全文获取类型
收费全文 | 633篇 |
免费 | 32篇 |
专业分类
化学 | 550篇 |
晶体学 | 10篇 |
力学 | 10篇 |
数学 | 36篇 |
物理学 | 59篇 |
出版年
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 16篇 |
2020年 | 18篇 |
2019年 | 32篇 |
2018年 | 30篇 |
2017年 | 22篇 |
2016年 | 34篇 |
2015年 | 28篇 |
2014年 | 47篇 |
2013年 | 56篇 |
2012年 | 52篇 |
2011年 | 55篇 |
2010年 | 25篇 |
2009年 | 23篇 |
2008年 | 26篇 |
2007年 | 29篇 |
2006年 | 19篇 |
2005年 | 18篇 |
2004年 | 15篇 |
2003年 | 13篇 |
2002年 | 14篇 |
2001年 | 3篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1987年 | 2篇 |
1985年 | 6篇 |
1983年 | 2篇 |
1980年 | 2篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1962年 | 2篇 |
1961年 | 5篇 |
1960年 | 1篇 |
1944年 | 1篇 |
1938年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有665条查询结果,搜索用时 62 毫秒
121.
Venkatapuram Padmavathi Annaji Venkata Nagendra Mohan Konda Mahesh 《Journal of heterocyclic chemistry》2008,45(4):1131-1138
Novel bisheterocycles, 1,2,3‐selenadiazoles, thiadiazoles and 2H‐diazaphospholes in combination with oxadiazoles, thiadiazoles and triazoles were prepared from phenacylsulfonylacetic acid methyl ester. 相似文献
122.
Venkatapuram Padmavathi Kaveti Sudheer Dandu Rangayapalle Chinna Venkata Subbaiah Konda Mahesh 《Journal of heterocyclic chemistry》2008,45(2):513-519
A new class of spiro heterocycles viz., spiropyrazolidinediones, isoxazolidinediones, pyrimidinetriones or thioxopyrimidinediones are developed from methyl 3‐aryl‐2‐(Z‐arylethenenylsulfonyl)acrylate by double Michael addition reaction with dimethyl malonate followed by cyclocondensation with appropriate nucleophiles. 相似文献
123.
Mudiganti NV Claessens S Habonimana P De Kimpe N 《The Journal of organic chemistry》2008,73(10):3867-3874
An efficient synthesis of naturally occurring compounds isolated from Pentas longiflora, cis-3,4-dihydroxy-3,4-dihydromollugin 2, and trans-3,4-dihydroxy-3,4-dihydromollugin 3 is described. The O-protected mollugins were dihydroxylated using OsO4 to achieve the corresponding cis-dihydroxy derivatives in excellent yield. The synthesis of trans-3,4-dihydroxy-3,4-dihydromollugin was achieved using Oxone in good yield. A mechanism for the formation of cis-3,4-dihydroxymollugin acetonide from the reaction of mollugin with Oxone is proposed. 相似文献
124.
Electrospinning is a well-known technique since 1544 to fabricate nanofibers using different materials like polymers, metals oxides, proteins, and many more. In recent years, electrospinning has become the most popular technique for manufacturing nanofibers due to its ease of use and economic viability. Nanofibers have remarkable properties like high surface-to-volume ratio, variable pore size distribution (10–100 nm), high porosity, low density, and are suitable for surface functionalization. Therefore, electrospun nanofibers have been utilized for numerous applications in the pharmaceutical and biomedical field like tissue engineering, scaffolds, grafts, drug delivery, and so on. In this review article, we will be focusing on the versatility, current scenario, and future endeavors of electrospun nanofibers for various biomedical applications. This review discusses the properties of nanofibers, the background of the electrospinning technique, and its emergence in chronological order. It also covers the various types of electrospinning methods and their mechanism, further elaborating the factors affecting the properties of nanofibers, and applications in tissue engineering, drug delivery, nanofibers as biosensor, skin cancer treatment, and magnetic nanofibers. 相似文献
125.
Vydyula Pavan Kumar Iragavarapu Suryanarayana Yadavalli Venkata Durga Nageswar Kakulapati Rama Rao 《Helvetica chimica acta》2008,91(4):753-758
Two modified β‐cyclodextrins, H‐2 and H‐3 , having a flexible appended moiety were studied for the chiral discrimination of the enantiomers of various amino acids by means of fluorescence as signaling option. These hosts quenched the fluorescence intensities of amino acids upon binding. The d‐ enantiomers were better recognized by these hosts. The association constants (Ks) and enantioselectivity factors (α) of the host?guest complexes were calculated. 相似文献
126.
