全文获取类型
收费全文 | 2787篇 |
免费 | 188篇 |
国内免费 | 235篇 |
专业分类
化学 | 1330篇 |
晶体学 | 38篇 |
力学 | 328篇 |
综合类 | 7篇 |
数学 | 592篇 |
物理学 | 915篇 |
出版年
2024年 | 2篇 |
2023年 | 73篇 |
2022年 | 58篇 |
2021年 | 73篇 |
2020年 | 101篇 |
2019年 | 82篇 |
2018年 | 79篇 |
2017年 | 87篇 |
2016年 | 97篇 |
2015年 | 70篇 |
2014年 | 154篇 |
2013年 | 199篇 |
2012年 | 161篇 |
2011年 | 220篇 |
2010年 | 129篇 |
2009年 | 162篇 |
2008年 | 184篇 |
2007年 | 182篇 |
2006年 | 148篇 |
2005年 | 102篇 |
2004年 | 115篇 |
2003年 | 86篇 |
2002年 | 58篇 |
2001年 | 69篇 |
2000年 | 63篇 |
1999年 | 63篇 |
1998年 | 72篇 |
1997年 | 55篇 |
1996年 | 39篇 |
1995年 | 40篇 |
1994年 | 30篇 |
1993年 | 32篇 |
1992年 | 24篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有3210条查询结果,搜索用时 31 毫秒
991.
Yong Li Tao Pang Junli Shi Xiuping Lu Jianhua Deng Qian Lin 《Journal of separation science》2014,37(21):3067-3073
Plant flavonoids are very important secondary metabolites for insect and virus control of their host plant and are potent nutrients for humans. To be able to understand the bioavailability and functions of plant flavonoids, it is necessary to reveal their exact chemical structures. Liquid chromatography with tandem mass spectrometry is a powerful approach for structural elucidation of metabolites. In this report, a two‐step precursor ion scanning based liquid chromatography with tandem mass spectrometry method was developed for the structural elucidation of plant flavonoids. The established method consists of the two‐step precursor ions scanning for possible flavonoids extraction, MS2 fragment spectra acquisition and comparison with an online database, liquid chromatography retention rules correction, and commercial standards verification. The developed method was used for the structure elucidation of flavonoids in flowers and leaves of tobacco (Nicotiana tabacum), and 17 flavonoids were identified in the tobacco variety Yunyan 97. Nine of the 17 identified flavonoids were considered to be found in tobacco flowers or/and leaves for the first time based on the available references. This method was proved to be very effective and can be used for the identification of flavonoids in other plants. 相似文献
992.
Stabilization of Human Telomeric G‐Quadruplex and Inhibition of Telomerase Activity by Propeller‐Shaped Trinuclear PtII Complexes 下载免费PDF全文
Cui‐Xia Xu Yong Shen Qian Hu Yu‐Xuan Zheng Qian Cao Prof. Peter Z. Qin Prof. Yong Zhao Prof. Liang‐Nian Ji Prof. Zong‐Wan Mao 《化学:亚洲杂志》2014,9(9):2519-2526
Two novel propeller‐shaped, trigeminal‐ligand‐containing, flexible trinuclear PtII complexes, {[Pt(dien)]3(ptp)}(NO3)6 ( 1 ) and {[Pt(dpa)]3(ptp)}(NO3)6 ( 2 ) (dien: diethylenetriamine; dpa: bis‐(2‐pyridylmethyl)amine; ptp: 6′‐(pyridin‐3‐yl)‐3,2′:4′,3′′‐terpyridine), have been designed and synthesized, and their interactions with G‐quadruplex (G4) sequences are characterized. A combination of biophysical and biochemical assays reveals that both PtII complexes exhibit higher affinity for human telomeric (hTel) and c‐myc promoter G4 sequences than duplex DNA. Complex 1 binds and stabilizes hTel G4 sequence more effectively than complex 2 . Both complexes are found to induce and stabilize either antiparallel or parallel conformation of G4 structures. Molecular docking studies indicate that complex 1 binds into the large groove of the antiparallel hTel G4 structure (PDB ID: 143D) and complex 2 stacks onto the exposed G‐quartet of the parallel hTel G4 structure (PDB ID: 1KF1). Telomeric repeat amplification protocol assays demonstrate that both complexes are good telomerase inhibitors, with IC50 values of (16.0±0.4) μM and (4.20±0.25) μM for 1 and 2 , respectively. Collectively, the results suggest that these propeller‐shaped flexible trinuclear PtII complexes are effective and selective G4 binders and good telomerase inhibitors. This work provides valuable information for the interaction between multinuclear metal complexes with G4 DNA. 相似文献
993.
Spherical photonic crystals (PCs), generated by assembly of monodisperse colloidal nanospheres in a spherical confined geometry, attract great attention recently owing to their potential applications in the fields of displays, sensors, optoelectronic devices, and others. Compared to their conventional film or bulk counterparts, the optical stop band of the spherical PCs is independent of the rotation under illumination of the surface of a fixed incident angle of the light, broadening their applications. In this paper, we will review recent advances in the field of spherical PCs including design, preparation and potential applications. Various preparation strategies for spherical PCs, including solvent-evaporation induced crystallization method, microfluidic-assisted approach, and others are outlined. Their applications based on the unique optical properties (such as photonic band gaps and structural colors) for sensing and displaying are then presented, followed by the perspective of this emerging field. 相似文献
994.
