全文获取类型
收费全文 | 4956篇 |
免费 | 121篇 |
国内免费 | 11篇 |
专业分类
化学 | 2901篇 |
晶体学 | 100篇 |
力学 | 167篇 |
综合类 | 1篇 |
数学 | 393篇 |
物理学 | 1526篇 |
出版年
2023年 | 29篇 |
2022年 | 56篇 |
2021年 | 45篇 |
2020年 | 71篇 |
2019年 | 77篇 |
2018年 | 71篇 |
2017年 | 64篇 |
2016年 | 143篇 |
2015年 | 84篇 |
2014年 | 132篇 |
2013年 | 294篇 |
2012年 | 272篇 |
2011年 | 355篇 |
2010年 | 231篇 |
2009年 | 203篇 |
2008年 | 275篇 |
2007年 | 317篇 |
2006年 | 249篇 |
2005年 | 224篇 |
2004年 | 171篇 |
2003年 | 152篇 |
2002年 | 117篇 |
2001年 | 71篇 |
2000年 | 59篇 |
1999年 | 55篇 |
1998年 | 41篇 |
1997年 | 46篇 |
1996年 | 55篇 |
1995年 | 60篇 |
1994年 | 44篇 |
1993年 | 53篇 |
1992年 | 45篇 |
1991年 | 39篇 |
1990年 | 41篇 |
1989年 | 39篇 |
1988年 | 36篇 |
1987年 | 42篇 |
1986年 | 46篇 |
1985年 | 65篇 |
1984年 | 41篇 |
1983年 | 32篇 |
1982年 | 58篇 |
1981年 | 59篇 |
1980年 | 32篇 |
1979年 | 42篇 |
1978年 | 37篇 |
1976年 | 29篇 |
1975年 | 30篇 |
1974年 | 33篇 |
1973年 | 30篇 |
排序方式: 共有5088条查询结果,搜索用时 828 毫秒
991.
Radical benzenoid structures, i.e., those which cannot have all electrons paired, are known to possess much larger structure counts than closed-shell benzenoids of similar size. Building on our previous work, we report methods for calculating eigenvectors, eigenvalues, and structure counts for benzenoid radicals, diradicals, and radicals of higher multiplicity. When a series of such species is constructed by repeated addition of an aufbau unit, structure counts can usually be expressed as a polynomial in one or two variables. Structure counts for radical series generated by repeated circumscribing, however, cannot. 相似文献
992.
Ali Mohammad Akbar Mirza Aminul H. Butcher Ray J. Rahman Mizanur 《Transition Metal Chemistry》2000,25(4):430-436
New complexes of general empirical formula, [M(NS)2] · nCHCl3 (M = NiII, CuII, PdII or PtII; NS = anionic form of the thiophene-2-aldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazate; n = 0, 1) have been synthesized and characterized by physico-chemical techniques. Magnetic and spectroscopic evidence support
a square-planar structure for these complexes. The crystal structures of the [Ni(tasbz)2] and [Cu(tasbz)2] · CHCl3 complexes (tasbz = anionic form of the thiophene-2-aldehyde Schiff base of S-benzyldithiocarbazate) have been determined by X-ray diffraction. Both complexes have a trans-planar structure in which the two Schiff base ligands are coordinated to the metal(II) ion as uninegatively charged bidentate
ligands via the thiolate sulfur and the azomethine nitrogen atoms.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
993.
Steady two-dimensional stagnation-point flow of an electrically conducting power-law fluid over a stretching surface is investigated when the surface is stretched in its own plane with a velocity proportional to the distance from the stagnation-point. We have discussed the uniqueness of the solution except when the ratio of free stream velocity and stretching velocity is equal to 1. The effect of magnetic field on the flow characteristic is explored numerically and it is concluded that the velocity at a point decreases/increases with increase in the magnetic field when the free stream velocity is less/greater than the stretching velocity. It is further observed that for a given value of magnetic parameter M, the dimensionless shear stress coefficient |F″(0)| increases with increase in power-law index n when the value of the ratio of free stream velocity and stretching velocity is close to 1 but not equal to 1. But when the value of this ratio further differs from 1, the variation of |F″(0)| with n is non-monotonic. 相似文献
994.
This paper focuses on a variational formulation for a magneto-active elastomer completely surrounded by free space. The free space is considered infinite, with an applied magnetic field or magnetic induction vector as the far field boundary conditions. In addition to the effect of the Maxwell stress exterior to the body on its surface, a mechanical load is applied over a portion of the surface, but no displacement constraints are considered. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
995.
