全文获取类型
收费全文 | 765篇 |
免费 | 72篇 |
出版年
2021年 | 10篇 |
2020年 | 10篇 |
2018年 | 8篇 |
2017年 | 13篇 |
2016年 | 7篇 |
2015年 | 30篇 |
2014年 | 26篇 |
2013年 | 30篇 |
2012年 | 41篇 |
2011年 | 24篇 |
2010年 | 22篇 |
2009年 | 16篇 |
2008年 | 25篇 |
2007年 | 25篇 |
2006年 | 28篇 |
2005年 | 19篇 |
2004年 | 21篇 |
2003年 | 19篇 |
2002年 | 16篇 |
2001年 | 28篇 |
2000年 | 20篇 |
1999年 | 19篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1992年 | 19篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 27篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 15篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 15篇 |
1972年 | 11篇 |
1971年 | 8篇 |
1970年 | 9篇 |
1967年 | 7篇 |
1966年 | 6篇 |
排序方式: 共有837条查询结果,搜索用时 15 毫秒
51.
Jan H. Nagel Marieka Gryzenhout Bernard Slippers Michael J. Wingfield Giles E.St.J. Hardy Michael J.C. Stukely Treena I. Burgess 《Fungal biology》2013,117(5):329-347
Surveys of Australian and South African rivers revealed numerous Phytophthora isolates residing in clade 6 of the genus, with internal transcribed spacer (ITS) gene regions that were either highly polymorphic or unsequenceable. These isolates were suspected to be hybrids. Three nuclear loci, the ITS region, two single copy loci (antisilencing factor (ASF) and G protein alpha subunit (GPA)), and one mitochondrial locus (cytochrome oxidase c subunit I (coxI)) were amplified and sequenced to test this hypothesis. Abundant recombination within the ITS region was observed. This, combined with phylogenetic comparisons of the other three loci, confirmed the presence of four different hybrid types involving the three described parent species Phytophthora amnicola, Phytophthora thermophila, and Phytophthora taxon PgChlamydo. In all cases, only a single coxI allele was detected, suggesting that hybrids arose from sexual recombination. All the hybrid isolates were sterile in culture and all their physiological traits tended to resemble those of the maternal parents. Nothing is known regarding their host range or pathogenicity. Nonetheless, as several isolates from Western Australia were obtained from the rhizosphere soil of dying plants, they should be regarded as potential threats to plant health. The frequent occurrence of the hybrids and their parent species in Australia strongly suggests an Australian origin and a subsequent introduction into South Africa. 相似文献
52.
Srinivasulu S Acharya AS Prabhakaran M Fabry ME Alami R Fiering SN Bouhasirra EE Nagel RL 《The protein journal》2007,26(8):523-532
Recombinant α-Savaria globin (αS49R) was assembled with βS chains by the alloplex intermediate pathway to generate tetrameric rHbS-Sarvaria (α2S49Rβ2E6V) that exhibited normal O2 affinity and co-operatively at pH 7.4. Allosteric effectors, 2,3-DPG, L35, and NaCl increased O2 affinity by 15%. Bohr effects were similar for rHbS-Savaria and HbS (0.38 ± 0.025 vs. 0.46 ± 0.03, respectively). The CSAT of HbS increased from 16.7 ± 0.8 to 27.0 ± 1.0 g/dL. Co-polymerization demonstrated inhibition predominantly by the Cis-dimer.
Molecular modeling indicated that the positive charge at α-49 generated a strong anion-binding site and reduced flexibility
of the CD-region by restricting movement in the E and F helices. The molecular distance between Arg-49 and Asn-78 in the neighboring
double strand decreased, and electrostatic repulsion between the inter-double strands increased, resulting in inhibition of
polymerization. The Savaria mutation may be useful for the design of super-inhibitory α-chains and gene therapy of sickle
cell anemia. 相似文献
53.
Sleep and Biological Rhythms - The main study aim was to compare the validity of children sleep apnea data obtained from standard polysomnography (PSG) to a home sleep apnea test (HSAT) accompanied... 相似文献
54.
55.
56.
In vertebrates, PDGFA and its receptor, PDGFRalpha, are expressed in the early embryo. Impairing their function causes an array of developmental defects, but the underlying target processes that are directly controlled by these factors are not well known. We show that in the Xenopus gastrula, PDGFA/PDGFRalpha signaling is required for the directional migration of mesodermal cells on the extracellular matrix of the blastocoel roof. Blocking PDGFRalpha function in the mesoderm does not inhibit migration per se, but results in movement that is randomized and no longer directed towards the animal pole. Likewise, compromising PDGFA function in the blastocoel roof substratum abolishes directionality of movement. Overexpression of wild-type PDGFA, or inhibition of PDGFA both lead to randomized migration, disorientation of polarized mesodermal cells, decreased movement towards the animal pole, and reduced head formation and axis elongation. This is consistent with an instructive role for PDGFA in the guidance of mesoderm migration. 相似文献
57.
