全文获取类型
收费全文 | 271篇 |
免费 | 32篇 |
出版年
2021年 | 5篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 3篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 5篇 |
2012年 | 13篇 |
2011年 | 19篇 |
2010年 | 8篇 |
2009年 | 6篇 |
2008年 | 12篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 13篇 |
2002年 | 12篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 16篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 9篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1979年 | 2篇 |
1961年 | 2篇 |
1944年 | 3篇 |
1943年 | 3篇 |
1942年 | 2篇 |
1941年 | 2篇 |
1940年 | 2篇 |
1925年 | 1篇 |
1921年 | 1篇 |
1918年 | 1篇 |
1915年 | 1篇 |
1914年 | 1篇 |
1913年 | 1篇 |
1888年 | 1篇 |
1887年 | 1篇 |
1882年 | 1篇 |
1875年 | 1篇 |
排序方式: 共有303条查询结果,搜索用时 31 毫秒
1.
Jeff A Johnson Heather RL Lerner Pamela C Rasmussen David P Mindell 《BMC evolutionary biology》2006,6(1):65-12
Background
Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis. 相似文献2.
Male rodents were studied before and after undergoing one of three treatment conditions for 9 days: 1) cage control (n = 15, CON), 2) horizontal suspension (n = 15, HOZ), and 3) head-down suspension (n = 18, HDT). Testing included measurements of maximal O2 uptake (VO2 max) and select cardiovascular responses to graded treadmill exercise. VO2 max expressed on an absolute basis (ml/min) was significantly decreased after HOZ (-14.1 +/- 2.5%) and HDT (-14.3 +/- 2.0%), while being essentially unchanged in CON (-1.0 +/- 3.3%). Significant reductions in body weight were observed after both HOZ (-10.1 +/- 4.2 g) and HDT (-22.5 +/- 3.3 g), whereas CON animals exhibited a significant increase in weight (10.4 +/- 3.8 g). As a result, when VO2 max was normalized for body weight, all groups exhibited similar significant reductions of 6-7%. Although no differences in heart rate and blood pressure response to graded exercise were observed, the HDT group exhibited greater increases in mesenteric resistance at the same absolute exercise intensity. Furthermore, both suspended groups had higher iliac resistance values during exercise at similar relative exercise conditions, suggesting that muscle blood flow during treadmill running may have been reduced after suspension. In general, the decrements associated with the HOZ and HDT conditions were similar. It was concluded that reduction in exercise capacity and altered cardiovascular responses to exercise observed after 6-9 days of suspension were attributable to a combination of hypokinesia, lack of hindlimb weight bearing, or restraint, rather than to hydrostatic influences associated with HDT. 相似文献
3.
Richard C. Woodman John T. Curnutte Bernard M. Babior 《Free radical biology & medicine》1988,5(5-6):355-361
We examined the effects of the recombinant human colony stimulating factors GM-CSF and G-CSF, cycloheximide (a protein synthesis inhibitor) and dihydrocytochalasin B (a microfilament disrupting agent) upon FMLP (N-formyl-methionyl-leucylphenylalanine)-stimulated O2 − production by neutrophils. We confirmed a time dependent augmentation of O2 − production following preincubation of neutrophils either alone or with colony stimulating factors. Furthermore, we found that GM-CSF, but not G-CSF, increased O2 − production at some concentrations of the stimulus. Preincubation of neutrophils with cycloheximide in the absence of CSF caused a marked fall in O2−-production that was first evident at 2 hours. The fall in O2−-forming capacity caused by cycloheximide was much less pronounced if dihydrocytochalasin B was also included in the preincubation buffer. These findings suggest a previously unrecognized role for de novo protein synthesis in maintaining the ability of neutrophils to manufacture O2−, and support earlier studies indicating that the cycling of FMLP receptors between the cell membrane and an intracellular compartment is important in determining the magnitude of the respiratory burst in FMLP-stimulated neutrophils. 相似文献
4.
M. M. Messmer A. E. Melchinger M. Lee W. L. Woodman E. A. Lee K. R. Lamkey 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1991,83(1):97-107
Summary Data for restriction fragment length polymorphisms (RFLPs) of 144 clone-enzyme combinations and for 22 allozyme loci from 21 U.S. Corn Belt maize (Zea mays L.) inbreds were analyzed. The genetic materials included 14 progenitors of the Iowa Stiff Stalk Synthetic (BSSS) maize population, both parents of one missing BSSS progenitor, four elite inbreds derived from BSSS, and inbred Mo17. Objectives were to characterize the genetic variation among these 21 inbreds for both allozymes and RFLPs, to compare the results from both types of molecular markers, and to estimate the proportion of unique alleles in the BSSS progenitors. Genetic diversity among the 21 inbreds was substantially greater for RFLPs than for allozymes, but the percentages of unique RFLP variants (27%) and unique allozyme alleles (25%) in the BSSS progenitors were similar. Genetic distances between inbreds, estimated as Rogers' distance (RD), were, on average, twice as large for RFLP (0.51) as for allozyme data (0.24). RDs obtained from allozyme and RFLP data for individual line combinations were only poorly correlated (r = 0.23); possible reasons for discrepancies are discussed. Principal component analysis of RFLP data, in contrast to allozyme data, resulted in separate groupings of the ten BSSS progenitors derived from the Reid Yellow Dent population, the four BSSS elite lines, and Mo17. The remaining six BSSS progenitors were genetically rather diverse and contributed a large number of rare alleles to BSSS. The results of this study corroborate the fact that RFLPs are superior to allozymes for characterizing the genetic diversity of maize breeding materials, because of (1) the almost unlimited number of markers available and (2) the greater amount of polymorphisms found. In particular, RFLPs allow related lines and inbreds with common genetic background to be identified, but a large number of probe-enzyme combinations is needed to estimate genetic distances with the precision required.Joint contribution from Cereal and Soybean Research Unit, USDA, Agricultural Research Service, and Journal Paper No. J-14236 of the Iowa Agricultural and Home Economics Experiment Station, Projects 2818 and 2778 相似文献
5.
