全文获取类型
收费全文 | 752109篇 |
免费 | 80863篇 |
国内免费 | 511篇 |
专业分类
833483篇 |
出版年
2016年 | 7530篇 |
2015年 | 10483篇 |
2014年 | 12393篇 |
2013年 | 18309篇 |
2012年 | 19941篇 |
2011年 | 20517篇 |
2010年 | 13848篇 |
2009年 | 12824篇 |
2008年 | 18310篇 |
2007年 | 19335篇 |
2006年 | 18260篇 |
2005年 | 17638篇 |
2004年 | 17586篇 |
2003年 | 17038篇 |
2002年 | 16837篇 |
2001年 | 32124篇 |
2000年 | 32627篇 |
1999年 | 26204篇 |
1998年 | 9054篇 |
1997年 | 9546篇 |
1996年 | 8995篇 |
1995年 | 8524篇 |
1994年 | 8377篇 |
1993年 | 8372篇 |
1992年 | 22040篇 |
1991年 | 21562篇 |
1990年 | 21359篇 |
1989年 | 20840篇 |
1988年 | 19653篇 |
1987年 | 18560篇 |
1986年 | 17560篇 |
1985年 | 17960篇 |
1984年 | 14931篇 |
1983年 | 12857篇 |
1982年 | 10055篇 |
1981年 | 9181篇 |
1980年 | 8478篇 |
1979年 | 14407篇 |
1978年 | 11476篇 |
1977年 | 10652篇 |
1976年 | 10126篇 |
1975年 | 11179篇 |
1974年 | 12278篇 |
1973年 | 12079篇 |
1972年 | 11190篇 |
1971年 | 10163篇 |
1970年 | 8806篇 |
1969年 | 8810篇 |
1968年 | 8105篇 |
1967年 | 6934篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
962.
Richard G. Condon 《Human ecology: an interdisciplinary journal》1991,19(3):287-321
Birth seasonally at high latitudes is a complex phenomenon which is undoubtedly affected by a subtle interaction between environmental rhythmicity (most notably in photoperiod and temperature) and cultural adaption. There is intriguing evidence that human gonadotrophic activity (and hence fertility) may be affected by seasonal fluctuations in light intensity and duration. Nevertheless, cultural factors are important insofar as they mediate between environmental rhythmicity and human fertility/birth patterns. This article examines the distribution of births over several decades in an Inuit community located 300 miles north of the Arctic Circle. Several shifts in birth seasonality are noted, the most significant of which is a dramatic shift from pronounced seasonality in the 1970s to non-seasonality in the 1980s. Longitudinal ethnographic fieldwork has allowed an examination of social and economic changes accounting for the rather sudden disappearance of birth seasonality. These include increasing reliance upon wage employment and social assistance, decreased dependence upon subsistence hunting and trapping, changing attitudes on the part of young people entering their prime reproductive years, and the introduction of television, radio, and southern-style recreational activities. 相似文献
963.
Effect of simultaneous application of heat and pressure on the survival of bacterial spores 总被引:1,自引:1,他引:0
C.G. MALLIDIS AND D. DRIZOU. 1991. The effect of simultaneous application of moderate hydrostatic pressure (10–300 atm) and heat on the survival of the Bacillus stearothermophilus spores in a flow-through system was investigated. A high heterogeneity of the sensitization of spores to heat by pressure was found. A higher degree of reduction of heat resistance was observed at the low than at the high temperatures tested. The simultaneous application of moderate pressure and heat can not be applied for the preservation of liquid foods due to the extreme heterogeneity of spore sensitization to heat by pressure. 相似文献
964.
In the red howler monkey, Alouatta seniculus stramineus (2n = 47, 48, or 49), variations in diploid chromosome number are due to different numbers of microchromosomes. Males exhibit a Y;autosome translocation involving the short arm of an individual biarmed autosome. Consequently, the sex-chromosome constitution in the male is X1X2Y1Y2, with X1 representing the original X chromosome, X2 the biarmed autosome (No. 7), Y1 the Y;7p translocation product, and Y2 the acrocentric homolog of 7q. In the first meiotic division, a quadrivalent with a chain configuration can be observed in spermatocytes. Females have an X1X1X2X2 sex-chromosome constitution. Chromosome heteromorphisms were observed in pair 13, due to a pericentric inversion, and pair 19, due to the presence of constitutive heterochromatin. Microchromosomes, which varied in number between individuals, were also heterochromatic. NOR-staining was observed at two separate sites on a single chromosome pair (No. 10). A comparison of A.s. stramineus with A.s. macconnelli shows that these two subspecies have identical diploid chromosome numbers (47, 48, or 49), again due to a varying number of microchromosomes, and that they share a similar sex-chromosome constitution. Their karyotypes, however, are not identical, but can be derived from each other by a reciprocal translocation. Further comparisons with other A. seniculus subspecies reported in the literature indicate that this taxon is not karyologically uniform and that substantial chromosome shuffling has occurred between populations that have been considered to be subspecies by taxonomic criteria based on their morphometric attributes. 相似文献
965.
T Tobe S Minoshima S Yamase N H Choi M Tomita N Shimizu 《Cytogenetics and cell genetics》1991,57(4):193-195
SP-40,40 is a serum glycoprotein consisting of two different subunits (alpha and beta) assembled into a dimer by disulfide bonds. Northern blot hybridization, using total RNA from several cell lines, showed that SP-40,40 is expressed in glioblastoma and testicular tumor cells, as well as hepatoma cells. Spot blot hybridization of flow-sorted human chromosomes, using a SP-40,40 cDNA fragment as a probe, localized the gene for SP-40,40 to human chromosome 8. This gene has been given the designation CLI, for complement lysis inhibitor, by the Human Gene Nomenclature Committee. 相似文献
966.
967.
968.
Abundance and distribution of cod Gadus morhua in various size intervals and age groups between 2000 and 2005 were followed in coastal trawl surveys. In spite of a reduction in fishing pressure in recent years and high cod recruitment in the Skagerrak region in 2001 and 2003, no recovery could be evidenced. The survey data clearly showed that low cod density areas were not recolonized, even though abundance of juvenile cod remained high for about a year after the recruitment episodes. Increased abundance of fish >400 mm total length was only discernible at some scattered locations where other studies also have suggested local populations still to be present. The intermittent high recruitment has been linked to an inflow of egg and larvae from the North Sea, a theory which also has gained support from genetic studies. It was thus argued that the disappearance of the juvenile cod from the inshore is an effect of a migratory behaviour; the fish of offshore origin eventually leave the coast for the open Skagerrak or the North Sea. These findings support a view on cod populations as essentially behavioural entities, whereas dispersal of early life stages may be less important as a structuring mechanism. 相似文献
969.
970.