全文获取类型
收费全文 | 9744篇 |
免费 | 684篇 |
国内免费 | 1009篇 |
专业分类
化学 | 4907篇 |
晶体学 | 127篇 |
力学 | 475篇 |
综合类 | 89篇 |
数学 | 549篇 |
物理学 | 1219篇 |
综合类 | 4071篇 |
出版年
2024年 | 24篇 |
2023年 | 90篇 |
2022年 | 168篇 |
2021年 | 173篇 |
2020年 | 248篇 |
2019年 | 234篇 |
2018年 | 204篇 |
2017年 | 343篇 |
2016年 | 348篇 |
2015年 | 309篇 |
2014年 | 413篇 |
2013年 | 593篇 |
2012年 | 602篇 |
2011年 | 533篇 |
2010年 | 392篇 |
2009年 | 514篇 |
2008年 | 557篇 |
2007年 | 608篇 |
2006年 | 603篇 |
2005年 | 563篇 |
2004年 | 536篇 |
2003年 | 442篇 |
2002年 | 414篇 |
2001年 | 354篇 |
2000年 | 280篇 |
1999年 | 287篇 |
1998年 | 229篇 |
1997年 | 204篇 |
1996年 | 182篇 |
1995年 | 171篇 |
1994年 | 160篇 |
1993年 | 140篇 |
1992年 | 112篇 |
1991年 | 99篇 |
1990年 | 84篇 |
1989年 | 67篇 |
1988年 | 48篇 |
1987年 | 29篇 |
1986年 | 17篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1974年 | 2篇 |
1955年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
1.
Two new divalent copper (C1) and zinc (C2) chelates having the formulae [M(PIMC)2] (where M = Cu(II), Zn(II) and PIMC = Ligand [(E)-3-(((3-hydroxypyridin-2-yl)imino)methyl)-4H-chromen-4-one] were obtained and characterized by several techniques. Structures and geometries of the synthesized complexes were judged based on the results of alternative analytical and spectral tools supporting the proposed formulae. IR spectral data confirmed the coordination of the ligands to the copper and zinc centers as monobasic tridentate in the enol form. Thermal analysis, UV-Vis spectra and magnetic moment confirmed the geometry around the copper center to be tetrahedral, square pyramidal and octahedral. Study of the binding ability of the synthesized compounds with Circulating tumor DNA (CT-DNA) bas been evaluated applying UV-Vis spectral titration and viscosity measurements. The copper and zinc oxides were achieved from the copper and zinc nano-particles structures Schiff base complexes as the raw material after calcination for 5 hr at 600°C. On the other hand, synthesized of C1 and C2 NPs were used as suitable precursors to the preparation of CuO and ZnO NPs. Finally, the synthesized of the two complexes exhibited enhanced activity against the tested bacterial (Staphylococcus aureus and Escherichia Coli) and fungal strains (Candida albicans and Aspergillus fumigatus) as compared to HPIMC. Among all these synthesized compounds, C1 exhibits good cleaving ability compared to other newly synthesized C2. 相似文献
2.
Lisa Lorentzen 《Numerical Algorithms》1995,10(1):69-111
Over the last 20 years a large number of algorithms has been published to improve the speed and domain of convergence of continued fractions. In this survey we show that these algorithms are strongly related. Actually, they essentially boil down to two main principles.We also prove some results on asymptotic expansions of tail values of limit periodic continued fractions.Dedicated to Luigi Gatteschi on his seventieth birthdayThis research was partially supported by The Norwegian Research Council and by the HMC project ROLLS, under contract CHRX-CT93-0416. 相似文献
3.
研究了RE_Mg合金对固体粉末法硼、铬、铝共渗层成分、组织和性能的影响 .发现随着RE_Mg合金加入量的增加 ,渗层中Al2 O3的量不断增多 ,当RE_Mg合金加入量为 5 %时 ,渗层中出现连续致密分布的Al2 O3黑区组织 ,对此进行了性能测试和机理探讨 相似文献
4.
5.
A. D. Matveev 《Journal of Applied Mechanics and Technical Physics》2003,44(5):721-726
Modified three-dimensional formulations of bending problems of homogeneous elastic plates and beams are considered. Modification of the known three-dimensional formulations reduces to using additional constraints imposed on displacement functions. An advantage of the formulations proposed is that complex fixing conditions of plates and beams can be taken into account. 相似文献
6.
