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981.
Growth,N2 fixation and photosynthesis in a cyanobacterium,Trichodesmium sp., under Fe stress 总被引:2,自引:0,他引:2
Trichodesmium sp., isolated from the Great Barrier Reef lagoon, was cultured in artificial seawater media containing a range of Fe concentration. Fe additions stimulated growth, N2 fixation, cellular chlorophyll a content, light-saturated chlorophyll a-specific gross photosynthetic capacity (Pm
chla) and the dark respiration rate (Rd
chla). Cell yields only doubled for 9 nM Fe relative to zero added Fe, whereas N2 fixation increased 11-fold considerably for 450 nM Fe. The results suggest that N2 fixation of Trichodesmium is more sensitive to Fe limitation than are the cell yields. 相似文献
982.
Angiostatin production in cultivation of recombinant Pichia pastoris fed with mixed carbon sources 总被引:4,自引:0,他引:4
A recombinant strain of Pichia pastoris with a phenotype of MutS was used to produce angiostatin. Due to the low methanol consumption rate of this strain, both methanol and glycerol feedings, that produced oscillation in dissolved O2 concentration, were used during the expression phase to improve cell growth and angiostatin expression. However, enhanced cell growth led to nitrogen limitation that suppressed further production of angiostatin, but addition of ammonia allowed angiostatin concentration to reach 108 mg l–1 after an expression period of 96 h. The ratio of consumed glycerol to methanol of 1.5:1 (w/w) in the expression phase suggested that methanol played an important role in the metabolism of carbon sources. 相似文献
983.
The aim of this study was to understand the relationship between production of food calls by maternal hens and food context. In a series of experiments with broody hens, we manipulated quality of items, quantity of food, food experience and dispersion of food items. We measured the frequency of food calling during standardized tests. Our results show that all the variables tested had significant effects on food calling. These results present some similarities and some discrepancies with previous reports on food calling by cockerels. 相似文献
984.
Previously we described the mosquito larvicidal properties of decomposed leaf-litter from deciduous trees, especially the alder Alnus glutinosa (L) Gaertn., due to toxic polyphenols and other secondary compounds. To further examine the biocontrol potential of toxic leaf-litter for mosquito control, feeding rates of third-instar mosquito larvae were assessed for examples of three genera: Anopheles stephensi Liston, Aedes aegypti (L) and Culex pipiens L. (Diptera: Culicidae). When immersed in a suspension of non-toxic leaf-litter particles (approximately 0.4 mm), pre-starved larvae of all three species ingested sufficient material in 30 min to fill the anterior gut lumen (thorax plus two to three abdominal segments). Gut filling peaked after 1-2 h ingestion time, filling the intestine up to six to seven abdominal segments for Ae. aegypti, but maxima of five abdominal segments for Cx. pipiens and An. stephensi. Using three methods to quantify consumption of three materials by third-instar larvae of Ae. aegypti, the average amount of leaf-litter (non-toxic 0.4 mm particles) ingested during 3 h was determined as approximately 20 microg/larva (by dry weight and by lignin spectrophotometric assay). Consumption of humine (approximately 100 microm particles extracted from leaf-litter) during 3 h was approximately 80 microg/larva for Ae. aegypti, but only approximately 30 microg/larva for Cx. pipiens and 15 microg/larva for An. stephensi, with good concordance of determinations by dry weight and by radiometric assay. Cellulose consumption by Ae. aegypti was intermediate: approximately 40 microg/larva determined by radiometric assay. Apparent differences between the amounts of these materials ingested by Ae. aegypti larvae (humine four-fold, cellulose two-fold more than leaf-litter) may be attributed to contrasts in palatability (perhaps related to particle size or form), rather than technical discrepancies, because there was good concordance between results of both methods used to determine the amounts of humine and leaf-litter ingested. Bioassays of toxic leaf-litter (decomposed 10 months) with 4-h exposure period (ingestion time) ranked the order of sensitivity: Ae. aegypti (LC50 < 0.03 g/L) > An. stephensi (LC50 = 0.35 g/L) > Cx. pipiens (LC20 > 0.4 g/L). When immersed in the high concentration of 0.5 g/L toxic leaf-litter (0.4 mm particles), as little as 15-30 min ingestion time (exposure period) was sufficient to kill the majority of larvae of all three species, as soon as the gut lumen was filled for only the first few abdominal segments. Possibilities for mosquito larval control with toxic leaf-litter products and the need for standardized ingestion bioassays of larvicidal particles are discussed. 相似文献
985.
