全文获取类型
收费全文 | 5134篇 |
免费 | 282篇 |
国内免费 | 3篇 |
专业分类
化学 | 3609篇 |
晶体学 | 42篇 |
力学 | 87篇 |
数学 | 768篇 |
物理学 | 913篇 |
出版年
2023年 | 45篇 |
2022年 | 32篇 |
2021年 | 73篇 |
2020年 | 96篇 |
2019年 | 82篇 |
2018年 | 114篇 |
2017年 | 113篇 |
2016年 | 193篇 |
2015年 | 168篇 |
2014年 | 177篇 |
2013年 | 355篇 |
2012年 | 404篇 |
2011年 | 461篇 |
2010年 | 225篇 |
2009年 | 183篇 |
2008年 | 340篇 |
2007年 | 361篇 |
2006年 | 287篇 |
2005年 | 288篇 |
2004年 | 242篇 |
2003年 | 187篇 |
2002年 | 151篇 |
2001年 | 134篇 |
2000年 | 108篇 |
1999年 | 65篇 |
1998年 | 46篇 |
1997年 | 28篇 |
1996年 | 53篇 |
1995年 | 43篇 |
1994年 | 41篇 |
1993年 | 37篇 |
1992年 | 42篇 |
1991年 | 28篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 22篇 |
1983年 | 14篇 |
1982年 | 22篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1974年 | 6篇 |
1973年 | 4篇 |
排序方式: 共有5419条查询结果,搜索用时 31 毫秒
151.
Ganesh K. Mothukuri Sangram S. Kale Carl L. Stenbratt Alessandro Zorzi Jonathan Vesin Julien Bortoli Chapalay Kaycie Deyle Gerardo Turcatti Laura Cendron Alessandro Angelini Christian Heinis 《Chemical science》2020,11(30):7858
Macrocycles provide an attractive modality for drug development, but generating ligands for new targets is hampered by the limited availability of large macrocycle libraries. We have established a solution-phase macrocycle synthesis strategy in which three building blocks are coupled sequentially in efficient alkylation reactions that eliminate the need for product purification. We demonstrate the power of the approach by combinatorially reacting 15 bromoacetamide-activated tripeptides, 42 amines, and 6 bis-electrophile cyclization linkers to generate a 3780-compound library with minimal effort. Screening against thrombin yielded a potent and selective inhibitor (Ki = 4.2 ± 0.8 nM) that efficiently blocked blood coagulation in human plasma. Structure–activity relationship and X-ray crystallography analysis revealed that two of the three building blocks acted synergistically and underscored the importance of combinatorial screening in macrocycle development. The three-component library synthesis approach is general and offers a promising avenue to generate macrocycle ligands to other targets.Combination of three efficient chemical reactions allows for solution-phase synthesis of 3780 macrocycles and identification of potent thrombin inhibitor. 相似文献
152.
153.
A method for simultaneous analysis of eight azolic fungicides: cyproconazole, diniconazole, tetraconazole, thiabendazole, flusilazole, triadimenol, triadimefon, carbendazim and the degradation product 2-aminobenzimidazole in wine samples is described. The compounds are isolated from the samples and concentrated by solid-phase extraction on polymeric cartridges. The determination is carried out by liquid chromatography with mass spectrometric detection in positive ionization and selected ion monitoring modes. The influence of parameters such as the mobile phase composition, column temperature, corona current and fragmentor voltage is studied and the proposed method is validated. Recoveries of the nine compounds added to wine samples range from 83 to 109%, with relative standard deviations below 10%. The quantitation limits are between 9 and 31 microg/L. Real wine samples are analyzed by the proposed method, also. 相似文献
154.
A mild and new procedure for the selective cleavage of an alkoxycarbonyl group (Boc, CBz) in N,N-dicarbamoyl-protected amino compounds is described. The method is based on the use of lithium bromide in acetonitrile and is compatible with a large range of other functionalities present in the substrates. Compared with other reported methodologies, the procedure is particularly useful for the Cbz-selective cleavage in N,N-Ts,Cbz-diprotected amines. A rationalization of the selectivity supported by ab initio calculations is also presented. 相似文献
155.
Cornejo A Fraile JM García JI García-Verdugo E Gil MJ Legarreta G Luis SV Martínez-Merino V Mayoral JA 《Organic letters》2002,4(22):3927-3930
[formula: see text] A chiral pyridine-bis(oxazoline) ligand, functionalized with a vinyl group in the pyridine ring, can be polymerized with styrene and divinylbenzene to obtain supported chiral ligands. As proof of the usefulness of this supported ligands, the corresponding ruthenium complexes are catalysts for the cyclopropanation reaction of styrene with ethyl diazoacetate with up to 85% ee. 相似文献
156.
