全文获取类型
收费全文 | 8154篇 |
免费 | 881篇 |
国内免费 | 3篇 |
出版年
2021年 | 132篇 |
2020年 | 92篇 |
2019年 | 100篇 |
2018年 | 97篇 |
2017年 | 93篇 |
2016年 | 156篇 |
2015年 | 280篇 |
2014年 | 306篇 |
2013年 | 399篇 |
2012年 | 496篇 |
2011年 | 460篇 |
2010年 | 253篇 |
2009年 | 219篇 |
2008年 | 338篇 |
2007年 | 360篇 |
2006年 | 325篇 |
2005年 | 294篇 |
2004年 | 292篇 |
2003年 | 240篇 |
2002年 | 261篇 |
2001年 | 176篇 |
2000年 | 181篇 |
1999年 | 170篇 |
1998年 | 113篇 |
1997年 | 103篇 |
1996年 | 63篇 |
1995年 | 80篇 |
1994年 | 76篇 |
1993年 | 87篇 |
1992年 | 118篇 |
1991年 | 138篇 |
1990年 | 132篇 |
1989年 | 142篇 |
1988年 | 129篇 |
1987年 | 131篇 |
1986年 | 113篇 |
1985年 | 116篇 |
1984年 | 106篇 |
1983年 | 86篇 |
1982年 | 117篇 |
1981年 | 122篇 |
1980年 | 102篇 |
1979年 | 107篇 |
1978年 | 70篇 |
1977年 | 66篇 |
1976年 | 62篇 |
1975年 | 62篇 |
1974年 | 58篇 |
1973年 | 57篇 |
1972年 | 71篇 |
排序方式: 共有9038条查询结果,搜索用时 46 毫秒
1.
E King 《BMJ (Clinical research ed.)》1983,286(6383):2059-2060
2.
A group of captive chimpanzees, consisting of one adult male and three mother/infant pairs, was systematically observed over a 15-month period. Over 200 hr of data were collected, using both sequential and time sampling techniques, and compared to the available data on wild chimps. Unlike many captive groups, most behavior patterns were remarkably similar, both qualitatively and quantitatively, to that of wild chimpanzees including: play, grooming, infant sexual development, tool use, food sharing, prosocial partner preferences, and aggressive displays. 相似文献
3.
Ferdinand Bohlmann Elena Tsankova Jasmin Jakupovic Robert M. King Harold Robinson 《Phytochemistry》1983,22(2):557-560
The investigation of Encelia canescens afforded, in addition to several known compounds, four new dimeric p-hydroxyacetophenone derivatives, two epimeric chromene dimers and two epimeric mixed dimers of euparin and encecalin. Furthermore, derivatives of tremetone and of encecalin were present. The structures were elucidated hy high field 1H NMR spectroscopy. 相似文献
4.
5.
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
6.
7.
Karlheinz Grillitsch Pablo Tarazona Lisa Klug Tamara Wriessnegger Günther Zellnig Erich Leitner Ivo Feussner Günther Daum 《生物化学与生物物理学报:生物膜》2014
Despite similarities of cellular membranes in all eukaryotes, every compartment displays characteristic and often unique features which are important for the functions of the specific organelles. In the present study, we biochemically characterized the plasma membrane of the methylotrophic yeast Pichia pastoris with emphasis on the lipids which form the matrix of this compartment. Prerequisite for this effort was the design of a standardized and reliable isolation protocol of the plasma membrane at high purity. Analysis of isolated plasma membrane samples from P. pastoris revealed an increase of phosphatidylserine and a decrease of phosphatidylcholine compared to bulk membranes. The amount of saturated fatty acids in the plasma membrane was higher than in total cell extracts. Ergosterol, the final product of the yeast sterol biosynthetic pathway, was found to be enriched in plasma membrane fractions, although markedly lower than in Saccharomyces cerevisiae. A further characteristic feature of the plasma membrane from P. pastoris was the enrichment of inositol phosphorylceramides over neutral sphingolipids, which accumulated in internal membranes. The detailed analysis of the P. pastoris plasma membrane is discussed in the light of cell biological features of this microorganism especially as a microbial cell factory for heterologous protein production. 相似文献
8.
The spontaneous allele quakingviable (qk
v
) exerts effects on myelination and spermiogenesis. The defects generated by qk
v
were not separated in a multilocus mapping cross that provided a mapping resolution of 0.1 centiMorgans (cM). Furthermore, no distortions suggestive of a large chromosomal anomaly associated with qk
v
were apparent. One plausible interpretation is that the quaking locus contains more than one functional domain, either organized into overlapping genes or expressed by alternative splicing mechanisms. The cloning needed to analyze this locus will be enhanced by the very high resolution of the meiotic mapping cross reported here. The recombinational distances on this qk
v
map were compressed compared with those previously reported in a high-resolution map for qk
1–1, an embryonic lethal allele of quaking induced by ethylnitrosourea. Additional crosses confirmed prior reports that the sex and the genetic background of the heterozygous parent can affect recombinational distances. These joint effects on recombination are strong enough to account for the discrepancy between the two maps. This variability of two-factor map values leads to the preferred multilocus map-building protocol discussed in the accompanying paper. 相似文献
9.
10.