Interspecific Differences of Leaf Gas Exchange and Water Relations of Three Evergreen Mediterranean Shrub Species 总被引:1,自引:1,他引:0
Leaf gas exchange and plant water relations of three co-occurring evergreen Mediterranean shrubs species, Quercus ilex L. and Phillyrea latifolia L. (typical evergreen sclerophyllous shrubs) and Cistus incanus L. (a drought semi-deciduous shrub), were investigated in order to evaluate possible differences in their adaptive strategies, in particular with respect to drought stress. C. incanus showed the highest annual rate of net photosynthetic rate (P
N) and stomatal conductance (g
s) decreasing by 67 and 69 %, respectively, in summer. P. latifolia and Q. ilex showed lower annual maximum P
N and g
s, although P
N was less lowered in summer (40 and 37 %, respectively). P. latifolia reached the lowest midday leaf water potential (1) during the drought period (–3.54±0.36 MPa), 11 % lower than in C. incanus and 19 % lower than in Q. ilex. Leaf relative water content (RWC) showed the same trend as 1. C. incanus showed the lowest RWC values during the drought period (60 %) while they were never below 76 % in P. latifolia and Q. ilex; moreover C. incanus showed the lowest recovery of 1 at sunset. Hence the studied species are well adapted to the prevailing environment in Mediterranean climate areas, but they show different adaptive strategies that may be useful for their co-occurrence in the same habitat. However, Q. ilex and P. latifolia by their water use strategy seem to be less sensitive to drought stress than C. incanus. 相似文献
986.
Biomass Partitioning and Gas Exchange in Dalbergia sissoo seedlings under water stress 总被引:3,自引:0,他引:3
Biomass, leaf water potential (l), net photosynthetic rate (P
N), transpiration rate (E), stomatal conductance (g
s), leaf to air temperature difference (T
diff), and instantaneous water use efficiency (WUE) were measured in the seedlings of Dalbergia sissoo Roxb. grown under irrigation of 20 (W1), 14 (W2), 10 (W3), and 8 (W4) mm. Treatments were maintained by re-irrigation when water content of the soil reached 7.4% in W1, 5.6% in W2, 4.3% in W3, and 3.2% in W4. Seedlings in a control (W5) were left without irrigation after maintaining the soil field capacity (10.7%). Seedlings of W1 had highest biomass that was one tenth in W5. Biomass allocation was highest in leaf in W2 and in root in W4 and W5 treatments. Difference between predawn leaf water potential (Pd) and midday (mid) increased with soil water stress and with vapour pressure deficit (VPD) in April and May slowing down the recovery in plant leaf water status after transpiration loss. P
N, E, and g
s declined and T
diff increased from W1 to W5. Their values were highly significant in April and May for the severely stressed seedlings of W4 and W5. P
N increased from 08:00 to 10:00 and E increased until 13:00 within the day for most of the seedlings whereas g
s decreased throughout the day from 08:00 to 17:00. P
N and E were highest in March but their values were low in January, February, April, and May. Large variations in physiological variables to air temperature, photosynthetically active radiation, and vapour pressure deficit (VPD) indicated greater sensitivity of the species to environmental factors. WUE increased from W1 to W2 but decreased drastically at high water stress particularly during hot summer showing a kind of adaptation in D. sissoo to water stress. However, low biomass and reduced physiological functions at <50% of soil field capacity suggest that this species does not produce significant biomass at severe soil water stress or drought of a prolonged period. 相似文献
987.
We raised leatherback posthatchlings in the laboratory for up to 7 weeks to study the role of visual and chemical cues in food recognition and food-seeking behavior. Turtles were reared on a formulated (artificial gelatinous) diet and had no contact with test materials until experiments began. Subjects were presented with visual cues (a plastic jellyfish; white plastic shapes [circle, square, diamond] similar in surface area to the plastic model), chemical cues (homogenates of lion's mane jellyfish, Cyanea capillata; moon jellyfish, Aurelia aurita; and a ctenophore, Ocyropsis sp., introduced through a water filter outflow), and visual and chemical cues presented simultaneously. Visual stimuli evoked an increase in swimming activity, biting, diving, and orientation toward the object. Chemical cues elicited an increase in biting, and orientation into water currents (rheotaxis). When chemical and visual stimuli were combined, turtles ignored currents and oriented toward the visual stimuli. We conclude that both cues are used to search for, and locate, food but that visual cues may be of primary importance. We hypothesize that under natural conditions turtles locate food visually, then, as a consequence of feeding, associate chemical with visual cues. Chemical cues then may function alone as a feeding attractant. 相似文献
988.
