全文获取类型
收费全文 | 2546篇 |
免费 | 84篇 |
国内免费 | 9篇 |
专业分类
化学 | 1635篇 |
晶体学 | 5篇 |
力学 | 41篇 |
数学 | 412篇 |
物理学 | 546篇 |
出版年
2023年 | 19篇 |
2022年 | 39篇 |
2021年 | 70篇 |
2020年 | 62篇 |
2019年 | 73篇 |
2018年 | 70篇 |
2017年 | 39篇 |
2016年 | 92篇 |
2015年 | 58篇 |
2014年 | 91篇 |
2013年 | 121篇 |
2012年 | 152篇 |
2011年 | 163篇 |
2010年 | 97篇 |
2009年 | 105篇 |
2008年 | 111篇 |
2007年 | 103篇 |
2006年 | 96篇 |
2005年 | 96篇 |
2004年 | 70篇 |
2003年 | 62篇 |
2002年 | 63篇 |
2001年 | 23篇 |
2000年 | 25篇 |
1999年 | 36篇 |
1998年 | 17篇 |
1997年 | 19篇 |
1996年 | 16篇 |
1995年 | 25篇 |
1994年 | 13篇 |
1993年 | 22篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1989年 | 16篇 |
1984年 | 16篇 |
1982年 | 12篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 16篇 |
1976年 | 21篇 |
1975年 | 20篇 |
1974年 | 10篇 |
1957年 | 13篇 |
1956年 | 17篇 |
1955年 | 11篇 |
1954年 | 14篇 |
1929年 | 9篇 |
1927年 | 11篇 |
1924年 | 9篇 |
1907年 | 11篇 |
排序方式: 共有2639条查询结果,搜索用时 15 毫秒
941.
Chen J Dexheimer TS Ai Y Liang Q Villamil MA Inglese J Maloney DJ Jadhav A Simeonov A Zhuang Z 《Chemistry & biology》2011,18(11):1390-1400
Ubiquitin-specific proteases (USPs) have in recent years emerged as a promising therapeutic target class. We identified selective small-molecule inhibitors against a deubiquitinase complex, the human USP1/UAF1, through quantitative high throughput screening (qHTS) of a collection of bioactive molecules. The top inhibitors, pimozide and GW7647, inhibited USP1/UAF1 noncompetitively with a K(i) of 0.5 and 0.7?μM, respectively, and displayed selectivity against a number of deubiquitinases, deSUMOylase, and cysteine proteases. The USP1/UAF1 inhibitors act synergistically with cisplatin in inhibiting cisplatin-resistant non-small cell lung cancer (NSCLC) cell proliferation. USP1/UAF1 represents a promising target for drug intervention because of its involvement in translesion synthesis and Fanconi anemia pathway?important for normal DNA damage response. Our results support USP1/UAF1 as a potential therapeutic target and provide an example of targeting the USP/WD40 repeat protein complex for inhibitor discovery. 相似文献
942.
Suturina EA Semenov NA Lonchakov AV Bagryanskaya IY Gatilov YV Irtegova IG Vasilieva NV Lork E Mews R Gritsan NP Zibarev AV 《The journal of physical chemistry. A》2011,115(18):4851-4860
According to the DFT calculations, [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (4), [1,2,5]selenadiazolo[3,4-c][1,2,5]thiadiazole (5), 3,4-dicyano-1,2,5-thiadiazole (6), and 3,4-dicyano-1,2,5-selenadiazole (7) have nearly the same positive electron affinity (EA). Under the CV conditions they readily produce long-lived π-delocalized radical anions (π-RAs) characterized by EPR. Whereas 4 and 5 were chemically reduced into the π-RAs with thiophenolate (PhS(-)), 6 did not react and 7 formed a product of hypercoordination at the Se center (9) isolated in the form of the thermally stable salt [K(18-crown-6)][9] (10). The latter type of reactivity has never been observed previously for any 1,2,5-chalcogenadiazole derivatives. The X-ray structure of salt 10 revealed that the Se-S distance in the anion 9 (2.722 ?) is ca. 0.5 ? longer than the sum of the covalent radii of these atoms but ca. 1 ? shorter than the sum of their van der Waals radii. According to the QTAIM and NBO analysis, the Se-S bond in 9 can be considered a donor-acceptor bond whose formation leads to transfer of ca. 40% of negative charge from PhS(-) onto the heterocycle. For various PhS(-)/1,2,5-chalcogenadiazole reaction systems, thermodynamics and kinetics were theoretically studied to rationalize the interchalcogen hypercoordination vs reduction to π-RA dichotomy. It is predicted that interaction between PhS(-) and 3,4-dicyano-1,2,5-telluradiazole (12), whose EA slightly exceeds that of 6 and 7, will lead to hypercoordinate anion (17) with the interchalcogen Te-S bond being stronger than the Se-S bond observed in anion 9. 相似文献
943.
