全文获取类型
收费全文 | 965篇 |
免费 | 61篇 |
出版年
2023年 | 7篇 |
2022年 | 24篇 |
2021年 | 36篇 |
2020年 | 19篇 |
2019年 | 31篇 |
2018年 | 27篇 |
2017年 | 31篇 |
2016年 | 39篇 |
2015年 | 62篇 |
2014年 | 70篇 |
2013年 | 69篇 |
2012年 | 65篇 |
2011年 | 80篇 |
2010年 | 38篇 |
2009年 | 51篇 |
2008年 | 38篇 |
2007年 | 43篇 |
2006年 | 47篇 |
2005年 | 50篇 |
2004年 | 23篇 |
2003年 | 29篇 |
2002年 | 23篇 |
2001年 | 9篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 13篇 |
1997年 | 9篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1968年 | 1篇 |
1956年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有1026条查询结果,搜索用时 46 毫秒
141.
Pires de Miranda M Alenquer M Marques S Rodrigues L Lopes F Bustelo XR Simas JP 《PloS one》2008,3(2):e1654
To establish latent infections in B-cells, gammaherpesviruses express proteins in the infected B-cells of the host that spuriously activate signalling pathways located downstream of the B-cell receptor. One such protein is M2, a murine gammaherpesvirus 68-encoded molecule that activates the Vav1/Rac1 pathway via the formation of trimolecular complexes with Scr family members. Previous reports have shown that the formation of this heteromolecular complex involves interactions between a proline rich region of M2 and the Vav1 and Fyn SH3 domains. Here, we show that the optimal association of these proteins requires a second structural motif encompassing two tyrosine residues (Tyr120 and 129). These residues are inducibly phosphorylated by Fyn in non-hematopoietic cells and constitutively phosphorylated in B-cells. We also demonstrate that the phosphorylation of Tyr120 creates specific docking sites for the SH2 domains of both Vav1 and Fyn, a condition sine qua non for the optimal association of these two signalling proteins in vivo. Interestingly, signaling experiments indicate that the expression of M2 in B-cells promotes the tyrosine phosphorylation of Vav1 and additional signaling proteins, a biological process that requires the integrity of both the M2 phosphotyrosine and proline rich region motifs. By infecting mice with viruses mutated in the m2 locus, we show that the integrity of each of these two M2 docking motifs is essential for the early steps of murine gammaherpesvirus-68 latency. Taken together, these results indicate that the M2 phosphotyrosine motif and the previously described M2 proline rich region work in a concerted manner to manipulate the signaling machinery of the host B-cell. 相似文献
142.
143.
Wolf M. Mooij Stephan Hülsmann Lisette N. De Senerpont Domis Bart A. Nolet Paul L. E. Bodelier Paul C. M. Boers L. Miguel Dionisio Pires Herman J. Gons Bas W. Ibelings Ruurd Noordhuis Rob Portielje Kirsten Wolfstein Eddy H. R. R. Lammens 《Aquatic Ecology》2005,39(4):381-400
Climate change will alter freshwater ecosystems but specific effects will vary among regions and the type of water body. Here,
we give an integrative review of the observed and predicted impacts of climate change on shallow lakes in the Netherlands
and put these impacts in an international perspective. Most of these lakes are man-made and have preset water levels and poorly
developed littoral zones. Relevant climatic factors for these ecosystems are temperature, ice-cover and wind. Secondary factors
affected by climate include nutrient loading, residence time and water levels. We reviewed the relevant literature in order
to assess the impact of climate change on these lakes. We focussed on six management objectives as bioindicators for the functioning
of these ecosystems: target species, nuisance species, invading species, transparency, carrying capacity and biodiversity.
We conclude that climate change will likely (i) reduce the numbers of several target species of birds; (ii) favour and stabilize
cyanobacterial dominance in phytoplankton communities; (iii) cause more serious incidents of botulism among waterfowl and
enhance the spreading of mosquito borne diseases; (iv) benefit invaders originating from the Ponto-Caspian region; (v) stabilize
turbid, phytoplankton-dominated systems, thus counteracting restoration measures; (vi) destabilize macrophyte-dominated clear-water
lakes; (vii) increase the carrying capacity of primary producers, especially phytoplankton, thus mimicking eutrophication;
(viii) affect higher trophic levels as a result of enhanced primary production; (ix) have a negative impact on biodiversity
which is linked to the clear water state; (x) affect biodiversity by changing the disturbance regime. Water managers can counteract
these developments by reduction of nutrient loading, development of the littoral zone, compartmentalization of lakes and fisheries
management. 相似文献
144.
N.J. Ribeiro O.C. Pires M. Mota E.C. Ferreira M.M. Alves 《Biotechnology letters》2001,23(22):1833-1839
An upflow velocity of 0.21 m h–1 was optimal to minimize the effect of organic shocks (from 6 to 30 kg COD m–3 d–1) when operating an upflow anaerobic filter for the treatment of an oleic acid-based effluent (50% w/v COD). This value represented the transition between a mass transfer controlled regime and a kinetic regime. Under hydraulic shock loads, an increase in upflow velocity from 0.3 to 0.4m h–1 decreased the removal efficiency from 68 to 51%. 相似文献
145.
