全文获取类型
收费全文 | 4748篇 |
免费 | 441篇 |
国内免费 | 27篇 |
专业分类
耳鼻咽喉 | 31篇 |
儿科学 | 125篇 |
妇产科学 | 112篇 |
基础医学 | 532篇 |
口腔科学 | 76篇 |
临床医学 | 461篇 |
内科学 | 952篇 |
皮肤病学 | 48篇 |
神经病学 | 240篇 |
特种医学 | 250篇 |
外科学 | 688篇 |
综合类 | 177篇 |
预防医学 | 451篇 |
眼科学 | 185篇 |
药学 | 323篇 |
中国医学 | 96篇 |
肿瘤学 | 469篇 |
出版年
2023年 | 43篇 |
2022年 | 57篇 |
2021年 | 95篇 |
2020年 | 65篇 |
2019年 | 111篇 |
2018年 | 101篇 |
2017年 | 89篇 |
2016年 | 86篇 |
2015年 | 127篇 |
2014年 | 152篇 |
2013年 | 191篇 |
2012年 | 271篇 |
2011年 | 268篇 |
2010年 | 177篇 |
2009年 | 173篇 |
2008年 | 264篇 |
2007年 | 264篇 |
2006年 | 235篇 |
2005年 | 262篇 |
2004年 | 204篇 |
2003年 | 209篇 |
2002年 | 163篇 |
2001年 | 113篇 |
2000年 | 121篇 |
1999年 | 122篇 |
1998年 | 67篇 |
1997年 | 72篇 |
1996年 | 72篇 |
1995年 | 45篇 |
1994年 | 55篇 |
1993年 | 46篇 |
1992年 | 92篇 |
1991年 | 76篇 |
1990年 | 69篇 |
1989年 | 67篇 |
1988年 | 80篇 |
1987年 | 74篇 |
1986年 | 66篇 |
1985年 | 47篇 |
1984年 | 30篇 |
1983年 | 32篇 |
1982年 | 38篇 |
1981年 | 22篇 |
1980年 | 18篇 |
1979年 | 20篇 |
1978年 | 23篇 |
1977年 | 15篇 |
1976年 | 28篇 |
1975年 | 14篇 |
1972年 | 12篇 |
排序方式: 共有5216条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
Chen SN Lankin DC Nikolic D Fabricant DS Lu ZZ Ramirez B van Breemen RB Fong HH Farnsworth NR Pauli GF 《Journal of natural products》2007,70(6):1016-1023
Extracts from the roots and rhizomes of black cohosh (Cimicifuga racemosa) are widely used as dietary supplements to alleviate menopausal symptoms. State-of-the-art quality control measures involve phytochemical fingerprinting of the triterpene glycosides for species identification and chemical standardization by HPLC. In the course of developing materials and methods for standardization procedures, the major C. racemosa triterpene glycoside (1) was isolated and initially thought to be cimicifugoside (2). Detailed HR-LC-MS and 1D and 2D NMR analysis of 1 and 2 unambiguously revealed that 1 is the chlorine-containing derivative of 2, namely, 25-chlorodeoxycimigenol-3-O-beta-d-xyloside. Accordingly, HPLC profiles of black cohosh preparations require revision of the assignments of the chlorinated (1) and nonchlorinated (2) pair. Besides explaining the substantial shift in polarity (DeltatR[RP-18] ca. 20 min), 25-deoxychlorination opens a new pathway of structural diversification in triterpene glycoside chemistry. As chemical conversion of 2 into 1 could be demonstrated, deoxychlorination may be interpreted as artifact formation. Simultaneously, however, it is a potentially significant pathway for the gastric in vivo conversion ("nature's prodrug") of the relatively polar triterpene glycosides into significantly less polar chlorinated derivatives with altered pharmacological properties. 相似文献
85.
