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   26225篇
  免费   2398篇
  国内免费   2903篇
  2024年   60篇
  2023年   393篇
  2022年   591篇
  2021年   1390篇
  2020年   1016篇
  2019年   1281篇
  2018年   1232篇
  2017年   840篇
  2016年   1171篇
  2015年   1726篇
  2014年   2063篇
  2013年   2150篇
  2012年   2529篇
  2011年   2255篇
  2010年   1438篇
  2009年   1353篇
  2008年   1457篇
  2007年   1350篇
  2006年   1131篇
  2005年   904篇
  2004年   851篇
  2003年   738篇
  2002年   617篇
  2001年   456篇
  2000年   408篇
  1999年   358篇
  1998年   257篇
  1997年   204篇
  1996年   220篇
  1995年   160篇
  1994年   172篇
  1993年   92篇
  1992年   127篇
  1991年   100篇
  1990年   92篇
  1989年   61篇
  1988年   58篇
  1987年   37篇
  1986年   28篇
  1985年   43篇
  1984年   19篇
  1983年   23篇
  1982年   20篇
  1981年   7篇
  1980年   4篇
  1978年   5篇
  1973年   5篇
  1972年   3篇
  1968年   3篇
  1965年   8篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
ObjectiveTo assess the benefits of regular exercise in reducing harms associated with betel quid (BQ) chewing.MethodsThe study cohort, 419,378 individuals, participated in a medical screening program between 1994 and 2008, with 38,324 male and 1,495 female chewers, who consumed 5–15 quids of BQ a day. Physical activity of each individual, based on “MET-hour/week”, was classified as “inactive” or “active”, where activity started from a daily 15 minutes/day or more of brisk walking (≥3.75 MET-hour/week). Hazard ratios for mortality and remaining years in life expectancy were calculated.ResultsNearly one fifth (18.7%) of men, but only 0.7% of women were chewers. Chewers had a 10-fold increase in oral cancer risk; and a 2-3-fold increase in mortality from lung, esophagus and liver cancer, cardiovascular disease, and diabetes, with doubling of all-cause mortality. More than half of chewers were physically inactive (59%). Physical activity was beneficial for chewers, with a reduction of all-cause mortality by 19%. Inactive chewers had their lifespan shortened by 6.3 years, compared to non-chewers, but being active, chewers improved their health by gaining 2.5 years. The improvement, however, fell short of offsetting the harms from chewing.ConclusionsChewers had serious health consequences, but being physically active, chewers could mitigate some of these adverse effects, and extend life expectancy by 2.5 years and reduce mortality by one fifth. Encouraging exercise, in addition to quitting chewing, remains the best advice for 1.5 million chewers in Taiwan.  相似文献   
992.
993.
The insect exoskeleton is mainly composed of chitin filaments linked by cuticle proteins. When insects molt, the cuticle of the exoskeleton is renewed by degrading the old chitin and cuticle proteins and synthesizing new ones. In this study, chitin‐binding activity of the wing disc cuticle protein BmWCP4 in Bombyx mori was studied. Sequence analysis showed that the protein had a conservative hydrophilic “R&R” chitin‐binding domain (CBD). Western blotting showed that BmWCP4 was predominately expressed in the wing disc‐containing epidermis during the late wandering and early pupal stages. The immunohistochemistry result showed that the BmWCP4 was mainly present in the wing disc tissues containing wing bud and trachea blast during day 2 of wandering stage. Recombinant full‐length BmWCP4 protein, “R&R” CBD peptide (CBD), non‐CBD peptide (BmWCP4‐CBD?), four single site‐directed mutated peptides (M1, M2, M3 and M4) and four‐sites‐mutated peptide (MF) were generated and purified, respectively, for in vitro chitin‐binding assay. The results indicated that both the full‐length protein and the “R&R” CBD peptide could bind with chitin, whereas the BmWCP4‐CBD? could not bind with chitin. The single residue mutants M1, M2, M3 and M4 reduced but did not completely abolish the chitin‐binding activity, while four‐sites‐mutated protein MF completely lost the chitin‐binding activity. These data indicate that BmWCP4 protein plays a critical role by binding to the chitin filaments in the wing during larva‐to‐pupa transformation. The conserved aromatic amino acids are critical in the interaction between chitin and the cuticle protein.  相似文献   
994.
报道1例由万博节皮菌Arthroderma vanbreuseghemii导致的面癣。患者女,9岁,面部大片红斑肿胀脱屑伴瘙痒7个月,被误诊为"多型红斑",口服激素3周,停药后皮损面积迅速扩大,伴鳞屑瘙痒。2015年4月21日就诊于我科,真菌直接镜检阳性,培养和PCR结果为万博节皮菌。给予口服伊曲康唑胶囊2个月后痊愈。  相似文献   
995.
