全文获取类型
收费全文 | 88423篇 |
免费 | 5196篇 |
国内免费 | 11篇 |
出版年
2022年 | 526篇 |
2021年 | 1177篇 |
2020年 | 975篇 |
2019年 | 1051篇 |
2018年 | 2351篇 |
2017年 | 2059篇 |
2016年 | 2825篇 |
2015年 | 3759篇 |
2014年 | 3892篇 |
2013年 | 5122篇 |
2012年 | 6021篇 |
2011年 | 5436篇 |
2010年 | 3488篇 |
2009年 | 2682篇 |
2008年 | 4269篇 |
2007年 | 4097篇 |
2006年 | 4003篇 |
2005年 | 3366篇 |
2004年 | 3364篇 |
2003年 | 3031篇 |
2002年 | 2793篇 |
2001年 | 2119篇 |
2000年 | 1976篇 |
1999年 | 1542篇 |
1998年 | 724篇 |
1997年 | 545篇 |
1996年 | 574篇 |
1995年 | 504篇 |
1992年 | 955篇 |
1991年 | 857篇 |
1990年 | 837篇 |
1989年 | 911篇 |
1988年 | 746篇 |
1987年 | 775篇 |
1986年 | 700篇 |
1985年 | 761篇 |
1984年 | 640篇 |
1983年 | 558篇 |
1979年 | 676篇 |
1978年 | 495篇 |
1977年 | 505篇 |
1975年 | 596篇 |
1974年 | 632篇 |
1973年 | 604篇 |
1972年 | 564篇 |
1971年 | 500篇 |
1970年 | 541篇 |
1969年 | 623篇 |
1968年 | 582篇 |
1967年 | 489篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Biologia Plantarum - New Chromatographic methods, chromatography in centrifugal field and thin-layer chromatography on alumina, were used for separating physiologically active gibberellins A1 and... 相似文献
972.
Summary
Drosophila paulistorum
Dobzhansky
et
Pavan is a complex of six races or incipient species. The races are mostly allopatric, but they are reproductively isolated sufficiently to permit them to exist also sympatrically in some places. The gene arrangements in the chromosomes of the races have been compared by means of examination of the giant chromosomes in the larval salivary glands; 28 strains of all races, and about an equal number of interracial hybrids have been studied.Chromosomal inversion polymorphism has been discovered in all races, even in the Guianan race of which only a single strain is available. Inversion heterozygotes are found in every one of the five chromosomal strands which the species has. Interracial hybrids tend to be heterozygous for more inversions than are present in the strains of the parental races. The Transitional race has however much the same gene arrangements as the widespread Andean — South Brazilian race.With the exception of the Transitional race, and of three other possible exceptions, each race has a collection of its own race-specific inversion polymorphs, not found in the other races. This very striking finding is discussed in connection with the hypothesis which envisages the origin of new species from marginal colonies at the periphery of the geographic distribution area of the ancestral species.The work reported in this article has been carried under Contract No. AT-(30-1)-1151, U.S. Atomic Energy Commission, mostly at the Department of Zoology, Columbia University, New York. 相似文献
973.
Eva Janovská 《Folia microbiologica》1964,9(4):256-258
Устойчивость каппа-фага (Serratia marcescens) и его мутанта «С» исследовалась в буферных растворах при pH от 2.5 до 12 с целью подтверждения, или опровержения, возможности их инактивирования в результате кратковременного доведения кислотности основной суспензии в течение приготовления концентрата фага до pH 4. Было установлено, что каппа-фаг и его с-мутант в среде с pH 4 и выше остаются относительно устойчивыми и что в этих пределах pH между обоими фагами нет существенных различий. Однако при низких pH (2,5–3,5) титр обоих фагов вскоре довольно резко падает, причем с-мутантинакмпбпруемся бысмрее, чем каппа-фаг. 相似文献
974.
975.
Dagmar Vraná 《Folia microbiologica》1964,9(3):150-155
A modification of the synchronization method forChlorella pyrenoidosa was suggested, based on the mechanical separation of small and large cells by differential centrifugation and dilution of the population after division to a constant density (maximally 3×106 cells/ml.). Using this system, with a 16-hour day and eight hours' darkness, the ontogenetic cycle ofChlorella pyrenoidosa takes 24 hours and synchronous growth and development can be maintained for eight generations. 相似文献
976.
The use of induced primuline fluorescence led to the discovery of a new type of yeast scars (multiple scars) in the generaKloeckera, Saccharomycodes, Nadsonia andHanseniaspora. The structure and ultrastructure of their surface was studied by electron microscopy, using carbon replicas and isolated cell walls. 相似文献
977.
The strainCandida utilis T 20 adapted to a high concentration of ethionine, excretes considerable amounts of methionine in a synthetic medium, about 40 times as much as the original non-adapted strain. At the same time, the amount of methionine in yeast cells incrncreased, predominantly in the pool (9 times as much as in the control). This ability to produce greater amounts of methionine in the pool or to excrete it into the medium is not permanent, since after 5 passages on agar with ut ethionine the amount of methionine was practically not increased as compared with the original non-adapted strain. An increase in free methionine and of methionine excreted into the medium was found on cultivating the strain in a molasses-containing medium, too. 相似文献
978.
979.
Gábor Pálfi 《Planta》1967,78(2):196-199
Summary It has been established that in intact plants suffering from scarcity of water as well as in isolated withering leaves the amount of proline increases considerably. The main factor in the isolated leaves is thus the scarcity of water and not the injury due to the defoliation. The proline content of the leaves withering in the dark increases only for a few days and then decreases with the diminution of the carbohydrates. Of the active substances tested only 2,4-DNP inhibited the proline synthesis during the withering. It is very probable that in the course of withering the great amount of proline forms during the oxidation of carbohydrates via -ketoglutarate. The oxydative phosphorylation is uncoupled by 2,4-DNP. Kinetin, 2,4-D and antimetabolites applied do not inhibit the abnormal increase of proline. 相似文献
980.
Summary In monogenic, recessive chloroplast mutants of maize which contain chlorophylls, and lycopene or -carotene but no normal carotenoids, great variability in the size of plastids was associated with a number of ultrastructural abnormalities. In the mutant accumulating lycopene some plastids contain dense bundles of lamellae, whereas the chloroplasts of the -carotene mutant show poor thylakoid development. Neither of the mutants was able to form normal grana.A comparison of chlorophyll/carotenoid ratios in different chloroplast fractions of normal and mutant leaves showed that plastids of small size and delicate structure contain relatively less chlorophyll than fully differentiated chloroplasts. 相似文献