全文获取类型
收费全文 | 11991篇 |
免费 | 1022篇 |
国内免费 | 1310篇 |
专业分类
耳鼻咽喉 | 16篇 |
儿科学 | 38篇 |
妇产科学 | 29篇 |
基础医学 | 1034篇 |
口腔科学 | 205篇 |
临床医学 | 541篇 |
内科学 | 1266篇 |
皮肤病学 | 318篇 |
神经病学 | 274篇 |
特种医学 | 634篇 |
外科学 | 393篇 |
综合类 | 1687篇 |
现状与发展 | 2篇 |
一般理论 | 1篇 |
预防医学 | 673篇 |
眼科学 | 113篇 |
药学 | 3850篇 |
3篇 | |
中国医学 | 2947篇 |
肿瘤学 | 299篇 |
出版年
2024年 | 59篇 |
2023年 | 189篇 |
2022年 | 351篇 |
2021年 | 504篇 |
2020年 | 354篇 |
2019年 | 301篇 |
2018年 | 296篇 |
2017年 | 384篇 |
2016年 | 407篇 |
2015年 | 471篇 |
2014年 | 693篇 |
2013年 | 940篇 |
2012年 | 738篇 |
2011年 | 878篇 |
2010年 | 658篇 |
2009年 | 603篇 |
2008年 | 635篇 |
2007年 | 548篇 |
2006年 | 583篇 |
2005年 | 482篇 |
2004年 | 394篇 |
2003年 | 369篇 |
2002年 | 330篇 |
2001年 | 294篇 |
2000年 | 201篇 |
1999年 | 189篇 |
1998年 | 206篇 |
1997年 | 184篇 |
1996年 | 182篇 |
1995年 | 163篇 |
1994年 | 170篇 |
1993年 | 150篇 |
1992年 | 166篇 |
1991年 | 134篇 |
1990年 | 105篇 |
1989年 | 118篇 |
1988年 | 100篇 |
1987年 | 106篇 |
1986年 | 73篇 |
1985年 | 99篇 |
1984年 | 76篇 |
1983年 | 55篇 |
1982年 | 69篇 |
1981年 | 56篇 |
1980年 | 55篇 |
1979年 | 44篇 |
1978年 | 34篇 |
1977年 | 34篇 |
1976年 | 26篇 |
1974年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
Jeffrey Buenaflor Parker Sommerville Hang Qian Christine Luscombe 《Macromolecular chemistry and physics.》2020,221(2)
A comparative study involving bimetallic nickel catalysts designed from disubstituted N,N,N′,N′‐tetra(diphenylphosphanylmethyl)benzene diamine bridging ligands is reported. Catalyst behavior is explored in the Kumada catalyst‐transfer polymerization (KCTP) using poly(3‐hexylthiophene) (P3HT) as the model system. The success of a controlled polymerization is monitored by analyzing monomer conversion, degree of polymerization, end‐group identity, and molecular weight distribution. The characterization of P3HT obtained from KCTP initiated with the bimetallic catalysts shows chain‐growth behavior; however, the presence of Br/Br end‐groups and broader molecular weight distribution reveals a reduced controlled polymerization compared to the commonly employed Ni(dppp)Cl2. The observed increase in intermolecular chain transfer and termination processes in KCTP initiation with the bimetallic catalysts can be attributed to a weaker Ni(0)‐π‐aryl complex interaction, which is caused by increased steric crowding of the coordination sphere. 相似文献
3.
4.
5.