Gandra R.F. Melo T.A. Matsumoto F.E. Pires M.F.C. Croce J. Gambale W. Paula C.R. 《Mycopathologia》2003,155(4):183-189
Crude extracts of the lipophilic yeast Malassezia furfur were obtained from 2, 6, 10 and 28 day old cultures. The in vitro cultivation periods corresponded, respectively, to the lag phase, middle of the log phase, end of log phase and the decline phase of the growth curve, which was based on viable cell counts obtained with a fluorescent viability test. Biochemical analyses showed that the protein and carbohydrate contents were greater in day 10 extracts. Seventy patients with different allergic manifestations and 30 healthy volunteers were skin prick tested using the extracts. Of these, thirteen (18.57%) patients gave positive responses. SDS PAGE gradient electrophoretic profiles of the preparations indicated that the 28 day extracts contained the greatest number of protein bands with molecular weights ranging mostly between 30 and 94 kDa. Immunoblots incubated with individual patient sera showed that four IgE binding M. furfur allergens of approximately 88, 61, 52 and 39 kDa were present in the 28 day extracts. The components identified could be used for detecting IgE mediated responses to M. furfur among individuals affected with different allergic conditions.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
146.
Roberto Gargione Junqueira Filho Andréa Beatriz Mendes-Bonato Maria Suely Pagliarini Nilton Cesar Pires Bione Cacilda Borges do Valle Maria Isabel de Oliveira Penteado 《Génome》2003,46(1):83-88
Meiotic division and male gametophyte development were analyzed in one tetraploid (2n = 4x = 36) accession of Brachiaria decumbens cv. Basilisk that showed some pollen sterility. Meiotic process was typical of polyploids in that it consisted of multiple chromosome associations. Precocious chromosome migration to the poles, laggards, and micronucleus formation were abundant in both meiosis I and II and resulted in tetrads with micronuclei. After callose dissolution, microspores were released into the anther locule and had the semblance of being normal. Although each microspore initiated its differentiation by pollen mitosis, in 43.24% of the microspores, nuclear polarization was not observed and the typical hemispherical cell plate was not detected. Division was symmetric and microspores lacked differentiation between the vegetative and the generative cell. Both nuclei were of equal size, presented equal chromatin condensation, and had a spherical shape. After the first pollen mitosis and cytokinesis, each cell underwent a new symmetric mitosis without nuclear polarization. At the end of the second pollen mitosis, four equal nuclei were observed in each pollen grain. After the second cytokinesis, the cells gave rise to four equal-sized pollen grains with a similar tetrad configuration that initially remained together. Sterile pollen grains resulted from abnormal pollen mitosis. This anomaly may be explained by a mutation, probably affecting microtubule cytoskeleton formation. The importance of this male-sterile mutation for Brachiaria breeding programs is discussed. 相似文献
147.
A. S. Pires N. Geraldo T. Cerqueira R. Abranches 《Molecular breeding : new strategies in plant improvement》2012,30(3):1431-1442
Plant genetic engineering has become an invaluable tool in plant research. Although plant transformation is a well-established technique, transgene expression is still unpredictable. Silencing may involve epigenetic modifications or nuclear and chromosomal localization of transgenes. In this way, understanding nuclear structure and organization is important not only for increasing our knowledge of fundamental aspects of the genome but also for taking the greatest advantage of inserting foreign genes and controlling their expression in biotechnological applications. Integrated approaches are clearly required in order to elucidate such complex processes. By combining the analysis of the physical position of transgenes with markers for epigenetic modifications in the plant genome we can better understand the factors affecting transgene expression levels and analyze the genomic environments of differentially expressed transgenes. Medicago truncatula Gaertn. has become a well-known model for the legume family and is used in studies ranging from nodulation to environmental stresses. More recently its use in biotechnology has been explored. In this report we describe the application of fluorescence in situ hybridization (FISH) to detect foreign DNA sequences and to determine the organization of the nucleolar organizer regions (NORs) genes in both metaphase chromosomes and interphase nuclei. We also studied chromatin distribution by immunodetection of epigenetic marks in M. truncatula interphase nuclei from tissue sections. We present evidence that M. truncatula is amenable to this kind of studies, which will in turn contribute to a better exploitation of biotechnology applications for this important plant family. 相似文献
148.
Ana Paula Junqueira-Kipnis Fábio Muniz de Oliveira Monalisa Martins Trentini Sangeeta Tiwari Bing Chen Danilo Pires Resende Bruna D. S. Silva Mei Chen Lydia Tesfa William R. Jacobs Jr André Kipnis 《PloS one》2013,8(11)
The development of a new vaccine as a substitute for Bacillus Calmette–Guerin or to improve its efficacy is one of the many World Health Organization goals to control tuberculosis. Mycobacterial vectors have been used successfully in the development of vaccines against tuberculosis. To enhance the potential utility of Mycobacterium smegmatis as a vaccine, it was transformed with a recombinant plasmid containing the partial sequences of the genes Ag85c, MPT51, and HspX (CMX) from M. tuberculosis. The newly generated recombinant strain mc2-CMX was tested in a murine model of infection. The recombinant vaccine induced specific IgG1 or IgG2a responses to CMX. CD4+ and CD8+ T cells from the lungs and spleen responded ex vivo to CMX, producing IFN-γ, IL17, TNF-α, and IL2. The vaccine thus induced a significant immune response in mice. Mice vaccinated with mc2-CMX and challenged with M. tuberculosis showed better protection than mice immunized with wild-type M. smegmatis or BCG. To increase the safety and immunogenicity of the CMX antigens, we used a recombinant strain of M. smegmatis, IKE (immune killing evasion), to express CMX. The recombinant vaccine IKE-CMX induced a better protective response than mc2-CMX. The data presented here suggest that the expression of CMX antigens improves the immune response and the protection induced in mice when M. smegmatis is used as vaccine against tuberculosis. 相似文献
149.
150.