全文获取类型
收费全文 | 1285篇 |
免费 | 57篇 |
专业分类
化学 | 841篇 |
晶体学 | 25篇 |
力学 | 46篇 |
数学 | 91篇 |
物理学 | 339篇 |
出版年
2023年 | 28篇 |
2022年 | 31篇 |
2021年 | 33篇 |
2020年 | 28篇 |
2019年 | 35篇 |
2018年 | 33篇 |
2017年 | 37篇 |
2016年 | 69篇 |
2015年 | 48篇 |
2014年 | 45篇 |
2013年 | 100篇 |
2012年 | 97篇 |
2011年 | 118篇 |
2010年 | 60篇 |
2009年 | 54篇 |
2008年 | 58篇 |
2007年 | 67篇 |
2006年 | 52篇 |
2005年 | 39篇 |
2004年 | 30篇 |
2003年 | 23篇 |
2002年 | 21篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 14篇 |
1982年 | 5篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1971年 | 7篇 |
1970年 | 6篇 |
排序方式: 共有1342条查询结果,搜索用时 15 毫秒
991.
Saha Badal C. Dien Bruce S. Bothast Rodney J. 《Applied biochemistry and biotechnology》1998,(1):115-125
Corn fiber, which consists of about 20% starch, 14% cellulose, and 35% hemicellulose, has the potential to serve as a low
cost feedstock for production of fuel ethanol. Currently, the use of corn fiber to produce fuel ethanol faces significant
technical and economic challenges. Its success depends largely on the development of environmentally friendly pretreatment
procedures, highly effective enzyme systems for conversion of pretreated corn fiber to fermentable sugars, and efficient microorganisms
to convert multiple sugars to ethanol. Several promising pretreatment and enzymatic processes for conversion of corn fiber
cellulose, hemicellulose, and remaining starch to fermentable sugars were evaluated. These hydrolyzates were then examined
for ethanol production in bioreactors, using genetically modified bacteria and yeast. Several novel enzymes were also developed
for use in pretreated corn fiber saccharification.
Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard
of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also
be suitable. 相似文献
992.
993.
994.
Permanganate, the versatile oxidizing agent, has limited solubility in non-polar media, which limits its use for oxidation of organic substrate in the non-aqueous media. But the combination of PTCs with permanganate makes it mild, selective and lipopathic. These lipopathic oxidants are useful for many important organic transformations. In this communication, we have presented the synthesis and utility of some selected lipopathic permanganate oxidants, which oxidize many functional groups, including alcohol, aldehyde, ether, alkane, alkene, alkyne, and oxime and have use in many synthetic organic procedures with chemo-, regio- and stereoselectivity. 相似文献
995.
Ajoy Saha Narendra A. Gajbhiye Biraj B. Basak Ponnuchamy Manivel 《International journal of environmental analytical chemistry》2018,98(7):622-643
Since the discovery of aflatoxins (AFs) in the 1960s, much research has focused on detecting the toxins in contaminated food and feedstuffs. But the quality determination in medicinal plant matrices with respect to AFs is scare. Hence, a simple, accurate and sensitive high-performance liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS) method was developed for simultaneous determination of AFs AFB1, AFB2, AFG1 and AFG2 in two Indian popular medicinal herbs i.e. senna (Cassia angustifolia) and kalmegh (Andrographis paniculata). AFs have been extracted from herb matrix using a QuEChERS (quick, easy, cheap, effective, rugged and safe)-based extraction procedure followed by applying primary secondary amine and C18 for further clean-up step and then were quantified under the multiple reaction monitoring together with positive ionisation modes. Matrix-matched calibration was used for quantification in order to reduce the matrix effect. Validation of the method was carried out in herbs by recovery experiments. Recoveries of the spiked samples were in the range of 61.9–111.5% with an inter-day and intraday relative standard deviation lower than 20.0%. Limits of detection and quantification ranged from 0.41 to 0.95 ng mL?1 and 1.2 to 3.8 μg kg?1, respectively. The expanded uncertainty of the method was <21% for all the toxins in both the herbs. Finally, the proposed method was successfully applied to determine AF residues in real field samples of senna and kalmegh obtained from different locations in India. 相似文献
996.
Subhan Md. Abdus Saha Pallab Chandra Sarker Prosenjit Al-Mamun Mohammad 《Research on Chemical Intermediates》2018,44(10):6311-6326
Research on Chemical Intermediates - A trimetallic, MoO3·CuO·ZnO nanocomposite was synthesized by co-precipitation method. The nanocomposite was characterized by X-ray... 相似文献
997.
Structural Chemistry - Matrix metalloproteinase-2 (MMP-2) is established as one of the most important metalloenzymes for targeting cancer. However, homologous MMP-9 of the gelatinase family is... 相似文献
998.
Flavones are present in a variety of medicines and natural products and are important structural motif due to their unique mode of physiological action. Hence the structural importance of flavone moiety has elicited a great deal of interest in the field of organic synthesis and chemical biology to develop some new and improved synthesis of this molecular skeleton. Herein, we have described an up to date overview on the recent advances in the diverse synthetic methodologies of flavones. The review covers the basic conceptual and practical catalytic synthesis like carbonylative annulation, cyclodehydration, Suzuki Miyaura coupling, Heck coupling, green methodologies, metal catalyzed reactions, organocatalytic transformations, microwave irradiation, etc. which are significant for constructing flavone skeleton. This review will satisfy the expectations of readers who are interested in the development of the field and looking for an update. It will stimulate researchers to develop new and creative synthetic access to this heterocyclic system, which will be instrumental in the advancement of flavone chemistry. 相似文献
999.
1000.
A convenient route for the synthesis of benzohydropentalene and benzohydroazulenes and is described for entry into a number of tri- and tetracyclic terpenoids. 相似文献