全文获取类型
收费全文 | 2787篇 |
免费 | 168篇 |
国内免费 | 2篇 |
专业分类
2957篇 |
出版年
2023年 | 21篇 |
2022年 | 26篇 |
2021年 | 41篇 |
2020年 | 38篇 |
2019年 | 30篇 |
2018年 | 118篇 |
2017年 | 98篇 |
2016年 | 126篇 |
2015年 | 88篇 |
2014年 | 117篇 |
2013年 | 195篇 |
2012年 | 178篇 |
2011年 | 208篇 |
2010年 | 145篇 |
2009年 | 102篇 |
2008年 | 60篇 |
2007年 | 59篇 |
2006年 | 68篇 |
2005年 | 22篇 |
2004年 | 24篇 |
2003年 | 24篇 |
2002年 | 24篇 |
2001年 | 36篇 |
2000年 | 31篇 |
1999年 | 28篇 |
1997年 | 33篇 |
1996年 | 36篇 |
1995年 | 30篇 |
1994年 | 36篇 |
1993年 | 23篇 |
1992年 | 34篇 |
1991年 | 29篇 |
1990年 | 22篇 |
1989年 | 28篇 |
1988年 | 21篇 |
1986年 | 30篇 |
1985年 | 28篇 |
1984年 | 37篇 |
1983年 | 31篇 |
1982年 | 25篇 |
1981年 | 28篇 |
1980年 | 22篇 |
1979年 | 31篇 |
1978年 | 25篇 |
1976年 | 21篇 |
1975年 | 21篇 |
1973年 | 27篇 |
1969年 | 21篇 |
1966年 | 22篇 |
1958年 | 20篇 |
排序方式: 共有2957条查询结果,搜索用时 15 毫秒
21.
Jlřina DvOřáková-Hladká 《Biologia Plantarum》1976,18(3):214-220
The paper deals with the problem of the significance of Ca2+ for the growth of algae, its participation in the process of nitrate and ammonium nitrogen utilization, and with the possibility of substituting Sr2+ for it. It was revealed that calcium represents a microbiogenous element for the algae tested, which takes part in the utilization of nitrate nitrogen. It cannot be replaced by strontium especially at a high growth rate of mixotrophically cultivated algae (ina glucose medium). 相似文献
22.
Summary Uptake and incidence of microperoxidase (Sigma) in the rat ova during cleavage at the 1-, 2-, 8-cell and blastocyst stages were studied after 30 min incubation with the enzyme (molecular weight of 1,900 and size of molecule of 2 nm).Evidence was furnished of the presence of a small amount of reaction product of microperoxidase in the zona pellucida and its local concentration in some parts of the perivitelline space. The larger part of surface of the ovum, however, was free of microperoxidase. In the cytoplasm microperoxidase was found in pinocytotic vesicles, less frequently in large vacuoles and starting with the eight-cell stage in secondary lysosomes. The largest amount of microperoxidase was ascertained at the stage of blastocyst, chiefly in the cells of the trophoblast. In the cells of the embryoblast, on the contrary, microperoxidase was found but occasionally. The reaction product of microperoxidase was also present in the intercellular space of ova in negligible amount, and likewise on the side of blastocysts' cavity. In comparison with the ingestion of horseradish peroxidase the incidence of microperoxidase in the segmenting rat ova was less frequent. 相似文献
23.
Ultrathin sectioning of submerged mycelium of Claviceps purpurea Tul. producing clavine alkaloids revealed yeast-like budding resulting in asexual sporesblastospores. These deciduous spores were born by extended hyphal cells and retained the same ultrastructure of cell organelles. Both the extended hyphae and the blastospores resembled the cells of ergot sclerotial tissue. A surface culture of C. purpurea Tul. producing no alkaloids was used as a reference. 相似文献
24.
Barley seeds were treated for 3 h at 25°C with 240 mM ethyl methanesulphonate (EMS), washed for 18 h, treated with various concentrations of unbuffered sodium azide (pH 6.7–7.3) for 3 h at 25°C, re-dried to 30% water content and either sown immediately or stored at 25°C for 12 days and then sown. The synergistic action of sodium azide post-treatment has been demonstrated only for the EMS-induced M1 germination reduction, while the EMS-induced M1 sterility and the yield of M2 chlorophyll mutants were unaffected. The ?storage” recovery from EMS-induced mutagenic effects was insensitive to sodium azide post-treatment. The 12 day-seed storage at 25°C brought about an improvement of M1 germination, M1 survival, M1 fertility and a decrease in the amount of M2 mutants, regardless of whether sodium azide post-treatment was applied or not. 相似文献
25.
