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   800篇
  免费   42篇
  2021年   5篇
  2020年   4篇
  2018年   8篇
  2017年   4篇
  2016年   19篇
  2015年   28篇
  2014年   23篇
  2013年   38篇
  2012年   30篇
  2011年   31篇
  2010年   32篇
  2009年   21篇
  2008年   37篇
  2007年   48篇
  2006年   25篇
  2005年   35篇
  2004年   38篇
  2003年   41篇
  2002年   38篇
  2001年   37篇
  2000年   24篇
  1999年   28篇
  1998年   9篇
  1997年   3篇
  1996年   10篇
  1995年   8篇
  1994年   4篇
  1993年   5篇
  1992年   19篇
  1991年   24篇
  1990年   28篇
  1989年   19篇
  1988年   12篇
  1987年   17篇
  1986年   12篇
  1985年   6篇
  1984年   12篇
  1983年   3篇
  1982年   3篇
  1981年   4篇
  1980年   3篇
  1979年   5篇
  1977年   3篇
  1976年   3篇
  1975年   4篇
  1974年   4篇
  1973年   3篇
  1972年   3篇
  1967年   3篇
  1961年   4篇
排序方式: 共有842条查询结果,搜索用时 265 毫秒
1.
2.
A low-pressure microwave-induced helium plasma serves as an excitation source for metal chlorides, nitrates, and sulfates vaporized from a filament, resulting in fractional vaporization and differential sensitivities of detection of the elements depending on the vapor pressures of their salts. The shapes of the single emission peaks, which are simple in the presence of potassium chloride, become complex and may double in number.  相似文献   
3.
Polarographic protein waves were studied by using model samples. Two samples were prepared by thiolation of natural and synthetic polymers which show no catalytic wave in the ammoniacal cobalt buffer. The one was made from bacterial α-amylase by thiolation with N-acetylhomocysteine and the other was made from polyvinylalcohol by esterification with thioglycolic acid. These thiolated polymers showed typical double waves similar to protein waves both in cobaltous and cobaltic media though minute differences were present between the waves of thiolated polyvinylalcohol and those of proteins.  相似文献   
4.
Altered protein expression and phosphorylation are common events during malignant transformation. These perturbations have been widely explored in the context of E-cadherin cell-cell adhesion complexes, which are central in the maintenance of the normal epithelial phenotype. A major component of these complexes is p120 catenin (p120), which binds and stabilizes E-cadherin to promote its adhesive and tumor suppressing function. However, p120 is also an essential mediator of pro-tumorigenic signals driven by oncogenes, such as Src, and can be phosphorylated at multiple sites. Although alterations in p120 expression have been extensively studied by immunohistochemistry (IHC) in the context of tumor progression, little is known about the status and role of p120 phosphorylation in cancer. Here we show that tyrosine and threonine phosphorylation of p120 in two sites, Y228 and T916, is elevated in renal and breast tumor tissue samples. We also show that tyrosine phosphorylation of p120 at its N-terminus, including at the Y228 site is required for its pro-tumorigenic potential. In contrast, phosphorylation of p120 at T916 does not affect this p120 function. However, phosphorylation of p120 at T916 interferes with epitope recognition of the most commonly used p120 antibody, namely pp120. As a result, this antibody selectively underrepresents p120 levels in tumor tissues, where p120 is phosphorylated. Overall, our data support a role of p120 phosphorylation as a marker and mediator of tumor transformation. Importantly, they also argue that the level and localization of p120 in human cancer tissues immunostained with pp120 needs to be re-evaluated.  相似文献   
5.
