全文获取类型
收费全文 | 2223篇 |
免费 | 370篇 |
国内免费 | 107篇 |
专业分类
化学 | 512篇 |
晶体学 | 50篇 |
力学 | 304篇 |
综合类 | 3篇 |
数学 | 68篇 |
物理学 | 1224篇 |
综合类 | 539篇 |
出版年
2024年 | 2篇 |
2023年 | 20篇 |
2022年 | 40篇 |
2021年 | 54篇 |
2020年 | 75篇 |
2019年 | 52篇 |
2018年 | 59篇 |
2017年 | 64篇 |
2016年 | 99篇 |
2015年 | 69篇 |
2014年 | 90篇 |
2013年 | 185篇 |
2012年 | 155篇 |
2011年 | 176篇 |
2010年 | 100篇 |
2009年 | 130篇 |
2008年 | 107篇 |
2007年 | 115篇 |
2006年 | 116篇 |
2005年 | 114篇 |
2004年 | 98篇 |
2003年 | 89篇 |
2002年 | 93篇 |
2001年 | 75篇 |
2000年 | 77篇 |
1999年 | 72篇 |
1998年 | 67篇 |
1997年 | 63篇 |
1996年 | 38篇 |
1995年 | 26篇 |
1994年 | 28篇 |
1993年 | 31篇 |
1992年 | 23篇 |
1991年 | 18篇 |
1990年 | 27篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有2700条查询结果,搜索用时 15 毫秒
31.
Micelles of different amphiphiles adopt different shapes and internal packing arrangements in water, depending on their chemical
structures and the conditions of the medium. Two microenvironmental features, namely the polarity and the microviscosity that
the aggregate offers to a solubilized molecule, have been monitored using extrinsic fluorescence probes. While the differences
between micelles of spherical and rod-like shapes are not always distinct, stacked micelles and peptide micelles offer distinctly
lower polarity and higher microviscosity to solubilizates than the others. 相似文献
32.
The d. c. component of birefringence of aqueous carboxymethylcellulose (CMC) under an a. c. electric field was measured at frequencies ranging from 0.1 Hz to 100 kHz. Three samples of different molecular weights were studied with varying degree of neutralization, polymer concentration and added salt concentration. The dispersion curve of birefringence consists of three relaxation bands,A, B andC in order of decreasing frequency. RelaxationB with a negative relaxation strength is ascribed to end-over-end rotation of almost rodlike CMC molecules. RelaxationA with a positive strength is attributed to the relaxation of electrical polarizability along the minor axis of molecule. RelaxationC possesses also a positive strength and is induced by clusters of CMC molecules.Dedicated to Prof. Dr. F. H. Müller. 相似文献
33.
An equation for determining the equilibrium association constant (KA) of cyclodextrin inclusion complex with fluorescence anisotropy is derived and used to determine KA of pyrene-B-cyclodextrin inclusion complex. The existing forms of cyclodextrin inclusion complex in solution, the interaction type of host with guest, and the possibility of application of B-cyclodextrin in the analysis of metal ions using naphthalene derivative as a ligand are discussed based on the equation derived along with the curve of fluorescence anisotropy versus cyclodextrin concentration of guest/cyclodextrin system. 相似文献
34.
Robert S. Walters 《Tetrahedron letters》2005,46(38):6487-6489
2′,3′,4′,5′,6′,7′-Hexahydrodispiro[cyclopropane-1,1′-anthracene-8′,1″-cyclopropane] (1) was prepared by double olefination (Wittig) and double methylenation (Furukawa) of 1,8-dioxo-1,2,3,4,5,6,7,8-octahydroanthracene (4) that was in turn prepared in two steps from 1,3-dibromobenzene. The X-ray structure of 1 shows that the C-9-H of its anthracene core is located 2.6 Å from the centroids of each of the flanking cyclopropane rings. The 1H NMR spectrum of 1 shows that the C-9-H resonance (δ 5.95) falls 0.84 ppm upfield from the C-10-H resonance (δ 6.79). 相似文献
35.
In this review, we summarize the number of scientific publications in the field of FP/FA sensor in recent five years, and introduce the recent progress of FP/FA sensor based on nanomaterial. The various analytical applications of FP/FA sensor based on nanomaterial are discussed. We also provide perspectives on the current challenges and future prospects in the promising field. 相似文献
36.
A series of dilute liquid crystalline solvents are used to study the effect of slight anisotropy caused by partial alignment on chemical shift and residual dipolar coupling (RDC) in small molecules. The residual dipolar couplings between protons in solutes are found to be almost independent of the local environment. It is also found that the chemical shift does not change over the concentration range observed. A linear relationship between residual dipolar coupling and liquid crystal concentration is observed at relatively low concentrations, but is severely violated at high concentrations. 相似文献
37.
