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   3698篇
  免费   311篇
  国内免费   2篇
  4011篇
  2024年   3篇
  2023年   16篇
  2022年   57篇
  2021年   89篇
  2020年   74篇
  2019年   84篇
  2018年   127篇
  2017年   110篇
  2016年   171篇
  2015年   226篇
  2014年   268篇
  2013年   311篇
  2012年   346篇
  2011年   327篇
  2010年   231篇
  2009年   192篇
  2008年   254篇
  2007年   220篇
  2006年   173篇
  2005年   181篇
  2004年   134篇
  2003年   100篇
  2002年   77篇
  2001年   46篇
  2000年   29篇
  1999年   26篇
  1998年   21篇
  1997年   16篇
  1996年   12篇
  1995年   10篇
  1994年   5篇
  1993年   8篇
  1992年   9篇
  1991年   2篇
  1990年   2篇
  1989年   4篇
  1988年   4篇
  1987年   7篇
  1986年   2篇
  1984年   5篇
  1983年   2篇
  1982年   3篇
  1980年   2篇
  1979年   2篇
  1975年   3篇
  1974年   2篇
  1968年   3篇
  1965年   3篇
  1960年   2篇
  1959年   1篇
排序方式: 共有4011条查询结果,搜索用时 0 毫秒
1.
A recombinant cell line (NIH3T3:pLtkSN) was made by infecting parental cells (NIH3T3) with a recombinant retrovirus (pLtkSN) encoding herpes simplex virus thymidine kinase (HSVtk) gene. The cells expressing HSVtk (NIH3T3:pLtkSN) grew 2.3 times more than the parental cells (NIH3T3) in Dulbecco's Modified Eagles Media containing 10% (v/v) horse serum. The NIH3T3:pLtkSN cells also showed a significant enhancement in the maximal cell concentration and the specific growth rate even at 2.5% serum concentration. The specific O2 uptake rate of NIH3T3 was 2.1 times greater than that of NIH3T3:pLtkSN. Under both O2-limited and O2-unlimited conditions, it appears that HSVtk plays an important role in enhancing the growth characteristics of animal cells.  相似文献   
2.
3.
The principal laboratory test used to confirm the pyometra diagnosis in the bitch has been the determination of the total white blood cell count in venous blood. A marked elevation is known to be a characteristic of the disease. In the present study, the white blood cell count was determined as well as the γ-globulin level. An elevation of the γ-globulin level and the total white blood cell count was very characteristic to the pyometra patients. The increase in the number of white blood cells nor the high γ-globulin level cannot be regarded specific for pyometra, therefore it was regarded important to find out a more specific test for pyometra. When sonicated E. coli bacteria were tested against sera from pyometra patients in electroimmunodiffusion, the precipitation was almost always detected when E. coli had been isolated from the uterus. This technique provides a quick method in detecting the causative E. coli infection. The present study suggests that whenever laboratory tests are used to confirm the pyometra diagnosis by the total white blood cell count, it is advantageous to analyze the total γ-globulin level in the serum as well as specific antibodies against a common E. coli antigen. Because of the reliability of the glutaraldehyde coagulation test and the simple technique, this can be suggested as the method of choice for an average small animal practice.  相似文献   
4.
Linear pentapeptides (Penta-cis-Apc-DPhe-Arg-Trp-Gly-NH2) containing 1-amino-4-phenylcyclohexane-1-carboxylic acid (cis-Apc) and substituted Apc are potent hMC4R agonists and they are inactive or weakly active in hMC1R, hMC3R, and hMC5R agonist assays. This study, together with our earlier report on 5-BrAtc, demonstrated the importance of replacing His6 with phenyl-containing rigid templates in achieving good hMC4R agonist potency and selectivity against hMC1R in linear pentapeptides.  相似文献   
5.
The increasing temperature in Arctic tundra deepens the active layer, which is the upper layer of permafrost soil that experiences repeated thawing and freezing. The increasing of soil temperature and the deepening of active layer seem to affect soil microbial communities. Therefore, information on soil microbial communities at various soil depths is essential to understand their potential responses to climate change in the active layer soil. We investigated the community structure of soil bacteria in the active layer from moist acidic tundra in Council, Alaska. We also interpreted their relationship with some relevant soil physicochemical characteristics along soil depth with a fine scale (5 cm depth interval). The bacterial community structure was found to change along soil depth. The relative abundances of Acidobacteria, Gammaproteobacteria, Planctomycetes, and candidate phylum WPS-2 rapidly decreased with soil depth, while those of Bacteroidetes, Chloroflexi, Gemmatimonadetes, and candidate AD3 rapidly increased. A structural shift was also found in the soil bacterial communities around 20 cm depth, where two organic (upper Oi and lower Oa) horizons are subdivided. The quality and the decomposition degree of organic matter might have influenced the bacterial community structure. Besides the organic matter quality, the vertical distribution of bacterial communities was also found to be related to soil pH and total phosphorus content. This study showed the vertical change of bacterial community in the active layer with a fine scale resolution and the possible influence of the quality of soil organic matter on shaping bacterial community structure.  相似文献   
6.
