首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1524篇
  免费   120篇
  2023年   13篇
  2022年   29篇
  2021年   70篇
  2020年   27篇
  2019年   37篇
  2018年   49篇
  2017年   40篇
  2016年   62篇
  2015年   96篇
  2014年   112篇
  2013年   141篇
  2012年   139篇
  2011年   159篇
  2010年   85篇
  2009年   58篇
  2008年   86篇
  2007年   88篇
  2006年   67篇
  2005年   44篇
  2004年   61篇
  2003年   46篇
  2002年   54篇
  2001年   16篇
  2000年   8篇
  1999年   5篇
  1998年   7篇
  1997年   6篇
  1996年   1篇
  1995年   2篇
  1994年   4篇
  1993年   2篇
  1992年   6篇
  1991年   3篇
  1990年   3篇
  1988年   3篇
  1987年   1篇
  1986年   2篇
  1984年   1篇
  1983年   2篇
  1982年   1篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1976年   1篇
  1972年   2篇
  1965年   1篇
排序方式: 共有1644条查询结果,搜索用时 15 毫秒
991.
An F1 mapping population was bred by crossing an accession of wild cardoon with a single Argentinian globe artichoke plant of the variety Estrella del Sur FCA with a view to generating new Cynara cardunculus linkage maps. Genotyping was conducting using a set of 553 SRAP, SSR, AFLP and SNP markers. The 1,465.5 cM map based on the segregation of alleles present in the wild cardoon parent comprised 214 loci distributed across 16 linkage groups (LGs), while the 910.1 cM globe artichoke-based map featured 141 loci falling into 12 LGs covering the total length. Three of the morphological traits (head spininess, leaf spininess and head color) for which the parents contrasted were inherited monogenically, and the genes conditioning them were mapped. A set of 48 co-dominant loci was used to align the LGs with those derived from a reference SSR-based consensus map of the species.  相似文献   
992.
This paper shows the application of mathematical modeling to scale-up a cycle developed with lab-scale equipment on two different production units. The above method is based on a simplified model of the process parameterized with experimentally determined heat and mass transfer coefficients. In this study, the overall heat transfer coefficient between product and shelf was determined by using the gravimetric procedure, while the dried product resistance to vapor flow was determined through the pressure rise test technique. Once model parameters were determined, the freeze-drying cycle of a parenteral product was developed via dynamic design space for a lab-scale unit. Then, mathematical modeling was used to scale-up the above cycle in the production equipment. In this way, appropriate values were determined for processing conditions, which allow the replication, in the industrial unit, of the product dynamics observed in the small scale freeze-dryer. This study also showed how inter-vial variability, as well as model parameter uncertainty, can be taken into account during scale-up calculations.  相似文献   
993.
DNA double-strand breaks (DSBs) are the most cytotoxic form of DNA damage, since they can lead to genome instability and chromosome rearrangements, which are hallmarks of cancer cells. To face this kind of lesion, eukaryotic cells developed two alternative repair pathways, homologous recombination (HR) and non-homologous end joining (NHEJ). Repair pathway choice is influenced by the cell cycle phase and depends upon the 5′-3′ nucleolytic processing of the break ends, since the generation of ssDNA tails strongly stimulates HR and inhibits NHEJ. A large amount of work has elucidated the key components of the DSBs repair machinery and how this crucial process is finely regulated. The emerging view suggests that besides endo/exonucleases and helicases activities required for end resection, molecular barrier factors are specifically loaded in the proximity of the break, where they physically or functionally limit DNA degradation, preventing excessive accumulation of ssDNA, which could be threatening for cell survival.  相似文献   
994.
The anterior inferotemporal cortex (IT) is the highest stage along the hierarchy of visual areas that, in primates, processes visual objects. Although several lines of evidence suggest that IT primarily represents visual shape information, some recent studies have argued that neuronal ensembles in IT code the semantic membership of visual objects (i.e., represent conceptual classes such as animate and inanimate objects). In this study, we investigated to what extent semantic, rather than purely visual information, is represented in IT by performing a multivariate analysis of IT responses to a set of visual objects. By relying on a variety of machine-learning approaches (including a cutting-edge clustering algorithm that has been recently developed in the domain of statistical physics), we found that, in most instances, IT representation of visual objects is accounted for by their similarity at the level of shape or, more surprisingly, low-level visual properties. Only in a few cases we observed IT representations of semantic classes that were not explainable by the visual similarity of their members. Overall, these findings reassert the primary function of IT as a conveyor of explicit visual shape information, and reveal that low-level visual properties are represented in IT to a greater extent than previously appreciated. In addition, our work demonstrates how combining a variety of state-of-the-art multivariate approaches, and carefully estimating the contribution of shape similarity to the representation of object categories, can substantially advance our understanding of neuronal coding of visual objects in cortex.  相似文献   
995.