Quantitative chemical exchange saturation transfer (qCEST) MRI – omega plot analysis of RF‐spillover‐corrected inverse CEST ratio asymmetry for simultaneous determination of labile proton ratio and exchange rate
下载免费PDF全文
![点击此处可从《NMR in biomedicine》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Renhua Wu Gang Xiao Iris Yuwen Zhou Chongzhao Ran Phillip Zhe Sun 《NMR in biomedicine》2015,28(3):376-383
Chemical exchange saturation transfer (CEST) MRI is sensitive to labile proton concentration and exchange rate, thus allowing measurement of dilute CEST agent and microenvironmental properties. However, CEST measurement depends not only on the CEST agent properties but also on the experimental conditions. Quantitative CEST (qCEST) analysis has been proposed to address the limitation of the commonly used simplistic CEST‐weighted calculation. Recent research has shown that the concomitant direct RF saturation (spillover) effect can be corrected using an inverse CEST ratio calculation. We postulated that a simplified qCEST analysis is feasible with omega plot analysis of the inverse CEST asymmetry calculation. Specifically, simulations showed that the numerically derived labile proton ratio and exchange rate were in good agreement with input values. In addition, the qCEST analysis was confirmed experimentally in a phantom with concurrent variation in CEST agent concentration and pH. Also, we demonstrated that the derived labile proton ratio increased linearly with creatine concentration (P < 0.01) while the pH‐dependent exchange rate followed a dominantly base‐catalyzed exchange relationship (P < 0.01). In summary, our study verified that a simplified qCEST analysis can simultaneously determine labile proton ratio and exchange rate in a relatively complex in vitro CEST system. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
化学药合成过程中水分残留不利于反应的进行,还影响药物及制剂的稳定性、理化性质、溶出及药理作用等,因此水分几乎是大多数药物合成中的必测项目,通过有效除水严格控制反应体系中水分的含量至关重要。本文综述了水分的存在形式,常见除水剂和脱水剂的种类、作用原理与除水能力,以及在药物合成的应用,为药物合成反应中水分的去除提供参考。 相似文献
7.
Fast CT-PRESS-based spiral chemical shift imaging at 3 Tesla. 总被引:2,自引:0,他引:2
Dirk Mayer Dong-Hyun Kim Elfar Adalsteinsson Daniel M Spielman 《Magnetic resonance in medicine》2006,55(5):974-978
A new sequence is presented that combines constant-time point-resolved spectroscopy (CT-PRESS) with fast spiral chemical shift imaging. It allows the acquisition of multivoxel spectra without line splitting with a minimum total measurement time of less than 5 min for a field of view of 24 cm and a nominal 1.5x1.5-cm2 in-plane resolution. Measurements were performed with 17 CS encoding steps in t1 (Deltat1=12.8 ms) and an average echo time of 151 ms, which was determined by simulating the CT-PRESS experiment for the spin systems of glutamate (Glu) and myo-inositol (mI). Signals from N-acetyl-aspartate, total creatine, choline-containing compounds (Cho), Glu, and mI were detected in a healthy volunteer with no or only minor baseline distortions within 14 min on a 3 T MR scanner. 相似文献
8.
综述了C_(60)化学研究的进展。C_(60)的化学反应性的研究展现了一个广阔的新领域,并使C_(60)作为一种新型的功能基团引入高分子成为现实。这些进展为进一步深入研究C_(60)尤其是C_(60)的材料化提供了前提。 相似文献
9.
10.
Prediction of steady state bioequivalence relationships using single dose data II-nonlinear kinetics
A J Jackson 《Biopharmaceutics & drug disposition》1989,10(5):489-503
Two nonlinear pharmacokinetic models were simulated to investigate the relationship between single and multiple dose bioequivalency parameters for drugs such as phenytoin and propranolol which exhibit either saturable elimination kinetics or a capacity limited first pass effect. Mean Tmax, Cmax and area under the plasma-concentration time curve values from 0 to infinity (AUC 0-infinity) were compared after a single and multiple dose(s) of a test or reference drug. The aim was to determine if there were systematic changes in the limits of the single dose confidence interval at steady state that would limit the usefulness of confidence intervals following a single dose in accurately predicting bioavailability following multiple dosing. The 90 per cent confidence interval expressed as a percentage of the reference mean for Tmax, Cmax, and AUC 0-infinity showed model dependent changes from single to multiple dosing in response to the level of data error and changes in absorption. Changes in clearance also seemed to have a marked effect on the observed limits of the single and multiple dose confidence intervals especially for Cmax which showed a characteristic change in the intervals as a function of the clearance ratio. The model used to describe phenytoin had confidence intervals for Cmax and AUC 0-infinity from single to multiple dosing that were similar to that seen for the experimental data. However, the model predictions for Tmax confidence intervals following single and multiple dosing was at variance with the experimental data for formulations A and B. 相似文献