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   4952篇
  免费   516篇
  国内免费   1篇
  5469篇
  2022年   33篇
  2021年   75篇
  2020年   62篇
  2019年   70篇
  2018年   84篇
  2017年   66篇
  2016年   124篇
  2015年   196篇
  2014年   199篇
  2013年   244篇
  2012年   345篇
  2011年   319篇
  2010年   172篇
  2009年   196篇
  2008年   252篇
  2007年   234篇
  2006年   243篇
  2005年   221篇
  2004年   235篇
  2003年   223篇
  2002年   236篇
  2001年   75篇
  2000年   73篇
  1999年   72篇
  1998年   75篇
  1997年   51篇
  1996年   51篇
  1995年   63篇
  1994年   42篇
  1993年   58篇
  1992年   43篇
  1991年   41篇
  1990年   65篇
  1989年   45篇
  1988年   45篇
  1987年   40篇
  1986年   30篇
  1985年   47篇
  1984年   57篇
  1983年   40篇
  1982年   43篇
  1981年   57篇
  1980年   43篇
  1979年   28篇
  1978年   54篇
  1977年   40篇
  1976年   47篇
  1975年   33篇
  1974年   42篇
  1973年   29篇
排序方式: 共有5469条查询结果,搜索用时 8 毫秒
991.
Butyrylcholinesterase (BChE) inactivates the appetite stimulating hormone octanoyl-ghrelin. The hypothesis was tested that BChE−/− mice would have abnormally high body weight and high levels of octanoyl-ghrelin. It was found that BChE−/− mice fed a standard 5% fat diet had normal body weight. However, BChE−/− mice fed a diet containing 11% fat became obese. Their obesity was not explained by increased levels of octanoyl-ghrelin, or by increased caloric intake, or by decreased exercise. Instead, a role for BChE in fat utilization was suggested.  相似文献   
992.
Over a period of two years, growth rate and health were measured for dairy calves allowed to suckle their mothers up to 6–8 weeks of age. Thirty-one calves were weighted weekly, and the mean daily growth rate was 1.2 ± 0.03 kg from birth up to 13 weeks of age. Illness in calves and young stock was not observed. In the cows, the mean incidences of ketosis, displaced abomasum, puerperal paresis, mastitis, teat injury and retained placenta were 0, 0, 8, 22, 1 and 1%, respectively, during a 6-year period. The mean daily gain of 56 growing bulls was 1.4 kg when slaughtered at 15 months of age, which is higher than the mean daily gain of 0.95 kg in the population. Probiotics, hormones and vaccines were not used, and antibiotics were only used for treating illness. The present study indicates many advantages and few problems when dairy calves are penned together with the cows and allowed natural feeding up to 6–8 weeks of age. This production system was easy to manage, preferred by the farmer, and may satisfy the public concern regarding the practice of immediate separation of cow and calf in commercial milk production.  相似文献   
993.
A significant consequence of ischemia/reperfusion (I/R) is mitochondrial respiratory dysfunction, leading to energetic deficits and cellular toxicity from reactive oxygen species (ROS). Mammalian complex I, a NADH-quinone oxidoreductase enzyme, is a multiple subunit enzyme that oxidizes NADH and pumps protons across the inner membrane. Damage to complex I leads to superoxide production which further damages complex I as well as other proteins, lipids and mtDNA. The yeast, S. cerevisiae, expresses internal rotenone insensitive NADH-quinone oxidoreductase (Ndi1); a single 56 kDa polypeptide which, like the multi-subunit mammalian complex I, serves as the entry site of electrons to the respiratory chain, but without proton pumping. Heterologous expression of Ndi1 in mammalian cells results in protein localization to the inner mitochondrial membrane which can function in parallel with endogenous complex I to oxidize NADH and pass electrons to ubiquinone. Expression of Ndi1 in HL-1 cardiomyocytes and in neonatal rat ventricular myocytes protected the cells from simulated ischemia/reperfusion (sI/R), accompanied by lower ROS production, and preservation of ATP levels and NAD+/NADH ratios. We next generated a fusion protein of Ndi1 and the 11aa protein transduction domain from HIV TAT. TAT-Ndi1 entered cardiomyocytes and localized to mitochondrial membranes. Furthermore, TAT-Ndi1 introduced into Langendorff-perfused rat hearts also localized to mitochondria. Perfusion of TAT-Ndi1 before 30 min no-flow ischemia and up to 2 hr reperfusion suppressed ROS production and preserved ATP stores. Importantly, TAT-Ndi1 infused before ischemia reduced infarct size by 62%; TAT-Ndi1 infused at the onset of reperfusion was equally cardioprotective. These results indicate that restoring NADH oxidation and electron flow at reperfusion can profoundly ameliorate reperfusion injury.  相似文献   
994.