Smooth muscle cells (SMCs) have a pivotal role in cardiovascular diseases and are responsible for hyaluronan (HA) deposition in thickening vessel walls. HA regulates SMC proliferation, migration, and inflammation, which accelerates neointima formation. We used the HA synthesis inhibitor 4-methylumbelliferone (4-MU) to reduce HA production in human aortic SMCs and found a significant increase of apoptotic cells. Interestingly, the exogenous addition of HA together with 4-MU reduced apoptosis. A similar anti-apoptotic effect was observed also by adding other glycosaminoglycans and glucose to 4-MU-treated cells. Furthermore, the anti-apoptotic effect of HA was mediated by Toll-like receptor 4, CD44, and PI3K but not by ERK1/2.  相似文献   
996.
Recruitment is a principal controlling factor in population dynamics of marine species. In marine invertebrates with a planktonic larval stage, such as echinoids, recruitment is assured by larval supply, settlement and juvenile survival. Larval supply and juvenile survival are affected by a wide range of factors, including temperature, presence of predators, quality and quantity of food. Echinoid larval settlement is mainly conditioned by the finding of a suitable substrate to metamorphose. The sea urchins Arbacia lixula and Paracentrotus lividus are considered key species of the Mediterranean infralittoral rocky shores. At high densities, the grazing activity of both species can produce and maintain barren grounds, a particular habitat condition characterized by extremely low cover values of erect algae with high presence of naked substrates and encrusting corallinales, poor in biodiversity and ecosystem functions. We tested the role of different settlement substrates on the metamorphosis competent larvae of the two species. Furthermore, from our larval rearing trails we were able to identify strong temperature effects on larval development of the two species. P. lividus and A. lixula larvae have been reared at 18 °C but for the second species it was necessary to use higher temperatures (22 °C) to perform settlement experiments, as in the 18 °C set all larvae died in the first week. Both species larvae have been fed Cricosphaera elongata. Metamorphosis of competent larvae has been induced using different substrates: naked stones, Lithophyllum incrustans, Stypocaulon scoparium, Corallina elongata, turf forming algae and Posidonia oceanica. For each species, two larval batches were used for settlement experiments; for each larval batch two replicates/substrates were set up. No differences in the rate of metamorphosis on any of the tested substrates were observed for P. lividus, while A. lixula showed to prefer naked stones and encrusting coralline algae Considering that A. lixula population growth may trigger barren extension on rocky shores, this may lead to a positive feedback between barren extension and A. lixula population density. Furthermore, our results suggest that the predicted rise in seawater temperature may favor A. lixula larval survival and inhibit P. lividus. Combining information on temperature tolerance with other sources of information for these species in the Mediterranean, it is possible to develop a conceptual model of the interaction between the two species and the alternative state of their habitats.  相似文献   
997.
Anisotropy is one of the most peculiar aspects of cortical bone mechanical behaviour, and the numerical approach can be successfully used to investigate aspects of bone tissue mechanics that analytical methods solve in approximate way or do not cover. In this work, nanoindentation experimental tests and finite element simulations were employed to investigate the elastic-inelastic anisotropic mechanical properties of cortical bone. The model allows for anisotropic elastic and post-yield behaviour of the tissue. A tension-compression mismatch and direction-dependent yield stresses are allowed for. Indentation experiments along the axial and transverse directions were simulated with the purpose to predict the indentation moduli and hardnesses along multiple orientations. Results showed that the experimental transverse-to-axial ratio of indentation moduli, equal to 0.74, is predicted with a ~3% discrepancy regardless the post-yield material behaviour; whereas, the transverse-to-axial hardness ratio, equal to 0.86, can be correctly simulated (discrepancy ~6% w.r.t. the experimental results) only employing an anisotropic post-elastic constitutive model. Further, direct comparison between the experimental and simulated indentation tests evidenced a good agreement in the loading branch of the indentation curves and in the peak loads for a transverse-to-axial yield stress ratio comparable to the experimentally obtained transverse-to-axial hardness ratio. In perspective, the present work results strongly support the coupling between indentation experiments and FEM simulations to get a deeper knowledge of bone tissue mechanical behaviour at the microstructural level. The present model could be used to assess the effect of variations of constitutive parameters due to age, injury, and/or disease on bone mechanical performance in the context of indentation testing.  相似文献   
998.
Lipase maturation factor 1 (Lmf1) is an endoplasmic reticulum (ER) membrane protein involved in the posttranslational folding and/or assembly of lipoprotein lipase (LPL) and hepatic lipase (HL) into active enzymes. Mutations in Lmf1 are associated with diminished LPL and HL activities ("combined lipase deficiency") and result in severe hypertriglyceridemia in mice as well as in human subjects. Here, we investigate whether endothelial lipase (EL) also requires Lmf1 to attain enzymatic activity. We demonstrate that cells harboring a (cld) loss-of-function mutation in the Lmf1 gene are unable to generate active EL, but they regain this capacity after reconstitution with the Lmf1 wild type. Furthermore, we show that cellular EL copurifies with Lmf1, indicating their physical interaction in the ER. Finally, we determined that post-heparin phospholipase activity in a patient with the LMF1(W464X) mutation is reduced by more than 95% compared with that in controls. Thus, our study indicates that EL is critically dependent on Lmf1 for its maturation in the ER and demonstrates that Lmf1 is a required factor for all three vascular lipases, LPL, HL, and EL.  相似文献   
999.
1000.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号