全文获取类型
收费全文 | 735篇 |
免费 | 36篇 |
国内免费 | 1篇 |
专业分类
化学 | 600篇 |
晶体学 | 7篇 |
力学 | 13篇 |
数学 | 36篇 |
物理学 | 116篇 |
出版年
2023年 | 6篇 |
2022年 | 12篇 |
2021年 | 18篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 13篇 |
2017年 | 23篇 |
2016年 | 33篇 |
2015年 | 23篇 |
2014年 | 45篇 |
2013年 | 71篇 |
2012年 | 38篇 |
2011年 | 50篇 |
2010年 | 30篇 |
2009年 | 35篇 |
2008年 | 43篇 |
2007年 | 37篇 |
2006年 | 32篇 |
2005年 | 24篇 |
2004年 | 22篇 |
2003年 | 15篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1990年 | 7篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1961年 | 2篇 |
1947年 | 2篇 |
1942年 | 2篇 |
1939年 | 2篇 |
1938年 | 2篇 |
排序方式: 共有772条查询结果,搜索用时 15 毫秒
81.
The development of new strategies for synthesis of six-membered O-heterocycles has remained a highly attractive but challenging proposition. An overview of the application of microwave irradiation in oxygen-containing six-membered heterocyclic compounds synthesis is presented, focusing on the developments in the past 5–10 years. This contribution covers the literature concerning the total synthesis of six membered O-heterocycles. 相似文献
82.
Solid-phase organic synthesis is a rapidly expanding area of synthetic chemistry that is being widely exploited in the search for new medicinally important compounds using combinatorial techniques. In recent decades, a large number of reports related to solid-phase synthesis of heterocycles have appeared because of the wide variety of their biological activity. In this review, we report the important role of solid-phase synthesis in the synthesis of nitrogen containing six-membered ring heterocycles. 相似文献
83.
Rao K Chodisetti B Gandi S Mangamoori LN Giri A 《Applied biochemistry and biotechnology》2011,165(5-6):1366-1378
Alpinia galanga is a rhizomatous herb rich in essential oils and various other significant phytoconstituents. Rapid direct regeneration was obtained from the rhizome explants (15.66 ± 0.57 shoots) on MS media supplemented with zeatin at a concentration of 2 mg/l. The callus cultures of A. galanga were initiated from the rhizome explants on MS media supplemented with 2 mg/l each of BAP, 2,4-D, and NAA. The callus was analyzed for the presence of a vital phytoconstituent--acetoxychavicol acetate (ACA) associated with various biological properties. ACA was detected in the young friable callus as well as the stationary phase callus. Moreover, the induction of morphogenetic response in callus resulted in higher accumulation of ACA. The phytohormone withdrawal from the propagation media and the subsequent transfer of callus to BAP (2 mg/l) containing MS media has resulted in multiple shoot induction. The regenerated (indirect) plants have shown 1.6-fold higher ACA content (1.253%) when compared to the control plant (0.783%). Micropropagation of such conventionally propagated plants is very essential to meet the commercial demand as well as to ensure easy storage and transportation of disease free stocks. 相似文献
84.
85.
Lactic acid produced by fermentation process mostly contains a number of aliphatic carboxylic acids as impurities. In this work, carboxylic acid impurities in lactic acid samples from a number of sources were determined at ppm levels. A simple HPLC method was developed that utilized a new generation polar embedded reverse phase, 20mM phosphate buffer at pH 2.20 (±0.05) and UV detection at 210 nm. The method enabled quantitative analysis of the above acids in lactic acid matrix. The experimental conditions for column temperature, mobile phase pH and flow rate were optimized. A detailed validation of the method was performed for linearity, precision, accuracy, selectivity, limit of detection (LOD), limit of quantitation (LOQ), ruggedness and repeatability and reproducibility (R&R). 相似文献
86.
Kumar KS Kumar PM Kumar KA Sreenivasulu M Jafar AA Rambabu D Krishna GR Reddy CM Kapavarapu R Shivakumar K Priya KK Parsa KV Pal M 《Chemical communications (Cambridge, England)》2011,47(17):5010-5012
Concurrent construction of five and six membered fused N-heretocyclic ring was achieved via a conceptually new three-component reaction affording 6,6a-dihydroisoindolo[2,1-a]quinazoline-5,11-diones as novel inhibitors of TNF-αin vitro. This represents one of the few examples of direct TNF-α inhibition by small molecules. 相似文献
87.
The natural abundance carbon-13 nuclear magnetic resonance spectra of some methaqualone metabolites were recorded using the pulse fourier transform technique. The chemical shift of various carbon resonances have been assigned on the basis of the chemical shift theory, multiplicities observed in SFORD spectrum and comparison with the chemical shifts of the corresponding carbons of methaqualone. 相似文献
88.
89.
J.C. Califano A. Uribe J.L. Chang C.L. Becker J.J. Napier V. Kishore D. Zhou G. Love K. Gernhardt J.C. Tolle 《Tetrahedron》2005,61(37):8821-8829
Oligomers of arginine, such as octa-d-arginine amide, are excellent transporters for active drugs through cell membranes and tissue. The synthesis of octa-d-arginine amide, as the nonahydrochloride salt, was approached via a solution phase synthetic route involving the preparation of an octa-d-ornithine intermediate, which was then converted into the desired octa-d-arginine compound through a guanidinylation step. The multi-step synthesis was carried out at pilot scale, resulting in the preparation of 700 g of the target molecule. No chromatographic purification was needed at any step of the process. 相似文献
90.
Glasses with composition xGeO2.(0.30−x)M2O.0.70B2O3 (M=Li, K) containing 2.0 mol% of V2O5 have been prepared in the range 0.00≤x≤0.15 by normal melt quenching method. Electron paramagnetic resonance (EPR), optical transmission and absorption spectra and dc conductivity of these glasses have been studied. Spin Hamiltonian parameters (SHPs) of VO2+ ions, dipolar hyperfine coupling parameter, P, Fermi contact interaction parameter, K and molecular orbital coefficients (α2 and γ2) have been calculated. In GeO2·Li2O·B2O3 glasses there is no change in the tetragonality of the V4+O6 complex and the size of 3dxy orbit also remains unchanged with increase in GeO2 content. In GeO2·K2O·B2O3 glasses, there is an increase in the tetragonality of the V4+O6 complex and the 3dxy orbit expands with increase in GeO2 content. Values of the theoretical optical basicity, Λth, have also been reported. Optical band gap decreases with increase in GeO2 content. The dc conductivity of these glasses decreases and the activation energy increases with increase in GeO2:M2O ratio. 相似文献