全文获取类型
收费全文 | 1643篇 |
免费 | 202篇 |
专业分类
1845篇 |
出版年
2022年 | 17篇 |
2021年 | 36篇 |
2020年 | 21篇 |
2018年 | 31篇 |
2017年 | 30篇 |
2016年 | 38篇 |
2015年 | 52篇 |
2014年 | 54篇 |
2013年 | 75篇 |
2012年 | 73篇 |
2011年 | 77篇 |
2010年 | 58篇 |
2009年 | 42篇 |
2008年 | 70篇 |
2007年 | 75篇 |
2006年 | 71篇 |
2005年 | 53篇 |
2004年 | 50篇 |
2003年 | 67篇 |
2002年 | 44篇 |
2001年 | 45篇 |
2000年 | 48篇 |
1999年 | 38篇 |
1998年 | 19篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1993年 | 15篇 |
1992年 | 31篇 |
1991年 | 34篇 |
1990年 | 26篇 |
1989年 | 35篇 |
1988年 | 29篇 |
1987年 | 42篇 |
1986年 | 30篇 |
1985年 | 27篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 25篇 |
1978年 | 22篇 |
1977年 | 17篇 |
1976年 | 16篇 |
1975年 | 22篇 |
1973年 | 21篇 |
1972年 | 21篇 |
1971年 | 14篇 |
1970年 | 14篇 |
排序方式: 共有1845条查询结果,搜索用时 15 毫秒
81.
Debashree De Piyali Datta Chakraborty Jyotirmoy Mitra Kanika Sharma Somnath Mandal Aneesha Das Saikat Chakrabarti Debasish Bhattacharyya 《PloS one》2013,8(3)
An aqueous extract of human placenta exhibits strong gelatinase/collagenase activity in zymography. 2-D gel electrophoresis of the extract with gelatin zymography in the second dimension displayed a single spot, identified as ubiquitin-like component upon MALDI/TOF MS/MS analysis. Immunoblot indicated presence of ubiquitin and absence of collagenase in the extract. Collagenase activity of the ubiquitin-like component was confirmed from the change in solubility of collagen in aqueous buffer, degradation of collagen by size-exclusion HPLC and atomic force microscopy. Quantification with DQ-gelatin showed that the extract contains 0.04 U/ml of collagenase activity that was inhibited up to 95% by ubiquitin antibody. Ubiquitin from bovine erythrocytes demonstrated mild collagenase activity. Bioinformatics studies suggest that placental ubiquitin and collagenase follow structurally divergent evolution. This thermostable intrinsic collagenase activity of placental extract might have wide physiological relevance in degrading and remodeling collagen as it is used as a drug for wound healing and pelvic inflammatory diseases. 相似文献
82.
Ruhar Singh Naveen Kumar Meena Trishala Das Ravi Datta Sharma 《Journal of biomolecular structure & dynamics》2020,38(17):5027-5036
AbstractThe funnel shaped energy landscape model of the protein folding suggests that progression of folding proceeds through multiple pathways, having the multiple intermediates which leads to multidimensional free-energy surface. Herein, we applied all-atom MD simulation to conduct a comparative study on the structure of β-lactoglobulin (β-LgA) in aqueous mixture of 8?M urea and 8?M dimethyl sulfoxide (DMSO), at different temperatures. The cumulative results of multiple simulations suggest a common unfolding pathway of β-LgA, occurred through the stable and meta-stable intermediates (I), in both urea and DMSO. However, the free-energy landscape (FEL) analyses show that the structural transitions of I-states are energetically different. In urea, FEL shows distinct ensemble of intermediates, I1 and I2, separated by the energy barrier of ~3.0?kcal mol?1. Similarly, we find the population of two distinct I1 and I2 states in DMSO, however, the I1 appeared transiently around ~30–35?ns and is short-lived. But, the I2 ensemble is observed structurally compact and long-lived (~50–150?ns) as compared to unfolding in urea. Furthermore, the I1 and I2 are separated through a high energy barrier of ~6.0?kcal mol?1. Thus, our results provide the structural insights of intermediates which essentially bear the signature of a different unfolding pathway of β-LgA in urea and DMSO. Abbreviations β-LgA β-lactoglobulin DMSO dimethyl sulfoxide FEL free-energy landscape GdmCl guanidinium chloride I intermediate state MG molten globule state PME particle mesh Ewald Q fraction of native contacts RMSD root mean square deviation RMSF root mean square fluctuation Rg radius of gyration SASA solvent Accessible Surface Area scSASA the side chain SASA Trp tryptophan Communicated by Ramaswamy H. Sarma 相似文献
83.
