全文获取类型
收费全文 | 841篇 |
免费 | 46篇 |
国内免费 | 26篇 |
专业分类
化学 | 482篇 |
晶体学 | 21篇 |
力学 | 42篇 |
综合类 | 1篇 |
数学 | 161篇 |
物理学 | 206篇 |
出版年
2023年 | 11篇 |
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 16篇 |
2019年 | 19篇 |
2018年 | 24篇 |
2017年 | 33篇 |
2016年 | 37篇 |
2015年 | 26篇 |
2014年 | 45篇 |
2013年 | 80篇 |
2012年 | 77篇 |
2011年 | 58篇 |
2010年 | 49篇 |
2009年 | 34篇 |
2008年 | 40篇 |
2007年 | 43篇 |
2006年 | 42篇 |
2005年 | 32篇 |
2004年 | 35篇 |
2003年 | 22篇 |
2002年 | 19篇 |
2001年 | 5篇 |
2000年 | 16篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 17篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1968年 | 1篇 |
1937年 | 2篇 |
排序方式: 共有913条查询结果,搜索用时 15 毫秒
111.
Vaden TD de Boer TS Simons JP Snoek LC Suhai S Paizs B 《The journal of physical chemistry. A》2008,112(20):4608-4616
The conformational structures of protonated polyalanine peptides, Ala(n)H(+), have been investigated in the gas phase for n = 3, 4, 5, and 7 using a combination of resonant-infrared multiphoton dissociation (R-IRMPD) spectroscopy in the NH and OH stretch regions and quantum chemical calculations. Agreement between theoretical IR and experimental R-IRMPD spectral features has enabled the assignment of specific hydrogen-bonded conformational motifs in the short protonated peptides and revealed their conformational evolution under elevated-temperature conditions, as a function of increasing chain length. The shortest peptide, Ala(3)H(+), adopts a mixture of extended and cyclic chain conformations, protonated, respectively, at a backbone carbonyl or the N-terminus. The longer peptides adopt folded, cyclic, and globular charge-solvated conformations protonated at the N-terminus, consistent with previous ion-mobility studies. The longest peptide, Ala(7)H(+), adopts a globular conformation with the N-terminus completely charge-solvated, demonstrating the emergence of "physiologically relevant" intramolecular interactions in the peptide backbone. The computed conformational relative free energies highlight the importance of entropic contributions in these peptides. 相似文献
112.
Machida S Usuba K Blaskovich MA Yano A Harada K Sebti SM Kato N Ohkanda J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(5):1392-1401
Synthetic chemical probes designed to simultaneously targeting multiple sites of protein surfaces are of interest owing to their potential application as site specific modulators of protein-protein interactions. A new approach toward bivalent inhibitors of mammalian type I geranylgeranyltransferase (GGTase I) based on module assembly for simultaneous recognition of both interior and exterior protein surfaces is reported. The inhibitors synthesized in this study consist of two modules linked by an alkyl spacer; one is the tetrapeptide CVIL module for binding to the interior protein surface (active pocket) and the other is a 3,4,5-alkoxy substituted benzoyl motif that contains three aminoalkyl groups designed to bind to the negatively charged protein exterior surface near the active site. The compounds were screened by two distinct enzyme inhibition assays based on fluorescence spectroscopy and incorporation of a [(3)H]-labeled prenyl group onto a protein substrate. The bivalent inhibitors block GGTase I enzymatic activity with K(i) values in the submicromolar range and are approximately one order of magnitude and more than 150 times more effective than the tetrapeptide CVIL and the methyl benzoate derivatives, respectively. The bivalent compounds 6 and 8 were shown to be competitive inhibitors, suggesting that the CVIL module anchors the whole molecule to the GGTase I active site and delivers the other module to the targeting protein surface. Thus, our module-assembly approach resulted in simultaneous multiple-site recognition, and as a consequence, synergetic inhibition of GGTase I activity, thereby providing a new approach in designing protein-surface-directed inhibitors for targeting protein-protein interactions. 相似文献
113.
114.
Shi FN Cunha-Silva L Ferreira RA Mafra L Trindade T Carlos LD Paz FA Rocha J 《Journal of the American Chemical Society》2008,130(1):150-167
Isostructural modular microporous Na2[Y(hedp)(H2O)0.67] and Na4[Ln2(hedp)2(H2O)2].nH2O (Ln = La, Ce, Nd, Eu, Gd, Tb, Er) framework-type, and layered orthorhombic [Eu(H2hedp)(H2O)2].H2O and Na0.9[Nd0.9Ge0.10(Hhedp)(H2O)2], monoclinic [Ln(H2hedp)(H2O)].3H2O (Ln = Y, Tb), and triclinic [Yb(H2hedp)].H2O coordination polymers based on etidronic acid (H5hedp) have been prepared by hydrothermal synthesis and characterized structurally by (among others) single-crystal and powder X-ray diffraction and solid-state NMR. The structure of the framework materials comprises eight-membered ring channels filled with Na+ and both free and lanthanide-coordinated water molecules, which are removed reversibly by calcination at 300 degrees C (structural integrity is preserved up to ca. 475 degrees C), denoting a clear zeolite-type behavior. Interesting photoluminescence properties, sensitive to the hydration degree, are reported for Na4[Eu2(hedp)2(H2O)2].H2O and its fully dehydrated form. The 3D framework and layered materials are, to a certain extent, interconvertable during the hydrothermal synthesis stage via the addition of HCl or NaCl: of the 3D framework Na4[Tb2(hedp)2(H2O)2].nH2O, affords layered [Tb(H2hedp) (H2O)].3H2O, whereas layered [Tb(H2hedp)(H2O)2].H2O reacts with sodium chloride yielding a material similar to Na4[Tb2(hedp)2(H2O)2].nH2O. In layered [Y(H2hedp)(H2O)].3H2O, noncoordinated water molecules are engaged in cooperative water-to-water hydrogen-bonding interactions, leading to the formation of a (H2O)13 cluster, which is the basis of an unprecedented two-dimensional water network present in the interlayer space. 相似文献
115.
