全文获取类型
收费全文 | 1274篇 |
免费 | 62篇 |
国内免费 | 3篇 |
出版年
2022年 | 24篇 |
2021年 | 39篇 |
2020年 | 25篇 |
2019年 | 28篇 |
2018年 | 33篇 |
2017年 | 35篇 |
2016年 | 41篇 |
2015年 | 47篇 |
2014年 | 67篇 |
2013年 | 91篇 |
2012年 | 98篇 |
2011年 | 76篇 |
2010年 | 61篇 |
2009年 | 34篇 |
2008年 | 54篇 |
2007年 | 49篇 |
2006年 | 56篇 |
2005年 | 46篇 |
2004年 | 24篇 |
2003年 | 25篇 |
2002年 | 21篇 |
2001年 | 24篇 |
2000年 | 21篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 10篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 19篇 |
1988年 | 12篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1974年 | 10篇 |
1973年 | 6篇 |
1970年 | 5篇 |
1969年 | 5篇 |
1968年 | 5篇 |
1967年 | 11篇 |
排序方式: 共有1339条查询结果,搜索用时 203 毫秒
81.
Ashis K. Mukherjee Tadi Satish Kumar Sudhir K. Rai Jetendra K. Roy 《Biotechnology and Bioprocess Engineering》2010,15(6):984-992
We report the statistical optimization of the immobilization of alkaline α-amylase [E.C. 3.2.1.1] from Bacillus alcalophilus onto nano-sized supermagnetic ironoxide nanoparticles (MNPs) for augmenting the cost effective industrial application of
MNP-bound α-amylase. Both Plackett-Burman factorial design and response surface methodology (RSM) were employed to screen
the influence of different parameters and the central effect of response on the α-amylase-iron oxide MNP binding process.
The high coefficient of determination (R2) and analysis of variance (ANOVA) of the quadratic model indicated the competence
of the proposed model. The size of the MNPs was confirmed by X-ray diffraction and scanning electron microscope analyses in
which Fourier transform infrared spectroscopy suggested immobilization of the enzyme on iron-oxide MNPs. A significant improvement
(∼ 26-fold) in specific activity, thermal and storage stability, and reusability of α-amylase after binding with iron-oxide
MNP reinforced the improved biotechnological potential of the α-amylase iron-oxide MNP bioconjugate compared to free α-amylase.
These results open new avenues for applying this MNP immobilized enzyme in different industrial sectors, notably in the paper
and brewing industries. 相似文献
82.
Guava (Psidium guajava L.), an important fruit crop of several tropical and sub-tropical countries, is facing several agronomic and horticultural
problems such as susceptibility to many pathogens, particularly guava wilting caused by Fusarium oxysporium psidii, low fruit growth, short shelf life of fruits, high seed content, and stress sensitivity. Conventional breeding techniques
have limited scope in improvement of guava owing to long juvenile period, self incompatibility, and heterozygous nature. Conventional
propagation methods, i.e., cutting, grafting or stool layering, for improvement of guava already exist, but the long juvenile
period has made them time consuming and cumbersome. Several biotechnological approaches such as genetic transformation may
be effective practical solutions for such problems and improvement of guava. The improvement of fruit trees through genetic
transformation requires an efficient regeneration system. During the past 2–3 decades, different approaches have been made
for in vitro propagation of guava. An overview on the in vitro regeneration of guava via organogenesis, somatic embryogenesis,
and synthetic seeds is presented. Organogenesis in several different genotypes through various explant selection from mature
tree and seedling plants has been achieved. Factors affecting somatic embryogenesis in guava have been reviewed. Production
of synthetic seeds using embryogenic propagules, i.e., somatic embryos and non-embryogenic vegetative propagules, i.e., shoot
tips and nodal segments have also been achieved. Development of synthetic seed in guava may be applicable for propagation,
short-term storage, and germplasm exchange, and distribution. An initial attempt for genetic transformation has also been
reported. The purpose of this review is to focus upon the current information on in vitro propagation and biotechnological
advances made in guava. 相似文献
83.