84.
Raquel Santiago-Arenas Buyung A. Fanshuri Sholih N. Hadi Hayat Ullah Avishek Datta 《The Annals of applied biology》2020,176(3):314-327
Sustainable rice production through selection of best suitable cultivar, water-efficient crop establishment method and optimum nitrogen (N) management practice is needed to feed the growing world population. Two polyhouse experiments were conducted to evaluate the response of rice to different rates and schedules of N application under different establishment methods subjected to alternate wetting and drying (AWD) irrigation. In the first experiment, the response of two rice cultivars (Pathumthani 1, RD57) under three establishment methods (transplanting [TP], wet direct seeding [WDS], dry direct seeding [DDS]) and five N rates (0 [N0], 30 [N30], 60 [N60], 90 [N90], 120 [N120] kg ha−1) was evaluated. The second experiment consisted of the same cultivars and establishment methods, but with four N application schedules (T1: 100% at basal; T2: 75% + 25% at basal and at active tillering, respectively; T3: 50% + 25% + 25% at basal, at active tillering and at panicle initiation, respectively; and T4: 25% + 25% + 25% + 25% each at basal, at active tillering, at panicle initiation and at early flowering or just before heading starts) applied at the rate of N60 kg ha−1. Plants were maintained under AWD irrigation (soil was saturated by applying water whenever soil water potential drops to −5 kPa during the implementation period) in both experiments. RD57 performed better than Pathumthani 1 having higher shoot dry matter, panicle number, grain yield, total N uptake and apparent N recovery efficiency. TP gave better response than WDS and DDS regardless of cultivars. Application of N120 resulted in better growth, yield and its components and total N uptake regardless of establishment methods and cultivars. Increasing N rate decreased N use efficiency (NUE). Scheduling the interval of N application to two or three times (T2 or T3) for RD57 and Pathumthani 1, respectively, provided overall better results, and could be recommended for the tested rice cultivars. An optimal N rate and selection of critical growth stages for N application would be very effective for maximising yield and NUE under the water-saving cultivation technique of AWD irrigation. 相似文献
85.
S. Datta R. G. Choudhary Md. Shamim Vishwa Dhar 《Archives Of Phytopathology And Plant Protection》2013,46(6):558-566
Fusarium species causing wilt diseases in different plants were characterised by comparing nonpathogenic and different pathogenic species using rDNA RFLP analysis. The ITS (internal transcribed spacer) region of 12 isolates belonging to the section Elegans, Laseola, Mortiella, Discolor, Gibbosum, Lateritium and Sporotrichiella were amplified by universal ITS primers (ITS-1 and ITS-4) using polymerase chain reaction (PCR). Amplified products, which ranged from 522 to 565 bp were obtained from all 12 Fusarium isolates. The amplified products were digested with seven restriction enzymes, and restriction fragment length polymorphism (RFLP) patterns were analysed. A dendrogram derived from PCR-RFLP analysis of the rDNA region divided the Fusarium isolates into three major groups. Assessment of molecular variability based on rDNA RFLP clearly indicated that Fusarium species are heterogeneous and most of the forma speciales have close evolutionary relationships. 相似文献
86.
87.
