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   13736篇
  免费   699篇
  国内免费   8篇
  14443篇
  2023年   27篇
  2022年   65篇
  2021年   114篇
  2020年   58篇
  2019年   85篇
  2018年   139篇
  2017年   145篇
  2016年   245篇
  2015年   376篇
  2014年   432篇
  2013年   1138篇
  2012年   766篇
  2011年   827篇
  2010年   481篇
  2009年   461篇
  2008年   779篇
  2007年   864篇
  2006年   852篇
  2005年   890篇
  2004年   972篇
  2003年   907篇
  2002年   856篇
  2001年   140篇
  2000年   97篇
  1999年   144篇
  1998年   220篇
  1997年   206篇
  1996年   169篇
  1995年   145篇
  1994年   114篇
  1993年   153篇
  1992年   127篇
  1991年   92篇
  1990年   93篇
  1989年   89篇
  1988年   85篇
  1987年   64篇
  1986年   75篇
  1985年   86篇
  1984年   101篇
  1983年   87篇
  1982年   106篇
  1981年   95篇
  1980年   83篇
  1979年   41篇
  1978年   47篇
  1977年   43篇
  1976年   51篇
  1974年   36篇
  1973年   33篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Background  Highly pathogenic avian influenza virus (HPAIV) infection has a high mortality rate in humans. Secondary bacterial pneumonia with HPAIV infection has not been reported in human patients, whereas seasonal influenza viruses sometimes enhance bacterial pneumonia, resulting in substantial morbidity and mortality. Therefore, if HPAIV infection were accompanied by bacterial infection, an increase in mortality would be expected. We examined whether a vaccine against HPAIV prevents severe morbidity caused by mixed infection with HPAIV and bacteria.
Methods  H7N7 subtype of HPAIV and Streptococcus pneumoniae were inoculated into cynomolgus macaques with or without vaccination of inactivated whole virus particles .
Results  Vaccination against H7N7 HPAIV decreased morbidity caused by HPAIV and pneumonia caused by S. pneumoniae . Bacterial replication in lungs was decreased by vaccination against HPAIV, although the reduction in bacterial colonies was not significant.
Conclusions  Vaccination against HPAIV reduces pneumonia caused by bacterial superinfection and may improve prognosis of HPAIV-infected patients.  相似文献   
82.
Biological availability of 33 esters, 17 ethers and 2 acetals of ethanediol, 1,2-propanediol, 1,3-butanediol and 1,4-butanediol was compared by mini-test with chicks. Chicks can utilize esters of ethanediol, 1,2-propanediol and 1,3-butanediol with acetic acid and fatty acids of carbon chain length from 5 to 12 with more improved palatability than that of free acids, while availability of esters of these glycols with propionic and butyric acids was low. Esters of 1,4-butanediol and ether derivatives of these glycols was not available, except ethyl ether of di-ethanediol which was partially available. Acetacetal of ethanediol was partially available but n-butyracetal was not.  相似文献   
83.
Shp2, a protein tyrosine phosphatase possessing SH2 domains, is utilized in the intracellular signaling of various growth factors. Shp2 is highly expressed in the CNS. Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, which also shows high levels of expression in the CNS, exerts neurotrophic and neuromodulatory effects in CNS neurons. We examined how BDNF utilizes Shp2 in its signaling pathway in cultured cerebral cortical neurons. We found that BDNF stimulated coprecipitation of several tyrosine-phosphorylated proteins with anti-Shp2 antibody and that Grb2 and phosphatidylinositol 3-kinase (PI3-K) were coprecipitated with anti-Shp2 antibody in response to BDNF. In addition, both anti-Grb2 and anti-PI3-K antibodies coprecipitated Shp2 in response to BDNF. The BDNF-stimulated coprecipitation of the tyrosine-phosphorylated proteins, Grb2, and PI3-K with anti-Shp2 antibody was completely inhibited by K252a, an inhibitor of TrkB receptor tyrosine kinase. This BDNF-stimulated Shp2 signaling was markedly sustained as well as BDNF-induced phosphorylation of TrkB and mitogen-activated protein kinases. In PC12 cells stably expressing TrkB, both BDNF and nerve growth factor stimulated Shp2 signaling similarly to that by BDNF in cultured cortical neurons. These results indicated that Shp2 shows cross-talk with various signaling molecules including Grb2 and PI3-K in BDNF-induced signaling and that Shp2 may be involved in the regulation of various actions of BDNF in CNS neurons.  相似文献   
84.
