全文获取类型
收费全文 | 309篇 |
免费 | 51篇 |
国内免费 | 1篇 |
出版年
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 15篇 |
2014年 | 8篇 |
2013年 | 9篇 |
2012年 | 14篇 |
2011年 | 18篇 |
2010年 | 19篇 |
2009年 | 15篇 |
2008年 | 13篇 |
2007年 | 10篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 12篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1919年 | 1篇 |
排序方式: 共有361条查询结果,搜索用时 905 毫秒
91.
Wingfield BD; Grant WS; Wolfaardt JF; Wingfield MJ 《Molecular biology and evolution》1994,11(3):376-383
The genus Ceratocystis sensu stricto includes important fungal pathogens of
woody and herbaceous plants. This genus is distinguished from species in
Ceratocystis sensu lato by the presence of Chalara anamorphs. Ascospore
shape has been used extensively in delineating Ceratocystis taxa, which
show a large variety of ascospore shapes. Sequence analysis of one region
of he 18S ribosomal RNA subunit and two regions of the 28S ribosomal RNA
subunit showed that there was a majority of multiple substitutions at
nucleotide sites and that there was a low transition/transversion ratio, T
= 0.72. Both of these results suggest that these are well established, old
species. Ascospore morphology, for the most part, was not congruent with
the molecular phylogeny, and the use of morphological characters may be
misleading in the taxonomy of these species.
相似文献
92.
Production and Purification of Thermostable Amylase and Protease of Thermomonospora viridis 总被引:2,自引:2,他引:0 下载免费PDF全文
Maximum yields of amylase were produced by the thermophilic actinomycete Thermomonospora viridis in a modified Simpson and McCoy medium containing 1.5% corn starch and 0.5% mycological peptone with an initial pH 7.0. Best yields of amylase were obtained after incubation for 48 h, when the pH of the medium had risen to 8.2. Amylase was purified 313-fold by precipitation with n-propyl alcohol, dialysis against tap water, adsorption on Ca3(PO4)2, and fractionation on Sephadex G-100. Protease was produced in nutrient broth containing 0.5% starch and 1.0% corn steep liquor and at an initial pH 7.0. Maximum yields of protease were produced after 42 h. The protease was purified 54-fold by precipitation with n-propyl alcohol, dialysis against tap water, adsorption on Ca3(PO4)2, and fractionation on Sephadex G-200. 相似文献
93.
MJ Doughty 《Biotechnic & histochemistry》2016,91(8):501-509
Goblet cells were visualized in impression cytology specimens from bulbar conjunctiva of the rabbit eye using Giemsa staining. Highly magnified images were used to generate outlines of the goblet cells and their characteristic eccentric nuclei. Using sets of 10 cells from 15 cytology specimens, I found that the longest dimension of the goblet cells averaged 16.7 ± 2.3 μm, the shortest dimension averaged 14.4 ± 1.8 μm and the nucleus averaged 6.3 ± 0.8 μm. The goblet cells were ellipsoid in shape and the longest:shortest cell dimension ratio averaged 1.169 ± 0.091. The goblet cell areas ranged from 108 to 338 μm2 (average 193 ± 50 μm2). The area could be predicted reliably from the longest and shortest dimensions (r2 = 0.903). The areas of goblet cell nuclei were 15–58 μm2 (average 33 ± μm2) and the nucleus:cytoplasm area fraction was predictably greater in smaller goblet cells and less in the larger goblet cells (Spearman correlation = 0.817). The nuclei were estimated to occupy an average of 9.5% of the cell volume. The differences in size, shape and nucleus:cytoplasm ratio may reflect differences in goblet cell maturation. 相似文献
94.
G. Engler C.M. Fogarty J.R. Banks G.K.H. Zupanc 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2000,186(7-8):645-660
Brown ghosts, Apteronotus leptorhynchus, are weakly electric gymnotiform fish whose wave-like electric organ discharges are distinguished by their enormous degree of regularity. Despite this constancy, two major types of transient electric organ discharge modulations occur: gradual frequency rises, which are characterized by a relatively fast increase in electric organ discharge frequency and a slow return to baseline frequency; and chirps, brief and complex frequency and amplitude modulations. Although in spontaneously generated gradual frequency rises both duration and amount of the frequency increase are highly variable, no distinct subtypes appear to exist. This contrasts with spontaneously generated chirps which could be divided into four "natural" subtypes based on duration, amount of frequency increase and amplitude reduction, and time-course of the frequency change. Under non-evoked conditions, gradual frequency rises and chirps occur rather rarely. External stimulation with an electrical sine wave mimicking the electric field of a neighboring fish leads to a dramatic increase in the rate of chirping not only during the 30 s of stimulation, but also in the period immediately following the stimulation. The rate of occurrence of gradual frequency rises is, however, unaffected by such a stimulation regime. 相似文献
95.
Fogarty KE Kidd JF Turner A Skepper JN Carmichael J Thorn P 《The Journal of biological chemistry》2000,275(29):22487-22494
The role of the cytoskeleton in regulating Ca(2+) release has been explored in epithelial cells. Trains of local Ca(2+) spikes were elicited in pancreatic acinar cells by infusion of inositol trisphosphate through a whole cell patch pipette, and the Ca(2+)-dependent Cl(-) current spikes were recorded. The spikes were only transiently inhibited by cytochalasin B, an agent that acts on microfilaments. In contrast, nocodazole (5-100 micrometer), an agent that disrupts the microtubular network, dose-dependently reduced spike frequency and decreased spike amplitude leading to total blockade of the response. Consistent with an effect of microtubular disruption, colchicine also inhibited spiking but neither Me(2)SO nor beta-lumicolchicine, an inactive analogue of colchicine, had any effect. The microtubule-stabilizing agent, taxol, also inhibited spiking. The nocodazole effects were not due to complete loss of function of the Ca(2+) signaling apparatus, because supramaximal carbachol concentrations were still able to mobilize a Ca(2+) response. Finally, as visualized by 2-photon excitation microscopy of ER-Tracker, nocodazole promoted a loss of the endoplasmic reticulum in the secretory pole region. We conclude that microtubules specifically maintain localized Ca(2+) spikes at least in part because of the local positioning of the endoplasmic reticulum. 相似文献
96.