Pollen grains of M, and C, generation plants of Trichosanthes anguina L. were studied after treatment of seeds with X-rays and colchicine respectively. Pollen sterility increased with increase in X-ray dose and colchicine concentration. The polar axis of X-irradiated populations was shorter than that of controls. But colchicine treatment resulted in larger pollen grains than the controls, although the exine did not increase as much. Ex-perimentally-produced tetraploids had larger pollen grains than diploids and triploids. The triploids were characterised by changes in pore morphology. Of 293 treated plants examined, 11 aberrant plants were isolated in the M, and C, generations. These plants had large and small fertile pollen grains, and also showed treatment effects in external morphology and chromosomal aberration during meiosis. The changes in polar diameter were not associated with variation in chromosomal material. 相似文献
88.
89.
Joao A. Ascensao Pratik Datta Baris Hancioglu Eduardo Sontag Maria L. Gennaro Oleg A. Igoshin 《PLoS computational biology》2016,12(2)
Understanding how dynamical responses of biological networks are constrained by underlying network topology is one of the fundamental goals of systems biology. Here we employ monotone systems theory to formulate a theorem stating necessary conditions for non-monotonic time-response of a biochemical network to a monotonic stimulus. We apply this theorem to analyze the non-monotonic dynamics of the σB-regulated glyoxylate shunt gene expression in Mycobacterium tuberculosis cells exposed to hypoxia. We first demonstrate that the known network structure is inconsistent with observed dynamics. To resolve this inconsistency we employ the formulated theorem, modeling simulations and optimization along with follow-up dynamic experimental measurements. We show a requirement for post-translational modulation of σB activity in order to reconcile the network dynamics with its topology. The results of this analysis make testable experimental predictions and demonstrate wider applicability of the developed methodology to a wide class of biological systems. 相似文献
90.
In an effort to build a comprehensive genomic approach to food safety challenges, the FDA has implemented a whole genome sequencing effort, GenomeTrakr, which involves the sequencing and analysis of genomes of foodborne pathogens. As a part of this effort, we routinely sequence whole genomes of Listeria monocytogenes (Lm) isolates associated with human listeriosis outbreaks, as well as those isolated through other sources. To rapidly establish genetic relatedness of these genomes, we evaluated tetranucleotide frequency analysis via the JSpecies program to provide a cursory analysis of strain relatedness. The JSpecies tetranucleotide (tetra) analysis plots standardized (z-score) tetramer word frequencies of two strains against each other and uses linear regression analysis to determine similarity (r2). This tool was able to validate the close relationships between outbreak related strains from four different outbreaks. Included in this study was the analysis of Lm strains isolated during the recent caramel apple outbreak and stone fruit incident in 2014. We identified that many of the isolates from these two outbreaks shared a common 4b variant (4bV) serotype, also designated as IVb-v1, using a qPCR protocol developed in our laboratory. The 4bV serotype is characterized by the presence of a 6.3 Kb DNA segment normally found in serotype 1/2a, 3a, 1/2c and 3c strains but not in serotype 4b or 1/2b strains. We decided to compare these strains at a genomic level using the JSpecies Tetra tool. Specifically, we compared several 4bV and 4b isolates and identified a high level of similarity between the stone fruit and apple 4bV strains, but not the 4b strains co-identified in the caramel apple outbreak or other 4b or 4bV strains in our collection. This finding was further substantiated by a SNP-based analysis. Additionally, we were able to identify close relatedness between isolates from clinical cases from 1993–1994 and a single case from 2011 as well as links between two isolates from over 30 years ago. The identification of these potential links shows that JSpecies Tetra analysis can be a useful tool in rapidly assessing genetic relatedness of Lm isolates during outbreak investigations and for comparing historical isolates. Our analyses led to the identification of a highly related clonal group involved in two separate outbreaks, stone fruit and caramel apple, and suggests the possibility of a new genotype that may be better adapted for certain foods and/or environment. 相似文献