全文获取类型
收费全文 | 645030篇 |
免费 | 67276篇 |
国内免费 | 324篇 |
专业分类
712630篇 |
出版年
2018年 | 6594篇 |
2017年 | 6253篇 |
2016年 | 8670篇 |
2015年 | 10807篇 |
2014年 | 12925篇 |
2013年 | 18343篇 |
2012年 | 21218篇 |
2011年 | 21950篇 |
2010年 | 14948篇 |
2009年 | 13379篇 |
2008年 | 19357篇 |
2007年 | 20105篇 |
2006年 | 18570篇 |
2005年 | 17953篇 |
2004年 | 17847篇 |
2003年 | 17022篇 |
2002年 | 16567篇 |
2001年 | 28987篇 |
2000年 | 28863篇 |
1999年 | 22886篇 |
1998年 | 7946篇 |
1997年 | 7980篇 |
1996年 | 7708篇 |
1995年 | 7009篇 |
1994年 | 7017篇 |
1993年 | 6817篇 |
1992年 | 18257篇 |
1991年 | 17811篇 |
1990年 | 17500篇 |
1989年 | 17342篇 |
1988年 | 15764篇 |
1987年 | 15043篇 |
1986年 | 13786篇 |
1985年 | 13810篇 |
1984年 | 11442篇 |
1983年 | 9768篇 |
1982年 | 7292篇 |
1981年 | 6540篇 |
1980年 | 6191篇 |
1979年 | 10697篇 |
1978年 | 8249篇 |
1977年 | 7579篇 |
1976年 | 7186篇 |
1975年 | 7970篇 |
1974年 | 8673篇 |
1973年 | 8504篇 |
1972年 | 7646篇 |
1971年 | 7125篇 |
1970年 | 5969篇 |
1969年 | 5826篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
G V Kolusheva 《Arkhiv anatomii, gistologii i émbriologii》1987,93(7):10-15
The electron microscopic method has revealed early maturation of the protein-synthesizing apparatus of some cells, on the one hand, and underdevelopment of neuroblast volumes, appearance of artificial contacts, axonal degeneration and destruction in large trunks, on the other hand. Compensatory-restorative processes in the cell on the 14th and 21st days of the postnatal development result in a complete restoration of morphological organization of neurons and interneuronal connections in the hypothalamus of offspring of the morphine-dependent rats. 相似文献
992.
M R Kopantseva M Z Liudvig I I Uspenski? N A Tamarina V A Tsatrian L I Korochkin 《Zhurnal obshche? biologii》1990,51(1):125-140
A comparative electrophoretic study or ejaculatory bulb proteins in 29 different Drosophila species has been carried out. In all analyzed species, ejaculatory bulb contains a major component (designated as PEB). It has molecular mass of 61-65 kDa in the species of virilis group, 33-36 kDa in species of obscura group, and 34-56 kDa in species of melanogaster group. Using immunoblotting technique, we have demonstrated that PEB is introduced into organs of female sex tract during mating. The nature and significance of revealed interspecific differences in PEB proteins has been discussed. 相似文献
993.
A hunter-killed wild turkey (Meleagris gallopavo silvestris) was submitted for examination because of numerous 2 to 30 mm diameter, yellowish, hard nodules in the skin. The nodules were confined to the skin and did not involve subcutaneous tissues. Nodules consisted of dilated feather follicles packed with a caseous tan to pale yellow material. Histologically, affected feather follicles were markedly dilated and filled with laminated keratin debris. The lesions were determined to be multiple feather follicle cysts of unknown etiology. 相似文献
994.
When the roots of Vicia faba L. beans were subjected to hypoxic stress, the activity of H+-ATPase on the peribacteroid membrane, as well as the transport of dicarboxylates (malate and succinate) mediated by this
enzyme, decreased. Since malate and succinate are the main carbon-containing metabolites involved in the energy supply to
bacteroids, this caused a change of the relation type from mutualism to commensalism, and the domination of the eukaryotes
over the prokaryotes consequently increased. 相似文献
995.
S Ikei M Ogawa T Beppu C Ohara K Sakamoto H Sameshima H Arakawa Y Yamaguchi T Yamanaka S Kudo 《Cytokine》1992,4(6):581-584
In an attempt to investigate the interaction between the changes of cytokines and acute phase reactants after transcatheter arterial chemoembolization therapy (TACE), the levels of interleukin 6 (IL-6), interleukin 8 (IL-8), C-reactive protein (CRP) and pancreatic secretory trypsin inhibitor (PSTI) in the blood of patients with unresectable hepatocellular carcinoma (HCC) were measured. Before the therapy, serum IL-6 and plasma IL-8 levels were detectable in 77.8% and 28.5%, respectively, of patients with HCC. Levels of serum IL-6 and plasma IL-8 increased after TACE and reached a peak on day 3 in all patients (18/18) and in 87.5% of patients (12/14), respectively. Both blood levels of IL-6 and IL-8 reached a peak earlier than those of CRP and PSTI did after the therapy. When the maximal values of IL-6 were compared with those of CRP and PSTI, there were significant positive correlations (r = 0.63, P < 0.01 and r = 0.81, P < 0.01, respectively). Similarly, comparisons of the maximal values of IL-8 with those of CRP and PSTI gave a significant correlation (r = 0.68, P < 0.01 and r = 0.67, P < 0.05, respectively). However, no significant correlation was found between the elevation of IL-6 and IL-8. 相似文献
996.
