全文获取类型
收费全文 | 3375篇 |
免费 | 278篇 |
国内免费 | 141篇 |
专业分类
3794篇 |
出版年
2023年 | 20篇 |
2022年 | 44篇 |
2021年 | 113篇 |
2020年 | 71篇 |
2019年 | 102篇 |
2018年 | 124篇 |
2017年 | 81篇 |
2016年 | 101篇 |
2015年 | 137篇 |
2014年 | 189篇 |
2013年 | 227篇 |
2012年 | 264篇 |
2011年 | 217篇 |
2010年 | 167篇 |
2009年 | 123篇 |
2008年 | 156篇 |
2007年 | 120篇 |
2006年 | 145篇 |
2005年 | 115篇 |
2004年 | 121篇 |
2003年 | 121篇 |
2002年 | 103篇 |
2001年 | 100篇 |
2000年 | 91篇 |
1999年 | 82篇 |
1998年 | 52篇 |
1997年 | 40篇 |
1996年 | 32篇 |
1995年 | 30篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 37篇 |
1991年 | 19篇 |
1990年 | 25篇 |
1989年 | 31篇 |
1988年 | 33篇 |
1987年 | 29篇 |
1986年 | 14篇 |
1985年 | 21篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 16篇 |
1976年 | 12篇 |
1974年 | 12篇 |
1973年 | 14篇 |
1972年 | 14篇 |
1971年 | 12篇 |
排序方式: 共有3794条查询结果,搜索用时 0 毫秒
1.
2.
M. P. De Leon T. Yanagi M. Kikuchi J. Mu O. Ayau V. Matta M. Paz S. Juarez H. Kanbara I. Tada K. Hirayama 《International journal for parasitology》1998,28(12):1867-1874
Fifty fresh isolates of Trypanosoma cruzi from Triatoma dimidiata vectors and 31 from patients with Chagas disease were analysed for DNA polymorphisms within the 432-bp core region of the cruzipain gene which encodes the active site of cathepsin L-like cystein proteinase. The cruzipain gene showed signs of polymorphism consisting of four different DNA sequences in Central and South American isolates of T. cruzi. The PCR fragments of Guatemalan isolates could be divided into three groups, Groups 1, 2 and 3, based on different patterns of single-stranded DNA conformation polymorphism. All of the strains isolated from Brazil, Chile, and Paraguay, except for the CL strain, showed a Group 4 pattern. Two to four isolates from each group were analysed by cloning and sequencing. A silent mutation occurred between Groups 1 and 2, and five nucleotides and two aa substitutions were detected between Groups 1 and 3. The DNA sequence of Group 4 contained five nucleotides and one aa substitution from Group 1. All of the DNA sequences corresponded well with the single-stranded DNA conformation polymorphism. The Group 1 isolates, the majority in the Guatemalan population (70/81, 86.4%), were isolated from both triatomines and humans, but Group 3 were isolated only from humans. Moreover, the Group 2 isolates were detected only in triatomine vectors (9/50; 18%), but never in humans (0/32, P<0.05) suggesting that this group has an independent life-cycle in sylvatic animals and is maintained by reservoir hosts other than humans. 相似文献
3.
4.
5.
Leandro Neves Faria Marlon Gomes Da Rocha Quirijn De Jong Van Lier Derblai Casaroli 《Plant and Soil》2010,331(1-2):299-311
Correct modeling of root water uptake partitioning over depth is an important issue in hydrological and crop growth models. Recently a physically based model to describe root water uptake was developed at single root scale and upscaled to the root system scale considering a homogeneous distribution of roots per soil layer. Root water uptake partitioning is calculated over soil layers or compartments as a function of respective soil hydraulic conditions, specifically the soil matric flux potential, root characteristics and a root system efficiency factor to compensate for within-layer root system heterogeneities. The performance of this model was tested in an experiment performed in two-compartment split-pot lysimeters with sorghum plants. The compartments were submitted to different irrigation cycles resulting in contrasting water contents over time. The root system efficiency factor was determined to be about 0.05. Release of water from roots to soil was predicted and observed on several occasions during the experiment; however, model predictions suggested root water release to occur more often and at a higher rate than observed. This may be due to not considering internal root system resistances, thus overestimating the ease with which roots can act as conductors of water. Excluding these erroneous predictions from the dataset, statistical indices show model performance to be of good quality. 相似文献
6.
M Roghani C Da Silva M Castagna 《Biochemical and biophysical research communications》1987,142(3):738-744
The major interaction site for tumor-promoting phorbol esters is the calcium-activated, phospholipid-dependent protein kinase (protein kinase C), a key-element in signal transduction. Binding of phorbol esters results in enzyme activation which mediates, at least in part, the action of these agents. We have investigated the effects of tumor promoter chloroform on protein kinase C activity. Like thrombin and 12-O-tetradecanoylphorbol-13-acetate (TPA), chloroform was able to activate protein kinase C in intact rabbit platelets. In addition, chloroform stimulated enzyme activity as well as TPA binding capacity in cell-free system. Scatchard analysis of the data has shown that chloroform increased the number of phorbol ester binding sites. Structurally related compounds, carbon tetrachloride and methylene chloride, activated the enzyme similarly. 相似文献
7.
8.
A G Maksina B A Da?niak I V Rakhmanova 《Nauchnye doklady vysshe? shkoly. Biologicheskie nauki》1988,(11):61-64
The structural changes in cat brain membranes under the injections of intramuscular streptomycin which is ototoxic antibiotic have been studied. The increase of membrane microviscosity in brain areas which are the direct projection of the auditory way has been revealed using fat acidic spin probe on the basis of stearic acid. The changes in membranes of other brain areas have not been found that exhibits a specific streptomycin influence on the auditory analyzer. The EPR spectra of the hydrocarbon spin label C12H25 localizing in near membrane region don't change in brain membranes of experimental animals compared with the normal ones. 相似文献
9.
10.