Ashley J. Locke Wayde N. Martens Ray L. Frost 《Journal of Raman spectroscopy : JRS》2007,38(11):1429-1435
Raman spectroscopy has been used to characterise four natural halotrichites: halotrichite FeSO4.Al2(SO4)3. 22H2O, apjohnite MnSO4.Al2(SO4)3.22H2O, pickingerite MgSO4.Al2(SO4)3.22H2O and wupatkiite CoSO4.Al2(SO4)3.22H2O. A comparison of the Raman spectra is made with the spectra of the equivalent synthetic pseudo‐alums. Energy dispersive X‐ray analysis (EDX) was used to determine the exact composition of the minerals. The Raman spectrum of apjohnite and halotrichite display intense symmetric bands at ∼985 cm−1 assigned to the ν1(SO4)2− symmetric stretching mode. For pickingerite and wupatkiite, an intense band at ∼995 cm−1 is observed. A second band is observed for these minerals at 976 cm−1 attributed to a water librational mode The series of bands for apjohnite at 1104, 1078 and 1054 cm−1, for halotrichite at 1106, 1072 and 1049 cm−1, for pickingerite at 1106, 1070 and 1049 cm−1 and for wupatkiite at 1106, 1075 and 1049 cm−1 are attributed to the ν3(SO4)2− antisymmetric stretching modes of ν3(Bg) SO4. Raman bands at around 474, 460 and 423 cm−1 are attributed to the ν2(Ag) SO4 mode. The band at 618 cm−1 is assigned to the ν4(Bg) SO4 mode. The splitting of the ν2, ν3 and ν4 modes is attributed to the reduction of symmetry of the SO4 and it is proposed that the sulphate coordinates to water in the hydrated aluminium in bidentate chelation. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
996.
Raman spectroscopy complemented with infrared spectroscopy has been used to study a series of selected natural halogenated carbonates from different origins, including bastnasite, parisite and northupite. The position of CO32− symmetric stretching vibration varies with the mineral composition. An additional band for northupite at 1107 cm−1 is observed. Raman spectra of bastnasite, parisite and northupite show single bands at 1433, 1420 and 1554 cm−1, respectively, assigned to the ν3 (CO3)2− asymmetric stretching mode. The observation of additional Raman bands for the ν3 modes for some halogenated carbonates is significant in that it shows distortion of the CaO6 octahedron. No ν2 Raman bending modes are observed for these minerals. The band is observed in the infrared spectra, and multiple ν2 modes at 844 and 867 cm−1 are observed for parisite. A single intense infrared band is found at 879 cm−1 for northupite. Raman bands are observed forthe carbonate ν4 in‐phase bending modes at 722 cm−1 for bastnasite, 736 and 684 cm−1 for parisite and 714 cm−1 for northupite. Multiple bands are observed in the OH stretching region for selected bastansites and parisites, indicating the presence of water and OH units in the mineral structure. The presence of such bands brings into question the actual formula of these halogenated carbonate minerals. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
997.
Summary: This communication describes the effect of organic modifier miscibility with the matrices, and the effect of the initial interlayer spacing of the organoclay, on the overall morphology and properties of an immiscible polycarbonate/poly(methyl methacrylate) blend. By varying the organic‐modifier‐specific interactions with the blend matrices at the same time as changing the initial interlayer spacing of the organoclay, different levels of compatibilization were revealed. The evidence for the interfacial compatibilization of the organoclay was assessed by scanning electron microscopy observations and was supported by differential scanning calorimetry analyses. The effect on the level of clay exfoliation was also examined.
998.
Kamlakar Avasthi Sangeeta Aswal Prakas R. Maulik 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(11):1324-1325
In the crystal structure of 1,1′-(1,3-propanediyl)bis(5-ethyl-6-methylthio-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-4-one), C19H24N8O2S2, the pairs of pyrazolo[3,4-d]pyrimidine rings of the molecule stack between the heterocyclic rings, due to intramolecular π–π interactions. The substituted ethyl and methyl groups are comparable as far as intramolecular stacking is concerned. 相似文献
999.
1000.
Quentin Coquerel Claire Legendre Jacinthe Frangieh Stephan De Waard Jrme Montnach Leos Cmarko Joseph Khoury Charifat Said Hassane Dimitri Brard Benjamin Siegler Ziad Fajloun Harold De Pomyers Kamel Mabrouk Norbert Weiss Daniel Henrion Pascal Richomme Csar Mattei Michel De Waard Anne-Marie Le Ray Christian Legros 《Molecules (Basel, Switzerland)》2022,27(13)
Voltage-gated Na+ (NaV) channels are significant therapeutic targets for the treatment of cardiac and neurological disorders, thus promoting the search for novel NaV channel ligands. With the objective of discovering new blockers of NaV channel ligands, we screened an In-House vegetal alkaloid library using fluorescence cell-based assays. We screened 62 isoquinoline alkaloids (IA) for their ability to decrease the FRET signal of voltage sensor probes (VSP), which were induced by the activation of NaV channels with batrachotoxin (BTX) in GH3b6 cells. This led to the selection of five IA: liriodenine, oxostephanine, thalmiculine, protopine, and bebeerine, inhibiting the BTX-induced VSP signal with micromolar IC50. These five alkaloids were then assayed using the Na+ fluorescent probe ANG-2 and the patch-clamp technique. Only oxostephanine and liriodenine were able to inhibit the BTX-induced ANG-2 signal in HEK293-hNaV1.3 cells. Indeed, liriodenine and oxostephanine decreased the effects of BTX on Na+ currents elicited by the hNaV1.3 channel, suggesting that conformation change induced by BTX binding could induce a bias in fluorescent assays. However, among the five IA selected in the VSP assay, only bebeerine exhibited strong inhibitory effects against Na+ currents elicited by the hNav1.2 and hNav1.6 channels, with IC50 values below 10 µM. So far, bebeerine is the first BBIQ to have been reported to block NaV channels, with promising therapeutical applications. 相似文献