Seven triterpenoids, 1  –  7 , two diarylheptanoids, 8 and 9 , four phenolic compounds, 10  –  13 , and three other compounds, 14  –  16 , were isolated from the hexane and MeOH extracts of the bark of Myrica cerifera L. (Myricaceae). Among these compounds, betulin ( 1 ), ursolic acid ( 3 ), and myricanol ( 8 ) exhibited cytotoxic activities against HL60 (leukemia), A549 (lung), and SK‐BR‐3 (breast) human cancer cell lines (IC50 3.1 – 24.2 μm ). Compound 8 induced apoptotic cell death in HL60 cells (IC50 5.3 μm ) upon evaluation of the apoptosis‐inducing activity by flow cytometric analysis and by Hoechst 33342 staining method. Western blot analysis on HL60 cells revealed that 8 activated caspases‐3, ‐8, and ‐9 suggesting that 8 induced apoptosis via both mitochondrial and death receptor pathways in HL60. Upon evaluation of the melanogenesis‐inhibitory activity in B16 melanoma cells induced with α‐melanocyte‐stimulating hormone (α‐MSH), erythrodiol ( 7 ), 4‐hydroxy‐2‐methoxyphenyl β‐d ‐glucopyranoside ( 13 ), and butyl quinate ( 15 ) exhibited inhibitory effects (65.4 – 86.0% melanin content) with no, or almost no, toxicity to the cells (85.9 – 107.4% cell viability) at 100 μm concentration. In addition, 8 , myricanone ( 9 ), myricitrin ( 10 ), protocatechuic acid ( 11 ), and gallic acid ( 12 ) revealed potent DPPH radical‐scavenging activities (IC50 6.9 – 20.5 μm ).  相似文献   
996.
A 3D‐printing technology and printed 3D lithium‐ion batteries (3D‐printed LIBs) based on LiMn0.21Fe0.79PO4@C (LMFP) nanocrystal cathodes are developed to achieve both ultrahigh rate and high capacity. Coin cells with 3D‐printed cathodes show impressive electrochemical performance: a capacity of 108.45 mAh g?1 at 100 C and a reversible capacity of 150.21 mAh g?1 at 10 C after 1000 cycles. In combination with simulation using a pseudo 2D hidden Markov model and experimental data of 3D‐printed and traditional electrodes, for the first time deep insight into how to achieve the ultrahigh rate performance for a cathode with LMFP nanocrystals is obtained. It is estimated that the Li‐ion diffusion in LMFP nanocrystal is not the rate‐limitation step for the rate to 100 C, however, that the electrolyte diffusion factors, such as solution intrinsic diffusion coefficient, efficiency porosity, and electrode thickness, will dominate ultrahigh rate performance of the cathode. Furthermore, the calculations indicate that the above factors play important roles in the equivalent diffusion coefficient with the electrode beyond a certain thickness, which determines the whole kinetic process in LIBs. This fundamental study should provide helpful guidance for future design of LIBs with superior electrochemical performance.  相似文献   
997.
998.
Bufalin (BF) exhibited antiproliferation and antimigration effects on human A549 lung cancer cells. To search its target‐related proteins, protein expression profiles of BF‐treated and control cells were compared using two quantitative proteomic methods, iTRAQ‐based and label‐free proteomic analysis. A total of 5428 proteins were identified in iTRAQ‐based analysis while 6632 proteins were identified in label‐free analysis. The number of common identified proteins of both methods was 4799 proteins. By application of 1.20‐fold for upregulated and 0.83‐fold for downregulated cutoff values, 273 and 802 differentially expressed proteins were found in iTRAQ‐based and label‐free analysis, respectively. The number of common differentially expressed proteins of both methods was 45 proteins. Results of bioinformational analysis using MetacoreTM showed that the two proteomic methods were complementary and both suggested the involvement of oxidative stress and regulation of gene expression in the effects of BF, and fibronectin‐related pathway was suggested to be an important pathway affected by BF. Western blotting assay results confirmed BF‐induced change in levels of fibronectin and other related proteins. Overexpression of fibronectin by plasmid transfection ameliorated antimigration effects of BF. Results of the present study provided information about possible target‐related proteins and signal network of BF.  相似文献   
999.
1000.
The ability of the white-rot fungus Ganoderma sp.En3 to decolorize different kinds of dyes widely applied in the textile and dyeing industry, including the anthraquinone dye Remazol Brilliant Blue R (RBBR), indigo dye indigo carmine and triphenylmethane dye methyl green, was evaluated in this study. Ganoderma sp.En3 had a strong capability of decolorizing high concentrations of RBBR, indigo carmine and methyl green. Obvious reduction of Chemical Oxygen Demand was observed after decolorization of different dyes. Ganoderma sp.En3 had a strong ability to tolerate RBBR, indigo carmine and methyl green with high concentrations. High concentrations of RBBR, indigo carmine and methyl green could also be efficiently decolorized by the crude enzyme of Ganoderma sp.En3. Different redox mediators such as syringaldehyde, acetosyringone and acetovanillone could enhance the decolorization capability for higher concentration of indigo carmine and methyl green. Different metal ions had little effect on the ability of the crude enzyme to decolorize indigo carmine and methyl green. Our study suggested that Ganoderma sp.En3 had a strong capability for decolorizing and tolerating high concentrations of different types of dyes such as RBBR, indigo carmine and methyl green.  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