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11.
Summary The effect of artificial acid rain on the reproduction and survival of the aphid Euceraphis betulae on silver birch was studied in Turku, southern Finland. Eight bioassays were done during 1984–1986. In four of the bioassays the aphids produced 40% to over 100% more progeny on birches watered with dilute sulphuric acid (pH 3.5) than on control trees. In four other cases the performance of aphids did not differ between the treatments. An index of aphid reproduction pooled over the whole study was significantly higher on acid-treated than on control birches. The reproduction of aphids on acid-treated birches was enhanced when precipitation was below long term average, suggesting an interaction between the stress caused by acid treatment and dry periods. 相似文献
12.
The activity of the enzymes 5'-nucleotidase (EC 3.1.3.5), adenosine nucleosidase (EC 3.2.2.7), adenine phosphoribosyl transferase (EC 2.4.2.7) and acid phosphatase (EC 3.1.3.2) was determined in sections of tomato plant ( Lycopersicon esculentum Mill. cv. Bellina). The distribution of the enzymes changed markedly during development and a role for these enzymes in cytokinin metabolism is suggested. 相似文献
13.
B. S. C. Leadbeater 《Protoplasma》1987,136(1):1-15
Summary InStephanoeca diplocostata microtubules are located in four positions namely: within the flagellar axoneme; just beneath the plasmalemma; associated with the silica deposition vesicles (SDVs) during early stages of costal strip deposition; and in the mitotic spindle. At the anterior end of the cell the 50–60 peripheral microtubules, which are organized more or less parallel to the long axis of the cell, converge around the base of the emergent flagellum. A short second flagellar base is positioned between the nucleus and the base of the emergent flagellum. Developing costal strips are located individually within SDVs in the peripheral cytoplasm. During the early stages of silica deposition each SDV is curved and subtended longitudinally on its concave side by two microtubules. When a costal strip has achieved sufficient rigidity to withstand bending the SDV-associated microtubules are depolymerized. Treatment of exponentially growing cells with sublethal concentrations of microtubule poisons, such as colchicine, podophyllotoxin, griseofulvin andVinca alkaloids depresses growth. Treatment with these drugs also affects the length and morphology of developing costal strips perhaps by interfering with the shaping and supporting functions of SDV-associated microtubules. Instead of being long and crescentic with a standard radius of curvature, costal strips of treated cells are usually short and misshapen, with irregular bends. After drug treatment, juveniles produced as a result of cell division do not develop flagella but can still assemble a lorica although it is usually misshapen. The role of microtubules and microfilaments in lorica production is discussed. 相似文献
14.
Summary Fathead minnows, Pimephales promelas, and yellow perch, Perca flavescens, were transferred from moderately soft Lake Superior water (hardness 45mg/l as CaCO3) to very soft diluted Lake Superior water (hardness 4.5mg/l). Sulfuric acid was added in some treatments by means of a multichannel diluter. In very soft water, chloride cells proliferated in the gills, especially in the epithelium of the secondary lamellae. When exposed to acid, chloride cells were damaged and less abundant in the secondary lamellae, and blood osmolality was reduced at pH 5.0 (x = 188 mOsm/kg, 9 days exposure; normal 280 mOsm/kg) for the minnows and pH 4.1 (x = 218 mOsm/kg, 58 days exposure; normal 329 mOsm/kg) for the perch. Certain chloride cells which form gland-like clusters in the primary lamellae of perch gills showed little damage even at pH 4.1. The present study supports the view that chloride cells proliferate in very soft fresh water to help maintain ionic balances, and that damage to these cells in acidified soft water may be related to diminished ionoregulatory capacity. The greater acid tolerance of chloride cells of, and the higher blood osmolality maintained by, perch could help to explain the greater tolerance of this species to low pH. In some cases, a species' ability to acclimate to very soft water and acidified soft water may depend upon the number, distribution, and physiology of its chloride cells. 相似文献
15.
