全文获取类型
收费全文 | 2930篇 |
免费 | 243篇 |
国内免费 | 164篇 |
出版年
2024年 | 10篇 |
2023年 | 43篇 |
2022年 | 31篇 |
2021年 | 55篇 |
2020年 | 130篇 |
2019年 | 98篇 |
2018年 | 107篇 |
2017年 | 107篇 |
2016年 | 74篇 |
2015年 | 69篇 |
2014年 | 105篇 |
2013年 | 212篇 |
2012年 | 64篇 |
2011年 | 103篇 |
2010年 | 86篇 |
2009年 | 124篇 |
2008年 | 131篇 |
2007年 | 142篇 |
2006年 | 137篇 |
2005年 | 105篇 |
2004年 | 91篇 |
2003年 | 89篇 |
2002年 | 83篇 |
2001年 | 54篇 |
2000年 | 50篇 |
1999年 | 55篇 |
1998年 | 58篇 |
1997年 | 53篇 |
1996年 | 55篇 |
1995年 | 66篇 |
1994年 | 67篇 |
1993年 | 44篇 |
1992年 | 63篇 |
1991年 | 43篇 |
1990年 | 62篇 |
1989年 | 43篇 |
1988年 | 53篇 |
1987年 | 41篇 |
1986年 | 34篇 |
1985年 | 40篇 |
1984年 | 50篇 |
1983年 | 24篇 |
1982年 | 35篇 |
1981年 | 42篇 |
1980年 | 30篇 |
1979年 | 28篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 14篇 |
1974年 | 8篇 |
排序方式: 共有3337条查询结果,搜索用时 296 毫秒
11.
Pisum sativum L. cv. Bodil was infected with various strains of Rhizobium leguminosarum (R501, 128c53, B155, 18a or 1044). The Rhizobium genotype influenced the activity of the plant enzyme phosphoenoipyruvate (PEP) carboxylase (EC 4.1.1.31), and the assimilation of fixed N in the root nodules. The specific activity of nodule PEP carboxylase was lowest in the symbioses, which accumulated the least total N (R501 and 128c53). The root bleeding sap of the less effective symbioses contained a lower proportion of asparagine and a higher proportion of glutamine than the more effective symbioses (B155,18a and 1044). The N yield of the symbioses was related neither to the net respiratory CO2 evolution of the root system nor to the nitrogenase linked nodule respiration. The lower yielding symbioses accumulated a larger proportion of the fixed N in the nodules due to a higher proportion of total dry weight contained in the nodule tissue. However, the concentration of soluble protein in the nodules of the lower-yielding symbioses was lower than that recorded for the higher yileding symbioses. The effect of the Rhizobium strains on N yield was maintained at maturity, and reflected in seed yields. 相似文献
12.
D. L. Zhang K. Q. Li W. Gu L. F. Hao 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,75(1):132-137
Summary Different phytohormone concentrations induced different fequencies of various chromosome aberrations in calli of Vicia faba. NAA 10 ppm plus KT 2.5 ppm produced more haploids and NAA 30 ppm plus NAA 7.5 ppm produced more tetraploids and breakage. The relationship among the aberrations was analyzed. The hypothesis of ploidy equilibrium was established. The chromosome doubling rate and reduction rate of each treated group were calculated in relation to the observed data and the hypothesis. The frequency of tetraploids and breakage are correlated with each other. The frequency of total aberrations is linearly correlated with that of micronucleus formation. The regression equation is x=31.92+ 10.67 y. 相似文献
13.
During growth on glycerol two marine Desulfovibrio strains that can grow on an unusually broad range of substrates contained high activities of glycerol kinase, NAD(P)-independent glycerol 3-phosphate dehydrogenase and the other enzymes necessary for the conversion of dihydroxyacetone phosphate to pyruvate. Glycerol dehydrogenase and a specific dihydroxyacetone kinase were absent. During growth on dihydroxyacetone, glycerol kinase is involved in the initial conversion of this compound to dihydroxyacetone phosphate which is then further metabolized. Some kinetic properties of the partially purified glycerol kinase were determined. The role of NAD as electron carrier in the energy metabolism during growth of these strains on glycerol and dihydroxyacetone is discussed.Glycerol also supported growth of three out of four classical Desulfovibrio strains tested. D. vulgaris strain Hildenborough grew slowly on glycerol and contained glycerol kinase, glycerol 3-phosphate dehydrogenase and enzymes for the dissimilation of dihydroxyacetone phosphate. In D. gigas which did not grow on glycerol the enzymes glycerol kinase and glycerol 3-phosphate dehydrogenase were absent in lactate-grown cells.Abbreviations DHA
dihydroxyacetone
- DHAP
dihydroxyacetone phosphate
- G3P
glycerol 3-phosphate
- GAP
glyceraldehyde 3-phosphate
- 3-PGA
3-phosphoglycerate
- 2-PGA
2-phosphoglycerate
- 2,3-DPGA
2,3-diphosphoglycerate
- PEP
phosphoenolpyruvate
- DH
dehydrogenase
- GK
glycerol kinase
- DHAK
dihydroxyacetone kinase
- TIM
triosephosphate isomerase
- PGK
3-phosphoglycerate kinase
- PK
pyruvate kinase
- LDH
lactate dehydrogenase
- DTT
dithiotreitol
- HEPES
4-(2-hydroxyethyl)-1-piperazine ethane sulfonic acid
- PIPES
piperazine-1,1-bis(2-ethane sulfonic acid)
- BV2+/BV+
oxidized/reduced benzylviologen
- PMS
phenazine methosulfate
- DCPIP
2,6-dichlorophenolindophenol
- MTT
3-(4,5-dimethylthiazol-2-yl)-2,4-diphenyltetrazolium bromide 相似文献
14.
