全文获取类型
收费全文 | 3134篇 |
免费 | 256篇 |
国内免费 | 110篇 |
专业分类
3500篇 |
出版年
2023年 | 23篇 |
2022年 | 43篇 |
2021年 | 117篇 |
2020年 | 66篇 |
2019年 | 98篇 |
2018年 | 114篇 |
2017年 | 78篇 |
2016年 | 87篇 |
2015年 | 138篇 |
2014年 | 183篇 |
2013年 | 228篇 |
2012年 | 254篇 |
2011年 | 198篇 |
2010年 | 147篇 |
2009年 | 105篇 |
2008年 | 145篇 |
2007年 | 118篇 |
2006年 | 127篇 |
2005年 | 110篇 |
2004年 | 114篇 |
2003年 | 117篇 |
2002年 | 99篇 |
2001年 | 100篇 |
2000年 | 78篇 |
1999年 | 77篇 |
1998年 | 39篇 |
1997年 | 27篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1993年 | 13篇 |
1992年 | 25篇 |
1991年 | 34篇 |
1990年 | 19篇 |
1989年 | 24篇 |
1988年 | 22篇 |
1987年 | 21篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1980年 | 11篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1973年 | 11篇 |
1972年 | 12篇 |
1971年 | 12篇 |
排序方式: 共有3500条查询结果,搜索用时 0 毫秒
1.
2.
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.
M Bernardi B Di Sarra G Montecchiani L Re L Rossini C Tonnini 《Bollettino della Società italiana di biologia sperimentale》1991,67(1):47-54
Spontaneous fluctuations in heart rate were analyzed by spectral analysis in the ether anesthetized and pithed adult rat. In order to investigate the changes in the spectral pattern of the fluctuations, the selective 5HT-2 and -3 isoreceptor blockers ritanserin and BRL 43694A were used. In both the experimental conditions, ritanserin blockade led to dose-dependent increased fluctuations in HR low and high frequencies. In both the anesthetized and pithed rats, the low frequency range HR fluctuations were drastically reduced by BRL 43694A. 相似文献
10.
In the current study the argyrophil staining technique for NOR proteins (Ag-NORs) has been performed on cases of different endometrial lesions, trying to find an aid in differentiating atypical hyperplasia from well differentiated carcinoma in biopsy specimens. We conclude that the Ag-NOR count, even though in endometrial carcinoma is significantly exceeding that of atypical hyperplastic endometrium, could be a misleading discriminator, because of a wide overlap of values in individual cases. 相似文献