全文获取类型
收费全文 | 493篇 |
免费 | 35篇 |
出版年
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 17篇 |
2017年 | 22篇 |
2016年 | 18篇 |
2015年 | 25篇 |
2014年 | 24篇 |
2013年 | 36篇 |
2012年 | 45篇 |
2011年 | 50篇 |
2010年 | 37篇 |
2009年 | 14篇 |
2008年 | 27篇 |
2007年 | 50篇 |
2006年 | 29篇 |
2005年 | 21篇 |
2004年 | 25篇 |
2003年 | 20篇 |
2002年 | 15篇 |
2001年 | 3篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1965年 | 1篇 |
1956年 | 1篇 |
1954年 | 1篇 |
1950年 | 1篇 |
1933年 | 2篇 |
1932年 | 1篇 |
排序方式: 共有528条查询结果,搜索用时 31 毫秒
101.
102.
Shelf Life Degradation of Bulk Heterojunction Solar Cells: Intrinsic Evolution of Charge Transfer Complex 下载免费PDF全文
Antonio Guerrero Hamed Heidari Teresa S. Ripolles Martin Pfannmöller Sara Bals Louis‐Dominique Kauffmann Juan Bisquert Germà Garcia‐Belmonte 《Liver Transplantation》2015,5(7)
Achievement of long‐term stability of organic photovoltaics is currently one of the major topics for this technology to reach maturity. Most of the techniques used to reveal degradation pathways are destructive and/or do not allow for real‐time measurements in operating devices. Here, three different, nondestructive techniques able to provide real‐time information, namely, film absorbance, capacitance–voltage (C–V), and impedance spectroscopy (IS), are combined over a period of 1 year using non‐accelerated intrinsic degradation conditions. It is discerned between chemical modifications in the active layer, physical processes taking place in the bulk of the blend from those at the active layer/contact interfaces. In particular, it is observed that during the ageing experiment, the main source for device performance degradation is the formation of donor–acceptor charge‐transfer complex (–) that acts as an exciton quencher. Generation of these radical species diminishes photocurrent and reduces open‐circuit voltage by the creation of electronic defect states. Conclusions extracted from absorption, C–V, and IS measurements will be further supported by a range of other techniques such as atomic force microscopy, X‐ray diffraction, and dark‐field imaging of scanning transmission electron microscopy on ultrathin cross‐sections. 相似文献
103.
VM Hernández-Rocamora B Reija C García P Natale C Alfonso AP Minton S Zorrilla G Rivas M Vicente 《The Journal of biological chemistry》2012,287(36):30097-30104
The full-length ZipA protein from Escherichia coli, one of the essential components of the division proto-ring that provides membrane tethering to the septation FtsZ protein, has been incorporated in single copy into nanodiscs formed by a membrane scaffold protein encircling an E. coli phospholipid mixture. This is an acellular system that reproduces the assembly of part of the cell division components. ZipA contained in nanodiscs (Nd-ZipA) retains the ability to interact with FtsZ oligomers and with FtsZ polymers. Interactions with FtsZ occur at similar strengths as those involved in the binding of the soluble form of ZipA, lacking the transmembrane region, suggesting that the transmembrane region of ZipA has little influence on the formation of the ZipA·FtsZ complex. Peptides containing partial sequences of the C terminus of FtsZ compete with FtsZ polymers for binding to Nd-ZipA. The affinity of Nd-ZipA for the FtsZ polymer formed with GTP or GMPCPP (a slowly hydrolyzable analog of GTP) is moderate (micromolar range) and of similar magnitude as for FtsZ-GDP oligomers. Polymerization does not stabilize the binding of FtsZ to ZipA. This supports the role of ZipA as a passive anchoring device for the proto-ring with little implication, if any, in the regulation of its assembly. Furthermore, it indicates that the tethering of FtsZ to the membrane shows sufficient plasticity to allow for its release from noncentral regions of the cytoplasmic membrane and its subsequent relocation to midcell when demanded by the assembly of a division ring. 相似文献
104.
105.
