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941.
Root growth and architecture are important for phosphorus acquisition due to the relative immobility of P in the soil. Fractal
geometry is a potential new approach to the analysis of root architecture. Substantial genetic variation in root growth and
architecture has been observed in common bean. Common bean (Phaseolus vulgaris L.) genotypes with contrasting root architecture
were grown under moderate and low P conditions in a field experiment. Linear and planar fractal dimension were measured by
tracing root intercepts with vertical planes. Linear fractal dimension increased over time in efficient genotypes, but remained
fairly constant over time in inefficient genotypes. Planar fractal dimension increased over time for all genotypes, but was
higher in efficient than inefficient genotypes at the end of the experiment. Planar fractal dimension of medium P plants was
found to correlate with shoot P content indicating fractal dimension to be a possible indicator for root P uptake. The increasing
fractal dimension over time indicates that fractal analysis is a sensitive measure of root branching intensity. A less destructive
method for acquisition of data that allows for continuous analysis of fractal geometry and thereby screening for more P efficient
genotypes in the field is suggested. This method will allow the researcher to conduct fractal analysis and still complete
field trials with final yield evaluation. 相似文献
942.
B. Desplanque P. Boudry K. Broomberg P. Saumitou-Laprade J. Cuguen H. Van Dijk 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1999,98(8):1194-1201
Beets belonging to the species Beta vulgaris L. can be found in crop, wild and weedy forms, all of which are interfertile. We studied the intra-specific genetic relationships
of about 300 individuals from 54 populations of various French geographic origins using nuclear molecular markers (five single-copy
RFLP loci and one microsatellite locus). The patterns of diversity were congruent for both types of markers. Genetic diversity
in wild beets appeared to be high, both in term of allele number and observed heterozygosity, whereas the narrowness of the
cultivated-beet gene pool was confirmed. Genetic distances between all forms showed that weed beets in northern France are
intermediates between sugar beet and inland wild beets in south-western France. This analysis allowed us to infer the paternal
origin of weed beets and furthermore, is in agreement with a previous study which focused on their maternal origin: weed beet
infesting sugar-beet fields originated from accidental and recurrent hybridization between cultivated lines and ruderal inland
wild beets during the production of commercial seeds in south-western France. Inland wild beets are genetically close to Mediterranean
coastal wild beets, but differ from other coastal forms (from Biscay, Brittany and northern France). The study of gene flow
in the beet complex contributes to the risk assessment of transgenic beets.
Received: 8 June 1998 / Accepted: 8 October 1998 相似文献
943.
Compensatory responses of caterpillars fed low quality food include increased consumption and utilization of essential nutrients. Information about an insect's responses to nutritional challenges from their host plants could benefit weed biological control efforts in the selection and establishment of new agents. The target weed, Pistia stratiotes L. (Araceae) is a floating aquatic plant that has relatively low nitrogen levels which are further diluted with high water content. Efforts to establish the insect Spodoptera pectinicornis (Hampson) (Lepidoptera: Noctuidae) for biological control of P. stratiotes could benefit by examining the nutritional responses of a similar widely established lepidopteran species, Samea multiplicalis (Guenèe) (Lepidoptera: Pyralidae). Larvae of this species were fed leaves of P. stratiotes plants that had been fertilized (NPK) at high and low rates. The leaves of the fertilized plants had a 4.3-fold increase in nitrogen (dry weight) and a 1.6-fold increase in water content. The results suggest that no compensatory increases occurred in larvae fed leaves from the low fertilized plants as no changes were found in fresh mass consumption or nitrogen utilization efficiency. Consequently, development time from second-third instars to pupation was delayed about 3 days compared with larvae fed the high nitrogen leaves. Furthermore, consumption of nitrogen was only 30% and its accumulation into larval tissues was only 60% compared with the larvae fed the high fertilized leaves. The resulting larvae had both a final biomass and a growth rate that were reduced by 40%. Regardless of plant fertilizer level, the larvae fed at a rate 5–10 times greater than that of similar lepidopteran species consuming either low or high quality diets, suggesting that the S. multiplicalis larvae may be functioning at their biological limit for ingesting food. 相似文献
944.
John G Nedruda 《FEMS immunology and medical microbiology》1999,24(2):243-250
Over the last decade animal models have been used extensively to investigate disease processes and therapy for Helicobacter pylori infections. The H. pylori animal models which have been used in pathogenesis and vaccine studies include the gnotobiotic pig, non-human primates, cats, dogs, and several species of rodents including mice, rats, gerbils and guinea pigs. H. felis infection of mice and H. mustelae infection of ferrets have also been used. Recently, investigators have begun using transgenic mice and gene-targeted 'knock-out' mice to investigate Helicobacter infections. Each of these animal models has distinct advantages and disadvantages which are discussed in this minireview. The choice of an animal model is dictated by factors such as cost and an understanding of how each model will or will not allow fulfillment of experimental objectives. 相似文献
945.
