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171.
Using [2-13C]uric acid as a test material, we developed a mass spectrometric procedure that detects and estimates the difference in 13C enrichment at the positions of carbons 2 and 8 of the purine ring. This method could replace radiochemical methods and could trace the incorporation of carbon fragments into the purine ring from 13C-labeled metabolites in humans. 相似文献
172.
Patel AP John Moody A Handy RD Robert Sneyd J 《Biochemical and biophysical research communications》2003,302(2):392-396
Rat hearts were perfused for 15min with buffer equilibrated with 0.01% or 0.05% CO. The buffer was equilibrated with 21% O(2) throughout. The ventricular glutathione content decreased by 76% and 84%, 90min post-exposure to 0.01% and 0.05% CO, respectively, compared with 0% CO controls (0.45+/-0.01 micromol/g wet tissue; +/-SEM, n=3). Both reduced and oxidised glutathione contributed to this decline. When ascorbate and Trolox C were included during exposure to 0.05% CO the glutathione pool was partly protected; here the glutathione decrease was 46%. In most hearts additional creatine kinase activity in the perfusate indicated minor tissue injury occurring immediately after the start and/or about 10min after the end of exposure to 0.01% CO or 0.05% CO. Ventricle lactate levels were unaffected by exposure to 0.01% CO. This evidence supports a role for oxidative stress in CO cardiotoxicity. 相似文献
173.
Two different isoforms of glucose-6-phosphate dehydrogenase (Glc6PDH; EC 1.1.1.49) have been partially purified from barley
(Hordeum vulgare L., cv. Alfeo) roots. The procedure included an ammonium sulfate step, Q-Sepharose and Reactive Blue agarose chromatography,
and led to 60-fold and 150-fold purification for the two enzymes, respectively. The Glc6PDH 1 isoform accounts for 17% of
total activity of the enzyme in roots, and is very sensitive to the effects of NADP+/NADPH ratio and dithiothreitol; the Glc6PDH 2 isoform is less affected by reducing power and represents 83% of the total
activity. The isoforms showed distinct pH optima, isoelectric points, K
m for glucose-6-phosphate and a different electrophoretic mobility. The kinetic properties for the two enzymes were affected
by ATP and metabolites. Both enzymes are inhibited to different extents by ATP when magnesium is omitted from the assay mixture,
whereas the addition of ATP-Mg2+ had no effect on Glc6PDH activities. The Glc6PDH isoforms are usually present in the plastids and cytosol of plant cells.
To verify the intracellular locations of the enzymes purified from barley roots, Glc6PDH was purified from isolated barley
root plastids; this isoform showed kinetic parameters coincident with those found for Glc6PDH 1, suggesting a plastid location;
the enzyme purified from the soluble fraction had kinetic parameters resembling those of Glc6PDH 2, confirming that this isoform
is present in the cytosol of barley roots.
Received: 21 June 2000 / Accepted: 28 July 2000 相似文献
174.
The effects of increased CO2 levels (10,000 μl l−1) in cultures of the green nitrophilic macroalga Ulva rigida C. Agardh were tested under conditions of N saturation and N limitation, using nitrate as the only N source. Enrichment with
CO2 enhanced growth, while net photosynthesis, gross photosynthesis, dark respiration rates and soluble protein content decreased.
The internal C pool remained constant at high CO2, while the assimilated C that was released to the external medium was less than half the values obtained under ambient CO2 levels. This higher retention of C provided the source for extra biomass production under N saturation. In N-sufficient thalli,
nitrate-uptake rate and the activity of nitrate reductase (EC 1.6.6.1) increased under high CO2 levels. This did not affect the N content or the internal C:N balance, implying that the extra N-assimilation capacity led
to the production of new biomass in proportion to C. Growth enhancement by increased level of CO2 was entirely dependent on the enhancement effect of CO2 on N-assimilation rates. The increase in nitrate reductase activity at high CO2 was not related to soluble carbohydrates or internal C. This indicates that the regulation of N assimilation by CO2 in U. rigida might involve a different pathway from that proposed for higher plants. The role of organic C release as an effective regulatory
mechanism maintaining the internal C:N balance in response to different CO2 levels is discussed.
Received: 27 March 2000 / Accepted: 9 October 2000 相似文献
175.
Promoter strength and tissue specificity effects on growth of tomato plants transformed with maize sucrose-phosphate synthase 总被引:10,自引:0,他引:10
Laporte MM Galagan JA Prasch AL Vanderveer PJ Hanson DT Shewmaker CK Sharkey TD 《Planta》2001,212(5-6):817-822
When sucrose-phosphate synthase (SPS; EC 2.4.1.14) is expressed in tomato (Lycopersicon esculentum Mill.) from a ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) small subunit (rbcS) promoter, yields are often unchanged but when SPS is expressed from a Cauliflower Mosaic Virus 35S promoter, yield is enhanced
up to 80%. Two explanations for this phenomenon are (i) that expression of SPS in tissues other than leaves accounts for the
increased yield or (ii) that the lower level of expression directed by the 35S promoter is more beneficial than the high level
of expression directed by the rbcS promoter. To test the first hypothesis, we conducted a reciprocal graft experiment, which showed that root SPS activity did
not substantially affect growth. To test the second hypothesis, we conducted a field trial using a backcrossed, segregating,
population of SPS-transformed plants derived from 35S and rbcS lines. The optimal dose of SPS activity for growth was approximately twice that of the wild type regardless of which promoter
was used. The effect of SPS on growth was the result of a shift in partitioning of carbon among starch, sucrose, and ionic
compounds (primarily amino acids), rather than of an increase in net photosynthesis. Excessive SPS activity resulted in a
decreased rate of amino acid synthesis, which could explain the non-linear response of plant growth to the level of SPS expression.
