44.
《Arabian Journal of Chemistry》2022,15(7):103922
Recently, the visible-light photoredox decarboxylative couplings of N-(acyloxy)phthalimides (NHPI esters) and its derivatives have become an efficient chemical transformation. Under visible light, the NHPI esters undergo a single-electron transfer (SET) process to afford the corresponding carbon or nitrogen radicals that participate in many chemical transformations. The photoredox decarboxylative couplings have been applied to achieve construction of an array of carbon–carbon and carbon–heteroatom bonds as well as the synthesis of carbocycles and heterocycles. This review categorises photocatalysts, discusses the application and catalysis mechanisms of NHPI esters, and details recent progress in this field. 相似文献
45.
《Arabian Journal of Chemistry》2022,15(2):103598
Wet granulation process is a major unit operation in production of pharmaceuticals as solid dosage oral formulation. Indeed, granulation is used to improve the formulation properties such as flowability, compressibility, and so on for pharmaceutical manufacturing. Different types of granulations can be used in pharmaceutical manufacturing in which the selection of proper process depends on the operational conditions as well as formulation properties. In current decades, twin-screw wet granulation has been of paramount interest owing to its superior properties. Pharmaceutical manufacturing industry are trying to move towards continuous mode by which the efficiency can be improved compared to the batch mode. Therefore, development of continuous granulation process is of great importance. In this review article, various processing units applicable for wet granulation of pharmaceutical formulations for solid dosage forms are reviewed and discussed. The advantages and disadvantages of the processes are discussed and listed along with modeling approaches for simulation of process. The governing models and numerical schemes applicable for design of wet granulation are also critically discussed. The main focus is on wet granulation as this method has attracted much attention in pharmaceutical processing. 相似文献
46.
《中国化学快报》2021,32(9):2828-2832
A mesoporous cobalt aluminate (CoAl2O4) spinel is synthesized through a combustion method and adopted for the activation of peroxymonosulfate (PMS) to degrade organic pollutants. Multiple characterization procedures are conducted to investigate the morphology and physicochemical properties of the CoAl2O4 spinel. Due to its mesoporous structure, large surface area, and high electrical conductivity, the obtained CoAl2O4 exhibits remarkable catalytic activity for Rhodamine B (RhB) degradation. Its RhB degradation rate is 89.0 and 10.5 times greater than those of Co3O4 and CoAl2O4 spinel prepared by a precipitation method, respectively. Moreover, the mesoporous CoAl2O4 spinel demonstrates a broad operating pH range and excellent recyclability. The influence of several parameters (catalyst amount, PMS concentration, initial pH, and coexisting inorganic anions) on the oxidation of RhB is evaluated. Through quenching tests and electron paramagnetic resonance experiments, sulfate radicals are identified as the predominant reactive species in RhB degradation. This paper provides new insights for the development of efficient, stable, and reusable cobalt-based heterogeneous catalysts and promotes the application of persulfate activation technology for the treatment of refractory organic wastewater. 相似文献
47.
48.
《Macromolecular theory and simulations》2017,26(4)
The method of moments is a simple, efficient method simulating polymerization processes. Its use is said to be limited in nonlinear free radical polymerizations with branching or crosslinking due to the assumptions needed. Here, moment equations are derived without assuming steady state, one radical per molecule, or a statistical distribution of connections. Equations are valid up to the gel point. The bulk solution is formally identical to the pseudo kinetic approach by Tobita and Hamielec if moments of dead polymer are replaced by the sum of dead and life polymers. The method relies on analytical solutions of the moments of the molecular weight distributions (MWD) of instantaneous primary chains. In emulsion polymerization compartmentalization of radicals complicates the calculation. An alternative approximation of these MWDs is presented. The present extension allows nonlinear free radical polymerization to be readily included in the computer based design and optimization of polymerization processes and to check more detailed calculations of the MWD.
49.
A parametric investigation of the friction performance of PC‐ABS parts processed by FDM additive manufacturing process 下载免费PDF全文
The friction performance is an important factor of parts processed by fused deposition modeling (FDM) for various engineering applications. It is one type of failure made of surface contact. The proper use of FDM process parameters can bring a significant reduction in friction and the amount of wear, thereby leading to a reduction in the material waste. To date, very little studies have been performed in this area. This paper investigates the effect of FDM manufacturing parameters on the friction performance of polycarbonate‐acrylonitrile butadiene styrene prototypes processed by FDM using definitive screening design and partial least squares method. The observation of surface morphology was obtained by the scanning electron microscopy to examine the effect of process parameters on the microstructure. The experimental results have shown that layer thickness, air gap, raster angle, and build orientation are the most influential factors affecting the friction performance of FDM manufactured parts. The proposed approach presented in this study provides an impetus to develop analytical modeling and functional relationships between FDM manufacturing parameters and friction performance. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
50.
Improving the water resistance of epoxy–anhydride matrices by the incorporation of bentonite 下载免费PDF全文
Epoxy–anhydride‐based polymers are commonly used as a matrix in pipeline systems exposed to water during their in‐service life. Water absorption at moderate temperatures and/or at long exposure times could lead to irreversible hydrolysis reaction decreasing considerably the polymer overall performance. A strategy to enhance the barrier properties of epoxy resins is to add nanofillers to traditional matrices. In this work, we added bentonite and chemically modified bentonite to this purpose. Water absorption of the resulting materials at three different temperatures (22°C, 80°C, and 93°C) was studied, and simultaneously, the evolution during the immersion tests of glass transition temperature and flexural modulus was recorded. Long‐term gravimetric results showed that composites with chemically modified bentonite produce a delay on the hydrolysis of epoxy–anhydride matrix, which is a relevant result, because of the tough application and uses of the system, from the technological point of view. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献