全文获取类型
收费全文 | 816篇 |
免费 | 83篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 14篇 |
2020年 | 20篇 |
2019年 | 22篇 |
2018年 | 24篇 |
2017年 | 21篇 |
2016年 | 32篇 |
2015年 | 40篇 |
2014年 | 37篇 |
2013年 | 64篇 |
2012年 | 61篇 |
2011年 | 48篇 |
2010年 | 43篇 |
2009年 | 37篇 |
2008年 | 44篇 |
2007年 | 55篇 |
2006年 | 43篇 |
2005年 | 34篇 |
2004年 | 40篇 |
2003年 | 28篇 |
2002年 | 24篇 |
2001年 | 14篇 |
2000年 | 20篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1966年 | 1篇 |
1941年 | 2篇 |
排序方式: 共有899条查询结果,搜索用时 31 毫秒
1.
Ivonne J. Garzn‐Ordua Shaun L. Winterton Yunlan Jiang Laura C.V. Breitkreuz Peter Duelli Michael S. Engel Norman D. Penny Catherine A. Tauber Atsushi Mochizuki Xingyue Liu 《Systematic Entomology》2019,44(3):499-513
We present a time‐calibrated phylogeny of the charismatic green lacewings (Neuroptera: Chrysopidae). Previous phylogenetic studies on the family using DNA sequences have suffered from sparse taxon sampling and/or limited amounts of data. Here we combine all available previously published DNA sequence data and add to it new DNA sequences generated for this study. We analysed these data in a supermatrix using Bayesian and maximum likelihood methods and provide a phylogenetic hypothesis for the family that recovers strong support for the monophyly of all subfamilies and resolves relationships among a large proportion of chrysopine genera. Chrysopinae tribes Leucochrysini and Belonopterygini were recovered as monophyletic sister clades, while the species‐rich tribe Chrysopini was rendered paraphyletic by Ankylopterygini. Relationships among the subfamilies were resolved, although with relatively low statistical support, and the topology varied based on the method of analysis. Greatest support was found for Apochrysinae as sister to Nothochrysinae and Chrysopinae, which is in contrast to traditional concepts that place Nothochrysinae as sister to the rest of the family. Divergence estimates suggest that the stem groups to the various subfamilies diverged during the Triassic‐Jurassic, and that stem groups of the chrysopine tribes diverged during the Cretaceous. 相似文献
2.
Ivonne Delgadillo 《Mycotoxin Research》1986,2(1):9-17
A method is described for the isolation and purification of ochratoxin A, ochratoxin B, ochratoxin ß mellein, 4-hydroxymellein and penicillic acid produced byAspergillus ochraceus in a synthetic liquid medium. Ochratoxin α, which was not found in the culture medium, was obtained by acid hydrolysis of ochratoxin A. A high pressure liquid Chromatograph equipped with Lichrosorb 100 and Lichrosorb RP-18 columns and UV and/or Refractive Index detectors was used. 相似文献
3.
Ana E. Lemus Felipe Vilchis Rebeca Damsky Bertha A. Ch vez Gustavo A. Garcí a Ivonne Grillasca Gregorio P rez-Palacios 《The Journal of steroid biochemistry and molecular biology》1992,41(3-8):881-890
Levonorgestrel (LNG) is a synthetic steroid that displays potent progestional and androgenic effects but it lacks estrogen-like activity. To examine the mode of action of this progestin, we studied its metabolism in vitro in target organs and the specific interactions of LNG and its metabolites with putative steroid receptors. The results demonstrated that [3H]LNG was efficiently converted to A-ring reduced derivatives when incubated with rat hypothalamus and pituitary. Under optimal incubation conditions, [3H]5-dihydro LNG (5-LNG) and [3H]3-5-tetrahydro LNG (3,5-LNG) were identified as the major metabolic conversion products, while [3H]3ß, 5-LNG formation occured to a lesser extent. A-ring reduction of LNG was NADPH-dependent. Assessment of the relative binding affinities of LNG and its derivatives to progesterone (PR), androgen (AR) and estrogen (ER) receptors by displacement analysis revealed that unchanged LNG binds with high affinity to PR and AR but not to ER. 5-LNG exhibited a diminished though significant interactions with PR and an enhanced binding affinity for AR as compared with LNG, indicating that 5-reduction of LNG increases its affinity for AR. The most striking finding was that further reduction of the 5-LNG molecule at C-3 abolished its binding activity to PR, AR, and even to ER. The overall data provides a plausible explanation for the lack of estrogen agonistic action of LNG and for its potent progestational and androgenic effects. 相似文献
4.