Chronic hypoxia attenuates resting and exercise-induced VEGF, flt-1, and flk-1 mRNA levels in skeletal muscle. 总被引:3,自引:0,他引:3
I M Olfert E C Breen O Mathieu-Costello P D Wagner 《Journal of applied physiology》2001,90(4):1532-1538
Vascular endothelial growth factor (VEGF) is a hypoxia-inducible angiogenic mitogen. However, chronic hypoxia is generally not found to increase mammalian skeletal muscle capillarity. We sought to determine the effect of chronic hypoxia (8 wk, inspired O2 fraction = 0.12) on skeletal muscle gene expression of VEGF, its receptors (flt-1 and flk-1), basic fibroblast growth factor, and transforming growth factor-beta1. Wistar rats were exposed to chronic hypoxia (n = 12) or room air (n = 12). After the exposure period, six animals from each group were subjected to a single 1-h treadmill exercise bout (18 m/min on a 10 degrees incline) in room air while the remaining six animals served as rest controls. Morphological analysis revealed that chronic hypoxia did not increase skeletal muscle capillarity. Northern blot analyses showed that chronic hypoxia decreased resting VEGF, flt-1, and flk-1 mRNA by 23, 68, and 42%, respectively (P < 0.05). The VEGF mRNA response to exercise was also decreased (4.1- and 2.7-fold increase in room air and chronic hypoxia, respectively, P < 0.05). In contrast, neither transforming growth factor-beta1 nor basic fibroblast growth factor mRNA was significantly altered by chronic hypoxia. In conclusion, prolonged exposure to hypoxia attenuated gene expression of VEGF and its receptors flt-1 and flk-1 in rat gastrocnemius muscle. These findings may provide an explanation for the lack of mammalian skeletal muscle angiogenesis that is observed after chronic hypoxia. 相似文献
997.
P. Cruz C. H. Mejia‐Ruiz R. Perez‐Enriquez A. M. Ibarra 《Molecular ecology resources》2002,2(3):239-241
Five polymorphic microsatellite loci were characterized for Penaeus (Litopenaeus) vannamei. Loci were isolated using a partial Sau3A1 genomic library by the sequencing of randomly selected clones and by a biotinylated (CT)10 and (GT)10 probes screening procedure. The last strategy resulted in the most useful data. About 40% of the clones showed a previously reported satellite/microsatellite (PVS1), reducing the chance of finding new microsatellite regions. Whereas two of the microsatellite loci with more than 10 alleles will be useful for mating analysis in a breeding program, the others might prove useful for population genetic studies. 相似文献
998.
In vivo neutralization of TNF-alpha promotes humoral autoimmunity by preventing the induction of CTL. 总被引:3,自引:0,他引:3
C S Via A Shustov V Rus T Lang P Nguyen F D Finkelman 《Journal of immunology (Baltimore, Md. : 1950)》2001,167(12):6821-6826
Neutralization of TNF-alpha in humans with rheumatoid arthritis or Crohn's disease has been associated with the development of humoral autoimmunity. To determine the effect of TNF-alpha neutralization on cell-mediated and humoral-mediated responses, we administered anti-TNF-alpha mAb to mice undergoing acute graft-vs-host disease (GVHD) using the parent-into-F(1) model. In vivo neutralization of TNF-alpha blocked the lymphocytopenic features characteristic of acute GVHD and induced a lupus-like chronic GVHD phenotype (lymphoproliferation and autoantibody production). These effects resulted from complete inhibition of detectable antihost CTL activity and required the presence of anti-TNF-alpha mAb for the first 4 days after parental cell transfer, indicating that TNF-alpha plays a critical role in the induction of CTL. Moreover, an in vivo blockade of TNF-alpha preferentially inhibited the production of IFN-gamma and blocked IFN-gamma-dependent up-regulation of Fas; however, cytokines such as IL-10, IL-6, or IL-4 were not inhibited. These results suggest that a therapeutic TNF-alpha blockade may promote humoral autoimmunity by selectively inhibiting the induction of a CTL response that would normally suppress autoreactive B cells. 相似文献
999.
1000.
A study was designed to find the prevalence of ear wax in children aged 3 to 10 years and to test the belief that large amounts of wax are unlikely to be seen when otitis media is present. Roughly a quarter of the children had appreciable amounts of wax, and there was a gradual decline in prevalence with age. The amount of ear wax appeared to decrease when otitis media was present. The results did not support removing wax when assessing children''s ears in general practice. 相似文献