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   476篇
  免费   13篇
  489篇
  2023年   1篇
  2022年   6篇
  2021年   8篇
  2020年   4篇
  2019年   9篇
  2018年   10篇
  2017年   6篇
  2016年   15篇
  2015年   13篇
  2014年   30篇
  2013年   27篇
  2012年   40篇
  2011年   60篇
  2010年   32篇
  2009年   14篇
  2008年   32篇
  2007年   26篇
  2006年   23篇
  2005年   24篇
  2004年   28篇
  2003年   26篇
  2002年   11篇
  2001年   5篇
  2000年   1篇
  1999年   2篇
  1998年   2篇
  1997年   4篇
  1996年   2篇
  1995年   2篇
  1994年   2篇
  1993年   1篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
  1988年   3篇
  1987年   2篇
  1984年   2篇
  1983年   1篇
  1982年   1篇
  1980年   4篇
  1979年   2篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1972年   1篇
排序方式: 共有489条查询结果,搜索用时 10 毫秒
171.
The group of organisms commonly referred to as genital mycoplasmas comprise species most often found in genitourinary tract of sexually active adults as common commensal inhabitants, or pathogens which can possibly cause many different pathologies like: non-gonococcal urethritis, bacterial vaginosis, cervicitis, endometritis or pelvic inflammatory disease. The problem of their morbidity and the possible influence they have on human fertility is still not clear. The aim of this study was to find out whether two investigated species- Ureaplasma urealyticum and Mycoplasma hominis can be detect more often in a group of infertile women. 74 women participated in the study and were assigned to one of 2 groups of patients: infertile women and fertile women without any sign of genital tract infection. Swabs from the cervical canal of the uterus and the fluid from the Douglas pouch were taken during the gynecological examination and laparoscopic procedure. Two diagnostic methods were used: biochemical method- commercial diagnostic kit- Mycoplasma IST 2 and PCR method. The results showed that Ureaplasma urealyticum and Mycoplasma hominis were detected among both fertile and infertile women with nearly the same frequency, much more often in cervical canal than in the Douglas pouch. Ureaplasma urealyticum was more common pathogen than Mycoplasma hominis in both groups and locations. The achieved results point out that the role of genital mycoplasmas in human infertility is still unclear and require further investigations.  相似文献   
172.
Historic emissions from a Ni refinery at Port Colborne, Ontario, caused Ni contamination of regional soils and raised concerns about potential Ni phytotoxicity. Previous tests revealed that if these soils were made alkaline and fertilized with Mn and other common nutrients as needed to maintain fertility of such alkaline soils, full remediation (prevention of Ni phytotoxicity) would be obtained. This experiment was conducted to test this method of remediation on diverse soils from Port Colborne, and to evaluate chemical extraction tests which would be predictive of plant uptake and potential for Ni phytotoxicity in Ni-contaminated soils. Ten soils with varied levels of Ni contamination and varied soil properties were amended with limestone or nitric acid to raise or lower pH so that a wide pH range could be examined for the soils. For lower Ni organic and mineral soils near the Ontario remediation limit (200 mg/kg), neither crop suffered Ni phytotoxicity at any pH tested. Only when more highly contaminated soils were strongly acidic did Ni phytotoxicity occur. Phytotoxic soils were fully remediated by making soils alkaline even for these Ni-sensitive crop species. Only the most contaminated organic soil remained slightly toxic – but this soil was remarkably contaminated (over 1.1% of Ni). The Sr nitrate extraction method was much more effective in predicting plant Ni concentrations than the DTPA method. This test provides an inexpensive soil extraction result highly predictive of potential for Ni phytotoxicity across soils.  相似文献   
173.
Coat colour anomalies in the common shrew, Sorex araneus L., in the geographical range of this species, including Poland, are extremely rare. This study describes atypically coloured common shrews. Light colouration of the coat is a result of lack ofpigment in the entire hair or hair fragments. It appears that atypically coloured shrews occur more often in isolated populations whose gene transfer with neighboring populations is limited.  相似文献   
174.
Membrane-permeable calmodulin inhibitors, such as the napthalenesulfonamide derivatives W-7/W-13, trifluoperazine, and calmidazolium, are used widely to investigate the role of calcium/calmodulin (Ca2+/CaM) in living cells. If two chemically different inhibitors (e.g. W-7 and trifluoperazine) produce similar effects, investigators often assume the effects are due to CaM inhibition. Zeta potential measurements, however, show that these amphipathic weak bases bind to phospholipid vesicles at the same concentrations as they inhibit Ca2+/CaM; this suggests that they also bind to the inner leaflet of the plasma membrane, reducing its negative electrostatic surface potential. This change will cause electrostatically bound clusters of basic residues on peripheral (e.g. Src and K-Ras4B) and integral (e.g. epidermal growth factor receptor (EGFR)) proteins to translocate from the membrane to the cytoplasm. We measured inhibitor-mediated translocation of a simple basic peptide corresponding to the calmodulin-binding juxtamembrane region of the EGFR on model membranes; W-7/W-13 causes translocation of this peptide from membrane to solution, suggesting that caution must be exercised when interpreting the results obtained with these inhibitors in living cells. We present evidence that they exert dual effects on autophosphorylation of EGFR; W-13 inhibits epidermal growth factor-dependent EGFR autophosphorylation under different experimental conditions, but in the absence of epidermal growth factor, W-13 stimulates autophosphorylation of the receptor in four different cell types. Our interpretation is that the former effect is due to W-13 inhibition of Ca2+/CaM, but the latter results could be due to binding of W-13 to the plasma membrane.  相似文献   
175.
