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   2604篇
  免费   229篇
  2022年   58篇
  2021年   81篇
  2020年   39篇
  2019年   45篇
  2018年   76篇
  2017年   61篇
  2016年   77篇
  2015年   114篇
  2014年   125篇
  2013年   141篇
  2012年   205篇
  2011年   152篇
  2010年   101篇
  2009年   73篇
  2008年   101篇
  2007年   87篇
  2006年   93篇
  2005年   72篇
  2004年   65篇
  2003年   66篇
  2002年   60篇
  2001年   49篇
  2000年   46篇
  1999年   41篇
  1998年   24篇
  1997年   18篇
  1996年   16篇
  1995年   23篇
  1994年   21篇
  1992年   33篇
  1991年   37篇
  1990年   41篇
  1989年   33篇
  1988年   48篇
  1987年   34篇
  1986年   27篇
  1985年   37篇
  1984年   28篇
  1983年   26篇
  1982年   24篇
  1981年   18篇
  1980年   15篇
  1979年   25篇
  1977年   19篇
  1976年   16篇
  1975年   27篇
  1974年   31篇
  1973年   27篇
  1972年   17篇
  1968年   16篇
排序方式: 共有2833条查询结果,搜索用时 15 毫秒
121.
122.
Prasad  Archana  Patel  Preeti  Pandey  Shatrujeet  Niranjan  Abhishek  Misra  Pratibha 《Protoplasma》2020,257(2):561-572
Protoplasma - Growth and production kinetics of three important glycoalkaloids viz. α-solanine, solanidine, and solasodine in two contrasting prickly and prickleless plants of Solanum viarum...  相似文献   
123.
Molecular Biology Reports - Introns experience lesser selection pressure, thus are liable for higher polymorphism. Intron Length Polymorphic (ILP) markers designed from exon-flanking introns...  相似文献   
124.
Sharma  Himanshu  Kumar  Pankaj  Singh  Abhishek  Aggarwal  Kanika  Roy  Joy  Sharma  Vikas  Rawat  Sandeep 《Molecular biology reports》2020,47(4):2447-2457
Molecular Biology Reports - The genus Rhododendron, known for large impressive flowers is widely distributed throughout the world. Rhododendrons have limited genetic information, despite of...  相似文献   
125.
Transforming growth factor β (TGFβ) is a prominent cytokine that promotes tumor progression by activating epithelial-to-mesenchymal transition (EMT). This study indicated that TGFβ exerted metastasis by inducing zinc finger E-box binding homeobox 1 (ZEB1) and a long noncoding RNA, LINC00273, expressions in A549 cells. Knocking down LINC00273 diminished TGFβ induced ZEB1 expression as well as metastasis. Mechanistically, LINC00273 acted as a molecular sponge of microRNA (miR)-200a-3p which liberate ZEB1 to perform its prometastatic functions. LINC00273 knockdown and miR200a3p mimic transfection of A549 cells were used for validating the link between TGFβ and LINC00273 induced metastasis. RNA pulldown and luciferase assay were performed to establish mir200a-3p-LINC00273 interaction. High expressions of LINC00273, TGFβ, and ZEB1 with concurrent low miR200a-3p expression had been verified in vivo and in patient samples. Overall, LINC00273 promoted TGFβ-induced lung cancer EMT through miR-200a-3p/ZEB1 feedback loop and may serve as a potential target for therapeutic intervention in lung cancer metastasis.  相似文献   
126.
The current study aims to determine the healing activity of water soluble polysaccharide-rich fraction of a wild mushroom, Termitomyces eurhizus (TEps) against the indomethacin induced gastric ulceration in mice model. Gastric tissue histology, myeloperoxidase (MPO) activity, cyclooxygenases (COX) 1 and 2 expression, prostaglandin E2 (PGE2) synthesis, and modulation of pro/anti inflammatory cytokines expression were studied for this purpose. Histological study shows that TEps (20 mg/kg) effectively healed the gastric ulceration. Based on biochemical results, the healing capacities of TEps could be attributed to reduction of MPO activity and protection of mucosal mucin content. Enhanced synthesis of PGE2 by modulation of COX-1 and COX-2 expression and a prominent shift of cytokines expression from pro (TNF-α, IL-1ß) to anti inflammatory (IL-10) side are also held responsible for ulcer healing. The preliminary study highlights the anti-ulcerogenic property of polysaccharide-rich fraction of Termitomyces eurhizus and opens an alternative cure for NSAID induced gastroduodenal diseases.  相似文献   
127.
