全文获取类型
收费全文 | 2603篇 |
免费 | 65篇 |
国内免费 | 8篇 |
专业分类
化学 | 1747篇 |
晶体学 | 23篇 |
力学 | 32篇 |
数学 | 582篇 |
物理学 | 292篇 |
出版年
2022年 | 17篇 |
2020年 | 46篇 |
2019年 | 29篇 |
2018年 | 17篇 |
2017年 | 25篇 |
2016年 | 42篇 |
2015年 | 68篇 |
2014年 | 52篇 |
2013年 | 92篇 |
2012年 | 92篇 |
2011年 | 100篇 |
2010年 | 76篇 |
2009年 | 59篇 |
2008年 | 119篇 |
2007年 | 111篇 |
2006年 | 96篇 |
2005年 | 103篇 |
2004年 | 83篇 |
2003年 | 64篇 |
2002年 | 52篇 |
2001年 | 23篇 |
2000年 | 32篇 |
1999年 | 25篇 |
1998年 | 30篇 |
1997年 | 22篇 |
1996年 | 23篇 |
1995年 | 27篇 |
1994年 | 28篇 |
1993年 | 35篇 |
1992年 | 28篇 |
1991年 | 18篇 |
1989年 | 26篇 |
1988年 | 31篇 |
1987年 | 31篇 |
1986年 | 18篇 |
1985年 | 35篇 |
1984年 | 46篇 |
1983年 | 27篇 |
1982年 | 21篇 |
1981年 | 32篇 |
1980年 | 39篇 |
1979年 | 24篇 |
1978年 | 25篇 |
1977年 | 27篇 |
1976年 | 23篇 |
1975年 | 29篇 |
1974年 | 27篇 |
1972年 | 18篇 |
1967年 | 18篇 |
1956年 | 28篇 |
排序方式: 共有2676条查询结果,搜索用时 15 毫秒
11.
12.
JiŘí Kvapil Josef Kvapil Bohumil Perner Michal Košelja Helena Jelínková 《Czechoslovak Journal of Physics》1990,40(11):1283-1287
The methods of growing YAG:Nd crystals with a flat interface and YAP:Nd crystals with a sharp conical interface are described. The form of the interface was controlled by the He and H2O content in the reducing atmosphere composed mainly of Ar and H2 as well as by axial temperature gradient above the melt level. The crystals of 120–180 mm in length were machined to the high-quality slabs. 相似文献
13.
Josef Schneid 《BIT Numerical Mathematics》1988,28(1):184-187
Lower bounds for are given for which equidistant s-point collocation methods areA()-stable for arbitrarys. 相似文献
14.
A. Goldmann G. Rosina E. Bertel F. P. Netzer 《Zeitschrift für Physik B Condensed Matter》1989,73(4):479-487
We report electron spectroscopic studies of the Rh(111) surface, with the aim to obtain bulk band-structure information. We have measured normal photoemision using tunable synchrotron radiation in the range of photon energies between 11 eV and 55 eV, and angle-dependent photoemission along the LUX and LKL azimuths using the He resonance lines (=21.2 eV, 40.8 eV). To complement these data, we studied angleresolved secondary electron emission after excitation with electrons and photons. We derive parts of the one-electron energy dispersionE(k) along L, and determine the energies of several bulk critical points (in eV):E(>
7+/8+)=–2.75±0.10,E(>
8+=–0.85±0.10,E(>
7–=16.1±0.5,E(>
6–/>
8–)=20.5±0.5,E(X
7+)=–5.0±0.1,E(L
6+)=–5.6±0.5,E(L
6+/L
4++5+)=–2.65±0.10,E(L
6+)=9.0±0.5 eV. Our results are compared to several available band structure calculations. 相似文献
15.
The mechanism of the unfolding of human serum albumin by urea was studied using d.c. polarography. It was found that this reaction is a complex process which cannot be described in terms of a two-state transition model. As well as the Brdi?ka catalytic current we have also studied the reduction current of disulfide groups in native and denatured human serum albumin. The number of cystine residues accessible for electrode reduction in native and denatured protein was calculated. On the basis of these results a scheme for the unfolding of human serum albumin by urea is proposed. 相似文献
16.
The reconstruction numberrn(G) of a graphG was introduced by Harary and Plantholt as the smallest number of vertex-deleted subgraphsG
i
=G – v
i
in the deck ofG which do not all appear in the deck of any other graph. For any graph theoretic propertyP, Harary defined theP-reconstruction number of a graph G P as the smallest number of theG
i
in the deck ofG, which do not all appear in the deck of any other graph inP We now study the maximal planar graph reconstruction numberrn(G), proving that its value is either 1 or 2 and characterizing those with value 1. 相似文献
17.