Kaufmann A Butcher P Maden K Walker S Widmer M 《Rapid communications in mass spectrometry : RCM》2011,25(7):979-992
The quantitative and confirmative performance of two different mass spectrometry (MS) techniques (high-resolution MS and tandem MS) was critically compared. Evaluated was a new extraction and clean-up protocol which was developed to cover more than 100 different veterinary drugs at trace levels in a number of animal tissues and honey matrices. Both detection techniques, high-resolution mass spectrometry (HRMS) (single-stage Orbitrap instrument operated at 50 000 full width at half maximum) and tandem mass spectrometry (MS/MS) (quadrupole technology) were used to validate the method according to the EU Commission Decision 2002/657/EEC. Equal or even a slightly better quantitative performance was observed for the HRMS-based approach. Sensitivity is higher for unit mass resolution MS/MS if only a subset of the 100 compounds has to be monitored. Confirmation of suspected positive findings can be done by evaluating the intensity ratio between different MS/MS transitions, or by accurate mass based product ion traces (no precursor selection applied). MS/MS relies on compound-specific optimized transitions; hence the second, confirmatory transition generally shows relatively high ion abundance (fragmentation efficacy). This is often not the case in single-stage HRMS, since a generic (not compound-optimized) collision energy is applied. Hence, confirmation of analytes present at low levels is superior when performed by MS/MS. Slightly better precision, but poorer accuracy (fortified matrix extracts versus pure standard solution) of ion ratios were observed when comparing data obtained by HRMS versus MS/MS. 相似文献
944.
Kanawati B von Saint Paul V Herrmann C Schäffner AR Schmitt-Kopplin P 《Rapid communications in mass spectrometry : RCM》2011,25(6):806-814
L-Ascorbic acid and two distinct anomers, namely the α-D-glucopyranosyl and β-D-glucopyranosyl-(1→2)-L-ascorbic acid (stereoisomers), were studied within the scope of collision-induced dissociation (CID) experiments, performed by linear ion acceleration and collision with argon atoms inside a hexapole quadrupole hexapole ion beam guide, which is coupled to an ion cyclotron resonance (ICR) cell with a 12 Tesla magnet for high-resolution measurements. Loss of C(2)H(4)O(2) neutral from the [M-H](-) anion of L-ascorbic acid was observed. Density functional theory (DFT) calculations on the 6-311+G(2d,p)//6-31+G(d) level of theory reveal a new concerted mechanism for an intramolecular gas-phase rearrangement, through which the observed ejected neutral C(2)H(4)O(2) can take place. A similar rearrangement also occurs in the case of α- and β-D-glucopyranosyl-(1→2)-L-ascorbic acid. For the α isomer, only homolytic glycoside fragmentation was observed. For the β isomer, both homolytic and heterolytic glycoside cleavages were possible. The mechanisms behind all observed fragmentation pathways were fully understood by the implementation of accurate DFT calculations. Stereoisomeric differentiation between α and β isomers of the L-ascorbic acid-2-O-glucoside could be revealed by tandem mass spectrometry (MS/MS) experiments and were explained theoretically. 相似文献
945.
Cao P Li H Zhang P Calzaferri GA 《Langmuir : the ACS journal of surfaces and colloids》2011,27(20):12614-12620
We report important progress made in the synthesis of oriented functional layers of nanochannel materials by using coordination chemistry as a tool. Zeolite L (ZL) crystals have been arranged into oriented layers through the coordinative interactions between a functional organic linker (L) and metal cations used for connecting the different parts. As organic linker we used a terpyridyl ligand bearing a urea group and a reactive siloxane part. Two strategies that lead to monolayers with different properties are described. The first consists of reacting the siloxane group of ligand L with OH groups of the substrate (S), and selectively reacting the siloxane group of L with OH groups located at the base of the ZL crystals. Next, metal cations M(n+), for example, Zn(2+) or Cu(2+), are coordinated to the terpy group on the modified substrate. To this the modified ZL is added and coordinatively bound by the terpy(Mn(n+))terpy interaction, leading to oriented ZL layers. The second method consists of reacting substrate S and ligand L in the presence of a metal cation. A layer with reactive siloxane groups is formed on S to which the ZL crystals are bound by the reaction of the hydroxyl groups of their base. Zn(2+), Cu(2+), and lanthanide ions Eu(3+) and Tb(3+)have been tested successfully, all of them leading to high-quality ZL monolayers with open channels, accessible for accepting guests, oriented perpendicularly with respect to the surface of S. 相似文献
946.
