全文获取类型
收费全文 | 22048篇 |
免费 | 1075篇 |
国内免费 | 1459篇 |
专业分类
化学 | 16288篇 |
晶体学 | 232篇 |
力学 | 540篇 |
综合类 | 12篇 |
数学 | 3327篇 |
物理学 | 4183篇 |
出版年
2023年 | 147篇 |
2022年 | 322篇 |
2021年 | 534篇 |
2020年 | 408篇 |
2019年 | 456篇 |
2018年 | 475篇 |
2017年 | 451篇 |
2016年 | 853篇 |
2015年 | 693篇 |
2014年 | 824篇 |
2013年 | 1869篇 |
2012年 | 1679篇 |
2011年 | 1814篇 |
2010年 | 1134篇 |
2009年 | 1276篇 |
2008年 | 1340篇 |
2007年 | 1277篇 |
2006年 | 1046篇 |
2005年 | 1016篇 |
2004年 | 1277篇 |
2003年 | 920篇 |
2002年 | 845篇 |
2001年 | 435篇 |
2000年 | 351篇 |
1999年 | 267篇 |
1998年 | 248篇 |
1997年 | 218篇 |
1996年 | 230篇 |
1995年 | 186篇 |
1994年 | 139篇 |
1993年 | 162篇 |
1992年 | 134篇 |
1991年 | 92篇 |
1990年 | 100篇 |
1989年 | 87篇 |
1988年 | 81篇 |
1987年 | 73篇 |
1986年 | 82篇 |
1985年 | 121篇 |
1984年 | 121篇 |
1983年 | 88篇 |
1982年 | 80篇 |
1981年 | 88篇 |
1980年 | 68篇 |
1979年 | 50篇 |
1978年 | 39篇 |
1977年 | 46篇 |
1976年 | 44篇 |
1975年 | 33篇 |
1974年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Tadeusz Bałaban 《Communications in Mathematical Physics》1987,109(2):249-301
We study four-dimensional pure gauge field theories by the renormalization group approach. The analysis is restricted to small field approximation. In this region we construct a sequence of localized effective actions by cluster expansions in one step renormalization transformations. We construct also -functions and we define a coupling constant renormalization by a recursive system of renormalization group equations. 相似文献
192.
193.
Alvaro M Corma A Das D Fornés V García H 《Chemical communications (Cambridge, England)》2004,(8):956-957
Preparation of hybrid organic-inorganic MCM-41 and SBA-15 silicas functionalized with perfluoroalkylsulfonic acid groups has been achieved in a single step by reacting the mesoporous silicas with 1,2,2-trifluoro-2-hydroxy-1-trifluoromethylethane sulfonic acid beta-sultone; the catalysts showed higher activity than commercial Nafion-silica composite for the esterification of long chain fatty acids with ethanol. 相似文献
194.
With the assistance of HPLC-ESI-MS/MS, the self-assembly products of serine and histidine penta-coordinated phosphorus compound were separated and identified. The expectative product was seryl-histidine dipeptide, but it was found that there was almost equimolar amount of histidyl-histidine dipeptide as well as seryl-histidine dipeptide. The mechanism was speculated that there was iigand exchange between penta-coordinated phosphoryl serine and histidine in the reaction process. As a result,two types of dipeptide were produced. 相似文献
195.
196.
Bañares L Aoiz FJ González-Lezana T Herrero VJ Tanarro I 《The Journal of chemical physics》2005,123(22):224301
Integral cross sections and thermal rate constants have been calculated for the N((2)D)+H(2) reaction and its isotopic variants N((2)D)+D(2) and the two-channel N((2)D)+HD by means of quasiclassical trajectory and statistical quantum-mechanical model methods on the latest ab initio potential-energy surface [T.-S. Ho et al., J. Chem. Phys. 119, 3063 (2003)]. The effect of rotational excitation of the diatom on the dynamics of these reactions has been investigated and interesting discrepancies between the classical and statistical model calculations have been found. Whereas a net effect of reagent rotation on reactivity is always observed in the classical calculations, only a very slight effect is observed in the case of the asymmetric N((2)D)+HD reaction for the statistical quantum-mechanical method. The thermal rate constants calculated on this Potential-Energy Surface using quasiclassical trajectory and statistical model methods are in good agreement with the experimental determinations, although the latter are somewhat larger. A reevaluation of the collinear barrier of the potential surface used in the present study seems timely. Further theoretical and experimental studies are needed for a full understanding of the dynamics of the title reaction. 相似文献
197.
Serrano MC Portolés MT Vallet-Regí M Izquierdo I Galletti L Comas JV Pagani R 《Macromolecular bioscience》2005,5(5):415-423
Tissue engineering offers the potential of providing vessels that can be used to replace diseased and damaged native blood vessels. The endothelization of a synthetic vascular graft minimizes the failures associated with blood clotting and platelet activation. The aim of this study was to culture vascular-derived endothelial and smooth muscle cells on both untreated and NaOH-treated poly(epsilon-caprolactone) (PCL) films, a biocompatible and bio-resorbable polymer, and to evaluate the behavior of both cell types as a preliminary study for vascular graft development. PCL films were prepared by hot pressing; characterized by DSC, IR, SEM, and scanning force microscopy; and treated with NaOH to increase the surface hydrophilicity before cell culture. Endothelial and smooth muscle cells, isolated from pig cava vein, were characterized by immunofluorescence and confocal microscopy studies of endothelial nitric oxide synthase and alpha-smooth muscle actin. Good adhesion, growth, viability and morphology of both the endothelial and smooth muscle cells on PCL films were obtained, but a light stimulation of mitochondrial activity was observed during short culture times. NaOH treatment improved the adhesion and enhanced the proliferation in both cell types. This verified the possible use of this modified polymer as a support in the preparation of a synthetic vascular graft. [Diagram: see text] SEM micrograph of smooth muscle cells cultured on NaOH-treated PCL film. (Original magnification: 1000x). 相似文献
198.
199.
Nanostructure Pt Electrode Obtained via Self-assembly of Nanoparticles on Conductive Oxide-coated Glass Substrate 总被引:1,自引:0,他引:1
Self-assembly of platinum nanoparticles were applied to fabrication of counter electrode for dye-sensitized solar cells on conductive oxide-coated glass substrate. The present Pt electrode exhibits high exchange current density of 220 mA/cm^2, which is comparable to those prepared by electrodeposition, magnetron sputtering or thermal decomposition of platinum chloride. After analysis by transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), it was found that the catalyst was structurally characterized as nanosized platinum metal clusters and was continuously arranged on electrode surface. The present nanostructure electrode had high electrocatalytic activity for the reduction of iodine in organic solution. 相似文献
200.
合成了两个异亚硝基乙酰丙酮亚胺Pd(II)配合物,Pd(o-BrC_6H_4-IAI)_2 (1) 和Pd(C_6H_5CH_2-IAI)_2 (2)(IAI = isonitrosoacetylacetoneimino),用IR和 Raman光谱对两个配合物进行了表征,并测定了配合物1的晶体结构。配合物1晶体 属单斜晶系,空间群为P2_1/c,晶胞参数:a = 0.8013(2) nm,b = 1.8775(4) nm,c = 0.7905(2) nm,β = 98.22(3)°,V = 1.1770(5) nm~3,Z = 2,D_c = 1.892 g·cm~(-3),F(000) = 656,R = 0.0663。在这两个配合物中,二齿 Schiff碱配体的异亚硝基(肟基)的N原子和亚胺的N原子与Pd(II)配位,形成反式 的PdN_4平面正方形配位构型。 相似文献