全文获取类型
收费全文 | 13028篇 |
免费 | 1365篇 |
国内免费 | 7篇 |
出版年
2021年 | 118篇 |
2020年 | 99篇 |
2019年 | 137篇 |
2018年 | 167篇 |
2017年 | 147篇 |
2016年 | 230篇 |
2015年 | 428篇 |
2014年 | 455篇 |
2013年 | 610篇 |
2012年 | 804篇 |
2011年 | 770篇 |
2010年 | 492篇 |
2009年 | 465篇 |
2008年 | 722篇 |
2007年 | 718篇 |
2006年 | 649篇 |
2005年 | 679篇 |
2004年 | 635篇 |
2003年 | 615篇 |
2002年 | 553篇 |
2001年 | 275篇 |
2000年 | 246篇 |
1999年 | 227篇 |
1998年 | 173篇 |
1997年 | 131篇 |
1996年 | 126篇 |
1995年 | 119篇 |
1994年 | 112篇 |
1993年 | 117篇 |
1992年 | 184篇 |
1991年 | 163篇 |
1990年 | 144篇 |
1989年 | 176篇 |
1988年 | 154篇 |
1987年 | 149篇 |
1986年 | 120篇 |
1985年 | 145篇 |
1984年 | 121篇 |
1983年 | 124篇 |
1982年 | 116篇 |
1981年 | 104篇 |
1980年 | 116篇 |
1979年 | 123篇 |
1978年 | 91篇 |
1977年 | 105篇 |
1976年 | 90篇 |
1975年 | 86篇 |
1974年 | 97篇 |
1973年 | 85篇 |
1972年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Imipramine (IMI; 20 mg/kg) in rats decreased the plasma tyrosine concentration by 21% (90 min), whereas norepinephrine (NE; 1.25 mg/kg) raised it by 72% (40 min). Since NE raised plasma tyrosine by stimulating alpha-adrenoceptors, as shown by phenoxybenzamine (PB) completely abolishing this increase, an experiment was done to find out whether IMI lowered plasma tyrosine by blocking alpha-adrenoceptors. In contrast to PB, IMI pretreatment failed to alter the NE-induced elevation in plasma tyrosine, suggesting that at this dose IMI is not an effective alpha-adrenergic antagonist in vivo. Thus, IMI would not appear to reduce plasma tyrosine by blocking alpha-adrenoceptors. In a separate experiment, propranolol blocked the ability of IMI to lower plasma tyrosine. Propranolol also prevented a 17% elevation in brain tryptophan levels induced by IMI but did not alter the 29% decrease in plasma tryptophan. PB by itself decreased plasma tyrosine, but this decrease was not greater by additionally treating with IMI. Salbutamol (10 mg/kg), a beta 2 agonist, lowered plasma tyrosine to 76% and raised brain tryptophan to 143% of control. These results suggest that IMI decreases tyrosine concentrations in plasma and raises tryptophan in brain by stimulating beta-adrenoceptors. 相似文献
93.
In C4 plants phosphoenolpyruvate (PEP) of the C4 cycle may betransported on a chloroplast transporter which also transports3-phosphoglycerate (3-PGA) and triosephosphates. In C3 plantsPEP is not considered to be effectively transported on the chloroplastphosphate translocator. The influences of certain organic phosphates,having a similar structure to either PEP or triose-phosphates,on 3-PGA dependent O2 evolution by C4 (Digitaria sanquinalisL. Scop.) and C3 (Hordeum vulgare L.) mesophyll chloroplastswere investigated. In the C4 mesophyll chloroplasts phosphoglycolatewas a competitive inhibitor (Ki = 2.1 mM) of 3-PGA dependentO2 evolution, and was as effective as previously reported forPEP. 2-Phosphoglycerate was also a competitive inhibitor (Kt= 8.6 mM) of O2 evolution in the C4 mesophyll chloroplasts with3-PGA as substrate, while phospholactate was a weak inhibitorand glyphosate had no effect. Neither PEP, phosphoglycolatenor 2-phosphoglycerate were effective inhibitors of 3- PGA dependentO2 evolution in the C3 chloroplasts. Phosphohydroxypyruvatewas a competitive inhibitor of 3-PGA dependent O22 evolutionin both chloroplast types. The selectivity in inhibition ofO2 evolution with 3-PGA as substrate suggests that the C4 mesophyllchloroplasts can recognize certain organic phosphates with thephosphate in the C-2 or C-3 position but that the C4 mesophyllchloroplasts can only effectively recognize certain organicphosphates with the phosphate in the C-3 position. The resultsalso support the view that 3-PGA and PEP are transported onthe same phosphate translocator in C4 mesophyll chloroplasts.
1 Current address: Department of Horticulture, 2001 Fyffe Court,The Ohio State University, Columbus, Ohio 43210-1096. (Received March 24, 1987; Accepted April 16, 1987) 相似文献
94.
95.
96.
97.
David G. Reid David M. Doddrell Dudley H. Williams Keith R. Fox 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,798(1):111-114
Uniformly 15N-labelled triostin A and echinomycin have been prepared by growing the producing organisms on enriched media and their 15N nuclear magnetic resonance spectra partially assigned by a combination of nuclear Overhauser effect and scalar coupling constant measurements. Selective feeding experiments using unlabelled L-tryptophan-supplemented media have shown that N-1 and N-4 of the quinoxaline rings have their origins in the indole and amino groups of tryptophan, respectively. 相似文献
98.
Background
Chow and Liu showed that the maximum likelihood tree for multivariate discrete distributions may be found using a maximum weight spanning tree algorithm, for example Kruskal's algorithm. The efficiency of the algorithm makes it tractable for high-dimensional problems. 相似文献99.
Jordan Bai Muhammad Farid Abdul-Rahman Anne Rifkin-Graboi Yap-Seng Chong Kenneth Kwek Seang-Mei Saw Keith M. Godfrey Peter D. Gluckman Marielle V. Fortier Michael J. Meaney Anqi Qiu 《PloS one》2012,7(10)
We studied a sample of 75 Chinese, 73 Malay, and 29 Indian healthy neonates taking part in a cohort study to examine potential differences in neonatal brain morphology and white matter microstructure as a function of ethnicity using both structural T2-weighted magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI). We first examined the differences in global size and morphology of the brain among the three groups. We then constructed the T2-weighted MRI and DTI atlases and employed voxel-based analysis to investigate ethnic differences in morphological shape of the brain from the T2-weighted MRI, and white matter microstructure measured by fractional anisotropy derived from DTI. Compared with Malay neonates, the brains of Indian neonates’ tended to be more elongated in anterior and posterior axis relative to the superior-inferior axis of the brain even though the total brain volume was similar among the three groups. Although most anatomical regions of the brain were similar among Chinese, Malay, and Indian neonates, there were anatomical variations in the spinal-cerebellar and cortical-striatal-thalamic neural circuits among the three populations. The population-related brain regions highlighted in our study are key anatomical substrates associated with sensorimotor functions. 相似文献
100.
Joshua R Edwards Evangelos A Diamantakos Jacob D Peuler Peter C Lamar Walter C Prozialeck 《BMC physiology》2007,7(1):1