全文获取类型
收费全文 | 7037篇 |
免费 | 633篇 |
国内免费 | 655篇 |
出版年
2024年 | 9篇 |
2023年 | 124篇 |
2022年 | 94篇 |
2021年 | 187篇 |
2020年 | 246篇 |
2019年 | 290篇 |
2018年 | 218篇 |
2017年 | 217篇 |
2016年 | 225篇 |
2015年 | 225篇 |
2014年 | 253篇 |
2013年 | 452篇 |
2012年 | 320篇 |
2011年 | 301篇 |
2010年 | 278篇 |
2009年 | 367篇 |
2008年 | 325篇 |
2007年 | 392篇 |
2006年 | 348篇 |
2005年 | 353篇 |
2004年 | 299篇 |
2003年 | 274篇 |
2002年 | 205篇 |
2001年 | 230篇 |
2000年 | 200篇 |
1999年 | 177篇 |
1998年 | 199篇 |
1997年 | 165篇 |
1996年 | 148篇 |
1995年 | 139篇 |
1994年 | 118篇 |
1993年 | 110篇 |
1992年 | 106篇 |
1991年 | 95篇 |
1990年 | 75篇 |
1989年 | 62篇 |
1988年 | 53篇 |
1987年 | 49篇 |
1986年 | 48篇 |
1985年 | 73篇 |
1984年 | 76篇 |
1983年 | 33篇 |
1982年 | 32篇 |
1981年 | 30篇 |
1980年 | 27篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 15篇 |
1973年 | 8篇 |
排序方式: 共有8325条查询结果,搜索用时 31 毫秒
81.
Edda De Rossi Giovanna Riccardi Anna Maria Sanangelantoni Orio Ciferri 《FEMS microbiology letters》1985,30(1-2):239-244
Abstract A Spirulina platensis gene library has been constructed using cosmid vector pMMB34. The cosmid bank was controlled for its random gene distribution by colony hybridization. Genes were identified using either homologous or heterologous probes of genes involved in photosynthesis (large and small subunit of d -ribulose 1,5-bisphosphate carboxylase, 32 kDa thylakoid protein, α, β subunits of C-phycocyanin) and protein synthesis (elongation factors EF-Tu, EF-G). 相似文献
82.
L. W. D. van Raamsdonk 《Plant Systematics and Evolution》1985,149(3-4):287-297
The pollen fertility and seed formation of six species of theOrnithogalum umbellatum/angustifolium complex and of seven related species were studied. Four types of pollen grains could be recognized. The pollen fertility varied greatly in this complex and is not related to the ploidy level. The seed formation ofO. umbellatum showed an adaptation to a subcontinental-Mediterranean climate, that ofO. angustifolium to an Atlantic climate. In both cases raindrops seem to be important for pollination, in view of the absence of insect pollinators. After open pollination 113 seedlings were obtained in four species. Their chromosome numbers were determined. Nearly all the cultivated seedlings were aneuploid, which points to a positive selection of euploids in nature, because aneuploid individuals are rare in the wild.Biosystematic Studies on theOrnithogalum umbellatum/angustifolium Complex III.—Previous parts of this series are Part I: Taxonomy. Proceeding Kon. Ned. Acad. Wet. series C,85 (4), 563–574 (1982) andvan Raamsdonk (1984). 相似文献
83.
J. P. Bakker 《Plant Ecology》1985,62(1-3):391-398
Grazing an abandoned salt marsh causes retrogressive succession, since mid salt-marsh communities change into lower salt-marsh communities. Grazing and mowing are compared in detail. Both management practices enhance species diversity in an abandoned salt marsh. This can be attributed to the removal of litter. The finding that lower salt-marsh species appear more with grazing than with mowing or abandoning is not related to a higher soil salinity as compared to mowing or abandoning, but probably to locally baring of the soil by grazing animals. Only species of pioneer or unstable environments seem to have a persistent seed bank, for other species seed dispersal seems to be a limiting factor for their establishment.Nomenclature follows Heukels & van Ooststroom (1977) for species; Westhoff & den Held (1969) for syntaxa.Mrs R. Rusthoven analyzed the soil samples, Mr E. Leeuwinga drawed the figures, and Mrs J. O'Brien corrected the English text. 相似文献
84.
Germination of freshly harvested seeds of a non-dormant (ND) line (Stonehouse 319) of wild oats ( Avena fatua L.) was inhibited by incubation of the seeds at relatively high temperatures of 25 and 30°C. The germination inhibition in these seeds appeared to be a case of thermo-inhibition which was the direct effect of hightemperature treatment (HIT), since it did not persist after transferring the seeds to an optimum germination temperature of 20°C. Even a prolonged HTT of 30°C for over 5 weeks did not prevent germination of about 80% of the seeds transferred to 20°C. However, in a significant proportion of the seeds, thermo-dormancy was induced by 10 days of HTT at 30°C if the seeds were then incubated at sub-optimal temperatures of 5 to 15°C. This thermo-dormancy would appear to be 'restrictive' in form, since its expression was restricted to very specific conditions. Relatively low inclubation temperaturs of 5 and 10°C markedly slowed germination whether HTT was applied or not. The results suggest that thermo-inhibition and thermo-dormancy, induced during seasonal temperature fluctuations, may provide a survival mechanism for seeds of such ND lines as Stonehouse 319. 相似文献
85.