T. Togashi Taizo Motomura Terunobu Ichimura Paul Alan Cox 《Sexual plant reproduction》1999,12(3):158-163
The role of phototactic behavior of gametes was tested experimentally in the slightly anisogamous marine green alga Monostroma angicava Kjellman, and the effect of phototaxis on mating efficiency was discovered. Both male and female gametes showed positive
phototaxis in response to a white light source. In contrast, they did not respond to a red light source. Their swimming velocity
did not differ between these two illuminating light sources. It was, therefore, suggested that the search ability of the gamete
itself might not vary between phototactic and non-phototactic conditions. The number of zygotes formed during the mating process
may be expressed as the product of the number of encounters between male and female gametes and the fraction of encounters
that result in sexual fusion. In this study, with high densities of male and female gametes mixed in test tubes, almost all
minor (fewer in number) gametes fused sexually within 10 min. After dilution of the gamete suspensions by half, mating efficiency
in test tubes illuminated by white light from above was higher than that in dark controls. This suggests that male and female
gametes gathered at the water surface through their positive phototaxis, thus increasing the rate of encounters. Mating efficiency
also decreased if the test tubes were illuminated from above by white light and also shaken. Since negative phototaxis is
clearly shown in planozygotes, we suggest that positive phototaxis of male and female gametes in M. angicava is an adaptive trait for increasing the rate of gametic encounters rather than for the dispersal of zygotes as previously
reported for zoospores of some marine algae.
Received: 12 February 1999 / Revision accepted: 24 May 1999 相似文献
946.
Sang Hyeon Kang Sang Taek Jung Taek Jin Kang Ryang Guk Kim Sang Hyuk Suh Ji Hyoung Woo Eun Yeol Lee Cha Yong Choi 《Biotechnology Techniques》1999,13(11):761-764
Each of the four nucleotides (A, C, G and T) was introduced as the base following the stop codon to investigate the effect of this fourth base on translational termination efficiency during the heterologous expression of human erythropoietin (hEPO) in E. coli. The efficiency of peptide chain termination in E. coli was markedly dependent on the fourth base. The choice of the fourth base was crucial to prevent the expression of undesirable proteins due to the translational infidelity such as frameshifting and stop codon read-through, and translational termination efficiency could be improved with adenosine as the fourth base. 相似文献
947.
948.
Simulated effects of low atmospheric CO2 on structure and composition of North American vegetation at the Last Glacial Maximum 总被引:1,自引:1,他引:0
Cowling Sharon A. 《Global Ecology and Biogeography》1999,8(2):81-93
1. Physiological experiments have indicated that the lower CO2 levels of the last glaciation (200 μmol mol?1) probably reduced plant water-use efficiency (WUE) and that they combined with increased aridity and colder temperatures to alter vegetation structure and composition at the Last Glacial Maximum (LGM). 2. The effects of low CO2 on vegetation structure were investigated using BIOME3 simulations of leaf area index (LAI), and a two-by-two factorial experimental design (modern/LGM CO2, modern/LGM climate).3. Using BIOME3, and a combination of lowered CO2 and simulated LGM climate (from the NCAR-CCM1 model), results in the introduction of additional xeric vegetation types between open woodland and closed-canopy forest along a latitudinal gradient in eastern North America.4. The simulated LAI of LGM vegetation was 25–60% lower in many regions of central and eastern United States relative to modern climate, indicating that glacial vegetation was much more open than today.5. Comparison of factorial simulations show that low atmospheric CO2 has the potential to alter vegetation structure (LAI) to a greater extent than LGM climate.6. If the magnitude of LAI reductions simulated for glacial North America were global, then low atmospheric CO2 may have promoted atmospheric warming and increased aridity, through alteration of rates of water and heat exchange with the atmosphere. 相似文献
949.
谷子叶片光合速率日变化及水分利用效率 总被引:2,自引:0,他引:2
通过降低空气湿度( 从约30 % 减少到5 % ) 、增加CO2 浓度( 从400 μl CO2/L增加到730 μl CO2/L) 、烫叶鞘破坏韧皮部等处理对谷子叶片光合速率日变化和水分利用效率(WUE) 进行了研究, 发现中午光合速率降低与光合产物积累有关; 虽然低大气相对湿度(5 % ) 使光合速率有所降低,但提高了WUE。而烫叶鞘使光合物质积累既抑制了光合速率,又降低了WUE。 相似文献
950.
小麦旗叶发育过程中光合效率的变化 总被引:3,自引:0,他引:3
作物的产量基本上取决于光合机构的大小和效率(Gardner等1985)。要不断提高作物的单位面积产量,除了尽可能满足水、肥供应以获得足够大的光合机构从而接受足够多的光能外,还必须提高叶片的光合效率。这是增加作物产量的一条必由之路。因此,很有必要深入开展光合效率调节控制机理的研究。关于叶片生长发育期间光合速率与叶片结构的变化,已经有大量的研究报告,并且有全面的综合评述(ˇCatsky和ˇSestàk1997)。然而,关于叶片生长发育期间光合效率特别是荧光参数如何变化的报告却很少。虽然ˇCatsky… 相似文献