全文获取类型
收费全文 | 1603篇 |
免费 | 79篇 |
国内免费 | 1篇 |
出版年
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 42篇 |
2020年 | 35篇 |
2019年 | 36篇 |
2018年 | 46篇 |
2017年 | 38篇 |
2016年 | 69篇 |
2015年 | 93篇 |
2014年 | 88篇 |
2013年 | 127篇 |
2012年 | 179篇 |
2011年 | 149篇 |
2010年 | 94篇 |
2009年 | 58篇 |
2008年 | 71篇 |
2007年 | 73篇 |
2006年 | 66篇 |
2005年 | 61篇 |
2004年 | 45篇 |
2003年 | 49篇 |
2002年 | 39篇 |
2001年 | 10篇 |
2000年 | 13篇 |
1999年 | 16篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1982年 | 9篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 5篇 |
排序方式: 共有1683条查询结果,搜索用时 15 毫秒
1.
The protein–nanomaterial interface 总被引:1,自引:1,他引:0
2.
Mutational, kinetic, and chemical modification experiments show that one of the three-way helical junctions in the Neurospora VS ribozyme contains a uridine turn that is important for organizing the functional three-dimensional structure of this junction. Disruption of the uridine turn disrupts the structure of the junction and decreases the self-cleavage activity of the ribozyme; however, substitution of the uridine turn with a variety of different hairpins, thereby transforming the three-way junction into a four-way junction, maintains catalytic activity. Chemical modification structure probing reveals that both the native junction and the hairpin-containing junction support the same tertiary interactions required elsewhere in the ribozyme for catalysis. These observations show that functionally equivalent three-dimensional RNA structures can be built from different secondary structure elements. 相似文献
3.
4.
5.
Sarvesh Kumar Sood 《Plant Systematics and Evolution》1992,179(1-2):95-105
InMalaxis saprophyta, anther wall development corresponds to the Monocotyledonous type. The uninucleate tapetum is of secretory type and the endothecium develops U- and V-shaped thickenings on the inner tangential and radial walls. Cytokinesis is simultaneous; tetrahedral, isobilateral and T-shaped tetrads are formed which are compactly aggregated in pollinia. At anthesis the microspore tetrads are 2-celled. The ovule is anatropous, bitegmic and both integuments are dermal in origin. A single hypodermal cell develops directly into a megaspore mother cell. Embryo sac development is predominantly monosporic and less often bisporic. Irrespective of the type of development, the mature embryo sac is 6-nucleate. Although double fertilization occurs, the primary endosperm nucleus degenerates. Embryogeny is of the Onagrad type. The mature embryo lacks differentiation into cotyledon, plumule and radicle. The reticulate seed coat is formed entirely by the outer layer of outer integument. There are three sterile and three fertile valves in the ovary. Although initially parenchymatous, the entire three sterile valves in the ovary and the upper half of the three fertile valves become sclerified after fertilization. The embryological characters support the disputed systematic position ofMalaxis within subtribeMalaxidinae ofEpidendreae. 相似文献
6.
Metabolism of Monoterpenes : Evidence for the Function of Monoterpene Catabolism in Peppermint (Mentha piperita) Rhizomes 总被引:1,自引:1,他引:0
l-Menthone of peppermint leaves is reduced to d-neomenthol which is glucosylated and transported to the rhizome, whereupon the β-d-glucoside is hydrolyzed, the aglycone oxidized back to l-menthone, and this ketone converted to l-3,4-menthone lactone. l-[G-3H]-3,4-Menthone lactone and its labeled progenitors, when incubated with excised mint rhizomes, gave rise to nonvolatile lipids as well as polar metabolites. The lipids thus generated consisted of labeled squalene and phytosterols in the nonsaponifiable fraction and C14-C26 fatty acids in the saponifiable fraction. These results imply degradation of the terpenoid to acetylcoenzyme A and reduced pyridine nucleotide, and reincorporation of label via these products. Starch and soluble carbohydrates were also found to be labeled; however, chemical degradation of the [3H]glucose obtained on hydrolysis of starch indicated the presence of tritium only on interior carbons, suggesting that labeling had occurred via reduced pyridine nucleotides. Analysis of the labeled organic acids revealed the presence of several hydroxy methylacyl intermediates suggesting the operation of a modified β-oxidation pathway in the degradation of the acyclic terpenoid skeleton. The results indicate that monoterpenes transported to the rhizome are oxidized to yield acetyl-coenzyme A and reduced pyridine nucleotides, and suggest that metabolic turnover of monoterpenes in mint represents a mechanism for recycling carbon and energy from foliar terpenes into other metabolites of the rhizome. 相似文献
7.