The pH of weak-acid solutions is controlled by acid concentration (HA + A–), the degree of acid dissociation (A–/HA), and the strength of the acids present (pKa). We developed an empirical approach that allows the relative importance of each of these factors to be estimated for soils. This empirical model was applied to soils collected from an old-field plantation of loblolly pine (Pinus taeda L.) at 5 and 25 years of age. During this period, soil pH dropped by 0.3 to 0.8 units, and extractable calcium, magnesium and potassium declined by 20 to 80%. The empirical model indicates that the decline in pH resulted largely from the reduction in base saturation of the exchange complex. However, the average acid strength of the exchange complex decreased during the 20 years, preventing a greater decline of perhaps 0.1 to 0.2 units in the observed pH. The rate of decrease in the acid neutralizing capacity to pH 3.5 was about 1.3 kmolc/ha annually, while the increase in base neutralizing capacity was about 2.7 and 1.6 kmolc/ha annually to pH 5.5 and 8.2, respectively. Extractable alkali and alkaline earth cations declined by about 2.2 kmolc/ha annually, matched by the rate of increase in aluminium. These changes demonstrated the dynamic nature of poorly buffered soils, and indicated that changes in soil acidity may be expected over a period of decades (especially following changes in land-use). 相似文献
16.
In this paper we demonstrate that the cytosofic low-Mr acid phosphatase purified from bovine liver has phosphotyrosine protein phosphatase acitivity on 32P-autophosphorylated epidermal growth factor (EGF) receptor. This activity was significantly inhibited by orthovanadate and p-hydroxymercuribenzoate; the latter result indicates that free sulfhydryl groups are required for phosphotyrosine phosphatase activity. The enzyme was active in a broad pH range, with maximum activity between pH 5.5 and 7.5. The apparent Km for 32P-EGF receptor dephosphorylation was 4 nM. The enzyme appeared to be specific for phosphotyrosine in that it dephosphorylated the autophosphorylated EGF receptor and L-phosphotyrosine, but not 32P-Ser-casein, L-phosphoserine or L-phosphothreonine. These data suggest that the cytosolic low-Mr acid phosphatase might play a regulatory role in EGF receptor-dependent transmembrane signalling. 相似文献
17.
Summary Flowering cultivars of Hibiscus rosa-sinensis L. were either cross-pollinated or self-pollinated. Fruit set was observed on 52% of the cross-fertilized flowers, while only 4.6% of the self-fertilized flowers were not abscised. Once during fruit and seed growth, the subtending leaf was exposed to 14CO2, and translocation of labelled photoassimilate was recorded by macro- and microautoradiography. Phloem transport into the raphe occurred in both fruits with fertilized and fruits with non-fertilized ovules. Since empty ovules showed some sink strength, it is assumed that growth of vegetative seed-tissue signalizes the retardation of completion of the abscission process. During fruit growth a considerable amount of starch is deposited in the distal layer of the abscission zone. Part of this starch is consumed during growth of cross-fertilized fruits. 相似文献
18.
Isamu Tanaka Akio Horie Joji Haratake Yasushi Kodama Kenzaburo Tsuchiya 《Biological trace element research》1988,16(1):19-26
There are few inhalation studies of nickel carcinogenesis. In this study, Wistar male rats were exposed to green nickel oxide
(NiO(G)) aerosols (mass median aerodynamic diameter, 0.6 μm) for 7 h/d, 5 d/wk for up to 12 mo. The average exposure concentration
was controlled at 0.3 and 1.2 mg/m3 during the exposure. For histopathological examination and measurement of the nickel concentration in rat organs, the rats
were sacrificed at 3, 6, and 12 mo of exposure and 8 mo clearance period following 12 mo of exposure.
The nickel content in rat lungs that was observed up to 2.6 mg after 12 mo exposure, was proportional to the exposure concentration
during the exposure. The clearance of the nickel from the lungs was very slow and the biological half time was determined
7.7 mo.
