全文获取类型
收费全文 | 15016篇 |
免费 | 991篇 |
国内免费 | 3篇 |
出版年
2023年 | 90篇 |
2022年 | 87篇 |
2021年 | 372篇 |
2020年 | 306篇 |
2019年 | 317篇 |
2018年 | 387篇 |
2017年 | 355篇 |
2016年 | 537篇 |
2015年 | 822篇 |
2014年 | 879篇 |
2013年 | 1026篇 |
2012年 | 1313篇 |
2011年 | 1160篇 |
2010年 | 749篇 |
2009年 | 705篇 |
2008年 | 939篇 |
2007年 | 880篇 |
2006年 | 806篇 |
2005年 | 769篇 |
2004年 | 718篇 |
2003年 | 638篇 |
2002年 | 599篇 |
2001年 | 133篇 |
2000年 | 90篇 |
1999年 | 112篇 |
1998年 | 121篇 |
1997年 | 110篇 |
1996年 | 96篇 |
1995年 | 90篇 |
1994年 | 87篇 |
1993年 | 59篇 |
1992年 | 53篇 |
1991年 | 62篇 |
1990年 | 56篇 |
1989年 | 31篇 |
1988年 | 37篇 |
1987年 | 28篇 |
1986年 | 20篇 |
1985年 | 39篇 |
1984年 | 54篇 |
1983年 | 20篇 |
1982年 | 25篇 |
1981年 | 26篇 |
1980年 | 27篇 |
1979年 | 17篇 |
1978年 | 20篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1975年 | 20篇 |
1969年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
The outer membrane protein (omp40) component from the chemolithoautotrophic acidophilic Thiobacillus ferrooxidans is apparently regulated by the external pH and the concentration of phosphorus. Its amino-terminal sequence showed little identity with the Escherichia coli OmpC, OmpF or PhoE porins, but was 38.5% identical to the outer membrane channel-forming protein NosA from Pseudomonas stutzeri, whose expression is also regulated environmentally. In addition, the partial amino acid sequence of T. ferrooxidans omp40 showed between 34 and 38% identity with the amino-terminal end of the small outer membrane proteins Rck and PagC from Salmonella typhimurium and OmpX from Enterobacter cloacae. 相似文献
3.
Luis Santamaría Jesús Balsa Beatriz Bidondo Angel Baltanás Carlos Montes 《Hydrobiologia》1992,246(2):89-98
Laboratory experiments and field data were used to determine salinity tolerance limits of three ostracode species (Prionocypris aragonica, Eucypris mareotica and Heterocypris barbara) from Iberian saline lakes. Salinity tolerance appeared related to ionic composition and temperature. Implications for ostracode ecology and geographical distribution are evaluated. 相似文献
4.
PPARγ and PGC-1α as Therapeutic Targets in Parkinson’s 总被引:1,自引:0,他引:1
5.
Matthew E. Downs Amanda Buch Carlos Sierra Maria Eleni Karakatsani Shangshang Chen Elisa E. Konofagou Vincent P. Ferrera 《PloS one》2015,10(5)
Focused Ultrasound (FUS) coupled with intravenous administration of microbubbles (MB) is a non-invasive technique that has been shown to reliably open (increase the permeability of) the blood-brain barrier (BBB) in multiple in vivo models including non-human primates (NHP). This procedure has shown promise for clinical and basic science applications, yet the safety and potential neurological effects of long term application in NHP requires further investigation under parameters shown to be efficacious in that species (500kHz, 200–400 kPa, 4–5μm MB, 2 minute sonication). In this study, we repeatedly opened the BBB in the caudate and putamen regions of the basal ganglia of 4 NHP using FUS with systemically-administered MB over 4–20 months. We assessed the safety of the FUS with MB procedure using MRI to detect edema or hemorrhaging in the brain. Contrast enhanced T1-weighted MRI sequences showed a 98% success rate for openings in the targeted regions. T2-weighted and SWI sequences indicated a lack edema in the majority of the cases. We investigated potential neurological effects of the FUS with MB procedure through quantitative cognitive testing of’ visual, cognitive, motivational, and motor function using a random dot motion task with reward magnitude bias presented on a touchpanel display. Reaction times during the task significantly increased on the day of the FUS with MB procedure. This increase returned to baseline within 4–5 days after the procedure. Visual motion discrimination thresholds were unaffected. Our results indicate FUS with MB can be a safe method for repeated opening of the BBB at the basal ganglia in NHP for up to 20 months without any long-term negative physiological or neurological effects with the parameters used. 相似文献
6.
7.
Carlos Alemn M. Cristina Vega Eloísa Navarro Jordi Puiggalí 《Journal of peptide science》1996,2(6):364-370
The conformational preferences of the methylenic sequence in the side chain of the glutamine residue were investigated by ab initio and semi-empirical quantum mechanical calculations and examination of both the Brookhaven Protein Databank and Cambridge Structural Data Base. The results were analysed on the basis of our previous findings about the folding of methylene groups in aliphatic segments. Both energy calculations and the crystallographic structure of small peptides indicate that methylene units of the glutamine residue tend to fold in a gauche conformation. In contrast, such groups usually adopt an all-trans conformation in proteins due basically to the entropic and solvent contributions. These results have been demonstrated by computing the entropic correction to the free energy and evaluating the solvent effects through SCRF calculations 相似文献
8.
9.
10.