全文获取类型
收费全文 | 1406篇 |
免费 | 44篇 |
国内免费 | 14篇 |
专业分类
化学 | 950篇 |
晶体学 | 15篇 |
力学 | 36篇 |
数学 | 282篇 |
物理学 | 181篇 |
出版年
2021年 | 10篇 |
2020年 | 13篇 |
2019年 | 14篇 |
2018年 | 21篇 |
2017年 | 10篇 |
2016年 | 25篇 |
2015年 | 23篇 |
2014年 | 22篇 |
2013年 | 79篇 |
2012年 | 75篇 |
2011年 | 59篇 |
2010年 | 47篇 |
2009年 | 26篇 |
2008年 | 62篇 |
2007年 | 65篇 |
2006年 | 82篇 |
2005年 | 49篇 |
2004年 | 55篇 |
2003年 | 46篇 |
2002年 | 51篇 |
2001年 | 25篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 17篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 14篇 |
1993年 | 27篇 |
1992年 | 16篇 |
1991年 | 14篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 23篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 29篇 |
1984年 | 28篇 |
1983年 | 10篇 |
1982年 | 31篇 |
1981年 | 15篇 |
1980年 | 23篇 |
1979年 | 19篇 |
1978年 | 17篇 |
1976年 | 18篇 |
1975年 | 10篇 |
1974年 | 12篇 |
1973年 | 21篇 |
1972年 | 14篇 |
1971年 | 10篇 |
排序方式: 共有1464条查询结果,搜索用时 203 毫秒
81.
The crystal and molecular structure of (2–3-η-2-Butyne-1,4-diol)-bis-(triphenylphosphan)-nickel(O) has been determined by X-ray structure analysis. It crystallizes in the tetragonal space group 14 with the cell parameters a = b = 22.277(3), and c = 15.118 (4) Å. The structure was solved by the heavy atom method and refined to R = 0.0716. The coordination geometry about the nickel atom is trigonal-planar. Each molecule is hydrogen bonded to two neighbours. The result is an eight-membered oxygen ring. 相似文献
82.
Debadi Chakraborty Mohit Bajaj Leslie Yeo James Friend Matteo Pasquali J. Ravi Prakash 《ournal of non Newtonian Fluid Mechanics》2010,165(19-20):1204-1218
We compute the flow of three viscoelastic fluids (Oldroyd-B, FENE-P, and Owens blood model) in a two-dimensional channel partly bounded by a tensioned membrane, a benchmark geometry for fluid–structure interactions. The predicted flow patterns are compared to those of a Newtonian liquid. We find that computations fail beyond a limiting Weissenberg number. Flow fields and membrane shape differ significantly because of the different degree of shear thinning and molecular extensibility underlying the three different microstructural models. 相似文献
83.
84.
85.
86.
Combinatorial libraries of substituted 3-thio-1,2,4-triazoles and 2-thioimidazoles were synthesized in good yield by alkylation of the products via the reaction of isothiocyanates and carboxylic acid hydrazides or beta-aminoketones, respectively. A total of 275 3-thio-1,2,4-triazoles and 283 2-thioimidazoles were synthesized out of the attempted 288 in each case. Most the yields were between 45% and 98%, and all the compounds synthesized were purified to >85% purity. Variations in yields revealed no definitive trends and were mainly attributed to bulky alkylating agents used and the plate well location of the reaction mixtures. 相似文献
87.
Field LD Ramadan SA Pierens GK 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,155(1):64-71
Cyclic J cross polarisation (CYCLCROP) is a sensitive method for the noninvasive monitoring of (13)C distributions and fluxes. The PRAWN rotating frame Hartmann-Hahn mixing sequence ameliorates problems associated with sensitivity to Hartmann-Hahn mismatch and reduces RF power deposition. The combination of CYCLCROP with echo planar imaging (EPI) for spatial encoding of the proton detected carbon signal allows efficient use of the available signal to be made, permitting a significant improvement in the temporal resolution of any study. We report here on some initial experiments to demonstrate the feasibility of echo planar proton detected (13)C imaging using CYCLCROP based upon the PRAWN module, including the application of the technique to the measurement of transport and accumulation of (13)C-labelled sucrose in a castor bean seedling. Two methods that can be used to eliminate the effect of the J-splitting in the EP images are presented. In addition, a fast, image-based B(1) field-mapping method which may be used to quantitatively map the low frequency RF field in a dual resonant ((13)C/(1)H) probe is presented. The technique utilises the above described imaging method, permitting fully quantitative, 64x64 axial field maps to be generated in about a minute. 相似文献
88.
Brian Spencer Robert A Marr Edward Rockenstein Leslie Crews Anthony Adame Rewati Potkar Christina Patrick Fred H Gage Inder M Verma Eliezer Masliah 《BMC neuroscience》2008,9(1):109
Background
Proteolytic degradation has emerged as a key pathway involved in controlling levels of the Alzheimer's disease (AD)-associated amyloid-β (Aβ) peptide in the brain. The endopeptidase, neprilysin, has been implicated as a major Aβ degrading enzyme in mice and humans. Previous short and intermediate term studies have shown the potential therapeutic application of neprilysin by delivering this enzyme into the brain of APP transgenic mice using gene transfer with viral vectors. However the effects of long-term neprilysin gene transfer on other aspects of Aβ associated pathology have not been explored yet in APP transgenic mice. 相似文献89.
90.
Martingales valued in certain subspaces ofL
1 总被引:1,自引:0,他引:1
A Banach subspaceE ofL
1 is constructed such thatE fails the Radon-Nikodym property, yetE has no bounded dyadicδ-tree for anyδ>0. The unit ball ofE is also relatively compact in the topology of convergence in probability, which implies thatE has the strong Schur property. The construction uses martingales and probabilistic techniques.
Supported in part by NSF-MCS-7827056. 相似文献