首页 | 官方网站   微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1832篇
  免费   105篇
  国内免费   117篇
生物科学   2054篇
  2024年   1篇
  2023年   16篇
  2022年   14篇
  2021年   27篇
  2020年   43篇
  2019年   45篇
  2018年   47篇
  2017年   45篇
  2016年   41篇
  2015年   41篇
  2014年   60篇
  2013年   185篇
  2012年   56篇
  2011年   58篇
  2010年   56篇
  2009年   74篇
  2008年   64篇
  2007年   70篇
  2006年   75篇
  2005年   101篇
  2004年   82篇
  2003年   99篇
  2002年   93篇
  2001年   63篇
  2000年   51篇
  1999年   45篇
  1998年   49篇
  1997年   44篇
  1996年   40篇
  1995年   37篇
  1994年   37篇
  1993年   47篇
  1992年   27篇
  1991年   31篇
  1990年   31篇
  1989年   22篇
  1988年   24篇
  1987年   20篇
  1986年   17篇
  1985年   10篇
  1984年   9篇
  1983年   10篇
  1982年   12篇
  1981年   10篇
  1980年   11篇
  1979年   10篇
  1978年   1篇
  1977年   2篇
  1974年   1篇
排序方式: 共有2054条查询结果,搜索用时 15 毫秒
1.
The occurrence of microfloral components on medicated and non-medicated swine and chicken feed pellets and crumbles, produced in a Manitoba feed mill between June 1991 and October 1992, was determined. Addition of medicates to feeds generally decreased bacterial incidence and increased that of Eurotium spp. fungi. The effect was less pronounced when copper sulphate was added to medicated swine feeds.Contribution No. 1662.  相似文献   
2.
In the estuaries near Falmouth (Cornwall, UK) levels of dissolved copper and zinc are high, due to drainage of copper and tin mines. Phytoplankton species composition in the autumn of 1989 deviated in the metal-contaminated Restronguet Creek from that in other estuarine branches,viz. Fal, Tresillian and Percuil. In the riverine part of Restronguet Creek (Carnon River)Euglena mutabilis, known as an acidophilic (pH 3) metal-resistant flagellate, occurred at micromolar Cu and Zn, whereas in the clean riversChlamydomonas sp. andOocystis sp. occurred at nanomolar Cu and Zn. An ordination analysis revealed the following patterns in Cu, Zn and phytoplankton species composition in the poly- and euhaline waters. Seston-bound Zn and dissolved Zn were in equilibrium,Katodinium rotundatum is Zn-tolerant, andSkeletonema costatum occurred in water with high contents of Cu in seston. However, none of the variables in these patterns correlated at a significant level (p>0.05). The results show that algae-metal interactions are complicated, and that statistical correlations foundin situ need experimental verification.Communication no. 542 of the Delta Institute for Hydrobiological Research.  相似文献   
3.
Abstract

In the present work, we have used copper sulphate (CuSO4·5H2O) enriched medium for effective control of visible and latent contamination. Among the different concentrations used, 1.25–2.5?mg/L resulted the most appropriate. In addition, the role of different nitrogen source and concentrations (NH4NO3 and KNO3), as different iron source (FeEDTA and FeEDDHA) has been investigated in the proliferation and rooting phases of European hazelnut (cv. Tonda Gentile Romana). The normal concentration of nitrogen present in Murashige and Skoog medium is too high for hazelnut micropropagation cv. Tonda Gentile Romana. A reduction of total nitrogen, accompanied by a reduction of ammonium forms, resulted in a better quality of the shoots. Similar results have been obtained when the common iron source FeEDTA has been replaced by the same concentration of FeEDDHA. An increase in rooting occurs when the amount of nitrogen was reduced in the rooting medium, particularly when the NH4NO3 was not present.  相似文献   
4.
Blackfoot disease (BFD) is an endemic peripheral vascular disorder resulting in gangrene of the lower extremities, especially the feet, among residents in a limited area on the southwest coast of Taiwan. In the present study, the concentrations of zinc, cadmium, lead, and copper in urine of BFD patients with matched normal controls are investigated by differential pulse anodic stripping voltammetry (DPASV) on a hanging mercury drop electrode (HMDE). The analytical results indicate that urinary copper, cadmium, and lead of the BFD patients are significantly higher than those of the controls. In addition, the patients showed a significantly lower concentration of zinc in the urine than the normal controls. The possible connection of these elements with the etiology of the disease is discussed.  相似文献   
5.
6.
ABSTRACT

