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991.
The effect of temperature on the aggregation of 3lR-8,12-diethyl farnesyl bacteriochlorophyll c in a mixture of n-pentane and methylcyclohexane (1/1, v/v) was studied by means of absorption, circular dichroism and fluorescence spectroscopy. At room temperature essentially only two aggregate species, absorbing at 702 nm (A-702) and 719 nm (A-719), were present. Upon cooling to 219 K, A-702 was quantitatively converted to A-719. Further lowering of the temperature led to the stepwise formation of larger aggregates by the conversion of A-719 to aggregate species absorbing at 743 nm (A-743) and 755 nm (A-755). All absorption changes were reversible. A-719 was highly fluorescent (maximum at 192 K: 744 nm), while A-743 and especially A-755 were weakly fluorescent. Below 130 K the mixture solidified, and no major changes in the absorption spectrum were observed upon further cooling. At 45 K, however, a relatively strong emission at 775 nm was observed. Below 200 K, the absorption, fluorescence and circular dichroism spectra resembled that of the chlorosome. These results open up the possibility to study higher aggregates of BChl c as models for the chlorosome by various methods at low temperature, thus avoiding interference by thermal processes.Abbreviations A-680, A-702, A-719, A-743 and A-755-
BChl c aggregates absorbing at the wavelengths indicated
- BChl-
bacteriochlorophyll
- R[E,E] BChl c
F-
the 31 R isomer of 8,12-diethyl BChl c esterified with farnesol (F), analogously
- M-
methyl
- Pr-
propyl
- S-
stearol (see Smith 1994)
- CD-
circular dichroism 相似文献
992.
J. Zhang V. K. Tiwari T. J. Golds N. W. Blackhall E. C. Cocking B. J. Mulligan J. B. Power M. R. Davey 《Plant Cell, Tissue and Organ Culture》1995,41(2):125-138
Cat gene expression has been investigated following PEG-mediated plasmid uptake into barley protoplasts. The uptake conditions optimised for transient expression were employed for stable transformation. Transformed protoplast-derived calli of the cvs. Dissa and Igri, were selected on medium containing G418 at 40 g ml–1 or kanamycin sulphate at 250 g ml–1. Absolute transformation frequencies of 28.9×10–5 and 21.3×10–5 were recorded for Dissa with kanamycin sulphate and G418 selection, respectively. The frequency for Igri was 11.5×10–5 with G418 selection. Antibiotic resistant protoplast-derived colonies expressed NPTII activity; Southern hybridisation confirmed integration of the nptII gene into barley genomic DNA.Abbreviations ABA
abscisic acid
- AC-CAP
acetylated chloramphenicol
- BAP
6-benzylaminopurine
-
cat
chloramphenicol acetyltransferase gene
- CAT
chloramphenicol acetyltransferase activity
- CaMV
cauliflower mosaic virus
- CAP
chloramphenicol, 2,4-d-2,4-dichlorophenoxyacetic acid
- GA3
gibberellic acid
- G418
Geneticin
-
gus
-glucuronidase gene
- HEPES
(N[2-hydroxyethyl] piperazine-N-[2-ethanesulphonic acid])
- IAA
indole acetic acid
- MES
2-N-morpholinoethane sulphonic acid
- NAA
-naphthaleneacetic acid
-
npt II
neomycin phosphotransferase gene
- NPTH
neomycin phosphotransferase activity
- PEG
polyethylene glycol
- SCV
settled cell volume 相似文献
993.
Sources of organic carbon in the littoral of Lake Gooimeer as indicated by stable carbon isotope and carbohydrate compositions 总被引:1,自引:1,他引:0
The relative importance of potential carbon sources in the littoral of Lake Gooimeer, a lake in the centre of the Netherlands, was studied using a combination of 13C/12C-ratio analysis and carbohydrate composition analysis. The littoral is covered on the land side by a 80 m wide Phragmites australis bed. Potential carbon sources were macrophyte litter, seston and benthic algae. Samples of potential carbon sources, sediments and benthic macrofauna from inside and outside the bed were analyzed for their13C/12C-ratio and some for their carbohydrate composition. Results indicate that inside the bed, macrophyte litter was the main source of carbon for both the sediment organic matter and the benthic macrofauna, and that algal material was of minor importance. Outside the bed, production by benthic algae was the main carbon source, with seston as a second source. No macrophyte derived material could be detected outside the reed bed.Abbreviations DOC
(Dissolved Organic Carbon)
- SOM
(Sediment Organic Matter) 相似文献
994.
