全文获取类型
收费全文 | 9634篇 |
免费 | 1489篇 |
国内免费 | 804篇 |
出版年
2024年 | 51篇 |
2023年 | 268篇 |
2022年 | 284篇 |
2021年 | 384篇 |
2020年 | 470篇 |
2019年 | 508篇 |
2018年 | 441篇 |
2017年 | 438篇 |
2016年 | 490篇 |
2015年 | 486篇 |
2014年 | 540篇 |
2013年 | 751篇 |
2012年 | 453篇 |
2011年 | 511篇 |
2010年 | 463篇 |
2009年 | 472篇 |
2008年 | 502篇 |
2007年 | 537篇 |
2006年 | 427篇 |
2005年 | 384篇 |
2004年 | 355篇 |
2003年 | 313篇 |
2002年 | 293篇 |
2001年 | 248篇 |
2000年 | 190篇 |
1999年 | 181篇 |
1998年 | 159篇 |
1997年 | 142篇 |
1996年 | 104篇 |
1995年 | 123篇 |
1994年 | 98篇 |
1993年 | 105篇 |
1992年 | 99篇 |
1991年 | 90篇 |
1990年 | 65篇 |
1989年 | 67篇 |
1988年 | 50篇 |
1987年 | 46篇 |
1986年 | 39篇 |
1985年 | 46篇 |
1984年 | 48篇 |
1983年 | 40篇 |
1982年 | 35篇 |
1981年 | 19篇 |
1980年 | 24篇 |
1979年 | 15篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
81.
Ken-ichi Miyaji 《Ecological Research》1986,1(3):303-322
In order to demonstrate in detail the relationship between the longevity and productivity of leaves within a canopy, a new
life table approach, the ‘bioeconomic life table’, was applied to the leaves of kidney bean plants (Phaseolus vulgaris L.) in relation to planting density and their position within the canopy.
The net photosynthetic rate for upper leaves under full daylight tended to decline gradually due to leaf senescence from about
20 days after leaf emergence, and for the lower leaves the decrease was very rapid due to both shading and senescence about
10 days after emergence.
Analysis of the survivorship curves and daily surplus production of leaves suggested that the lower and middle leaves, especially
the latter, survived without surplus production of dry matter after they had reached mean longevity, and while the upper leaves
at high density had a much shorter mean longevity, they had very large values of daily surplus production throughout the survival
period.
For the total foliage, the summed value of accumulated surplus production during the survival period was about five times
as large as the summed value of the dry weight of the dead leaves, regardless of planting density.
The daily rate of canopy leaf respiration was almost proportional to that of canopy gross photosynthesis for the various leaf
area indices of the canopy, so that there was no optimum leaf area index that maximized canopy daily surplus production. 相似文献
82.
83.
84.
Quantitative determination of 5-methylcytosine in DNA by reverse-phase high-performance liquid chromatography 总被引:7,自引:0,他引:7
A method to separate the four major bases (cytosine, guanine, thymine and adenine) and the two minor modified bases (5-methylcytosine and 6N-methyladenine) in DNA has been developed. For optimal separation, several different buffer systems are available for isocratic elution. The 12 5-methylcytosine (5-mC) residues in the plasmid pBR322 can be determined with a deviation of less than 3% of the expected value and have been used for internal standardization. Formic acid hydrolysis of bases and probably of DNA does not lead to the deamination of cytosine or 5-mC and thus can be used routinely for DNA hydrolysis. Adenovirus or baculovirus DNA does not contain detectable amounts of 5-mC. The distribution of 5-mC in hamster cell DNA appears to be nonrandom in that different 5'-CpG-3'-containing restriction sites are methylated to different extents. 相似文献
85.
Jane C. Gallagher 《Journal of phycology》1983,19(4):539-542
Skeletonema costatum (Grev.) Cl. exhibits an asexual means, of increasing cell size that is more common than auxosporulation. This phenomenon accounts for the genetic stability of S. costatum in culture and for the deficiency of heterozygotes in natural populations, and has important implications far the life history of this species. 相似文献
86.
Abstract: A simple, rapid method is presented for the determination of acetylcholine (ACh) and choline (Ch) in neuronal tissue using HPLC with electrochemical detection. The method is based on the separation of ACh and Ch by reverse-phase HPLC and mixing the effluent as it emerges from the column with acetylcholinesterase and Ch oxidase, which converts endogenous Ch and Ch produced by the hydrolysis of ACh to betaine and hydrogen peroxide. Production of hydrogen peroxide is continuously monitored electrochemically. The sensitivity of the procedure is 1 pmol for Ch and 2 pmol for ACh. Specificity of the method is based on HPLC, two specific enzymatic reactions, and the detection of hydrogen peroxide. 相似文献
87.
KABITA ROY 《The Journal of eukaryotic microbiology》1989,36(1):20-23
Morphology and life history of 3 cephaline gregarines found in the gut of the pest of stored fruit, Oryzaephilus mercator. are described. Of these 3, 2 are new species. The 3 species are (1) Hirmocystis minuta (Ishii, 1914) (LP TL = 1:7 – 1:22, WP/WD = 1:1, 6–1:7); (2) Amsotobus indicus n. sp. (LP/TL = 1:3–1:6, WP/WD = 1:1 – 1:1.3); (3) Leidyana oryzaephili n. sp. (LP/TL = 1:2 – 1:12; WP/WD = 1:1–1:1.6). 相似文献
88.
Willy R. G. Baeyens Betty Lin Ling Udo A. Th. Brinkman Stephen G. Schulman 《Luminescence》1989,4(1):484-499
An overview is presented of the physicochemical basis of luminescence, and its application to the detection of chemicals (drugs, biomedically important compounds, environmentally active substances) in liquid chromatographic systems. 相似文献
89.
贵州省赤水县桫椤调查初报 总被引:4,自引:0,他引:4
国家一级重点保护植物桫椤,目前世界上少数国家尚存,国内除华南、西南地区及台湾等少数省份外亦不多见。其中贵州省赤水县桫椤不仅面积广,且数量多,生长旺。据不完全统计,全县35个乡中,有20个乡有分布,面积 相似文献
90.
Food preferences and nematode parasitism were studied in natural populations of mycophagousDrosophila in and near Sapporo, northern Japan. Species which preferred fresh mushrooms showed species-specific responses toPleurotus mushrooms:D. pirka bred only onPleurotus cornucopiae, D. trivitata onP. cornucopiae andP. ostreatus, D. trilineata on these twoPleurotus mushrooms and some other mushrooms, whileD. sexvittata bred on a wide variety of mushrooms but seldom onPleurotus mushrooms. Species which preferred decayed mushrooms (D. quadrivittata, D. histrioides, D. testacea and species of thequinaria species-group) showed host preferences different from those of the above species. The rate of parasitism by nematodes was
generally higher in species which prefer decayed mushrooms than in species which prefer fresh mushrooms. Among species which
prefer fresh mushrooms, onlyD. trilineata was parasitized frequently by nematodes. It was not clear what factors determine the rate of parasitism in these mycophagousDrosophila.
D. pirka, D. trivittata andD. trilineata passed through three or four generations per year and entered reproductive diapause in early September in and near Sapporo.
Bionomics of Drosophilidae (Diptera) in Hokkaido, IX. 相似文献