全文获取类型
收费全文 | 8365篇 |
免费 | 852篇 |
国内免费 | 1252篇 |
专业分类
耳鼻咽喉 | 12篇 |
儿科学 | 24篇 |
妇产科学 | 13篇 |
基础医学 | 365篇 |
口腔科学 | 124篇 |
临床医学 | 340篇 |
内科学 | 672篇 |
皮肤病学 | 291篇 |
神经病学 | 127篇 |
特种医学 | 469篇 |
外科学 | 166篇 |
综合类 | 1321篇 |
现状与发展 | 2篇 |
一般理论 | 1篇 |
预防医学 | 593篇 |
眼科学 | 101篇 |
药学 | 2841篇 |
3篇 | |
中国医学 | 2847篇 |
肿瘤学 | 157篇 |
出版年
2024年 | 81篇 |
2023年 | 161篇 |
2022年 | 335篇 |
2021年 | 394篇 |
2020年 | 326篇 |
2019年 | 229篇 |
2018年 | 229篇 |
2017年 | 322篇 |
2016年 | 343篇 |
2015年 | 374篇 |
2014年 | 576篇 |
2013年 | 715篇 |
2012年 | 595篇 |
2011年 | 703篇 |
2010年 | 546篇 |
2009年 | 488篇 |
2008年 | 509篇 |
2007年 | 406篇 |
2006年 | 457篇 |
2005年 | 371篇 |
2004年 | 289篇 |
2003年 | 263篇 |
2002年 | 220篇 |
2001年 | 213篇 |
2000年 | 125篇 |
1999年 | 125篇 |
1998年 | 128篇 |
1997年 | 100篇 |
1996年 | 93篇 |
1995年 | 80篇 |
1994年 | 85篇 |
1993年 | 75篇 |
1992年 | 88篇 |
1991年 | 58篇 |
1990年 | 50篇 |
1989年 | 39篇 |
1988年 | 43篇 |
1987年 | 44篇 |
1986年 | 30篇 |
1985年 | 31篇 |
1984年 | 16篇 |
1983年 | 25篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1974年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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
2.
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
3.
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
4.
5.
Abstract: Native chemical ligation has proven to be a powerful method for the synthesis of small proteins and the semisynthesis of larger ones. The essential synthetic intermediates, which are C‐terminal peptide thioesters, cannot survive the repetitive piperidine deprotection steps of Nα‐9‐fluorenylmethoxycarbonyl (Fmoc) chemistry. Therefore, peptide scientists who prefer to not use Nα‐t‐butyloxycarbonyl (Boc) chemistry need to adopt more esoteric strategies and tactics in order to integrate ligation approaches with Fmoc chemistry. In the present work, side‐chain and backbone anchoring strategies have been used to prepare the required suitably (partially) protected and/or activated peptide intermediates spanning the length of bovine pancreatic trypsin inhibitor (BPTI). Three separate strategies for managing the critical N‐terminal cysteine residue have been developed: (i) incorporation of Nα‐9‐fluorenylmethoxycarbonyl‐S‐(N‐methyl‐N‐phenylcarbamoyl)sulfenylcysteine [Fmoc‐Cys(Snm)‐OH], allowing creation of an otherwise fully protected resin‐bound intermediate with N‐terminal free Cys; (ii) incorporation of Nα‐9‐fluorenylmethoxycarbonyl‐S‐triphenylmethylcysteine [Fmoc‐Cys(Trt)‐OH], generating a stable Fmoc‐Cys(H)‐peptide upon acidolytic cleavage; and (iii) incorporation of Nα‐t‐butyloxycarbonyl‐S‐fluorenylmethylcysteine [Boc‐Cys(Fm)‐OH], generating a stable H‐Cys(Fm)‐peptide upon cleavage. In separate stages of these strategies, thioesters are established at the C‐termini by selective deprotection and coupling steps carried out while peptides remain bound to the supports. Pilot native chemical ligations were pursued directly on‐resin, as well as in solution after cleavage/purification. 相似文献
6.
化学实验进行开放式教学的研究 总被引:7,自引:0,他引:7
通过与传统的化学实验教学模式的比较,详述了开放式教学模式的特点,并且针对实施过程中所遇到的问题提出了详尽的解决方案。 相似文献
7.
介绍国内外近年来报道的新型经皮渗透促进剂的研究与开发进展,重点介绍若干具代表性的新合成的化合物以及新发现的天然产物,包括内酰胺类、糖苷类、氨基酸衍生物、聚合物、挥发油和酶类等,为合成和发现更加安全、高效的促渗剂提供线索. 相似文献
8.
9.
替硝唑葡萄糖注射液的稳定性研究 总被引:6,自引:0,他引:6
采用反相HPLC法测定替硝唑葡萄糖注射液中替硝唑的含量,用加温加速实验研究该制剂的热稳定动力学。结果表明,替硝唑的热降解反应为一级动力学过程,在50、65、80、95℃时的降解速度常数分别为5.58×10-4、2.66×10-3、8.10×10-3、2.82×10-2d-1,为8.3年,半衰期为39.5年。 相似文献
10.
Arsenical necrosis of the jaws 总被引:3,自引:0,他引:3
A. B. D. BATAINEH M. A. O. AL-OMARI A. I. OWAIS 《International endodontic journal》1997,30(4):283-287
After a brief historical review of the use of arsenic in dental practice two cases of arsenical necrosis of the jaws, affecting the maxilla and mandible respectively, are reported. Both patients were treated conservatively over an extended period with excellent results. It is concluded that there is no justification, whatsoever, for the use of arsenic in modern dental practice and that, although prolonged, conservative treatment of chemical necrosis of the jaws is preferable to more radical treatment. 相似文献