全文获取类型
收费全文 | 838篇 |
免费 | 120篇 |
出版年
2021年 | 9篇 |
2018年 | 12篇 |
2016年 | 12篇 |
2015年 | 24篇 |
2014年 | 24篇 |
2013年 | 46篇 |
2012年 | 41篇 |
2011年 | 48篇 |
2010年 | 33篇 |
2009年 | 35篇 |
2008年 | 39篇 |
2007年 | 26篇 |
2006年 | 28篇 |
2005年 | 33篇 |
2004年 | 28篇 |
2003年 | 27篇 |
2002年 | 24篇 |
2001年 | 38篇 |
2000年 | 31篇 |
1999年 | 33篇 |
1998年 | 19篇 |
1997年 | 18篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 19篇 |
1991年 | 27篇 |
1990年 | 10篇 |
1989年 | 21篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 20篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 20篇 |
1981年 | 8篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 9篇 |
1972年 | 7篇 |
1971年 | 16篇 |
1970年 | 4篇 |
1969年 | 7篇 |
1967年 | 3篇 |
排序方式: 共有958条查询结果,搜索用时 453 毫秒
101.
In cancer, glucose uptake and glycolysis are increased regardless of the oxygen concentration in the cell, a phenomenon known as the Warburg effect. Several (but not all) glycolytic enzymes have been investigated as potential therapeutic targets for cancer treatment using RNAi. Here, four previously untargeted glycolytic enzymes, aldolase A, glyceraldehyde 3-phosphate dehydrogenase, triose phosphate isomerase, and enolase 1, are targeted using RNAi in Ras-transformed NIH-3T3 cells. Of these enzymes, knockdown of aldolase causes the greatest effect, inhibiting cell proliferation by 90%. This defect is rescued by expression of exogenous aldolase. However, aldolase knockdown does not affect glycolytic flux or intracellular ATP concentration, indicating a non-metabolic cause for the cell proliferation defect. Furthermore, this defect could be rescued with an enzymatically dead aldolase variant that retains the known F-actin binding ability of aldolase. One possible model for how aldolase knockdown may inhibit transformed cell proliferation is through its disruption of actin-cytoskeleton dynamics in cell division. Consistent with this hypothesis, aldolase knockdown cells show increased multinucleation. These results are compared with other studies targeting glycolytic enzymes with RNAi in the context of cancer cell proliferation and suggest that aldolase may be a useful target in the treatment of cancer. 相似文献
102.
MH Kim AL Tsuhako EW Co DT Aftab F Bentzien J Chen W Cheng S Engst L Goon RR Klein DT Le M Mac JJ Parks F Qian M Rodriquez TJ Stout JH Till KA Won X Wu FM Yakes P Yu W Zhang Y Zhao P Lamb JM Nuss W Xu 《Bioorganic & medicinal chemistry letters》2012,22(15):4979-4985
Variously substituted indolin-2-ones were synthesized and evaluated for activity against KDR, Flt-1, FGFR-1 and PDGFR. Extension at the 5-position of the oxindole ring with ethyl piperidine (compound 7i) proved to be the most beneficial for attaining both biochemical and cellular potencies. Further optimization of 7i to balance biochemical and cellular potencies with favorable ADME/ PK properties led to the identification of 8h, a compound with a clean CYP profile, acceptable pharmacokinetic and toxicity profiles, and robust efficacy in multiple xenograft tumor models. 相似文献
103.
104.