26.
27.
Sporopollenin layers in the cell wall of coccal green algae are responsible for the resistance of cell walls to destructive processes during fossilization as well as during chemical preparation of samples for pollen-analysis. Pollen slides of samples from limnic sediments thus also contain some algal cell walls. Although some pollen-analysts tried to stress this fact, the finds of algae in pollen slides have not been paid systematic attention yet, despite their potential use for a more accurate palaeoecological reconstruction. The article summarizes the results of palaeoecological studies showing how the algae can be used in palaeoecological reconstruction of past environments. The possibility of utilizing the indicative value of algal finds is demonstrated on examples of algal communities from fossil, subrecent and recent sediments from different longitudes, latitudes, and altitudes. The identification and indicative values of species and varieties ofPediastrum are included in a special review (Komárek &; Jankovská, Biblioth. Phycol., in press). The contemporary knowledge of ecological requirements of the given taxa, completed by information from their fossil finds, makes possible the reconstruction of trophic and temperature conditions and of the purity of the water environment of the past water biotopes. 相似文献
28.
Martina Kyselková Jiří Janata Markéta Ságová-Marečková Jan Kopecký 《Archives of microbiology》2010,192(3):195-200
In acetohydroxy acid synthase from Streptomyces cinnamonensis mutants affected in valine regulation, the impact of mutations on interactions between the catalytic and the regulatory subunits
was examined using yeast two-hybrid system. Mutations in the catalytic and the regulatory subunits were projected into homology
models of the respective proteins. Two changes in the catalytic subunit, E139A (α domain) and ΔQ217 (β domain), both located
on the surface of the catalytic subunit dimer, lowered the interaction with the regulatory subunit. Three consecutive changes
in the N-terminal part of the regulatory subunit were examined. Changes G16D and V17D in a loop and adjacent α-helix of ACT
domain affected the interaction considerably, indicating that this region might be in contact with the catalytic subunit during
allosteric regulation. In contrast, the adjacent mutation L18F did not influence the interaction at all. Thus, L18 might participate
in valine binding or conformational change transfer within the regulatory subunits. Shortening of the regulatory subunit to
107 residues reduced the interaction essentially, suggesting that the C-terminal part of the regulatory subunit is also important
for the catalytic subunit binding. 相似文献
29.
Jiří Váňa 《Plant Systematics and Evolution》1970,118(5):572-579
Summary A second species of the hitherto monotypic genusKymatocalyx
Herz. is described and figured in detail. The new combinationKymatocalyx dominicensis (Spruce) comb. nova is proposed. 相似文献
30.
Zdenka Otýpková Milan Chytrý Lubomír Tichý Vilém Pechanec Jan W. Jongepier Ondřej Hájek 《Biologia》2011,66(2):266-274
The flora of the White Carpathians, a mountain range in the south-east of the Czech Republic, is documented by about 485,000
records of vascular plant occurrences collected since the mid-19th century. A total of 1299 species recorded in 93 grid cells of 2.8 × 3.1 km were used for an analysis of spatial patterns
of floristic diversity in the White Carpathians. Multivariate statistical techniques such as ordination and classification
were used to reveal the main gradients in floristic composition and species richness, and measured environmental data and
Ellenberg indicator values were used to assess underlying environmental factors. There is a striking floristic contrast between
the western and eastern part of the study area, which is associated with differences in climate, mean altitude, topographic
heterogeneity measured as altitudinal range, and land use. The western part is characterised by thermophilous, continental
and calcicolous species of open habitats. In contrast, the more forested eastern part along the state border with Slovakia
and the north-eastern part of the area are characterised by acidophilous species with higher moisture requirements. This pattern
is consistent with the established phytogeographical division of the Czech Republic into the phytogeographical regions of
Thermophyticum and Mesophyticum. The further division of the area into four regions, based on classified grid data, is also
similar to the current division into phytogeographical districts, except for the Javorníky district. There are two distinct
hot spots of species richness, in the western and the extreme north-eastern part. A poorer flora was found in landscapes with
intensive agriculture. Species richness is associated with different environmental factors than species composition, namely
with soil types and land-use categories. Alien species are more common in areas with a higher incidence of arable land and
built-up areas, and less common in areas dominated by grasslands and forests. 相似文献