全文获取类型
收费全文 | 668篇 |
免费 | 25篇 |
国内免费 | 1篇 |
出版年
2023年 | 2篇 |
2022年 | 13篇 |
2021年 | 15篇 |
2020年 | 18篇 |
2019年 | 15篇 |
2018年 | 27篇 |
2017年 | 14篇 |
2016年 | 26篇 |
2015年 | 38篇 |
2014年 | 46篇 |
2013年 | 66篇 |
2012年 | 44篇 |
2011年 | 55篇 |
2010年 | 38篇 |
2009年 | 26篇 |
2008年 | 40篇 |
2007年 | 35篇 |
2006年 | 30篇 |
2005年 | 23篇 |
2004年 | 14篇 |
2003年 | 18篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1994年 | 3篇 |
1991年 | 2篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1968年 | 1篇 |
1966年 | 2篇 |
1906年 | 1篇 |
排序方式: 共有694条查询结果,搜索用时 15 毫秒
81.
Angusamy Annapoorani Abdul Karim Kamil Abdul Jabbar Syed Khadar Syed Musthafa Shunmugiah Karutha Pandian Arumugam Veera Ravi 《Indian journal of microbiology》2012,52(2):160-166
The focal intent of this study was to find out an alternative strategy for the antibiotic usage against bacterial infections. The quorum sensing inhibitory (QSI) activity of marine sponges collected from Palk Bay, India was evaluated against acyl homoserine lactone (AHL) mediated violacein production in Chromobacterium violaceum (ATCC 12472), CV026 and virulence gene expressions in clinical isolate Serratia marcescens PS1. Out of 29 marine sponges tested, the methanol extracts of Aphrocallistes bocagei (TS 8), Haliclona (Gellius) megastoma (TS 25) and Clathria atrasanguinea (TS 27) inhibited the AHL mediated violacein production in C. violaceum (ATCC 12472) and CV026. Further, these sponge extracts inhibited the AHL dependent prodigiosin pigment, virulence enzymes such as protease, hemolysin production and biofilm formation in S. marcescens PS1. However, these sponge extracts were not inhibitory to bacterial growth, which reveals the fact that the QSI activity of these extracts was not related to static or killing effects on bacteria. Based on the obtained results, it is envisaged that the marine sponges could pave the way to prevent quorum sensing (QS) mediated bacterial infections. 相似文献
82.
Soykan CU Brand LA Ries L Stromberg JC Hass C Simmons DA Patterson WJ Sabo JL 《PloS one》2012,7(1):e28235
Riparian areas are noted for their high biodiversity, but this has rarely been tested across a wide range of taxonomic groups. We set out to describe species richness, species abundance, and community similarity patterns for 11 taxonomic groups (forbs & grasses, shrubs, trees, solpugids, spiders, scarab beetles, butterflies, lizards, birds, rodents, and mammalian carnivores) individually and for all groups combined along a riparian-upland gradient in semiarid southeastern Arizona, USA. Additionally, we assessed whether biological characteristics could explain variation in diversity along the gradient using five traits (trophic level, body size, life span, thermoregulatory mechanism, and taxonomic affiliation). At the level of individual groups diversity patterns varied along the gradient, with some having greater richness and/or abundance in riparian zones whereas others were more diverse and/or abundant in upland zones. Across all taxa combined, riparian zones contained significantly more species than the uplands. Community similarity between riparian and upland zones was low, and beta diversity was significantly greater than expected for most taxonomic groups, though biological traits explained little variance in diversity along the gradient. These results indicate heterogeneity amongst taxa in how they respond to the factors that structure ecological communities in riparian landscapes. Nevertheless, across taxonomic groups the overall pattern is one of greater species richness and abundance in riparian zones, coupled with a distinct suite of species. 相似文献
83.
The stock market is considered essential for economic growth and expected to contribute to improved productivity. An efficient pricing mechanism of the stock market can be a driving force for channeling savings into profitable investments and thus facilitating optimal allocation of capital. This study investigated the technical efficiency of selected groups of companies of Bangladesh Stock Market that is the Dhaka Stock Exchange (DSE) market, using the stochastic frontier production function approach. For this, the authors considered the Cobb-Douglas Stochastic frontier in which the technical inefficiency effects are defined by a model with two distributional assumptions. Truncated normal and half-normal distributions were used in the model and both time-variant and time-invariant inefficiency effects were estimated. The results reveal that technical efficiency decreased gradually over the reference period and that truncated normal distribution is preferable to half-normal distribution for technical inefficiency effects. The value of technical efficiency was high for the investment group and low for the bank group, as compared with other groups in the DSE market for both distributions in time-varying environment whereas it was high for the investment group but low for the ceramic group as compared with other groups in the DSE market for both distributions in time-invariant situation. 相似文献
84.
Banking system plays an important role in the economic development of any country. Domestic banks, which are the main components of the banking system, have to be efficient; otherwise, they may create obstacle in the process of development in any economy. This study examines the technical efficiency of the Malaysian domestic banks listed in the Kuala Lumpur Stock Exchange (KLSE) market over the period 2005-2010. A parametric approach, Stochastic Frontier Approach (SFA), is used in this analysis. The findings show that Malaysian domestic banks have exhibited an average overall efficiency of 94 percent, implying that sample banks have wasted an average of 6 percent of their inputs. Among the banks, RHBCAP is found to be highly efficient with a score of 0.986 and PBBANK is noted to have the lowest efficiency with a score of 0.918. The results also show that the level of efficiency has increased during the period of study, and that the technical efficiency effect has fluctuated considerably over time. 相似文献
85.