Jiménez-Palomares M Ramos-Rodríguez JJ López-Acosta JF Pacheco-Herrero M Lechuga-Sancho AM Perdomo G García-Alloza M Cózar-Castellano I 《American journal of physiology. Endocrinology and metabolism》2012,302(11):E1373-E1380
Type 2 diabetes (T2D) mellitus and Alzheimer's disease (AD) are two prevalent diseases with comparable pathophysiological features and genetic predisposition. Patients with AD are more susceptible to develop T2D. However, the molecular mechanism linking AD and T2D remains elusive. In this study, we have generated a new mouse model to test the hypothesis that AD would prompt the onset of T2D in mice. To test our hypothesis, we crossed Alzheimer APPswe/PS1dE9 (APP/PS1) transgenic mice with mice partially deficient in leptin signaling (db/+). Body weight, plasma glucose, and insulin levels were monitored. Phenotypic characterization of glucose metabolism was performed using glucose and insulin tolerance tests. β-Cell mass, islet volume, and islet number were analyzed by histomorphometry. APP/PS1 coexpression in mice with intact leptin receptor signaling did not show any metabolic perturbations in glucose metabolism or insulin sensitivity. In contrast, APP/PS1 coexpression in db/+ mice resulted in nonfasting hyperglycemia, hyperinsulinemia, and hypercholesterolemia without changes in body weight. Conversely, fasting blood glucose and cholesterol levels remained unchanged. Coinciding with altered glucose metabolism, APP/PS1 coexpression in db/+ mice resulted in glucose intolerance, insulin resistance, and impaired insulin signaling. In addition, histomorphometric analysis of pancreata revealed augmented β-cell mass. Taken together, these findings provide experimental evidence to support the notion that aberrant Aβ production might be a mechanistic link underlying the pathology of insulin resistance and T2D in AD. 相似文献
106.
Bravo-Almonacid F Rudoy V Welin B Segretin ME Bedogni MC Stolowicz F Criscuolo M Foti M Gomez M López M Serino G Cabral S Dos Santos C Huarte M Mentaberry A 《Transgenic research》2012,21(5):967-982
Solanum tuberosum ssp. tuberosum (cv. Spunta) was transformed with a chimeric transgene containing the Potato virus Y (PVY) coat protein (CP) sequence. Screening for PVY resistance under greenhouse conditions yielded over 100 independent candidate lines. Successive field testing of selected lines allowed the identification of two genetically stable PVY-resistant lines, SY230 and SY233, which were further evaluated in field trials at different potato-producing regions in Argentina. In total, more than 2,000 individuals from each line were tested along a 6-year period. While no or negligible PVY infection was observed in the transgenic lines, infection rates of control plants were consistently high and reached levels of up to 70-80%. Parallel field studies were performed in virus-free environments to assess the agronomical performance of the selected lines. Tubers collected from these assays exhibited agronomical traits and biochemical compositions indistinguishable from those of the non-transformed Spunta cultivar. In addition, an interspecific out-crossing trial to determine the magnitude of possible natural gene flow between transgenic line SY233 and its wild relative Solanum chacoense was performed. This trial yielded negative results, suggesting an extremely low probability for such an event to occur. 相似文献
107.
González GE Rodríguez M Donato M Palleiro J D'Annunzio V Morales C Gelpi RJ 《Canadian journal of physiology and pharmacology》2006,84(2):265-272
The aims of the present study were to determine whether the transitory systolic overshoot (TSO) that occurs in the early reperfusion (R) of the stunned myocardium is accompanied by diastolic alterations, and to determine whether the R with low Ca2+ Krebs-Henseleit's solution or with adenosine modifies these alterations. Isolated-isovolumic rabbit hearts were divided in 3 groups (G). G1 (n = 11) was perfused with Krebs-Henseleit's solution, subjected to 15 min of global ischemia and 30 min R; G2 (n = 10) was reperfused during the first 10 min with Krebs-Henseleit's solution [Ca2+] = 1 mmol/L, which was increased in the perfusate to 1.5 mmol/L up to 20 min R and at 2.5 mmol/L from 20 to 30 min R. G3 (n = 12) was perfused with Krebs-Henseleit's solution with adenosine (0.03 microg x kg(-1) x min(-1)) from 10 min before ischemia and during all R. Left ventricular (LV) +dP/dtmax (mmHg/s), LV end diastolic pressure (LVEDP, mmHg), and 1 relaxation index (t(1/2)) were measured in preischemic state, at 30, 50, 60, 70, 90, and 120 s R, and then at 5 and 30 min R. The +dP/dtmax recovered to 621 +/- 77 mmHg/s (p > 0.05), 346 +/- 31 mmHg/s (p < 0.05 vs. G1), and 533 +/- 76 mmHg/s (p > 0.05) from preischemic value of 730 +/- 39, 690 +/- 32, and 758 +/- 57 in G1, G2, and G3, respectively. The LVEDP in G1 and G3 increased early in the R, and it was negatively correlated with the +dP/dtmax (r = -0.63, p = 0.0369; and r = -0.71, p = 0.0090, respectively). The R with low Ca2+ abolished this correlation and attenuated the TSO phase. The correlation between LVEDP and +dP/dtmax in G1 and G3 and the lack of correlation in G2 suggests there are common mechanisms for the systolic and diastolic alterations during the TSO phase that are possibly related to Ca2+ overload but not with the vascular tone. 相似文献
108.
