全文获取类型
收费全文 | 33552篇 |
免费 | 4715篇 |
国内免费 | 19470篇 |
专业分类
57737篇 |
出版年
2024年 | 466篇 |
2023年 | 1207篇 |
2022年 | 1889篇 |
2021年 | 2114篇 |
2020年 | 1931篇 |
2019年 | 2163篇 |
2018年 | 1509篇 |
2017年 | 1434篇 |
2016年 | 1478篇 |
2015年 | 2102篇 |
2014年 | 2987篇 |
2013年 | 2615篇 |
2012年 | 3647篇 |
2011年 | 3504篇 |
2010年 | 2921篇 |
2009年 | 3003篇 |
2008年 | 3278篇 |
2007年 | 3115篇 |
2006年 | 2946篇 |
2005年 | 2408篇 |
2004年 | 1868篇 |
2003年 | 1580篇 |
2002年 | 1440篇 |
2001年 | 1384篇 |
2000年 | 1322篇 |
1999年 | 816篇 |
1998年 | 435篇 |
1997年 | 234篇 |
1996年 | 216篇 |
1995年 | 171篇 |
1994年 | 157篇 |
1993年 | 118篇 |
1992年 | 108篇 |
1991年 | 110篇 |
1990年 | 97篇 |
1989年 | 103篇 |
1988年 | 90篇 |
1987年 | 71篇 |
1986年 | 59篇 |
1985年 | 83篇 |
1984年 | 49篇 |
1983年 | 56篇 |
1982年 | 69篇 |
1981年 | 35篇 |
1980年 | 18篇 |
1978年 | 18篇 |
1958年 | 21篇 |
1957年 | 19篇 |
1954年 | 19篇 |
1950年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
HAN-QI YANG HONG WANG DE-ZHU LI 《Botanical journal of the Linnean Society. Linnean Society of London》2008,156(3):411-423
The foliage leaf epidermis of 35 species representing 12 key genera of woody bamboos of the Asian tropics was investigated using light and scanning electron microscopy. The results indicated that papillae forms and distributional patterns around the stomatal apparatus of the abaxial foliage leaf epidermis were usually constant and were of great taxonomic significance at the specific and generic levels. However, papillae characters were not suitable for dividing subtribes within woody bamboos of the Asian tropics. On the basis of papillae characters, Schizostachyum s.s. and Cephalostachyum were confirmed, but their delimitations should be modified. The transfer of Leptocanna chinensis and Schizostachyum sanguineum into Cephalostachyum was supported, and Cephalostachyum virgatum and C . pergracile were confirmed to be members of Schizostachyum s.s. The subtribe Racemobambosinae did not obtain support and Racemobambos appeared to be better placed in subtribe Bambusinae. Neomicrocalamus was supported as a close relative and better treated as a synonym of Racemobambos . Gigantochloa was closely related to Dendrocalamus . © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 411–423. 相似文献
3.
4.
多种天敌控制多种害虫的模糊数学模型 总被引:2,自引:0,他引:2
从生态经济学的原理出发,利用模糊集理论,探讨如何评价天敌控制多种害虫的为害作用,提出了多种天敌控制多种害虫的模糊数学模型。同时又得到了天敌对害虫的控制能力C,影响率G,影响强度H,及权数ω(x)的计算公式,以及在天敌作用下安全度的讨论与分析。 相似文献
5.
In searching for differentially expressed genes in human uterine leiomyomas (ULs), suppression sub-tractive hybridization was used to construct an UL up-regulated library, which turned out to represent 88genes. After two rounds of screening by reverse Northern analysis, twenty genes were proved to be up-regulated, including seventeen known genes and three genes with unknown function. All these genes werefirstly associated with UL. Three genes with notable difference were selected for Northern confirmationOur results proved the authenticity of the twenty genes. One gene named Phospholipase A2 (PLA2) showedup-regulation in 4/6 of the patients and investigation of tissue distribution indicated that it had obviousexpression in prostate, testis, liver, heart and skeletal muscle. 相似文献
6.
7.
8.
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
9.
10.
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