全文获取类型
收费全文 | 384篇 |
免费 | 14篇 |
国内免费 | 2篇 |
专业分类
化学 | 274篇 |
晶体学 | 5篇 |
力学 | 3篇 |
数学 | 36篇 |
物理学 | 82篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 13篇 |
2015年 | 12篇 |
2014年 | 13篇 |
2013年 | 21篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 12篇 |
2009年 | 18篇 |
2008年 | 30篇 |
2007年 | 26篇 |
2006年 | 20篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 12篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1968年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有400条查询结果,搜索用时 15 毫秒
1.
2.
We investigate optimal harvesting control in a predator–prey model in which the prey population is represented by a first-order
partial differential equation with age-structure and the predator population is represented by an ordinary differential equation
in time. The controls are the proportions of the populations to be harvested, and the objective functional represents the
profit from harvesting. The existence and uniqueness of the optimal control pair are established. 相似文献
3.
4.
5.
α,ω-Difluoropolydimethylsiloxanes F[(CH3)2SiO]n(CH3)2SiF have been prepared by reaction of (CH3)2SiF2 with cyclic dimethylsiloxanes [(CH3)2SiO]n (n = 3 or 4). An equilibrium is reached in the redistribution of fluorine vs. oxygen atoms after ca. 24 h at 200°C or 15 days at 150°C when catalysed by AlCl3. 16 equilibrated samples of varied (R = F/Si) overall compositions have been analysed by 1H and 19F NMR and by VPC. The presence of rings has been established for the lower values of R. The molecular constitution of the equilibrated samples is described by a set of constants. The abundance of the end units is slightly larger than expected from random distribution. The good resolution of the spectra permits the distinguishing of the 9th order of environment of the end units and the 5th order for the middle units and the verification that there is no preferential association among the building units, and thus the proportion of chains of various lengths obeys Flory's random distribution mode. The equilibrium molecular constitution of these α,ω-difluorosiloxanes is close to that of their dichloro analogs; the substitution of chlorine by fluorine atoms at the end of the chains thus appears to cause little perturbation. On the other hand, the kinetic evolution of the reaction appears to be different, since the first species which forms is always the pyro moleculeinstead of long chains and large rings as in the case of the chloro analogs. 相似文献
6.
Purification of NAD glycohydrolase from Neurospora crassa conidia by a polyclonal immunoadsorbent. 总被引:1,自引:0,他引:1
M Pace D Agnellini G Lippoli P G Pietta P L Mauri S Cinquanta 《Journal of chromatography. A》1991,539(2):517-523
NAD glycohydrolase from Neurospora crassa conidia was purified by affinity chromatography on a column of polyclonal antibodies bound to an agarose matrix. The procedure was easy, non-denaturating and suitable for repetitive use of the gel. The enzyme obtained appeared homogeneous by sodiumdodecyl sulphate-polyacrylamide gel electrophoresis. 相似文献
7.
Christov A Korol RM Dai E Liu L Guan H Bernards MA Cavers PB Susko D Lucas A 《Photochemistry and photobiology》2005,81(2):457-466
Altered collagen and elastin content correlates closely with remodeling of the arterial wall after injury. Optical analytical approaches have been shown to detect qualitative changes in plaque composition, but the capacity for detection of quantitative changes in arterial collagen and elastin content in vivo is not known. We have assessed fluorescence spectroscopy for detection of quantitative changes in arterial composition in situ, in rabbit models of angioplasty and stent implant. Fluorescence emission intensity (FEI) recorded at sites remote from the primary implant site was correlated with immunohistochemical (IH) analysis and extracted elastin and collagen. FEI was significantly decreased (P<0.05) after treatment with anti-inflammatory agents, and plaque area decreased on comparison with saline-treated rabbits after stent implant or angioplasty (Por=0.961) analysis were detected by multiple regression (MR) analysis. Good correlations also were found for FEI with elastin and collagen measured by high-performance liquid chromatography; MR analysis provided highly predictive values for collagen and elastin (R2>or=0.994). Fluorescence spectroscopic analysis detects quantitative compositional changes in arterial connective tissue in vivo, demonstrating changes at sites remote from primary angioplasty and stent implant sites. 相似文献
8.
9.
The microchromatographic procedure for the quantitative analysis of the hemoglobin components in a hemolysate uses columns of DEAE-cellulose in a plastic drinking straw with a glycine-KCN-NaCl developer. Not only may the method be used for the quantitative analysis of Hb-F but also for the analysis of the varied components in mixtures of hemoglobins. 相似文献
10.
Renee J. Soukup-Hein Jeff Schneiderheinze Paul Mehelic Daniel W. Armstrong 《Chromatographia》2007,66(7-8):461-468
Previous work on the LC separation of peptides had shown that macrocyclic glycopeptide stationary phases to be selective for
peptides of five to thirteen amino acids in length. In this work, the selectivity of the teicoplanin stationary phase is compared
to that of a C18 stationary phase for seven diastereomeric enkephalin peptides. The teicoplanin stationary phase separated
all seven diastereomeric enkephalin peptides in a single chromatographic run. The insertion of d-amino acids into the primary enkephalin sequence produced areas of hydrophobicity that influenced retention order on the
C18 stationary phase. However, analogous trends are not observed on the teicoplanin stationary phase, which is more polar
and structurally diverse. Optimization of the mobile phase and the use of a step-gradient for the enkephalin separation on
the teicoplanin stationary phase is discussed. Also, the selectivity of macrocyclic glycopeptide stationary phases for peptides
of 14, 28, 30, and 36 amino acids also is investigated and compared to separation on a C18 stationary phase. A method for
eluting peptides with multiple basic amino acids, which tend to be strongly retained on the macrocyclic glycopeptide stationary
phases, is presented. 相似文献