Glanders is highly contagious disease of equines, caused by Burkholderia mallei. The disease though rare, can be transmitted to humans. Here, we report a strategy for rapid detection of B. mallei from environmental samples. Different bacteriological media were evaluated and brain heart infusion broth medium with selective
supplements (BHIB-SS) of penicillin (200 U/ml) and crystal violet (1:10,00000) was found to support the maximum growth of
B. mallei even in the presence of other bacteria like Escherichia coli and Staphylococcus aureus. A polymerase chain reaction (PCR) and a DNA hybridization method was standardized for 823 bp specific dNA sequence of B. mallei. To enable the quicker and direct enrichment of B. mallei bacteria from environmental samples, an immunomagnetic separation (IMS) method was also standardized. Water, husk, grass
and gram samples were artificially contaminated by B. mallei bacteria and after enrichment of B. mallei in BHIB-SS, detection was carried out by PCR and DNA hybridization. PCR was found to be a better method of the two with a
detection limit of 104–106 CFU/ml (6 h enrichment in BHIB-SS) in water and other particulate matrices. Detection by PCR in the above samples without
enrichment in BHIBSS was carried out following IMS where the detection limit was about 1–2 log higher than PCR following enrichment
in BHIB-SS. We recommend PCR for 823 bp for detection of B. mallei from environmental samples either following enrichment in BHIB-SS or IMS. IMS-PCR method may be preferred in situations where
numbers of B. mallei bacteria are expected to be high and results are required in short time. 相似文献
84.
Shashi Kant Singh Manoj K. Rai Pooja Asthana L. Sahoo 《Acta Physiologiae Plantarum》2010,32(3):607-610
Nodal segments obtained from in vitro proliferated shoots of Eclipta alba (L.) Hassk, were encapsulated in calcium alginate beads for large-scale clonal propagation, short-term conservation and germplasm
exchange and distribution. The best gel complexation was achieved using 3% sodium alginate and 100 mM CaCl2·2H2O. Maximum percent response (100%) for conversion of encapsulated nodal segments into plantlets was obtained on 0.7% agar-solidified
full-strength MS medium containing 0.88 μM BAP. Encapsulated nodal segments could be stored at low temperature (4°C) up to
60 days with a survival frequency of 51.2%. The well-developed plantlets regenerated from encapsulated nodal segments were
hardened-off successfully with 90% survival frequency. 相似文献
85.
Sanjay Dwivedi R. D. Tripathi Sudhakar Srivastava Ragini Singh Amit Kumar Preeti Tripathi Richa Dave U. N. Rai Debasis Chakrabarty P. K. Trivedi R. Tuli B. Adhikari M. K. Bag 《Protoplasma》2010,245(1-4):113-124
The exposure of paddy fields to arsenic (As) through groundwater irrigation is a serious concern that may not only lead to As accumulation to unacceptable levels but also interfere with mineral nutrients in rice grains. In the present field study, profiling of the mineral nutrients (iron (Fe), phosphorous, zinc, and selenium (Se)) was done in various rice genotypes with respect to As accumulation. A significant genotypic variation was observed in elemental retention on root Fe plaque and their accumulation in various plant parts including grains, specific As uptake (29–167 mg kg?1 dw), as well as As transfer factor (4–45%). Grains retained the least level of As (0.7–3%) with inorganic As species being the dominant forms, while organic As species, viz., dimethylarsinic acid and monomethylarsonic acid, were non-detectable. In all tested varieties, the level of Se was low (0.05–0.12 mg kg?1 dw), whereas that of As was high (0.4–1.68 mg kg?1 dw), considering their safe/recommended daily intake limits, which may not warrant their human consumption. Hence, their utilization may increase the risk of arsenicosis, when grown in As-contaminated areas. 相似文献
86.
Chromium and its compounds may cause disturbance in the nutrient level of the plants. Iron, manganese, copper, and zinc are
essential nutrient elements and required for balanced growth and development of plants, but chromium uptake sometimes disturbed
their concentration in plants. Therefore, in the present paper, an effort has been made to observe the effect of different
levels of Cr on nutrient uptake of Phyllanthus amarus and Solanum nigrum, the medicinally important plants of indigenous systems of medicine having hepatoprotective and diuretic properties. The
study revealed that Cr causes significant changes in nutrient uptake as compared to control plants. Besides, Cr-treated plants
showed growth depression and decrease in fresh and dry weight too. With the increase in Cr supply, accumulation of Cr in roots
was increased significantly. Concentration of manganese and zinc was also increased. However, copper concentration in both
the plants seemed less affected by Cr. 相似文献
87.
Leaf wounding and the wound signaling peptide systemin induce expression of wound response genes while the fungal toxin fusicoccin
(FC) induces expression of pathogenesis-related genes. Consistent with their functional differences, FC and systemin regulate
the extracellular pH in opposite ways, with systemin inducing an alkalinization and FC an acidification response. Here we
show that systemin, wounding and FC activate the same mitogen-activated protein kinases (MAPKs; MPKs) MPK1 and 2 in tomato
(Lycopersicon esculentum) leaves and L. peruvianum suspension-cultured cells. Wounding and FC activated an additional MAPK, MPK3. Pronounced differences were observed with
regard to MAPK activation kinetics. FC induced prolonged, and systemin transient activity of the MAPKs. This shows that functionally
different elicitors engage the same signaling components, yet induce signal-specific activation dynamics. A comparative analysis
of pH effects and MAPK activity in response to specific treatments revealed that the kinetics of pH changes and MAPK activation
did not correlate. Simultaneous application of FC and systemin did not lead to immediate pH changes but resulted in rapid
increases in MAPK activity. Furthermore, changes in extracellular pH could be induced without concomitant MAPK activation
by exchanging conditioned medium with fresh medium. This shows that changes in the extracellular pH are neither required nor
sufficient for MAPK activation, suggesting that signaling pathways involving MAPKs and extracellular pH changes operate in
parallel and are not part of the same linear pathway. 相似文献
88.