Chi-Man Koon Subiyanto Fong Elaine Wat Yan-Ping Wang David Wing-Shing Cheung Clara Bik-San Lau Ping-Chung Leung Han-Dong Sun Qin-Shi Zhao Kwok-Pui Fung 《Journal of ethnopharmacology》2014
Ethnopharmacological relevance
Erigerontis Herba is widely used as a traditional Chinese medicine and is commonly used for neuroprotection and vascular protection.Aim of study
In this study, the vasodilator effects of Erigerontis Herba (DZXX) were investigated using rat isolated aorta rings.Material and method
The involvement of endothelium in the vasorelaxation was studied by comparing response of endothelium-intact and endothelium-denuded aorta rings which precontracted with U46619. The involvement of K+ channels was studied by pretreatment of the aorta rings with various K+ channel inhibitors. The involvement of Ca2+ channel was studied by incubating aorta rings with Ca2+-free solution, primed with U46619 prior to elicit contraction by addition of Ca2+ solution.Results
DZXX (0.2–2 mg/ml) induced a concentration-dependent relaxation on U44619-precontracted aorta rings with EC50 of 0.354±0.036 mg/ml. Removal of endothelium or pretreatment with a BKCa inhibitor iberiotoxin, KIR inhibitor barium chloride or Kv inhibitor 4-aminopyridine produced no effect on the DZXX-induced vasorelaxation. However, pretreatment with a KATP inhibitor glibenclamide or a non-selective K+ channel inhibitor tetraethylammonium produced significant inhibition on the DZXX-induced vasorelaxation by 29.9% and 21.3%, respectively. Pretreatment with DZXX (0.4, 1.2 and 2 mg/ml) produced a concentration-dependent inhibition on Ca2+-induced vasoconstriction.Conclusions
These results suggest that the vasodilator effect of DZXX was endothelium-independent, mediated by decreasing the influx of Ca2+ by calcium channel inhibition and increasing the influx of K+ by opening of a KATP channel. 相似文献86.
A series of analogues of gamma-aminobutyric acid (GABA) has been investigated for GABA mimetic activity on the isolated guinea-pig ileum, facilitation of [3H]diazepam binding in rat brain membranes and inhibition of [3H]GABA uptake from rat brain cortical slices. The derivatives tested include six racemic amino acids, all of which contain a 'GABA backbone' with the conformation restricted by a cyclopentane or cyclopentene ring system. From the more potent analogues, five optically pure compounds, including (+)-(4S)-4-aminocyclopent-1-ene-1-carboxylic acid and its (-)-4R enantiomer, have also been assessed as GABA agonists. Of the racemic analogues, 4-aminocyclopent-1-ene-1-carboxylic acid and trans-3-aminocyclopentane-1-carboxylic acid were the most potent at GABAA receptors, while most of the analogues had considerable activity on GABA uptake. The individual resolved isomers of 4-aminocyclopent-1-ene-carboxylic acid and of trans-3-aminocyclopentane-1-carboxylic acid displayed great specificity for GABA receptor and GABA uptake sites. For example (+)-(4S)-4-aminocyclopent-1-ene-1-carboxylic acid was approximately twice as potent as GABA and about 600 times more active than the (-)-4R isomer on the guinea-pig ileum, while it was not significantly active as a GABA uptake inhibitor at 500 microM. On the other hand, its (-)-4R isomer was selective for inhibiting GABA uptake with an IC50 equal to that of racemic nipecotic acid. 相似文献
87.
Subramanyam Vankadara Monique Danielle Dawson Jia Yi Fong Qin Yao Oh Qi An Ang Boping Liu Hong Yun Chang Judice Koh Xiaoying Koh Qian Wen Tan Joma Joy Cheng San Brian Chia 《ACS medicinal chemistry letters》2022,13(8):1345
The SARS-CoV-2 pandemic is currently causing an unprecedented global health emergency since its emergence in December 2019. In December 2021, the FDA granted emergency use authorization to nirmatrelvir, a SARS-CoV-2 main protease inhibitor, for treating infected patients. This peptidomimetic is designed with a nitrile warhead, which forms a covalent bond to the viral protease. Herein, we investigate nirmatrelvir analogs with different warheads and their inhibitory activities. In addition, antiviral activities against human alphacoronavirus 229E was also investigated along with a cell-based assay. We discovered that the hydroxymethylketone and ketobenzothiazole warheads were equipotent to the nitrile warhead, suggesting that these analogs can also be used for treating coronavirus infections. 相似文献
88.
