全文获取类型
收费全文 | 19867篇 |
免费 | 959篇 |
国内免费 | 407篇 |
专业分类
化学 | 14598篇 |
晶体学 | 130篇 |
力学 | 533篇 |
综合类 | 40篇 |
数学 | 2590篇 |
物理学 | 3342篇 |
出版年
2023年 | 178篇 |
2022年 | 663篇 |
2021年 | 702篇 |
2020年 | 526篇 |
2019年 | 542篇 |
2018年 | 433篇 |
2017年 | 379篇 |
2016年 | 686篇 |
2015年 | 709篇 |
2014年 | 674篇 |
2013年 | 1274篇 |
2012年 | 1301篇 |
2011年 | 1484篇 |
2010年 | 918篇 |
2009年 | 900篇 |
2008年 | 1202篇 |
2007年 | 1155篇 |
2006年 | 1006篇 |
2005年 | 892篇 |
2004年 | 766篇 |
2003年 | 639篇 |
2002年 | 594篇 |
2001年 | 310篇 |
2000年 | 230篇 |
1999年 | 216篇 |
1998年 | 179篇 |
1997年 | 155篇 |
1996年 | 199篇 |
1995年 | 144篇 |
1994年 | 158篇 |
1993年 | 135篇 |
1992年 | 109篇 |
1991年 | 115篇 |
1990年 | 97篇 |
1989年 | 106篇 |
1988年 | 86篇 |
1987年 | 75篇 |
1986年 | 71篇 |
1985年 | 95篇 |
1984年 | 124篇 |
1983年 | 62篇 |
1982年 | 101篇 |
1981年 | 81篇 |
1980年 | 77篇 |
1979年 | 84篇 |
1978年 | 81篇 |
1977年 | 55篇 |
1976年 | 56篇 |
1975年 | 40篇 |
1974年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Synthesis of Highly Substituted γ‐Butyrolactones by a Gold‐Catalyzed Cascade Reaction of Benzyl Esters 下载免费PDF全文
Maria Camila Blanco Jaimes Alexander Ahrens Daniel Pflästerer Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):427-433
Easily accessible benzylic esters of 3‐butynoic acids in a gold‐catalyzed cyclization/rearrangement cascade reaction provided 3‐propargyl γ‐butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C?C bond is an intermolecular process. Initially propargylic–benzylic esters were used, but alkyl‐substituted benzylic esters worked equally well. In the case of the propargylic–benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl‐substituted γ‐butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one‐pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact. 相似文献
3.
4.
5.
6.
Functional Binding Surface of a β‐Hairpin VEGF Receptor Targeting Peptide Determined by NMR Spectroscopy in Living Cells 下载免费PDF全文
Dr. Donatella Diana Anna Russomanno Dr. Lucia De Rosa Dr. Rossella Di Stasi Dr. Domenica Capasso Dr. Sonia Di Gaetano Dr. Alessandra Romanelli Dr. Luigi Russo Dr. Luca D. D'Andrea Prof. Roberto Fattorusso 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):91-95
In this study, the functional interaction of HPLW peptide with VEGFR2 (Vascular Endothelial Growth Factor Receptor 2) was determined by using fast 15N‐edited NMR spectroscopic experiments. To this aim, 15N uniformly labelled HPLW has been added to Porcine Aortic Endothelial Cells. The acquisition of isotope‐edited NMR spectroscopic experiments, including 15N relaxation measurements, allowed a precise characterization of the in‐cell HPLW epitope recognized by VEGFR2. 相似文献
7.
8.
9.
Development and validation of a reversed‐phase HPLC method for CYP1A2 phenotyping by use of a caffeine metabolite ratio in saliva 下载免费PDF全文
Elias Begas Evangelos Kouvaras Andreas K. Tsakalof Maria Bounitsi Eftihia Konstadinos Asprodini 《Biomedical chromatography : BMC》2015,29(11):1657-1663
CYP1A2 is important for metabolizing various clinically used drugs. Phenotyping of CYP1A2 may prove helpful for drug individualization therapy. Several HPLC methods have been developed for quantification of caffeine metabolites in plasma and urine. Aim of the present study was to develop a valid and simple HPLC method for evaluating CYP1A2 activity during exposure in xenobiotics by the use of human saliva. Caffeine and paraxanthine were isolated from saliva by liquid‐liquid extraction (chlorophorm/isopropanol 85/15v/v). Extracts were analyzed by reversed‐phase HPLC on a C18 column with mobile phase 0.1% acetic acid/methanol/acetonitrile (80/20/2 v/v) and detected at 273nm. Caffeine and paraxanthine elution times were <13min with no interferences from impurities or caffeine metabolites. Detector response was linear (0.10–8.00µg/ml, R2>0.99), recovery was >93% and bias <4.47%. Intra‐ and inter‐day precision was <5.14% (n=6). The limit of quantitation was 0.10µg/ml and the limit of detection was 0.018±0.002µg/mL for paraxanthine and 0.032±0.002µg/ml for caffeine. Paraxanthine/caffeine ratio of 34 healthy volunteers was significantly higher in smokers (p<0.001). Saliva paraxanthine/caffeine ratios and urine metabolite ratios were highly correlated (r=0.85, p<0.001). The method can be used for the monitoring of CYP1A2 activity in clinical practice and in studies relevant to exposure to environmental and pharmacological xenobiotics. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
10.
Metabolic profiles of dioscin in rats revealed by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry 下载免费PDF全文
He Zhu Jin‐Di Xu Qian Mao Hong Shen Ming Kong Jian‐Ping Chen Song‐Lin Li 《Biomedical chromatography : BMC》2015,29(9):1415-1421
Dioscin (DIS), one of the most abundant bioactive steroidal saponins in Dioscorea sp., is used as a complementary medicine to treat coronary disease and angina pectoris in China. Although the pharmacological activities and pharmacokinetics of DIS have been well demonstrated, information regarding the final metabolic fates is very limited. This study investigated the in vivo metabolic profiles of DIS after oral administration by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry method. The structures of the metabolites were identified and tentatively characterized by means of comparing the molecular mass, retention time and fragmentation pattern of the analytes with those of the parent compound. A total of eight metabolites, including seven phase I and one phase II metabolites, were detected and tentatively identified for the first time. Oxidation, deglycosylation and glucuronidation were found to be the major metabolic processes of the compound in rats. In addition, a possible metabolic pathway on the biotransformation of DIS in vivo was proposed. This study provides valuable and new information on the metabolism of DIS, which will be helpful for further understanding its mechanism of action. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献