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   2470篇
  免费   131篇
  国内免费   11篇
  2612篇
  2024年   4篇
  2023年   29篇
  2022年   66篇
  2021年   123篇
  2020年   73篇
  2019年   64篇
  2018年   113篇
  2017年   82篇
  2016年   101篇
  2015年   155篇
  2014年   177篇
  2013年   218篇
  2012年   204篇
  2011年   183篇
  2010年   113篇
  2009年   111篇
  2008年   118篇
  2007年   114篇
  2006年   114篇
  2005年   70篇
  2004年   56篇
  2003年   50篇
  2002年   38篇
  2001年   13篇
  2000年   13篇
  1999年   12篇
  1998年   16篇
  1997年   17篇
  1996年   12篇
  1995年   5篇
  1994年   8篇
  1993年   13篇
  1991年   8篇
  1990年   5篇
  1989年   8篇
  1988年   4篇
  1987年   8篇
  1986年   4篇
  1985年   8篇
  1984年   7篇
  1983年   7篇
  1981年   5篇
  1980年   10篇
  1979年   4篇
  1978年   6篇
  1977年   8篇
  1976年   4篇
  1972年   4篇
  1971年   7篇
  1969年   3篇
排序方式: 共有2612条查询结果,搜索用时 15 毫秒
991.
Food waste (FW) minimization at the source by using food waste biodigester (FWBs) has a vast potential to lower down the impact of increasing organic fraction in municipal solid waste generation. To this end, this research sought to check the performance of locally isolated hydrolase-producing bacteria (HPB) to improve food waste biodegradation rate. Two under-explored HPB identified as Bacillus paralicheniformis GRA2 and Bacillus velezensis TAP5 were able to produce maximum amylase, cellulase, protease and lipase activities, and demonstrated a significant hydrolase synergy in co-culture fermentation. In vitro biodegradation analysis of both autoclaved and non-autoclaved FW revealed that the HPB inoculation was effective to degrade total solids (>62%), protein (>19%), total fat (>51), total sugar (>86%), reducing sugar (>38%) and starch (>50%) after 8-day incubation. All co-culture treatments were recorded superior to the respective monocultures and the uninoculated control. The results of FW biodegradation using batch-biodigester trial indicated that the 1500 mL and 1000 mL inoculum size of HPB inoculant reached a plateau on the 4th day, with gross biodegradation percentage (GBP) of >85% as compared to control (66.4%). The 1000 mL inoculum was sufficient to achieve the maximum GBP (>90%) of FW after an 8-day biodigestion in a FWB.  相似文献   
992.
Diluents and various biological products have been used in different animal species, with promising outcomes in post-thaw sperm quality. Nevertheless, only a few reports are available for the semen of Arabian horses. Edible bird’s nest (EBN) – a product of the salivary secretions of swiftlet species is widely known to have both antioxidant and anti-inflammatory properties. Presently, there is no data available on the role of EBN supplemented in different extenders and its effect on semen quality in stallion semen. Two in vitro experiments were conducted to examine the effects of edible bird’s nest (EBN) on the quality of chilled and post-thawed cryopreserved Arabian stallion spermatozoa. In experiment one, 10 ejaculates were collected, divided into two equal parts, diluted using EquiPlus® and INRA 96® and supplemented with 0 % (control), 0.12 %, 0.24 % EBN concentrations. The semen samples were stored at 5 ℃ and observed at 0, 24, and 48 h. Sperm kinetics variables (% total motility [TM] and progressive motility [PM], curvilinear velocity; VCL, straightness; VSL, average path velocity; VAP) were analyzed using computerized assisted sperm analysis. For chilled semen, there was no significant difference in any of the sperm quality parameters between control (0 %), 0.12 %, and 0.24 % EBN supplementation either in INRA96® or EquiPlus®. In experiment two, nine ejaculates were diluted and cryopreserved using EquiPlus Freeze® and INRA Freeze® containing 0 %, 2.4 %, and 4.8 % EBN, and evaluated after thawing. Sperm kinetics, DNA integrity and antioxidant capacity - Biological Anti-oxidant Potential (BAP) and Reactive Oxygen Metabolites (d-ROMs) test were evaluated. In chilled semen, there was no significant difference in any of the sperm quality parameters between control (0 %), 0.12 %, and 0.24 % EBN supplementation either in INRA96® or EquiPlus®. For frozen semen supplemented with 2.4 % and 4.8 % EBN had higher sperm motility parameters compared to control in INRA Freeze® and EquiPlus Freeze®, but the values were not statistically significant (P > 0.05). Also, EBN supplementation had no significant effects on the DNA integrity, biological antioxidant potential, and reactive oxygen metabolites. EBN supplementation had no significant effects on sperm quality and antioxidant status in chilled and frozen Arabian Stallion semen. Future studies might consider different methods of EBN preparation and concentrations to elucidate the potential biological impact of EBN in Arabian stallion semen.  相似文献   
993.
