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61.
N. Bouchriti A. El Marrakchi A. Fahim S. M. Goyal 《World journal of microbiology & biotechnology》1992,8(5):546-549
A 3-year bacteriological survey of an oyster-growing area in Morocco, where the Japanese oyster (Crassostrea gigas) is grown, showed that the contamination of this lagunar ecosystem was not continuous but intermittent and that animal manure and human recreational activities were important sources of pollution. The major source of contamination was of animal origin, except during the summer, when human contamination prevailed. 相似文献
62.
用相关和回归处理方法,研究了8条正常狗咽喉部高频喷射通气时,调节驱动压、呼吸比和频率对喷气量、吸入气氧浓度、动脉血气及气道内压的作用。结果显示,驱动压和呼吸此对各观察指标几乎有同等重要的作用,频率的影响很小,喷气量与吸入气氧浓度、动脉血气、气道内压间存在显著的正相关关系。说明调节参数的意义主要在于改变了喷气量。 相似文献
63.
Abstract.
- 1 Multiple mating and its effect on reproductive performance of female Epiphyas postvittana (Walker) moths were studied under controlled conditions.
- 2 The age at which the moths mated for the first time ranged from the first to the tenth day after emergence, but 71% of first matings were during the first 3 days.
- 3 The majority (63%) of females had one or two spermatophores in the bursa copulatrix. Some (24%) were found with three to five spermatophores, whereas no successful mating occurred among 13% of individuals. The number of matings was partly dependent on the number of mates available to the female. Between the range of sex ratios of one male to one female and four males to one female maximal mating success occurred at the ratio of three males to one female.
- 4 Virgin females were capable of egg-laying, but mating stimulated and accelerated oviposition. Mated individuals laid twice as many eggs as unmated ones.
- 5 The level of copulatory activity did not influence the longevity of females irrespective of the number of males available to them.
- 6 Sex ratios with greater than one male to a female improved the reproductive success by marginally increasing fecundity and fertility.
- 7 It is concluded that multiple mating would enhance population growth, and is of particular benefit to populations with a preponderance of females, as is known to occur naturally in this species.
64.
Synopsis The very sparse data that are available on the abundance, population structure and biology of the coelacanth Latimeria chalumnae off Grand Comoro are summarised, and some simple numerical analyses are carried out to explore certain aspects of the population dynamics, particularly the age-profile of the population. The object has not been to provide estimates of key demographic parameters, such as mortality rates, but to propose various scenarios that are useful for comparison with real data as they become available. The analysis also makes it possible to reach some preliminary conclusions that are relevant to the management of the coelacanth population. For instance, it appears that the catch rate of coelacanths by artisanal fishermen may have a negligible effect on coelacanth survivorship, and it is more likely that population size and structure are determined by natural mortality rates and birth rates. It is suggested that predation is the main cause of natural mortality and that the main predators of coelacanths are likely to be large sharks. Interference with the traditional patterns of the Comoran artisanal fishery may threaten the coelacanth. Several important gaps in our knowledge of coelacanth demography are identified. 相似文献
65.
On nonparametric discrimination using density differences 总被引:2,自引:0,他引:2
66.
67.
68.
Summary A re-examination of earlier NPK fertilization experiments in Douglas fir stands on sandy soils shows the effects of high nitrogen
input by air pollution during the last 10–15 years on plant nutrition at these sites. In 1960, experimental plots showed a
positive growth reaction to nitrogen, phosphorus, and potassium fertilization. All suffered from severe phosphorus deficiency
in 1984, low phosphorus in the needles was invariably accompanied by a high nitrogen content, with all N/P ratios between
20 and 30. The same conclusion emerges from an independent investigation of nutrient status of a selection of Douglas fir
stands. Hence, if stand productivity and a balanced nutrient status of the trees is to be maintained, the increase in atmospheric
input of nitrogen calls for supplementary fertilization. Given the current N/P ratios in the needles, a positive growth response
to phosphorus fertilization is to be expected. 相似文献
69.
Soil respiration of Alaskan tundra at elevated atmospheric carbon dioxide concentrations 总被引:3,自引:0,他引:3
Summary CO2 efflux from tussock tundra in Alaska that had been exposed to elevated CO2 for 2.5 growing seasons was measured to assess the effect of long- and short-term CO2 enrichment on soil respiration. Long-term treatments were: 348, 514, and 683 μll−1 CO2 and 680 μll−1 CO2+4°C above ambient. Measurements were made at 5 CO2 concentrations between 87 and 680 μll−1 CO2. Neither long- or short-term CO2 enrichment significantly affected soil CO2 efflux. Tundra developed at elevated temperature and 680 μll−1 CO2 had slightly higher, but not statistically different, mean respiration rates compared to untreated tundra and to tundra under
CO2 control alone. 相似文献
70.
Summary Non-symbiotic heterotrophic N2 fixation in coniferous bark litter was investigated with the acetylene reduction assay under aerobic and anaerobic conditions. The litter studied was composed essentially of bark, of pH 5 and a C/N ratio of 101; the ratio of available C to available N, which governs N2 fixation, was considerably higher. The rate of N2 fixation was estimated as 2.5–4.4 g N. g–1 dry wt. day–1. Nitrogenase activity was still evident after seven months of incubation under aerobic conditions. The N2-ase activity was O2 dependent: under anaerobic conditions no N2-ase activity was found unless a fermentable C source was added. The importance of N2 fixation in N-poor litter for the maintenance of soil fertility is emphasized. 相似文献