全文获取类型
收费全文 | 4472篇 |
免费 | 303篇 |
国内免费 | 1篇 |
出版年
2023年 | 26篇 |
2022年 | 25篇 |
2021年 | 91篇 |
2020年 | 65篇 |
2019年 | 79篇 |
2018年 | 121篇 |
2017年 | 103篇 |
2016年 | 147篇 |
2015年 | 205篇 |
2014年 | 249篇 |
2013年 | 335篇 |
2012年 | 379篇 |
2011年 | 369篇 |
2010年 | 248篇 |
2009年 | 210篇 |
2008年 | 263篇 |
2007年 | 270篇 |
2006年 | 258篇 |
2005年 | 250篇 |
2004年 | 221篇 |
2003年 | 201篇 |
2002年 | 185篇 |
2001年 | 49篇 |
2000年 | 36篇 |
1999年 | 34篇 |
1998年 | 44篇 |
1997年 | 29篇 |
1996年 | 22篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 22篇 |
1992年 | 21篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 17篇 |
1978年 | 9篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 3篇 |
排序方式: 共有4776条查询结果,搜索用时 35 毫秒
1.
The psbQ gene encoding a 16-kDa polypeptide of the oxygen-evolving complex of photosystem II has been isolated from Arabidopsis thaliana and characterized. The gene consists of a 28 nucleotide long leader sequence, two introns and three exons encoding a 223-amino-acid precursor polypeptide. The first 75 amino acids act as a transit peptide for the translocation of the polypeptide into the thylakoid lumen. Expression studies show that the gene is light-inducible and expresses only in green tissues with high steady-state mRNA levels in leaves. Using this gene as a probe, restriction fragment length polymorphism between two ecotypes, Columbia and Estland, has also been detected. 相似文献
2.
Shull A. Franklin und Ladoff Sonia 《Molecular & general genetics : MGG》1918,19(1-2):110-115
3.
Legionella pneumophila in Cooling Towers: Fluctuations in Counts, Determination of Genetic Variability by Pulsed-Field Gel Electrophoresis (PFGE), and Persistence of PFGE Patterns 下载免费PDF全文
Sonia Ragull Marian Garcia-Nuez Maria Luisa Pedro-Botet Nieves Sopena Maria Esteve Rafael Montenegro Miquel Sabri 《Applied microbiology》2007,73(16):5382-5384
The concentrations of Legionella pneumophila in cooling towers may vary considerably over short periods of time, producing significant fluctuations throughout the year. Despite genetic variability, in small geographical areas the same indistinguishable pulsed-field gel electrophoresis patterns may be shared among different cooling towers and persist over time. 相似文献
4.
The production of d-aminoacylase by Alcaligenes denitrificans and Alcaligenes faecalis has been studied. The enzyme was inducibly produced and N-acetyl-d-leucine and N-acetyl-d-valine were the most effective inducers. d-methionine, d-valine, d-phenylalamine and d-leucine were produced by the enzymic hydrolysis of the appropriate N-acetyl-d-amino-acids with whole cell biomass. The hydrolysis of N-acetyl-d-methionine by A. denitrificans and N-acetyl-d-valine by A. faecalis was preferential. Maximum yields of d-methionine and d-valine were 94.3 and 84.7% at a specific product formation rate of 20.10 and 19.19 μmol min−1 mg−1 of wet cells at 20 mM substrate concentration and 5 mg ml−1 of cell density. 相似文献
5.
Sonia Coni Silvia Maria Serrao Zuleyha Nihan Yurtsever Laura Di Magno Rosa Bordone Camilla Bertani Valerio Licursi Zaira Ianniello Paola Infante Marta Moretti Marialaura Petroni Francesca Guerrieri Alessandro Fatica Alberto Macone Enrico De Smaele Lucia Di Marcotullio Giuseppe Giannini Marella Maroder Enzo Agostinelli Gianluca Canettieri 《Cell death & disease》2020,11(12)
6.
7.
8.
Seema Bhargava Sathnur Pushpakumar Naira Metreveli Srikanth Givvimani Suresh C. Tyagi 《Molecular biology reports》2014,41(8):4889-4898
Hyperhomocysteinemia (HHcy) is associated with cognitive decline and hearing loss due to vascular dysfunction. Although we have shown that HHcy-induced increased expression of matrix metalloproteinase-9 (MMP-9) is associated with cochlear pathology in cystathionine-β-synthase heterozygous (CBS+/?) mice, it is still unclear whether MMP-9 contributes to functional deficit in cognition and hearing. Therefore, we hypothesize that HHcy-induced MMP-9 activation causes vascular, cerebral and cochlear remodeling resulting in diminished cognition and hearing. Wildtype (WT), CBS+/?, MMP-9?/? and CBS+/?/MMP-9?/? double knock-out (DKO) mice were genotyped and used. Doppler flowmetry of internal carotid artery (ICA) was performed for peak systolic velocity [PSV], pulsatility index [PI] and resistive index [RI]. Cognitive functions were assessed by Novel Object Recognition Test (NORT) and for cochlear function Auditory brainstem response (ABR) was elicited. Peak systolic velocity, pulsatility and resistive indices of ICA were decreased in CBS+/? mice, indicating reduced perfusion. ABR threshold was increased and maximum ABR amplitude and NORT indices (recognition, discrimination) were decreased in CBS+/? mice compared to WT and MMP-9?/?. All these parameters were attenuated in DKO mice suggesting a significant role of MMP-9 in HHcy-induced vascular, neural and cochlear pathophysiology. Regression analysis of PSV with ABR and cognitive parameters revealed significant correlation (0.44–0.58). For the first time, MMP-9 has been correlated directly to functional deficits of brain and cochlea, and found to have a significant role. Our data suggests a dual pathology of HHcy occurring due to a decrease in blood supply (vasculo-neural and vasculo-cochlear) and direct tissue remodeling. 相似文献
9.
The morphological changes in the gill chloride cells of the armored catfish, Hypostomus tietensis , were investigated after 15 days' exposure to either distilled or hard water. The thickness of the water–blood barrier in the lamellae increased significantly in fish kept in distilled water due to the high proliferation of chloride cells. The apical surface of about 68% of chloride cells was sharply reduced by the development of an apical crypt with a sponge-like surface, although no change in the chloride cell fractional area was found. In contrast, H. tietensis kept in Na+ , Cl− and Ca2+ rich water displayed no significant changes in the number of chloride cells or in their apical surface morphology compared with the control fish. Chloride cell response to ion challenge in H. tietensis suggested the involvement of different strategies to maintain homeostasis in ion-poor water, which may be related to the life history of species. 相似文献
10.
Transport of a uremic solute effected by a combined dialysis and ultrafiltration procedure in a hollow-fibre artificial kidney,
is investigated theoretically under standard assumptions. An exact analytical solution for the concentration profile in a
blood channel is obtained by using the method of separation of variables. The necessary requirement that the solution must
tend to that of pure dialysis, in the limit ultrafiltration tending to zero, is fulfilled. Exact analytical expressions are
derived for the eigenconstants of the solution. In using the solution, the solute clearance is emphasized. Diffusive and ultrafiltration
components of the solute clearance are defined and studied. The combined procedure is examined for middle versus small molecules
and for polyacrylonitrile versus cuprophan hollow-fibres. 相似文献