全文获取类型
收费全文 | 11742篇 |
免费 | 1442篇 |
国内免费 | 109篇 |
出版年
2023年 | 38篇 |
2022年 | 78篇 |
2021年 | 153篇 |
2020年 | 131篇 |
2019年 | 163篇 |
2018年 | 208篇 |
2017年 | 193篇 |
2016年 | 282篇 |
2015年 | 362篇 |
2014年 | 420篇 |
2013年 | 467篇 |
2012年 | 567篇 |
2011年 | 549篇 |
2010年 | 365篇 |
2009年 | 373篇 |
2008年 | 463篇 |
2007年 | 447篇 |
2006年 | 376篇 |
2005年 | 347篇 |
2004年 | 337篇 |
2003年 | 299篇 |
2002年 | 274篇 |
2001年 | 1132篇 |
2000年 | 976篇 |
1999年 | 707篇 |
1998年 | 216篇 |
1997年 | 224篇 |
1996年 | 170篇 |
1995年 | 147篇 |
1994年 | 150篇 |
1993年 | 104篇 |
1992年 | 364篇 |
1991年 | 321篇 |
1990年 | 281篇 |
1989年 | 218篇 |
1988年 | 196篇 |
1987年 | 137篇 |
1986年 | 146篇 |
1985年 | 110篇 |
1984年 | 62篇 |
1983年 | 63篇 |
1981年 | 28篇 |
1979年 | 38篇 |
1978年 | 29篇 |
1976年 | 37篇 |
1975年 | 35篇 |
1973年 | 39篇 |
1972年 | 50篇 |
1971年 | 45篇 |
1970年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Parikh NA Katsetos CD Ashraf QM Haider SH Legido A Delivoria-Papadopoulos M Mishra OP 《Neurochemical research》2003,28(9):1351-1357
Hypoxia results in generation of nitric oxide (NO) free radicals, activation of caspase-3, and genomic DNA fragmentation. The present study tests the hypothesis that hypoxia-induced caspase-3 activation and DNA fragmentation are nitric oxide mediated. Studies were conducted in newborn piglets, divided into normoxic (n = 5), hypoxic (n = 5), and hypoxic-7-NINA (n = 6). Hypoxic-7-NINA group received the neuronal nitric oxide synthase inhibitor, 7-Nitroindazole (7-NINA). Caspase-3 activity was determined spectrofluorometrically using enzyme-specific substrates. Sections from the neocortex were stained with an antiserum recognizing active caspase-3. Purified DNA was separated by gel electrophoresis. Administration of 7-NINA resulted in decreased immunoreactivity of caspase-3 (mean LI: 20.2%) as compared to the untreated hypoxia group (mean LI: 57.5%) (P < 0.05). 7-NINA attenuated caspase-3 enzymatic activity as well in comparison to the untreated hypoxia group (P < 0.05). Furthermore, multiple low molecular weight bands corresponding to DNA fragments were present in the hypoxic but not in the normoxic or hypoxic-7-NINA groups. Inhibition of nNOS abates the hypoxia-induced increase in active caspase-3 immunoreactivity, as well as enzymatic activity in cortical neurons, and DNA fragmentation in brain homogenates. We conclude that the coordinate increase of capase-3 activity and fragmentation of nuclear DNA in the hypoxic newborn piglet brain are NO mediated. 相似文献
994.
Zhou X Yin W Doi SQ Robinson SW Takeyasu K Fan X 《American journal of physiology. Cell physiology》2003,285(2):C319-C326
The signaling pathway that transduces the stimulatory effect of low K+ on the biosynthesis of Na,K-ATPase remains largely unknown. The present study was undertaken to examine whether reactive oxygen species (ROS) mediated the effect of low K+ in Madin-Darby canine kidney (MDCK) cells. Low K+ increased ROS activity in a time- and dose-dependent manner, and this effect was abrogated by catalase and N-acetylcysteine (NAC). To determine the role of ROS in low-K+-induced gene expression, the cells were first stably transfected with expression constructs in which the reporter gene chloramphenicol acetyl transferase (CAT) was under the control of the avian Na,K-ATPase -subunit 1.9 kb and 900-bp 5'-flanking regions that have a negative regulatory element. Low K+ increased the CAT expression in both constructs. Catalase or NAC inhibited the effect of low K+. To determine whether the increased CAT activity was mediated through releasing the repressive effect or a direct stimulation of the promoter, the cells were transfected with a CAT expression construct directed by a 96-bp promoter fragment that has no negative regulatory element. Low K+ also augmented the CAT activity expressed by this construct. More importantly, both catalase and NAC abolished the effect of low K+. Moreover, catalase and NAC also inhibited low-K+-induced increases in the Na,K-ATPase 1- and 1-subunit protein abundance and ouabain binding sites. The antioxidants had no significant effect on the basal levels of CAT activity, protein abundance, or ouabain binding sites. In conclusion, low K+ enhances the Na,K-ATPase gene expression by a direct stimulation of the promoter activity, and ROS mediate this stimulation and also low-K+-induced increases in the Na,K-ATPase protein contents and cell surface molecules. Madin-Darby canine kidney cells; N-acetylcysteine; catalase 相似文献
995.
Ni L Zheng XS Somers PK Hoong LK Hill RR Marino EM Suen KL Saxena U Meng CQ 《Bioorganic & medicinal chemistry letters》2003,13(4):745-748
alpha,beta-Unsaturated sulfones have been discovered from a combinatorial library as leads for a new series of inhibitors of inducible VCAM-1 expression. Although not essential, further conjugation of the sulfonyl group to another vinyl group or a phenyl group increases the potency dramatically. 相似文献
996.