J. P. Tamang S. Dewan B. Tamang A. Rai U. Schillinger W. H. Holzapfel 《Indian journal of microbiology》2007,47(2):119-125
Hamei and Marcha are mixed dough inocula used as starters for preparation of various indigenous alcoholic beverages in Manipur and Sikkim
in India, respectively. These starters are traditionally prepared from rice with wild herbs and spices. Samples of Hamei and Marcha, collected from Manipur and Sikkim, respectively, were analysed for lactic acid bacterial composition. The population of
lactic acid bacteria (LAB) was 6.9 and 7.1 Log cfu/g in Hamei and Marcha, respectively. On the basis of phenotypic and genotypic characters, LAB strains isolated from Hamei and Marcha were identified as Pediococcus pentosaceus, Lactobacillus plantarum and Lactobacillus brevis. Technological properties of LAB such as antimicrobial properties, effect on acidification, ability to produce biogenic amines
and ethanol, degree of hydrophobicity and enzymatic activities were also performed. Pediococcus pentosaceus HS: B1, isolated from Hamei, was found to produce bacteriocin. None of the strains produced biogenic amines. LAB strains showed a strong acidifying ability
and they also produced a wide spectrum of enzymes. 相似文献
89.
Many clinical trials compare two or more treatment groups by using a binary outcome measure. For example, the goal could be to determine whether the frequency of pain episodes is significantly reduced in the treatment group (arm A) as compared to the control group (arm B). However, for ethical or regulatory reasons, group sequential designs are commonly employed. Then, based on a binomial distribution, the stopping boundaries for the interim analyses are constructed for assessing the difference in the response probabilities between the two groups. This is easily accomplished by using any of the standard procedures, e.g., those discussed by Jennison and Turnbull (2000), and using one of the most commonly used software packages, East (2000). Several factors are known to often affect the primary outcome of interest, but their true distributions are not known in advance. In addition, these factors may cause heterogeneous treatment responses among individuals in a group, and their exact effect size may be unknown. To limit the effect of such factors on the comparison of the two arms, stratified randomization is used in the actual conduct of the trial. Then, a stratified analysis based on the odds ratio proposed in Jennison and Turnbull (2000, pages 251-252) and consistent with the stratified design is undertaken. However, the stopping rules used for the interim analyses are those obtained for determining the differences in response rates in a design that was not stratified. The purpose of this paper is to assess the robustness of such an approach on the performance of the odds ratio test when the underlying distribution and effect size of the factors that influence the outcome may vary. The simulation studies indicate that, in general, the stratified approach offers consistently better results than does the unstratified approach, as long as the difference in the weighted average of the response probabilities across strata between the two groups remains closer to the hypothesized values, irrespective of the differences in the (allocation) distributions and heterogeneous response rate. However, if the response probabilities deviate significantly from the hypothesized values so that the difference in the weighted average is less than the hypothesized value, then the proposed study could be significantly underpowered. 相似文献
90.
The role of mitochondria in causing diseases is becoming evident as more and more studies are focusing on this organelle of
the cell. This is largely attributed to its reactive oxygen species (ROS) production property. In the context of diabetes,
ROS is suggested to trigger different forms of insulin resistance involving different mechanisms. The suggestive role of a
mtDNA variant G10398A in increasing ROS production and the impaired response to oxidative stress due to T16189C variant is
worth addressing as genetic susceptibility factors in type 2 diabetes mellitus (T2DM). A case control study on 312 T2DM cases
and ethnically matched 466 controls involving two North Indian populations, referred as cohort 1 and cohort 2 (in a replicative
study), was undertaken to test such a genetic association. A statistically significant association was observed for 10398A
allele in both the cohorts [cohort1 (OR = 2.67 95% CI 1.77–4.00); cohort2 (OR = 1.76 95%CI 1.12–2.77)]. The analysis of G10398A/T16189C
haplotypic combinations revealed that 10398A/16189C haplotype provides a risk in both the cohorts. To sum up the study suggests
that 10398A and 16189C alleles provide susceptiblity to T2DM independently as well as together. 相似文献