全文获取类型
收费全文 | 438928篇 |
免费 | 4331篇 |
国内免费 | 1221篇 |
专业分类
化学 | 234960篇 |
晶体学 | 6687篇 |
力学 | 18889篇 |
综合类 | 13篇 |
数学 | 50085篇 |
物理学 | 133846篇 |
出版年
2021年 | 4106篇 |
2020年 | 4688篇 |
2019年 | 4988篇 |
2018年 | 5885篇 |
2017年 | 5764篇 |
2016年 | 9007篇 |
2015年 | 5563篇 |
2014年 | 8547篇 |
2013年 | 20197篇 |
2012年 | 15657篇 |
2011年 | 19263篇 |
2010年 | 13503篇 |
2009年 | 13357篇 |
2008年 | 17652篇 |
2007年 | 17550篇 |
2006年 | 16256篇 |
2005年 | 14558篇 |
2004年 | 13527篇 |
2003年 | 11892篇 |
2002年 | 11729篇 |
2001年 | 13429篇 |
2000年 | 10086篇 |
1999年 | 7917篇 |
1998年 | 6570篇 |
1997年 | 6314篇 |
1996年 | 6081篇 |
1995年 | 5472篇 |
1994年 | 5393篇 |
1993年 | 5199篇 |
1992年 | 5828篇 |
1991年 | 5924篇 |
1990年 | 5664篇 |
1989年 | 5473篇 |
1988年 | 5493篇 |
1987年 | 5377篇 |
1986年 | 5093篇 |
1985年 | 6564篇 |
1984年 | 6695篇 |
1983年 | 5303篇 |
1982年 | 5388篇 |
1981年 | 5367篇 |
1980年 | 4955篇 |
1979年 | 5353篇 |
1978年 | 5491篇 |
1977年 | 5385篇 |
1976年 | 5328篇 |
1975年 | 4915篇 |
1974年 | 4886篇 |
1973年 | 4880篇 |
1972年 | 3456篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
M.M. Elseweidy N.N. Younis S.E. Elswefy F.R. Abdallah S.I. El-Dahmy G. Elnagar 《Natural product research》2015,29(10):961-965
The anti-atherogenic potentials of total ginger (Zingiber officinale) extract (TGE) or curcuminoids extracted from turmeric (Curcuma longa), members of family Zingiberaceae, were compared in hypercholesterolaemia. Rabbits were fed either normal or atherogenic diet. The rabbits on atherogenic diet received treatments with TGE or curcumenoids and placebo concurrently for 6 weeks (n = 6). The anti-atherogenic effects of curcuminoids and ginger are mediated via multiple mechanisms. This effect was correlated with their ability to lower cholesteryl ester transfer protein activity. Ginger extract exerted preferential effects on plasma lipids, reverse cholesterol transport, cholesterol synthesis and inflammatory status. Curcuminoids, however, showed superior antioxidant activity. 相似文献
62.
63.
Konstantin Dirian Susanne Backes Claudia Backes Volker Strauss Fabian Rodler Frank Hauke Andreas Hirsch Dirk M. Guldi 《Chemical science》2015,6(12):6886-6895
A water soluble naphthalenebisimide derivative (NBI) was synthesized and probed to individualize, suspend, and stabilize single wall carbon nanotubes (SWCNTs). Besides a comprehensive photophysical and electrochemical characterization of NBI, stable suspensions of SWCNTs were realized in buffered D2O. Overall, the dispersion efficiency of the NBI surfactant was determined by comparison with naphthalene based references. Successful individualization of SWCNTs was corroborated in several microscopic assays. In addition, emission spectroscopy points to the strong quenching of SWCNT centered band gap emission, when NBIs are immobilized onto SWCNTs. The origin of the quenching was found to be strong electronic communication, which leads to charge separation between NBIs and photoexcited SWCNTs, and, which yields reduced NBIs as well oxidized SWCNTs. Notably, electrochemical considerations revealed that the energy content of these charge separated states is one of the highest reported for SWCNT based electron donor–acceptor hybrids so far. 相似文献
64.
65.
Wavelength selection framework for classifying food and pharmaceutical samples into multiple classes
M. Anzanello F. Fogliatto M. C. A. Marcelo D. Pozebon M. F. Ferro 《Journal of Chemometrics》2016,30(6):346-353
Near infrared (NIR) spectroscopy is an efficient, low‐cost analytical technique widely applied to identify the origin of food and pharmaceutical products. NIR spectra‐based classification strategies typically use thousands of equally spaced wavelengths as input information, some of which may not carry relevant information for product classification. When that is the case, the performance of predictive and exploratory multivariate techniques may be undermined by such noisy information. In this paper, we propose an iterative framework for selecting subsets of NIR wavelengths aimed at classifying samples into categories. For that matter, we integrate Principal Components Analysis (PCA) and three classification techniques: k‐Nearest Neighbor (KNN), Probabilistic Neural Network (PNN) and Linear Discriminant Analysis (LDA). PCA is first applied to NIR data, and a wavelength importance index is derived based on the PCA loadings. Samples are then categorized using the wavelength with the highest index and the classification accuracy is calculated; next, the wavelength with the second highest index is inserted into the dataset and a new classification is performed. This forward‐based iterative procedure is carried out until all original wavelengths are inserted into the dataset used for classification. The subset of wavelengths leading to the maximum accuracy is chosen as the recommended subset. Our propositions performed remarkably well when applied to four datasets related to food and pharmaceutical products. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
66.
Russian Journal of Applied Chemistry - An increase in the production and consumption of polyurethane products used in heavy and light industry, in the construction industry, automotive, medicine,... 相似文献
67.
Russian Journal of Organic Chemistry - A new series of 4-(1H-imidazol-4-yl)-2-(substituted phenyl)-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidines have been synthesized via a one-pot reaction... 相似文献
68.
Russian Journal of Organic Chemistry - A series of novel fused thiadiazine derivatives have been simply synthesized through the reaction of hydrazinecarbodithioic acid with various cyclic... 相似文献
69.
Brandaleze Elena Ávalos M. Benavidez Edgardo 《Journal of Thermal Analysis and Calorimetry》2022,147(1):219-228
Journal of Thermal Analysis and Calorimetry - Recent advances in the technology of black refractories for steel continuous casting promote the development of materials that operate at extreme... 相似文献