Chelsea N. Widener Alexandria N. Bone Mykhaylo Ozerov Rachael Richardson 路正光 Komalavalli Thirunavukkuarasu Dmitry Smirnov 陈学太 薛子陵 《无机化学学报》2020,36(6):1149-1156
最近Ruamps和同事发现三角双锥构型的Ni(Ⅱ)配合物[Ni(Me6tren)Cl]ClO4(1,Me6tren=tris(2-(dimethylamino)ethyl)amine)具有大的单轴磁各向异性(J.Am.Chem.Soc.,2013,135:3017-3026)。他们利用HF-EPR研究获得横向零场分裂(ZFS)参数E=1.56(5)cm-1但未能确定轴向零场分裂参数D。在本工作中,我们利用0~17.5 T和5 K的变磁场远红外光谱(FIRMS)来检测自旋基态S=1中的MS=±1和MS=0态之间的磁跃迁。在FIRMS中直接观察到Zeeman分裂态之间的跃迁,得出轴向ZFS参数D=-110.7(3)cm-1。我们对1的晶体结构进行了Hirshfeld表面分析,揭示了1分子中的阳离子与阴离子之间以及分子之间的相互作用。 相似文献
38.
The effect of nonradiative reverse energy transport (NRET) in two donor-acceptor systems was studied experimentally. It was found that the NRET occurring in system I; rhodamine 6G (donor) and rhodamine B (acceptor), considerably lowers the emission anisotropy at medium and high concentrations. These results qualitatively confirm the predictions of the approximate theoretical approach of L. Kulak and C. Bojarski (see the preceding paper). In system II; rhodamine 6G (donor) and Nile Blue (acceptor), for which the NRET process does not occur, a good agreement with no-back-transport theory was obtained. 相似文献
39.
A. A. Isaeva A. I. Baranov Th. Doert M. Ruck V. A. Kulbachinskii R. A. Lunin B. A. Popovkin 《Russian Chemical Bulletin》2007,56(9):1694-1700
New metal-rich mixed nickel-silicon and nickel-germanium chalcogenides, Ni5.68SiSe2, Ni5.46GeSe2, and Ni5.42GeTe2, were synthesized by high-temperature ceramic techniques. The X-ray diffraction study of single crystals grown from a molten
flux revealed that the compounds are isostructural and crystallize in the tetragonal system (space group I4/mmm, Z = 2). These compounds are the first members of the family of M7−δEX2-type (M = Ni or Pd; E = Sn or Sb; X is chalcogen) intergrowth structures containing “light” p elements E. Resistivity measurements on pressed textured pellets showed that both selenides are anisotropic metallic conductors
in the directions parallel and perpendicular to the heterometallic bond systems. The geometric criteria of stability of the
intergrowth structure type under consideration are discussed.
Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1632–1638, September, 2007. 相似文献
40.
Marvaud V Decroix C Scuiller A Tuyèras F Guyard-Duhayon C Vaissermann J Marrot J Gonnet F Verdaguer M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(8):1692-1705
Following a bottom-up approach to nanomaterials, we present a rational synthetic route to high-spin and anisotropic molecules based on hexacyanometalate [M(CN)(6)](3-) cores. Part 1 of this series was devoted to isotropic heptanuclear clusters; herein, we discuss the nuclearity and the structural anisotropy of nickel(II) derivatives. By changing either the stoichiometry, the nature of the terminal ligand, or the counterion, it is possible to tune the nuclearity of the polynuclear compounds and therefore to control the structural anisotropy. We present the synthesis and the characterisation by mass spectrometry, X-ray crystallography and magnetic susceptibility of bi-, tri-, tetra-, hexa- and heptanuclear species [M(CN)(n)(CN-M'L)(6-n)](m+) (with n=0-5; M=Cr(III), Co(III), M'=Ni(II); L=pentadentate ligand). Thus, with M=Cr(III), d(3), S=3/2, a dinuclear complex [Cr(III)(CN)(5)(CN-NiL(n))](9+), (L(n)=polydentate ligand) was built and characterised, showing a spin ground state, S(G)=5/2, with a ferromagnetic interaction J(Cr,Cu)=+18.5 cm(-1). With M=Co(III) (d(6), S=0) were built di-, tri-, tetra-, hexa and hepanuclear CoNi species: CoNi, CoNi(2), CoNi(3), CoNi(5) and CoNi(6). By a first approximation, they behave as one, two, three, five and six isolated nickel(II) complexes, respectively, but more accurate studies allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'-Co-M'. 相似文献