全文获取类型
收费全文 | 1343篇 |
免费 | 60篇 |
国内免费 | 3篇 |
专业分类
1406篇 |
出版年
2023年 | 7篇 |
2022年 | 21篇 |
2021年 | 43篇 |
2020年 | 23篇 |
2019年 | 30篇 |
2018年 | 34篇 |
2017年 | 37篇 |
2016年 | 43篇 |
2015年 | 51篇 |
2014年 | 75篇 |
2013年 | 94篇 |
2012年 | 103篇 |
2011年 | 79篇 |
2010年 | 58篇 |
2009年 | 39篇 |
2008年 | 60篇 |
2007年 | 54篇 |
2006年 | 63篇 |
2005年 | 51篇 |
2004年 | 18篇 |
2003年 | 22篇 |
2002年 | 20篇 |
2001年 | 29篇 |
2000年 | 23篇 |
1999年 | 15篇 |
1998年 | 10篇 |
1997年 | 14篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 11篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 19篇 |
1988年 | 12篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1977年 | 6篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1970年 | 5篇 |
1969年 | 5篇 |
1968年 | 5篇 |
1967年 | 11篇 |
排序方式: 共有1406条查询结果,搜索用时 0 毫秒
11.
Studies on the osmotic optima for growth of some Aspergilli isolated from Indian Usar (alkaline) soils have revealed the occurrence of four osmophilic and twenty-five other species which can be categorised as facultative tolerant on the basis of their osmotic concentration optima. In addition, the Usar soil strains possess a comparatively greater osmotic tolerance than their fertile soil counterparts which may be attributed to the relatively hypertonic conditions prevailing in Usar soils. 相似文献
12.
13.
Summary Literature pertaining to sclerotial Aspergilli has been reviewed in brief. Observations on the effect of certain environmental conditions viz. pH, light, temperature of incubation, oxygen-deficient conditions and various relative humidity values on sclerotia production byAspergillus niger
van Tieghem, (two strains),A. flavus
Link (two strains),A. sclerotiorum
Hüber (one strain) andA. paradoxus
Fennell &Raper (one strain) and on cleistothecia production byA. nidulans (Eidam)Wint. (one strain) have been presented. Optimum pH for sclerotia or cleistothecia production was 7.5. In other respects sclerotia and cleistothecia behaved similarly. In general, condition showing maximum sclerotia or cleistothecia production was the one that showed maximum vegetative growth. Certain strains of the same species reponded differently to the same condition. Light completely inhibited sclerotia formation in one strain ofA. flavus. InA. paradoxus, in general, conditions favouring sclerotia production were those that inhibited (or retarded) the formation of conidial heads and the yellow pigment in the medium. Oxygen-deficient conditions inhibited or retarded sclerotia or cleistothecia formation. Production of sclerotia and cleistothecia increased with an increase in relative humidity values. No definite correlation could be observed between extent of sporulation and sclerotia or cleistothecia production except in case of relative humidity. Parallelism in the behaviour of sclerotia and cleistothecia production inAspergillus lends further support in favour of the hypothesis that in this genus sclerotia are sterile stromata. 相似文献
14.
Tso-Yu Chiang Rajendra Rai Terrance G. Cooper George A. Marzluf 《Molecular genetics and genomics : MGG》1994,245(4):512-516
NIT2, a positive-acting regulatory protein in Neurospora crassa, activates the expression of a series of unlinked structural genes that encode nitrogen catabolic enzymes. NIT2 binding sites in the promoter regions of nit3, alc and lao have at least two GATA sequence elements. We have examined the binding affinity of the NIT2 protein for the yeast DAL5 wild-type upstream activation sequence UASNTR, which contains two GATA elements, and for a series of mutated binding sites, each differing from the wild-type site by a single base. Substitution for individual nucleotides within 5′ or 3′ sequences that flank the GATA elements had only modest effects upon NIT2 binding. In contrast, nearly all substitutions within the GATA elements almost completely eliminated NIT2 binding, demonstrating the importance of the GATA sequence for NIT2 binding. Four high-affinity binding sites for the NIT2 protein were found within a central region of the nit-2 gene itself. 相似文献
15.
16.
Synechococcus sp. PCC7942 Transformed with Escherichia coli bet Genes Produces Glycine Betaine from Choline and Acquires Resistance to Salt Stress 总被引:10,自引:3,他引:7 下载免费PDF全文
Synechococcus sp. PCC7942, a fresh water cyanobacterium, was transformed by a shuttle plasmid that contains a 9-kb fragment encoding the Escherichia coli bet gene cluster, i.e. betA (choline dehydrogenase), betB (betaine aldehyde dehydrogenase), betI (a putative regulatory protein), and betT (the choline transport system). The expression of these genes was demonstrated in the cyanobacterial cells (bet-containing cells) by northern blot analysis, as well as by the detection of glycine betaine by 1H nuclear magnetic resonance in cells supplemented with choline. Endogenous choline was not detected in either control or bet-containing cells. Both control and bet-containing cyanobacterial cells were found to import choline in an energy-dependent process, although this import was restricted only to bet-containing cells in conditions of salt stress. Glycine betaine was found to accumulate to a concentration of 45 mM in bet-containing cyanobacterial cells, and this resulted in a stabilization of the photosynthetic activities of photosystems I and II, higher phycobilisome contents, and general protective effects against salt stress when compared to control cells. The growth of bet-containing cells was much faster in the presence of 0.375 M NaCl than that of control cells, indicating that the transformant acquired resistance to salt stress. 相似文献
17.
