全文获取类型
收费全文 | 375篇 |
免费 | 31篇 |
专业分类
406篇 |
出版年
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 13篇 |
2017年 | 11篇 |
2016年 | 9篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 33篇 |
2012年 | 26篇 |
2011年 | 23篇 |
2010年 | 14篇 |
2009年 | 20篇 |
2008年 | 13篇 |
2007年 | 26篇 |
2006年 | 9篇 |
2005年 | 16篇 |
2004年 | 15篇 |
2003年 | 20篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1996年 | 9篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有406条查询结果,搜索用时 15 毫秒
1.
Shiva K. Sharma Madho S. Bisht Maharaj K. Pandit 《Plant Systematics and Evolution》2010,287(1-2):29-36
In higher plants, synaptic mutation-associated gametic abnormalities are reported mostly in crop plants, but studies have rarely focused on the natural plant populations. This is particularly so in threatened herbaceous perennials, some of which are known to suffer from loss of sexual reproduction driven by the genetic mutations. Cytological investigations of Panax species, viz. P. sikkimensis, P. sokpayensis and P. bipinnatifidus, revealed that all the species were diploid with 2n = 24 chromosomes. Natural occurrence of synaptic mutation was recorded in Panax sikkimensis in the Kalep population of North Sikkim, India. We recorded that 86.03% of pollen mother cells (PMCs) lacked bivalent formation and had 24 distinct univalents at prophase I in the mutant plants of P. sikkimensis. We found a significantly lower mean number of chiasmata per cell (0.31 ± 0.91; t test = 38.24, P < 0.001) in the mutant plants as compared to the normal plants (21.04 ± 4.56). The chromosomal associations in the PMCs of the synaptic mutants ranged from 25% bivalents and 75% univalents to 100% univalents at diplotene/diakinesis. The unequal distribution of chromosomes at anaphase I and II resulted in the formation of microspores and microcytes of differing sizes. The pollen stainability test in the mutant population of P. sikkimensis revealed very low (0.12%) pollen fertility reflecting the consequences of synaptic mutation. Synaptic mutation in the herbaceous perennial P. sikkimensis was considered to be responsible for the male sterility in the species. 相似文献
2.
Prediction of the recognition sites on 16S and 23S rRNAs from E. coli for the formation of 16S-23S rRNA complex 总被引:1,自引:0,他引:1
T A Thanaraj A S Kolaskar M W Pandit 《Journal of biomolecular structure & dynamics》1988,6(3):587-592
Interactions between RNA molecules have been postulated to play an important role in the assembly of ribosomes. Using the sequence analysis and the search of continuous complementary regions on 16S rRNA and 23S rRNA, the recognition sites involved in the formation of ribosome of E. coli are postulated. The number of postulated sites was narrowed down by taking available experimental data. The suggestive evidence for correct postulation is obtained from sequence comparison studies of 16S and 23S rRNAs from various species. The sites 891-899 and 1195-1203 on 16S rRNA along with the corresponding complementary sites 1904-1912 and 760-768 on 23S rRNA are predicted to be the most probable candidates for the sites of recognition between 16S and 23S rRNAs. The possibility of the involvement of the additional site 630-638 on 16S rRNA with its complementary site 2031-2039 on 23S rRNA cannot be ruled out. 相似文献
3.
Rabbit intestinal glucoamylase-maltase was examined in detail with respect to its molecular weight, sedimentation, diffusion and viscosity. It is a large asymmetrical molecule, with a molecular weight of 750 000-760 000. Its appearance under the electron microscope supports the idea that it is a long string (62.0 nm) consisting of eight beads of diameter 6.0 nm each and a surface-to-surface interbead distance of approx. 2.0 nm. The shape of the enzyme derived from its hydrodynamic behaviour by using the string-of-spherical-beads model originally proposed by Kuhn [(1932) Z. Phys. Chem. Abt. A 161, 1-32] and later modified by Shulman [(1953) J. Am. Chem. Soc. 75, 5846-5852] fits moderately well with the electron-microscopic picture. The beads might represent about six subunits, and the absence of sulphur from the enzyme and the inability to dissociate the enzyme by conventional methods indicate the possibility of unusual covalent cross-linking between the subunits and between the beads. 相似文献
4.
