全文获取类型
收费全文 | 636篇 |
免费 | 39篇 |
国内免费 | 1篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 19篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 21篇 |
2017年 | 13篇 |
2016年 | 22篇 |
2015年 | 17篇 |
2014年 | 28篇 |
2013年 | 49篇 |
2012年 | 61篇 |
2011年 | 46篇 |
2010年 | 33篇 |
2009年 | 29篇 |
2008年 | 36篇 |
2007年 | 45篇 |
2006年 | 34篇 |
2005年 | 29篇 |
2004年 | 36篇 |
2003年 | 25篇 |
2002年 | 21篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有676条查询结果,搜索用时 15 毫秒
581.
Kumar S Khanduja KL Verma N Verma SC Avti PK Pathak CM 《Molecular and cellular biochemistry》2008,307(1-2):109-119
We investigated the in vitro efficacy of all-trans retinoic acid (ATRA) and alpha-tocopherol succinate (α-TS) alone and in combination on the induction of cell death in freshly
isolated leukemic cells obtained from chronic myeloid leukemia (CML) patients. In vitro cytotoxicity and induction of lipid
peroxidation by ATRA (10 μM) and α-TS (25 or 50 μM) were evaluated in primary leukemic cells by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
bromide] assay and malondialdehyde formation respectively. Treatment of leukemic cells with α-TS alone or in combination with
ATRA significantly (P < 0.05) decreased the cell viability in a concentration and time dependent manner as compared to peripheral blood mononuclear
cells obtained from normal healthy controls. Lipid peroxidation was enhanced by 98% (P < 0.05) on combined treatment of cells with ATRA (10 μM) and α-TS (50 μM). ATRA alone did not enhance the externalization
of phosphatidyl serine as studied by annexin-V binding using fluorescence activated cell sorter analysis, whereas in combination
with α-TS it increased to 400% at 12 h. The treatment of leukemic cells to combination of ATRA with α-TS significantly decreased
(P < 0.05) mitochondrial membrane potential and enhanced lysosomal destabilization. The combination of these drugs also increased
mitochondrial and cytosolic reactive oxygen species (ROS) production, nitric oxide levels, and caspase-3 activity significantly
and caused DNA fragmentation at 24 h in a concentration dependent manner in the leukemic cells. Our data suggest that ATRA
in combination with α-TS efficiently induces apoptosis in leukemic cells, which may be a useful therapeutic modality in CML
patients. 相似文献
582.
583.
Asha Chandola-Saklani Ashish Thapliyal Kiran Negi Subhash C. Diyundi Bimalendu Choudhary 《Chronobiology international》2004,21(4):553-569
In some long-lived organisms, particularly in tropical birds and migrants that spend part of the year close to the equator, endogenous circannual rhythms have been demonstrated in seasonal events like reproduction, molt, and migration. These, like the circadian rhythms, are expressed only in constant conditions of illumination with a periodicity deviating from 1 yr. If birds followed this periodicity, they would soon be out of phase with the annual calendar and perish and, therefore, they would need to be synchronized. However, almost nothing is known as to how synchronization is achieved in birds. Herein, with the help of a suitable model, viz., the tropical spotted munia and long-term experiments conducted in series over a 5-yr period, we provide direct evidence for the first time indicating that the segment of annual photocycle with maximal rate of increase prior to vernal equinox (approximately between mid-February and mid-March) synchronizes the circannual reproductive cycle with the monsoon period of ample food supply through a phase delay. Data also indicate, contrary to the prevalent view, that birds in the tropics can perceive minor changes in day-length, that birds respond to progressive changes in day-length as distinct from responding to fixed photoperiods of particular durations, and that birds can actually distinguish the quality of the environmental signal, viz., vernal equinox from early spring, or increasing days of spring from decreasing days of autumn. The underlying mechanisms, although yet to be identified, appear to involve a gonado-inhibitory rather than the conventional gonado-stimulatory response to increasing day-length. The photoperiodic responses of spotted munia are distinctly different from that of any “long-day” birds described thus far and do not conform to the prevalent “circadian coincidence” hypothesis of photoperiodism. 相似文献
584.
Arora K Chaubey A Singhal R Singh RP Pandey MK Samanta SB Malhotra BD Chand S 《Biosensors & bioelectronics》2006,21(9):1777-1783
Double stranded calf thymus deoxyribonucleic acid (DNA) was physisorbed onto polypyrrole-polyvinyl sulphonate (PPY-PVS) films electrochemically deposited onto indium-tin-oxide (ITO) coated glass plates. These DNA immobilized PPY-PVS films optimized for various conditions, such as polymerization potential, pH of buffer, DNA concentration and scan rate were characterized using Fourier-transform infrared (FT-IR) spectroscopy, atomic force microscopy (AFM) and cyclic voltammetry (CV) techniques, respectively. The amperometric response studies of these DNA/PPY-PVS electrodes were carried out as a function of 2-aminoantharcene (2-AA, 0.01-20 ppm) and o-chlorophenol (OCP, 0.1-30 ppm) concentration, respectively at 25 degrees C. The observed amperometric current arising due to oxidation of guanine in the DNA/PPY-PVS films decreased linearly with the increase in the concentration of 2-AA and OCP. It has been revealed that 10 ppm of 2-AA is sufficient to reduce the observed guanine oxidation peak current by approximately -95+/-10% as compared to the reported values. A 25 ppm of OCP was capable enough to reduce the guanine oxidation current to zero. These DNA/PPY-PVS electrodes were found to have a shelf life of about 4 months when stored at 25 degrees C. 相似文献
585.
