全文获取类型
收费全文 | 1732篇 |
免费 | 209篇 |
出版年
2021年 | 18篇 |
2020年 | 16篇 |
2019年 | 20篇 |
2018年 | 23篇 |
2017年 | 15篇 |
2016年 | 31篇 |
2015年 | 52篇 |
2014年 | 64篇 |
2013年 | 79篇 |
2012年 | 83篇 |
2011年 | 73篇 |
2010年 | 51篇 |
2009年 | 51篇 |
2008年 | 58篇 |
2007年 | 63篇 |
2006年 | 52篇 |
2005年 | 59篇 |
2004年 | 60篇 |
2003年 | 41篇 |
2002年 | 63篇 |
2001年 | 49篇 |
2000年 | 76篇 |
1999年 | 66篇 |
1998年 | 30篇 |
1997年 | 19篇 |
1996年 | 32篇 |
1995年 | 24篇 |
1994年 | 29篇 |
1993年 | 14篇 |
1992年 | 36篇 |
1991年 | 38篇 |
1990年 | 47篇 |
1989年 | 37篇 |
1988年 | 35篇 |
1987年 | 36篇 |
1986年 | 33篇 |
1985年 | 36篇 |
1984年 | 24篇 |
1983年 | 26篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1979年 | 17篇 |
1978年 | 18篇 |
1977年 | 14篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1974年 | 11篇 |
1973年 | 14篇 |
1972年 | 13篇 |
1971年 | 10篇 |
排序方式: 共有1941条查询结果,搜索用时 15 毫秒
961.
Bord na Móna (the Irish PeatDevelopment Corporation) began peatextraction at Bellacorick, in County Mayo,in the north-west of Ireland in 1961. Thepeat production area comprised 8000 ha ofAtlantic blanket bog. To date, about 25%of the area has been taken out ofproduction as the peat resources wereexhausted. The cutaway landscape isheterogeneous, with some intact bogremnants among gravel hills bared throughpeat erosion, shallow acid highly-humifiedpeat deposits overlying relatively levelglacial till, and occasional pockets ofmineral-enriched peat in depressions. Theaims of the work described here are (a) toprovide a baseline vegetation survey of thecutaway, (b) to test potential managementtools for accelerating re-vegetation, and(c) to promote the re-establishment ofpeatland characteristics where possible.Thirteen plant communities were recorded onthe cutaway bog at Bellacorick. Extensiveareas of cutaway are colonised by Juncus effusus. Peatland communities havedeveloped where the drainage of cutaway hasbeen impeded and the water-table remains ator above the surface. Remnants of intactAtlantic blanket bog within the productionarea provide a local source of propagulesfor colonisation of adjacent bare cutaway.They also constitute locations for plantswith restricted distributions within theproduction area.Experimental plots were used to show thepositive impacts of (a) re-wetting ofcutaway surfaces in promoting thecolonisation and spread of Sphagnum,and (b) ridging of exposed gravel till thatprovides waterlogged and sheltered furrowsin which accelerated plant colonisationtakes place.A management plan is currently beingdevised for the rehabilitation of theBellacorick cutaway. Bog remnants should bemaintained as an essential part ofrehabilitation management. Rehabilitationwill include restoration of peat-formingconditions facilitated by waterlogging,which has been shown in experimental trialsto be enhanced by dam construction,infilling of drains and surface ridging. AtBellacorick, it is evident that, with time,peat-forming conditions can be restoredwith minimal management and economic cost. 相似文献
962.
Roula Thomas Sonia I Patenaude C Roger MacKenzie Rebecca To Tomoko Hirama N Martin Young Stephen V Evans 《The Journal of biological chemistry》2002,277(3):2059-2064
The specificity of antibody recognition of the ABO blood group trisaccharide antigens has been explored by crystal structure analysis and mutation methods. The crystal structure of the Fv corresponding to the anti-blood group A antibody AC1001 has been determined to 2.2-A resolution and reveals a binding pocket that is complementary to the blood group A-trisaccharide antigen. The effect of mutating specific residues lining this pocket on binding to the A and B blood group oligosaccharide antigens was investigated through a panel of single point mutations and through a phage library of mutations in complementarity determining region H3. Both approaches gave several mutants with improved affinity for antigen. Surface plasmon resonance indicated up to 8-fold enhancement in affinity for the A-pentasaccharide with no observable binding to the blood group B antigen. This is the first example of single point mutations in a carbohydrate-binding antibody resulting in significant increases in binding affinity without loss of specificity. 相似文献
963.