O'Malley YQ Abdalla MY McCormick ML Reszka KJ Denning GM Britigan BE 《American journal of physiology. Lung cellular and molecular physiology》2003,284(2):L420-L430
The Pseudomonas aeruginosa secretory product pyocyanin damages lung epithelium, likely due to redox cycling of pyocyanin and resultant superoxide and H(2)O(2) generation. Subcellular site(s) of pyocyanin redox cycling and toxicity have not been well studied. Therefore, pyocyanin's effects on subcellular parameters in the A549 human type II alveolar epithelial cell line were examined. Confocal and electron microscopy studies suggested mitochondrial redox cycling of pyocyanin and extracellular H(2)O(2) release, respectively. Pyocyanin decreased mitochondrial and cytoplasmic aconitase activity, ATP levels, cellular reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide, and mitochondrial membrane potential. These effects were transient at low pyocyanin concentrations and were linked to apparent cell-mediated metabolism of pyocyanin. Overexpression of MnSOD, but not CuZnSOD or catalase, protected cellular aconitase, but not ATP, from pyocyanin-mediated depletion. This suggests that loss of aconitase activity is not responsible for ATP depletion. How pyocyanin leads to ATP depletion, the mechanism of cellular metabolism of pyocyanin, and the impact of mitochondrial pyocyanin redox cycling on other cellular events are important areas for future study. 相似文献
997.
Liu JQ Sham JS Shimoda LA Kuppusamy P Sylvester JT 《American journal of physiology. Lung cellular and molecular physiology》2003,285(2):L322-L333
To determine whether reactive oxygen species (ROS) play an essential role in hypoxic pulmonary vasoconstriction (HPV) and the cellular locus of ROS production and action during HPV, we measured internal diameter (ID) at constant transmural pressure, lucigenin-derived chemiluminescence (LDCL), and electron paramagnetic resonance (EPR) spin adduct spectra in small distal porcine pulmonary arteries, and dichlorofluorescein (DCF) fluorescence in myocytes isolated from these arteries. Hypoxia (4% O2) decreased ID, increased DCF fluorescence, tended to increase LDCL, and in some preparations produced EPR spectra consistent with hydroxyl and alkyl radicals. Superoxide dismutase (SOD, 150 U/ml) or SOD + catalase (CAT, 200 U/ml) did not alter ID during normoxia but reduced or abolished the constriction induced by hypoxia. SOD also blocked HPV in endothelium-denuded arteries after restoration of the response by exposure to 10-10 M endothelin-1. Confocal fluorescence microscopy demonstrated that labeled SOD and CAT entered pulmonary arterial myocytes. SOD, SOD + CAT, and CAT blocked the increase in DCF fluorescence induced by hypoxia, but SOD + CAT and CAT also caused a stable increase in fluorescence during normoxia, suggesting that CAT diminished efflux of DCF from cells or oxidized the dye directly. We conclude that HPV required increased concentrations of ROS produced by and acting on pulmonary arterial smooth muscle rather than endothelium. 相似文献
998.
999.
The expression, inheritance, and linkage relationships of three genetic traits were studied in the malaria vector Anopheles gambiae. Red stripe (Rs) is a common phenotypic polymorphism in numerous A. gambiae populations, whereas frizzled (f) and homochromy1 (hom1) were isolated from (60)Co-irradiated mosquitoes. Red stripe appears as a diffuse stripe of pigment on the dorsum of larvae and pupae and is variable in expressivity and penetrance. Our data demonstrate that Red stripe results from a heterozygous collarless genotype (i.e., c+ c, chromosome 2) and is essentially sex-limited to females. frizzled is a sex-linked recessive semi-lethal identified by deformed lateral larval setae; its lethality manifests as low rates of adult emergence and brief adult survival. frizzled is located on the X chromosome between pink eye and Mosaic, 3 cM from Mosaic and approximately 12 cM from pink eye. Finally, the mutation homochromy1 (hom1) is on chromosome 2 and causes a recessive phenotype that prevents normal darkening of larvae when reared in a black container. Unlike mutants with this characteristic described thus far, the eye color of hom1 mutants is normal. We determined that hom1 is located between Dieldrin resistance and collarless, approximately 3 cM from the latter. We discuss the possibility of differences in male and female recombination values and the range of values that have been observed in test crosses for chromosome 2 markers. 相似文献
1000.
Fitzgerald JC Gao GP Reyes-Sandoval A Pavlakis GN Xiang ZQ Wlazlo AP Giles-Davis W Wilson JM Ertl HC 《Journal of immunology (Baltimore, Md. : 1950)》2003,170(3):1416-1422
In animal models, E1-deleted human adenoviral recombinants of the serotype 5 (AdHu5) have shown high efficacy as vaccine carriers for different Ags including those of HIV-1. Humans are infected by common serotypes of human adenovirus such as AdHu5 early in life and a significant percentage has high levels of neutralizing Abs to these serotypes, which will very likely impair the efficacy of recombinant vaccines based on the homologous virus. To circumvent this problem, a novel replication-defective adenoviral vaccine carrier based on an E1-deleted recombinant of the chimpanzee adenovirus 68 (AdC68) was developed. An AdC68 construct expressing a codon-optimized, truncated form of gag of HIV-1 induces CD8(+) T cells to gag in mice which at the height of the immune response encompass nearly 20% of the entire splenic CD8(+) T cell population. The vaccine-induced immune response provides protection to challenge with a vaccinia gag recombinant virus. Induction of transgene-specific CD8(+) T cells and protection against viral challenge elicited by the AdC68 vaccines is not strongly inhibited in animals preimmune to AdHu5 virus. However, the response elicited by the AdHu5 vaccine is greatly attenuated in AdHu5 preimmune animals. 相似文献