7.
This study was performed to examine the use of NaOCl as an alternative antimicrobial compound in winemaking because of the potential health problems that may arise as a result of the use of SO2. For this, the blank (non-treated), control (SO2-added), and sample (NaOCl-treated) wines were made, and microbial and chemical changes including sensory characteristics were analyzed during the fermentation periods. Treatment of grapes with NaOCl decreased the initial contaminating microbial population in grape must, resulting in higher growth of yeast and lactic acid bacteria. After 200 days of fermentation, the chemical analysis of sample wine revealed that it had higher ethanol content, redness (a*), and concentrations of fruity ester compounds and lower total acidity than the control. In the sensory analyses, the sample wine obtained a higher overall acceptability score (5.70) than the control (4.26). This result reveals that NaOCl can be used as an alternative to SO2 in winemaking for inhibiting the growth of contaminating microorganisms.  相似文献   
8.
Members of the Pumilio (Pum) family of RNA-binding proteins act as translational repressors and are required for germ cell development and asymmetric division. We identified the chicken Pum1 and Pum2 genes and analyzed their expression patterns in various tissues. Comparative sequence analysis of the Pum1 and Pum2 proteins from the drosophila, chicken, mouse, and human revealed a high degree of evolutionary conservation in terms of the levels of homology of the peptide sequences and the structure of Pumilio homology domain (PUM-HD), C-terminal RNA-binding domain, with similar spacing between the adjacent Pum eight tandem repeats. In addition, phylogenetic patterns of pumilio family showed that Pum 1 and 2 of chicken are more closely related to those of mouse and human than other species and Pum1 is more conserved than Pum2. Using real-time RT-PCR, the expression levels of the Pum1 and Pum2 genes were found to be highest in hatched female gonads, and high-level expression of Pum2 was detected in 12-day and hatched gonads among the various chicken embryonic tissues tested. In adult tissues, the expression levels of Pum1 and Pum2 were expressed at higher levels in the testis and muscle than in any other tissue. The characteristics of the tissue-specific expression of Pum genes suggest that Pum1 and Pum2 have effects crucially in particular stage during development of chicken gonads depending on sexual maturation.  相似文献   
9.
The aim of this study is to investigate the capability of an apoA-I mimetic with multiple amphipathic helices to form HDL-like particles in vitro and in vivo. To generate multivalent helices and to track the peptide mimetic, we have constructed a peptibody by fusing two tandem repeats of 4F peptide to the C terminus of a murine IgG Fc fragment. The resultant peptidbody, mFc-2X4F, dose-dependently promoted cholesterol efflux in vitro, and the efflux potency was superior to monomeric 4F peptide. Like apoA-I, mFc-2X4F stabilized ABCA1 in J774A.1 and THP1 cells. The peptibody formed larger HDL particles when incubated with cultured cells compared with those by apoA-I. Interestingly, when administered to mice, mFc-2X4F increased both pre-β and α-1 HDL subfractions. The lipid-bound mFc-2X4F was mostly in the α-1 migrating subfraction. Most importantly, mFc-2X4F and apoA-I were found to coexist in the same HDL particles formed in vivo. These data suggest that the apoA-I mimetic peptibody is capable of mimicking apoA-I to generate HDL particles. The peptibody and apoA-I may work cooperatively to generate larger HDL particles in vivo, either at the cholesterol efflux stage and/or via fusion of HDL particles that were generated by the peptibody and apoA-I individually.  相似文献   
10.
The inactivating efficiency of alternating high-voltage pulsed (AHVP) current was investigated in brine (20 w/v% NaCl) and saline (0.9 w/v% NaCl) inoculated with 1x 107 cells/ml of Listeria monocytogenes. AHVP current at 12 V with 1 pulse completely inactivated L. monocytogenes in brine within 3 ms, while the bacteria in saline were fully inactivated by 10-pulsed electric treatment at 12 V within the same time. Electron microscopic observation demonstrated substantial structural damage of electrically treated L. monocytogenes in brine. These results suggest that AHVP treatment would be effective for the rapid and complete inactivation of L. monocytogenes in brine or saline solution.  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