Yun Qu My-Chau Tran Nicholas P. Farrell 《Journal of biological inorganic chemistry》2009,14(6):969-977
Combined multidimensional nuclear magnetic resonance spectroscopy and electrospray mass spectrometry was used to analyze the
platinated DNA adduct of the phase II anticancer drug [{trans-PtCl(NH3)2}2-μ-{trans-Pt(NH3)2(NH2(CH2)6NH2)2}](NO3)4 (BBR3464) with [5′-d(ACG*TATACG*T)-3′]2. Two 1,2-interstrand cross-links were formed by concomitant binding of two trinuclear moieties to the oligonucleotide. The
four DNA-bound platinum atoms coordinated in the major groove at N7 positions of guanines in the 3′ → 3′ direction and the
central platinum unit is expected to lie in the DNA minor groove. This is the first report of such a DNA lesion. The melting
temperature of the adduct is 76 °C and is 42 °C higher than that of the unplatinated DNA. The sugar residues of the platinated
bases are in the N-type conformation and the G9 nucleoside is in the syn orientation, while the G3 nucleoside appears to retain the anti configuration. The secondary structure of DNA was significantly changed upon cross-linking of the two BBR3464 molecules.
Base destacking occurs between A1/C2 and C2/G3 and weakened stacking is seen for the C8/G9 and G9/T10 bases. The lack of Watson–Crick
base pairing is also seen for A1–T10 and C2–G9 base pairs, whereas Watson–Crick base pairs in the central sequence of the
DNA (T4 → A7) are well maintained. While DNA repair proteins may “see” different platinated adducts as bulky “lesions”, the
subtle differences involved in base pairing and stacking, as summarized here, may extend to their role as a substrate for
repair enzymes. Thus, differences in protein recognition and repair efficiency among the various interstrand cross-links are
likely and a subject worthy of detailed exploration.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
964.
The aims of this study were to assess changes in heavy metal availability in two contrasting feedstocks during aerobic composting, and the availability of said metals in the finished composts. A high C-to-N ratio mixed biodegradable municipal solid waste (MSW) feedstock was successfully composted on its own and in combination with green waste. Changes in heavy metal speciation throughout the composting process were studied using the modified BCR sequential extraction protocol. It was found that total Cu, Pb and Zn concentrations increased over time due to the progressive mineralization of the compost feedstock. Metals were fractionated differently within the two feedstocks, although only Cu showed significant redistribution (mostly to the oxidisable fraction) over the 5 month composting period. The MSW-derived composts performed comparably with other commercially-available composts in a series of plant growth trials. Plant metal accumulation was not influenced by the heavy metals present in the MSW-derived compost implying that they are not plant available. It is recommended that these relatively low value/quality composts may be used for remediation of acidic heavy metal contaminated sites. 相似文献
965.
966.
967.
Selection on parental performance opposes selection for larger body mass in a wild population of blue tits
下载免费PDF全文
![点击此处可从《Evolution; international journal of organic evolution》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Caroline E. Thomson Florian Bayer Nicholas Crouch Samantha Farrell Elizabeth Heap Elizabeth Mittell Mar Zurita‐Cassinello Jarrod D. Hadfield 《Evolution; international journal of organic evolution》2017,71(3):716-732
There is abundant evidence in many taxa for positive directional selection on body size, and yet little evidence for microevolutionary change. In many species, variation in body size is partly determined by the actions of parents, so a proposed explanation for stasis is the presence of a negative genetic correlation between direct and parental effects. Consequently, selecting genes for increased body size would result in a correlated decline in parental effects, reducing body size in the following generation. We show that these arguments implicitly assume that parental care is cost free, and that including a cost alters the predicted genetic architectures needed to explain stasis. Using a large cross‐fostered population of blue tits, we estimate direct selection on parental effects for body mass, and show it is negative. Negative selection is consistent with a cost to parental care, mainly acting through a reduction in current fecundity rather than survival. Under these conditions, evolutionary stasis is possible for moderately negative genetic correlations between direct and parental effects. This is in contrast to the implausibly extreme correlations needed when care is assumed to be cost‐free. Thus, we highlight the importance of accounting correctly for complete selection acting on traits across generations. 相似文献
968.
