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   12278篇
  免费   1008篇
  国内免费   1661篇
  14947篇
  2024年   53篇
  2023年   233篇
  2022年   509篇
  2021年   773篇
  2020年   561篇
  2019年   681篇
  2018年   548篇
  2017年   434篇
  2016年   580篇
  2015年   846篇
  2014年   958篇
  2013年   991篇
  2012年   1211篇
  2011年   1036篇
  2010年   619篇
  2009年   540篇
  2008年   653篇
  2007年   486篇
  2006年   467篇
  2005年   406篇
  2004年   383篇
  2003年   278篇
  2002年   273篇
  2001年   218篇
  2000年   184篇
  1999年   168篇
  1998年   124篇
  1997年   106篇
  1996年   77篇
  1995年   96篇
  1994年   65篇
  1993年   54篇
  1992年   63篇
  1991年   48篇
  1990年   44篇
  1989年   50篇
  1988年   26篇
  1987年   23篇
  1986年   18篇
  1985年   22篇
  1984年   13篇
  1983年   16篇
  1982年   8篇
  1981年   3篇
  1950年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Biodegradation of volatile organic compounds by five fungal species   总被引:4,自引:0,他引:4  
Five fungal species, Cladosporium resinae (ATCC 34066), Cladosporium sphaerospermum (ATCC 200384), Exophiala lecanii-corni (CBS 102400), Mucor rouxii (ATCC 44260), and Phanerochaete chrysosporium (ATCC 24725), were tested for their ability to degrade nine compounds commonly found in industrial off-gas emissions. Fungal cultures inoculated on ceramic support media were provided with volatile organic compounds (VOCs) via the vapor phase as their sole carbon and energy sources. Compounds tested included aromatic hydrocarbons (benzene, ethylbenzene, toluene, and styrene), ketones (methyl ethyl ketone, methyl isobutyl ketone, and methyl propyl ketone), and organic acids ( n-butyl acetate, ethyl 3-ethoxypropionate). Experiments were conducted using three pH values ranging from 3.5 to 6.5. Fungal ability to degrade each VOC was determined by observing the presence or absence of visible growth on the ceramic support medium during a 30-day test period. Results indicate that E. lecanii-corni and C. sphaerospermum can readily utilize each of the nine VOCs as a sole carbon and energy source. P. chrysosporium was able to degrade all VOCs tested except for styrene under the conditions imposed. C. resinae was able to degrade both organic acids, all of the ketones, and some of the aromatic compounds (ethylbenzene and toluene); however, it was not able to grow utilizing benzene or styrene under the conditions tested. With the VOCs tested, M. rouxiiproduced visible growth only when supplied with n-butyl acetate or ethyl 3-ethoxypropionate. Maximum growth for most fungi was observed at a pH of approximately 5.0. The experimental protocol utilized in these studies is a useful tool for assessing the ability of different fungal species to degrade gas-phase VOCs under conditions expected in a biofilter application.  相似文献   
992.
An E1B-defective adenovirus, named r2/Ad carrying the neo expression cassette, was constructed by homologous recombination. The construction, selection (using neomycin as a selective marker), and propagation of the recombinant virus was performed in human embryonic kidney 293 cells (HEK 293). An in vitro study demonstrated that this recombinant virus has the ability to replicate in and lyse some p53-deficient human tumor cells such as human glioma tumor cells (U251) and human bladder cells (EJ), but not in some cells with functional p53, such as human adenocarcinoma cells (A549) and human fibroblast cells (MRC-5). Also, based on the cytopathic effect (CPE), it was demonstrated, under identical conditions, that the U251 cells were more sensitive to r2/Ad replication than the EJ cells. In this paper, we report that r2/Ad could be very useful in studying the in vitro selective replication of E1B-defective adenovirus and has great potential in cancer gene therapy.  相似文献   
993.
研究了草酸对NY3菌(Pseudomona aeruginosa NY3)降解烷烃的影响作用。研究发现,草酸能促进菌体降解十四烷,且最佳投加浓度在1 g/L左右。投加草酸8 h内对十四烷去除率最大,可提高约15.2%。草酸促进降解主要是其改变菌体胞外液分泌成分。紫外光谱结果表明,共存草酸使胞外液中吩嗪-羧酸PCA分泌量大大提高。从气相和液质测定结果看,NY3菌代谢体系中,胞外液中PCA分泌量与十四烷的同步降解率呈正相关。体外实验表明,将试剂级PCA投加在NY3菌以"十六烷+草酸"为碳源生长的胞外液中,发现PCA投加量与其对十四烷的降解效果也呈正相关。与未投加PCA相比,PCA投加2μmol/L,12 h内胞外液对十四烷的去除率提高了约13.1%。结果表明,草酸能促进NY3菌降解十四烷主要是由于其可使菌体胞外液中PCA的分泌量大大提高。本文研究了共存草酸在铜绿假单胞菌NY3降解烃类污染物过程中的作用及其作用机理,为后续优化设计铜绿假单胞菌NY3处理实际烃类污染物的应用提供参考。  相似文献   
994.
一株絮凝剂产生菌的筛选及其絮凝特性研究   总被引:9,自引:3,他引:9  
目的:筛选并研究对有毒物质有一定耐受性的絮凝剂产生菌。方法:利用含苯酚、邻苯二甲酸二丁酯和Pb2(SO4)3的分离培养基从土壤和活性污泥中分离筛选絮凝剂产生菌,对所得的菌种进行摇瓶发酵试验,分别考察其产絮凝剂的周期、絮凝活性分布以及对有毒物质的耐受性等特征,通过提取絮凝剂,将其絮凝活性与其它絮凝剂进行比较。结果:得到一株对苯酚具有一定耐受性的絮凝剂产生菌B2(Serratiasp.),其产絮凝剂的最佳培养时间为48h,絮凝率高于80%。苯酚浓度达0.6g/L时,B2菌的絮凝活性仍高于70%。其90%的絮凝物质集中于菌体,且热稳定性好,对多种悬浊液的絮凝活性高于硫酸铝、PAC。结论:新型絮凝剂产生菌B2对苯酚耐受性强,且絮凝剂提取简便,具有重要的研究价值。  相似文献   
995.
Niu W  Qi Y 《PloS one》2011,6(2):e17052