86.
In the present study we examined the effect of seminal plasma (SP) on angiogenesis in the porcine oviduct. Gene expressions of vascular endothelial growth factor (VEGF) and its two receptors (Flt-1: fms-like tyrosine kinase and Flk-1/KDR: fetal liver kinase-1/kinase insert domain-containing receptor) as well as fibroblast growth factors (FGF-1 and 2) and von Willenbrand factor (VWF) were determined in the oviduct of SP-treated and control (PBS-treated) gilts. Moreover, vascular density (VD) indicated by endothelial cell area immunolocalized by VWF staining, was assessed in the oviducts. Real-time PCR revealed significantly higher expression of FGF-2 and VWF on day 1 (p < 0.05) after SP administration in comparison to control animals. In contrast, Flt-1 mRNA level on day 1 was lower in SP-treated gilts compared to controls (p < 0.05). In the examined oviductal sections, VD did not differ between control and SP-treated animals. However, in SP-treated animals VD was higher on day 5 than on day 1 (p < 0.05) or 3 (p < 0.01). SP had no significant effect on VEGF, Flk-1/KDR and FGF-1 mRNA expression. In conclusion, our results suggest that SP affects the vascular network by changing the expression of factors contributing to angiogenesis. 相似文献
87.
González S Moreno-Delgado D Moreno E Pérez-Capote K Franco R Mallol J Cortés A Casadó V Lluís C Ortiz J Ferré S Canela E McCormick PJ 《PLoS biology》2012,10(6):e1001347
The role of the pineal gland is to translate the rhythmic cycles of night and day encoded by the retina into hormonal signals that are transmitted to the rest of the neuronal system in the form of serotonin and melatonin synthesis and release. Here we describe that the production of both melatonin and serotonin by the pineal gland is regulated by a circadian-related heteromerization of adrenergic and dopamine D4 receptors. Through α1
B-D4 and β1-D4 receptor heteromers dopamine inhibits adrenergic receptor signaling and blocks the synthesis of melatonin induced by adrenergic receptor ligands. This inhibition was not observed at hours of the day when D4 was not expressed. These data provide a new perspective on dopamine function and constitute the first example of a circadian-controlled receptor heteromer. The unanticipated heteromerization between adrenergic and dopamine D4 receptors provides a feedback mechanism for the neuronal hormone system in the form of dopamine to control circadian inputs. 相似文献
88.
89.
Radziewicz H Ibegbu CC Hon H Osborn MK Obideen K Wehbi M Freeman GJ Lennox JL Workowski KA Hanson HL Grakoui A 《Journal of virology》2008,82(20):9808-9822
A majority of patients infected with hepatitis C virus (HCV) do not sustain an effective T-cell response, and viremia persists. The mechanism leading to failure of the HCV-specific CD8+ T-cell response in patients developing chronic infection is unclear. We investigated apoptosis susceptibility of HCV-specific CD8+ T cells during the acute and chronic stages of infection. Although HCV-specific CD8+ T cells in the blood during the acute phase of infection and in the liver during the chronic phase were highly activated and expressed an effector phenotype, the majority was undergoing apoptosis. In contrast, peripheral blood HCV-specific CD8+ T cells during the chronic phase expressed a resting memory phenotype. Apoptosis susceptibility of HCV-specific CD8+ T cells was associated with very high levels of programmed death-1 (PD-1) and low CD127 expression and with significant functional T-cell deficits. Further evaluation of the “death phase” of HCV-specific CD8+ T cells during acute HCV infection showed that the majority of cells were dying by a process of cytokine withdrawal, mediated by activated caspase 9. Contraction during the acute phase occurred rapidly via this process despite the persistence of the virus. Remarkably, in the chronic phase of HCV infection, at the site of infection in the liver, a substantial frequency of caspase 9-mediated T-cell death was also present. This study highlights the importance of cytokine deprivation-mediated apoptosis with consequent down-modulation of the immune response to HCV during acute and chronic infections. 相似文献
90.
Improving the efficacy of antidotal treatment of poisonings with nerve agents is still a challenge for the scientific community. This study investigated the interactions of four bispyridinium oximes with human erythrocyte acetylcholinesterase (AChE) and their effects on soman- and tabun-poisoned mice. Oximes HI-6 and TMB-4 were used for comparison. These oximes inhibited AchE with inhibitory potency (IC(50)) ranging from 0.02 to 1.0 mM. The best reactivating potency (%R) was obtained with K074, when AChE was inhibited by tabun. The protective potency (P(50)) of all oximes in human erythrocyte AChE inhibited by soman and tabun could not be determined. In tabun-poisoned mice very good antidotal efficacy was obtained with K027, K048, and K074, which makes them interesting for future investigation. The combination of HI-6 and atropine is the therapy of choice for soman poisoning. 相似文献