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   37042篇
  免费   3113篇
  国内免费   2983篇
  43138篇
  2024年   95篇
  2023年   555篇
  2022年   1277篇
  2021年   2093篇
  2020年   1337篇
  2019年   1713篇
  2018年   1611篇
  2017年   1201篇
  2016年   1623篇
  2015年   2363篇
  2014年   2802篇
  2013年   3027篇
  2012年   3429篇
  2011年   3010篇
  2010年   1858篇
  2009年   1592篇
  2008年   1824篇
  2007年   1540篇
  2006年   1368篇
  2005年   1137篇
  2004年   982篇
  2003年   832篇
  2002年   752篇
  2001年   622篇
  2000年   547篇
  1999年   559篇
  1998年   302篇
  1997年   329篇
  1996年   314篇
  1995年   311篇
  1994年   283篇
  1993年   206篇
  1992年   328篇
  1991年   228篇
  1990年   195篇
  1989年   194篇
  1988年   117篇
  1987年   116篇
  1986年   87篇
  1985年   92篇
  1984年   53篇
  1983年   49篇
  1982年   28篇
  1981年   23篇
  1980年   26篇
  1979年   17篇
  1972年   11篇
  1971年   9篇
  1970年   9篇
  1969年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Zhou  Hai-Yan  Li  Yi-Zuo  Jiang  Rui  Hu  Hai-Feng  Wang  Yuan-Shan  Liu  Zhi-Qiang  Xue  Ya-Ping  Zheng  Yu-Guo 《Bioprocess and biosystems engineering》2019,42(10):1573-1582
Bioprocess and Biosystems Engineering - R-2-(4-hydroxyphenoxy)propionic acid (R-HPPA) is a key intermediate of the enantiomerically pure phenoxypropionic acid herbicides. R-HPPA could be...  相似文献   
992.
Dai  Chunxiao  Ma  Qiao  Li  Yan  Zhou  Duandi  Yang  Bingyu  Qu  Yuanyuan 《Bioprocess and biosystems engineering》2019,42(12):1963-1971
Bioprocess and Biosystems Engineering - Indigo, one of the most widely used dyes, is mainly produced by chemical processes, which generate amounts of pollutants and need high energy consumption....  相似文献   
993.
Auxin polar transport is crucial in regulating plant growth and patterning. As auxin efflux carriers, the PIN FORMED (PIN) proteins are responsible for transportation of auxin out of the cell. There are eight and ten PIN members in Arabidopsis (AtPIN) and Medicago truncatula (MtPIN), respectively. Compared with MtPIN10/SMOOTH LEAF MARGIN1 (SLM1), MtPIN4 exhibits a closer relationship with AtPIN1 based phylogenetic analysis. In addition, the gene structure and distribution of transmembrane segments of MtPIN4, MtPIN5 and MtPIN10/SLM1 are similar, implying possible redundant roles among them. However, analysis using Gene Expression Atlas revealed different expression patterns among MtPIN4, MtPIN5 and MtPIN10/SLM1. Loss of function of MtPIN10/SLM1 in M. truncatula resulted in pleiotropic phenotypes in different organs, which are similar with the defects in the pin1 mutant of Arabidopsis, suggesting that the MtPIN10/SLM1 is a putative ortholog of AtPIN1. MtPIN4, MtPIN5 and MtPIN10/SLM1 may have limited redundant functions in the development of M. truncatula. The creation of double and triple mutants will help to elucidate their potential roles in auxin transport and plant development.  相似文献   
994.
995.
When males fight for access to females, such conflict rarely escalates into lethal fight because the risks and costs involved, that is, severe injury or death, are too high. The social spider mite, Stigmaeopsis miscanthi, does exhibit lethal male fights, and this male–male aggressiveness varies among populations. To understand the evolution of lethal fighting, we investigated aggressiveness in 42 populations and phylogenetic relationships in 47 populations along the Japanese archipelago. By analysis of the male weapon morph, a proxy for aggressiveness, we confirmed the existence of a mildly aggressive (ML) form, besides the low aggression (LW) and high aggression (HG) forms reported earlier. To evaluate demographic history of these three forms, we employed the approximate Bayesian computation approach using mtCOI sequences and taking into consideration the postlast glacial expansion history of the host plant, Miscanthus sinensis. As results, hierarchical split models are more likely to explain the observed genetic pattern than admixture models, and the ML form in the subtropical region was considered the ancestral group. The inferred demographic history was consistent with the one reconstructed for the host plant in a previous study. The LW form was split from the ML form during the last glacial period (20,000–40,000 years BP), and subsequently, the HG form was split from the ML form at the end of or after the last glacial period (5,494–10,988 years BP). The results also suggest that the mite invaded Japan more than once, resulting in the present parapatric distribution of LW and HG forms in eastern Japan.  相似文献   
996.