Amyotrophic lateral sclerosis (ALS) is an adult-onset motor neuron degenerative disease. Given that oxidative stress and resulting chronic neuronal inflammation are thought to be central pathogenic, anti-oxidative agents and modulators of neuronal inflammation could be potential therapies for ALS. We report here that the novel small molecular compound, 2-[mesityl(methyl)amino]-N-[4-(pyridin-2-yl)-1H-imidazol-2-yl] acetamide trihydrochloride (WN1316) selectively suppresses oxidative stress-induced cell death and neuronal inflammation in the late-stage ALS mice. WN1316 has high blood-brain-barrier permeability and water solubility, and boosts both neuronal apoptosis inhibitory protein (NAIP) and NF-E2-related factor 2 (Nrf2) which governed glutathione (GSH)-related anti-oxidation pathway protecting motor neurons against oxidative injuries. Post-onset oral administration of low dose (1–100 µg/kg/day) WN1316 in ALS(SOD1H46R) and ALS(SOD1G93A) mice resulted in sustained improved motor function and post onset survival rate. Immunohistochemical analysis revealed less DNA oxidative damage and motor neuronal inflammation as well as repression of both microgliosis and astrocytosis, concomitant down regulation of interleukin-1β and inducible nitric oxide synthase, and preservation of the motoneurons in anterior horn of lumbar spinal cord and skeletal muscle (quadriceps femoris). Thus, WN1316 would be a novel therapeutic agent for ALS.  相似文献   
6.
7.
8.
The aim of the present study was to examine whether zinc (Zn) deficiency augmented the frequency of micronuclei, an indicator of chromosome aberration, and the induction of 8-hydroxy-2′-deoxyguanosine (8-OHdG), a marker of cellular DNA damage derived from oxidative stress, in rat bone marrow cells or not. Both the frequency of micronuclei and the induction of 8-OHdG were significantly increased in rats fed with a Zn-deficient versus a standard diet for 6 weeks (p?<?0.005). The supplementation of Zn with a standard diet for 4 weeks to rats fed with a Zn-deficient diet for 6 weeks restored the enhanced induction of micronuclei and 8-OHdG to levels comparable to those seen in rats fed with a standard diet for 10 weeks, indicating that the shortage of Zn in the body is involved in the induction of micronuclei and 8-OHdG. Again, the membrane-permeable superoxide dismutase mimetic superoxide scavenger, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, treatment (100 μmol/kg, twice a day) for 10 days prior to the termination of dietary treatment reduced the induction of micronuclei and 8-OHdG in rats fed with a Zn-deficient diet for 6 weeks to levels comparable to those in rats fed with a standard diet for 6 weeks, indicating that superoxide radical participates in the induction of micronuclei and 8-OHdG. In fact, the endogenous superoxide scavenger, Cu/Zn superoxide dismutase, was significantly reduced in the bone marrow cells of rats fed with a Zn-deficient diet for 6 weeks when compared to those of rats fed with a standard diet for 6 weeks (p?<?0.005). These observations demonstrate that Zn deficiency elevates the frequency of micronuclei and the induction of 8-OHdG through an increase in the biological action of the superoxide radical. This suggests an increase in carcinogenic initiation resulting from Zn deficiency-induced oxidative stress.  相似文献   
9.
Vitamin B6 is synthesized by green Cytisus scoparius callus and green Phellodendron amurense callus cultured on Linsmaier and Skoog Agar-medium with 10?5m of ±-naphthaleneacetic acid (NAA) and 10?6 m of 6-benzyladenine (BA). Even when thiamine and inositol were omitted from this medium, the growth and vitamin B6 content of Cytisus scoparius callus did not change. Vitamin B6 contents of clones of the calluses varied and were unstable during long-term subculture. Clonal selection was repeated to obtain stable strains with high vitamin B6 content, and the vitamin B6 content of one strain of green Cytisus scoparius callus became 4-times higher than that of the green leaves.  相似文献   
10.
The functional properties of gluten obtained by treating with chymotrypsin at alkali pH were investigated. The gluten was treated by chymotrypsin at pH 10.0 and 20°C, and was found to be deamidated to a state that was scarcely subject to proteolysis by chymotrypsin. The degree of deamidation of the gluten reached about 25% by this treatment for 2 hr. The functional properties of the gluten thus obtained were investigated in regard to deamidation. The enzymatically deamidated gluten greatly improved such functional properties as solubility and emulsifying ability. In particular, the solubility of the treated gluten was remarkably high in the pH range of 5 to 8, in which native gluten is insoluble. It was apparent that the improvement in functional properties of gluten was mainly due to the deamidation induced by treating with chymotrypsin at pH 10.0 and 20°C.  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