Yizhou Wang Maria Papanatsiou Cornelia Eisenach Rucha Karnik Mary Williams Adrian Hills Virgilio L. Lew Michael R. Blatt 《Plant physiology》2012,160(4):1956-1967
Stomata account for much of the 70% of global water usage associated with agriculture and have a profound impact on the water and carbon cycles of the world. Stomata have long been modeled mathematically, but until now, no systems analysis of a plant cell has yielded detail sufficient to guide phenotypic and mutational analysis. Here, we demonstrate the predictive power of a systems dynamic model in Arabidopsis (Arabidopsis thaliana) to explain the paradoxical suppression of channels that facilitate K+ uptake, slowing stomatal opening, by mutation of the SLAC1 anion channel, which mediates solute loss for closure. The model showed how anion accumulation in the mutant suppressed the H+ load on the cytosol and promoted Ca2+ influx to elevate cytosolic pH (pHi) and free cytosolic Ca2+ concentration ([Ca2+]i), in turn regulating the K+ channels. We have confirmed these predictions, measuring pHi and [Ca2+]i in vivo, and report that experimental manipulation of pHi and [Ca2+]i is sufficient to recover K+ channel activities and accelerate stomatal opening in the slac1 mutant. Thus, we uncover a previously unrecognized signaling network that ameliorates the effects of the slac1 mutant on transpiration by regulating the K+ channels. Additionally, these findings underscore the importance of H+-coupled anion transport for pHi homeostasis.Guard cells surround stomatal pores in the epidermis of plant leaves and regulate pore aperture to balance the demands for CO2 in photosynthesis with the need to conserve water by the plant. Transpiration through stomata accounts for much of the 70% of global water usage associated with agriculture, and it has a profound impact on the water and carbon cycles of the world (Gedney et al., 2006; Betts et al., 2007). Guard cells open the pore by transport and accumulation of osmotically active solutes, mainly K+ and Cl− and the organic anion malate2− (Mal), to drive water uptake and cell expansion. They close the pore by coordinating the release of these solutes through K+ and anion channels at the plasma membrane. The past half-century has generated a wealth of knowledge on guard cell transport, signaling, and homeostasis, resolving the properties of the major transport processes and metabolic pathways for osmotic solute uptake and accumulation, and many of the signaling pathways that control them (Blatt, 2000; Schroeder et al., 2001; McAinsh and Pittman, 2009; Hills et al., 2012). Even so, much of stomatal dynamics remains unresolved, especially how the entire network of transporters in guard cells works to modulate solute flux and how this network is integrated with organic acid metabolism (Wang and Blatt, 2011) to achieve a dynamic range of stomatal apertures.This gap in understanding is most evident in a number of often unexpected observations, many of which have led necessarily to ad hoc interpretations. Among these, recent studies highlighted a diurnal variation in the free cytosolic Ca2+ concentration ([Ca2+]i), high in the daytime despite the activation of primary ion-exporting ATPases, and have been interpreted to require complex levels of regulation (Dodd et al., 2007). Other findings wholly defy intuitive explanation. For example, the tpk1 mutant of Arabidopsis (Arabidopsis thaliana) removes a major pathway for K+ flux across the tonoplast and suppresses stomatal closure, yet the mutant has no significant effect on cellular K+ content (Gobert et al., 2007). Similarly, the Arabidopsis clcc mutant eliminates the H+-Cl− antiporter at the tonoplast; it affects Cl− uptake, reduces vacuolar Cl− content, and slows stomatal opening; however, counterintuitively, it also suppresses stomatal closure (Jossier et al., 2010). In work leading to this study, we observed that the slac1 anion channel mutant of Arabidopsis paradoxically profoundly alters the activities of the two predominant K+ channels at the guard cell plasma membrane. The SLAC1 anion channel is a major pathway for anion loss from the guard cells during stomatal closure (Negi et al., 2008; Vahisalu et al., 2008), and its mutation leads to incomplete and slowed closure of stomata in response to physiologically relevant signals of