首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   749篇
  免费   37篇
  国内免费   1篇
  2024年   1篇
  2023年   6篇
  2022年   3篇
  2021年   8篇
  2020年   5篇
  2019年   3篇
  2018年   5篇
  2017年   13篇
  2016年   15篇
  2015年   23篇
  2014年   28篇
  2013年   64篇
  2012年   43篇
  2011年   46篇
  2010年   34篇
  2009年   31篇
  2008年   46篇
  2007年   38篇
  2006年   48篇
  2005年   38篇
  2004年   46篇
  2003年   49篇
  2002年   37篇
  2001年   10篇
  2000年   7篇
  1999年   8篇
  1998年   12篇
  1997年   16篇
  1996年   9篇
  1995年   11篇
  1994年   6篇
  1993年   7篇
  1992年   9篇
  1991年   4篇
  1990年   4篇
  1989年   9篇
  1987年   3篇
  1986年   3篇
  1985年   3篇
  1984年   1篇
  1983年   4篇
  1982年   3篇
  1981年   6篇
  1980年   7篇
  1979年   7篇
  1978年   2篇
  1977年   1篇
  1976年   3篇
  1975年   2篇
排序方式: 共有787条查询结果,搜索用时 421 毫秒
141.
Slightly acidic electrolysed (SAE) water is a sanitizer with strong bactericidal activity due to hypochlorous acid. We assessed the safety of SAE water as drinking water for mice at a 5 ppm total residual chlorine (TRC) concentration to examine the possibility of SAE water as a labour- and energy-saving alternative to sterile water. We provided SAE water or sterile water to mice for 12 weeks, during which time we recorded changes in body weight and weekly water and food intakes. At the end of the experiment, all of the subject animals were sacrificed to assess serum aspartate aminotransferase, alanine aminotransferase and creatinine levels and to examine the main organs histopathologically under a light microscope. In addition, we investigated the bacteria levels of both types of water. We found no difference in functional and morphological health condition indices between the groups. Compared with sterile water, SAE water had a relatively higher ability to suppress bacterial growth. We suggest that SAE water at 5 ppm TRC is a safe and useful alternative to sterile water for use as drinking water in laboratory animal facilities.  相似文献   
142.
143.
Cheumatopsyche brevilineata (Iwata, 1927 Iwata, M. (1927), ‘Trichopterous Larvae from Japan’, Zoological Magazine, 39, 209272. (In Japanese) [Google Scholar]) is a filter-feeding caddisfly without distinct separable generations. We conducted a life history survey of C. brevilineata under a natural thermal regime. This caddis species had a multivoltine life history and their generations partially overlapped each other. From the seasonal change of larval and pupal density, we recognized one overwintering generation and three non-winter generations. We propose a new method to estimate the population size of fourth instar larvae from each generation by using the ‘development zero’ and ‘effective degree-days’ methods. The second non-winter generation, developing under the hottest water temperature regime, had the largest population size and highest observed density. The overwintering generation, which developed under the coolest thermal regime, showed the smallest population size but its observed density was not the smallest.  相似文献   
144.
Spontaneously hypertensive rats (SHRs) are used as a model for attention-deficit/hyperactivity disorder (ADHD), since SHRs are hyperactive and show defective sustained attention in behavioral tasks. The psychostimulants amphetamine and methylphenidate and the selective norepinephrine reuptake inhibitor atomoxetine are used as ADHD medications. The effects of high K+ stimulation or psychostimulants on brain norepinephrine or dopamine release in SHRs have been previously studied both in vitro and in vivo, but the effects of atomoxetine on these neurotransmitters have not. The present study examined the effects of administration of atomoxetine on extracellular norepinephrine, dopamine, and serotonin levels in the prefrontal cortex of juvenile SHRs and Wistar-Kyoto (WKY) rats. Baseline levels of prefrontal norepinephrine, dopamine, and serotonin were similar in SHRs and WKY rats. Systemic administration of atomoxetine (3 mg/kg) induced similar increases in prefrontal norepinephrine and dopamine, but not serotonin, levels in both strains. Furthermore, there was no difference in high K+-induced increases in extracellular norepinephrine, dopamine, and serotonin levels in the prefrontal cortex between SHRs and WKY rats. These findings indicate that monoamine systems in the prefrontal cortex are similar between SHRs and WKY rats.  相似文献   
145.

Purpose

To design a mathematical model that can predict the relationship between the ganglion cell complex (GCC) thickness and visual field sensitivity (VFS) in glaucoma patients.

Design

Retrospective cross-sectional case series.

Method

Within 3 months from VFS measurements by the Humphrey field analyzer 10-2 program, 83 eyes underwent macular GCC thickness measurements by spectral-domain optical coherence tomography (SD-OCT). Data were used to construct a multiple logistic model that depicted the relationship between the explanatory variables (GCC thickness, age, sex, and spherical equivalent of refractive errors) determined by a regression analysis and the mean VFS corresponding to the SD-OCT scanned area. Analyses were performed in half or 8 segmented local areas as well as in whole scanned areas. A simple logistic model that included GCC thickness as the single explanatory variable was also constructed. The ability of the logistic models to depict the real GCC thickness/VFS in SAP distribution was analyzed by the χ2 test of goodness-of-fit. The significance of the model effect was analyzed by analysis of variance (ANOVA).