The Effects of Prenatal Iron Deficiency and Risperidone Treatment on the Rat Frontal Cortex: A Proteomic Analysis
下载免费PDF全文
![点击此处可从《Proteomics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Lorna Farrelly Maria Victoria Rosato‐Siri Melanie Föcking Martin Codagnone Analia Reines Patrick Dicker Kieran Wynne Michael Farrell Mary Cannon Gerard Cagney Juana Maria Pasquini David R. Cotter 《Proteomics》2017,17(17-18)
Prenatal iron deficiency (pID) has been described to increase the risk for neurodevelopmental disorders such as autism and schizophrenia; however, the precise molecular mechanisms are still unknown. Here, we utilized high‐throughput MS to examine the proteomic effects of pID in adulthood on the rat frontal cortex area (FCA). In addition, the FCA proteome was examined in adulthood following risperidone treatment in adolescence to see if these effects could be prevented. We identified 1501 proteins of which 100 were significantly differentially expressed in the FCA at postnatal day 90. Pathway analysis of proteins affected by pID revealed changes in metabolic processes, including the tricyclic acid cycle, mitochondrial dysfunction, and P13K/Akt signaling. Interestingly, most of these protein changes were not present in the adult pID offspring who received risperidone in adolescence. Considering the link between pID and several neurodevelopmental disorders such as autism and schizophrenia these presented results bring new perspectives to understand the role of iron in metabolic pathways and provide novel biomarkers for future studies of pID. 相似文献
969.
Research on male courtship behavior of moths has focused on documenting stereotyped sequences for successful copulation. We characterized successful male courtship behavior among 126 virgin mating pairs of Ostrinia nubilalis. Using Markov analysis, stereotypy indices, and a novel application of ecological network analysis, we found high variability in these sequences. Fifteen courtship behaviors were described and 96 behavioral transitions were observed, 39 of which occurred only once. The number of courtship bouts ranged from one to ten, the number of behavioral transitions ranged from four to 41, and the number of copulation attempts ranged from one to 29. Only 23% of males used a common, simple behavioral sequence. Females exhibited acceptance or rejection behaviors in 40% of the sequences, but these did not explain the high variability in male courtship sequences. About half of the transitions occurred non-randomly, and stereotypy was low. Network analysis revealed that the courtship sequences started and ended with stereotyped behaviors and the high variability occurred in the middle of the sequences. Whole system analysis showed that the courtship sequences were more variable than for optimal transfer of information. Overall, these results suggest that the sequence of behaviors may be less important than the occurrence of certain behavioral elements for successful mating. 相似文献
970.
Murray LA Argentieri RL Farrell FX Bracht M Sheng H Whitaker B Beck H Tsui P Cochlin K Evanoff HL Hogaboam CM Das AM 《The international journal of biochemistry & cell biology》2008,40(10):2174-2182
One of the hallmarks of idiopathic pulmonary fibrosis with a usual interstitial pneumonia histological pathology (IPF/UIP) is excess collagen deposition, due to enhanced fibroblast extracellular matrix synthetic activity. Studies using murine models of lung fibrosis have elucidated a pro-fibrotic pathway involving IL-13 driving CCL2, which in turn drives TGFbeta1 in lung fibroblasts. Therefore, we sought to determine whether this pathway exists in the human fibrotic setting by evaluating human IPF/UIP fibroblasts. IPF/UIP fibroblasts have an increased baseline fibrotic phenotype compared to non-fibrotic fibroblasts. Interestingly, non-fibrotic fibroblasts responded in a pro-fibrotic manner to TGFbeta1 but were relatively non-responsive to IL-13 or CCL2, whereas, IPF/UIP cells were hyper-responsive to TGFbeta1, IL-13 and CCL2. Interestingly, TGFbeta1, CCL2 and IL-13 all upregulated TGFbeta receptor and IL-13 receptor expression, suggesting an ability of the mediators to modulate the function of each other. Furthermore, in vivo, neutralization of both JE and MCP5, the two functional orthologs of CCL2, during bleomycin-induced pulmonary fibrosis significantly reduced collagen deposition as well as JE and CCR2 expression. Also in the bleomycin model, CTGF, which is highly induced following TGFbeta stimulation, was attenuated with anti-JE/anti-MCP5 treatment. Overall this study demonstrates an interplay between TGFbeta1, IL-13 and CCL2 in IPF/UIP, where these three mediators feedback on each other, promoting the fibrotic response. 相似文献