Brenda J. Biggs Michael K. Smith Kenneth J. Scott 《Plant Cell, Tissue and Organ Culture》1986,6(3):229-234
Cassava fertility and seed viability are frequently low, which can be a disadvantage in a breeding programme. An embryo culture method is described whereby embryonic axes are excised from mature seeds and placed on a culture medium containing 1.23 M indolebutyric acid (IBA) at 30°C under continuous light. The number of plants recovered by embryo culture was much greater than the number recovered from conventional seed germination procedures. 相似文献
86.
In a succession of seed harvests of carrot, the highest percentage and most rapid germination was obtained from seed harvested 51 days after anthesis (DAA) when dried by conditioning at 25°C and 60% RH for one week and from seeeds harvested 65 or 79 DAA with or without conditioning treatment. Seed from these harvests had reached maximum weight when dried, had embryos of maximum length and were considered mature. The germinaton of seed from these treatments was unaffected by a mixture of the gibberellins A4 and A7 (GA4/7) applied in the incubation medium. Seed harvested 37 DAA also gave maximum percentage germination when it was both conditioned and incubated in GA4/7 solution. Seed harvested earlier than this germinated poorly. Germination times of both mature and immature seed were reduced after storage for 18 months but there was no response to GA4/7.Abbreviations ABA
abscisic acid
- DAA
days after anthesis
- GA
gibberellin 相似文献
87.
Extract of alfalfa seed (ethanolic 50 % v/v) prevents the development of plaque formation and hyperlipidaemia in cholesterol
fed rabbits. It inhibits the elevation of serum total cholesterol, triglycerides, phospholipids, LDL-cholesterol and total
cholesterol/phospholipid ratio, while HDL-cholesterol/total cholesterol ratio increases, which is associated with a reduced
incidence of atherosclerosis. Further reduction in total cholesterol and phospholipid contents of liver and heart muscle are
suggestive of a beneficial role of the seed extract. The possible mechanisms of action are discussed. 相似文献
88.
D. Vakeria G. A. Codd A. M. Hawthornthwaite W. D. P. Stewart 《Archives of microbiology》1986,145(3):228-233
A gene bank of the nutritionally versatile, nitrogen-fixing cyanobacterium Chlorogloeopsis fritschii was constructed in Charon 4A. 2,800 recombinants containing 10–20 kbp C. fritschii DNA fragments were screened by Southern hybridization using probes containing the genes for the large (LSU) and small (SSU) subunits of ribulose bisphosphate carboxylase/oxygenase (RuBisCO) from Anacystis nidulans. A single recombinant plaque (CDG1) containing a 10.9 kbp EcoR1 fragment from C. fritschii hybridized to both the LSU and SSU probes, indicating a possible linkage of these RuBisCO genes in C. fritschii. RuBisCO activity and protein were detected in CDG1 lysates of Escherichia coli. Hybridization was also obtained between C. fritschii DNA and the LSU probe from Chlamydomonas reinhardtii, although no homology was detected using the LSU probe from maize or the SSU probe from pea.Abbreviations RuBisCO
d-ribulose 1,5-bisphosphate carboxylase/oxygenase
- RuBP
d-ribulose 1,5-bisphosphate
- LSU
large subunit of RuBisCO
- SSU
small subunit of RuBisCO
- SDS
sodium dodecyl sulphate
- DOC
deoxycholate 相似文献
89.
A. Ma Fernández-Peralta J. J. González-Aguilera 《Plant Systematics and Evolution》1986,152(3-4):167-183
Six closely related taxa of the sect.Eusideritis of the genusSideritis (S. leucantha, S. pusilla, S. flavovirens, S. granatensis, S. biflora andS. osteoxylla) are analysed to elucidate their phylogenetic relationships and position within the sect.Eusideritis. Meiotic behaviour, karyotype features, size and fertility of pollen grains, DNA amounts and seed protein profiles are reviewed. A polyploid origin of the group (from x = 7) and the further diversification through dysploidy and chromosome repatterning is postulated.S. osteoxylla is apparently of hybrid origin. 相似文献
90.
Seed protein electrophoresis of four chromosomes races ofFestuca arundinacea, F. mairei and their progenitors showed variation in banding patterns. High protein similarities betweenF. arundinacea, F. mairei, F. scariosa, andF. pratensis indicate close phylogenetic relationships of these species. The ancestry ofF. arundinacea cytotypes could be narrowed to three diploid species:F. scariosa, F. pratensis, andF. rubra or to their close relatives. 相似文献