Modifying FTY720, an immunosuppressant modulator, led to a new series of well phosphorylated tetralin analogs as potent S1P1 receptor agonists. The stereochemistry effect of tetralin ring was probed, and (?)-(R)-2-amino-2-((S)-6-octyl-1,2,3,4-tetrahydronaphthalen-2-yl)propan-1-ol was identified as a good SphK2 substrate and potent S1P1 agonist with good oral bioavailability.  相似文献   
995.
Four cases of vesicoureteral reflux are discussed by prominent pediatric urologists. The condition can range from minimal reflux into the distal ureter to massive reflux causing tortuosity of the ureter and hydronephrosis. Treatment options range from medical management to tapering of the ureter with reimplantation. The cross-trigonal technique is popular among pediatric urologists, and the Politano-Leadbetter technique is a very successful technique that has stood the test of time. The extravesical approach to ureteral reimplantation reduces morbidity, shortens hospital stays, reduces medical costs, and maintains the high success rates of the intravesical techniques. Subureteric injection of bulking agents to correct the reflux holds promise as an alternative to open surgery, but presents the challenge of identifying the ideal bulking agent.  相似文献   
996.
997.
Five men with cystic fibrosis delivered semen samples which were analysed for the content of the four main groups of prostaglandins (PGs). No PGs could be found in any of the specimens. The results of the present study provide further evidence that the seminal vesicles constitute the dominant site of production of PGs in human semen.  相似文献   
998.
In simian virus 40 (SV40)-transformed cells, a tight complex is formed between the viral large T antigen (large T) and p53. It has been proposed that this complex interferes with the antiproliferative activity of p53. This notion was tested in primary rat fibroblasts by assessing the ability of SV40-mediated transformation to be spared from the inhibitory effect of wild-type (wt) p53. The data indicate that relative to transformation induced by myc plus ras, SV40-plus-ras-mediated focus formation was indeed much less suppressed by p53 plasmids. A majority of the resultant cell lines made a p53 protein with properties characteristic of a wt conformation. Furthermore, cell lines expressing stably both SV40 large T and a temperature-sensitive p53 mutant continued to proliferate at a temperature at which this p53 assumes wt-like properties and normally causes a growth arrest. Surprisingly, at least partial resistance to the growth-inhibitory effect of wt p53 was also evident when transformation was mediated by an SV40 deletion mutant, encoding a large T which does not bind p53 detectably. In addition to supporting the idea that SV40 can overcome the growth-restrictive activity of wt p53, these findings strongly suggest that at least part of this effect does not require a stable association between p53 and large T.  相似文献   
999.
Through the use of computational modeling, a series of pyrimidinetrione-based inhibitors of MMP-13 was designed based on a lead inhibitor identified through file screening. Incorporation of a biaryl ether moiety at the C-5 position of the pyrimidinetrione ring resulted in a dramatic enhancement of MMP-13 potency. Protein crystallography revealed that this moiety binds in the S(1)(') pocket of the enzyme. Optimization of the C-4 substituent of the terminal aromatic ring led to incorporation of selectivity versus MMP-14 (MT-1 MMP). Structure activity relationships of the biaryl ether substituent are presented as is pharmacokinetic data for a compound that meets our in vitro potency and selectivity goals.  相似文献   
1000.
Huntington’s disease (HD) is a neurodegenerative disorder caused by a poly-CAG expansion in the first exon of the HTT gene, resulting in an extended poly-glutamine tract in the N-terminal domain of the Huntingtin (Htt) protein product. Proteolytic fragments of the poly-glutamine–containing N-terminal domain form intranuclear aggregates that are correlated with HD. Post-translational modification of Htt has been shown to alter its function and aggregation properties. However, the effect of N-terminal Htt acetylation has not yet been considered. Here, we developed a bacterial system to produce unmodified or N-terminally acetylated and aggregation-inducible Htt protein. We used this system together with biochemical, biophysical, and imaging studies to confirm that the Htt N-terminus is an in vitro substrate for the NatA N-terminal acetyltransferase and show that N-terminal acetylation promotes aggregation. These studies represent the first link between N-terminal acetylation and the promotion of a neurodegenerative disease and implicates NatA-mediated Htt acetylation as a new potential therapeutic target in HD.  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