首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   716篇
  免费   83篇
  799篇
  2022年   7篇
  2021年   7篇
  2020年   12篇
  2019年   17篇
  2018年   25篇
  2017年   23篇
  2016年   23篇
  2015年   27篇
  2014年   35篇
  2013年   43篇
  2012年   64篇
  2011年   62篇
  2010年   33篇
  2009年   39篇
  2008年   40篇
  2007年   33篇
  2006年   32篇
  2005年   17篇
  2004年   30篇
  2003年   27篇
  2002年   18篇
  2001年   20篇
  2000年   24篇
  1999年   19篇
  1998年   4篇
  1997年   7篇
  1996年   8篇
  1995年   4篇
  1994年   4篇
  1993年   3篇
  1992年   14篇
  1991年   6篇
  1990年   10篇
  1989年   10篇
  1988年   6篇
  1987年   4篇
  1986年   11篇
  1985年   1篇
  1984年   5篇
  1983年   4篇
  1982年   3篇
  1979年   3篇
  1976年   1篇
  1974年   2篇
  1973年   1篇
  1972年   3篇
  1971年   2篇
  1970年   2篇
  1969年   2篇
  1964年   1篇
排序方式: 共有799条查询结果,搜索用时 15 毫秒
111.
112.
A method for the simultaneous determination of HEPP ( -3-hydroxy-3-ethyl-3-phenylpropionamide), a member of a new homologous series of phenylamide-derivative anticonvulsants, with six other antiepileptic drugs (ethosuximide, primidone, phenobarbital, phenytoin, carbamazepine and clonazepam) in plasma by high-performance liquid chromatography is described. These drugs are extracted from plasma by adding an equal volume of acetonitrile. An aliquot of the extract is then injected on a reversed-phase column with a acetonitrile-methanol-phosphate buffer mobile phase. The total time required for the whole analytical process, including the plasma pretreatment and chromatography, is approximately 30 min. The assay method is simple, rapid and reproducible, and therefore considered suitable for routine use in clinical investigations monitoring HEPP simultaneously with common antiepileptic drugs.  相似文献   
113.
114.
Endozoicomonas bacteria were found highly associated with the coral Stylophora pistillata, and these bacteria are also ubiquitously associated with diverse corals worldwide. Novel Endozoicomonas-specific probes revealed that Endozoicomonas bacteria were abundant in the endodermal tissues of S. pistillata and appear to have an intimate relationship with the coral.  相似文献   
115.
An extracellular peroxygenase of Agrocybe aegerita catalyzed the H2O2-dependent hydroxylation of the multi-function beta-adrenergic blocker propranolol (1-naphthalen-1-yloxy-3-(propan-2-ylamino)propan-2-ol) and the non-steroidal anti-inflammatory drug diclofenac (2-[2-[(2,6-dichlorophenyl)amino]phenyl]acetic acid) to give the human drug metabolites 5-hydroxypropranolol (5-OHP) and 4′-hydroxydiclofenac (4′-OHD). The reactions proceeded regioselectively with high isomeric purity and gave the desired 5-OHP and 4′-OHD in yields up to 20% and 65%, respectively. 18O-labeling experiments showed that the phenolic hydroxyl groups in 5-OHP and 4′-OHD originated from H2O2, which establishes that the reaction is mechanistically a peroxygenation. Our results raise the possibility that fungal peroxygenases may be useful for versatile, cost-effective, and scalable syntheses of drug metabolites.  相似文献   
116.

Aim

In this study, we intend to compare two different setup procedures for female breast cancer patients.

Background

Imaging in radiotherapy provides a precise localization of the tumour, increasing the accuracy of the treatment delivery in breast cancer.

Materials and methods

Twenty breast cancer patients who underwent whole breast radiotherapy (WBRT) were selected for this study. Patients were divided into two groups of ten. Group one (G1) was positioned by tattoos and then the patient positioning was adjusted with the aid of AlignRT (Vision RT, London, UK). In group two (G2), patients were positioned only by tattoos. For both groups, the first 15 fractions were analyzed, a daily kilovoltage (kV) cone beam computed tomography (CBCT) image was made and then the rotational and translational displacements and, posteriorly, the systematic (Σ) and random (σ) errors were analyzed.

Results

The comparison of CBCT displacements for the two groups showed a statistically significant difference in the translational left–right (LR) direction (ρ = 0.03), considering that the procedure with AlignRT system has smaller lateral displacements. The results of systematic (Σ) and random (σ) errors showed that for translational displacements the group positioned only by tattoos (G2) demonstrated higher values of errors when compared with the group positioned with the aid of AlignRT (G1).

Conclusions

AlignRT could help the positioning of breast cancer patients; however, it should be used with another imaging method.  相似文献   
117.
118.
We extend a recently proposed mixed quantum/classical method for computing the vibronic electronic circular dichroism (ECD) spectrum of molecules with different conformers, to cases where more than one hindered rotation is present. The method generalizes the standard procedure, based on the simple Boltzmann average of the vibronic spectra of the stable conformers, and includes the contribution of structures that sample all the accessible conformational space. It is applied to the simulation of the ECD spectrum of (S)‐2,2,2‐trifluoroanthrylethanol, a molecule with easily interconvertible conformers, whose spectrum exhibits a pattern of alternating positive and negative vibronic peaks. Results are in very good agreement with experiment and show that spectra averaged over all the sampled conformational space can deviate significantly from the simple average of the contributions of the stable conformers. The present mixed quantum/classical method is able to capture the effect of the nonlinear dependence of the rotatory strength on the molecular structure and of the anharmonic couplings among the modes responsible for molecular flexibility. Despite its computational cost, the procedure is still affordable and promises to be useful in all cases where the ECD shape arises from a subtle balance between vibronic effects and conformational variety.  相似文献   
119.
120.
Intact cockroaches, headless insects and isolated segments of the animal were trained to avoid electric shocks, contingent upon an electric signal which was applied a fraction of a second prior to the shocks. The results showed that all the intact insects learned to avoid the shocks in approximately ten sessions, on a schedule of two daily sessions and ten trials per session. The retention of the learned responses was further tested; it showed that there was no decrement of avoidance reactions till the end of insect life in the experimental conditions. Furthermore, this retention of the learned behaviour was not affected by the severance of the head nor even by the isolation of a single ganglion, once the behaviour had been established.The learning ability of the headless animals, and of the isolated segments, was different. There is evidence that both types of preparations demonstrated some degree of learning, but a majority of them failed to reach the criterion of 100 per cent avoidances in a training schedule, exactly the same as for the intact cockroach. Nevertheless, if the headless insects were given a mass training of fourteen sessions per day, all of them reached the criterion. The retention of the isolated segment was found to be less than 1 day long, and that of the headless insects lasted at most 2 or 3 days after the last training session.It is interpreted that long-term memory can be established in the intact animals and, once it has been accomplished, the acquired behaviour can be retained by the lower portions of the central nervous system.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号