Toll-like receptors (TLRs) play a key role in linking pathogen recognition with the induction of innate immunity. They have been implicated in the pathogenesis of chronic inflammatory diseases, representing potential targets for prevention/treatment. Vegetable-rich diets are associated with the reduced risk of several inflammatory disorders. In the present study, based on an extensive screening of vegetable extracts for TLR-inhibiting activity in HEK293 cells co-expressing TLR with the NF-κB reporter gene, we found cabbage and onion extracts to be the richest sources of a TLR signaling inhibitor. To identify the active substances, we performed activity-guiding separation of the principal inhibitors and identified 3-methylsulfinylpropyl isothiocyanate (iberin) from the cabbage and quercetin and quercetin 4′-O-β-glucoside from the onion, among which iberin showed the most potent inhibitory effect. It was revealed that iberin specifically acted on the dimerization step of TLRs in the TLR signaling pathway. To gain insight into the inhibitory mechanism of TLR dimerization, we developed a novel probe combining an isothiocyanate-reactive group and an alkyne functionality for click chemistry and detected the probe bound to the TLRs in living cells, suggesting that iberin disrupts dimerization of the TLRs via covalent binding. Furthermore, we designed a variety of iberin analogues and found that the inhibition potency was influenced by the oxidation state of the sulfur. Modeling studies of the iberin analogues showed that the oxidation state of sulfur might influence the global shape of the isothiocyanates. These findings establish the TLR dimerization step as a target of food-derived anti-inflammatory compounds.  相似文献   
85.
Arabis gemmifera is a hyperaccumulator of Cd and Zn   总被引:1,自引:0,他引:1  
Hyperaccumulators are essential for phytoremediation of heavy metals. In Europe and North America, many studies have been conducted to find more effective plants for phytoremediation of various pollutants. In Japan, this field of research has just recently come more into focus. A type of fern in Japan, Athyrium yokoscense, is well known as a hyperaccumulator of Cd and Zn. However, it is not suitable for phytoremediation because it is a summer green and grows slowly. Therefore, in order to find hyperaccumulators other than from A. yokoscense, we surveyed plants growing at polluted sites in Japan. We found that the Brassicae Arabis gemmifera is a hyperaccumulator of Cd and Zn, with phytoextraction capacities almost equal to Thlaspi caerulescens.  相似文献   
86.
87.
Diamine oxidase (DAO) (EC 1.4.3.6) was purified from pea epicotyls to homogeneity by the criterion of polyacrylamide gel electrophoresis (PAGE). The pu  相似文献   
88.
Thelohanellus hovorkai (Myxosporea: Myxozoa) was transmitted to common carp Cyprinus carpio by exposing fish to Aurantiactinomyxon spores collected from the oligochaete Branchiura sowerbyi. The morphological characteristics of the actinosporean stage are described in detail. B. sowerbyi were exposed to T. hovorkai spores isolated from the experimentally infected carp, and after 3 and 4 months the worms exhibited prevalences of the actinosporean stage at 19.47% (7/36) and 14.6% (6/41), respectively. Control, unexposed worms were negative for the actinosporean infection. This is the first report of an Aurantiactinomyxon transforming into a myxosporean belonging to the suborder Platysporina.  相似文献   
89.
The sulfated glycosaminoglycans synthesized in the forelimb plates of rats on days 12, 13, 14, and 15 of gestation were characterized by their susceptibility to various glycosaminoglycan lyases. On days 12 and 13, heparan sulfate accounted for approximately 65% of the newly synthesized sulfated glycosaminoglycans. Small amounts of dermatan sulfate and chondroitin sulfates were also observed. On day 14, the relative amount of chondroitin 4-sulfate began to increase, there being a compensatory decrease in the amount of heparan sulfate. 35S-Sulfate-labeled material was extracted from day-13 forelimb plates with 4 M guanidine/HCl without proteolysis. Using ultracentrifugation on a sucrose density gradient, the extract was separated into two peaks: a light peak (L) mainly composed of heparan sulfate, and a faster-sedimenting peak (M) mainly composed of chondroitin sulfate. The cartilage-type proteoglycan (H) was first detectable on day 14 of gestation, indicating that chondrogenesis in rat forelimb plates starts on day 14 of gestation. In addition to these previously identified glycosaminoglycans or proteoglycans, we isolated an unknown component in the glycosaminoglycan preparations obtained from limb plates during these developmental stages. This component was not found in glycosaminoglycan preparations obtained either from the brain or tail of rat fetuses at the same stages.  相似文献   
90.
To evaluate the role of pyrophosphate-dependent phosphofructokinase (PFP. EC 2.7.1.90) in the sugar metabolism of pollen. its occurrence and properties were studied in pollen grains of several plants including camellia ( Camellia japonica L.). In all pollen samples, PFP was strongly activated by fructose-2,6-bisphosphate (F2,6BP), and the activity of F2,6BP-activated PFP was higher than that of phosphofructokinase (PFK. EC 2.7.1.11). PFP partially purified from camellia pollen required Mg2+ for activity with an optimum at 1 m M . and was almost unaflected by a variety of metabolites at 1 m M . Its molecular mass was around 220 kDa, and apparent Km values for F6P, PPi. F1, 6BP and Pi were 294, 4, 20 and 580 u M , respectively. The levels of F2.6BP. PPi and F6P in camellia pollen were sufficent to support the forward reaction by PFP, and PFP, was 20- to 40-fold more active than PFK during pollen growth. These results suggest that pollen PFP plays a role in glycolysis but not gluconeogenesis. and the possible relevance of this to pollen tube growth is discussed.  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