Summary Root exudate from seedlings ofCicer arietinum L. was collected in a chamber under aseptic conditions. The exudate was fractionated into anion, cation and neutral fractions.
The anionic fraction was made up of galacturonic acid, gluconic acid, mannuronic acid and two unidentified compounds withR
f
values 0.56 and 0.62. The cationic fraction contained alanine, arginine, aspartic acid, cystine, glycine, histidine, isoleucine,
leucine, lysine and serine. The neutral fraction was made up of arabinose, galactose, glucose, ribose and xylose. The amino
acids contributed to the bulk of the root exudate. The ratio of anionic, cationic and neutral fraction was 1∶7∶2. The crude
root exudate was tested for its chemotactic ability using the capillary tube method. It was highly chemotactic for theRhizobium sp. The individual fractions and their various combinations were tested for chemotaxis. The chemotactic response of the Cicer
strain of Rhizobium was least with anionic fraction most with cationic fraction and intermediate with neutral fraction. Maximum
chemotactic response among the fractional combinations was obtained with all the three fractions and least with cationic plus
neutral factions. Individual compounds constituting the various fractions were also tried for their ability to elicit chemotactic
response. The organism exhibited maximum positive chemotactic response to histidine and negative response to alanine among
the amino acids and to glucose and gluconic acid among the sugars and sugar acids. 相似文献
18.
Data on genetic polymorphism, scored at two morphological loci, showed peripheral, isolated roadside colonies of slender oat (Avena barbata) to be significantly less polymorphic than the large central populations in continuous stands. The role of random drift (founder effect) was evident in the genetic structure of such roadside colonies which were, however, not monomorphic. Multilocus associations also suggested large Hill-Robertson effect in generating gametic disequilibria. Such isolates with varying amounts of elapsed time since the founder events could offer useful material for a study of evolutionary processes including the selection-drift balance. 相似文献
19.
Mahendra Rai Dnyaneshwar Rathod Gauravi Agarkar Mudasir Dar Marian Brestic Glaucia Maria Pastore Mario Roberto Marostica Junior 《Symbiosis (Philadelphia, Pa.)》2014,62(2):63-79
Agricultural productivity suffers a heavy loss due to plant pathogens, insect pests and various abiotic stresses. Agriculture being the world’s largest economic sector, it is the need of time to find and establish the ideal strategy for sustainable agriculture and improvement in crop growth. Endophytes are microorganisms that asymptomatically grow within the plant tissues without causing any disease to the host. Endophytic fungi live in symbiotic association with plants and play an important role in plant growth promotion, higher seed yield and plants resistant to various biotic, abiotic stresses and diseases. Many are able to produce antimicrobial compounds, plant growth hormones and various agrochemical bioactive metabolites. These mycoendophytes hold enormous potential for the development of eco-friendly and economically viable agricultural products. In this review we focused on the endophytic fungi recovered from different medicinal plants, their active principles involved in plant growth enhancement and the applications of fungal endophytes in agriculture. Moreover, we also discussed about endophytic fungi and their pragmatic approach towards sustainable food and agriculture. 相似文献
20.
Chandana Basu Mallick Florin Mircea Iliescu M?rt M?ls Sarah Hill Rakesh Tamang Gyaneshwer Chaubey Rie Goto Simon Y. W. Ho Irene Gallego Romero Federica Crivellaro Georgi Hudjashov Niraj Rai Mait Metspalu C. G. Nicholas Mascie-Taylor Ramasamy Pitchappan Lalji Singh Marta Mirazon-Lahr Kumarasamy Thangaraj Richard Villems Toomas Kivisild 《PLoS genetics》2013,9(11)
Skin pigmentation is one of the most variable phenotypic traits in humans. A non-synonymous substitution (rs1426654) in the third exon of SLC24A5 accounts for lighter skin in Europeans but not in East Asians. A previous genome-wide association study carried out in a heterogeneous sample of UK immigrants of South Asian descent suggested that this gene also contributes significantly to skin pigmentation variation among South Asians. In the present study, we have quantitatively assessed skin pigmentation for a largely homogeneous cohort of 1228 individuals from the Southern region of the Indian subcontinent. Our data confirm significant association of rs1426654 SNP with skin pigmentation, explaining about 27% of total phenotypic variation in the cohort studied. Our extensive survey of the polymorphism in 1573 individuals from 54 ethnic populations across the Indian subcontinent reveals wide presence of the derived-A allele, although the frequencies vary substantially among populations. We also show that the geospatial pattern of this allele is complex, but most importantly, reflects strong influence of language, geography and demographic history of the populations. Sequencing 11.74 kb of SLC24A5 in 95 individuals worldwide reveals that the rs1426654-A alleles in South Asian and West Eurasian populations are monophyletic and occur on the background of a common haplotype that is characterized by low genetic diversity. We date the coalescence of the light skin associated allele at 22–28 KYA. Both our sequence and genome-wide genotype data confirm that this gene has been a target for positive selection among Europeans. However, the latter also shows additional evidence of selection in populations of the Middle East, Central Asia, Pakistan and North India but not in South India. 相似文献