Received: 23 May 2000 / Accepted: 24 July 2000 相似文献
176.
Stable isotope and trace element geochemistry of Upper Cretaceous carbonates and belemnite rostra (Middle Campanian, north Germany) 总被引:1,自引:0,他引:1
Trace element contents and stable isotopic composition of Middle Campanian marl-limestone rhythmites and belemnite rostra of Belemnitella mucronata were investigated. High strontium and low iron as well as manganese and magnesium contents of belemnite calcite and bulk rock samples suggest no diagenetic overprint. However, the orange-coloured cathodoluminescence of coccolith-rich sediments indicates diagenetic cementation and/or recrystallization. The non-luminescent belemnite rostra reveal an extraordinary preservation of the microstructures that is interpreted to have been favoured by a silification of the outer rim of the belemnite rostra. Carbon isotope ratios of the coccolith limestones and belemnite rostra are comparable, with higher δ13C variations observed for belemnite calcite. The 1.5-2‰ depletion in δ18O of the marl-limestone rhythmites relative to belemnite calcite is explained by diagenetic alteration of the sediments. Palaeotemperatures, calculated from the δ18O values of the well-preserved belemnite rostra, are around 12.5 ± 2 °C and suggest rather low sea-surface temperatures for the Middle Campanian epicontinental sea of north Germany assuming a water depth of less than 100 m. 相似文献
177.
Ogawa K 《Journal of plant research》2002,115(6):449-453
The carbon balance in reproductive organs over the whole reproductive period was estimated for 20 woody species on the basis
of the published data on the final dry weight and CO2 exchange of reproductive organs. The relationship between net respiration and dry weight growth was formulated by a linear
function with a negative y-intercept. From this linear relationship, linear relations of dry weight growth and net respiration to net translocation
were derived. The size dependence of net respiration showed that the net respiration changed from negative to positive as
the final dry weight of the reproductive organ exceeded 0.481 g. The cost for translocation per unit dry weight was much lower
in the species with small reproductive organs (<0.481 g) because of their photosynthetic contribution to the weight growth.
The relation of dry weight growth/net translocation ratio to net translocation was expressed as a hyperbolic function. The
dry weight growth/net translocation ratio remained at 0.650, in the higher range of net translocation, irrespective of woody
species.
Electronic Publication 相似文献
178.
Nobuhiko?NaritaEmail author Masayuki?Sagisaka Atsushi?Inaba 《The International Journal of Life Cycle Assessment》2002,7(5):277-282
The goal of this study was to calculate the average CO2 emissions for manufacturing three commodity plastics, polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC)
in Japan. The CO2 emissions were calculated from cradle to gate, excluding the calcination processes after use. As the results, the followings
were observed:
1) The gross CO2 emissions for the manufacture of plastics in Japan were 1.3, 1.4, and 1.7 kg-CO2/kg-PE, PP, and PVC, respectively. These mainly reflected the difference of CO2 emissions for the in-house electricity generation. 2) The CO2 emissions for the electricity used for manufacturing PVC were higher than that used for PE and PP, because additional electricity
was required for the electrolysis to produce chlorine. The gross electricity consumption for manufacturing PVC was 1.3 kWh/kg-PVC,
and the other plastics consumed 0.5 kWh/kg-Products. In addition, the effects of energy saving were studied using a projected
gas-diffusion electrode for the electrolysis of salt on the reduction of CO2 emissions. It was estimated that the reduction in CO2 emissions was 7% compared with the present PVC manufacturing processes. 相似文献
179.
Fuentes-Noriega I Ruiz-Ramírez L Tovar Tovar A Rico-Morales H Gracia-Mora I 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2002,766(1):115-121
In order to measure changes in physiological CO concentrations in blood with good accuracy, a method was developed using gas chromatography with flame ionisation detection (250 degrees C). A nickel catalyst system was fitted to convert CO to methane at 375 degrees C after separation with a molecular sieve column at 35 degrees C. Helium was used as carrier at 30 ml/min. Porcine or human blood (400 microl) was sampled in gastight tubes and treated with sulfuric acid and saponin (800 microl). Accuracy was 1.4% and 1.5% (RSD), respectively. Precision was 2.8% (porcine blood). Limit of detection was 0.01 nmol/ml gas and limit of quantification 12 nmol/ml blood. Calibration was made in the interval 12-514 nmol/ml blood (corresponding to 0.1-6% COHb). Samples were stable for at least a month at +4 degrees C. This paper describes a method with high sensitivity and good accuracy, suitable for analysis of low CO concentrations. 相似文献
180.
To answer the question whether some inselbergs are better sources thanothers, thus potentially affecting processes in inselberg landscapes,inselberg-matrix affinities and the influence of regional physicalenvironmental parameters (latitude, longitude, distance from coast andmainland)and parameters operating on landscape level (elevation and geology) wereinvestigated. All investigated environmental parameters affected the observedpatternsto some extend. Distance from mainland and geographic position were importantona regional level, while elevation only influenced the observed trends wheninvestigated at a local level. Parameters determining bettersources within the selected study areas and sites, here simply definedasshowing higher floristic affinities with the surrounding, appeared to beinselbergs: (a) in southern Namibia and thus in an inland position; (b) at adistancefrom other mountainous habitats; and (c) of low elevation. Although theimportanceof inselbergs for conservation and maintenanceof biodiversity is evident, this study points towards a complex situation,ruling out the sole effect of any one of the parameters investigated atregionaland landscape level. Further observations and analysis at a local level maygivesome pointers and assist in identifying critical aspects important forconservation and range management. 相似文献