We describe a convergent synthesis of eight 1,3,5- and 1,2,4,5-substituted benzene derivatives with long rigid arms containing 4-pyridyl, 2,2'-bipyridyl, and 2,2'-bipyrimidyl termini, meant to be used as trigonal or tetragonal connectors for the construction of large molecular structures. The synthesis involved copper-free Pd-mediated coupling of terminal acetylenes to aryl halides. First, one of the termini of 1,3-diethynylbicyclo[1.1.1]pentane was coupled with a brominated aza heterocycle, and second, 3 equiv of the resulting extended arm were coupled with 1,3,5-triiodobenzene or 4 with 1,2,4,5-tetraiodobenzene. An improved large-scale synthesis for 1,3-diethynylbicyclo[1.1.1]pentane is described. The structures of two of the arms were determined by single-crystal X-ray analysis. Several long molecular rods with 4-pyridyl termini were obtained as byproducts, and a single-crystal X-ray structure is reported for the shortest of these. 相似文献
18.
Josef Janča 《Mikrochimica acta》1994,112(5-6):197-215
The primary field forces can generate spatially oriented gradient of the effective property of a continuum or pseudo-continuum fluid (carrier liquid). When this gradient is coupled with the action of a secondary field of identical or different nature the isoperichoric focused zones of the dispersed species can appear. Consequently, they can be separated according to differences responding to the property gradient of the carrier liquid. This concept can be applied under static (non-flow) conditions in thin layer focusing as well as under dynamic conditions with the elution due to the carrier liquid flow in focusing field-flow fractionation. The gradient established by the action of the primary field and the concentration distribution of the isoperichoric focused zone formed by the coupled effect of the gradient and of the primary or secondary field are described theoretically. The rigorous relationship describing the shape of the focused zone is compared with the approximate solutions. The performances of the proposed principle were evaluated by model calculations. Potential experimental configurations considering the implementation of the static and dynamic conditions are discussed. The generalized isoperichoric focusing theory can be applied to describe the particular processes operating in analytical and preparative focusing separations of the particles of various, but especially of biological origin. 相似文献
19.
Richard Barner Josef Hübscher John J. Daly Peter Schnholzer 《Helvetica chimica acta》1981,64(3):915-938
Configuration of the Vitamin-D3-Metabolite 25,26-Dihydroxycholecalciferol: Synthesis of (25S,26)- and (25R,26)-Dihydroxycholecalciferol For selective synthesis of the title compounds, (25S)- 1b and (25R)- 1b (Scheme 1), the protected cholesterol precursors (25S)- 6 and (25R)- 6 were prepared from stigmasterol-derived steroid-units 4a-d and C5-side chain building blocks 5a–d by Grignard- or Wittig-coupling (Scheme 2), the configuration at C(25) of the target compounds being already present in the C5-units. Conversion of the cholesterol intermediates to the corresponding vitamin-D3 derivatives was carried out via the 7,8-didehydrocholesterol compounds (25S)- 2b and (25R)- 2b (Scheme 1), using the established photochemical-thermal transformation of the 5,7-diene system to the seco-triene system of cholecalciferol. The configuration at C(25) of the cholesterol precursors as assigned on basis of the known configuration of the C5-units used, was found to be in agreement with the result of a single crystal X-ray analysis on compound 11 . The configuration at C(25) remained untouched on conversion of the cholesterol ring system to the seco-triene system of vitamin D3 as evident from comparison of the lanthanide-induced CD. Cotton effects observed for (25S)- 3b and (25S) 1b . 25,26-Dihydroxycholecalciferol observed as a natural vitamin-D3 metabolite has (25S)-configuration. 相似文献
20.
Indications for the occurrence of nitric oxide synthases in Dictyostelium, Neurospora, Phycomyces and the leguminous plant Mucuna hassjoo as well as a physiological role of nitric oxide in Neurospora crassa are demonstrated. An exogenous nitric oxide donor, sodium nitroprus-side, inhibited light-stimulated conidiation in N. crassa. Specific inhibitors of nitric oxide synthase, like the arginine derivatives NG-nitro-L-arginine (L-NA) and NG-nitro-L-arginine-methyl ester (L-NAME), enhanced conidiation in darkness and in the light, whereas the stereo-isomer D-NAME was inactive. This communication reports to our knowledge the first time the presence of enzymatic activity of nitric oxide synthase in fungi and a higher plant and an effect of nitric oxide in fungal photophysiology. 相似文献