全文获取类型
收费全文 | 459篇 |
免费 | 27篇 |
国内免费 | 19篇 |
专业分类
化学 | 274篇 |
晶体学 | 1篇 |
力学 | 33篇 |
数学 | 111篇 |
物理学 | 86篇 |
出版年
2023年 | 2篇 |
2022年 | 14篇 |
2021年 | 17篇 |
2020年 | 20篇 |
2019年 | 24篇 |
2018年 | 13篇 |
2017年 | 22篇 |
2016年 | 24篇 |
2015年 | 24篇 |
2014年 | 30篇 |
2013年 | 59篇 |
2012年 | 34篇 |
2011年 | 38篇 |
2010年 | 34篇 |
2009年 | 18篇 |
2008年 | 24篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1966年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有505条查询结果,搜索用时 78 毫秒
1.
The Effect of the Spacer of Bis(biurea) Ligands on the Structure of A2L3‐type (A=anion) Phosphate Complexes
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Biao Wu Dr. Shaoguang Li Prof. Yibo Lei Prof. Huaiming Hu Dr. Nader de Sousa Amadeu Prof. Dr. Christoph Janiak Dr. Jennifer S. Mathieson Dr. De‐Liang Long Prof. Leroy Cronin Prof. Xiao‐Juan Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2588-2593
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes. 相似文献
2.
An admissible minimax estimator of a bounded scale-parameter in a subclass of the exponential family under scale-invariant squared-error loss 总被引:3,自引:0,他引:3
Mohammad Jafari Jozani Nader Nematollahi Khalil Shafie 《Statistics & probability letters》2002,60(4):437-444
A subclass of the scale-parameter exponential family is considered and for the rth power of the scale parameter, which is lower bounded, an admissible minimax estimator under scale-invariant squared-error loss is presented. Also, an admissible minimax estimator of a lower-bounded parameter in the family of transformed chi-square distributions is given. These estimators are the pointwise limits of a sequence of Bayes estimators. Some examples are given. 相似文献
3.
Miklos Ajtai James Aspnes Moni Naor Yuval Rabani Leonard J Schulman Orli Waarts 《Journal of Algorithms in Cognition, Informatics and Logic》1998,29(2):306-357
On-line machine scheduling has been studied extensively, but the fundamental issue of fairness in scheduling is still mostly open. In this paper we explore the issue in settings where there are long-lived processes which should be repeatedly scheduled for various tasks throughout the lifetime of a system. For any such instance we develop a notion ofdesiredload of a process, which is a function of the tasks it participates in. Theunfairnessof a system is the maximum, taken over all processes, of the difference between the desired load and the actual load.An example of such a setting is thecarpool problemsuggested by Fagin and Williams [IBM Journal of Research and Development27(2) (1983), 133–139]. In this problem, a set ofnpeople form a carpool. On each day a subset of the people arrive and one of them is designated as the driver. A scheduling rule is required so that the driver will be determined in a “fair” way.We investigate this problem under various assumptions on the input distribution. We also show that the carpool problems can capture several other problems of fairness in scheduling. 相似文献
4.
We prove that the renormalized solutions of the Boltzmann equation considered in a bounded domain with different types of (kinetic) boundary conditions converge to the Stokes‐Fourier system with different types of (fluid) boundary conditions when the main free path goes to zero. This extends the work of F. Golse and D. Levermore [9] to the case of a bounded domain. © 2003 Wiley Periodicals, Inc. 相似文献
5.
The phase diagram of the nematic mesophase present in the tetradecyltrimethylammonium bromide/sodium bromide/water ternary system was determined. A calamitic nematic mesophase (NC) was observed which extends to very high concentrations of electrolyte. The order parameters of the surfactant head group in the mesophases were studied by the NMR quadrupolar splitting of the deuterated surfactant. On increasing the temperature of nematic mesophases with low electrolyte concentrations, a phase separation occurs with the formation of a more highly ordered hexagonal phase and an isotropic phase. Diffusion measurements of the isotropic micellar solution by the NMR PFG method were used to estimate hydrodynamic radii at low surfactant concentrations and to study micelle diffusion as the concentration of the surfactant was increased to the liquid crystalline region. At higher surfactant concentrations, the diffusion coefficient reached a limiting value. The calamitic nematic mesophase in this surfactant/electrolyte/water system appears to be formed by long wormlike micelles. 相似文献
6.
Khodabakhsh NIKNAM Mohammad Ali ZOLFIGOL Zahra HOSSIENINEJAD Nader DANESHVAR 《催化学报》2007,28(7):591-595
以金属硫酸氢盐M(HSO4)n(Ca(HSO4)2,Zn(HSO4)2和过硫酸氢钾制剂oxone○R)为催化剂催化醛、1,3-二羰基化合物和尿素进行缩合反应,在90℃及无溶剂的条件下高收率、一锅法合成了3,4-二氢嘧啶-2(1H)-酮. 相似文献
7.
Impedance biosensors are a class of electrical biosensors that show promise for point-of-care and other applications due to low cost, ease of miniaturization, and label-free operation. Unlabeled DNA and protein targets can be detected by monitoring changes in surface impedance when a target molecule binds to an immobilized probe. The affinity capture step leads to challenges shared by all label-free affinity biosensors; these challenges are discussed along with others unique to impedance readout. Various possible mechanisms for impedance change upon target binding are discussed. We critically summarize accomplishments of past label-free impedance biosensors and identify areas for future research. 相似文献
8.
9.
Moni Chauhan Claude Chuit Robert J. P. Corriu Catherine Rey Jean-Paul Declercq Antoine Dubourg 《Journal of organometallic chemistry》1996,510(1-2):173-179
The X-ray structure analysis of bis(8-dimethylamino-l-naphthyl)phenylphosphane (3) and of the corresponding sulphide 4 has revealed hexacoordination at phosphorus in both cases, the N … P separations being less than the sum of the van der Waal radii. Furthermore, in both cases the overall geometry corresponds to a distorted bicapped tetrahedron. The optimum geometry calculated for 4 via the
program developed by Autodesk (MM + method) suggests that the structure of the molecule is a function not only of steric requirements but also of electronic effects. 相似文献
10.