全文获取类型
收费全文 | 85937篇 |
免费 | 4966篇 |
国内免费 | 10篇 |
出版年
2022年 | 481篇 |
2021年 | 1131篇 |
2020年 | 980篇 |
2019年 | 1004篇 |
2018年 | 2308篇 |
2017年 | 2014篇 |
2016年 | 2737篇 |
2015年 | 3627篇 |
2014年 | 3792篇 |
2013年 | 4987篇 |
2012年 | 5833篇 |
2011年 | 5188篇 |
2010年 | 3371篇 |
2009年 | 2568篇 |
2008年 | 4109篇 |
2007年 | 3931篇 |
2006年 | 3881篇 |
2005年 | 3232篇 |
2004年 | 3237篇 |
2003年 | 2897篇 |
2002年 | 2641篇 |
2001年 | 2084篇 |
2000年 | 1940篇 |
1999年 | 1503篇 |
1998年 | 705篇 |
1997年 | 496篇 |
1996年 | 547篇 |
1995年 | 500篇 |
1992年 | 941篇 |
1991年 | 857篇 |
1990年 | 845篇 |
1989年 | 914篇 |
1988年 | 751篇 |
1987年 | 762篇 |
1986年 | 699篇 |
1985年 | 765篇 |
1984年 | 634篇 |
1983年 | 556篇 |
1979年 | 679篇 |
1978年 | 494篇 |
1977年 | 498篇 |
1975年 | 590篇 |
1974年 | 626篇 |
1973年 | 597篇 |
1972年 | 551篇 |
1971年 | 492篇 |
1970年 | 543篇 |
1969年 | 611篇 |
1968年 | 574篇 |
1967年 | 479篇 |
排序方式: 共有10000条查询结果,搜索用时 476 毫秒
931.
Potato leafroll virus induces considerable disturbances of phosphorus metabolism in leafroll-infected potato plants. Each variety reacts differently in this respect on the infection, to some extent being dependent on the susceptibility of the respective variety to leafroll and to the season as well. In varieties particularly susceptible to leafroll as in Apta and Sieglinde there is a decrease of total P after infection. On the contrary, varieties showing medium susceptibility such as varieties Tatranka, Rita and Ambra react to leafroll infection with a considerable increase of total P. In the comparatively less susceptible variety Krasava, there is no change in the level of total P after infection. In autumn, however, a slight decrease of total P even in the medium susceptible variety Tatranka, and the less susceptible variety, Krasava, can be found. Our results shed a new light on existing controversies in literature regarding phosphorus content in leafroll-infected potato plants. When the changes in the contents of various phosphorus fractions in the infected plants are compared we can observe a tendency of lowmolecular fractions to rise. Among the different phosphorus fractions one common feature could be seen, except for the hypersensitive resistant variety Apta, namely, that the acid-soluble organic phosphates in the stems of all varieties examined, were considerably higher than in healthy stems. 相似文献
932.
V práci byly studovány rozdíly v ú?innosti kyseliny β-(3-pyridyl)-propionové (VIII) a β-(3-pyridyl)-akrylové (IX) v závislosti na stupni nenasycení pobo?ného ?etězce. Obě kyseliny inhibují r?st ko?ene i hypokotyluSinapis alba L. a zp?sobují inhibici sukcinátdehydrogenázového enzymového systému. Kyselina IX inhibuje zmíněný systém p?ibli?ně na dvojnásobek inhibice kyseliny VIII. Cytochromoxydázový systém z?stává témě? neovlivněn. Na základě experimen tálních výsledk? byla zp?esněna strukturní podmínka fytotoxické aktivity modelových slou?enin typu I v tom smyslu, ?e v?echny slou?eniny této struktury inhibují kromě r?stu také aktivitu sukcinátdehydrogenázového systému. 相似文献
933.
934.
935.
Summary The study of the cell division cycle by means of caffeine labelling inAllium roots, at 15° C, employing intact root and decapitated roots at several levels (0.5, 1.0, 1.5, 2.0, and 2.5 mm) has shown that the number of cycles developed by the cells is constant at each meristem level. This number and the durations of the cycles are not affected by the decapitation. It is suggested that the cell cycle is controlled in the meristematic cells by an intracellular programme which would be developed throughout the meristem.However, the larger the region decapitated is, the more decreases the growth rate of the roots. The removal of the root cap (about 0.5 mm) did not modify the rate of root growth, although it blocked the geotropic response. The quiescent center is proposed as a source of auxin controlling cell elongation. 相似文献
936.
937.
938.
Z. Polák 《Biologia Plantarum》1967,9(5):354-359
Identification trials were carried out to determine a virus-like disease ofImpatiene parviflora DC. Two forms of foliar symptoms were observed:
- a)Chiorotie and necrotic areas sometimes fallen out, leaving the leaves “shot holed”; 相似文献
939.
The differentiation of tissues is closely connected with the proteosynthesis. One can therfore assume that tissues with different types of cell growth (meristematic or elongation growth) and with different degrees of differentiation are different in their protein composition. In order to compare the protein composition of different plant organs, the method of disc electrophoresis on a polyacrylamide gel has been used by some authors. As compared with other methods used up to now, e. g. isolating proteins on DEAE cellulose or in Sephadex, this method does not need so much material and its resolution ability seems to be higher. It is also quicker and enables the study of several samples simultaneously. Its disadvantage is that proteins can be identified mainly by means of Rf and their quantity, measured from the intensity of staining of individual fractions in the gel, which may be misleading due to different sorption capacity of different proteins (Fri?Fri?ová 1967). None the less, it is good for comparison of protein composition of individual parts of the plant body. Different methods have been used to compare protein composition of individual growth zones in roots.Barsky,Ivanov andPushakova (1965) used luminiscence microscopy and found that in maize roots it is not possible to find substantial differences by this method.Morgan andReith (1954) arrived at similar conclusions. On the other hand,Steward et al. (1965) andMorris (1966) found qualitative differences in protein composition of different parts of pea roots using acrylamide electrophoresis. The results of the last named authors show considerable discrepancies in details, due perhaps to a different method of extraction (buffer, pH, purifying method). We have used acrylamide gel electrophoresis for investigating proteins in precisely defined growth zones of theVicia faba root. 相似文献
940.
In our present work the formation of chromosome aberrations has been studied in dependence on the tima interval between sonication and fixation of the primary root tips of Vicia faba. Maximum occurrence of aberrations was recorded immediately after sonication. The results of our experiments pointed to the fact that the frequency of the induced changes was independent on the sonic waves intensity within the range of 0-2—3-0 W/cm2 and on ultrasond treatment duration within the range of 1—20 min. Studies of the distribution of chromosome abnormalities caused by ultrasound between the large and small chromosomes of theVicia faba meristematic cells in various time intervals showed that the frequency of the aberrations in both chromosome groups was proportional to its total metaphase lengths. Analysis of the type of aberrations observed in various time intervals after sonication indicated the simultaneous formation of chromosome and chromatide abnormalities. 相似文献