全文获取类型
收费全文 | 1206篇 |
免费 | 60篇 |
国内免费 | 3篇 |
专业分类
化学 | 1010篇 |
晶体学 | 7篇 |
力学 | 23篇 |
数学 | 98篇 |
物理学 | 131篇 |
出版年
2023年 | 7篇 |
2022年 | 27篇 |
2021年 | 49篇 |
2020年 | 40篇 |
2019年 | 45篇 |
2018年 | 46篇 |
2017年 | 35篇 |
2016年 | 59篇 |
2015年 | 57篇 |
2014年 | 38篇 |
2013年 | 84篇 |
2012年 | 76篇 |
2011年 | 102篇 |
2010年 | 55篇 |
2009年 | 50篇 |
2008年 | 78篇 |
2007年 | 84篇 |
2006年 | 60篇 |
2005年 | 67篇 |
2004年 | 55篇 |
2003年 | 34篇 |
2002年 | 30篇 |
2001年 | 20篇 |
2000年 | 14篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1269条查询结果,搜索用时 15 毫秒
991.
Leonid I. Klushin Tatiana M. Birshtein Anna A. Mercurieva 《Macromolecular theory and simulations》1998,7(5):483-495
A mean-field theory of deformation-induced microphase segregation in bridging polymeric brushes anchored to two parallel surfaces is presented. Models with isotropic and orientation-dependent liquid-crystalline interactions between segments are considered. For the first model, the problem is similar to that of classical liquid-vapor phase separation, and the phase diagram in the P-T plane has a line of first-order transitions terminating at the critical point. We show that the critical pressure is negative implying that a free brush tethered only to one surface always exists at supercritical conditions and hence cannot undergo the collapse phase transition. In the second model, the free energy density depends on two coupled order parameters, one related to segment density and the other to the orientational order, which strongly modifies the phase behavior. Depending on the grafting density the system is described by a phase diagram of a regular or a singular type. In the regular phase diagram the first-order transition line terminates at the critical point. In a singular diagram, the first-order transition line extends to infinity; the critical point corresponds to infinite pressure so that the system undergoes the phase transition at arbitrary external pressures. Regular phase diagrams correspond to dense grafting, and singular ones to sparse grafting. The change from a regular phase behavior to another occurs at a certain marginal value of the grafting density. On approaching this value the critical point on the regular diagram moves to infinity, logarithmically with the deviation from the critical grafting density. We relate the analytical properties of the free energy density as a function of the segment concentration to the type of the phase diagram and the shape of the coexistence curve in the temperature- concentration plane. 相似文献
992.
Nonlinear Dynamics - An optimal control problem is solved for a two-body limbless locomotor crawling along a straight line on a horizontal rough plane. Coulomb’s dry friction acts between the... 相似文献
993.
Jajcay Robert Jajcayová Tatiana Szakács Nóra Szendrei Mária B. 《Journal of Algebraic Combinatorics》2021,53(3):829-849
Journal of Algebraic Combinatorics - A partial automorphism of a finite graph is an isomorphism between its vertex-induced subgraphs. The set of all partial automorphisms of a given finite graph... 相似文献
994.
Xavier Deraet Tatiana Woller Ruben Van Lommel Prof. Frank De Proft Prof. Guido Verniest Prof. Mercedes Alonso 《ChemistryOpen》2019,8(6):788-806
The performance of density functionals and wavefunction methods for describing the thermodynamics and kinetics of hydride reductions of 2-substituted cyclohexanones has been evaluated for the first time. A variety of exchange correlation functionals ranging from generalized gradient approximations to double hybrids have been tested and their performance to describe the facial selectivity of hydride reductions of cyclohexanones has been carefully assessed relative to the CCSD(T) method. Among the tested methods, an approach in which single-point energy calculations using the double hybrid B2PLYP−D3 functional on ωB97X−D optimized geometries provides the most accurate transition state energies for these kinetically-controlled reactions. Moreover, the role of torsional strain, temperature, solvation, noncovalent interactions on the stereoselectivity of these reductions was elucidated. Our results indicate a prominent role of the substituent on the cis/trans ratios driven by the delicate interplay between torsional strain and dispersion interactions. 相似文献
995.
Deogratias Geradius Al-Qurashi Ohoud S. Wazzan Nuha Seriani Nicola Pogrebnaya Tatiana Pogrebnoi Alexander 《Structural chemistry》2020,31(6):2451-2461
Structural Chemistry - Design and synthesis of new potent sensitizers are of interest for realization of high-efficiency Dye Sensitized Solar Cells (DSSCs). Modification of the... 相似文献
996.