Hideki Takahashi Ko Shimamoto Yoshio Ehara 《Molecular & general genetics : MGG》1989,216(2-3):188-194
Summary In order to study possible functions of the inclusion body matrix protein (IBMP) encoded by gene VI of cauliflower mosaic virus (CaMV), the XbaI fragment containing the gene VI of a Japanese strain of CaMV (CaMV S-Japan) was transferred to tobacco plants by Ti mediated transformation. Eight out of 18 kanamycin resistant plants (40%) expressed detectable levels of IBMP. Those transgenic plants expressing IBMP produced leaves with light green color, and their growth was suppressed as compared with control plants. Symptom-like necrotic spots also appeared on the leaves and stems of the mature transgenic plants. Furthermore, in these transgenic plants, pathogenesis-related proteins 1a, 1b and 1c were highly expressed and the activity of 1,3--glucanase was increased up to eightfold. From these results, we concluded that expression of the IBMP is associated with symptom development. 相似文献
15.
Alfalfa (Medicago sativa L.) growth and nodulation in acid soil is reduced because the plant and its bacterial symbiontRhizobium meliloti cannot tolerate acid, aluminum-rich soil. A study was conducted to determine if a relatively acid-tolerant alfalfa germplasm combined with a relatively acid-tolerantR. meliloti strain could overcome these limitations. In a light room study, an acid-tolerant alfalfa germplasm inoculated with a more acid-tolerantR. meliloti strain produced greater top growth, nodule number and weight, and acetylene reduction values in an unlimed soil (pH 4.6) than the same germplasm inoculated with a relatively acid-sensitiveR. meliloti strain or an acid-sensitive germplasm inoculated with either a relatively acid-tolerant or acid-sensitiveR. meliloti strain. 相似文献
16.
Nitrate reduction in roots and shoots and exchange of reduced N between organs were quantitatively estimated in intact 13-d-old seedlings of two-row barley (Hordeum vulgare L. cv. Daisengold) using the 15N-incorporation model (A. Gojon et al. (1986) Plant Physiol. 82, 254–260), except that NH
+
4
was replaced by NO
-
2
. N-depleted seedlings were exposed to media containing both nitrate (1.8 mM) and nitrite (0.2 mM) under a light-dark cycle of 12:12 h at 20°C; the media contained different amounts of 15N labeling. Experiments were started either immediately after the beginning (expt. 1) or immediately prior to the end (expt. 2) of the light period, and plants were sampled subsequently at each light-dark transition throughout 36 h. The plants effectively utilized 15NO
-
3
and accumulated it as reduced 15N, predominantly in the shoots. Accumulation of reduced 15N in both experiments was nearly the same at the end of the experiment but the accumulation pattern in roots and shoots during each 12-h period differed greatly depending on time and the light conditions. In expt. 1, the roots accounted for 31% (light), 58% (dark), and 9% (light) of nitrate reduction by the whole plants, while in expt. 2 the contributions of the root were 82% (dark), 20% (light), and 29% (dark), during each of the three 12-h periods. Xylem transport of nitrate drastically decreased in the dark, but that of reduced N rather increased. The downward translocation of reduced 15N increased while nitrate reduction in the root decreased, whereas upward translocation decreased while nitrate reduction in the shoot increased. We conclude that the cycling of reduced N through the plant is important for N feeding of each organ, and that the transport system of reduced N by way of xylem and phloem, as well as nitrate reduction by root and shoot, can be modulated in response to the relative magnitude of reduced-N demands by the root and shoot, with the one or the other predominating under different circumstances.Symbols Anl
accumulation of reduced 15N from 15NO
-
3
in 14NO
-
3
-fed roots of divided root system
- Ar
accumulation in root of reduced 15N from 15NO
-
3
- As
accumulation in shoot of reduced 15N from 15NO
-
3
- Rr
15NO
-
3
reduction in root
- Rs
15NO
-
3
reduction in shoot
- Tp
translocation to root of shoot-reduced 15N from 15NO
-
3
in phloem
- Tx
translocation to shoot of root-reduced 15N from 15NO
-
3
in xylem 相似文献
17.