A novel mutant enzyme namely H43T CGTase can produce up to 39% γ-cyclodextrin (γ-CD) compared to the native enzyme which produces only 10% γ-CD. The effect of the reaction conditions on γ-CD production was studied using this mutant CGTase. The effects of substrate–buffer combination, starch pretreatment and concentration, pH, additives and finally the use of a debranching enzyme improved the γ-CD ratio further. The tapioca–acetate pair gave the highest conversion (16% conversion) among four types of starch and four buffer system combinations. Gelatinized starch was preferred compared to raw tapioca starch in producing a high percentage of γ-CD and conversion rate. Higher pH especially pH 8–9 led to a higher proportion of γ-CD, and was relatively more apparent when the concentration of starch was increased. Forty-six percent γ-CD was produced using 2.5% gelatinized tapioca starch at pH 8. Pullulanase enzyme was found to be useful in reducing the viscosity of tapioca starch paste thus increasing the efficiency of utilization of starch by CGTase by at least 20- to 30-fold. Up to 48% γ-CD can be produced when 4% pullulanase-pretreated tapioca starch was reacted with the CGTase mutant. It was also found that the supplementation of the reaction mixture with glucose, toluene, or cyclododecanone improved the γ-CD yield by 42.2, 46.4, 43.4, and 43.4%, respectively. All the parameters involved have been shown to affect the product specificity of the mutant H43T CGTase transglycosylation mechanism.  相似文献   
994.
ABSTRACT: BACKGROUND: Uropathogenic E.coli (UPEC) are among major pathogens causing urinary tract infections. Virulence factors are mainly responsible for the severity of these emerging infections. This study was planned to investigate the distribution of virulence genes and cytotoxic effects of UPEC isolates with reference to phylogenetic groups (B2, B1, D and A) to understand the presence and impact of virulence factors in the severity of infection in Faisalabad region of Pakistan. METHODS: In this study phylogenetic analysis, virulence gene identification and cytotoxicity of 59 uropathogenic E.coli isolates obtained from non-hospitalized patients was studied. RESULTS: Among 59 isolates, phylogenetic group B2 (50%) was most dominant followed by groups A, B1 (19% each) and D (12 %). Isolates present in group D showed highest presence of virulence genes. The prevalence hlyA (37%) was highest followed by sfaDE (27%), papC (24%), cnf1 (20%), eaeA (19%) and afaBC3 (14%). Highly hemolytic and highly verotoxic isolates mainly belonged to group D and B2. We also found two isolates with simultaneous presence of three fimbrial adhesin genes present on pap, afa, and sfa operons. This has not been reported before and underlines the dynamic nature of these UPEC isolates. CONCLUSIONS: It was concluded that in local UPEC isolates from non-hospitalized patients, group B2 was more prevalent. However, group D isolates were most versatile as all were equipped with virulence genes and showed highest level of cytotoxicity.  相似文献   
995.
Brain cytokines, induced by various inflammatory challenges, have been linked to sickness behaviors, including fatigue. However, the relationship between brain cytokines and fatigue after exercise is not well understood. Delayed recovery of running performance after muscle-damaging downhill running is associated with increased brain IL-1beta concentration compared with uphill running. However, there has been no systematic evaluation of the direct effect of brain IL-1beta on running performance after exercise-induced muscle damage. This study examined the specific role of brain IL-1beta on running performance (either treadmill or wheel running) after uphill and downhill running by manipulating brain IL-1beta activity via intracerebroventricular injection of either IL-1 receptor antagonist (ra; downhill runners) or IL-1beta (uphill runners). Male C57BL/6 mice were assigned to the following groups: uphill-saline, uphill-IL-1beta, downhill-saline, or downhill-IL-1ra. Mice initially ran on a motor-driven treadmill at 22 m/min and -14% or +14% grade for 150 min. After the run, at 8 h (wheel cage) or 22 h (treadmill), uphill mice received intracerebroventricular injections of IL-1beta (900 pg in 2 microl saline) or saline (2 microl), whereas downhill runners received IL-1ra (1.8 microg in 2 microl saline) or saline (2 microl). Later (2 h), running performance was measured (wheel running activity and treadmill run to fatigue). Injection of IL-1beta significantly decreased wheel running activity in uphill runners (P<0.01), whereas IL-1ra improved wheel running in downhill runners (P<0.05). Similarly, IL-1beta decreased and Il-1ra increased run time to fatigue in the uphill and downhill runners, respectively (P<0.01). These results support the hypothesis that increased brain IL-1beta plays an important role in fatigue after muscle-damaging exercise.  相似文献   
996.
997.
998.
999.