The life-history ofNeurospora in nature has remained largely unknown. The present study attempts to remedy this. The following conclusions are based on
observation ofNeurospora on fire-scorched sugar cane in agricultural fields, and reconstruction experiments using a colour mutant to inoculate sugar
cane burned in the laboratory. The fungus persists in soil as heat- resistant dormant ascospores. These are activated by a
chemical(s) released into soil from the burnt substrate. The chief diffusible activator of ascospores is furfural and the
germinating ascospores infect the scorched substrate. An invasive mycelium grows progressively upwards inside the juicy sugar
cane and produces copious macroconidia externally through fire- induced openings formed in the plant tissue, or by the mechanical
rupturing of the plant epidermal tissue by the mass of mycelium. The loose conidia are dispersed by wind and/or foraged by
microfauna. It is suggested that the constant production of macroconidia, and their ready dispersal, serve a physiological
role: to drain the substrate of minerals and soluble sugars, thereby creating nutritional conditions which stimulate sexual
reproduction by the fungus. Sexual reproduction in the sugar- depleted cellulosic substrate occurs after macroconidiation
has ceased totally and is favoured by the humid conditions prevailing during the monsoon rains. Profuse micro-conidiophores
and protoperithecia are produced simultaneously in the pockets below the loosened epidermal tissue. Presumably protoperithecia
are fertilized by microconidia which are possibly transmitted by nematodes active in the dead plant tissue. Mature perithecia
release ascospores in situ which are passively liberated in the soil by the disintegration of the plant material and are,
apparently, distributed by rain or irrigation water. 相似文献
5.
C A Haasnoot U K Pandit C Kruk C W Hilbers 《Journal of biomolecular structure & dynamics》1984,2(2):449-467
1H-NMR spectra of bleomycin A2 recorded at 500 MHz in D2O and H2O at 24 degrees C and 3 degrees C were investigated. Resonances of the individual spin systems were identified by using two-dimensional correlation spectroscopy (COSY), two-dimensional spin echo correlated spectroscopy (SECSY) and by the application of two-dimensional Nuclear Overhauser Effect spectroscopy (NOESY). Employment of these techniques allowed the assignment of 113 exchangeable and 59 non-exchangeable protons in the 1H NMR spectrum of bleomycin A2. By means of 2D NOE spectroscopy also interresidual connectivities could be observed. Comparison of the NOESY spectra at 3 degrees C and 24 degrees C suggest that at low temperatures the central party of the bleomycin A2 molecule tends to adopt an extended conformation. 相似文献
6.
The group of Caspian ponies studied contained some animals with 65 chromosomes and others with 64 chromosomes. The morphology and G-banding pattern of the chromosomes resembled those of Equus caballus and E. przewalskii. The karyogram of animals with 65 chromosomes was identical to that of the cross between E. caballus and E. przewalskii. It is suggested that the Caspian pony is the product of natural hybridization between E. caballus and E. prezwalskii. Low reproductive effeciency of the Caspian pony is suggested as the cause of decline in the population of these animals. 相似文献
7.
8.
Yan G. Ni Jon H. Condra Laura Orsatti Xun Shen Stefania Di Marco Shilpa Pandit Matthew J. Bottomley Lionello Ruggeri Richard T. Cummings Rose M. Cubbon Joseph C. Santoro Anka Ehrhardt Dale Lewis Timothy S. Fisher Sookhee Ha Leila Njimoluh Dana D. Wood Holly A. Hammond Douglas Wisniewski Cinzia Volpari Alessia Noto Paola Lo Surdo Brian Hubbard Andrea Carf�� Ayesha Sitlani 《The Journal of biological chemistry》2010,285(17):12882-12891
9.
10.
The self-association of diisopropylphosphoryl(DIP)-alpha-chymotrypsin is studied in order to find out whether the active site of the enzyme is involved in its self-association behaviour or not. Sedimentation coefficient as well as the weight-average (Archibald) molecular weight data are obtained as a function of concentration using an analytical ultracentrifugation technique. The analysis indicated that the experimental data fits the model of indefinite self-association. The comparison of the data with earlier data on alpha-chymotrypsin revealed that after the modification at the active site, the association constant for the self-association is reduced by about 47%, and the system deviated from ideality. Results showed further that Ser-195, at the active site, appears to be involved in the self-association behaviour of alpha-chymotrypsin; however, the participation of other groups at the active site is also implicated. 相似文献