Dr. Angele McGrady Sharon Williams Utz Marilynn Woerner Guillermo A. A. Bernal James T. Higgins 《Applied psychophysiology and biofeedback》1986,11(2):95-103
This paper describes differences in response in seventeen patients with essential hypertension who participated in a treatment program consisting of electromyograph biofeedback assisted relaxation training. Responders were found to have higher treatment values of urinary and plasma cortisol, Trait Anxiety and forehead muscle tension compared to treatment failures. Responders also sustained greater decreases in plasma, and urinary cortisol after treatment. These data are discussed in light of the ability to predict which hypertensive patients may be most benefitted by a relaxation based treatment.We would like to thank Dr. Charles Spielberger for his permission to use the State-Trait Anxiety Inventory. We thank Michael Robinson for assistance with statistical analysis. 相似文献
5.
Comparison of the chemical changes in the rhizosphere of the nickel hyperaccumulator Alyssum murale with the non-accumulator Raphanus sativus 总被引:2,自引:1,他引:1
Changes in pH and redox potential were studied in the rhizosphere soil of a nickel hyperaccumulator plant (Alyssum murale) and of a crop plant, radish (Raphanus sativus). Differences in rhizosphere pH and reducing activity were found between the lateral and the main roots of both species,
but the pH changes in the rhizosphere were similar in both species. Changes in pH were associated with the relative uptakes
of cations and anions; whether the concentrations of heavy metals in the growth medium did not have any effect on the rhizosphere
pH. The source of nitrogen (ammonium or nitrate) was the major factor determining the pH of the rhizosphere of both species.
The redox potential of the rhizosphere was influenced by both the N-source and the concentrations of heavy metals. When heavy
metals were not present in the growth medium, and nitrate was the N-source, the reducing capacity of A. murale roots was enhanced. However, the reducing activity of A. murale was always smaller than that of radish. Therefore, the mechanism of metal solubilization by the hyperaccumulator plant does
not involve either the reduction of pH in the rhizosphere or the release of reductants from roots. The acidification and reducing
activity of the roots of A. murale was always smaller than that of R. sativus. 相似文献
6.
In contrast to its usual habitat as a copepod that may occurin shelf or slope waters with low oxygen content between depthsfrom the surface to >2000 m, Rhincalanus nasutus was foundin a shallow (<60 m) embayment, the Arauco Gulf in Chile.Here, we document the complex life history of this copepod wheredid and ontogenetic vertical migratory behavior was co-ordinatedwith the circulation pattern which helped to retain a summerresident population in the vicinity of the gulf. With the onsetof the upwelling season in the southern summer, the mid-depthEquatorial Sub Surface Waters intrude into the gulf, leadingto the formation of a strong thermocline at 1020 m andthe development of a two-layer circulation pattern. CopepoditesI, C.II and C.III (first stage to exhibit migratory behavior)were found within the gulf in the layer where the net transportwas at a minimum while chlorophyll-a concentrations were ata maximum. Older stages (C.IV-C.VI females and males) migratefrom their daytime depth in the bottom, shoreward-moving, low-oxygenlayer, to their night-time depth in the shallow seaward-movinglayer. The population of copepods retained in the area thuslyreproduce, as reflected in the sequential pulses of differentdevelopmental stages. Because coastal intrusions such as thisof R.nasutus have been documented for several other speciesduring the seasons of maximum phytoplankton production (upwelling),they may form part of a more widespread reproductive strategyof the larger zooplankton of coastal upwelling systems thanpreviously suspected. 相似文献
7.