Venkata Swamy Tangeti Ramesh Varma K. G. V. Siva Prasad K. V. V. V. Satyanarayana 《合成通讯》2016,46(7):613-619
An efficient method was developed for the synthesis of dihydrofuran substituted coumarin from a one-pot, four-component reaction of 2-hydroxy aromatic aldehydes, 6-methyl, 4-hydroxy pyranone, aromatic aldehyde, and pyridinium ylide in the presence of tri-ethylamine under microwave irradiation. The reaction proceeds under solvent-free conditions to afford C3-dihydrofuran substituted coumarin in a diastereoselective manner in good yields (71–89%). 相似文献
127.
An efficient method was developed for the diastereoselective synthesis of novel fused dihydro-1H-furo[2,3-c]pyrazole by a one-pot, four-component reaction of β-keto ester, hydrazine, aromatic aldehyde, and pyridinium ylide in the presence of triethylamine under microwave irradiation in solvent-free conditions in good yields. The merits of this cascade Knoevenagel condensation/Michael addition/cyclization sequence include its high atom economy, good yields, and efficiency of producing three new bonds (two C–C and one C–O) and two stereocenters in a single operation. 相似文献
128.
Srishti Shukla Dommati Anand Kumar Sanga Venkata Anusha 《Natural product research》2016,30(5):583-589
Effect of aqueous methanol extract of different colour sweet bell peppers (Capsicum annuum L.) on parameters of diabesity and carbonyl stress was analysed in vitro. Yellow pepper displayed significantly (p < 0.001) higher intestinal α-glucosidase inhibitory activity than green and red pepper. Porcine pancreatic lipase inhibitory activity was significantly (p < 0.01) high in yellow and red pepper than in green pepper. Green and red pepper inhibited vesperlysine-type advanced glycation end products (AGEs) more potently than yellow pepper; however, pentosidine-type AGEs were similarly inhibited by all three peppers. Yellow and red pepper inhibited lipid peroxidation more potently (p < 0.01) than green pepper. Total polyphenol content and free radicals scavenging activities in yellow and red bell peppers were higher than in green pepper. Total flavonoid content was high in green pepper than that present in yellow and red peppers. Green pepper displayed presence of proanthocyanins; however, oligomeric anthocyanins were detected in yellow and red peppers. 相似文献
129.
Kondepati VR Oszinda T Heise HM Luig K Mueller R Schroeder O Keese M Backhaus J 《Analytical and bioanalytical chemistry》2007,387(5):1633-1641
We have investigated the application of near-infrared spectroscopy for detection of human primary pancreatic and colorectal
cancers. Spectra from cancerous and normal tissue were collected from a total of 37 surgically resected pancreatic and colorectal
patient tissue specimens using a fibre-optic probe. Major spectral differences were observed in the CH-stretching first (6,000–5,400 cm−1) and second overtone (9,000–7,900 cm−1) regions. By use of artificial neural networks, linear discriminant analysis, and cluster analysis as pattern-recognition
methods the spectra were classified into cancerous and normal tissue groups with accuracy up to 89%. We also explored differences
between the spectra obtained from colorectal and pancreatic tissue. Spectral data from cancerous and normal tissue were classified
organ-specifically into four groups with accuracy between 80 and 83%. Our results indicate that CH-overtone regions, besides
serving as diagnostic markers for NIR spectroscopic diagnosis of primary human pancreas and colorectal cancers, are also useful
for elucidating differences between the spectra obtained from colorectal and pancreatic cancerous tissue. 相似文献
130.
Padmavathi V Venkata Subbaiah DR Mahesh K Radha Lakshmi T 《Chemical & pharmaceutical bulletin》2007,55(12):1704-1709
Novel amino-pyrazolone, amino-isoxazolone and amino-pyrimidinone derivatives were prepared from ethyl 4-phenylsulfonyl-2-(2'-phenylsulfonylethyl)-2-cyanobutyrate (1), ethyl 4-arylsulfonyl-3-aryl-2-cyanobutyrate (7) and ethyl 4-arylmethylsulfonyl-3-aryl-2-cyanobutyrate (8). The lead molecules have been tested for their antimicrobial activity and antioxidant property. 相似文献