Nitrate and nitrite was reduced by Escherichia coli E4 in a l-lactate (5 mM) limited culture in a chemostat operated at dissolved oxygen concentrations corresponding to 90–100% air saturation. Nitrate reductase and nitrite reductase activity was regulated by the growth rate, and oxygen and nitrate concentrations. At a low growth rate (0.11 h–1) nitrate and nitrite reductase activities of 200 nmol · mg–1 protein · min–1 and 250 nmol · mg–1 protein · min–1 were measured, respectively. At a high growth rate (0.55 h–1) both enzyme activities were considerably lower (25 and 12 nmol mg–1 · protein · min–1). The steady state nitrite concentration in the chemostat was controlled by the combined action of the nitrate and nitrite reductase. Both nitrate and nitrite reductase activity were inversely proportional to the growth rate. The nitrite reductase activity decreased faster with growth rate than the nitrate reductase. The chemostat biomass concentration of E. coli E4, with ammonium either solely or combined with nitrate as a source of nitrogen, remained constant throughout all growth rates and was not affected by nitrite concentrations. Contrary to batch, E. coli E4 was able to grow in continuous cultures on nitrate as the sole source of nitrogen. When cultivated with nitrate as the sole source of nitrogen the chemostat biomass concentration is related to the activity of nitrate and nitrite reductase and hence, inversely proportional to growth rate. 相似文献
18.
The ethanol-oxidizing, proton-reducing Pelobacter acetylenicus was grown in chemostat cocultures with either Acetobacterium woodii, Methanobacterium bryantii, or Desulfovibrio desulfuricans. Stable steady state conditions with tightly coupled growth were reached at various dilution rates between 0.02 and 0.14 h-1. Both ethanol and H2 steady state concentrations increased with growth rate and were lower in cocultures with the sulfate reducer < methanogen < homoacetogen. Due to the higher affinity for H2, D. desulfuricans outcompeted M. bryantii, and this one A. woodii when inoculated in cocultures with P. acetylenicus. Cocultures with A. woodii had lower H2 steady state concentrations when bicarbonate reduction was replaced by the energetically more favourable caffeate reduction. Similarly, cocultures with D. desulfuricans had lower H2 concentrations with nitrate than with sulfate as electron acceptor. The Gibbs free energy (G) available to the H2-producing P. acetylenicus was independent of growth rate and the H2-utilizing partner, whereas the G available to the latter increased with growth rate and the energy yielding potential of the H2 oxidation reaction. The critical Gibbs free energy (Gc), i.e. the minimum energy required for H2 production and H2 oxidation, was-5.5 to-8.0 kJ mol-1 H2 for P. acetylenicus,-5.1 to-6.3 kJ mol-1 H2 for A. woodii,-7.5 to-9.1 kJ mol-1 H2 for M. bryantii, and-10.3 to-12.3 kJ mol-1 H2 for D. desulfuricans. Obviously, the potentially available energy was used more efficiently by homoacetogens > methanogens > sulfate reducers. 相似文献
19.
Isolation and characterization of a bacterium that mineralizes toluene in the absence of molecular oxygen 总被引:25,自引:0,他引:25
J. Dolfing J. Zeyer P. Binder-Eicher R. P. Schwarzenbach 《Archives of microbiology》1990,154(4):336-341
A bacterium tentatively identified as a Pseudomonas sp. was isolated from a laboratory aquifer column in which toluene was degraded under denitrifying conditions. The organism mineralized toluene in pure culture in the absence of molecular oxygen. In carbon balance studies using [ring-UL-14C]toluene, more than 50% of the radioactivity was recovered as 14CO2. Nitrate and nitrous oxide served as electron acceptors for toluene mineralization. The organism was also able to degrade m-xylene, benzoate, benzaldehyde, p-cresol, p-hydroxybenzaldehyde, p-hydroxybenzoate and cyclohexanecarboxylic acid in the absence of molecular oxygen. 相似文献
20.
Akira Hiraishi 《Archives of microbiology》1988,150(1):56-60
Nineteen established and one undesignated species of the Rhodospirillaceae were examined for fumarate reduction in connection with their quinone systems. The fumarate reductase activity with reduced methyl viologen (MVH) or FMNH2 as electron donor was found in membrane (chromatophore) preparations from phototrophically grown cells of all species containing menaquinone (MK) and/or rhodoquinone. The species having ubiquinone as the sole quinone contained no fumarate reductase activity, except some Rhodobacter species showing the FMNH2-dependent activity. The MVH-fumarate reductase activity of the MK-type species was not inhibited by Triton X-100 or acetone treatment, suggesting the presence of a fumarate reductase reacting directly with MVH, while such an enzyme was absent in the MK-lacking strains, with few exceptions. The FMNH2-fumarate reduction system was abolished by a detergent or acetone extraction in all bacteria but differed much among species with different quinone types as to the response to respiratory inhibitors. These differences in fumarate-reducing properties and quinone systems among the phototrophic bacteria are discussed from evolutionary and taxonomic viewpoints.Non-standard abbreviations RQ
rhodoquinone
- MK
menaquinone
- MVH
reduced methyl viologen
- HOQNO
2-n-heptyl-4-hydroxyquinoline-N-oxide
- TTFA
2-thenoyltrifluoroacetone 相似文献