Background

Mounting evidence has suggested that α-adducin and G-protein β3 (GNB3) genes are logical candidates for salt-sensitive hypertension. Some, but not all, studies have reported that α-adducin G460T and GNB3 C825T polymorphisms may influence the risk of the disease. To comprehensively address this issue, we performed a meta-analysis to evaluate the influence of these two polymorphisms on hypertension and potential biases in Chinese.

Methods

Data were analyzed using Stata (v11.0) and random-effects model was applied irrespective of between-studies heterogeneity, which was evaluated via subgroup and meta-regression analyses. Study quality was assessed in duplicate. Publication bias was weighed using Egger''s test and funnel plot.

Results

36 study populations totaling 9042 hypertensive patients and 8399 controls were finally identified. Overall, in allelic/genotypic/dominant/recessive models, no significant association was identified for both G460T and C825T polymorphisms (P>0.05) and there was possible heterogeneity (I 2>25%). Subgroup analyses by study design indicated that the magnitude of association in population-based studies was marginally significantly strengthened for α-adducin G460T allelic model (OR = 1.12; 95% CI: 1:00–1.25; P = 0.043). Moreover, subgroup analyses by geographic distribution indicated comparison of 825T with 825C yielded a marginally significant increased risk in southern Chinese only (OR = 1.48; 95% CI: 1.01–2.16; P = 0.045). Further meta-regression analyses showed that geographic regions were a significant source of between-study heterogeneity for both polymorphisms. There was a possibility of publication bias for G460T, but not for C825T.

