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41.
Maize (Zea mays L.) and ricebean (Vigna umbellata [Thumb.] Ohwi and Ohashi) were grown in intercrop and monoculture on Tropaqualf soils under rainfed conditions in Northern
Thailand yearly from 1983 to 1986. De Wit's replacement design was used to compare intercrops and monocultures with a constant
plant density equivalent to 80 000 maize or 160 000 ricebean plants ha−1. Combined nitrogen was applied at varying levels to 200 kg N ha−1. In the final two seasons the intercrop ratio of maize: ricebean was also varied. At the time of maize maturity intercrops
yielded upt 49 kg ha−1 more N in the above ground plant parts than the best monoculture. Dry matter, grain and nitrogen yield of maize and ricebean
in intercrop relative to their monoculture yields (RY, relative yield) were significantly greater than their respective share
of the plant population. Relative yield totals (RYT) for grain, dry matter and nitrogen were always greater than 1.
Nitrogen uptake per maize plant increased with progressive replacement of maize by ricebean plants. This increase was similar
to that obtained by applying combined N. Available soil nitrogen tended to decrease with increasing maize:ricebean ratio.
Increasing the maize:ricebean ratio increased the % of nitrogen derived from fixation in ricebean, the increase being equivalent
to that obtained by decreasing combined nitrogen application. Approximately the same amount of fertilizer and soil nitrogen
was taken up by maize plus ricebean in intercrop as the maize monoculture. The results suggest that the improved nitrogen
economy of the intercrop resulted from the strong competitiveness of maize in the use of mineral nitrogen and the enhancement
of nitrogen fixation in intercropped ricebean which made it less dependent on the depleted pool of soil nitrogen. 相似文献
42.
R. Chima Wokocha 《Plant and Soil》1988,106(1):146-148
Populations of viable sclerotia ofSclerotium rolfsii were highest in soil in a field in which tomato was planted for three successive years before sampling and in one in which
tomato followed groundnut in the 2 years prior to this study. The lowest sclerotial numbers were recorded in fields in which
groundnut followed maize or in which maize or sorghum was the last crop before sampling. 相似文献
43.
用杀虫双大粒剂防治水稻二化螟和三化螟的研究 总被引:2,自引:0,他引:2
本文报告一种防治水稻螟虫的杀虫双新剂型和使用效果.含有效成份5%的杀虫双大粒剂,每公斤含2000粒左右,在每亩1—1.25公斤的用量下,药效显著优于六六六、呋喃丹及杀虫脒等残留和高毒性农药.处理一亩田只需数分钟.在七个县和四个农场共266440亩稻田的示范试验中,防治效果达84.5—100%.杀虫双在田水中扩散迅速,24小时内即可扩散分布到全田.持效期较长,可达两周之久.但在蝗虫已蛀入稻茎后施用大粒剂,有效施药期只有3—4天.本文对杀虫双大粒剂的使用技术进行了经济效益、社会效益和生态效益方面的评价. 相似文献
44.
Four aerial survey projects were conducted between 1977 and 1986 to determine the abundance, density and distribution of West Indian manatees (Trichechus manatus), in the northern Banana River, Kennedy Space Center, Florida. Manatee density and distribution within selected portions of the 78.5 km2 study area were determined. Peak numbers of manatees occurred in spring of each year. The maximum counts increased from 56 in 1978 to 297 in 1986. Manatee abundance was lowest in the winter of each year. Mean density per flight increased from 0.52 manatees/km2 in 1977–78 to 2.73/km2 in 1984–86. This increase may reflect increases in the east coast population or shifts in the population distribution. Distributional changes were observed in the study area through time, with a lower percentage of manatees occurring in industrial areas and a correspondingly higher percentage of manatees in nonindustrial areas by 1985. 相似文献
45.
Construction of a new universal vector for insertional mutagenesis by homologous recombination 总被引:1,自引:0,他引:1
We describe here the construction of a vector (pSSC-9) which can be used for the insertional mutagenesis of any gene for which genomic sequences have been cloned. This vector contains a neomycin-resistance-encoding gene (neoR) which is driven by a modified thymidine kinase (tk) promoter for positive selection. Flanking neoR are two tk genes driven by their own promoters for negative selection of nonhomologous insertions. The neoR and tk cassettes are separated by four unique cloning sites on the right-hand side of the neoR cassette and three unique sites on the left-hand side. The vector also includes two SfiI sites, one on each side of the tk cassettes, for the excision of the cloned genomic DNA fragments along with the selectable markers. Electroporation of pSSC-9 into mouse embryonic stem (ES) cells and cultured diploid mouse adrenal Y-1 cells conferred resistance to G418 and sensitivity to ganciclovir in both cell lines. These results illustrate the expression of the positive and negative selectable markers in two different cell lines and thus suggest that the vector could be used in ES cells, as well as in cultured somatic cells. 相似文献
46.
