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   683篇
  免费   36篇
  国内免费   3篇
  722篇
  2024年   3篇
  2023年   21篇
  2022年   38篇
  2021年   58篇
  2020年   27篇
  2019年   40篇
  2018年   41篇
  2017年   22篇
  2016年   37篇
  2015年   35篇
  2014年   54篇
  2013年   63篇
  2012年   55篇
  2011年   40篇
  2010年   30篇
  2009年   6篇
  2008年   19篇
  2007年   18篇
  2006年   10篇
  2005年   17篇
  2004年   18篇
  2003年   8篇
  2002年   12篇
  2001年   8篇
  2000年   5篇
  1999年   6篇
  1998年   4篇
  1997年   7篇
  1996年   3篇
  1995年   1篇
  1994年   4篇
  1993年   3篇
  1992年   3篇
  1991年   1篇
  1988年   1篇
  1984年   2篇
  1973年   1篇
  1872年   1篇
排序方式: 共有722条查询结果,搜索用时 15 毫秒
711.
Improving grain filling in the presernt farming systems is crucial where grain filling is a concern due to the extreme use of chemical fertilizers (CF). A field experiment was conducted at the experimental station of Guangxi University, China in 2019 to test the hypothesis that cattle manure (CM) and poultry manure (PM) combined with CF could improve rice grain filling rate, yield, biochemical and qualitative attributes. A total of six treatments, i.e., no fertilizer (T1), 100% CF (T2), 60% CM + 40% CF (T3), 30% CM + 70% CF (T4), 60% PM + 40% CF (T5), and 30% PM + 70% CF (T6) were used in this study. Results showed that the combined treatment T6increased starch metabolizing enzymes activity (SMEs), such as ADP-glucose phosphorylase (ADGPase) by 8 and 12%, soluble starch synthase (SSS) by 7 and 10%, granule bound starch synthesis (GBSS) by 7 and 9%, and starch branching enzyme (SBE) by 14 and 21% in the early and late seasons, respectively, compared with T2. Similarly, higher rice grain yield, grain filling rate, starch, and amylose content were also recorded in combined treatments. In terms of seasons, higher activity of SMEs , grain starch, and amylose content was noted in the late-season compared to the early season. The increment in these traits was mainly attributed to a lower temperature in the late season during the grain filling period. Furthermore, our results suggested that an increment in starch accumulation and grain filling rate were mainly associated with the enhanced sink capacity by regulating key enzyme activities involved in Suc-to-starch conversion. In-addition, RT-qPCR analysis showed higher expression levels of AGPS2b, SSS1, GBSS1, and GBSE11b genes, which resultantly increased the activities of SMEs during the grain filling period under combined treatments. Linear regression analysis revealed that the activity of ADGPase, SSS, GBSS, and SBE were highly positively correlated with starch and amylose accumulation. Thus, we concluded that a combination of 30% N from PM or CM with 70% N from CF is a promising option in terms of improving rice grain yield and quality. Our study provides a sustainable fertilizer management strategy to enhance rice grain yield and quality at the lowest environmental cost.  相似文献   
712.
The human-to-human transmitted respiratory illness in COVID-19 affected by the pathogenic Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2), which appeared in the last of December 2019 in Wuhan, China, and rapidly spread in many countries. Thereon, based on the urgent need for therapeutic molecules, we conducted in silico based docking and simulation molecular interaction studies on repurposing drugs, targeting SARS-CoV-2 spike protein. Further, the best binding energy of doxorubicin interacting with virus spike protein (PDB: 6VYB) was observed to be −6.38 kcal/mol and it was followed by exemestane and gatifloxacin. The molecular simulation dynamics analysis of doxorubicin, Reference Mean Square Deviation (RMSD), Root Mean Square fluctuation (RMSF), Radius of Gyration (Rg), and formation of hydrogen bonds plot interpretation suggested, a significant deviation and fluctuation of Doxorubicin-Spike RBD complex during the whole simulation period. The Rg analysis has stated that the Doxorubicin-Spike RBD complex was stable during 15,000–35,000 ps MDS. The results have suggested that doxorubicin could inhibit the virus spike protein and prevent the access of the SARS-CoV-2 to the host cell. Thus, in-vitro/in-vivo research on these drugs could be advantageous to evaluate significant molecules that control the COVID-19 disease.  相似文献   
713.