Introduction

Activation of the inflammasome has been implicated in the pathology of various autoinflammatory and autoimmune diseases. While the NLRP3 inflammasome has been linked to arthritis progression, little is known about its synovial regulation or contribution to joint histopathology. Regulators of inflammation activation, such as interleukin (IL)-10, may have the potential to limit the inflammasome-driven arthritic disease course and associated structural damage. Hence, we used IL-10-deficient (IL-10KO) mice to assess NLRP3 inflammasome-driven arthritic pathology.

Methods

Antigen-induced arthritis (AIA) was established in IL-10KO mice and wild-type controls. Using histological and radiographic approaches together with quantitative real-time PCR of synovial mRNA studies, we explored the regulation of inflammasome components. These were combined with selective blocking agents and ex vivo investigative studies in osteoclast differentiation assays.

Results

In AIA, IL-10KO mice display severe disease with increased histological and radiographic joint scores. Here, focal bone erosions were associated with increased tartrate-resistant acid phosphatase (TRAP)-positive cells and a localized expression of IL-1β. When compared to controls, IL-10KO synovium showed increased expression of Il1b, Il33 and NLRP3 inflammasome components. Synovial Nlrp3 and Casp1 expression further correlated with Acp5 (encoding TRAP), while neutralization of IL-10 receptor signaling in control mice caused increased expression of Nlrp3 and Casp1. In ex vivo osteoclast differentiation assays, addition of exogenous IL-10 or selective blockade of the NLRP3 inflammasome inhibited osteoclastogenesis.

Conclusions

These data provide a link between IL-10, synovial regulation of the NLRP3 inflammasome and the degree of bone erosions observed in inflammatory arthritis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-014-0419-y) contains supplementary material, which is available to authorized users.  相似文献   
1000.
BackgroundLow fruit and vegetable (FV) intake is a leading risk factor for chronic disease globally as well as in the United States. Much of the population does not consume the recommended servings of FV daily. This paper describes the development of psychosocial measures of FV intake for inclusion in the U.S. National Cancer Institute’s 2007 Food Attitudes and Behaviors Survey.MethodsThis was a cross-sectional study among 3,397 adults from the United States.Scales included conventional constructs shown to be correlated with fruit and vegetable intake (FVI) in prior studies (e.g., self-efficacy, social support), and novel constructs that have been measured in few- to- no studies (e.g., views on vegetarianism, neophobia). FVI was assessed with an eight-item screener. Exploratory factor analysis, Cronbach’s alpha, and regression analyses were conducted.ResultsPsychosocial scales with Cronbach’s alpha ≥0.68 were self-efficacy, social support, perceived barriers and benefits of eating FVs, views on vegetarianism, autonomous and controlled motivation, and preference for FVs. Conventional scales that were associated (p<0.05) with FVI were self-efficacy, social support, and perceived barriers to eating FVs. Novel scales that were associated (p<0.05) with FVI were autonomous motivation, and preference for vegetables. Other single items that were associated (p<0.05) with FVI included knowledge of FV recommendations, FVI “while growing up”, and daily water consumption.ConclusionThese findings may inform future behavioral interventions as well as further exploration of other potential factors to promote and support FVI.  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