全文获取类型
收费全文 | 368篇 |
免费 | 18篇 |
国内免费 | 4篇 |
专业分类
化学 | 249篇 |
晶体学 | 4篇 |
力学 | 18篇 |
数学 | 31篇 |
物理学 | 88篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 14篇 |
2013年 | 29篇 |
2012年 | 27篇 |
2011年 | 29篇 |
2010年 | 20篇 |
2009年 | 12篇 |
2008年 | 29篇 |
2007年 | 23篇 |
2006年 | 25篇 |
2005年 | 23篇 |
2004年 | 16篇 |
2003年 | 18篇 |
2002年 | 14篇 |
2001年 | 13篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1981年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有390条查询结果,搜索用时 31 毫秒
91.
Thin-layer chromatography (TLC) was used to screen for acetylcholinesterase inhibitors from Amaryllidaceae extracts. The TLC plate was developed and then stained using Ellman's reagent, 5,5'-dithiobis-(2-nitrobenzoic acid), to detect acetylcholinesterase activity. The advantages of this TLC assay method were that we could dereplicate the known inhibitor galanthamine, widely occurring in Amaryllidaceae, at an early stage of the isolation procedure. Moreover, there is no disturbance from sample dissolving solvents as in the microplate assay, and it is a very simple method. The detection limits were 10-200 ng for several known acetylcholinesterase inhibitors tested, and it is thus more sensitive than UV or Dragendorff's reagent detection. Also the minimal detectable amount for an acetylcholinesterase inhibitor tested was much less than that needed for the microplate assay. We screened 15 Amaryllidaceae extracts using this TLC method, and chose candidates for acetylcholinesterase inhibitor isolation. 相似文献
92.
[reaction: see text] The first use of cationic silver (AgSbF4) as a catalyst for intra- and intermolecular alkyne-carbonyl coupling to form conjugated enones is described, and a comparison to corresponding Br?nsted acid (HBF4) and Lewis acid (BF3) catalyst systems is made. Notably, intermolecular coupling proceeds stereoselectively to afford the corresponding trisubstituted enones as single geometrical isomers. This transformation represents a completely atom economical alternative to the use of stabilized Wittig reagents in carbonyl olefination and may be viewed as a formal alkyne-carbonyl metathesis. 相似文献
93.
Kim WS Kim J Park JK Mukamel S Rhee SK Choi YK Lee JY 《The journal of physical chemistry. B》2005,109(7):2686-2692
We investigate the structures, NMR chemical shifts, absorption spectra, frontier molecular orbitals, and transition density matrices of pi-stacked polyfluorenes by ab initio calculations. For F1-F4, we consider two different conformations, syn and anti. The simulated 1H NMR chemical shifts are in good agreement with the previous experiment, and the significantly upfielded chemical shifts explain that the fluorene moieties are stacked on each other. It is found that the relative stability for syn and anti conformers is almost equivalent in B3LYP calculations; however, the syn conformer becomes much more stable than the anti conformer in MP2 calculations, which is consistent with the experimental finding that only the syn conformers are relevant. The vertical detachment energy, which is linearly proportional to the ionization potential, shows the same size dependence as the previous experiment. The electron attachment energy decreases exponentially as the size increases, which implies that the electron transport would be possible even for long chains such as F3 and F4. This was evident from the frontier molecular orbitals (HOMO and LUMO). Also, it is found that the syn conformers are very favorable for electron transport through the pi-stacked fluorene moieties. 相似文献
94.
This paper describes a simple plasma-based dry etching method that enables patterned cell culture inside microfluidic devices by allowing patterning, fluidic bonding and sterilization steps to be carried out in a single step. This plasma-based dry etching method was used to pattern cell-adhesive and non-adhesive areas on the glass and polystyrene substrates. The patterned substrate was used for selective attachment and growth of human umbilical vein endothelial cells, MDA-MB-231 human breast cancer cells, NIH 3T3 mouse fibroblasts, and primary rat cortical neurons. Finally, we have successfully combined the dry-patterned substrate with a microfluidic device. Patterned primary rat neurons were maintained for up to 6 days inside the microfluidic devices and the neurons' somas and processes were confined to the cell-adhesive region. The method developed in this work offers a convenient way of micropatterning biomaterials for selective attachment of cells on the substrates, and enables culturing of patterned cells inside microfluidic devices for a number of biological research applications where cells need to be exposed to well-controlled fluidic microenvironment. 相似文献
95.