Although the rats were exposed continuously to NiO(G), for 12 mo and kept for 8 mo clearance period, there were no malignant
tumors in any of the exposed animals. 相似文献
19.
Sources,fates, and impacts of nitrogen inputs to terrestrial ecosystems: review and synthesis 总被引:1,自引:0,他引:1
The relative importance of nitrogen inputs from atmospheric deposition and biological fixation is reviewed in a number of diverse, non-agricultural terrestrial ecosystems. Bulk precipitation inputs of N (l–l2 kg N ha–1 yr–1) are the same order of magnitude as, or frequently larger than, the usual range of inputs from nonsymbiotic fixation (< 1=" –=" 5=" kg=" n=">–1 yr–1), especially in areas influenced by industrial activity. Bulk precipitation measurements may underestimate total atmospheric deposition by 30–40% because they generally do not include all forms of wet and dry deposition. Symbiotic fixation generally ranges from 10–160 kg N ha–1 yr–1) in ecosystems where N-fixing species are present during early successional stages, and may exceed the range under unusual conditions.Rates of both symbiotic and nonsymbiotic fixation appear to be greater during early successional stages of forest development, where they have major impacts on nitrogen dynamics and ecosystem productivity. Fates and impacts of these nitrogen inputs are important considerations that are inadequately understood. These input processes are highly variable in space and time, and few sites have adequate comparative information on both nitrogen deposition and fixation.
相似文献
| - more intensive studies of total atmospheric deposition, especially of dry deposition, are needed over a wide range of ecosystems; |
| - additional studies of symbiotic fixation are needed that carefully quantify variation over space and time, examine more factors regulating fixation, and focus upon the availability of N and its effects upon productivity and other nutrient cycling processes; |
| - process-level studies of associative N-fixation should be conducted over a range of ecosystems to determine the universal importance of rhizosphere fixation; |
| - further examination of the role of free-living fixation in wood decomposition and soil organic matter genesis is needed, with attention upon spatial and temporal variation; and |
| - investigations of long-term biogeochemical impacts of these inputs must be integrated with process-level studies using modern modelling techniques. |
20.
Hasenstein, K. H. and Evans, M. L. 1988. The influence of calcium and pH on growth in primary roots of Zea mays. - Physiol. Plant. 72: 466–470.
We investigated the interaction of Ca2+ and pH on root elongation in Zea mays L. cv. B73 × Missouri 17 and cv. Merit. Seedlings were raised to contain high levels of Ca2+ (HC, imbibed and raised in 10 m M CaCl2 ) or low levels of Ca2+ (LC, imbibed and raised in distilled water). In HC roots, lowering the pH (5 m M MES/Tris) from 6.5 to 4.5 resulted in strong, long-lasting growth promotion. Surprisingly, increasing the pH from 6.5 to 8.5 also resulted in strong growth promotion. In LC roots acidification of the medium (pH 6.5 to 4.5) resulted in transient growth stimulation followed by a gradual decline in the growth rate toward zero. Exposure of LC roots to high pH (pH shift from 6.5 to 8.5) also promoted growth. Addition of EGTA resulted in strong growth promotion in both LC and HC roots. The ability of EGTA to stimulate growth appeared not to be related to H+ release from EGTA upon Ca2+ chelation since, 1) LC roots showed a strong and prolonged response to EGTA, but only a transient response to acid pH, and 2) promotion of growth by EGTA was observed in strongly buffered solutions. We also examined the pH dependence of the release of 45 Ca2+ from roots of 3-day-old seedlings grown from grains imbibed in 45 Ca2+ . Release of 45 Ca2+ from the root into agar blocks placed on the root surface was greater the more acidic the pH of the blocks. The results indicate that Ca2+ may be necessary for the acid growth response in roots. 相似文献
We investigated the interaction of Ca