dark, high CO2, and the water-stress hormone abscisic acid. Guard cells of the slac1 mutant accumulate substantially higher levels of Cl−, Mal, and also K+ when compared with guard cells of wild-type Arabidopsis (Negi et al., 2008). The latter observation is consistent with additional impacts on K+ transport; however, a straightforward explanation for these findings has not been not forthcoming.Quantitative systems analysis offers one approach to such problems. Efforts to model stomatal function generally have been driven by a “top-down” approach (Farquhar and Wong, 1984; Eamus and Shanahan, 2002) and have not incorporated detail essential to understanding the molecular and cellular mechanics that drive stomatal movement. Only recently we elaborated a quantitative systems dynamic approach to modeling the stomatal guard cell that incorporates all of the fundamental properties of the transporters at the plasma membrane and tonoplast, the salient features of osmolite metabolism, and the essential cytosolic pH (pHi) and [Ca2+]i buffering characteristics that have been described in the literature (Hills et al., 2012). The model resolved with this approach (Chen et al., 2012b) successfully recapitulated a wide range of known stomatal behaviors, including transport and aperture dependencies on extracellular pH, KCl, and CaCl2 concentrations, diurnal changes in [Ca2+]i (Dodd et al., 2007), and oscillations in membrane voltage and [Ca2+]i thought to facilitate stomatal closure (Blatt, 2000; McAinsh and Pittman, 2009; Chen et al., 2012b). We have used this approach to resolve the mechanism behind the counterintuitive alterations in K+ channel activity uncovered in the slac1 mutant of Arabidopsis. Here, we show how anion accumulation in the mutant affects the H+ and Ca2+ loads on the cytosol, elevating pHi and [Ca2+]i, and in turn regulating the K+ channels. We have validated the key predictions of the model and, in so doing, have uncovered a previously unrecognized homeostatic network that ameliorates the effects of the slac1 mutant on transpiration from the plant. 相似文献
105.
106.
Ryanne JM Lemmens Annick AA Timmermans Yvonne JM Janssen-Potten Rob JEM Smeets Henk AM Seelen 《BMC neurology》2012,12(1):1-17
Background
Loss of arm-hand performance due to a hemiparesis as a result of stroke or cerebral palsy (CP), leads to large problems in daily life of these patients. Assessment of arm-hand performance is important in both clinical practice and research. To gain more insight in e.g. effectiveness of common therapies for different patient populations with similar clinical characteristics, consensus regarding the choice and use of outcome measures is paramount. To guide this choice, an overview of available instruments is necessary. The aim of this systematic review is to identify, evaluate and categorize instruments, reported to be valid and reliable, assessing arm-hand performance at the ICF activity level in patients with stroke or cerebral palsy.Methods
A systematic literature search was performed to identify articles containing instruments assessing arm-hand skilled performance in patients with stroke or cerebral palsy. Instruments were identified and divided into the categories capacity, perceived performance and actual performance. A second search was performed to obtain information on their content and psychometrics.Results
Regarding capacity, perceived performance and actual performance, 18, 9 and 3 instruments were included respectively. Only 3 of all included instruments were used and tested in both patient populations. The content of the instruments differed widely regarding the ICF levels measured, assessment of the amount of use versus the quality of use, the inclusion of unimanual and/or bimanual tasks and the inclusion of basic and/or extended tasks.Conclusions
Although many instruments assess capacity and perceived performance, a dearth exists of instruments assessing actual performance. In addition, instruments appropriate for more than one patient population are sparse. For actual performance, new instruments have to be developed, with specific focus on the usability in different patient populations and the assessment of quality of use as well as amount of use. Also, consensus about the choice and use of instruments within and across populations is needed. 相似文献107.