J. Cegarra C. Paredes A. Roig M. P. Bernal D. García 《International biodeterioration & biodegradation》1996,38(3-4)
Vast amounts of olive mill wastewaters (OMW) are produced in Mediterranean countries, where their treatment and disposal are becoming a serious environmental problem. Increasing attention has been paid to discovering a use for OMW and a wide range of technological treatments are available nowadays for reducing their pollutant effects and for their transformation into valuable products, the most suitable procedures being found to involve recycling rather than the detoxication of these wastes. Direct application of OMW to soil has been considered as an inexpensive method of disposal and recovery of their mineral and organic components but, because of their organic acid and phenol contents, OMW are also a source of pollution. By using composting technologies, it is possible to transform either fresh OMW or sludge from pond-stored OMW mixed with appropriate plant waste waterials (carriers) into organic fertilizers (composts) with no phytotoxicity to improve soil fertility and plant production, the process involving the microbial degradation of the polluting load of the wastes. Results of field and pot experiments using OMW-composts to cultivate horticultural and other crops have shown that yields obtained with organic fertilization are similar, and sometimes higher, to those obtained with a balanced mineral fertilizer. A comparison between the macro and micronutrient contents of plants cultivated with organic or mineral fertilizers did not generally reveal important differences. However, the cases of iron and manganese are worth mentioning as their bio-availability may be linked to the soil humic complexes originated by the OMW organic fertilizers. 相似文献
8.
When protamine is added to actin, different supramolecular structures are formed depending on the molar ratio of the two proteins and of the ionic strength of the medium. At low ionic strength, and going from a molar ratio of protamine to G-actin of 4:1, 2:1 and 1:1, globular aggregates are first converted into extended structures and then to long threads in which the constituent ATP–G-actin is rapidly exchangeable with the actin of the medium. At high ionic strength {Tyrode [(1910) Arch. Int. Pharmacodyn. Ther. 20, 205–212] solution}, starting from G-actin and protamine in the 1:1 molar ratio, long ropes are formed that can be resolved into intertwining filaments of 4–5nm diameter. The addition of protamine in a 1:1 molar ratio to a solution of F-actin in Tyrode solution causes the breakage of the actin filaments, which is also revealed by the decrease of the viscosity of the solution and the formation of ordered latero-lateral aggregates. The structures formed by reaction of protamine with G-actin can be separated from free G-actin and protamine by filtration through 0.45μm-pore-size Millipore filters. This technique has been exploited to study the exchange reaction between free actin and the actin–protamine complexes. For these studies the 1:1 actin–protamine complex formed at low ionic strength and the 2:1 actin–protamine complex formed in the presence of 23nm-free Mg2+ have been selected. In the first case the exchange reaction is practically complete in the dead time of the experiment (20s). In the second case, where the complex operates like a true ATPase, the rate of the exchange is initially comparable with the rate of the ATP cleavage. Later on, however, the complex undergoes a change and the rate of the exchange between free actin and the actin bound to protamine becomes lower than the rate of the ATPase reaction. It is proposed that the ATP exchanges for ADP directly on the G-actin bound in the complex. 相似文献
9.
David García‐Bernal Marta Palomo Carlos M. Martínez Jos E. Milln‐Rivero Ana I. García‐Guilln Miguel Blanquer Maribel Díaz‐Ricart Robert Sackstein Enric Carreras Jose M. Moraleda 《Journal of cellular and molecular medicine》2020,24(14):8031-8044
Allogeneic hematopoietic stem cell transplantation (allo‐HCT) is an effective therapy for the treatment of high‐risk haematological malignant disorders and other life‐threatening haematological and genetic diseases. Acute graft‐versus‐host disease (aGvHD) remains the most frequent cause of non‐relapse mortality following allo‐HCT and limits its extensive clinical application. Current pharmacologic agents used for prophylaxis and treatment of aGvHD are not uniformly successful and have serious secondary side effects. Therefore, more effective and safe prophylaxis and therapy for aGvHD are an unmet clinical need. Defibrotide is a multi‐target drug successfully employed for prophylaxis and treatment of veno‐occlusive disease/sinusoidal obstruction syndrome. Recent preliminary clinical data have suggested some efficacy of defibrotide in the prevention of aGvHD after allo‐HCT. Using a fully MHC‐mismatched murine model of allo‐HCT, we report here that defibrotide, either in prophylaxis or treatment, is effective in preventing T cell and neutrophil infiltration and aGvHD‐associated tissue injury, thus reducing aGvHD incidence and severity, with significantly improved survival after allo‐HCT. Moreover, we performed in vitro mechanistic studies using human cells revealing that defibrotide inhibits leucocyte‐endothelial interactions by down‐regulating expression of key endothelial adhesion molecules involved in leucocyte trafficking. Together, these findings provide evidence that defibrotide may represent an effective and safe clinical alternative for both prophylaxis and treatment of aGvHD after allo‐HCT, paving the way for new therapeutic approaches. 相似文献
10.