Results

Scatter plots between the GCC thickness and the mean VFS showed sigmoid curves. The χ2 test of goodness-of-fit revealed that the multiple logistic models showed a good fit for the real GCC thickness/VFS distribution in all areas except the nasal-inferior-outer area. ANOVA revealed that all of the multiple logistic models significantly predicted the VFS based on the explanatory variables. Although simple logistic models also exhibited significant VFS predictability based on the GCC thickness, the model effect was less than that observed for the multiple logistic models.

Conclusions

The currently proposed logistic models are useful methods for depicting relationships between the explanatory variables, including the GCC thickness, and the mean VFS in glaucoma patients.  相似文献   
146.
Transitions between sex determination systems have occurred in many lineages of squamates and it follows that novel sex chromosomes will also have arisen multiple times. The formation of sex chromosomes may be reinforced by inhibition of recombination and the accumulation of repetitive DNA sequences. The karyotypes of monitor lizards are known to be highly conserved yet the sex chromosomes in this family have not been fully investigated. Here, we compare male and female karyotypes of three Australian monitor lizards, Varanus acanthurus, V. gouldii and V. rosenbergi, from two different clades. V. acanthurus belongs to the acanthurus clade and the other two belong to the gouldii clade. We applied C-banding and comparative genomic hybridization to reveal that these species have ZZ/ZW sex micro-chromosomes in which the W chromosome is highly differentiated from the Z chromosome. In combination with previous reports, all six Varanus species in which sex chromosomes have been identified have ZZ/ZW sex chromosomes, spanning several clades on the varanid phylogeny, making it likely that the ZZ/ZW sex chromosome is ancestral for this family. However, repetitive sequences of these ZW chromosome pairs differed among species. In particular, an (AAT)n microsatellite repeat motif mapped by fluorescence in situ hybridization on part of W chromosome in V. acanthurus only, whereas a (CGG)n motif mapped onto the W chromosomes of V. gouldii and V. rosenbergi. Furthermore, the W chromosome probe for V. acanthurus produced hybridization signals only on the centromeric regions of W chromosomes of the other two species. These results suggest that the W chromosome sequences were not conserved between gouldii and acanthurus clades and that these repetitive sequences have been amplified rapidly and independently on the W chromosome of the two clades after their divergence.  相似文献   
147.
148.
The possible involvement of ethylene in in vitrorooting of faba bean (Vicia faba L.) shootsregenerated on medium containing thidiazuron wasinvestigated. The effects of the ethylene precursor1-aminocyclopropane-1-carboxylic acid (ACC) and threeethylene inhibitors, silver nitrate (AgNO3),acetyl salicylic acid (ASA) and cobalt chloride(CoCl2) on root formation were tested in vitrousing TDZ-induced shoots of faba bean accession 760.ACC inhibited root formation. In contrast, ethyleneinhibitors promoted root formation, AgNO3 at theappropriate concentrations enhanced root emergence andincreased root number per shoot, root growth rate, androot length. Both CoCl2 and ASA at theappropriate concentrations increased rootingefficiency. These promotive effects may result from areduction in ethylene concentration or inhibition ofethylene action. The results offer a new approach toimprove the rooting efficiency of TDZ-induced shootsof faba bean and possibly of other plant species.  相似文献   
149.
150.
The lung collectin surfactant protein A (SP-A) has been implicated in the regulation of pulmonary host defense and inflammation. Zymosan induces proinflammatory cytokines in immune cells. Toll-like receptor (TLR)2 has been shown to be involved in zymosan-induced signaling. We first investigated the interaction of TLR2 with zymosan. Zymosan cosedimented the soluble form of rTLR2 possessing the putative extracellular domain (sTLR2). sTLR2 directly bound to zymosan with an apparent binding constant of 48 nM. We next examined whether SP-A modulated zymosan-induced cellular responses. SP-A significantly attenuated zymosan-induced TNF-alpha secretion in RAW264.7 cells and alveolar macrophages in a concentration-dependent manner. Although zymosan failed to cosediment SP-A, SP-A significantly reduced zymosan-elicited NF-kappaB activation in TLR2-transfected human embryonic kidney 293 cells. Because we have shown that SP-A binds to sTLR2, we also examined whether SP-A affected the binding of sTLR2 to zymosan. SP-A significantly attenuated the direct binding of sTLR2 to zymosan in a concentration-dependent fashion. From these results, we conclude that 1) TLR2 directly binds zymosan, 2) SP-A can alter zymosan-TLR2 interaction, and 3) SP-A down-regulates TLR2-mediated signaling and TNF-alpha secretion stimulated by zymosan. This study supports an important role of SP-A in controlling pulmonary inflammation caused by microbial pathogens.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号