Successful therapy of twin‐to‐twin transfusion syndrome requires accurate imaging to guide laser photocoagulation of the anastomosing placental vessels. Photoacoustic (PA) imaging is an alternative imaging method that provides contrast for hemoglobin, and in this study, it was used to visualize chorionic superficial and subsurface vasculature in human placentas. The strong potential of PA imaging to guide minimally invasive fetal therapies was demonstrated. Further details can be found in the article by Efthymios Maneas, Rosalind Aughwane, Nam Huynh, et al. ( e201900167 ).

  相似文献   

714.
Porcine luteal cells were obtained from corpora lutea on the 5th, 13th and 17th days of the estrous cycle. The cells were suspended at a concentration of 5 × 104 cells/ml in Eagle's medium with 2% human serum albumin. These cells were incubated with or without 0.01, 0.1, 1 or 10 μg/ml porcine prolactin. The amount of progesterone in cultures was estimated by a radio-immunological method after 30 min, 3 h and 6 h of culturing.Luteal cells obtained on the 5th day of the estrous cycle and incubated without prolactin secreted 71.24 ± 21.91 ng progesterone/ml of medium, whereas under the influence of prolactin at 0.01, 0.1, 1 and 10 μg/ml, 39.06 ± 13.33, 44.31 ± 12.69, 44.88 ± 16.85 and 51.62 ± 15.01 ng progesterone/ml (P<0.01) were secreted. Luteal cells from the 13th day of the estrous cycle incubated without prolactin secreted on average 70.72 ± 9.21 ng progesterone/ml of medium, whereas under the influence of different prolactin doses 50.75 ± 8.52, 46.54 ± 7.13, 43.30 ± 6.78 and 41.68 ± 7.21 ng progesterone/ml (P<0.01) were secreted.Prolactin did not change progesterone secretion by luteal cells obtained on the 17th day of the estrous cycle. An influence of the incubation time on progesterone secretion by these cells was observed: after 30 min of incubation the cells secreted 8.83 ± 2.95 ng/ml, after 3 h 8.12 ± 2.57 ng/ml and after 6 h 6.86 ± 1.91 ng/ml, irrespective of the amount of PRL added.The results suggest that prolactin plays a role in the luteolysis of the corpus luteum.  相似文献   
715.
Recent findings suggest that ephrinA5 (Efna5) has a novel role in female mouse fertility, in addition to its well-defined role as a neurogenesis factor. Nevertheless, its physiological roles in ovarian granulosa cells (GC) have not been determined. In this study, mouse GC were cultured and transfected with ephrin A5 siRNA and negative control to determine the effects of Efna5 on GC apoptosis, proliferation, cell cycle progression, and related signaling pathways. To understand the mode signaling, the mRNA expression levels of Efna5 receptors (Eph receptor A5, Eph receptor A3, Eph receptor A8, and Eph receptor B2) were examined. Both mRNA and protein expressions of apoptosis-related factors (Bax, Bcl-2, Caspase 8, Caspase 3, and Tnfα) and a proliferation marker, Pcna, were investigated. Additionally, the role of Efna5 on paracrine oocyte-secreted factors and steroidogenesis hormones were also explored. Efna5 silencing suppressed GC apoptosis by downregulating Bax and upregulating Bcl-2 in a Caspase 8-dependent manner. Efna5 knockdown promoted GC proliferation via p-Akt and p-ERK pathway activation. The inhibition of Efna5 enhanced BMH15 and estradiol expression, but suppressed GDF9, while progesterone level remained unaltered. These results demonstrated that Efna5 is a pro-apoptotic agent in GC and plays important role in folliculogenesis by mediating apoptosis, proliferation, and steroidogenesis in female mouse. Therefore Efna5 might be potential therapeutic target for female fertility disorders.  相似文献   
716.