Alex Viguerie Mengying Xiao 《Numerical Methods for Partial Differential Equations》2019,35(2):805-829
This paper continues some recent work on the numerical solution of the steady incompressible Navier–Stokes equations. We present a new method, similar to the one presented in Rebholz et al., but with superior convergence and numerical properties. The method is efficient as it allows one to solve the same symmetric positive‐definite system for the pressure at each iteration, allowing for the simple preconditioning and the reuse of preconditioners. We also demonstrate how one can replace the Schur complement system with a diagonal matrix inversion while maintaining accuracy and convergence, at a small fraction of the numerical cost. Convergence is analyzed for Newton and Picard‐type algorithms, as well as for the Schur complement approximation. 相似文献
995.
E. Banu Altinta Soner Kili 《Journal of polymer science. Part A, Polymer chemistry》2004,42(15):3708-3719
Secondary‐amine‐functional microparticles were prepared in the range of 50–250 μm through the suspension polymerization of styrene, divinylbenzene (DVB), and 2‐(tert‐butylamino)ethyl methacrylate (tBAEMA). This study focused on the effects of the DVB, tBAEMA, initiator, and stabilizer concentrations and shaking rate on the experimental amine content, swelling ratio, average particle size, and particle size distribution. The suspension polymerization experiments were carried out in two different systems. In the first system, an organic phase, including the monomers and initiator, was dispersed in an aqueous medium in the presence of Al2(SO4)3. Al2(SO4)3, in the presence of an amine monomer (pH ~ 10), formed colloidal Al(OH)3, which built a nonsticky layer on the surface of the polymerizing droplets that prevented them from coalescing and aggregating. Individual and spherical particles within the range of 50–200 μm were obtained by this polymerization method. The second method was similar to the first polymerization protocol, except that a certain amount of sodium dodecyl sulfate was added as a costabilizer in the presence of Al2(SO4)3. In these experiments, individual and spherical particles were obtained within the range of 130–250 μm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem: 3708–3719, 2004 相似文献
996.
Akhlesh Lakhtakia 《Optics Communications》2007,275(2):283-287
The insertion of a structurally chiral layer defect between two identical chiral mirrors, made of periodic structurally chiral materials such as chiral liquid crystals and chiral sculptured thin films, generates two different types of spectral holes, depending on the thicknesses of the chiral mirrors and the central layer defect. 相似文献
997.
Mannar R. Maurya 《Journal of Chemical Sciences》2006,118(6):503-511
Vanadium(V) complexes with hydrazone-based ONO and ONN donor ligands that partly model active-site structures of vanadate-dependent
haloperoxidases have been reported. On reaction with [VO(acac)2] (Hacac = acetylacetone) under nitrogen, these ligands generally provide oxovanadium(IV) complexes [VO(ONO)X] (X = solvent
or nothing) and [VO(acac)(ONN)], respectively. Under aerobic conditions, these oxovanadium(IV) species undergo oxidation to
give oxovanadium(V), dioxovanadium (V) or μ-oxobisoxovanadium(V) species depending upon the nature of the ligand. Anionic
and neutral dioxovanadium(V) complexes slowly deoxygenate in methanol to give monooxo complexes [VO(OMe)(MeOH)(ONO)]. The
anionic complexes [VO2(ONO)]- can also be convertedin situ on acidification to oxohydroxo complexes [VO(OH)(HONO)]+ and to peroxo complexes [VO(O2)(ONO)]-, and thus to the species assumed to be intermediates in the haloperoxidases activity of the enzymes. In the presence of catechol
(H2cat) and benzohydroxamic acid (H2bha), oxovanadium (IV) complexes, [VO (acac)(ONN)] gave mixed-chelate oxovanadium(V) complexes [VO(cat)(ONN)] and [VO(bha)(ONN)]
respectively. These complexes are not very stable in solution and slowly convert to the corresponding dioxo species [VO2(ONN)] as observed by51V NMR and electronic absorption spectroscopic studies. 相似文献
998.
P. D. Panagiotopoulos 《Meccanica》1992,27(1):25-33
The present paper presents several new applications of the theory of fractals in structural mechanics. Until now most of the existing applications of the theory of fractals concern the calculation of fractal dimensions in physical phenomena, especially with respect to dynamical systems. The present paper deals with several other aspects of the theory of fractals which, from the standpoint of mechanics, seem to be of greater importance. Indeed the methods of fractal analysis permit the formulation and solution of difficult or yet unsolved mechanical problems or their treatment from an entirely new point of view. This paper is a first attempt towards this direction.A first version of this paper was presented at the International Meeting New Developments in Structural Mechanics in Catania, Italy, 4–6 July 1990. The meeting was dedicated to the memory of Professor Manfredi Romano. 相似文献
999.
Modal analysis as a diagnostic tool in structural mechanics is gaining popularity, but its use requires some caution. Here we discuss two applications of an identification technique, based on the measurement of the eigenfrequencies only, to steel beams under various damage conditions.
Sommario L' analisi modale come strumento diagnostico in meccanica delle strutture ha suscitato crescente interesse in anni recenti, ma il suo impiego pratico presenta ancora aspetti delicati. Qui si discutono due applicazioni su travi in acciaio sotto varie condizioni di danneggiamento in cui l' analisi e' fatta sulla base delle sole frequenze proprie.相似文献
1000.
A structural investigation on single crystals of MyMo6Se8 Chevrel phases (M=3d: Ti, Fe, and Co) has been carried out. These latter compounds as well as others with Cr, Mn, and Ni atoms make part of a new original family of Chevrel phases. The M ions occupy new interstices in the tridimensional channels network never observed in the other classical Chevrel phases as Liy, Cuy Mo6X8. They occupy only cavity 2 centered on
and with a progressive delocalization of the M cation versus the nature of the cation from the center of the cavity to the outside . The position in cavity 2 is different from the position of the Cu (2) atoms, the second position of the copper atoms in the channels of the CuyMo6X8 compounds. This new position reinforces the interaction with the Mo6 cluster, and may be able to involve new remarkable physical properties as thermoelectric properties. 相似文献