Reverse microdialysis of a dopamine D2 receptor antagonist alters extracellular adenosine levels in the rat nucleus accumbens 总被引:2,自引:0,他引:2
Recent evidence suggests that modulation of dopaminergic transmission alters striatal levels of extracellular adenosine. The present study used reverse microdialysis of the selective dopamine D2 receptor antagonist raclopride to investigate whether a blockade of dopamine D2 receptors modifies extracellular adenosine concentrations in the nucleus accumbens. Results reveal that perfusion of raclopride produced an increase of dialysate adenosine which was significant with a high (10 mM) and intermediate (1 mM) drug concentration, but not with lower drug concentrations (10 and 100 μM). Thus, the present study demonstrates that a selective blockade of dopamine D2 receptors in the nucleus accumbens produced a pronounced increase of extracellular adenosine. The cellular mechanisms underlying this effect are yet unknown. It is suggested that the increase of extracellular adenosine might be related to a homeostatic modulatory mechanism proposed to be a key function of adenosine in response to neuronal metabolic challenges. 相似文献
58.
Protein kinase-independent activation of CFTR by phosphatidylinositol phosphates 总被引:3,自引:0,他引:3
下载免费PDF全文
![点击此处可从《EMBO reports》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel that is expressed in many epithelia and in the heart. Phosphorylation of CFTR by protein kinases is thought to be an absolute prerequisite for the opening of CFTR channels. In addition, nucleoside triphosphates were shown to regulate the opening of phosphorylated CFTR. Here, we report that phosphatidylinositol 4,5-bisphosphate (PIP2) activates human CFTR, resulting in ATP responsiveness of PIP2-treated CFTR. PIP2 alone is not sufficient to open CFTR, but ATP opens nonphosphorylated CFTR after application of PIP2. The effect of PIP2 is independent of protein kinases, as PIP2 activates CFTR in the complete absence of Mg. Phosphatidylinositol and phosphatidylinositol monophosphate activate CFTR less efficiently than PIP2. PIP2 application to phosphorylated CFTR may inhibit the CFTR chloride current. We suggest that regulation of CFTR by PIP2 is a previously unrecognized, alternative mechanism to control chloride conductance. 相似文献
59.
Effects on interfacial properties and cell adhesion of surface modification by pectic hairy regions 总被引:1,自引:0,他引:1
Morra M Cassinelli C Cascardo G Nagel MD Della Volpe C Siboni S Maniglio D Brugnara M Ceccone G Schols HA Ulvskov P 《Biomacromolecules》2004,5(6):2094-2104
Polystyrene Petri dishes, aminated by a plasma deposition process, were surface modified by the covalent linking of two different enzymatically modified hairy regions (HRs) from pectin containing, for example, rhamnogalacturonan-I and xylogalacturonan structural elements. The two polysaccharide preparations share the same structural elements of apple pectin, but the relative amounts and lengths of the neutral side chains present differ. Surface analysis by X-ray photoelectron spectroscopy, contact angle measurement, and atomic force microscope (AFM) force-separation curves was used to characterize the effects on surface chemistry and interfacial forces of the surface modification process. Cell adhesion experiments using continuous L-929 fibroblasts and primary aortic smooth muscle cells were performed to evaluate the effect of the polysaccharide nature on cell adhesion. Results show that immobilization of the HR affects the interfacial field of forces and the cell behavior: "equilibrium" contact angles, obtained by a recently introduced vibrational approach, decrease after HR immobilization reaching a value close to 20 degrees . AFM force-separation curves show a more extended (or softer) interface in the case of the HR bearing longer side chains. Accordingly, depending on the HR preparation, cells shifted from spread morphology and adhesion behavior quantitatively comparable to that observed on conventional tissue culture polystyrene to rounded morphology and significantly lower adhesion. These data show that engineering of plant pectins can be a valuable tool to prepare novel and finely tuned polysaccharides having different chemico-physical and biological properties, to be used in the surface modification of medical devices and materials. 相似文献
60.
We examined the effect of inbreeding on fitness (through both male and female functions) and changes in self-fertility in the partially self-incompatible species Campanula rapunculoides. Individuals in natural populations of C. rapunculoides varied extensively in their strength of self-incompatibility (SI). We crossed 11 individuals that differed in their strength of SI to generate families with four levels of inbreeding (f = 0.0, 0.25, 0.5, and 0.75). Progeny were scored for three traits related to male fitness and for outcrossed and selfed seed production. Analyses of variance revealed significant inbreeding depression for the three male traits and seed set. Families with strong or weak SI differed in their response to inbreeding. Families with weak SI had lower levels of inbreeding depression for most traits than families with strong SI, but strong SI families had a greater increase in selfed seed set, but not self-fertility, with inbreeding. Finally, we found evidence of a significant linear response to inbreeding for all three male reproductive traits and outcrossed seed, indicating that inbreeding depression was primarily caused by partially or fully recessive deleterious alleles. Variation in genetic load was associated with variation in self-fertility, a finding that suggests an evolutionary role for partial self-fertility in natural populations of C. rapunculoides. 相似文献