8.
Protoplasma - Picrorhiza kurroa Royle ex Benth is a valuable medicinal herb of North-Western Himalayas due to presence of two major bioactive compounds, picroside-I and picroside-II used in the... 相似文献
9.
Alka Dr. Vijay K. Vishvakarma Sandeep Yadav Prof. Dr. Prashant Singh Dr. Pallavi Jain 《化学与生物多样性》2023,20(6):e202300042
Mn(II) and Co(II) complexes of methyl-(Z)−N′-carbamothioylcarbamohydrazonate Schiff base ligand were synthesized. The ligand and metal salts were taken in 2 : 1 stoichiometric ratio. All the synthesized complexes were characterized using elemental analysis, molar conductance, magnetic moment and various spectroscopic techniques (FT-IR, UV/VIS, EPR) techniques. Elemental and spectroscopic results verified bidentate donor nature of the ligand and octahedral geometry of all the complexes. The non-electrolytic nature of Mn(II) and Co(II) complexes were suggested by conductivity data analysis. In vitro antibacterial (E. coli and S. aureus) and antifungal (C. albicans and C. tropicalis) screening were achieved by employing agar well diffusion method which revealed better antimicrobial activity of Co(II) complexes than Mn(II) complexes. In silico SwissADME study predicted the drug-likeness probability of ligand and complexes. The interaction of two bacterial proteins (E. coli and S. aureus) with compounds was also analyzed using molecular docking study, which corroborate the in vitro analysis. 相似文献
10.
Marjon J. H. van Haandel I. M. C. M. Rietjens Ans E. M. F. Soffers Cees Veeger Jacques Vervoort Sandeep Modi Madhu S. Mondal Prasanta K. Patel Digambar V. Behere 《Journal of biological inorganic chemistry》1996,1(5):460-467
The second-order rate constants for the oxidation of a series of phenol derivatives by horseradish peroxidase compound II
were compared to computer-calculated chemical parameters characteristic for this reaction step. The phenol derivatives studied
were phenol, 4-chlorophenol, 3-hydroxyphenol, 3-methylphenol, 4-methylphenol, 4-hydroxybenzoate, 4-methoxyphenol and 4-hydroxybenzaldehyde.
Assuming a reaction of the phenolic substrates in their non-dissociated, uncharged forms, clear correlations (r = 0.977 and r = 0.905) were obtained between the natural logarithm of the second-order rate constants (ln k
app and ln k
2 respectively) for their oxidation by compound II and their calculated ionisation potential, i.e. minus the energy of their
highest occupied molecular orbital [E(HOMO)]. In addition to this first approach in which the quantitative structure-activity
relationship (QSAR) was based on a calculated frontier orbital parameter of the substrate, in a second and third approach
the relative heat of formation (ΔΔHF) calculated for the process of one-electron abstraction and H• abstraction from the phenol derivatives was used as a parameter. Plots of the natural logarithms of the second-order rate
constants (k
app and k
2) for the reaction and the calculated ΔΔHF values for the process of one-electron abstraction also provide clear QSARs with
correlation coefficients of –0.968 and –0.926 respectively. Plots of the natural logarithms of the second-order rate constants
(k
app and k
2) for the reaction and the calculated ΔΔHF values for the process of H• abstraction provide QSARs with correlation coefficients of –0.989 and –0.922 respectively. Since both mechanisms considered,
i.e. initial electron abstraction versus initial H• abstraction, provided clear QSARs, the results could not be used to discriminate between these two possible mechanisms for
phenol oxidation by horseradish peroxidase compound II. The computer calculation-based QSARs thus obtained for the oxidation
of the various phenol derivatives by compound II from horseradish peroxidase indicate the validity of the approaches investigated,
i.e. both the frontier orbital approach and the approach in which the process is described by calculated relative heats of
formation. The results also indicate that outcomes from computer calculations on relatively unrelated phenol derivatives can
be reliably compared to one another. Furthermore, as the actual oxidation of peroxidase substrates by compound II is known
to be the rate-limiting step in the overall catalysis by horseradish peroxidase, the QSARs of the present study may have implications
for the differences in the overall rate of substrate oxidation of the phenol derivatives by horseradish peroxidase.
Received: 29 March 1996 / Accepted: 17 July 1996 相似文献