全文获取类型
收费全文 | 7591篇 |
免费 | 50篇 |
国内免费 | 14篇 |
专业分类
林业 | 727篇 |
农学 | 252篇 |
基础科学 | 50篇 |
933篇 | |
综合类 | 354篇 |
农作物 | 515篇 |
水产渔业 | 479篇 |
畜牧兽医 | 3636篇 |
园艺 | 198篇 |
植物保护 | 511篇 |
出版年
2022年 | 11篇 |
2019年 | 11篇 |
2018年 | 122篇 |
2017年 | 190篇 |
2016年 | 170篇 |
2015年 | 235篇 |
2014年 | 202篇 |
2013年 | 160篇 |
2012年 | 455篇 |
2011年 | 312篇 |
2010年 | 113篇 |
2009年 | 79篇 |
2008年 | 68篇 |
2007年 | 47篇 |
2006年 | 43篇 |
2005年 | 775篇 |
2004年 | 657篇 |
2003年 | 450篇 |
2002年 | 112篇 |
2001年 | 135篇 |
2000年 | 35篇 |
1999年 | 147篇 |
1992年 | 118篇 |
1991年 | 148篇 |
1990年 | 171篇 |
1989年 | 149篇 |
1988年 | 172篇 |
1987年 | 115篇 |
1986年 | 145篇 |
1985年 | 117篇 |
1984年 | 92篇 |
1983年 | 81篇 |
1982年 | 34篇 |
1981年 | 17篇 |
1980年 | 24篇 |
1979年 | 136篇 |
1978年 | 99篇 |
1977年 | 92篇 |
1976年 | 77篇 |
1975年 | 137篇 |
1974年 | 130篇 |
1973年 | 117篇 |
1972年 | 139篇 |
1971年 | 120篇 |
1970年 | 88篇 |
1969年 | 103篇 |
1968年 | 114篇 |
1967年 | 125篇 |
1966年 | 103篇 |
1965年 | 70篇 |
排序方式: 共有7655条查询结果,搜索用时 359 毫秒
111.
Helvécio De-Polli Eiichi Matsui Johanna D?bereiner Eneas Salati 《Soil biology & biochemistry》1977,9(2):119-123
Intact soil cores containing plants of Paspalum notatum or Digitaria decumbens were selected with the acetylene reduction method, and then exposed to 15N15 to confirm nitrogen fixation in tropical grass-bacteria associations. In a preliminary experiment with P. notatum15N2 incorporation was slow but progressive during 24 h in roots but translocation to rhizomes and leaves ceased after 17h. With improved assay chambers, enrichments of 0.151 and 0.563 15N atom % excess were obtained in roots of D. decumbens cv transvala and P. notatum systems respectively, after 3 days. Enrichments in rhizomes were similar to those of roots; however in the leaves only 8% of root enrichment was observed. The addition of sucrose to the soil doubled N2-fixation in roots in both grass species studied, but did not result in increased incorporation into the leaves of P. notatum. 相似文献
112.
L J Nu?ez-Vergara J A Squella E M Gonzalez 《Journal of the Association of Official Analytical Chemists》1979,62(3):556-559
A polarographic method has been developed for the quantitative analysis of cephradine and its dosage forms. Direct determinations on capsules are carried out; excipients and coloring matter do not interfere in the determination. The electroactive product is formed by acidic hydrolysis with 5.0N HCl and heating at 80 degrees C for 60 min. Two polarographic waves are obtained: I = -0.46 V and II = -0.78 v vs. SCE. Both reduction waves are diffusion controlled. Wave I is preferred for analytical purposes. The precise chemical identity of the electroactive product has not been determined, but UV spectral data and the TLC Rf value are reported. A linear relation is established for levels of cephradine between 10(-2) and 10(-5)M in 5.0N HCl. 相似文献
113.
114.
Keita?KodamaEmail author Takashi?Yamakawa Takamichi?Shimizu Ichiro?Aoki 《Fisheries Science》2005,71(1):141-150
ABSTRACT: In this study, the age composition of the Japanese mantis shrimp, Oratosquilla oratoria , in Tokyo Bay, central Japan, was investigated using lipofuscin, an autofluorescent pigment, as an age marker. Lipofuscin in a histological section of protocerebral bridge cell mass (PBCM) in the brain was identified by confocal microscopy, and its concentration was quantified by image analysis. Modal analysis of the lipofuscin concentration showed four regularly-spaced modes that could each be regarded as a distinct age group. This implied a constant lipofuscin accumulation in PBCM at a 6.5 × 10−2 % volume fraction per year; it also implied the existence of individuals that are at least 4 years old. The lipofuscin concentration was found to be a more appropriate index than body length for estimating the age of O. oratoria , because the modal analysis on the body–length histogram failed to detect apparent age groups. This was probably a result of the declining growth rate with age and the individual variations in growth through molting leading to considerable overlap in the size between different age groups. The lipofuscin analysis suggested that fast-growing individuals in each cohort are recruited to the fishery, and most individuals attain the exploitable size between 2 and 3 years of age. 相似文献
115.
Kazufumi?OsakoEmail author Mohammed?Anwar?Hossain Koichi?Kuwahara Akira?Okamoto Atsuko?Yamaguchi Yukinori?Nozaki 《Fisheries Science》2005,71(6):1347-1355
ABSTRACT: To explore the potential utility of underutilized fish in the fish sauce industry, fish sauces were prepared from both raw and heat-induced meat of Japanese anchovy Engraulis japonica and rabbit fish Siganus fuscescens using wheat malt, and their quality aspects and sensory properties were assessed. Proximate composition of the fish meat represents protein as the major component (16.0–17.8%), other than moisture. Analyses of free amino acids, peptides including oligopeptides, and organic acids contents in fish sauces revealed suitability of both raw and heat-induced meat of the selected species in commercial fish sauce production. The variations in taste of raw meat fish sauces were species-specific, but the taste of fish sauces from heat-induced meat were similar. 相似文献
116.