Interstitial retinol-binding protein and cellular retinal-binding protein in the mammalian pineal 总被引:1,自引:0,他引:1
Antibodies against bovine interstitial retinol-binding protein (IRBP) and cellular retinal-binding protein (CRA1BP) were used in immunochemical and immunocytochemical studies of the pineal glands of cattle, hamsters and rats (RCS and RCS-rdy+). On immunoblots, IRBP (Mr 144,000) was identified in cattle, hamster and rat pineal extracts. The abundance of IRBP in bovine pineals was 33 +/- 6 ng.mg-1 (mean +/- SD, n = 12) soluble protein. RCS (Royal College of Surgeons) rat pineals gave a strong IRBP reaction on immunoblots, even when virtually no IRBP could be found in the eye due to photoreceptor degeneration. In the hamster retina IRBP immunostaining was distributed throughout the entire interphotoreceptor matrix and the outer segment layer. The pineal also showed strong IRBP-like immunostaining scattered uniformly throughout the gland. Other hamster brain regions showed no specific immunostaining; however, an immunoreactive protein with the same Mr as IRBP was detected on Western blots of bovine cerebral cortex, spinal cord and brainstem soluble proteins. Immunoreactive proteins at lower Mr were also detected in these tissues. CRA1BP immunoreactivity (Mr about 32,000) was observed in immunoblots of bovine, hamster and rat pineal proteins. These findings suggest that some mammalian pinealocytes are related to the retinal cells that contain CRA1BP (i.e. pigment epithelium, Muller cells) while others are related to the photoreceptors, which synthesize IRBP. 相似文献
89.
In a chemical study of taxonomically related Taxaceae plants of Yunnan Province, China, seven compounds, including a new amentoflavone biflavonoid, 2,3-dihydro-7,7' '-dimethoxyamentoflavone (1), were isolated from Amentotaxus yunnanensis, and 12 isolates were obtained from Torreya yunnanensis. From the latter plant, a new abietane diterpene, torreyayunnin (7), is reported for the first time. The known isolates from A. yunnanensis have been identified as sequoiaflavone (3), sotetsuflavone (4), 7,7' '-dimethoxyamentoflavone (5), lutein, beta-sitosterol, and sequoyitol. Amentoflavone (2), sotetsuflavone (4), sciadopitysin (6), 12-hydroxydehydroabietinol, meridinol, balanophonin, (+)-pinoresinol monomethyl ether, (+)-pinoresinol monomethyl ether glucoside, erythro-1-(4-hydroxy-3-methoxyphenyl)-2-[4-[2-formyl-(E)-vinyl]-2- methoxyphenoxy]propane-1,3-diol, threo-1-(4-hydroxy-3-methoxyphenyl)-2- [4-[2-formyl-(E)-vinyl]-2-methoxyphenoxy] propane-1,3-diol, and (E)-2-butenedioic acid were identified as known isolates from T. yunnanensis. The presence of the amentoflavone biflavonoids (1, 3-5) in A. yunnanensis supports its placement in the Taxaceae. The occurrence of the biflavonoid sotetsuflavone (4) in both A. yunnanensis and T. yunnanensis suggests that these two genera are closely related. The identification and structural elucidation of these isolates were based on spectral data analysis including 1D and 2D NMR. 相似文献
90.
青蒿挥发油成分的GC-MS分析与化学计量学解析法 总被引:1,自引:0,他引:1
目的:分析青蒿挥发油的化学成分.方法:用水蒸气蒸馏法从青蒿中提取挥发油成分,采用气相色谱-质谱(GC-MS)联用技术,结合化学计量学解析法(CRM)对重叠色谱峰进行分辨解析,并利用程序升温保留指数辅助定性.结果:共分辨出73个色谱峰,鉴定了其中66个组分,占青蒿挥发油总含量的95.25%,其主要化学成分为:丁子香烯、丁子香烯环氧化物、稚槛蓝(树)油烯、α-甜没药萜醇等.结论:使用CRM解析色谱峰,比单独使用GC-MS法能更真实、全面地反映其挥发油化学成分. 相似文献