We have calculated the positions of the avoided level crossings between (n+2)s, np states and nd, k Stark states in the Rydberg Stark states of the potassium atom with principal quantum number n comprised between 12 and 17. We have also studied the adiabatic electric field ionization thresholds for the above Rydberg
states. Both the ionization thresholds and the positions of avoided crossings have been calculated using the recently developed
Stark-adapted quantum defect orbital (SQDO) formalism. The presently reported values appear to be in very good agreement with
the available theoretical and experimental data. 相似文献
157.
J. M. Navarrete T. Martínez L. Cabrera 《Journal of Radioanalytical and Nuclear Chemistry》2007,272(2):277-279
After the Chernobyl accident in 1986, Mexico imported from an European country 28,000 tons of contaminated powder milk with
the fission product 137Cs. When the contamination was detected, the alarm among the authorities and population spread out very quickly and of course
the product was retired at once from the foodstuff market. Nevertheless, the public panic grew up in such a manner, that even
the way to manage and to dispose safely this material, considered highly dangerous, was largely discussed. Now, about two
decades ago from this event, a study has been performed to compare the level of radioactivity due to both radioisotopes present
in one saved sample: the artificial contaminant 137Cs, beside the natural, all around present 40K, in order to evaluate in a more realistic way how risky was the management, possible consumption, and final disposition
of this nourishment. This paper considers results obtained within an uncertainty degree equal to ±5%, and set up conclusions
by comparing artificial and natural radioactivity present in that contaminated powder milk. 相似文献
158.
Cid MB Alfonso F Martín-Lomas M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(3):928-938
The stereochemical outcome of glycosylations with 2-azido-2-deoxy-D-gluco- and D-galactopyranosyl trichloroacetimidates as glycosyl donors has been investigated by using a series of chiro-inositol derivatives as glycosyl acceptors. The influence of the absolute configuration, the conformation and the conformational flexibility of the glycosyl acceptor has been studied by using different glycosyl donors under similar pre-established experimental conditions. Although the structure of the acceptor may play a role in governing the stereochemistry of these glycosylations, the results show that, in general terms, the relative influence of these factors is difficult to evaluate. For a given set of experimental conditions, the stereochemical course of these glycosylations depends on structural features of both glycosyl donor and glycosyl acceptor. It is a balance of these factors, where the structure of the glycosyl donor always plays a major role, which determines the stereochemistry of the coupling reaction. Therefore, the examples reported in the literature in which the structure of the glycosyl acceptor appears to be crucial in determining the stereochemistry of the reaction constitute particularly favorable cases which do not presently allow any further generalization. 相似文献
159.
Abderaouf Ahaidar David FernándezOlga Pérez Gerardo DanelónCarmen Cuevas Ignacio ManzanaresFernando Albericio John A. JouleMercedes Álvarez 《Tetrahedron letters》2003,44(33):6191-6194
The total synthesis of variolin B from 4-methoxy-7-azaindole is described. The preparation of the protected amino derivative 10 and a coupling reaction of the iodo derivative 12 with 2-acetylamino-4-trimethylstannylpyrimidine are the key steps of the sequence. The use of N-tosyldichloromethanimine for the cyclisation step afforded a good entry to the 9-aminopyrido[3′,2′:4,5]pyrrolo[1,2-c]pyrimidine system. Variolin B was obtained from the triply protected tetracyclic compound 13 in two steps. 相似文献
160.
Estela M. Alvarez Patricia H. Risso Carlos A. Gatti Martín S. Armesto Mariano Burgos Verónica M. Relling 《Colloid and polymer science》2006,284(9):1016-1023
Colloidal casein aggregates (CCA) prepared from soluble whole bovine caseinates in the presence of Ca2+ and phosphate (Pi) ions by addition of different citrate (Cit) concentrations showed different mineral and proteic composition. Citrate concentration conditions the Ca and Pi concentrations incorporated into CCA, probably due to the complexing effect of this anion on calcium. A significant change in the incorporated Ca/Pi ratio at 8 mM citrate could very likely be associated to changes in CCA net charge. The incorporation of individual caseins to the colloidal particles obtained, as well as their average size and size distribution, depended also on the Cit concentration used [Cit]P. αS- and β-caseins assembled in the CCA structure sharply decreased at a [Cit]P higher than 15 mM, i.e., at a low Ca2+ concentration in the aggregates, showing that the presence of this cation is necessary for the incorporation of these caseins. An inverse relationship between the aggregation step rate in CCA enzymic coagulation and their average size was observed. The aggregation rate vs the average size curve obtained at [Cit]P 8 mM clearly differed from the curves obtained at 10 and 12 mM, respectively, a fact probably related to a change in the CCA net charge. This behavior showed the effect of citrate concentration on CCA functional properties. 相似文献