全文获取类型
收费全文 | 663篇 |
免费 | 69篇 |
国内免费 | 25篇 |
出版年
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 12篇 |
2020年 | 16篇 |
2019年 | 28篇 |
2018年 | 23篇 |
2017年 | 24篇 |
2016年 | 23篇 |
2015年 | 16篇 |
2014年 | 41篇 |
2013年 | 59篇 |
2012年 | 33篇 |
2011年 | 38篇 |
2010年 | 34篇 |
2009年 | 24篇 |
2008年 | 24篇 |
2007年 | 32篇 |
2006年 | 35篇 |
2005年 | 24篇 |
2004年 | 15篇 |
2003年 | 18篇 |
2002年 | 14篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 18篇 |
1997年 | 10篇 |
1996年 | 12篇 |
1995年 | 9篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有757条查询结果,搜索用时 15 毫秒
71.
The inhibitory neuromodulator taurine is involved in osmoregulation and cell volume adjustments in the central nervous system. In addition, taurine protects neural cells from excitotoxicity and prevents harmful metabolic events evoked by cell-damaging conditions. The release of taurine in nervous cell preparations is greatly enhanced by glutamate receptor agonists and various cell-damaging conditions. NO-generating compounds also increase taurine release in the mouse hippocampus. The further involvement of the NO/cGMP pathway and protein kinases in preloaded [3H]taurine release from hippocampal slices from adult (3-month-old) and developing (7-day-old) mice in normoxia and in ischemia was now studied using a superfusion system. The release was enhanced by 8-Br-cGMP and the phosphodiesterase inhibitor 2-(2-propyloxyphenyl)-8-azapurin-6-one (zaprinast), particularly in the immature hippocampus, indicating that increased cGMP levels induce taurine release. The release was also increased by the inhibitor of soluble guanylyl cyclase, 1H-(1,2,4)oxadiazolo-(4,3a)quinoxalin-1-one (ODQ) and the protein kinase C activator 4-phorbol 12-myristate 13-acetate (PMA), but only in the adult hippocampus. The ischemia-induced release was also enhanced by increased cGMP levels in both adult and developing mice, whereas protein kinase inhibitors had no effects in any conditions. The results demonstrate that cGMP is able to modulate hippocampal taurine release in both adult and developing mice, the rise in cGMP levels evoking taurine release in normoxia and in ischemia. This could be part of the neuroprotective properties of taurine, being thus important particularly in cell-damaging conditions and in preventing excitotoxicity. 相似文献
72.
Influence of the yeast strain on the changes of the amino acids,peptides and proteins during sparkling wine production by the traditional method 总被引:2,自引:0,他引:2
Martínez-Rodríguez AJ Carrascosa AV Martín-Alvarez PJ Moreno-Arribas V Polo MC 《Journal of industrial microbiology & biotechnology》2002,29(6):314-322
The influence of five yeast strains on the nitrogen fractions, amino acids, peptides and proteins, during 12 months of aging
of sparkling wines produced by the traditional or Champenoise method, was studied. High-performance liquid chromatography
(HPLC) techniques were used for analysis of the amino acid and peptide fractions. Proteins plus polypeptides were determined
by the colorimetric Bradford method. Four main stages were detected in the aging of wines with yeast. In the first stage,
a second fermentation took place; amino acids and proteins plus polypeptides diminished, and peptides were liberated. In the
second stage, there was a release of amino acids and proteins, and peptides were degraded. In the third stage, the release
of proteins and peptides predominated. In the fourth stage, the amino acid concentration diminished. The yeast strain used
influenced the content of free amino acids and peptides and the aging time in all the nitrogen fractions.
Received 25 March 2002/ Accepted in revised form 31 July 2002 相似文献
73.
