全文获取类型
收费全文 | 17791篇 |
免费 | 1522篇 |
国内免费 | 9篇 |
出版年
2023年 | 90篇 |
2022年 | 189篇 |
2021年 | 396篇 |
2020年 | 225篇 |
2019年 | 279篇 |
2018年 | 356篇 |
2017年 | 310篇 |
2016年 | 489篇 |
2015年 | 828篇 |
2014年 | 911篇 |
2013年 | 1079篇 |
2012年 | 1441篇 |
2011年 | 1316篇 |
2010年 | 881篇 |
2009年 | 839篇 |
2008年 | 1099篇 |
2007年 | 1111篇 |
2006年 | 984篇 |
2005年 | 1026篇 |
2004年 | 933篇 |
2003年 | 859篇 |
2002年 | 828篇 |
2001年 | 150篇 |
2000年 | 130篇 |
1999年 | 187篇 |
1998年 | 239篇 |
1997年 | 164篇 |
1996年 | 142篇 |
1995年 | 111篇 |
1994年 | 122篇 |
1993年 | 120篇 |
1992年 | 103篇 |
1991年 | 84篇 |
1990年 | 119篇 |
1989年 | 99篇 |
1988年 | 84篇 |
1987年 | 88篇 |
1986年 | 49篇 |
1985年 | 81篇 |
1984年 | 91篇 |
1983年 | 59篇 |
1982年 | 79篇 |
1981年 | 68篇 |
1980年 | 49篇 |
1979年 | 46篇 |
1978年 | 37篇 |
1977年 | 34篇 |
1976年 | 30篇 |
1975年 | 20篇 |
1974年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
The purpose of this investigation was to determine whether Madurella mycetomatis, the most frequent agent of eumycotic mycetomas, produces siderophores and synthesizes new outer membrane proteins under iron-starvation conditions. Siderophore production, only of the hydroxamate type, was demonstrated in all nine strains tested. It was regulated by extracellular iron concentrations. Under iron-restricted conditions, M. mycetomatis expressed various outer membrane iron-regulated proteins, particularly of 24-kilodalton, that may participate in iron metabolism. 相似文献
202.
Characterization of Superoxide dismutase genes from Gram-positive bacteria by polymerase chain reaction using degenerate primers 总被引:13,自引:0,他引:13
Abstract An internal fragment representing approximately 85% of sod genes from seven Gram-positive bacteria was amplified by using degenerate primers in a polymerase chain reaction assay. The DNA sequences of sod polymerase chain reaction products from Clostridium perfringens, Enterococcus faecalis, Enterococcus faecium, Lactococcus lactis, Staphylococcus aureus, Streptococcus agalactiae, Streptococcus pneumoniae , and Streptococcus pyogenes were determined. Comparisons of their deduced amino acid sequences with those of the corresponding regions of the SOD proteins from Bacillus stearothermophilus, Listeria monocytogenes , and Streptococcus mutans revealed strong relatedness. Phylogenetic analysis of SOD peptides showed that members of the genera Streptococcus and those of the genera Enterococcus constitute two well-supported monophyletic groups. The method described in this study provides a means for easy recovery of sod genes and the construction of sod mutants of various Gram-positive pathogens. 相似文献
203.
Patrick H. Brown Steven A. Weinbaum Geno A. Picchioni 《Trees - Structure and Function》1995,9(3):158-164
The influence of alternate bearing on nutrient utilization and total tree nutrient content was investigated in mature pistachio
(Pistacia vera L. cv Kerman trees). Removal of N, P and Zn in fruit and abscised leaves of cropping (‘on’) trees averaged 5, 6, and 2 times,
respectively, the removal in abscised leaflets of the non-fruiting, ‘off’ year trees. One hundred and thirty-five kg N, 131
kg K, 86 kg Ca, 39 kg Mg and 18 kg P per hectare were removed in fruits and abscised leaves in ‘on’ year trees. Tree nutrient
contents and, presumably, the size of nutrient storage pools in dormant trees varied between ‘on’ and ‘off’ years. There was
22% and 14% more N and P, respectively, in dormant trees following ‘off’ than ‘on’ years. The greater N and P accumulation
in ‘off’ year trees is depleted in support of the large fruit demand for N and P during ‘on’ years. In contrast to N and P,
there was greater K and Ca accumulation in perennial tree parts during ‘on’ years than during ‘off’ years. The greater K accumulation
in perennial tree parts and approximately 30% greater removal of K in annual organs during ‘on’ than ‘off’ years suggests
that K uptake could be 4 times higher in ‘on’ year trees than in (non-cropping), ‘off’ year trees. 相似文献
204.
205.
206.
