全文获取类型
收费全文 | 169427篇 |
免费 | 4825篇 |
国内免费 | 820篇 |
专业分类
175072篇 |
出版年
2023年 | 458篇 |
2021年 | 937篇 |
2020年 | 849篇 |
2019年 | 820篇 |
2018年 | 13368篇 |
2017年 | 11999篇 |
2016年 | 9724篇 |
2015年 | 4007篇 |
2014年 | 3791篇 |
2013年 | 4935篇 |
2012年 | 9427篇 |
2011年 | 16998篇 |
2010年 | 14547篇 |
2009年 | 10122篇 |
2008年 | 13134篇 |
2007年 | 14499篇 |
2006年 | 3804篇 |
2005年 | 3491篇 |
2004年 | 3943篇 |
2003年 | 3671篇 |
2002年 | 3207篇 |
2001年 | 2267篇 |
2000年 | 2044篇 |
1999年 | 1471篇 |
1998年 | 638篇 |
1997年 | 466篇 |
1996年 | 514篇 |
1992年 | 927篇 |
1991年 | 866篇 |
1990年 | 823篇 |
1989年 | 896篇 |
1988年 | 746篇 |
1987年 | 764篇 |
1986年 | 688篇 |
1985年 | 749篇 |
1984年 | 628篇 |
1983年 | 561篇 |
1979年 | 669篇 |
1978年 | 489篇 |
1977年 | 489篇 |
1975年 | 589篇 |
1974年 | 623篇 |
1973年 | 595篇 |
1972年 | 793篇 |
1971年 | 765篇 |
1970年 | 541篇 |
1969年 | 610篇 |
1968年 | 573篇 |
1967年 | 479篇 |
1966年 | 466篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Chromosome counts of some Mongolian plants 总被引:1,自引:0,他引:1
The paper gives the chromosome numbers of 45 species from 72 Mongolian localities, belonging to the genera:Amygdalus, Asparagus, Astragalus, Cancrinia, Caragana, Chamaerhodos, Chelidonium, Chesneya, Dianthus, Hypecoum, Lathyrus, Lilium, Oxytropis, Papaver, Potentilla, Schizonepeta, Sibbaldia, Thermopsis, Trifolium, Trigonella, Vicia. Chromosome morphology of three species ofChamaerhodos and taxonomical remarks on some other species are added. A new combinationSibbaldia sericea (Grubov) Soják is proposed. 相似文献
992.
Arnošt Pilát 《Folia Geobotanica》1969,4(3):225-234
The meadow plant communities,Arrhenatheretum elatioris alopecuretosum pratensis R. Tx. 1937 andMesobrometum erecti stipetosum Vicherek 1960, were chosen for investigations of the underground plant parts. Apparent differences in underground dry weight and its seasonal changes in both the communities were observed. Differences in the soil environment in different periods of the year are reflected in the character of time changes in underground dry weight. The soil environment affects not only the total underground biomass and their changes in time, but also the activity of soil microflora and, consequently, the decomposition rate of dead underground plant parts. 相似文献
993.
Anna Chrtková-Žertová 《Folia Geobotanica》1969,4(3):303-311
In der ArtVicia sepium L. kann man in Mitteleuropa und in südlichen Teilen von Nordeuropa drei Varietäten unterscheiden: 1. var.sepium mit breiten Blättchen und einem kahlen bis angedrückt behaarten Kelch, 2. var.montana Koch mit schmalen Blättchen und einem kahlen oder zerstreut angedrückt behaarten Kelch, und 3. var.eriocalyx ?elak. mit breiten bis mittelbreiten Blättchen und einem abstehend langbehaarten Kelch, noch mit einer niedrigen und einer hohen Wuchsform. Bei allen Proben wurde die Chromosomezahl 2n=14 festgestellt. 相似文献
994.
Deoxyribonucleic acid base composition of Micrococcus roseus 总被引:1,自引:0,他引:1
995.
Synthesis of two hydroxy-derivatives of nalidixic acid as a result of microbial transformation was demonstrated in certain
species of the genusAspergillus. Aspergillus alliaceus produced 7-hydroxy-nalidixic acid andAspergillus niger 6-hydroxy-nalidixic acid. It was demonstrated that the antibacterial activity of both hydroxy-derivatives (tested inEscherichia coli) was lower than that of the initial nalidixis acid. 相似文献
996.
Neonatal bursectomy and irradiation led to a negative antibody response to bovine serum albumin andSalmonella paratyphi A. In the case of immunization with ΦX 174 phage and sheep erythrocytes a substantial depression of antibody formation was recorded. In addition, neonatal thymectomy and irradiation partially depressed the antibody response to BSA,Salmonella paratyphi A and ΦX 174 phage, on immunization with sheep erythrocytes the ability to form antibodies was almost uninfluenced 相似文献
997.
The ultrastructure of spores ofClaviceps purpurea (Fr.) Tul. 总被引:1,自引:0,他引:1
The ultrastructure of saprophytic and parasitic spores of the AscomyceteClaviceps purpurea (Fr.) Tul. was studied. Considerable differences were found to exist between the saprophytic and parasitic spores as to morphology and fine structure. The reason for the different ultrastructural morphology is probably connected with the intensity of cell metabolism. Whereas the parasitic spores obtained from the honeydew possess the character of a resting cell with a thick electron-dense cytoplasm, abundant lipid bodies, few mitochondria, an underdeveloped and hence little active endoplasmic reticulum and with a homogenous thick cell wall, the saprophytic spores appear as cells with higher metabolic rate, containing more numerous mitochondria, a thinner cytoplasm, a highly developed endoplasmic reticulum, fewer lipid bodies and abundant large vacuoles as well as frequently a new wall layer. 相似文献
998.
The ability of the yeastCandida lipolytica 4-1 to oxidize and utilize various pure aliphatic hydrocarbons occurring in gas oil was studied. It was found that the given strain ofCandida lipolytica oxidized n-alkanes without adaptation, starting with heptane, and utilized them for growth, starting with nonane. Isoalkanes with a single methyl group in the side chain were also oxidized and utilized for growth, but less than the corresponding n-alkanes. The site of the methyl group in the isoalkane chain influences its conversion to biomass. Branched chains at both ends of the isoalkane molecule prevent its utilization for growth ofCandida lipolytica. 1-olefines are also oxidized and utilized for growth, though less than the corresponding n-paraffins. Alkylaromatic hydrocarbons are oxidized from amylbenzene up to decylbenzene, which is utilized only slightly for growth of the yeast. 相似文献
999.
1000.