代谢性谷氨酸受体及其在疼痛机制中的作用 总被引:1,自引:0,他引:1
代谢性谷氨酸受体是一个新的G-蛋白相关受体家族,各类亚型在分子生物学特征、神经药理学特征和中枢神经系统分布方面有所不同。根据其序列的同源性程度可将其分为三组。近来的研究证实代谢性谷氨酸受体在痛信息传递机制中具有重要作用。本文将对代谢性谷氨酸受体在上述机制中的可能作用作一综述。 相似文献
74.
Neuronal signaling systems and ethanol dependence 总被引:2,自引:0,他引:2
Subhash C. Pandey 《Molecular neurobiology》1998,17(1-3):1-15
In recent years there have been remarkable developments toward the understanding of the molecular and/or cellular changes
in the neuronal second-messenger pathways during ethanol dependence. In general, it is believed that the cyclic adenosine
3′, 5′-monophosphate (cAMP) and the phosphoinositide (PI) signal-transduction pathways may be the intracellular targets that
mediate the action of ethanol and ultimately contribute to the molecular events involved in the development of ethanol tolerance
and dependence. Several laboratories have demonstrated that acute ethanol exposure increases, whereas protracted ethanol exposure
decreases, agonist-stimulated adenylate cyclase activity in a variety of cell systems, including the rodent brain. Recent
studies indicate that various postreceptor events of the cAMP signal transduction cascade (i.e., Gs protein, protein kinase A [PKA], and cAMP-responsive element binding protein [CREB]) in the rodent brain are also modulated
by chronic ethanol exposure. The PI signal-transduction cascade represents another important second-messenger system that
is modulated by both acute and chronic ethanol exposure in a variety of cell systems. It has been shown that protracted ethanol
exposure significantly decreases phospholipase C (PLC) activity in the cerebral cortex of mice and rats. The decreased PLC
activity during chronic ethanol exposure may be caused by a decrease in the protein levels of the PLC-Β1 isozyme but not of PLC-δ1 or PLC-γ1 isozymes in the rat cerebral cortex. Protein kinase C (PKC), which is a key step in the Pi-signaling cascade, has been shown
to be altered in a variety of cell systems by acute or chronic ethanol exposure. It appears from the literature that PKC plays
an important role in the modulation of the function of various neurotransmitter receptors (e.g., γ-aminobutyrate type A [GABAa],
N-methyl-D-aspartate [NMDA], serotonin2A [5-HT2a], and 5-HT2C, and muscarinic [m1] receptors) resulting from ethanol exposure.
The findings described in this review article indicate that neuronal-signaling proteins represent a molecular locus for the
action of ethanol and are possibly involved in the neuroadaptational mechanisms to protracted ethanol exposure. These findings
support the notion that alterations in the cAMP and the PI-signaling cascades during chronic ethanol exposure could be the
critical molecular events associated with the development of ethanol dependence. 相似文献
75.
传染性法氏囊病病毒在次代鸡胚成纤维细胞上的增殖 总被引:2,自引:0,他引:2
研究了用次代鸡胚成纤维细胞(SCEF)增殖传染性法氏囊病病毒(IBDV)的可能性。在研究了原代鸡胚成纤维细胞(PCEF)与SCEF的生长特性的基础上,就各种培养方式采用PCEF与SCEF增殖IBDV进行了比较。结果表明,可用SCEF代替PCEF进行IBDV的增殖培养。 相似文献
76.
Stephen W. Jones 《Journal of bioenergetics and biomembranes》1998,30(4):299-312
Voltage-dependent calcium channels couple electrical signals to cellular responses in excitable cells. Calcium channels are crucial for excitation–secretion coupling in neurons and endocrine cells, and excitation–contraction coupling in muscle. Several pharmacologically and kinetically distinct calcium channel types have been identified at the electrophysiological and molecular levels. This review summarizes the basic properties of voltage-dependent calcium channels, including mechanisms of ion permeation and block, gating kinetics, and modulation by G proteins and second messengers. 相似文献
77.
