全文获取类型
收费全文 | 924篇 |
免费 | 39篇 |
国内免费 | 3篇 |
专业分类
化学 | 703篇 |
晶体学 | 30篇 |
力学 | 27篇 |
数学 | 48篇 |
物理学 | 158篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 16篇 |
2021年 | 24篇 |
2020年 | 29篇 |
2019年 | 24篇 |
2018年 | 41篇 |
2017年 | 40篇 |
2016年 | 39篇 |
2015年 | 29篇 |
2014年 | 52篇 |
2013年 | 58篇 |
2012年 | 90篇 |
2011年 | 72篇 |
2010年 | 48篇 |
2009年 | 39篇 |
2008年 | 46篇 |
2007年 | 51篇 |
2006年 | 35篇 |
2005年 | 34篇 |
2004年 | 29篇 |
2003年 | 26篇 |
2002年 | 15篇 |
2001年 | 18篇 |
2000年 | 17篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 10篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有966条查询结果,搜索用时 15 毫秒
961.
The main question of this research is: Who should undertake promotional and brand-image advertising if the franchisor and franchisees act so as to maximize their respective profits? To address this question, we study a two-stage advertising game between a franchisor and two adjacent franchisees. In the first stage of the game, the franchisor chooses between three advertising models – centralizing or delegating the two types of advertising to the franchisees or delegating only promotional advertising. In the second stage, given the franchisor’s choice of an advertising model, the two franchisees decide whether or not to cooperate. Our main findings are that (1) the franchisees should cooperate if the franchisor delegates either both brand-image and promotional advertising or promotional advertising, although cooperation between franchisees does not necessary improve the franchisor’s profits. (2) The choice of an advertising arrangement critically depends on the margins as well as the costs of performing both promotional and brand-image advertising. We also discuss the conditions under which the three advertising models should be implemented. 相似文献
962.
Vinay Vishwanath Michael Sulyok Roman Labuda Wolfgang Bicker Rudolf Krska 《Analytical and bioanalytical chemistry》2009,395(5):1355-1372
This paper describes the application of a previously published multi-mycotoxin method for food and feed matrices based on
liquid chromatography/electrospray ionization-tandem mass spectrometry (HPLC/ESI-MS/MS) to the analysis of microbial metabolites
in indoor matrices. The range of investigated analytes has been extended by 99 fungal and bacterial metabolites to cover now
186 compounds overall. The method is based on a single extraction step using an acidified acetonitrile/water mixture (which
has been determined to be preferable to methanol and ethyl acetate) followed by analysis of the diluted crude extract. The
analytical signal of one third of the investigated analytes was reduced by more than 50% due to matrix effects in a spiked
extract of house dust, whereas the other investigated materials were less critical in that aspect. For determination of method
performance characteristics, a spiked reference material for house dust was chosen as a model sample for an extremely complex
matrix. With few exceptions, coefficients of variation of the whole procedure of <10% and limits of detection of <50 μg kg−1 were obtained. The apparent recoveries were below 50% for half of the investigated analytes due to incomplete extraction
and/or detection-related matrix effects. The application of the method to 14 samples from damp buildings revealed the presence
of 20 different analytes at concentrations of up to 130 mg kg−1. Most of these compounds have never been identified before in real-world samples, although they are known to be produced
by indoor-relevant fungi. This underlines the great value of the described method for the on-site determination of microbial
metabolites.
相似文献
963.
Bibhuti Bhusan Champati Bhuban Mohan Padhiari Asit Ray Tarun Halder Sudipta Jena Ambika Sahoo Basudeba Kar Pradeep Kumar Kamila Pratap Chandra Panda Biswajit Ghosh Sanghamitra Nayak 《Molecules (Basel, Switzerland)》2022,27(9)
Andrographolide, the principal secondary metabolite of Andrographis paniculata, displays a wide spectrum of medicinal activities. The content of andrographolide varies significantly in the species collected from different geographical regions. Therefore, this study aims at investigating the role of different abiotic factors and selecting suitable sites for the cultivation of A. paniculata with high andrographolide content using a multilayer perceptron artificial neural network (MLP-ANN) approach. A total of 150 accessions of A. paniculata collected from different regions of Odisha and West Bengal in eastern India showed a variation in andrographolide content in the range of 0.28–5.45% on a dry weight basis. The MLP-ANN was trained using climatic factors and soil nutrients as the input layer and the andrographolide content as the output layer. The best topological ANN architecture, consisting of 14 input neurons, 12 hidden neurons, and 1 output neuron, could predict the andrographolide content with 90% accuracy. The developed ANN model showed good predictive performance with a correlation coefficient (R2) of 0.9716 and a root-mean-square error (RMSE) of 0.18. The global sensitivity analysis revealed nitrogen followed by phosphorus and potassium as the predominant input variables influencing the andrographolide content. The andrographolide content could be increased from 3.38% to 4.90% by optimizing these sensitive factors. The result showed that the ANN approach is reliable for the prediction of suitable sites for the optimum andrographolide yield in A. paniculata. 相似文献
964.
Sanjeev Kumar Tharun Kumar Sabbi Rasika Pingale Pradeep Girase Vinaykumar Kanchupalli 《Chemical record (New York, N.Y.)》2023,23(3):e202200228
Transition metal-catalyzed C−H functionalization of diverse arenes with alkyne units has attracted enormous attention for decades since they provide straightforward access to various functionalization/annulations, which are commonly present in bioactive compounds and natural products. Recently, conjugated alkynes (1,3-diynes) have been utilized as key coupling partner in many C−H activation reactions due to their versatile characteristic properties. The presence of two C≡C bonds in conjugated 1,3-diyne brings the new diversity in synthetic transformations, such as chemo-, regioselective pathways, mono-bis functionalizations, cascade annulations, etc. Herein, we summarized the latest developments in the realm of transition-metal-catalyzed C−H functionalizations of diverse arenes with 1,3-diynes. Moreover, we highlighted the diverse transformations, conditions, mechanisms and applications of the corresponding reaction in detail. 相似文献
965.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献
966.
Adimule Vinayak Bhat Vinay S. Joshi Rajeev Batakurki Sheetal Hegde Gurumurthy Yallur Basappa C. 《Journal of Solid State Electrochemistry》2023,27(2):511-529
Journal of Solid State Electrochemistry - In the present investigation, we have synthesized samarium (Sm) nanoparticles (NPs) and anchored them onto the surface of CuO:CoO nanostructure (NS) by... 相似文献