The energization of the active sucrose release from bean seed-coat halves was investigated. For this purpose, seed coat tissues adjacent to the apoplastic space were exposed to a variety of treatments and proton and photosynthate release were measured. Fusicoccin (10–5 moll–1) stimulated proton pump activities. Orthovanadate (2×10–4 moll–1) and abscisic acid (10–5 moll–1) diminished the proton extrusion evoked by fusicoccin. Fusicoccin inhibited sucrose release, whereas orthovanadate and abscisic acid stimulated it. Addition of 100 mmoll–1 K+ had a promotory effect on photosynthate unloading, fading away with time. This extra unloading was linearly related to an enhanced proton loss. It was concluded that the photosynthate unloading apparently is not a proton/sucrose antiport and that a pump-leak system for photosynthate release is unlikely. A tentative model for photosynthate/proton symport not directly linked to proton pumping is presented as the mechanism of unloading.Abbreviations ABA
abscisic acid
- CCCP
carbonyl cyanide m-chlorophenyl hydrazone
- DTE
diethioerythritol
- FC
fusicoccin
- MES
2-(N-morpholino) ethanesulfonic acid monohydrate
- NEM
n-ethylmaleimide
- PCMBS
p-chloromercuriphenylsulfonic acid
- TRIS
2-amino-2-(hydroxymethyl) propane-1,3 diol
- VAN
sodium orthovanadate 相似文献
207.
Three distinct states can be identified for cells of the green alga Chlorella vulgaris; State 1 and State 2 obtained by preillumination in far-red and red light, respectively, and the dark state obtained by dark-adaptation. Addition of the inhibitor DCMU to algal cells leads to an initial rapid increase in chlorophyll-a fluorescence reflecting the closure of Photosystem II traps. This, in the case of dark and state-2-adapted algae is followed by a slow light-dependent increase to a fluorescence yield typical of State-1-adapted cells. Measurements of low temperature (77 K) emission spectra indicate that the low fluorescence yields of dark and State-2-adapted algae reflect similar balances in excitation-energy distribution between the two photosystems. In both cases, the balance favours PS I and the slow fluorescence increase seen in the poisoned algae reflects a redressing of this balance in favour of PS II. The low fluorescence yield of State-2-adapted algae is thought to be associated with the phosphorylation of chlorophyll a/b light-harvesting protein (Biochim. Biophys. Acta (1983) 724, 94–103). Measurements of the uncoupler and ATPase sensitivity of the light-dependent increases seen in DCMU-poisoned cells indicate that the low fluorescence yield of dark-adapted algae is of different origin. Evidence is presented showing that the light-driven changes in excitation-energy distribution seen in green algae involve two distinct processes; a low-intensity, wavelenght-independent change reflecting simple light/dark changes and a higher intensity, wavelength-dependent change reflecting State 1/State 2 adaptation. The former changes appear to be associated with changes in the local ionic environment within the algal chloroplast, whilst the latter appear to reflect changes in the phosphorylation state of chlorophyll a/b light-harvesting protein. 相似文献
208.
Patrick von Aderkas 《Economic botany》1984,38(1):14-23
Although the ostrich fern, Matteuccia struthiopteris,is distributed throughout much of the Northern Hemisphere, its consumption as a spring vegetable has been largely restricted to the tables of the Maritime Provinces in Canada and neighboring Maine in the United States. However, in little more than a decade the demand has expanded beyond these traditional boundaries, due to the present availability of the frozen product. The heart of the industry is undoubtedly New Brunswick. The harvest of 200 t/yr is approximately 4 times that of Maine, and from an historical vantage the traditional use as a spring vegetable is with the New Brunswickers as well. In light of the present high demand for the product and the reports of localized overpicking, a review of the economic history, resource management and attempts at cultivation is presented. 相似文献
209.
Application of the Indirect Immunoperoxidase Stain Technique to the Flagella of Azospirillum brasilense 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
An indirect immunoperoxidase stain was used to demonstrate by electron microscopy that an antigenic difference exists between the polar flagellum and the lateral flagella of Azospirillum brasilense ATCC 29145. 相似文献
210.
Bergmann Pascale Seyer Patrick Burkard Gérard Weil Jacques-Henri 《Plant molecular biology》1984,3(1):29-36
Tobacco chloroplast tRNAs have been purified by two-dimensional polyacrylamide gel electrophoresis, identified by aminoacylation, labelled at their 3-end and hybridized to tobacco chloroplast DNA restriction fragments, in order to establish a tRNA gene map. These hybridization studies have revealed the localization of at least seven genes in each inverted repeat region, a minimum of 22 tRNA genes in the large single copy region and one tRNA gene in the small single copy region. Comparison of the tobacco chloroplast tRNA gene map to that of maize shows many similarities, but also some differences suggesting that DNA sequence rearrangements have occurred in the chloroplast genome during evolution. 相似文献