ABSTRACT: The effects caused by suspended particles in seawater and sediment cover of the substrate on the attachment to the substrate of zoospores, and on the subsequent growth and survival of gametophytes of the brown alga Eisenia bicyclis were examined in the laboratory. The attachment rate to the substrate of the zoospores was remarkably reduced by the sediment cover on the substrate, and it decreased to 3.8% of the no-sediment control by a slight sediment cover of 3.0 mg/cm2 (0.048 mm in thickness). The growth of gametophytes was not inhibited at 10 mg/cm2 or less of sediment cover, though it was stopped at 30 mg/cm2 . The survival rate of gametophytes became 39.4% at 5 mg/cm2 on the substrate, and gametophytes were all blighted at 30 mg/cm2 . The ratio of male to female of the surviving gametophytes became 81.5:18.5, when the sediment cover was 10 mg/cm2 . The rate of total loss ( TL [%]) of zoospores and gametophytes of Eisenia bicyclis was obtained from the following equation: TL = 100 (1 − exp[−0.0339 C ] exp[−1.24 Q ]), where, C (mg/L) and Q (mg/cm2 ) indicate the concentration of suspended particles in seawater and the sediment on the substrate, respectively. 相似文献
117.
Helena Khatoon Sanjoy Banerjee Fatimah Md Yusoff Mohamed Shariff 《Aquaculture Research》2010,41(9):1348-1355
Marine periphytic cyanobacteria and diatoms have been examined as a potential source of feed supplement for rearing aquatic larvae in the aquaculture industry. Culture of the periphytic diatom Amphora sp., Navicula sp., Cymbella sp. and the cyanobacteria Oscillatoria sp. at different salinities showed significant changes in biomass and specific growth rates. Diatoms growth was significantly higher at 35 g L−1, while for cyanobacteria growth was better at 25 g L−1. Significantly higher levels of protein and lipid were found in diatoms at low salinities (15–25 g L−1) and an increase in carbohydrate at high salinities (30–35 g L−1). Conversely, cyanobacteria showed a significantly higher lipid content at 30–35 g L−1 compared with other salinity levels but no significant changes were observed in the protein and carbohydrate contents at different salinity levels. The present findings can be taken into consideration when culturing marine periphytic Amphora sp., Navicula sp., Cymbella sp. and Oscillatoria sp. to provide appropriate levels of protein, lipid and carbohydrate as feed supplement as well as for bioremediation in aquaculture. 相似文献
118.
Bj?rn Berger Andreas Brühschwein Lina Eddicks Andrea Meyer-Lindenberg 《The Canadian veterinary journal. La revue veterinaire canadienne》2016,57(4):377-381
A unicameral bone cyst in the proximal humerus of a 3-year-old Norwegian forest cat was diagnosed by dynamic contrast-enhanced magnetic resonance imaging, surgical exploration, and histopathology. Surgical curettage and incorporation of bone cement led to full recovery. An osteosarcoma developed at the surgical site 17 months later. Thoracic radiographs showed pulmonary lesions consistent with metastasis. 相似文献
119.
A Markos A Blah?sková M Kalous E Bysková K Byska E Nohynková 《Folia parasitologica》1989,36(3):225-238
Bloodforms of Trypanosoma brucei brucei STIB 247 taken from rats and containing more than 80 per cent short stumpy forms, differentiated in vitro to procyclic forms in medium SDM 79 (Brun and Sch?nenberger 1979), enriched with 3 mmol.dm-3 cis-aconitate. Cell division was abolished by the addition of hydroxyurea (200 micrograms.ml-1) or arabinosyl adenine (20 micrograms.ml-1 to the cultivation medium, or by the omission of serum from the medium. The ultrastructure of exponentially growing controls was rearranged within 24 h. The endogenous respiration and the respiration stimulated by proline, succinate, and 2-oxoglutarate were detectable within 12 h; after 48 h the respiration rates were comparable to those found in the established procyclic forms. After 12 h the respiration was inhibited by 200 mumol.dm-3 KCN, and by 20 mumol.dm-3 antimycin to the extent found in procyclic forms. Hydroxyurea did not significantly affect respiration. Activities of procyclic-stage enzyme markers malate dehydrogenase, threonine dehydrogenase, succinate: cytochrome c reductase, and NADH: cytochrome c reductase rose within 48 h of differentiation to values which were close to those found in established procyclic forms. The activity of glutamate dehydrogenase (NAD-specific), however, was only 1/3 of that in the procyclics, and no citrate synthase was detected in differentiating culture. Glycosomal malate dehydrogenase was detected after 6 h. In the presence of hydroxyurea or arabinosyl adenine, or in the absence of serum, respiration rates, marker enzyme activities, and glycosomal malate dehydrogenase developed to the extent comparable to the untreated controls. The results suggest that it is possible to separate the process of differentiation from cell proliferation. Cell division is not a necessary prerequisite of differentiation. 相似文献
120.
The ultrastructure of the flame cell, excretory capillaries, ducts, collecting ducts, excretory bladder, and excretory pore of Brachylaimus aequans was studied 6-8 days p.i. The excretory ducts, collecting ducts and excretory bladder are provided with numerous lamellae on the luminal side. The cilia of lateral flames in the excretory ducts have a triated rootlet. The excretory pore is covered by a tegument identical with the body tegument. The syncytium of the excretory bladder is connected with the tegument of the excretory pore by means of a septate desmosome. No lipid or excretory corpuscles have been demonstrated in the excretory system. 相似文献