The industrial application of organophosphates provides the opportunity for environmental exposure. While the toxicity of organophosphate compounds has been the target of significant work, studies directed towards the identification of metabolite markers to assess phosphate exposure are more limited. In this study the urine metabolite profiles for rats following single dose exposure to either tributyl phosphate (TBP, 15 mg/kg body weight) or triphenyl phosphate (TPP, 2 and 20 mg/kg body weight) were characterized using proton nuclear magnetic resonance (1H NMR) and orthogonal-partial least squares discriminate analysis (O-PLSDA). Using the developed O-PLSDA models it was possible to clearly identify TBP or TPP exposed animals. The performance of these models was validated using cross validation and permutation testing. Utilizing the variable importance in projection (VIP) coefficients from the O-PLSDA the metabolites that were most responsible for the classification of TBP or TPP exposure were determined. This initial study demonstrates the potential for NMR metabonomic studies for the identification and separation of environmental exposure to organophosphates.  相似文献   
717.
Methyl‐eugenol (ME) (1,2‐dimethoxy‐4‐(2‐propenyl)benzene), a natural phytochemical, did enhance male Bactrocera carambolae Drew & Hancock (Diptera: Tephritidae) mating competitiveness 3 d after ingestion. Enhanced male mating competitiveness can significantly increase the effectiveness of the sterile insect technique (SIT). ME application to mass reared sterile flies by feeding is infeasible. ME application by aromatherapy however, would be a very practical way of ME application in fly emergence and release facilities. This approach was shown to enhance mating competitiveness of B. carambolae 3 d posttreatment (DPT). Despite this added benefit, every additional day of delaying release will reduce sterile fly quality and will add cost to SIT application. The present study was planned to assess the effects of ME‐aromatherapy on male B. carambolae mating competitiveness 1DPT and 2DPT. ME aromatherapy 1DPT or 2DPT did enhance mating competitiveness of B. carambolae males whereas ME feeding 1DPT and 2DPT did not. Male mating competitiveness was enhanced by the ME aromatherapy irrespective if they received 1DPT, 2DPT or 3DPT. ME aromatherapy, being a viable approach for its application, did enhance mating competitiveness of male B. carambolae 1 d posttreatment as ME feeding did 3 d after ingestion.  相似文献   
718.

Globally, water resources contaminated with petroleum hydrocarbons are under much consideration due to their hazardous effects on human beings as well as on plants and animals in the ecosystem. Petroleum hydrocarbons are classified as recalcitrant pollutants in nature. These petroleum products are mostly released in the water resources during the petroleum refining process by oil refineries. The conventional clean-up technologies for hydrocarbons contaminated water have more destructive effects on the aquatic and land ecosystems. Consequently, to develop cost-effective and more environment-friendly techniques that clean up the environment and restore the marine ecosystem to its original forms. Keeping in view, this review article explores the detailed information on fabrication, cost-effectiveness, and an overview of innovation of the floating treatment wetlands (FTWs) using plants and bacterial combined functions to remediate the petroleum hydrocarbons contaminated water. The review also discusses the improvement of microbial efficacy for hydrocarbon degradation using FTWs. The review article shows the various applications of FTWs to remove different organic pollutants in petroleum hydrocarbons contaminated water. The review also describes the prospective benefits of FTWs for their multiple uses for removal of hydrocarbons, chemical oxygen demand (COD), biochemical oxygen demand (BOD), phenol, and solids from hydrocarbons contaminated water. This review widely discusses the role of hydrocarbons in degrading bacteria, and wetland plants and the mechanism involved during the remediation process of hydrocarbons in FTWs. It further demonstrates features disturbing the treatment efficiency of FTWs, and finally, it is concluded by successful applications of FTWs and various suggestions for potential future research prospects.

Graphical Abstract
  相似文献   
719.
720.
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