The nature of bonding at the interface between deposited silver/palladium and clean Al-terminated (001) surface of α-Al2O3 has been investigated using a periodic ab initio method. Substantial inter-planar relaxations within the alumina were found at both the interfaces and the bulk. The periodic calculation with both Ag and Pd deposition shows that 10% of loading on alumina results maximum stability. Surface energy and work function calculations were performed to propose the stability for the metals on the studied surfaces. The deposited Ag forms a three-dimensional (3-D) cluster on top of the alumina surface. The Pd cluster formed on the alumina surface is two-dimensional (2-D) and is distorted to accommodate the Ag cluster in its domain. A further low index calculation can explain the reason for a higher stability of the membrane generated over alumina support with silver and palladium. The results are discussed in view of the existing experimental data and models of metal-oxide interface and a reason for the difference of activity of the metal interaction with alumina surface is postulated.  相似文献   
128.
Enantiornithes is the most speciose clade of Cretaceous birds, but many taxa are known from isolated postcranial skeletons. Two embryonic enantiornithine bird skeletons of Gobipipus reshetovi gen. et sp. nov. from the Upper Cretaceous (Campanian) Barun Goyot Formation of the Gobi Desert in Mongolia provide new insights into the anatomy, radiation, and mode of development of early avialans. In recent times, both enantiornithine and ornithuromorph birds are known from the Barun Goyot Formation as well as from the Djadokhta and Nemegt Formations. The 80-million-year-old Gobipipus skeletons encased within eggshells shows several features characteristic of enantiornithine birds. The wing skeleton and shoulder girdle show morphological features indicating that Gobipipus achieved sophisticated powered flight. Gobipipus reshetovi gen. et sp. nov. is quite distinct from the sympatric enantiornithine species Gobipteryx minuta from the same strata in many anatomical features. Phylogenetic analysis of 26 avialan ingroup taxa based on distribution of 202 characters indicate that Gobipipus is a basal member of enantiornithine birds along with Confuciusornis and shares more characters with ornithuromorphs than previously recognized. The embryonic nature of Gobipipus specimens sheds new light on the developmental history of enantiornithine birds. The well-ossified bones of the fore- and hind limbs, and fusion of many skeletal elements indicate a precocial mode of development in Gobipipus. Apparently Gobipipus hatchlings could walk away from the ground nests as soon as they emerged from their eggs. The asymmetry of egg poles are unique features of Gobipipus eggs (oogenus Gobioolithus) among Cretaceous avialans. The microstructure of the shell in Gobioolithus eggs with the embryos of Gobipipus is typical avian (of ornithoid basic type) and less ratite-like in morphology of the spongy layer than is that in the other possible egg-remains of enantiornitine birds (oofamily Laevisoolithidae).  相似文献   
129.
Various simple mathematical models have been used to investigate dengue transmission. Some of these models explicitly model the mosquito population, while others model the mosquitoes implicitly in the transmission term. We study the impact of modeling assumptions on the dynamics of dengue in Thailand by fitting dengue hemorrhagic fever (DHF) data to simple vector–host and SIR models using Bayesian Markov chain Monte Carlo estimation. The parameter estimates obtained for both models were consistent with previous studies. Most importantly, model selection found that the SIR model was substantially better than the vector–host model for the DHF data from Thailand. Therefore, explicitly incorporating the mosquito population may not be necessary in modeling dengue transmission for some populations.  相似文献   
130.
Antimicrobial peptides (AMPs) are multifunctional components of the innate immune system. Chemotherapeutic agents used for treatment of visceral leishmaniasis (VL) are now threatened due to the emergence of acquired drug resistance and toxicity. AMPs are attractive alternative to conventional pharmaceuticals. In this study, first time we explored the antileishmanial activity of spinigerin originally derived from Pseudacanthotermes spiniger. Leishmania donovani promastigotes present apoptosis-like cell death upon exposure to spinigerin (IC50, 150 μM). The infection rate was reduced by 20% upon exposure to 150 μM spinigerin but no cytotoxicity on host macrophages was observed. Elevation of intracellular ROS level and down-regulation of two ROS detoxifying enzymes, ascorbate peroxidase (APx) and trypanothione reductase (TR) suggested essential role of ROS machinery during spinigerin mediated cell death. About 97% cell population was found to be Annexin-V positive; 44% cells being highly Annexin-V positive. Moreover, we observed morphological changes like cell rounding, nuclear condensation, oligonucleosomal DNA degradation and TUNEL positive cells without loss of membrane integrity upon spinigerin exposure, suggests apoptosis-like death. Interestingly, collapse in mitochondrial membrane potential and increased level of intracellular ROS and calcium were not associated with caspase like activity. Computational analysis suggests spiningerin interacts with trypanothione reductase and thus probably interferes its function to detoxify the toxic ROS level. Therefore, spinigerin induces apoptosis-like cell death in L. donovani in a caspase-independent manner. The study elucidates the antileishmanial property of spinigerin that may be considered for future chemotherapeutic option alone or adjunct with other drug regimens for improved treatment of visceral leishmaniasis.  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