Stefanie?HellwegEmail author Thomas?B.?Hofstetter Konrad?Hungerbuhler 《The International Journal of Life Cycle Assessment》2003,8(1):8-18
Background In Life-Cycle Assessment (LCA), decision makers are often faced with tradeoffs between current and future impacts. One typical
example is waste incineration, where immediate emissions to the air from the incineration process have to be weighted against
future emissions of slag landfills. Long-term impacts are either completely taken into account or they are entirely disregarded
in case of a temporal cut-off. Temporal cutoffs are a special case of discounting.
Objective In this paper, discounting is defined as valuing damages differently at different points of time using a positive or negative
discount rate. Apart from temporal cut-offs, discounting has rarely been applied in LCA so far. It is the goal of this paper
to discuss the concept of discounting and its applicability in the context of LCA.
Methods For this purpose, we first review the arguments for discounting and its principles in economic sciences. Discounting in economics
can be motivated by pure time preference, productivity of capital, diminishing marginal utility of consumption, and uncertainties.
The nominal discount rate additionally includes changes in the price level. These arguments and their justification are discussed
in the context of environmental impacts harming future generations.
Results and Discussion It is concluded that discounting across generations because of pure time preference contradicts fundamental ethical values
and should therefore not be applied in LCA. However, it has to be acknowledged that in practice decision makers often use
positive discount rates because of pure time preference — either because they might profit from imposing environmental damage
on others instead of themselves or because people in the far future are not of immediate concern to them. Discounting because
of the productivity of capital assumes a relationship between monetary values and environmental impact. If such a relationship
is accepted, discounting could be applied. However, future generations should be compensated for the environmental damage.
It is likely that they would demand a higher compensation if the real per capita income increases. As both the compensation
and the discount rate are related to economic growth, the overall discount rate might be close to zero. It is shown that the
overall discount rate might even be negative considering that the required compensation could increase (even to infinite)
if natural assets remain scarce, whereas the utility of consumption diminishes with increasing income. Uncertainties could
justify both positive and negative discount rates. Since the relationship between uncertainties and the magnitude of damage
is generally not exponential, we recommend to model changes in the magnitude of damage in scenario analysis instead of considering
it in discounting (which requires an exponential function of time in the case of a constant discount rate). We investigated
the influence of discounting in a case study of heavy metal emissions from slag landfills. It could be shown that even small
discount rates of less than 1 % lead to a significant reduction of the impact score, whereas negative discount rates inflate
the results.
Conclusions and Recommendations Discounting is only applicable when temporally differentiated data is available. In some cases, such a temporal differentiation
is necessary to take sound decisions, especially when long emission periods are involved. An example is the disposal of nuclear
or heavy metal-containing waste. In these cases, the results might completely depend on the discount rate. This paper helps
to structure arguments and thus to support the decision about whether or not discounting should be applied in an LCA. 相似文献
989.
Some authors have reported that as the applied agitation rate increases, the apparent activity of the endoglucanases from Trichoderma reesei towards cotton cellulose increases more markedly than does the apparent activity of the cellobiohydrolases. This suggests that the quality of cellulase finishing effects on cellulosic textiles may be machine-type dependent. The present work using total crude, endoglucanase-rich and cellobiohydrolase-rich cellulases from T. reesei confirmed that the final properties of woven, cotton fabrics treated under realistic processing conditions in a jet machine, were measurably and perceivably different from those of the same fabrics, treated using the same processing conditions of temperature, time, pH, enzyme concentration and fabric to liquor ratio, but in a winch machine. The results are interpreted in terms of the effects of agitation rate on the adsorption–desorption behaviour of the T. reesei endoglucanases and cellobiohydrolases. 相似文献
990.
P. Proietti 《Photosynthetica》2001,38(3):397-402
The effect on traits of photosynthesis and water relations of assimilate demand was studied in olive tree that has strong
alternate bearing. The diurnal and seasonal leaf gas exchanges, area dry mass, and saccharide and chlorophyll (Chl) contents
were measured by comparing shoots with fruit of "on-trees" (heavy fruit load) with shoots without fruit on both "on-trees"
and "off-trees" (light fruit load). In spite of large seasonal and diurnal differences, leaf net photosynthetic rate (P
N), stomatal conductance (g
s), sub-stomatal CO2 concentration (C
1), transpiration rate (E), and respiration rate (R
D) were not significantly influenced by fruit load or by the presence or absence of fruit on the shoot. An only exception was
at the beginning of July when the one-year-old leaves on shoots with fruit had slightly higher P
N and E than leaves on shoots without fruit. Water content, Chl and saccharide contents, and area dry mass of the leaf were not substantially
influenced by the presence/absence of fruit on the shoot or fruit load. Hence the sink demand, associated with fruit growth,
did not improve leaf photosynthetic efficiency in olive.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献