Armentano RL Santana DB Cabrera Fischer EI Graf S Cámpos HP Germán YZ Carmen Saldías MD Alvarez I 《Cryobiology》2006,52(1):17-26
The surgical options in arterial reconstruction are: the use of autologous arteries; autologous veins; or expanded polytetrafluoroethylene (ePTFE) grafts. However, the development of intimal hyperplasia when using veins or ePTFE grafts has been associated with graft failure. Since autologous arteries are not always available, the use of cryopreserved arteries has to be considered. The aims of this study were: (a) to compare the viscoelastic properties of stored cryopreserved arteries and fresh arteries by in vitro analysis; and (b) to compare the viscoelastic properties of arteries measured non-invasively in normotensive patients, with fresh arteries, cryopreserved arteries, and ePTFE segments. The viscoelastic studies were performed in normotensive patients using stress-strain analysis with non-invasive measurement of pressure and diameter in the common carotid artery, and in vitro measurements of pressure and diameter in arteries and prostheses. The in vitro studies showed that the elastic modulus (E), viscous modulus (eta), Stiffness Index (SI), Peterson modulus (Ep), and the pulse wave velocity (PWV) values for human cryopreserved carotid arteries were similar to the values obtained non-invasively in normotensive subjects (P>0.05) and to human fresh vessels (P>0.05). In vitro, the SI, Ep, PWV, and E values of ePTFE were significantly higher than the observed values in subjects and with fresh and cryopreserved arteries (P<0.05); on the other hand the ePTFE eta values were the lowest (P<0.05). We concluded that cryopreserved arteries have similar viscoelastic properties to those obtained in vivo in the arteries of normotensive subjects and in vitro in fresh arteries. Consequently, we conclude that the cryopreservation procedure does not modify the mechanical properties of the arterial wall. 相似文献
109.
Mariana Melchiorre Germán Robert Victorio Trippi Roberto Racca H. Ramiro Lascano 《Plant Growth Regulation》2009,57(1):57-68
In previous works, we have established a correlation between antioxidant system response and tolerance to drought, osmotic
stress and photooxidative stress of different wheat cultivars with contrasting drought tolerance. In the present work, a protocol
to obtain and transform wheat protoplasts was established. Transgenic protoplasts with Manganese Superoxide Dismutase (Mn-SOD)
(E.C.: 1.15.1.1) and Glutathione Reductase (GR) (E.C.: 1.6.4.2) overexpression in chloroplasts were obtained, and their responses
to photooxidative stress were characterized. Protoplasts with Mn-SOD or GR overexpression, showed different responses and
tolerance to photooxidative stress. Protoplasts with Mn-SOD overexpression showed lower levels of oxidative damage, higher
level of endogenous hydrogen peroxide and a great induction of total SOD and GR activities during photooxidative treatments.
In protoplasts with GR overexpression the oxidative damage provoked by the photooxidative treatment was similar to control
protoplasts, the GSH content and GSH/GSH + GSSG ratio were higher than control and Mn-SOD transformed protoplast, and total
SOD and GR activities were not induced. Our results suggest that the differential responses and tolerance to photooxidative
stress given by Mn-SOD or GR overexpression, also depend on the effects of these enzyme activities over the cellular redox
state balance, which modulate the responses to photooxidative stress. 相似文献
110.
Variation in local environments may lead to variation in the selection pressures and differentiation among local populations
even at microgeographic scale. We investigated variation in temperature-induced plasticity in larval life-history traits among
populations of an isolated pool frog (Rana lessonae) metapopulation in Central Sweden. Successful breeding of this northern fringe metapopulation is highly dependent on early
summer temperature, however, the metapopulation shows very little variation in molecular genetic markers suggesting limited
potential for local differentiation. We exposed larvae from three closely-located populations to two temperatures (20 and
25°C) in laboratory to investigate their growth and development responses to temperature variation. In general, larvae exposed
to warmer temperature experienced higher survival and metamorphosed faster, but at a smaller size than those at low temperature.
We found differences among the populations in both trait mean values and in the plastic responses. Among-family variation
within populations was found in growth rate and time to metamorphosis, as well as in plasticity suggesting that these traits
have a capacity to evolve. Our results indicate ample phenotypic variation within and among these closely-located populations
despite the low molecular genetic variation. The differences in pond temperature characteristics detected in the study in
the three localities may suggest that differential selection is acting in the populations. The strong differentiation found
in the larval traits implies that understanding the factors that influence the potential of the populations to adapt to environmental
changes may be essential for successful conservation strategies. 相似文献