全文获取类型
收费全文 | 4034篇 |
免费 | 131篇 |
国内免费 | 26篇 |
学科分类
数理化 | 4191篇 |
出版年
2023年 | 29篇 |
2022年 | 68篇 |
2021年 | 105篇 |
2020年 | 95篇 |
2019年 | 112篇 |
2018年 | 128篇 |
2017年 | 97篇 |
2016年 | 151篇 |
2015年 | 137篇 |
2014年 | 163篇 |
2013年 | 232篇 |
2012年 | 266篇 |
2011年 | 302篇 |
2010年 | 188篇 |
2009年 | 138篇 |
2008年 | 278篇 |
2007年 | 269篇 |
2006年 | 238篇 |
2005年 | 206篇 |
2004年 | 161篇 |
2003年 | 130篇 |
2002年 | 118篇 |
2001年 | 53篇 |
2000年 | 46篇 |
1999年 | 47篇 |
1998年 | 38篇 |
1997年 | 30篇 |
1996年 | 36篇 |
1995年 | 23篇 |
1994年 | 34篇 |
1993年 | 16篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 12篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有4191条查询结果,搜索用时 0 毫秒
101.
Łukasz Wiśniewski Katarína Vaňková Pavel Ačai Milan Polakovič 《Chemical Papers》2014,68(12):1649-1655
Galacto-oligosaccharides are typically produced by an enzymatic reaction when the post-reaction mixture contains considerable amounts of lactose and glucose and a smaller amount of galactose. In order to develop a process of chromatographic removal of saccharide impurities, adsorption equilibria and kinetics of these di- and monosaccharides were investigated for Diaion UBK 530, an industrialgrade strong cation-exchanger in the Na+ form. Frontal chromatographic experiments were carried out in the temperature range of 30–70°C and a broad interval of saccharide concentrations up to 350 g L?1. Breakthrough curves were described using the equilibrium-dispersive model with the linear adsorption isotherm. Both the distribution and the axial dispersion coefficient values depended on the saccharide molecule type and size. No significant effect of temperature or concentration on the distribution coefficient was observed. The apparent dispersion coefficients of all saccharides exhibited some decrease with the temperature, which was caused by the decrease of the intraparticle mass transfer resistance. An analysis showed that both the intraparticle mass transfer and the axial dispersion had a significant influence on the front dispersion. 相似文献
102.
Marketa Kominkova Petr Michalek Amitava Moulick Barbora Nemcova Ondrej Zitka Pavel Kopel Miroslava Beklova Vojtech Adam Rene Kizek 《Chromatographia》2014,77(21-22):1441-1449
Biosynthesis belongs to one of the new possibilities of nanoparticles preparation, whereas its main advantage is biocompatibility. In addition, the ability of obtaining the raw material for such synthesis from the soil environment is beneficial and could be useful for remediation. However, the knowledge of mechanisms that are necessary for the biosynthesis or effect on the bio-synthesizing organisms is still insufficient. In this study, we attempted to evaluate the effect of quantum dots (QDs) not only on a model organism of collembolans, but also on another soil organism—earthworm Eisenia fetida—and in also one widespread microorganism such as Escherichia coli. Primarily, we determined 28EC50 as 72.4 μmol L?1 for CdTe QDs in collembolans. Further, we studied the effect of QDs biosynthesis in E. fetida and E. coli. Using determination of QDs, low-molecular thiols and antioxidant activities, we found differences between both organisms and also between ways how they behave in the presence of Cd and/or Cd and Te. The biosynthesis in earthworms can be considered as its own protective mechanism; however, in E. coli, it is probably a by-product of protective mechanisms. 相似文献
103.
104.
J. Pavel M. Glogarov D. Demus A. Mdicke G. Pelzl 《Crystal Research and Technology》1983,18(7):915-921
The binary mixtures of the substance providing cholesteric phase exhibit a chiral SmC* phase for certain concentration and temperature range. This phase was verified to be ferroelectric. The temperature dependences of the spontaneous polarization and the coercive field were determined for three concentrations. The pitch of the helical structure is approximately indirectly proportional to the molar concentration of the cholesteric substance and varies from 3 μm to about 25 μm in the concentration range from 20 mol% to 5 mol% of the cholesteric substance. For the lower concentrations the sample is unwound in planar samples due to the surface anchoring. Two possible unwound planar configurations can be switched by electric field. 相似文献
105.
On a ferroelectric liquid crystal DOBAMBC transitions between helical and twisted structures are observed if changing the temperature. The twisted structure appears when the helical pitch becomes comparable to the sample thickness, From the switching process of the twisted DOBAMBC samples in an electric field the polarity of surface layers is determined. Low signal di- electric permittivity shows an increase below the transition to the ferroelectric phase, which is a consequence of the twisted structure deformation in the electric field. 相似文献
106.
107.
T. V. Gubanova I. K. Garkushin A. V. Mal’tseva 《Russian Journal of Inorganic Chemistry》2016,61(9):1163-1168
The Li, Cs||F, NO3 ternary reciprocal system was for the first time described and experimentally studied by differential thermal analysis and differential scanning calorimetry. Phase equilibrium states were determined, and so were the compositions and melting points of two ternary eutectics. Reactions describing the chemical interaction in the system were presented. 相似文献
108.
Practical synthesis of 1,3-diaryl-substituted 3-isothiocyanatopropan-1-ones based on the reaction of chalcones with thiocyanic acid generated in situ by treatment of thiocyanate ammonium with dilute sulfuric acid has been developed. 相似文献
109.
110.
Elena G. Shcherbakova Dr. Valentina Brega Dr. Tsuyoshi Minami Sara Sheykhi Prof. Dr. Tony D. James Prof. Dr. Pavel Anzenbacher Jr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):10074-10080
A highly accurate and reliable screening method for enantiomeric excess of amine derivatives in the presence of water is reported. The fluorescence‐based screening system has been realized by self‐assembly of chiral diol‐type dyes (BINOL, VANOL and VAPOL), 2‐formylphenylboronic acid, and chiral amines forming iminoboronate esters. The structure and chirality of the amine analytes determine the stability of the diastereomeric iminoboronate esters, which in turn display differential fluorescence. The fluorescence signal reflects the enantiomeric purity of the chiral amines and was utilized in high‐throughput arrays. The arrays were able to recognize enantiomeric excess of amines, amino esters, and amino alcohols. In addition to qualitative analysis, quantitative experiments were successfully performed. Studies of the role of additives such as water or citrate were carried out to gain insight into the stability of the iminoboronate esters. It is shown that the above additives destabilize less stable esters while the stable esters remain unchanged. Thus, the presence of water and citrate leads to increased difference between the diastereomeric iminoboronates and contributes to the enantiodiscrimination of the chiral amines. 相似文献