Reinout Raijmakers Joyce JBC van Beers Mahmoud El-Azzouny Natasja FC Visser Borut Bo?i? Ger JM Pruijn Albert JR Heck 《Arthritis research & therapy》2012,14(3):R114-10
Introduction
Rheumatoid arthritis (RA) is an autoimmune disease characterized by inflammation of the joints and the presence of autoantibodies directed against proteins containing the non-standard arginine-derived amino acid citrulline. The protein fibrinogen, which has an essential role in blood clotting, is one of the most prominent citrullinated autoantigens in RA, particularly because it can be found in the inflamed tissue of affected joints. Here, we set out to analyze the presence of citrullinated endogenous peptides in the synovial fluid of RA and arthritic control patients.Methods
Endogenous peptides were isolated from the synovial fluid of RA patients and controls by filtration and solid phase extraction. The peptides were identified and quantified using high-resolution liquid chromatography-mass spectrometry.Results
Our data reveal that the synovial fluid of RA patients contains soluble endogenous peptides, derived from fibrinogen, containing significant amounts of citrulline residues and, in some cases, also phosphorylated serine. Several citrullinated peptides are found to be more abundantly present in the synovial fluid of RA patients compared to patients suffering from other inflammatory diseases affecting the joints.Conclusions
The increased presence of citrullinated peptides in RA patients points toward a possible specific role of these peptides in the immune response at the basis of the recognition of citrullinated peptides and proteins by RA patient autoantibodies. 相似文献108.
Electrical phenotypes of calcium transport mutant strains of a filamentous fungus, Neurospora crassa
We characterized the electrical phenotypes of mutants with mutations in genes encoding calcium transporters-a mechanosensitive channel homolog (MscS), a Ca(2+)/H(+) exchange protein (cax), and Ca(2+)-ATPases (nca-1, nca-2, nca-3)-as well as those of double mutants (the nca-2 cax, nca-2 nca-3, and nca-3 cax mutants). The electrical characterization used dual impalements to obtain cable-corrected current-voltage measurements. Only two types of mutants (the MscS mutant; the nca-2 mutant and nca-2-containing double mutants) exhibited lower resting potentials. For the nca-2 mutant, on the basis of unchanged conductance and cyanide-induced depolarization of the potential, the cause is attenuated H(+)-ATPase activity. The growth of the nca-2 mutant-containing strains was inhibited by elevated extracellular Ca(2+) levels, indicative of lesions in Ca(2+) homeostasis. However, the net Ca(2+) effluxes of the nca-2 mutant, measured noninvasively with a self-referencing Ca(2+)-selective microelectrode, were similar to those of the wild type. All of the mutants exhibited osmosensitivity similar to that of the wild type (the turgor of the nca-2 mutant was also similar to that of the wild type), suggesting that Ca(2+) signaling does not play a role in osmoregulation. The hyphal tip morphology and tip-localized mitochondria of the nca-2 mutant were similar to those of the wild type, even when the external [Ca(2+)] was elevated. Thus, although Ca(2+) homeostasis is perturbed in the nca-2 mutant (B. J. Bowman et al., Eukaryot. Cell 10:654-661, 2011), the phenotype does not extend to tip growth or to osmoregulation but is revealed by lower H(+)-ATPase activity. 相似文献
109.
S Chen AJ de Craen Y Raz E Derhovanessian AC Vossen WG Rudi G Pawelec AB Maier 《Immunity & ageing : I & A》2012,9(1):18-7
ABSTRACT: BACKGROUND: Cytomegalovirus (CMV) infection has been reported to contribute to the pathogenesis of type 1 diabetes and post-transplantation diabetes. However, CMV infection has not been evaluated as a possible risk factor for type 2 diabetes. Our aim was to investigate potential associations between CMV seropositivity, CMV IgG antibody level and glucose regulation in the oldest old. RESULTS: CMV seropositive subjects were more likely to have type 2 diabetes (17.2% vs 7.9%, p = 0.016), had a higher level of HbA1c (p = 0.014) and higher non-fasting glucose (p = 0.024) in the oldest olds. These associations remained significant after adjustment for possible confounders. CMV IgG antibody level was not significantly associated with glucose regulation (all p > 0.05). CONCLUSIONS: In the oldest old, CMV seropositivity is significantly associated with various indicators of glucose regulation. This finding suggests that CMV infection might be a risk factor for the development of type 2 diabetes in the elderly. 相似文献
110.