Second‐derivative synchronous spectrofluorimetric determination of nebivolol hydrochloride and amlodipine besylate in their combined dosage form
下载免费PDF全文
![点击此处可从《Luminescence》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A rapid, simple, accurate and highly sensitive spectrofluorimetric method was developed for the simultaneous analysis of nebivolol hydrochloride (NEB) and amlodipine besylate (AML). The method was based on measuring the synchronous fluorescence intensity of the drugs at Δλ = 40 nm in methanol. Various experimental parameters affecting the synchronous fluorescence of the studied drugs were carefully studied and optimized. The calibration plots were rectilinear over concentration ranges of 0.05–1.5 µg/mL and 0.5–10 µg/mL for NEB and AML with limits of detection (LOD) of 0.010 and 0.051 µg/mL and limits of quantitation (LOQ) of 0.031 and 0.156, respectively. The peak amplitudes (2D) of the second derivative synchronous fluorimetry (SDSF) were estimated at 282 nm for NEB and at 393 nm for AML. Good linearity was obtained over the concentration ranges. The proposed method was successfully applied to the determination of the studied compounds in laboratory‐prepared mixtures, commercial single and laboratory‐prepared tablets. The results were in good agreement with those obtained using the comparison method. The mean percent recoveries were found to be 100.12 ± 0.77 and 99.91 ± 0.77 for NEB and AML, respectively. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
78.
79.
Christiaan P. Beljaars 《Biochemical and biophysical research communications》2010,392(3):346-350
In antioxidant competition assays, an antioxidant (A) and a detector compound (D) compete for a reactive species (R). In the evaluation of these assays, it is tacitly assumed that all of R is captured by either D or A. Due to the - by definition - high reactivity of R, unspecific reactions of R are likely to occur and neglecting these reactions will result in a systematic underestimation of antioxidant activity. It was shown that in the standard hydroxyl radical scavenging assay this was indeed the case; the inaccurate mathematical evaluation resulted in an underestimation of antioxidant activity of 25% in this competition assay. The systematic underestimation of antioxidant activity can be prevented by using an adjusted Stern-Volmer equation that takes into account that only part of R is captured by D or A. 相似文献
80.
Ryo Nagao Tatsuya Tomo Eri Noguchi Takehiro Suzuki Yasuhiro Kashino Masahiko Ikeuchi 《BBA》2010,1797(2):160-166
Oxygen-evolving Photosystem II particles (crude PSII) retaining a high oxygen-evolving activity have been prepared from a marine centric diatom, Chaetoceros gracilis (Nagao et al., 2007). The crude PSII, however, contained a large amount of fucoxanthin chlorophyll a/c-binding proteins (FCP). In this study, a purified PSII complex which was deprived of major components of FCP was isolated by one step of anion exchange chromatography from the crude PSII treated with Triton X-100. The purified PSII was still associated with the five extrinsic proteins of PsbO, PsbQ', PsbV, Psb31 and PsbU, and showed a high oxygen-evolving activity of 2135 μmol O2 (mg Chl a)− 1 h− 1 in the presence of phenyl-p-benzoquinone which was virtually independent of the addition of CaCl2. This activity is more than 2.5-fold higher than the activity of the crude PSII. The activity was completely inhibited by 3-(3,4)-dichlorophenyl-(1,1)-dimethylurea (DCMU). The purified PSII contained 42 molecules of Chl a, 2 molecules of diadinoxanthin and 2 molecules of Chl c on the basis of two molecules of pheophytin a, and showed typical absorption and fluorescence spectra similar to those of purified PSIIs from the other organisms. In this study, we also found that the crude PSII was significantly labile, as a significant inactivation of oxygen evolution, chlorophyll bleaching and degradation of PSII subunits were observed during incubation at 25 °C in the dark. In contrast, these inactivation, bleaching and degradation were scarcely detected in the purified PSII. Thus, we succeeded for the first time in preparation of a stable PSII from diatom cells. 相似文献