Thomas J. Thekkumkara Jing Du David E. Dostal Thomas J. Motel Walter G. Thomas Kenneth M. Baker 《Molecular and cellular biochemistry》1995,146(1):79-89
The octapeptide angiotensin II mediates the physiological actions of the renin-angiotensin system through activation of several angiotensin II receptor subtypes; in particular the AT1. In many tissues, the presence of multiple angiotensin II receptor subtypes, together with a low number of receptors, makes it difficult to study biological responses to physiological concentrations (10–11–10–9 M) of angiotensin II. Also, cultured cells show diminished angiotensin II receptor binding with respect to time in culture and passage number. To address these problems, we expressed the recombinant AT1A receptor in CHO-K1 cells. The stably transfected receptor was characterized using radioligand binding studies and functional coupling to cytosolic free calcium. Radioligand binding of [125I] angiotensin II to the angiotensin II receptor was specific, saturable, reversible and modulated by guanine nucleotides. Like the endogenous AT1A receptor, reported in a variety of tissues, the specific, noncompetitive, nonpeptide AII receptor antagonist, EXP3174, blocked binding of [125I] angiotensin II to the transfected receptor. Scatchard analysis demonstrated that the transfected receptor had a dissociation constant of 1.9 nM with a density of 3.4 pmol/mg protein.An important feature of many of the responses to angiotensin II is the rapid desensitization that occurs following agonist occupancy and the development of tachyphylaxis. In AT1A receptor transfected CHO-K1 cells, angiotensin II (10–9 M) stimulated a rapid increase in cytosolic free calcium that was completely desensitized within 50 sec following receptor occupancy. Agonist induced desensitization was unaffected when receptor internalization was blocked by pretreatment with concanavalin A or incubation at 4°C, and no changes in AT1A receptor affinity or number were observed. Receptor desensitization was also unaffected by inhibition or activation of protein kinase C. Thus, we have established a permanent, high-level transfectant of the AT1A receptor in CHO-K1 cells and have shown that these receptors rapidly desensitize following exposure to physiological concentrations of agonist. The mechanism of rapid desensitization is not related to receptor sequestration, internalization or controlled by PKC phosphorylation. This provides an excellent model for studying AII actions mediated through a specific receptor subtype, at subnanomolar concentrations. 相似文献
995.
Jan M. Visser Guus C. Stefess Lesley a. Robertson J. Gijs Kuenen 《Antonie van Leeuwenhoek》1997,72(2):127-134
The floating filter technique was successfully adapted for the isolation of the dominant, chemolithoautotrophic, sulfide-oxidizing bacterium from a sulfur-producing reactor after conventional isolation techniques had failed. The inoculated polycarbonate filters, floating on mineral medium, were incubated under gaseous hydrogen sulfide at non-toxic levels. This technique gave 200-fold higher recoveries than conventional isolation techniques. Viable counts on the filters, making up 15% of the total count, appeared to be all of the same species. Chemostat cultures of the new isolate had a very high sulfur-forming capacity, converting almost all hydrogen sulfide in the medium to elemental sulfur under high sulfide loads (27.5 mmol l-1 h-1) and fully aerobic conditions. This behaviour closely resembled that of the microbial community in the sulfur-producing reactor. Moreover, similar protein patterns were obtained by electrophoresis of cell-free extracts from the isolate and the mixed culture. It has therefore been concluded that this isolate represents the dominant sulfide-oxidizing population in the reactor. The isolate has been shown to be a new Thiobacillus species, related to Thiobacillus neapolitanus. In view of the general confusion currently surrounding the taxonomy of the thiobacilli, a new species has not been formally created. Instead, the isolate has been given the working name Thiobacillus sp. W5. 相似文献
996.
Potential canopy influences on the isotopic composition of nitrogen and sulphur in atmospheric deposition 总被引:7,自引:0,他引:7
Isotopic studies of nitrogen and sulphur inputs to plant/soil systems commonly rely on limited published data for the 15N/14N and 34S/32S ratios of nitrate, ammonium and sulphate in rainfall. For systems with well-developed plant canopies, however, inputs of
these ions from dry deposition or particulates may be more important than rainfall. The manner in which isotopic fractionation
between ions and gases may lead to dry deposition and particulates having 15N/14N or 34S/32S ratios different from those of rainfall is considered. Data for rainfall and throughfall in coniferous plantations are then
discussed, and suggest that: (1) in line with expectations, nitrate washed from the canopy has 15N/14N ratios higher than those in rainfall; (2) the 15N/14N ratios of ammonium washed from the canopy are variable, with high ratios being found for canopies of higher pH in conditions
of elevated ambient ammonia gas concentrations; and (3) in accord with expectations and previous work, 34S/32S ratios of sulphate washed from the canopy are not substantially different from those in rainfall. The study suggests that
if atmospheric inputs are relevant to isotopic studies of the sources of nitrogen for canopied systems, then confident interpretation
will require analysis of these inputs.
Received: 3 March 1996 / Accepted: 28 September 1996 相似文献
997.
SO2对鲜葡萄采后熏蒸处理的组织解剖研究 总被引:12,自引:0,他引:12
SO2对鲜食葡萄的伤害是渐进性的,且各组织受SO2伤害的情况与其结构及对SO2的敏感性有关。伤害作用起始于膜系统。通过组织解剖观察可见,伤害部位首先表现为细胞壁变性,细胞染色异常,细胞质变性形成颗粒状或物质,从而发生质壁分离现象,并且由于膜系统的破坏,细胞内含物外渗,细胞壁变形呈波齿状,最终完全变形破碎,导致细胞崩溃死亡。 相似文献
998.
