全文获取类型
收费全文 | 1489篇 |
免费 | 18篇 |
国内免费 | 6篇 |
专业分类
化学 | 885篇 |
晶体学 | 9篇 |
力学 | 59篇 |
数学 | 394篇 |
物理学 | 166篇 |
出版年
2019年 | 15篇 |
2017年 | 9篇 |
2016年 | 25篇 |
2015年 | 16篇 |
2014年 | 26篇 |
2013年 | 89篇 |
2012年 | 46篇 |
2011年 | 47篇 |
2010年 | 38篇 |
2009年 | 27篇 |
2008年 | 63篇 |
2007年 | 64篇 |
2006年 | 48篇 |
2005年 | 67篇 |
2004年 | 45篇 |
2003年 | 43篇 |
2002年 | 35篇 |
2001年 | 39篇 |
2000年 | 33篇 |
1999年 | 13篇 |
1998年 | 17篇 |
1997年 | 16篇 |
1996年 | 23篇 |
1995年 | 20篇 |
1994年 | 19篇 |
1993年 | 19篇 |
1992年 | 19篇 |
1991年 | 16篇 |
1990年 | 20篇 |
1989年 | 21篇 |
1988年 | 26篇 |
1987年 | 27篇 |
1986年 | 14篇 |
1985年 | 29篇 |
1984年 | 21篇 |
1983年 | 25篇 |
1982年 | 31篇 |
1981年 | 25篇 |
1980年 | 26篇 |
1979年 | 29篇 |
1978年 | 18篇 |
1977年 | 27篇 |
1976年 | 13篇 |
1975年 | 20篇 |
1974年 | 27篇 |
1973年 | 22篇 |
1972年 | 13篇 |
1971年 | 13篇 |
1969年 | 12篇 |
1965年 | 9篇 |
排序方式: 共有1513条查询结果,搜索用时 31 毫秒
101.
Approximation in the finite element method 总被引:2,自引:0,他引:2
Gilbert Strang 《Numerische Mathematik》1972,19(1):81-98
Summary The rate of convergence of the finite element method depends on the order to which the solutionu can be approximated by the trial space of piecewise polynomials. We attempt to unify the many published estimates, by proving that if the trial space is complete through polynomials of degreek–1, then it contains a functionv
h
such that |u–v
h
|
s
ch
k–s|u|
k
. The derivatives of orders andk are measured either in the maximum norm or in the mean-square norm, and the estimate can be made local: the error in a given element depends on the diameterh
i
of that element. The proof applies to domains in any number of dimensions, and employs a uniformity assumption which avoids degenerate element shapes.This research was supported by the National Science Foundation (GP-13778). 相似文献
102.
103.
G. V. Veriovkin E. N. Gilbert V. A. Mikhailov V. A. Yakhina 《Journal of Radioanalytical and Nuclear Chemistry》1980,59(2):361-365
A neutron activation (NA) method for the determination of 24 microimpurities in germanium has been developed. The method is based on the separation of the matrix and isotopes genetically connected by extraction chromatography. 相似文献
104.
A method of calculating expressions of the type which is simpler than that based on Wick's theorem is proposed. Expressions of the above type are widely used in studying the effects of temperature in electron and neutron diffraction. 相似文献
105.
Base-promoted reaction of dimethyl diazomethylphosphonate () with dialkyl and cyclic ketones affords species having the chemical properties associated with vinylidenes () or their equivalents. Data are presented showing that diazoethenes () are unexpectedly unstable, losing nitrogen even at ?78°C to give the corresponding carbenes or carbenoids. 相似文献
106.
The 13C chemical shifts and one-bond carbon-hydrogen coupling constants have been obtained for some hydroxycoumarins and their corresponding acetoxy and methoxy derivatives. The changes in the one-bond carbon-hydrogen coupling constants resulting from the conversion of a hydroxy group to an acetoxy group represent a simple method of assignment of the 13C NMR signals in coumarins which contain one or more hydroxy groups in the benzenoid ring. 相似文献
107.
M. A. Collins und R. G. Gilbert 《Colloid and polymer science》1978,256(8):827
Ohne Zusammenfassung 相似文献
108.
109.
110.
Determination of processed animal proteins, including meat and bone meal, in animal feed 总被引:1,自引:0,他引:1
Gizzi G von Holst C Baeten V Berben G van Raamsdonk L 《Journal of AOAC International》2004,87(6):1334-1341
An intercomparison study was conducted to determine the presence of processed animal proteins (PAPs), including meat and bone meal (MBM) from various species, in animal feed. The performances of different methods, such as microscopy, polymerase chain reaction (PCR), immunoassays, and a protocol based on iquid chromatography (LC), were compared. Laboratories were asked to analyze for PAPs from all terrestrial animals and fish (total PAPs); mammalian PAPs; ruminant PAPs; and porcine PAPs. They were free to use their method of choice. In addition, laboratories using microscopy were asked to determine the presence of PAPs from terrestrial animals, which is applicable only to microscopy. For total PAPs microscopy, LC and some immunoassays showed sufficient results at a concentration as low as 0.1% MBM in the feed. In contrast, PCR was not fit for purpose. In differentiating between MBM from terrestrial animals and fishmeal, microscopy detected 0.5% of terrestrial MBM in feed in the presence of 5% fishmeal, but was less successful when the concentration of MBM from terrestrial animals was 0.1%. The animal-specific determination of MBM from mammals or, more specifically from either ruminants or pigs, by PCR showed poor results, as indicated by a high number of false-positive and false-negative results. The only PCR method that scored quite well was applied by a member of the organizer team of the study. Immunoassays scored much better than PCR, showing sufficient sensitivity but some deficiency in terms of specificity. The results also demonstrated that the reliable determination of MBM from ruminants has not been resolved, especially for low concentrations of MBM (0.1%) in feed. Comparison of the results for mammalian MBM from all methods indicated that, for control purposes, the immunoassay method, especially when applied as dipsticks, could be used as a rapid screening method combined with microscopy to confirm the positive samples. However, implementation of such a system would require that the immunoassays were previously validated to demonstrate that this approach is fit for purpose. The determination of ruminant or porcine PAPs by immunoassays was more difficult, partly because the MBM in this study contained about 50% bovine and porcine material, thereby reducing the target concentration level to 0.05%. 相似文献