6.
L. S. Young I. S. Bevan M. A. Johnson P. I. Blomfield T. Bromidge N. J. Maitland C. B. Woodman 《BMJ (Clinical research ed.)》1989,298(6665):14-18
The polymerase chain reaction is an in vitro method for primer directed enzymatic amplification of specific target DNA sequences. The technique was used to detect human papillomavirus types 11 and 16 simultaneously in cellular DNA recovered from cervical smears in 38 women referred for colposcopy to evaluate cytological abnormality and 10 women with no history of cytological abnormality. The polymerase chain reaction was shown to be both specific and sensitive in detecting human papillomavirus DNA such that a single human papillomavirus molecule was detected in 10(5) cells. Of the 38 women with cytological abnormality, all were positive for human papillomavirus on testing with the polymerase chain reaction; 36 were infected with human papillomavirus type 16 and 22 dually infected with human papillomavirus types 11 and 16. Seven of the 10 women with no cytological abnormality were also infected with human papillomavirus type 11 or 16. The use of the polymerase chain reaction will facilitate epidemiological investigation of the aetiological role of human papillomavirus in cervical neoplasia. This preliminary analysis suggests that the prevalence of human papillomavirus infection is greater than previously reported. 相似文献
7.
8.
alpha 1-Proteinase inhibitor (alpha 1-PI), a member of the serine
proteinase inhibitor superfamily, has a primary role in controlling
neutrophil elastase activity within the mammalian circulation. Several
studies have indicated that the reactive center region of alpha 1-PI, the
amino acid sequence of which is critical to recognition of and binding to
target proteinases, is highly divergent within and among species. This
appears to be a consequence of accelerated rates of evolution that may have
been driven by positive Darwinian selection. In order to examine this and
other features of alpha 1-PI evolution in more detail, we have isolated and
sequenced cDNAs representing alpha 1- PI mRNAs of the mouse species Mus
saxicola and Mus minutoides and have compared these with a number of other
mammalian alpha 1-PI mRNAs. Relative to other mammalian mRNAs, the extent
of nonsynonymous substitution is generally high throughout the alpha 1-PI
mRNA molecule, indicating greater overall rates of amino acid substitution.
Within and among mouse species, the 5'-half of the mRNA, but not the
3'-half, has been homogenized by concerted evolution. Finally, the reactive
center is under diversifying or positive Darwinian selection in murid
rodents (rats, mice) and guinea pigs yet is under purifying selection in
primates and artiodactyls. The significance of these findings to alpha 1-PI
function and the possible selective forces driving evolution of serpins in
general are discussed.
相似文献
9.
Multiple N-ethylmaleimide-sensitive components are required for endosomal vesicle fusion. 总被引:11,自引:5,他引:6
下载免费PDF全文
![点击此处可从《Molecular biology of the cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This report examines the inhibition of endosomal vesicle fusion by the alkylating agent N-ethylmaleimide (NEM). The concentration of NEM required to inhibit vesicle fusion depended upon whether membrane and cytosolic fractions were treated separately or together, enabling the resolution of at least two components to the inhibition. The first component is inactivated at low levels of NEM when cytosolic and membrane fractions are treated together. On the contrary, inhibition of the second component required higher levels of NEM but was achieved by treating cytosol and membranes separately. Reconstitution studies indicated that both components were cytosolic and that neither corresponded to the ubiquitous NEM-sensitive fusion protein (NSF). The role of NSF in this fusion reaction was further examined using salt-washed membranes depleted of NSF protein. Under these conditions the fusion reaction was fully dependent upon added NSF whose activity, in this context, was sensitive to NEM treatment. From these data we conclude that NSF activity during endosomal vesicle fusion can be dissected into several steps, only a subset of which (perhaps attachment of NSF to the membrane) are sensitive to NEM. Fusion between salt-washed endosomal membranes was also dependent on soluble NSF attachment proteins. 相似文献
10.
Tipton CM Grindeland RE Woodman CR Gosselink K Linderman JK Mukku VR Gooselink K 《Journal of gravitational physiology : a journal of the International Society for Gravitational Physiology》1994,1(1):P75-P76
The primary purpose of this investigation was to secure select anatomical and physiological measurements from hypophysectomized rats and their sham-operated control to determine how various endocrine influences could be modified by conditions of simulated microgravity. The focal point of the study was the exercise responses after head-down suspension; however, we were also interested in obtaining insights on nonexercise-related mechanisms. Since more details and information concerning this study will be published elsewhere, we will highlight those findings which warrant further research. 相似文献