Yin Z Patel SJ Wang WL Wang G Chan WL Rao KR Alam J Jeyaraj DA Ngew X Patel V Beer D Lim SP Vasudevan SG Keller TH 《Bioorganic & medicinal chemistry letters》2006,16(1):36-39
Substrate-based tetrapeptide inhibitors with various warheads were designed, synthesized, and evaluated against the Dengue virus NS3 protease. Effective inhibition was achieved by peptide inhibitors with electrophilic warheads such as aldehyde, trifluoromethyl ketone, and boronic acid. A boronic acid has the highest affinity, exhibiting a K(i) of 43 nM. 相似文献
586.
587.
Gelatin is a popular tissue simulant used in biomedical applications. The uniaxial compressive stress–strain response of gelatin was determined at a range of strain rates. In the quasistatic regime, gelatin strength remained relatively constant. With increase in loading rate, the compressive strength increased from 3 kPa at a strain rate of around 0.0013/s to 6 MPa at a strain rate of around 3200/s. This dramatic increase in strength of gelatin at high rates is attributed to its shear-thickening behavior and is argued on the basis of hydrocluster formation mechanism and differences in internal energy dissipation mechanism under static and dynamic loading. 相似文献
588.
Subhash Chandra Yadav N. K. Prasanna Kumari Medicherla V. Jagannadham 《European biophysics journal : EBJ》2010,39(12):1581-1588
The effect of deglycosylation on the physiological and functional organization of milin was studied under different denaturizing
conditions. Trifluoromethanesulfonic acid mediated deglycosylation resulted in insoluble milin, which was found to be soluble
only in 1.5 M GuHCl with native-like folded structure. Kinetic stability, proteolytic activity, and dimeric association were
lost in deglycosylated milin. Urea-induced unfolding revealed two inactive, highly stable equilibrium intermediates at pH
7.0 and pH 2.0. These intermediates were stable between 5.5–6.5 and 5.0–6.0 M total chaotropes (urea + 1.5 M GuHCl) at pH
7.0 and pH 2.0, respectively. GuHCl-induced unfolding was cooperative and noncoincidental with a broad transition range (2.0–5.0 M)
at pH 7.0 and pH 2.0. Equilibrium unfolding of deglycosylated milin by urea and GuHCl substantiates the involvement of various
inactive monomeric intermediates. This study provides a way to understand the role of glycosylation in the unfolding mechanism,
stability, and functional activity of the serine protease milin. 相似文献
589.
We investigated geographical variations in three fitness-related traits (body melanisation, ovariole number and fecundity) in laboratory-reared offspring of 10 populations of Drosophila melanogaster. The populations were collected from adjacent lowland and highland localities (-80-100 km apart) in the tropical as well as subtropical regions (11.15-31.06°N) covering a linear distance about 3 000 kilometers from south to north on the Indian subcontinent. Persistence of within- as well as between-population differences at 21 ℃ suggest that observed variations in fitness-related traits have a genetic basis. Populations from higher altitudes showed consistently higher trait values (1.4-fold increase) as compared with their corresponding lowland populations. By contrast, latitudinal variations were about two-fold higher across the entire continent. Along latitude as well as altitude, population means showed higher correlation values (r 〉 0.98) between all the three fitness traits. However, on the basis of within-population analysis (assorted darker and lighter flies), changes in body melanisation were significantly correlated with fecundity but not with ovariole number. Thus, analysis of within-population trait variability should be preferred as compared with data on population means for adaptive significance of fitness-related traits. In the present study, the role of climatic selection is evident from regression analysis with changes in annual average temperature of the sites of origin of populations along latitude as well as altitude. 相似文献
590.
Rahul Caprihan Subhash Wadhwa Satish Kumar 《Flexible Services and Manufacturing Journal》2004,16(3):251-275
Manufacturing systems with varying levels and types of flexibility employ alternative scheduling strategies to exploit flexibility for performance enhancement. Scheduling decisions in manufacturing systems are influenced by time delays due to information handling activities such as information collection, transfer, and processing. More specifically, scheduling strategies implicitly involve information intensive activities that may entail significant time delays for implementation, depending on the extant shop floor automation and integration within a flexible system. These are information delays and we believe that most contemporary flexible systems must inherently cope with some level of information delay when implementing on-line scheduling strategies. This paper conceptualizes the manifestation of information delays in the context of scheduling decisions within flexible systems through the definition of three key delay modes: (i) Mode 1 information-transfer delay; (ii) Mode 2 decision-implementation delay; and (iii) Mode 3 status-review delay. We then stress the need and importance of devising suitable on-line scheduling strategies for countering the effect of information delays by demonstrating the efficacy of a novel scheduling strategy on a single machine. While opening a new scheduling dimension with potential research ramifications, this paper highlights the fact that the concept of information delay can effectively capture the synergism issues related with flexibility, integration, and automation in the context of scheduling decisions within semi-automated flexible systems. 相似文献