全文获取类型
收费全文 | 1379950篇 |
免费 | 29671篇 |
国内免费 | 7801篇 |
专业分类
化学 | 696140篇 |
晶体学 | 20476篇 |
力学 | 75671篇 |
综合类 | 106篇 |
数学 | 244327篇 |
物理学 | 380702篇 |
出版年
2021年 | 13561篇 |
2020年 | 15964篇 |
2019年 | 16099篇 |
2018年 | 14024篇 |
2016年 | 28550篇 |
2015年 | 20936篇 |
2014年 | 30521篇 |
2013年 | 74471篇 |
2012年 | 40228篇 |
2011年 | 39161篇 |
2010年 | 38528篇 |
2009年 | 40502篇 |
2008年 | 37695篇 |
2007年 | 33828篇 |
2006年 | 38422篇 |
2005年 | 31484篇 |
2004年 | 32136篇 |
2003年 | 29887篇 |
2002年 | 30657篇 |
2001年 | 30774篇 |
2000年 | 26144篇 |
1999年 | 23148篇 |
1998年 | 21259篇 |
1997年 | 21149篇 |
1996年 | 21215篇 |
1995年 | 19270篇 |
1994年 | 18717篇 |
1993年 | 18302篇 |
1992年 | 18573篇 |
1991年 | 18786篇 |
1990年 | 18004篇 |
1989年 | 18034篇 |
1988年 | 17638篇 |
1987年 | 17568篇 |
1986年 | 16515篇 |
1985年 | 22871篇 |
1984年 | 23982篇 |
1983年 | 20098篇 |
1982年 | 21722篇 |
1981年 | 20959篇 |
1980年 | 20286篇 |
1979年 | 20601篇 |
1978年 | 21802篇 |
1977年 | 21422篇 |
1976年 | 21135篇 |
1975年 | 19841篇 |
1974年 | 19494篇 |
1973年 | 19907篇 |
1972年 | 14426篇 |
1967年 | 12654篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
221.
Simen Gjelseth Antonsen Arne Joakim C. Bunkan Tomas Mikoviny Yngve Stenstrøm Armin Wisthaler 《Molecular physics》2020,118(15)
The kinetics of the O3, OH and NO3 radical reactions with diazomethane were studied in smog chamber experiments employing long-path FTIR and PTR-ToF-MS detection. The rate coefficients were determined to be k CH2NN+O3?=?(3.2?±?0.4)?×?10?17 and k CH2NN+OH?=?(1.68?±?0.12)?×?10?10 cm3 molecule?1 s?1 at 295?±?3?K and 1013?±?30 hPa, whereas the CH2NN?+?NO3 reaction was too fast to be determined in the static smog chamber experiments. Formaldehyde was the sole product observed in all the reactions. The experimental results are supported by CCSD(T*)-F12a/aug-cc-pVTZ//M062X/aug-cc-pVTZ calculations showing the reactions to proceed exclusively via addition to the carbon atom. The atmospheric fate of diazomethane is discussed. 相似文献
222.
223.
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
224.
225.
226.
Ivanov K. A. Gubaidullin A. R. Morozov K. M. Sasin M. E. Kaliteevskii M. A. 《Optics and Spectroscopy》2019,126(6):787-787
Optics and Spectroscopy - 10.1134/S0030400X17050095 相似文献
227.
Kaplunov I. A. Kolesnikov A. I. Kropotov G. I. Rogalin V. E. 《Optics and Spectroscopy》2019,126(3):191-194
Optics and Spectroscopy - The transmission of intrinsic, antimony-doped, and gallium-doped Ge single crystals in the THz spectral range have been experimentally investigated. It is shown that the... 相似文献
228.
Thomas Marmin Prof. Yves L. Dory 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(27):6707-6711
Cyclohexane and cyclotri-β-alanyl have been used as scaffolds for the design of new C3-symmetric rings incorporating conjugated alkenes and dienes. All three C3-symmetric lactams share the same triangular shape and their crystal system is trigonal. They all belong to the R3 space group, R3m, R3 and R3c, for the increasingly large 12-, 18- and 24-membered rigid rings, respectively. All lactams stack on top of each other, through H-bonds and van der Waals noncovalent interactions, leading to endless supramolecular cylinders and tubes. The largest member of the family leads to tubes, the central pores of which is wide enough to let water in. A common feature of all the lactams is their very large dipole, of around 9 D, according to DFT calculations. Surprisingly, all the resulting cylinders and tubes pack side by side in the crystals, with all the dipoles pointing to the same direction. As a result, all three crystals are anisotropic and appear to be the first members of a new kind of highly polar crystals. 相似文献
229.
Dr. Sebastian Lars Müller Xinglong Zhou Dr. Peter Leonard Oxana Korzhenko Dr. Constantin Daniliuc Prof. Dr. Frank Seela 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(12):3077-3090
Silver-mediated α-dC–Ag+–β-dC hybrid base pairs decorated with 5-iodo- or 5-octadiynyl residues are well accommodated in duplex DNA. A strong Tm increase and favorable thermodynamic data for duplex DNA were observed after addition of silver ions. The phenomenon is particularly obvious when both nucleobases of the base pairs are functionalized. Neither the position of the base pair, nor the type of 5-substituent had a negative influence. On the contrary, functionalization of conventional silver-mediated β-dC–Ag+–β-dC homo base pairs showed a negative impact induced by the bulky substituents. To this end, cytosine modified 12-mer oligodeoxynucleotides were prepared by solid-phase synthesis employing new α-anomeric 2′-deoxycytidine phosphoramidites. A multigram scale synthesis was developed for 5-iodo-α-d -2′-deoxycytidine ( 1 ) employing the direct glycosylation of cytosine with Hoffer's α-d -halogenose followed by separation of anomeric DMT nucleosides. Regarding base-pair stability and functionalization silver-mediated α/β-dC hybrid base pairs were found to be superior to β/β-dC homo pairs. According to their extraordinary properties, they might find applications in DNA diagnostics, material science, or nanotechnology. 相似文献
230.
Dr. Liat Avram Dr. Václav Havel Ronit Shusterman-Krush Dr. Mark A. Iron Dr. Moritz Zaiss Prof. Vladimír Šindelář Dr. Amnon Bar-Shir 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(7):1687-1690
The accumulated knowledge regarding molecular architectures is based on established, reliable, and accessible analytical tools that provide robust structural and functional information on assemblies. However, both the dynamicity and low population of noncovalently interacting moieties within studied molecular systems limit the efficiency and accuracy of traditional methods. Herein, the use of a saturation transfer-based NMR approach to study the dynamic binding characteristics of an anion to a series of synthetic receptors derived from bambusuril macrocycles is demonstrated. The exchange rates of BF4− are mediated by the side chains on the receptor (100 s−1<kex<5000 s−1), which play a critical role in receptor-anion binding dynamics. The signal amplification obtained with this approach allows for the identification of different types of intermolecular interactions between the receptor and the anion, something that could not have been detected by techniques hitherto used to study molecular assemblies. These findings, which are supported by a computational molecular dynamic study, demonstrate the uniqueness and added value of this NMR method. 相似文献