Victor N. Mikheev Dmitry S. Pavlov Daria Pakulska 《Environmental Biology of Fishes》1992,35(4):351-360
Synopsis Swimming speed and swimming path of goldfish and tetra larvae were studied in aquaria containing food patches composed of decapsulated cysts and immobilized nauplii of Artemia salina or sparsely distributed prey. The mean swimming speed of starved larvae in the medium without food was about four times higher than the speed of larvae feeding in a patch. Satiated larvae swam about 1.5 times slower than hungry fish. Consumption of single prey items by starved larvae caused the following sequence of swimming responses: handling pause (cessation of swimming), slow swimming in a restricted area, and fast swimming (approximately twice as fast as hungry larvae before encountering food) accompanied by a widening of the area searched (area increased searching). Mean swimming speed was constant over a broad range (101–103 ind·1–1 of food density, although at extreme (high or low) values of food density it depended on swimming responses of the predator. Frequency of visits to the different parts of the aquarium strongly depended on encounters of hungry fish with food particles or patches. 相似文献
47.
It has been known for several decades that cultured murine cells undergo a defined series of changes, i.e., anin vitro evolution, which includes crisis, spontaneous transformation (immortalization), aneuploidy, and spontaneous neoplastic transformation. These changes have been shown to be caused by thein vitro environment rather than an inherent instability of the murine phenotype or genotype. Serum amine oxidases were recently identified as a predominant cause of crisis. These enzymes generate hydrogen peroxide from polyamine substrates that enter the extracellular milieu. This finding implicates free-radical toxicity as the underlying cause ofin vitro evolution. We propose an oxyradical hypothesis to explain each of the stages ofin vitro evolution and discuss its significance for cytotechnology and long-term cultivation of mammalian cell types.ORR, CDER, FDA Mod-1, Room 2023, 8301 Muirkirk Road, Laurel MD 20708, USA 相似文献
48.
Donna Robbins Colin A. Chapman Richard W. Wrangham 《Primates; journal of primatology》1991,32(3):301-305
Gibbons and spider monkeys have similar diets, body size, and locomotor patterns. They are therefore expected to be subject
to similar socioecological rules. However their grouping patterns differ. Gibbons live in small stable groups, whereas spider
monkey form unstable sub-groups that vary from small to large during different seasons. If similar principles apply to the
two species, food abundance should vary more for spider monkeys than for gibbons; food density should be similar for the two
species when spider monkey sub-groups are the same size as gibbon groups; and the highest level of food abundance should be
higher for spider monkeys than for gibbons. These predictions are upheld for a comparison of particular populations ofHylobates muelleri andAteles geoffroyi. 相似文献
49.
A new tissue isolation technique was used to create intact midgut epithelial wholemounts from three Trichoplusia ni (Lepidoptera: Noctuidae) larval instars. The protease, dispase, removed the basal lamina and associated connective tissue and allowed for high resolution light microscopy of entire epithelia. Columnar, goblet, differentiating, and stem cells were characterized by double fluorescent labelling of f-actin and nuclei. A comparison of cell populations by digital image analysis revealed significant regional and temporal changes in the density and number of differentiating and stem cells. Growth of the midgut epithelium from third to fourth instar, and from fourth to fifth instar, was accomplished by both cell differentiation and cell division. Cell division however, was greatly reduced from fourth to fifth instar with a concomitant sharp decrease in the stem cell population. 相似文献
50.
The spatial distribution and abundance of the brine shrimp, Artemia monica, in Mono Lake, California were determined during 1982 and 1983. Peak abundances of shrimp occur in midsummer and reach densities of 15–17 individuals l-1 in the nearshore regions and 6–8 individuals 1-1 in the pelagic region. The brine shrimp were non-uniformly distributed both vertically and horizontally. The coefficient of variation in shrimp abundance among stations within the nearshore region was similar to that found in the pelagic region. On two of the nine dates, nearshore densities were 3 to 4 times greater than those in the pelagic zone, and on average the brine shrimp appear to be slightly over-dispersed to the nearshore region. However, including nearshore abundances in lakewide estimates will usually result in a change of less than a 10%. 相似文献