全文获取类型
收费全文 | 270篇 |
免费 | 15篇 |
国内免费 | 5篇 |
专业分类
化学 | 181篇 |
晶体学 | 3篇 |
力学 | 14篇 |
数学 | 38篇 |
物理学 | 54篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 5篇 |
2015年 | 7篇 |
2014年 | 15篇 |
2013年 | 27篇 |
2012年 | 31篇 |
2011年 | 19篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 19篇 |
2007年 | 22篇 |
2006年 | 15篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有290条查询结果,搜索用时 15 毫秒
1.
Danny E. Akin W. Herbert Morrison III Luanne L. Rigsby Franklin E. Barton II David S. Himmelsbach Kevin B. Hicks 《Applied biochemistry and biotechnology》2006,129(1-3):104-116
Information is presented on structure, composition, and response to enzymes of corn stover related to barriers for bioconversion
to ethanol. Aromatic compounds occurred in most tissue cell walls. Ferulic acid esterase treatment before cellulase treatment
significantly improved dry weight loss and release of phenolic acids and sugars in most fractions over cellulase alone. Leaf
fractions were considerably higher in dry weight loss and released sugars with esterase treatment, but stem pith cells gave
up the most phenolic acids. Results help identify plant fractions more appropriate for coproducts and bioconversion and those
more suitable as residues for soil erosion control. 相似文献
2.
S. Akin S. Isikli F. Korkusuz M. Ungan A. Senkoylu 《Journal of Radioanalytical and Nuclear Chemistry》2004,259(2):361-364
The aim of this study was to investigate the relationship between BMD and age at lumbar spine and proximal femur in Turkish
males. Two hundred ninety healthy males (aged 20-59 years) were investigated. BMD of the lumbar spine had its peak at ages
30-39, however, the peak for the proximal femur was between the ages of 20 and 29. There was a significant decrease in BMD
at proximal femur after these peak values with increasing age. In conclusion, there was a significant correlation between
age and the proximal femoral BMD in males and age has a strong predictive power on proximal femur BMD score.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
We show that a theorem of Shchepin and Repovš concerning the smoothness of compacta follows from the theory of semicontinuous relations. 相似文献
4.
Briggs TF Winemiller MD Collum DB Parsons RL Davulcu AH Harris GD Fortunak JM Confalone PN 《Journal of the American Chemical Society》2004,126(17):5427-5435
The 1,2-addition of lithium phenylacetylide (PhCCLi) to quinazolinones was investigated using a combination of structural and rate studies. (6)Li, (13)C, and (19)F NMR spectroscopies show that deprotonation of quinazolinones and phenylacetylene in THF/pentane solutions with lithium hexamethyldisilazide affords a mixture of lithium quinazolinide/PhCCLi mixed dimer and mixed tetramer along with PhCCLi dimer. Although the mixed tetramer dominates at high mixed aggregate concentrations and low temperatures used for the structural studies, the mixed dimer is the dominant form at the low total mixed aggregate concentrations, high THF concentrations, and ambient temperatures used to investigate the 1,2-addition. Monitoring the reaction rates using (19)F NMR spectroscopy revealed a first-order dependence on mixed dimer, a zeroth-order dependence on THF, and a half-order dependence on the PhCCLi concentration. The rate law is consistent with the addition of a disolvated PhCCLi monomer to the mixed dimer. Investigation of the 1,2-addition of PhCCLi to an O-protected quinazolinone implicates reaction via trisolvated PhCCLi monomers. 相似文献
5.
Summary Compounds of the type PdL2X2 (L=1-methylimidazole, 1-vinylimidazole, 1-n-butylimidazole, 1,2-dimethylimidazole, 1-vinyl-2-methylimidazole, 1,2-dimethyl-5-nitroimidazole, 2-isopropyl-4(5)-nitroimidazole and 2-methyl-4(5)-nitro-imidazole; X=Cl or Br) are obtained by treating PdX2 (1 mole) with solutions of the ligands L (2 moles). An excess of L gives PdL4X2 complexes (L=1-methylimidazole, 1-vinylimidazole, 1,2-dimethylimidazole and 1-vinyl-2-methylimidazole). The compounds were characterized by chemical analyses, molar conductivity measurements and i.r. spectra. 相似文献
6.
The elasticity of the polyacrylamide (PAAm)-kappa carrageenan (κC) composite was determined as a function of (w/v-%) κC content at 40 °C. The gel composites studied contained various percentages (w/v-%) of κC. The elasticity of the swollen PAAm-κC composite was characterized by using the tensile testing technique. This study investigated the elasticity and the percolation threshold of PAAm-κC composite as a function of κC content. It is understood that the compressive elastic modulus decreases up to 1 (w/v-%) of κC and then increases at contents above 1(w/v-%) of κC. The critical exponent of elasticity y was determined between 1 and 1.6 (w/v-%) of κC and found to be 0.68. The observed elastic percolation threshold is consistent with the suggested values of the superelastic percolation network. 相似文献
7.
Pranita Bora Dr. Basanta Saikia Dr. Bipul Sarma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(3):699-710
Nucleation events and crystal growth can be guided by molecular recognition at interfaces through intermolecular interactions. The short-acting antimicrobial sulfa drug sulfathiazole is known for its concomitant crystallization, which has five known polymorphs, due to conformational flexibility and hydrogen-bond synthon variation. In its development stage of a drug the issue of concomitant crystallization needs to be addressed with respect to patent litigation, including legal actions to protect patents against infringement. A functional self-assembled monolayer (SAM) of organic thiol on a gold surface has been employed as an efficient approach to control concomitant nucleation of such flexible drugs. The crystallization on a SAM surface is mostly kinetically driven and often leads to the nucleation of novel metastable forms. Spectroscopic, thermal analysis and X-ray diffraction studies reveal that a previously unknown, sixth form of the drug nucleates on the designed SAM surface. 相似文献
8.
Rectangular plates on distributed elastic foundations are widely employed in footings and raft foundations of variety of structures. In particular, mounted columns and single footings may partially occupy the rectangular plate of any kind. 相似文献
9.
10.
Gheorghe Ilia Adriana Popa Smaranda Iliescu Alina Bora Gheorghe Dehelean Aurelia Pascariu 《Phosphorus, sulfur, and silicon and the related elements》2013,188(7):1513-1519
Some mixed phosphites having two different alkyl chain were obtained as forerunners for mixed phosphates Mixed dialkyl phosphates were obtained in good yields (40-80%) by phase transfer catalysis in liquid-liquid sistem, starting from different dialkyl phosphites and aliphatic alcohols. The reaction conditions were optimized in order to obtain good yields in phosphites and phosphates respectively. Compounds were analyzed by IR, P 31 -NMR. 相似文献