Dr. Jamie A. Leitch Tatiana Rogova Prof. Dr. Fernanda Duarte Prof. Dr. Darren J. Dixon 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(10):4150-4159
The construction of diverse sp3-rich skeletal ring systems is of importance to drug discovery programmes and natural product synthesis. Herein, we report the photocatalytic construction of 2,7-diazabicyclo[3.2.1]octanes (bridged 1,3-diazepanes) via a reductive diversion of the Minisci reaction. The fused tricyclic product is proposed to form via radical addition to the C4 position of 4-substituted quinoline substrates, with subsequent Hantzsch ester-promoted reduction to a dihydropyridine intermediate which undergoes in situ two-electron ring closure to form the bridged diazepane architecture. A wide scope of N-arylimine and quinoline derivatives was demonstrated and good efficiency was observed in the construction of sterically congested all-carbon quaternary centers. Computational and experimental mechanistic studies provided insights into the reaction mechanism and observed regioselectivity/diastereoselectivity. 相似文献
997.
Oleg A. Levitskiy Yuri K. Grishin Ksenia A. Paseshnichenko Konstantin A. Kochetkov Tatiana V. Magdesieva 《Tetrahedron letters》2018,59(29):2831-2834
One-pot method for direct stereoselective (S)-α-thioalkylation of glycine in Ni(II) coordination environment was elaborated. The reaction of electrochemically deprotonated Ni(II) glycine/Schiff-base complex containing (S)-o-[N-(N′-benzylprolyl)amino]benzophenone as an auxiliary chiral moiety with alkyl thiocyanates leads to the α-thioalkylated derivatives in a practical ca.70% chemical yield and stereoselectivity (de 80%). 相似文献
998.
Tatiana A. Molden Marcella C. Grillo Dr. Dmitry M. Kolpashchikov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(7):2421-2426
DNA-based computers can potentially analyze complex sets of biological markers, thereby advancing diagnostics and the treatment of diseases. Despite extensive efforts, DNA processors have not yet been developed due, in part, to limitations in the ability to integrate available logic gates into circuits. We have designed a NAND gate, which is one of the functionally complete set of logic connectives. The gate's design avoids stem-loop-folded DNA fragments, and is capable of reusable operations in RNase H-containing buffer. The output of the gate can be translated into RNA-cleaving activity or a fluorescent signal produced either by a deoxyribozyme or a molecular beacon probe. Furthermore, three NAND-gate-forming DNA strands were crosslinked by click chemistry and purified in a simple procedure that allowed ≈1013 gates to be manufactured in 16 h, with a hands-on time of about 30 min. Two NAND gates can be joined into one association that performs a new logic function simply by adding a DNA linker strand. Approaches developed in this work could contribute to the development of biocompatible DNA logic circuits for biotechnological and medical applications. 相似文献
999.
Antoine Versini Dr. Ludovic Colombeau Dr. Antje Hienzsch Christine Gaillet Dr. Pascal Retailleau Dr. Sylvain Debieu Dr. Sebastian Müller Dr. Tatiana Cañeque Prof. Raphaël Rodriguez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(33):7416-7424
Salinomycin ( 1 ) exhibits a large spectrum of biological activities including the capacity to selectively eradicate cancer stem cells (CSC), making it and its derivatives promising candidates for the development of drug leads against CSC. It has been previously shown that salinomycin and its C20-propargylamine derivative (Ironomycin ( 2 )) accumulate in lysosomes and sequester iron in this organelle. Herein, a library of salinomycin derivatives is reported, including products of C20-amination, C1-esterification, C9-oxidation, and C28-dehydration. The biological activity of these compounds is evaluated against transformed human mammary epithelial HMLER CD24low/CD44high cells, a well-established model of breast CSC, and HMLER CD24high/CD44low cells deprived of CSC properties. Unlike other structural alterations, derivative 4 , which displays a cyclopropylamine at position C20, showed a strikingly low IC50 value of 23 nm against HMLER CD24low/CD44high cells. This study provides highly selective molecules to target the CSC niche, a potential interesting advance for drug development to prevent cancer resistance. 相似文献
1000.
Natalia E. Moskaleva Pavel A. Markin Roman M. Kuznetsov Tatiana M. Andronova Svetlana A. Appolonova 《Biomedical chromatography : BMC》2020,34(12):e4948
GMDP (glucosoaminyl-muramyl-dipeptide), a synthetic analog of the peptidoglycan fragment of the bacterial cell wall, is an active component of the immunomodulatory drug Licopid. But the pharmacokinetic parameters of GMDP in humans after oral administration have not been investigated yet. The present study aimed at developing and validating a sensitive LC–MS/MS method for the analysis of GMDP in human plasma. The sample was prepared by solid-phase extraction using Strata-X 33 μm polymeric reversed-phase 60 mg/3 mL cartridges Phenomenex (Torrance, CA, USA). The analytes were separated using an Acquity UPLC BEN C18 column, 1.7 μm 2.1 × 50 mm Waters (Milford, USA). GMDP and internal standard growth hormone releasing peptide-2 (pralmorelin) were ionized in positive electrospray ionization mode and detected in multiple reaction monitoring mode. The developed method was validated within a linear range of 50–3000 pg/mL for GMDP. Accuracy for all analytes, given as the deviation between the nominal and measured concentration and assay variability , ranged from 1.61 to 3.02% and from 0.89 to 1.79%, respectively, for both within- and between-run variabilities. The developed and validated HPLC–MS/MS method was successfully used to obtain the plasma pharmacokinetic profiles of GMDP distribution in human plasma. 相似文献