全文获取类型
收费全文 | 7947篇 |
免费 | 472篇 |
国内免费 | 1218篇 |
出版年
2023年 | 151篇 |
2022年 | 197篇 |
2021年 | 249篇 |
2020年 | 226篇 |
2019年 | 315篇 |
2018年 | 331篇 |
2017年 | 217篇 |
2016年 | 181篇 |
2015年 | 197篇 |
2014年 | 469篇 |
2013年 | 543篇 |
2012年 | 308篇 |
2011年 | 437篇 |
2010年 | 356篇 |
2009年 | 388篇 |
2008年 | 401篇 |
2007年 | 502篇 |
2006年 | 366篇 |
2005年 | 307篇 |
2004年 | 222篇 |
2003年 | 233篇 |
2002年 | 198篇 |
2001年 | 169篇 |
2000年 | 150篇 |
1999年 | 125篇 |
1998年 | 95篇 |
1997年 | 85篇 |
1996年 | 89篇 |
1995年 | 85篇 |
1994年 | 71篇 |
1993年 | 68篇 |
1992年 | 65篇 |
1991年 | 97篇 |
1990年 | 50篇 |
1989年 | 53篇 |
1988年 | 54篇 |
1987年 | 54篇 |
1985年 | 94篇 |
1984年 | 161篇 |
1983年 | 132篇 |
1982年 | 158篇 |
1981年 | 113篇 |
1980年 | 151篇 |
1979年 | 137篇 |
1978年 | 110篇 |
1977年 | 114篇 |
1976年 | 90篇 |
1975年 | 56篇 |
1974年 | 66篇 |
1973年 | 56篇 |
排序方式: 共有9637条查询结果,搜索用时 15 毫秒
31.
Isolde Hagemann 《Plant Systematics and Evolution》1987,155(1-4):165-187
The morphology, altitudinal distribution and phytocoenology ofHypericum empetrifolium
Willd., var.oliganthum
Rech. fil. and var.tortuosum
Rech. fil. are reassessed and as a result, the taxa are treated at subspecific rank. Essential characters proved to be growth form, number of flowers, foliage and epidermal surface characters, shape of seeds and testa sculpturing.The different growth forms can be interpreted as adaptations to the local habitats.Hypericum empetrifolium
Willd. subsp.empetrifolium is a low subshrub of various vegetation types known as phrygana whereasHypericum empetrifolium
Willd. subsp.oliganthum (Rech. f.)Hagemann grows as a cushion-like dwarf shrub in chasmophyte associations rich in relic species.Hypericum empetrifolium
Willd. subsp.tortuosum (Rech. f.)Hagemann is confined in the high mountain regions and grows as a true dwarf espalier shrub with low spreading shoots.Dedicated to Hofrat Univ.-Prof. DrK. H. Rechinger on the occasion of his 80th birthday. 相似文献
32.
33.
34.
Testing for symmetry 总被引:1,自引:0,他引:1
35.
36.
In vivo effect of abscisic acid (ABA) on photosynthetic oxygen evolution was investigated in barley chloroplasts. The most important kinetic parameters of O2-producing reactions were changed. The results show inhibition of the O2-flash yields at ABA concentrations of 10 mol/l and 100 mol/l and an increase in the degree of damping of the oscillations. ABA has a marked effect on the distribution of the oxygenevolving centers in S0 and S1 states and on sum of the centers (S0+S1) estimated according to the Kok model. In addition, the amplitude and the shape of the initial oxygen burst under continuous illumination are also significantly altered. At a concentration of 100 mol/l, ABA strongly inhibits Hill reaction activity measured by DCPIP reduction. The results cannot be explained by the hypothesis of socalled stomata effect. On the other hand, no effects were observed on the investigated parameters in experiments involving ABA applied in vitro to isolated chloroplasts. It is hypothesized that ABA disrupts the granal chloroplasts structure and raises the degree of participation of the cooperative mechanism of O2-evolution connected with the functioning of PS II centers in the stroma situated thylakoids.Abbreviations DCPIP
2,6-Dichlorophenolindophenol
- DCMU
3-(3,4-dichlorophenil)-1,1-dimethylurea
- HEPES
N-2-Hydroxyethylpiperazine-N-2-ethane sulfonic acid
- PSII
photosystem II
- RubisCO
Ribulose-1,5-bis-phosphate carboxylase-oxygenase 相似文献
37.
J. B. T. M. Roerdink 《Journal of mathematical biology》1989,27(3):309-319
In a previous paper (J. Math. Biol. 26, 199–215 (1988)) we calculated the mean and variance of the long-run geometric growth rate of a discrete-time population model with two age classes in a random environment. The formula which was used in that paper as the starting point for the computation of the variance represents only the contribution of the one-period variances. Here we supplement these results by a calculation of the exact variance. All qualitative conclusions reached before are unaffected. 相似文献
38.
Realized heritabilities were estimated for the character of phenthoate resistance in two local strains of the diamond-back moth, Plutella xylostella L. (Lepidoptera: Yponomeutidae), by performing artificial laboratory selection for resistance and susceptibility to phenthoate. Heritability estimates indicated that such traits are moderately heritable (
2=0.42 and 0.41 in the resistant selection and
2=0.31 and 0.21 in the susceptible selection), and give an experimental basis accounting for rapid evolutionary changes of phenthoate resistance observed in field populations of this insect.The observed changes in variances of phenthoate susceptibility are discussed in relation to the additive genetic variance eliminated by directional selection. The explanation stresses the importance on the underlying genetic system.
Résumé L'héritabilité de la résistance au phenthoate obtenue chez deux souches locales de P. xylostella L. (Lep.; Yponomeutidae) a été calculée en procédant au laboratoire à des sélections artificielles pour la résistance et pour la sensibilité à cet insecticide. Les calculs de l'héritabilité ont montré que de tels caractères sont moyennement héritables ( 2=0,42 et 0,41 lors de la sélection pour la résistance, et 2=0,31 et 0,21 lors de la sélection pour la sensibilité), et ont fourni la base expérimentale rendant compte des changements évolutifs rapides observés pour la résistance au phenthoate chez des populations naturelles de cet insecte.Les changements observés de la variance de la sensibilité au phenthoate sont discutés en fonction de la variance génétique additive éliminée par la sélection orientée. L'explication insiste sur l'importance du système génétique souligné.相似文献
39.
Kunio Yonemasu Takako Sasaki Yoshiko Dohi Charles M. Lapière Betty Nusgens 《生物化学与生物物理学报:疾病的分子基础》1990,1096(1):47-51
C1q, a collagen-like complement protein, was purified from the serum of a ddermatosparactic calf which lacks procollagen N-terminal proteinase (pN-proteinase). The specific hemolytic activity of the serum Clq from the dermatosparactic animal was identical to that of C1q from a normal calf. Gel-filtration of serum from dermatosparactic calf, on Sepharose 6B, showed the presence of C1q-antigenic material at only one position which was identical to the elution position of normal bovine C1q. No differdence, under dissociating conditions, could be seen in the size of the chains of C1q in specific immunoprecipitates isolated from the sera of dermatosparactic and normal animals, as judged by polyacrylamidegel electrophoresis (PAGE) in the presence of sodium dodecyl sulfate (SDS). The C1q from the dermatosparactic animal showed the same N-terminal amino acid and typtic-digest peptide pattern on HPLC as C1q from the normal calf. These results strongly suggest that pN-proteinase is not involved in the extracellular processing of C1q. 相似文献
40.