全文获取类型
收费全文 | 704894篇 |
免费 | 84249篇 |
国内免费 | 394篇 |
出版年
2018年 | 6029篇 |
2016年 | 8423篇 |
2015年 | 12123篇 |
2014年 | 13918篇 |
2013年 | 19894篇 |
2012年 | 22430篇 |
2011年 | 22726篇 |
2010年 | 15168篇 |
2009年 | 13875篇 |
2008年 | 19921篇 |
2007年 | 20775篇 |
2006年 | 19077篇 |
2005年 | 18649篇 |
2004年 | 18431篇 |
2003年 | 17724篇 |
2002年 | 17191篇 |
2001年 | 31827篇 |
2000年 | 32017篇 |
1999年 | 25642篇 |
1998年 | 9318篇 |
1997年 | 9627篇 |
1996年 | 9246篇 |
1995年 | 8642篇 |
1994年 | 8631篇 |
1993年 | 8426篇 |
1992年 | 21034篇 |
1991年 | 20206篇 |
1990年 | 19807篇 |
1989年 | 19469篇 |
1988年 | 17710篇 |
1987年 | 17050篇 |
1986年 | 15643篇 |
1985年 | 15600篇 |
1984年 | 13029篇 |
1983年 | 11419篇 |
1982年 | 9009篇 |
1981年 | 8048篇 |
1980年 | 7617篇 |
1979年 | 12715篇 |
1978年 | 9718篇 |
1977年 | 9008篇 |
1976年 | 8413篇 |
1975年 | 9018篇 |
1974年 | 9788篇 |
1973年 | 9709篇 |
1972年 | 8856篇 |
1971年 | 8217篇 |
1970年 | 6910篇 |
1969年 | 6763篇 |
1968年 | 5948篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
Slash pine needles and cortex oleoresin have been found to contain a new major diterpene constituent, imbricataloic acid. The closely related imbricatoloic acid, previously reported only in Araucaria imbricata, was found to be present in small amounts in slash pine needle extract. Spectral data are given for an unidentified diterpene alcohol isolated from the cortex oleoresin. 相似文献
954.
Observations on the staining of bacillus megaterium with triphenyltetrazolium 总被引:3,自引:0,他引:3
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
WEIBULL C 《Journal of bacteriology》1953,66(2):137-139
955.
Glycogen debranching enzyme: purification, antibody characterization, and immunoblot analyses of type III glycogen storage disease. 总被引:2,自引:1,他引:1
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Type III glycogen storage disease is caused by a deficiency of glycogen debranching-enzyme activity. Many patients with this disease have both liver and muscle involvement, whereas others have only liver involvement without clinical or laboratory evidence of myopathy. To improve our understanding of the molecular basis of the disease, debranching enzyme was purified 238-fold from porcine skeletal muscle. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis the purified enzyme gave a single band with a relative molecular weight of 160,000 that migrated to the same position as purified rabbit-muscle debranching enzyme. Antiserum against porcine debranching enzyme was prepared in rabbit. The antiserum reacted against porcine debranching enzyme with a single precipitin line and demonstrated a reaction having complete identity to those of both the enzyme present in crude muscle and the enzyme present in liver extracts. Incubation of antiserum with purified porcine debranching enzyme inhibited almost all enzyme activity, whereas such treatment with preimmune serum had little effect. The antiserum also inhibited debranching-enzyme activity in crude liver extracts from both pigs and humans to the same extent as was observed in muscle. Immunoblot analysis probed with anti-porcine-muscle debranching-enzyme antiserum showed that the antiserum can detect debranching enzyme in both human muscle and human liver. The bands detected in human samples by the antiserum were the same size as the one detected in porcine muscle. Five patients with Type III and six patients with other types of glycogen storage disease were subjected to immunoblot analysis. Although anti-porcine antiserum detected specific bands in all liver and muscle samples from patients with other types of glycogen storage disease (Types I, II, and IX), the antiserum detected no cross-reactive material in any of the liver or muscle samples from patients with Type III glycogen storage disease. These data indicate (1) immunochemical similarity of debranching enzyme in liver and muscle and (2) that deficiency of debranching-enzyme activity in Type III glycogen storage disease is due to absence of debrancher protein in the patients that we studied. 相似文献
956.