Ji HY Lee HW Chang SG Lee JJ Rhee JK Kim WB Lee HS 《Biomedical chromatography : BMC》2004,18(2):86-89
A liquid chromatography-tandem mass spectrometric (LC/MS/MS) method for the determination of a new ox-azolidinone antibiotic DA-7867, (S)-[N-3-(4-(2-(1-methyl-5-tetrazolyl)-pyridine-5-yl)-3- fl uorophenyl)-2-oxo-5-oxazolidinyl]methyl acetamide, in human plasma was developed. DA-7867 and internal standard, linezolid, were extracted from human plasma with ethyl acetate at acidic pH. A reverse-phase LC separation was performed on Luna C(8) column with the mixture of acetonitrile-ammonium formate (10 mm, pH 4.5; 35:65, v/v) as mobile phase. The analytes were determined using an electrospray ionization tandem mass spectrometry in the multiple-reaction-monitoring mode. The lower limits of quanti fi cation for DA-7867 was 2.5 ng/mL. The single liquid-liquid extraction quantitatively recovered DA-7867 and internal standard from plasma samples at the ranges of 82.2-86.7%. DA-7867 was stable in blank human plasma at room temperature for 24 h and following three freeze-thaw cycles. 相似文献
96.
Wansoo T. Rhee 《Random Structures and Algorithms》1999,15(2):165-175
In this problem, we are given N uniformly distributed random intervals of [0, 1]. For each random interval I, we are given a weight XI. These weights are independent, independent of the intervals, and satisfy P(XI≤t)=tα, where α>0. A packing of the family is a disjoint subfamily ℐ of intervals. Its cost is Cℐ=|Rℐ|+∑I∈ℐ XI|I|, where Rℐ is the part of [0, 1] that is not covered by ℐ. We are interested in the optimal (=minimal) cost WN among all packings of the random family. We prove that if α<1, then there exists a constant K, depending upon α only such that If α=1, we prove that for some constant K we have This differs from the limit at α=1 in the previous formula by a factor log N. The reasons for this unexpected “discontinuity” are somewhat deep. ©1999 John Wiley & Sons, Inc. Random Struct. Alg., 15: 165–175, 1999 相似文献
97.
Seong Keun Sonn Seungwoon Seo Jaemoon Yang Ki Sook Oh Hsiuchen Chen David C. Chan Kunsoo Rhee Kyung S. Lee Young Yang Goo Taeg Oh 《Experimental & molecular medicine》2021,53(11):1769
C1q/TNF-related protein 1 (CTRP1) is a CTRP family member that has collagenous and globular C1q-like domains. The secreted form of CTRP1 is known to be associated with cardiovascular and metabolic diseases, but its cellular roles have not yet been elucidated. Here, we showed that cytosolic CTRP1 localizes to the endoplasmic reticulum (ER) membrane and that knockout or depletion of CTRP1 leads to mitochondrial fission defects, as demonstrated by mitochondrial elongation. Mitochondrial fission events are known to occur through an interaction between mitochondria and the ER, but we do not know whether the ER and/or its associated proteins participate directly in the entire mitochondrial fission event. Interestingly, we herein showed that ablation of CTRP1 suppresses the recruitment of DRP1 to mitochondria and provided evidence suggesting that the ER–mitochondrion interaction is required for the proper regulation of mitochondrial morphology. We further report that CTRP1 inactivation-induced mitochondrial fission defects induce apoptotic resistance and neuronal degeneration, which are also associated with ablation of DRP1. These results demonstrate for the first time that cytosolic CTRP1 is an ER transmembrane protein that acts as a key regulator of mitochondrial fission, providing new insight into the etiology of metabolic and neurodegenerative disorders.Subject terms: Endoplasmic reticulum, Mitochondria 相似文献
98.
Y.P. Lee K.W. Kim J.Y. Rhee Y.V. Kudryavtsev V.V. Nemoshkalenko V.G. Prokhorov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):451-459
The influence of the structural disorder on the electron transport properties of Co0.50Ti0.50 alloy films in a temperature range of 4.2-300 K has been investigated at zero and 0.5 T of magnetic field. The disordered
state in the alloy films was obtained by vapor quenching deposition onto substrates cooled by liquid nitrogen. The changes
in the transport properties of the alloy films caused by the order-disorder structural transformation and the external magnetic
field are explained by the analyses using various models for the electron transport in the disordered systems.
Received 18 May 1999 and Received in final form 18 January 2000 相似文献
99.
An effective thermoelastic-numerical hybrid method is demonstrated for obtaining stress information on, and adjacent to, geometric
discontinuities in orthotropic composites. This includes determining stress intensity factors. The technique involves evaluating
the stress functions from measured thermoelastic data around the external boundary of a subregion containing the geometric
discontinuity of interest. Knowing the stress functions, stresses throughout the subregion surrounding the geometric discontinuity,
and stress intensity factors, are available. 相似文献
100.
本文采用加权直方图分析方法和蒙特卡洛重采样方法进行自由基校正研究. 生成的自由能表面几乎可以收敛到具有足够采样情况的精准表面,并且比常规的加权直方图分析校正方法能更稳定地处理采样不足的情况,为检测能级校正表面的不确定性提供指南,并且定义了明确的标准用以确定能改善其视觉效果的自由能表面平滑程度. 本文通过水中的丙氨酸二肽和KillerRed蛋白质子转移的自由能图证明该方法的优势,说明蒙特卡洛重采样法可以作为在产生自由能表面实际的系统中的实用工具. 相似文献