PATRICK MORDELET GARRY COOK LUC ABBADIE MICHELINE GRABLY ANDR MARIOTTP 《Austral ecology》1996,21(3):336-340
Abstract The natural abundance of the stable isotope 15N was measured in different vegetation components and in the soil of a northern Australian savanna. Most of the vegetation was found to be 15N-depleted compared to atmospheric N2. Herbaceous legumes, perennial grasses, tree legumes, non-legume trees and annual grasses exhibited mean δ15N of ? 1.7, ? 0.8, ? 0.7, 0.0 and + 0.3‰, respectively. These results are in good agreement with previous studies. Legumes exhibit slightly negative values, indicating that they are likely to be nitrogen-fixing plants. Non-legume plants have a δ15N close to zero, which could equally result from non-symbiotic fixation, soil organic matter mineralization, or fresh root litter mineralization. In contrast, soil organic matter was 15N-enriched. Values of δ15N increased with depth and were + 2.5, + 5.2 and +6.1‰ in the 0–10, 10–20 and 20–40cm layers, respectively. Soil organic matter δ15N shows a typical profile of mature soils. 相似文献
999.
Rates of in situ sulfate reduction (SRR) in planted and unplanted rice fieldsoil were measured by the 35SO2–
4-radiotracermethod using soil microcosms. The concentration of 35SO2–
4 decreased exponentially with time.However, time course experiments indicated that incubation times of10–30 min were appropriate for measurements of SRRusing a single time point in routine assays. Unplanted microcosmsshowed high SRR of 177 nmol cm-3 d-1 inthe uppermost centimeter where average sulfate concentrations were<33 µM. Fine scaled measurements (1 mmresolution) localized highest SRR (<100 nmol cm-3d-1) at the oxic/anoxic interface at 2–5 mmdepth. In planted rice field soil, SRR of <310 nmolcm-3 d-1 were observed at 0–2cm depth. Sulfate reduction rates were determined at a millimeter-scalewith distance to a two dimensional root compartment. The SRR was highestat 0–1.5 mm distance to the root layer with rates up to500 nmol cm-3 d-1, indicating a highstimulation potential of the rice roots. SRR seemed to be mainlydependent on the in situ sulfate porewater concentrations. At thesoil surface of unplanted microcosms sulfate concentration decreasedfrom <150 µM to <10 µM within the first 8 mm of depth. In planted microcosmssulfate concentration varied from 87–99 µMsulfate at the 0–3 mm distance to the root layer to48–62 µM sulfate at a root distance>4 mm from the roots.The depth distribution of inorganic sulfur compounds was determinedfor planted and unplanted rice field soil. Sulfate, acid volatilesulfide (AVS) and chromium reducible sulfide (CRS) were up to 20 foldhigher in planted than in unplanted microcosms. CRS was the majorinsoluble sulfur fraction with concentrations >1.7µmol cm-3. Organic sulfur accounted for25–46% of the total sulfurpresent (269 µg/g dw) in an unplanted microcosm.The biogeochemical role of sulfate reduction forshort-term accumulation of inorganic sulfur compounds(FeS, FeS_2 and S°) in rice soil wasdetermined in a time course experiment with incubationperiods of 5, 10, 20, 30 and 60 min. The relativedistribution of CRS and AVS formation showedlittle depth dependence, whereas the formation of35S° seemed to be the highest in themore oxidized upper soil layers and near the root surface.AV35S was the first major product of sulfatereduction after 20–30 min, whereas CR35Swas formed, as AV35S and 35S°decreased, at longer incubation periods of >30 min. 相似文献
1000.
Hans Dreisig 《Evolutionary ecology》1997,11(5):543-555
Diurnal hawkmoths, Hemaris fuciformis, and bumblebees, Bombus pasquorum, were observed foraging for nectar in flowers of Viscaria vulgaris. The hawkmoths hovered in front of the flowers, while the bees perched on them. The hawkmoths had a faster probing rate than the bees, and consequently also had higher gross and net rates of energy gain. A model is presented that shows that hovering only yields a higher net rate of energy gain (NREG) than perching when nectar volumes are high due to low competition for the resource. The difference in NREG of perchers and hoverers decreases with an increase of competition, and eventually perching yields the highest NREG. This is an effect of the higher cost of hovering. The results suggest that hovering can only evolve as a pure evolutionarily stable strategy (ESS) if competition is reduced, for example by co-evolutionary specializations with plants. The possibility that it has evolved as a mixed ESS (i.e. individuals can both hover and perch depending on the resource level) is discussed. The evolution of optimal foraging strategies is discussed, and it is pointed out that the rate of gain of an animal is independent of the strategy used when all competing foragers use the same strategy, but competitively superior strategies will nevertheless evolve because they are ESSs. Competition between strategies with different energy costs are special, because resource availability determines which strategy is competitively superior. A high-cost strategy can only evolve as a pure ESS at high resource levels, or as a mixed ESS at intermediate levels. 相似文献