N Thorne M Shen WA Lea A Simeonov S Lovell DS Auld J Inglese 《Chemistry & biology》2012,19(8):1060-1072
- Download : Download high-res image (480KB)
- Download : Download full-size image
947.
Alexey Borisovich Umanskii Anton Mihaylovich Klyushnikov 《Journal of Radioanalytical and Nuclear Chemistry》2012,293(1):193-198
A process of ferrous ion oxidation by sodium nitrite in sulfate uranium in situ leaching solutions was investigated. Kinetic, spectrophotometric, and heat effect studies have been made in order to investigate the chemistry of the oxidation process. As a result the method of ferrous ion oxidation in uranium in situ leaching solution was developed that makes possible to decrease sodium nitrite consumption by 20?C30 times comparing with traditional oxidation technique. It was founded also that process of ferrous ion oxidation can be conducted with partial sodium nitrite recirculation. 相似文献
948.
Building on results for the adsorption of benzene on Pt(111), the adsorption of benzaldehyde is investigated using density functional theory. Benzaldehyde is found to chemisorb preferentially with its aromatic ring in the flat-lying bridge geometry that is also preferred for benzene. Across the investigated geometries, adsorption is homogeneously weakened compared to corresponding benzene geometries. This is found to be true for very different adsorption modes, namely, η(6) and η(8) modes, the latter having metal atoms inserted in the carbonyl bond. Reorientation and diffusion of benzaldehyde is found to have low energy barriers. Aggregation of molecules in dimers bound by aryl C-H···O hydrogen bonds is investigated, and specific configurations are found to be up to 0.15 eV more favorable than optimally configured, separated adsorbates. The binding is significantly stronger than what is found for gas phase dimers, suggesting an enhancing effect of the metal interaction. 相似文献
949.
Stasyuk AJ Banasiewicz M Cyrański MK Gryko DT 《The Journal of organic chemistry》2012,77(13):5552-5558
A short and efficient route to a broad range of imidazo[1,2-a]pyridines from 2-aminopyridines and acetophenones is achieved by a tandem, one-pot process starting with an Ortoleva-King reaction. Optimal conditions for the first step were established after examining various reaction parameters (solvent, reagent ratios, and temperature). The conditions identified (1st step, neat, 2.3 equiv of 2-aminopyridine, 1.20 equiv of I(2), 4 h, 110 °C; 2nd step, NaOH(aq), 1 h, 100 °C) resulted in the formation of imidazo[1,2-a]pyridines in 40-60% yields. The synthesis is compatible with various functionalities (OH, NMe(2), Br, OMe). Products containing a 2-(2'-hydroxyphenyl) substituent undergo excited state intramolecular proton transfer (ESIPT) in nonpolar and polar-aprotic solvents. Although ESIPT-type emission in nonpolar solvents is weak, the Stokes shifts are very high (11000 cm(-1)). The comparison of the properties of six ESIPT-capable imidazo[1,2-a]pyridines shows the influence of various substituents on emission characteristics. All of them also display strong, solid-state emission in blue-green-yellow region. 2-Aryl-imidazo[1,2-a]pyridines not capable of ESIPT emit in the blue region, displaying high fluorescence quantum yield. 相似文献
950.
Dubrovskiy AV Markina NA Larock RC 《Combinatorial chemistry & high throughput screening》2012,15(6):451-472
The iodocyclization of functionally-substituted alkynes provides an excellent way to prepare a wide range of iodoheterocycles, which can then be readily elaborated through palladium-catalyzed Suzuki-Miyaura, Sonogashira, Heck, Hartwig-Buchwald, and carbonylation processes into libraries of medicinally relevant heterocycles. The synthesis of libraries of indoles, benzofurans, benzothiophenes, isocoumarins and pyrones, cyclic imidates, isoxazoles, furans using this approach is reviewed. This technology is very versatile, proceeds under mild reaction conditions in high yields, and tolerates considerable functionality. 相似文献