Obesity-inducing lesions of the central nervous system alter leptin uptake by the blood-brain barrier. 总被引:1,自引:0,他引:1
Leptin regulates body adiposity by decreasing feeding and increasing thermogenesis. Obese humans and some obese rodents are resistant to peripherally administered leptin, suggesting a defect in the transport of leptin across the blood-brain barrier (BBB). Defective transport of exogenous leptin occurs in some models of obesity, but in other models transport is normal. This shows that factors other than obesity are associated with impairment of leptin transport across the BBB. In order to further investigate these factors, we determined leptin transport in rats made obese by lesioning of the ventromedial hypothalamus (VMH), paraventricular nucleus (PVN), or posterodorsal amygdala (PDA). These regions all contain leptin receptors and lesions there induce obesity and hyperleptinemia and alter the levels of many feeding hormones which might participate in leptin transporter regulation. We measured the uptake of radioactively labeled leptin by the BBB by multiple-time regression analysis which divides uptake into a reversible phase (Vi, e.g., receptor/transporter binding to the brain endothelial cell) and an irreversible phase (Ki, complete transport across the BBB). Leptin uptake was not affected in rats with VMH lesions. No significant change occurred in the entry rate (Ki) for any group, although Ki declined by over 35% in rats with PVN lesions. Decreased uptake was observed in rats with PVN lesions and with PDA lesions. This was primarily due to a reduced Vi (about 21% for the PDA). This decreased uptake is most likely explained by decreased binding of leptin to the brain endothelial cell, which could be because of decreased binding by either receptors or transporters. This suggests that some of the feeding hormones controlled by the PVN and PDA may participate in regulating leptin uptake by the BBB. 相似文献
957.
Wetlands Ecology and Management - 相似文献
958.
959.
E. B. Naimark 《Paleontological Journal》2014,48(2):166-176
The validity of Eurudagnostus Lermontova, 1951 was confirmed by reexamination of the collection from the Boshe-Kul’ core. The diagnoses of genera of Agnostidae were reviewed, and Eurudagnostus falls well within the concept of the family Agnostidae. The diagnostic features of Eurudagnostus include a delicate border furrows, the transglabellar furrow bent posteriad or straight, short pygidial axis, incomplete transaxial F1, absent or very poorly developed median preglabellar furrow, and absent lanceolate field on the posteroaxis. Following revision the genus comprises 12 valid species, including some species and varieties previously assigned to other genera. ?Eurudagnostus brevispinus Lermontova, 1951 is synonymized with E. chiushuensis (Kobayashi, 1931). Two species, E. chiushuensis and ?E. intermedius (Palmer, 1968) appeared to have inter-continental distribution in the Cambrian-Ordovician beds, and E. mutabilis (Ergaliev, 1980) is also more widely distributed than previously recognized. 相似文献
960.
There is an urgent need for effective prophylactic measures against Mycobacterium tuberculosis (Mtb) infection, particularly given the highly variable efficacy of Bacille Calmette-Guerin (BCG), the only licensed vaccine against tuberculosis (TB). Most studies indicate that cell-mediated immune responses involving both CD4+ and CD8+ T cells are necessary for effective immunity against Mtb. Genetic vaccination induces humoral and cellular immune responses, including CD4+ and CD8+ T-cell responses, against a variety of bacterial, viral, parasitic and tumor antigens, and this strategy may therefore hold promise for the development of more effective TB vaccines. Novel formulations and delivery strategies to improve the immunogenicity of DNA-based vaccines have recently been evaluated, and have shown varying degrees of success. In the present study, we evaluated DNA-launched Venezuelan equine encephalitis replicons (Vrep) encoding a novel fusion of the mycobacterial antigens α-crystallin (Acr) and antigen 85B (Ag85B), termed Vrep-Acr/Ag85B, for their immunogenicity and protective efficacy in a murine model of pulmonary TB. Vrep-Acr/Ag85B generated antigen-specific CD4+ and CD8+ T cell responses that persisted for at least 10 wk post-immunization. Interestingly, parenterally administered Vrep-Acr/Ag85B also induced T cell responses in the lung tissues, the primary site of infection, and inhibited bacterial growth in both the lungs and spleens following aerosol challenge with Mtb. DNA-launched Vrep may, therefore, represent an effective approach to the development of gene-based vaccines against TB, particularly as components of heterologous prime-boost strategies or as BCG boosters. 相似文献