Conclusions

Our overall results suggest null association of α-adducin G460T and GNB3 C825T polymorphisms with hypertension in Chinese but indicate local marginal significance of C825T, as a putative salt-sensitive switch, in southern Chinese.  相似文献   
996.
APaleogenemammalianfauna,herenamedtheShanghuangfauna,wasdiscoverednearthevillageofShanghuang,closetoLiyangCity,JiangsuProvince,China(Fig.1).Atpresent,rouglilysixtyspeciesoffossilmammalshavebeenrecogniedintheShanghuangfauna.Manyofthesemammaltaxaarenewtoscience,andothersrepresentnewoccurrencesfortheEoceneofChina.ParticularlywellrepresentedintheShanghuangfaunaaremicromammals(includingmarsupials,insectivores,rodents,lagomorphs,primates,andbats)thathaveseldomifeverbeenfoundinotherEoceneAsianl…  相似文献   
997.
目的:对比两种不同的四联疗法对幽门螺杆菌根除失败后的根除率,选择可以有效弥补传统三联疗法的幽门螺杆菌根除失败措施的四联疗法。方法:选择2010年8月到2012年8月期间在我院住院治疗的幽门螺杆菌根除失败后患者90例作为研究对象。随机分为实验组和对照组,实验组的患者采取序贯疗法,对照组的患者采取标准四联疗法。对比两组的根除率以及临床疗效。结果:实验组患者的根除率为86.7%,对照组患者根除率为51.0%;实验组患者的临床总有效率为95.6%,对照组的临床有效率为77.8%;实验组的不良反应的总发生率为4.4%,对照组不良反应总发生率为20.0%。两组比较差异明显,P均0.05,具有统计学意义。结论:序贯疗法对幽门螺杆菌根除失败后的根除率以及疗效高于标准四联疗法。  相似文献   
998.
以富贵草(Pachysandra terminalis Sieb.et Zucc.)(以下简称PT)为实验材料,采用开放式浸杀法研究其植物原粉及提取物(PT-Ⅰ)对钉螺的杀灭效果和对鱼类的毒性作用。结果表明PT原粉浓度为17.5 mg/L时,钉螺72 h死亡率为93.4%,120 h死亡率达100.0%;其24、72、120、168 h的LC50分别为42.28、7.20、4.20、3.17 mg/L。PT原粉浓度为75.0 mg/L时,经168 h鱼死亡率为0。使用浓度为35.0、17.5、8.75、4.38 mg/L的PT原粉,分别浸泡1、2、18、42 h时,抑制钉螺上爬率均达到100%。原粉经提取分离得到PT-Ⅰ组分,以1.40 mg/L的PT-Ⅰ组分分别浸杀钉螺24、48、72、96、120 h,钉螺死亡率分别为36.7%、73.3%、96.7%、96.7%、100.0%。表明PT具有很好的杀灭钉螺、抑制钉螺上爬效果,且对鱼毒性较低,是一种较有研究价值的灭螺植物。  相似文献   
999.
牙鲆变态中IGF-I基因表达及甲状腺激素对其的调节作用   总被引:1,自引:0,他引:1  
胰岛素样生长因子(Insulin-like growth factors,IGFs)是一类具有胰岛素样代谢和促有丝分裂功能的蛋白质,参与脊椎动物的胚胎发育、生长和生殖。IGF系统包括两个配体(IGF-Ⅰ、IGF-Ⅱ)、IGF受体(IGF-I receptor,IGF-I R;IGF-II receptor,IGF-ⅡR)以及IGF结合蛋白(IGF binding  相似文献   
1000.
王慕瑶  曾杜文  王淇  李俊  邹岳  赵心清 《微生物学报》2022,62(11):4155-4164
【目的】对我国西藏地区来源的不同酵母菌株进行有机酸发酵性能测试,此外,对具有良好产酸性能的分离自松萝内部的酿酒酵母菌株Saccharomy cescerevisiae 2-2进行耐酸性能分析,并探究其耐酸较强的分子机制。【方法】比较不同糖浓度培养基液体发酵培养过程中pH的变化,并比较低pH胁迫条件下菌株的生长,检测酿酒酵母菌株的产酸潜力和耐酸特性;对菌株2-2和模式酵母菌株S288C进行比较基因组分析,并利用实时荧光定量聚合酶链式反应(real-time fluorescence quantitative polymerase chain reaction,RT-qPCR)分析关键基因的转录,探究菌株2-2耐酸分子机制。【结果】松萝内生酿酒酵母2-2在所有检测的菌株中产酸潜力较大,耐酸性能较好。在菌株2-2中与胁迫耐受性相关的基因PDR15、PDR12和SUR1在低pH胁迫条件下存在显著的上调或下调,但这些基因转录变化趋势与菌株S288C相反。【结论】松萝内生酿酒酵母2-2是一株产酸耐酸性能较好的菌株,对其独特的调节机制进行深入分析,有希望选育性能更好的产酸酵母菌株。  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