全文获取类型
收费全文 | 390712篇 |
免费 | 4259篇 |
国内免费 | 1341篇 |
专业分类
化学 | 200587篇 |
晶体学 | 6414篇 |
力学 | 17458篇 |
综合类 | 13篇 |
数学 | 46421篇 |
物理学 | 125419篇 |
出版年
2020年 | 3260篇 |
2019年 | 3586篇 |
2018年 | 4658篇 |
2017年 | 4679篇 |
2016年 | 7057篇 |
2015年 | 4342篇 |
2014年 | 7025篇 |
2013年 | 17271篇 |
2012年 | 13230篇 |
2011年 | 16044篇 |
2010年 | 11374篇 |
2009年 | 11337篇 |
2008年 | 14822篇 |
2007年 | 14770篇 |
2006年 | 14017篇 |
2005年 | 13004篇 |
2004年 | 12211篇 |
2003年 | 10586篇 |
2002年 | 10154篇 |
2001年 | 11461篇 |
2000年 | 8816篇 |
1999年 | 6843篇 |
1998年 | 5739篇 |
1997年 | 5613篇 |
1996年 | 5402篇 |
1995年 | 4957篇 |
1994年 | 4872篇 |
1993年 | 4884篇 |
1992年 | 5298篇 |
1991年 | 5293篇 |
1990年 | 5019篇 |
1989年 | 4890篇 |
1988年 | 4882篇 |
1987年 | 4768篇 |
1986年 | 4551篇 |
1985年 | 6107篇 |
1984年 | 6343篇 |
1983年 | 5294篇 |
1982年 | 5551篇 |
1981年 | 5335篇 |
1980年 | 5213篇 |
1979年 | 5472篇 |
1978年 | 5578篇 |
1977年 | 5429篇 |
1976年 | 5540篇 |
1975年 | 5178篇 |
1974年 | 5194篇 |
1973年 | 5371篇 |
1972年 | 3667篇 |
1971年 | 3038篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
921.
Imaging mass spectrometry requires the acquisition and interpretation of hundreds to thousands of individual spectra in order to map the mineral phases within heterogeneous geomatrices. A fuzzy logic inference engine (FLIE) was developed to automate data interpretation. To evaluate the strengths and limitations of FLIE, the chemical images obtained using FLIE were compared with those developed using two chemometric methods: principle component analysis (PCA) and cluster analysis (K-Means). Two heterogeneous geomatrices, a low-grade chalcopyrite ore and basalt, were imaged using a laser-desorption Fourier transform mass spectrometer. Similar mineral distribution patterns in the chalcopyrite ore sample were obtained by the three data analysis methods with most of the differences occurring at the interfaces between mineral phases. PCA missed one minor mineral phase in the chalcopyrite ore sample and did not clearly differentiate among the mineral classes of the basalt. K-Means cluster analysis differentiated among the various mineral phases in both samples, but improperly grouped some spectra in the chalcopyrite sample that only contained unanticipated high mass peaks. Unlike the chemometric methods, FLIE was able to classify spectra as unknowns for those spectra that fell below the confidence level threshold. A nearest neighbor approach, included in FLIE, was used to classify the unknowns to form a visually complete image; however, the unknowns identified by FLIE can be informative because they highlight potential problems or overlooked results. In conclusion, this study validated the fuzzy logic-based approach used in our laboratory and reveald some limitations in the three techniques that were evaluated. 相似文献
922.
L. Landström D. Brodoceanu K. Piglmayer D. Bäuerle 《Applied Physics A: Materials Science & Processing》2006,84(4):373-377
Extraordinary optical transmission through metal-coated close-packed monolayers has been observed. The monolayers consist of silica (a-SiO2) or polystyrene microspheres that form two-dimensional close-packed lattices by self-assembly. Metal layers of Ag, Au and Ni with different thicknesses (larger than the skin depth) were evaporated onto such lattices by means of standard techniques. The optical transmission spectra investigated between 300 and 2500 nm show pronounced peaks that scale with the diameter and the optical properties of the composite slabs. The enhanced transmission observed is most likely mediated via plasmons. PACS 78.66.-w; 81.16.Dn; 82.70.Dd 相似文献
923.
N. Raju T. Špaček J. Ježek I. M. Caminiti F. Leinisch K. Hideg P. Ježek W. E. Trommer 《Applied magnetic resonance》2006,30(3-4):373-383
Electron paramagnetic resonance (EPR) spectroscopy of spin-labeled fatty acids was used to investigate their interaction withEscherichia coli-expressed human mitochondrial uncoupling protein UCP2 refolded from inclusion bodies in nonaethylene glycol monododecyl ether (C12E9) micelles. 5-DOXYL-stearic acid and 4-PROXYL-palmitic acid bound to UCP2 exhibited additional clearly separated h+1I, h?1I “immobile” peaks in the low- and high-field region, respectively, separated by 42 and 44 Gauss, and extensively reduced h+1M, h?1M “mobile” peaks, separated by about 30 G, whereas with 7-DOXYL-stearic acid the I and M peaks were smoothed together into one wide peak. Competition of 4-PROXYL-palmitic acid with added palmitic acid, arachidonic acid, and all-cis-8,11,14-eicosatrienoic acid and of 7-DOXYL-stearic acid with arachidonic acid was indicated by the disappearance of the h+1I, h?1I “immobile” peaks, whereas redistribution in micelles without protein was indicated by the rising of the h+1M, h?1M “mobile” peaks. In conclusion, a competition of palmitic, arachidonic, and eicosatrienoic acid within a putative fatty acid binding site was observed for mitochondrial uncoupling protein UCP2. This finding together with the observation of EPR spectra of highly immobilized probes exclusively in the presence of the recombinant UCP2 suggest the existence of a fatty acid binding site on UCP2 which is a prerequisite of the fatty acid cycling mechanism as previously postulated for UCP1. 相似文献
924.
925.
926.
P Rabindra Reddy P R Prasad Reddy M Harilatha Reddy 《Journal of Chemical Sciences》1987,99(5-6):297-303
Studies on interaction of La(III), Pr(III), Nd(III), Sm(III), Gd(III), Dy(III) and Er(III) with inosine and xanthosine in
a 1:1 ratio have been carried out by potentiometric equilibrium measurements at 35±0·1°C and 0·1 M (KNO3) ionic strength. Investigations were also made for the interaction of these metal ions and nucleosides with the biologically
important secondary ligands glycine and histidine. These investigations were undertaken with a view to assess the influence
of charge on the structure and stability of 1:1 metal-inosine/xanthosine systems.
DBT/India overseas Fellow at Harvard University (1986–88). 相似文献
927.
928.
We investigate the existence and stability of solutions for higher-order two-point boundary value problems in case the differential
operator is not necessarily positive definite, i.e. with superlinear nonlinearities. We write an abstract realization of the
Dirichlet problem and provide abstract existence and stability results which are further applied to concrete problems. 相似文献
929.
We consider a shock-type wave solution of the modified quintic complex Ginzburg-Landau equation and make a numerical study
of its spatiotemporal stability. Discussions related to the behavior of this front wave are introduced and it is shown how
the velocities of the wave can be used to collect information concerning the pattern formation in the system.
Published in Neliniini Kolyvannya, Vol. 10, No. 2, pp. 270–276, April–June, 2007. 相似文献
930.
We show how methods for estimating the concentration function of the sum of independent random variables can be used to obtain estimates of the concentration function for the values of additive functions under suitable conditions. Previously obtained estimates of the concentration function are consequences of the estimate obtained in the present paper for functions from of the class under consideration. 相似文献