Deep dormancy of apple (Malus domestica Borkh.) seeds is terminated by a 3-month-long cold stratification. It is expressed by rapid germination of seeds and undisturbed growth of seedlings. However, stimulation of germination of isolated apple embryos is also observed after applying inhibitors of cytochrome c oxidase: nitric oxide (NO) or hydrogen cyanide (HCN) during the first 3–6 h of imbibition of dormant embryos. The aim of this work was to compare the effect of yet another toxic gaseous molecule carbon monoxide (CO) with the effects of HCN and NO on germination of apple embryos and growth and development of young seedlings. We demonstrated that stimulation of germination after short-term pre-treatment with HCN, NO or CO was accompanied by enhanced NO emission from the embryo axes during their elongation. Moreover, similarly high NO production from non-dormant embryos, after cold stratification, was detected. Therefore, we propose that NO may act as signaling molecule in apple embryo dormancy break.  相似文献   
176.
The Effect of Acute Hypoxia on Synaptosomes from Rat Brain   总被引:4,自引:4,他引:4  
Abstract: Synaptosomes have been isolated from the brains of nonanesthetized and nembutal-anesthetized rats subjected to 30 min hypoxia induced by breathing 7% oxygen in nitrogen. The respiratory rate was depressed in synaptosomes from starved hypoxic animals but was not significantly different from the respective control values in preparations from fed hypoxic animals, anesthetized animals, and hypoxic nonanesthetized animals allowed to recover from the hypoxic episode by 60 min of normoxic conditions. Observations are also reported concerning the levels of various metabolites in the synaptosomes isolated from the brains of the same groups of animals. It is suggested that hypoxia results in damage to the synaptosomal and/or mitochondrial membrane, which modifies substrate oxidation in the mitochondria and decreases availability of reducing equivalents for the respiratory chain. Results obtained on afflicted and recovered animals indicate that synaptosomal preparations provide a useful model for the study of hypoxic damage.  相似文献   
177.
Southern analysis showed that Gr-EXPB1, a functional expansin from the potato cyst nematode Globodera rostochiensis, is member of a multigene family, and EST data suggest expansins to be present in other plant parasitic nematodes as well. Homology modeling predicted that Gr-EXPB1 domain 1 (D1) has a flat beta-barrel structure with surface-exposed aromatic rings, whereas the 3D structure of Gr-EXPB1-D2 was remarkably similar to plant expansins. Gr-EXPB1 shows highest sequence similarity to two extracellular proteins from saprophytic soil-inhabiting Actinobacteria, and includes a bacterial type II carbohydrate-binding module. These results support the hypothesis that a number of pathogenicity factors of cyst nematodes is of procaryotic origin and were acquired by horizontal gene transfer.  相似文献   
178.
The NADP-dependent isocitrate dehydrogenase obtained from brain cytosol of control and hypoxic animals was purified 36-fold by a combination of chromatography on DE-32 cellulose, CM cellulose, and DEAE-Sephadex and electrophoresis. Hypoxia did not change the molecular weight (about 165,000) of the enzyme, which was composed of two subunits of 80,000 daltons each.  相似文献   
179.
180.
Engraftment of muscle-derived cells (MDCs) into the urethral sphincter may cure urinary incontinence. However, poor cell survival after injection prompted us to evaluate whether 24-h preincubation with sodium ascorbate (ASC) or basic fibroblast growth factor (bFGF) prior to cell transfer improves the survival of MDCs facing oxidative stress in vitro. We examined MDCs isolated from female rats for the presence of myogenic markers and for the ability to differentiate and respond to growth factors. Isolated cells were positive for desmin, M-cadherin, and myogenin. The fusion index exceeded 29%, and Akt kinase was phosphorylated at Ser473 residue upon exposure to insulin-like growth factor 1 (100 ng/ml). We then autologously transplanted MDCs transfected with lacZ marker gene into urethral wall of the rats; 2 wk later, the urethra and caudal wall of the urinary bladder were harvested from these animals. Serial cryosections revealed that transplanted cells formed multinuclear clusters at injection sites. In addition, we found that the viability of MDCs exposed to a cytotoxic concentration of H2O2 was higher after preincubation with 0.1 mM ASC (2.6-fold), 10 ng/ml bFGF (2.9-fold), or 20 ng/ml bFGF (3.5-fold) than that after exposure to H2O2 only. We conclude that preincubation with ASC or bFGF increases the resistance of MDCs to oxidative stress in vitro. Pretreatment with either agent might be used to enhance survival of MDCs after transplantation.  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