A new electroactive polynuclear inorganic compound of rare earth metal, gadolinium hexacyanoferrate (GdHCF), was prepared and characterized using the techniques of FTIR spectroscopy, thermogravimetric analysis (TG), UV-Vis spectrometry, X-ray photoelectron spectroscopy (XPS), ICP atomic emission spectroscopy, and EDX. The results of ICP atomic emission spectroscopy, EDX, and TGA indicated that the prepared GdHCF sample had a stoichiometry of NaGdFe(CN)6·12H2O (when GdHCF was prepared in NaCl solution). The FTIR spectrum of GdHCF showed that there were two types of water molecules in the structure of GdHCF: one was the interstitial water (5 H2O), which resulted from the association of water due to H-bonding, and the other was water coordinated with Gd (7 H2O). The results obtained using XPS showed that the oxidation state of Fe and Gd in the GdHCF sample was +2 and +3, respectively. GdHCF was immobilized on the surface of spectroscopically pure graphite (SG) electrode forming the GdHCF/SG electrode, and the solid-state electrochemistry of the resultant electrode was studied using cyclic voltammetry. The cyclic voltammetric results indicated that the GdHCF/SG electrode exhibited a pair of well-defined and stable redox peaks with the formal potential of E0′=(197±3) mV. The effects of the concentration of the supporting electrolyte on the electrochemical characteristics of GdHCF were studied, and the results showed that the value of E0′ increased linearly with the activity of the cationic ion of the supporting electrolyte (lgaNa+), with a slope of 54.1 mV, which may become a novel method for determining the activity of Na+ in solution. Further experimental results indicated that GdHCF had electrocatalytic activities toward the oxidation of dopamine (DA) and ascorbic acid (AA), and the electrocatalytic current increased linearly with the concentration of DA (or AA) in the range of 1.0–10.0 mmol·L?1 (for DA) or 0.5–20.0 mmol·L?1 (for AA). 相似文献
7.
曾六川 《高等学校计算数学学报(英文版)》2003,12(1)
The purpose of this paper is to investigate the problem of approximating fixed points of non-Lipschitizian asymptotically pseudocontractive mappings in an arbitrary real Banach space by the modified Ishikawa iterative sequences with errors. 相似文献
8.
Kazuaki Okamoto Suprakas Sinha Ray Masami Okamoto 《Journal of polymer science. Part A, Polymer chemistry》2003,41(24):3160-3172
A series of new poly(butylene succinate) (PBS)/layered silicate nanocomposites were prepared successfully by simple melt extrusion of PBS and organically modified layered silicates (OMLS). Three different types of OMLS were used for the preparation of nanocomposites: two functionalized ammonium salts modified montmorillonite and a phosphonium salt modified saponite. The structure of the nanocomposites in the nanometer scale was characterized with wide-angle X-ray diffraction and transmission electron microscopic observations. With three different types of layered silicates modified with three different types of surfactants, the effect of OMLS in nanocomposites was investigated by focusing on four major aspects: structural analysis, materials properties, melt rheological behavior, and biodegradability. Interestingly, all these nanocomposites exhibited concurrent improvements of material properties when compared with pure PBS. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3160–3172, 2003 相似文献
9.
The measuring elements of both dry‐ and wet‐type gas meters are composed of a diaphragm and rotary drum. In this article an explanation on the principle of measuring and the structure of the gas meter for each of these two types was discussed. Such applications were made as follows: synthetic rubber was used for the measuring diaphragm, engineering plastic was employed instead of metal for the measuring drum, and poly(butylene terephthalate) (PBT) was used for the casing, respectively. As a result, an improvement in the gas resistance performance and productivity, which led to a lighter weight, more compactness and a lower cost of productions was achieved. Also the influence of the solubility of the measured gas to the plastic on the measured valve was discussed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
10.
The room temperature structure of perovskite CeAlO3 has been reinvestigated by X-ray powder diffraction. The Rietveld refinement has confirmed the tetragonal symmetry; but revealed a super cell, a=5.32489(6) Å and c=7.58976(10) Å, with the space group I4/mcm. In CeAlO3, the distortion from the ideal cubic perovskite is caused by the cooperative tilting of the AlO6 octahedra around the primitive cubic [001]p-axis. 相似文献