97.
P Saurus S Kuusela E Lehtonen M E Hyv?nen M Ristola C L Fogarty J Tienari M I Lassenius C Forsblom M Lehto M A Saleem P-H Groop H Holth?fer S Lehtonen 《Cell death & disease》2015,6(5):e1752
High serum lipopolysaccharide (LPS) activity in normoalbuminuric patients with type 1 diabetes (T1D) predicts the progression of diabetic nephropathy (DN), but the mechanisms behind this remain unclear. We observed that treatment of cultured human podocytes with sera from normoalbuminuric T1D patients with high LPS activity downregulated 3-phosphoinositide-dependent kinase-1 (PDK1), an activator of the Akt cell survival pathway, and induced apoptosis. Knockdown of PDK1 in cultured human podocytes inhibited antiapoptotic Akt pathway, stimulated proapoptotic p38 MAPK pathway, and increased apoptosis demonstrating an antiapoptotic role for PDK1 in podocytes. Interestingly, PDK1 was downregulated in the glomeruli of diabetic rats and patients with type 2 diabetes before the onset of proteinuria, further suggesting that reduced expression of PDK1 associates with podocyte injury and development of DN. Treatment of podocytes in vitro and mice in vivo with LPS reduced PDK1 expression and induced apoptosis, which were prevented by inhibiting the Toll-like receptor (TLR) signaling pathway with the immunomodulatory agent GIT27. Our data show that LPS downregulates the cell survival factor PDK1 and induces podocyte apoptosis, and that blocking the TLR pathway with GIT27 may provide a non-nephrotoxic means to prevent the progression of DN.Lipopolysaccharides (LPS) are fat-soluble outer membrane components of the Gram-negative bacteria. It has been shown that normoalbuminuric patients with type 1 diabetes (T1D) who progress to microalbuminuria have higher baseline serum LPS activity than normoalbuminuric non-progressors.1 This indicates that high LPS activity in sera of patients with T1D is associated with the development of microalbuminuria.1 The origin of circulating endotoxins in patients with diabetes is not yet fully known. In addition to severe bacterial infections,2 underlying systemic diseases (e.g., periodontitis) and life-style related factors (e.g., high-fat diet) may increase plasma levels of endotoxins in humans.3, 4, 5 Interestingly, LPS in the sera of septic patients has previously been shown to induce apoptosis of kidney cells,6 but the mechanism is not known.Podocytes are terminally differentiated and highly specialized cells that are required for normal glomerular function. Podocyte loss due to apoptosis or detachment is a key component of progressive glomerulosclerosis. Podocyte loss has been reported in patients with T1D7 and type 2 diabetes (T2D) with or without diabetic nephropathy (DN),8, 9, 10 and Verzola et al.8 reported glomerular apoptosis in the kidneys of patients with DN. In Pima Indians with T2D, decreasing number of podocytes per glomerulus has been shown to be the strongest indicator of the progression of the renal disease.9 Podocytes are also detected in the urine in patients with diabetes, and podocyte number in urine correlates with the severity of the disease.10 These data indicate that analysis of the regulation of apoptosis in podocytes is essential for better understanding of the pathophysiological mechanisms of glomerular diseases.The central role of the phosphoinositide 3-kinase (PI3K)-dependent Akt signaling pathway in the regulation of cell survival raises the molecules that modulate its activity to key roles in regulating apoptosis in podocytes. 3-Phosphoinositide-dependent protein kinase-1 (PDK1) is a 63-kDa serine/threonine kinase that functions downstream of PI3K but upstream of Akt and serves as a major regulatory point in Akt signaling.11 Mice lacking PDK1 die in utero, and mice that lack PDK1 specifically in the pancreatic β cells develop progressive hyperglycemia as a result of the loss of islet mass.12, 13We hypothesized that PDK1, the key regulator of the PI3K/Akt-mediated cell survival pathway, could have a role in regulating podocyte apoptosis, and that high LPS activity could downregulate PDK1, consequently inducing apoptosis and podocyte injury. 相似文献
98.
99.
What's in a name; Genetic structure in Solanum section Petota studied using population-genetic tools
Mirjam MJ Jacobs Marinus JM Smulders Ronald G van den Berg Ben Vosman 《BMC evolutionary biology》2011,11(1):42
Background
The taxonomy and systematic relationships among species of Solanum section Petota are complicated and the section seems overclassified. Many of the presumed (sub)species from South America are very similar and they are able to exchange genetic material. We applied a population genetic approach to evaluate support for subgroups within this material, using AFLP data. Our approach is based on the following assumptions: (i) accessions that may exchange genetic material can be analyzed as if they are part of one gene pool, and (ii) genetic differentiation among species is expected to be higher than within species. 相似文献100.
Susan C Burleigh Teun van de Laar Corné JM Stroop Wout MJ van Grunsven Niaobh O’Donoghue Pauline M Rudd Gavin P Davey 《BMC biotechnology》2011,11(1):1-17