Quan Huang Sa Li Prof. Yuqin Jiang Dr. Xiao-Feng Xia 《European journal of organic chemistry》2023,26(23):e202300266
Described herein is the development of a desaturation and N-β-nitration reaction of cyclic amides, which is achieved by a selective hydrogen atom transfer (HAT)/oxidative desaturation/electrophilic nitration process. In this procedure, di-tert-butyl peroxide (DTBP) acted both as the oxidant and HAT reagent, and electrophilic NOBF4 as nitration source. Notably, the application of produced cyclic nitroene-sulfonamides was showcased by their efficient transformations into 3-piperidones and poly-substituted piperidine derivatives. 相似文献
116.
Ying Liu Zhongrun Yuan Sa Liu Xiupeng Zhong Yanyan Wang Renjian Xie Wenjing Song Li Ren 《Macromolecular bioscience》2023,23(11):2300153
Hydrogels are extensively investigated as biomimetic extracellular matrix (ECM) scaffolds in tissue engineering. The physiological properties of ECM affect cellular behaviors, which is an inspiration for cell-based therapies. Photocurable hyaluronic acid (HA) hydrogel (AHAMA-PBA) modified with 3-aminophenylboronic acid, sodium periodate, and methacrylic anhydride simultaneously is constructed in this study. Chondrocytes are then cultured on the surface of the hydrogels to evaluate the effect of the physicochemical properties of the hydrogels on modulating cellular behaviors. Cell viability assays demonstrate that the hydrogel is non-toxic to chondrocytes. The existence of phenylboronic acid (PBA) moieties enhances the interaction of chondrocytes and hydrogel, promoting cell adhesion and aggregation through filopodia. RT-PCR indicates that the gene expression levels of type II collagen, Aggrecan, and Sox9 are significantly up-regulated in chondrocytes cultured on hydrogels. Moreover, the mechanical properties of the hydrogels have a significant effect on the cell phenotype, with soft gels (≈2 kPa) promoting chondrocytes to exhibit a hyaline phenotype. Overall, PBA-functionalized HA hydrogel with low stiffness exhibits the best effect on promoting the chondrocyte phenotype, which is a promising biomaterial for cartilage regeneration. 相似文献
117.
A Variety of Phase‐Transition Behaviors in a Niccolite Series of [NH3(CH2)4NH3][M(HCOO)3]2 下载免费PDF全文
Ran Shang Sa Chen Ke‐Li Hu Prof. Bing‐Wu Wang Prof. Zhe‐Ming Wang Prof. Song Gao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(18):6199-6203
A niccolite series of [bnH22+][M(HCOO)3]2 (bnH22+=1,4‐butyldiammonium) shows four kinds of metal‐dependent phase transitions, from high temperature para‐electric phases to low‐temperature ferro‐, antiferro‐, glass‐like, and para‐electric phases. The conformational flexibility of bnH22+ and the different size, mass, and bonding character of the metal ion lead to various disorder‐order transitions of bnH22+ in the lattice and relevant framework modulations, thus different phase transitions and dielectric responses. The magnetic members display a coexistence or combination of electric and magnetic orderings in the low‐temperature region. 相似文献
118.
119.
The first hyperpolarizability of two tungsten-carbonyl complexes, tungsten pentacarbonyl pyridine and tungsten pentacarbonyl trans-1,2-bis(4-pyridyl)-ethylene, has been studied by the high-level TDDFT method. The consideration of the solvent effect and intermolecular pi-pi weak interaction in the calculations quantitatively improve the final result of both the electronic excitations and the first hyperpolarizabilities. By using the orbital decomposition scheme (J. Phys. Chem. A 2006, 110, 1014-1021), the NLO mechanisms of these two complexes have been ascribed to the dominant contribution from the metal-to-ligand charge transfer, with HOMO --> LUMO character, and the indispensable contribution from the intraligand charge transfer as well. A supplementary formula has been proposed to implement the orbital-pair transition analysis. This study reports the significant influences of solvation and intermolecular interactions on the first hyperpolarizabilities of organometallic NLO chromophores. 相似文献
120.
Sañudo EC Muryn CA Helliwell MA Timco GA Wernsdorfer W Winpenny RE 《Chemical communications (Cambridge, England)》2007,(8):801-803
Cyclic octanuclear complexes, each containing seven group 13 metals and one d-block metal are reported and preliminary physical characterisation of the compounds discussed. 相似文献