怀地黄脱毒种苗大田生长性状及产量品质   总被引:2,自引:0,他引:2  
为研究怀地黄(Rehmannia glutinosa)脱毒种苗大田生长、产量和品质状况,对大田中不同时期脱毒苗和非脱毒苗的形态指标、生理特性、光合特性、产量及品质等进行了测定。结果表明,脱毒苗的株高、冠幅、叶片数、最大叶面积、功能叶片的光合色素含量和净光合速率等各项指标均优于非脱毒苗,块根产量提高、品质改善,增产幅度在77.35%以上,药用成分梓醇含量提高了32.90%。  相似文献   
997.
寄主利它素对稻螟赤眼蜂寄生行为的影响   总被引:6,自引:0,他引:6  
邹卫辉  雷朝亮  张帆 《昆虫知识》2002,39(5):370-373
对稻螟赤眼蜂Trichogrammajaponicum(Ashmead)在寄主定位过程中所利用的寄主利它素的存在部位、作用方式及其应用效果作了初步研究。生测结果表明 :寄主利它素存在于三化螟Tryporyzaincertu las(Walker)卵块盖毛和成虫鳞片中 ,其中以盖毛中利它素含量最高 ,雌蛾鳞片次之 ,雄蛾鳞片含量最少。结果还表明盖毛在卵块上的完整性对稻螟赤眼蜂的寄主搜索行为有明显影响。室内应用效果表明利它素可以使稻螟赤眼蜂对寄主卵寄生率提高 1 0 %以上。  相似文献   
998.
The mechanism of local inflammation and systemic injury in chronic periodontitis is complicated, in which and exosomes play an important role. In our study, we found that T helper cell 17 (Th17)/regulatory T cell (Treg) balance is destabilized in the peripheral blood of patients with periodontitis, with upregulated Th17 or downregulated Treg, respectively. Porphyromonas gingivalis lipopolysaccharide (LPS) was used to simulate the inflammatory microenvironment of chronic periodontitis. The exosomes were extracted from periodontal ligament stem cells (PDLSCs) in LPS-induced periodontitis environment, which inversely effected on CD4+ T cells under normal and inflammatory conditions. Furthermore, compared with exosomes from normal PDLSCs, lower expression of microRNA-155-5p (miR-155-5p) and higher expression of Sirtuin-1 (SIRT1) were observed in exosomes from LPS-stimulated PDLSCs. Exosomes from PDLSCs alleviated inflammatory microenvironment through Th17/Treg/miR-155-5p/SIRT1 regulatory network. This study aimed to find the “switching” factors that affected the further deterioration of periodontitis to maximally control the multiple downstream damage signal factors to further understand periodontitis and find new targets for its treatment.  相似文献   
999.
胃肠道肿瘤已经成为我国的高发肿瘤,降低肿瘤的复发转移是目前研究的热点问题。四君子汤的应用在降低胃肠肿瘤患者术后复发转移中的确起到了重要的作用。本文检索了近10年国内外的相关文献,分别从中医理论的认识、临床研究、实验研究及药理研究等方面,总结四君子汤在胃肠肿瘤患者术后复发转移的防治方面的进展。  相似文献   
1000.
Autophagy is not only involved in development, but also has been proved to attend immune response against invading pathogens. Autophagy protein 5 (ATG5) is an important autophagic protein, which plays a crucial role in autophagosome elongation. Although ATG5 has been well studied in mammal, yeast, and Drosophila, little is known about ATG5 in lepidopteran insects. We cloned putative SeAtg5 gene from Spodoptera exigua larvae by the rapid amplification of cDNA ends method, and its characteristics and the influences of multiple exogenous factors on its expression levels were then investigated. The results showed that the putative S. exigua SeATG5 protein is highly homologous to other insect ATG5 proteins, which has a conserved Pfm domain and multiple phosphorylation sites. Next, fluorescence microscope observation showed that mCherry‐SeATG5 was distributed in both nucleus and cytoplasm of Spodoptera litura Sl‐HP cells and partially co‐localized with BmATG6‐GFP, but it almost has no significant co‐localization with GFP‐HaATG8. Then, the Western blot analysis demonstrated that GFP‐SeATG5 conjugated with ATG12. Moreover, real‐time PCR revealed that its expression levels significantly increased at the initiation of pupation and the stage of adult. In addition, the expression levels of SeAtg5 can be enhanced by the starvation, UV radiation, and infection of baculovirus and bacterium. However, the expression levels of SeAtg5 decreased at 24 h post treatments in all these treatments except in starvation. These results suggested that SeATG5 might be involved in response of S. exigua under various stress conditions.  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