A method has been developed for impregnating alginate-based wound dressings with trace elements required for wound healing and for quantifying the transfer from these dressing to wound fluid (for which a substitute—blood serum—was used in these experiments). Under ideal conditions, up to 85% can be carried across from the tow to the wound fluid.  相似文献   
7.
Abstract

Bacteria from two areas in Wales have been extracted and partially identified. The areas are a copper impregnated bog in the Coed-Y-Brenin Forest with low pH and high carbon and copper content, and the Morfa Harlech salt marshes which have neutral pH and lower copper and carbon. Bacillus spp. was the predominant bacterium in both soils, but there was increased diversity of bacteria in the salt marsh soils. Bacteria from the Cu-rich, Coed-Y-Brenin soils showed higher growth densities in nutrient agar plates containing 10, 30 and 100 μg cm?3 Cu than bacteria from the salt marsh soils, indicating that bacteria from the Coed-Y-Brenin soils could tolerate higher copper concentrations. Pseudomonas spp. from both study areas grew better in media with added Cu at low levels. The possibility is discussed that the bacteria play a part in the bioavailability of Cu particularly in the copper-rich Coed-Y-Brenin area.  相似文献   
8.
9.
The effect of calcium, copper ions and salicylic acid (SA) amendment on the incidence of basal stem rot and activity of secondary metabolites in oil palm seedlings were investigated in glasshouse study. Disease incidence (DI) in positive control (T8) was 75% at nine months after inoculation (9 MAI). However, weekly pre-immunisation with Ca2+?+?Cu2+?+?SA prior to inoculation significantly suppressed DI and delayed disease onset as noted in T7. In the present study, the lowest %DI was observed in T7 (15%) followed by T1, T5, T6, T3, T4 and T2. The Ca2+, Cu2+ and SA amendments were resulted in earlier and higher accumulation of plant secondary metabolites as noted in leaves, stems and root tissues in response to invasion by Ganoderma boninense. High total phenolic content concentration was detected in T7 (leaf: 233.38 ± 0.12 mg/g; stem: 132.78 ± 0.04 mg/g and root: 86.98 ± 0.28 mg/g). Similar trend was obtained in peroxidase activity, total lignin content and hydrogen peroxide scavenging activity. These results suggested that it could be due to the accumulation of phenolics, peroxidase activities, lignin content and hydrogen peroxide scavenging activities in oil palm seedling tissues which might have collectively contributed to induce resistance against G. boninense.  相似文献   
10.
Proteins anchor copper(II) ions mainly by imidazole from histidine residues located in different positions in the primary protein structures. However, the motifs with histidine in the first three N-terminal positions (His1, His2, and His3) show unique Cu(II)-binding properties, such as availability from the surface of the protein, high flexibility, and high Cu(II) exchangeability with other ligands. It makes such sequences beneficial for the fast exchange of Cu(II) between ligands. Furthermore, sequences with His1 and His2, thus, non-saturating the Cu(II) coordination sphere, are redox-active and may play a role in Cu(II) reduction to Cu(I). All human protein sequences deposited in UniProt Knowledgebase were browsed for those containing His1, His2, or His3. Proteolytically modified sequences (with the removal of a propeptide or Met residue) were taken for the analysis. Finally, the sequences were sorted out according to the subcellular localization of the proteins to match the respective sequences with the probability of interaction with divalent copper.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司    京ICP备09084417号-23

京公网安备 11010802026262号