全文获取类型
收费全文 | 358篇 |
免费 | 46篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 14篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 26篇 |
2015年 | 22篇 |
2014年 | 26篇 |
2013年 | 31篇 |
2012年 | 31篇 |
2011年 | 33篇 |
2010年 | 14篇 |
2009年 | 14篇 |
2008年 | 28篇 |
2007年 | 10篇 |
2006年 | 18篇 |
2005年 | 17篇 |
2004年 | 19篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1987年 | 4篇 |
1982年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有404条查询结果,搜索用时 15 毫秒
61.
Impacts of natural factors and farming practices on greenhouse gas emissions in the North China Plain: A meta‐analysis 下载免费PDF全文
Requirements for mitigation of the continued increase in greenhouse gas (GHG ) emissions are much needed for the North China Plain (NCP ). We conducted a meta‐analysis of 76 published studies of 24 sites in the NCP to examine the effects of natural conditions and farming practices on GHG emissions in that region. We found that N2O was the main component of the area‐scaled total GHG balance, and the CH 4 contribution was <5%. Precipitation, temperature, soil pH , and texture had no significant impacts on annual GHG emissions, because of limited variation of these factors in the NCP . The N2O emissions increased exponentially with mineral fertilizer N application rate, with y = 0.2389e0.0058x for wheat season and y = 0.365e0.0071x for maize season. Emission factors were estimated at 0.37% for wheat and 0.90% for maize at conventional fertilizer N application rates. The agronomic optimal N rates (241 and 185 kg N ha?1 for wheat and maize, respectively) exhibited great potential for reducing N2O emissions, by 0.39 (29%) and 1.71 (56%) kg N2O‐N ha?1 season?1 for the wheat and maize seasons, respectively. Mixed application of organic manure with reduced mineral fertilizer N could reduce annual N2O emissions by 16% relative to mineral N application alone while maintaining a high crop yield. Compared with conventional tillage, no‐tillage significantly reduced N2O emissions by ~30% in the wheat season, whereas it increased those emissions by ~10% in the maize season. This may have resulted from the lower soil temperature in winter and increased soil moisture in summer under no‐tillage practice. Straw incorporation significantly increased annual N2O emissions, by 26% relative to straw removal. Our analysis indicates that these farming practices could be further tested to mitigate GHG emission and maintain high crop yields in the NCP . 相似文献
62.
Pete Beckman Kamil Iskra Kazutomo Yoshii Susan Coghlan Aroon Nataraj 《Cluster computing》2008,11(1):3-16
We investigate operating system noise, which we identify as one of the main reasons for a lack of synchronicity in parallel
applications. Using a microbenchmark, we measure the noise on several contemporary platforms and find that, even with a general-purpose
operating system, noise can be limited if certain precautions are taken. We then inject artificially generated noise into
a massively parallel system and measure its influence on the performance of collective operations. Our experiments indicate
that on extreme-scale platforms, the performance is correlated with the largest interruption to the application, even if the
probability of such an interruption on a single process is extremely small. We demonstrate that synchronizing the noise can
significantly reduce its negative influence.
相似文献
Aroon NatarajEmail: |
63.
Zhao X Deyanova EG Lubbers LS Zafian P Li JJ Liaw A Song Q Du Y Settlage RE Hickey GJ Yates NA Hendrickson RC 《Journal of proteome research》2008,7(10):4373-4383
Estrogens are a class of steroid hormones that interact with two related but distinct nuclear receptors, estrogen receptor (ER) alpha and beta. To identify potential ER biomarkers, we profiled the rat plasma glycoproteome after treatment with vehicle or 17beta-estradiol (E2) or an ERalpha-selective agonist PPT by differential mass spectrometry. Our comparative proteomic experiment identifies novel E2- and PPT-responsive proteins, such as serine protease inhibitor family members. 相似文献
64.
65.
Kralt D Light B Cheang M MacNair T Wiebe L Limerick B Sarsfield P Hammond G MacDonald K Trepman E Embil JM 《Mycopathologia》2009,167(3):115-124
Background Blastomycosis is an uncommon granulomatous infection caused by the thermally dimorphic fungus Blastomyces dermatitidis. The most frequent clinical infections involve the lung, skin, and bone. Pulmonary manifestations range from asymptomatic
self-limited infection to severe diffuse pneumonia causing respiratory failure.
Objectives To establish the clinical characteristics and outcomes of patients with pulmonary blastomycosis diagnosed at hospitals in
Manitoba and northwestern Ontario, Canada.
Methods A retrospective review of medical records was done for 318 patients with blastomycosis in these regions.
Results The majority of patients were Caucasian (198 (62.5%) patients), male (193 (61%) patients), and residents of Ontario (209 (65.7%)
patients). Most patients were treated in an inpatient hospital ward (266 (84%) patients) and survived (294 (92%) patients).
Pulmonary involvement, either alone or associated with other sites, was present in 296 (93%) of the 318 patients; 22 (7%)
patients had no evidence of pulmonary blastomycosis. The majority of patients had localized lung disease (1–3 quadrants on
chest radiograph involved; 225 (82%) patients). Of 294 (92%) patients requiring hospitalization, 266 (90%) patients received
all inpatient care on a general medical ward; 28 (10%) patients received some care in the intensive care unit (ICU). Factors
associated with ICU admission included diffuse pulmonary disease (four quadrants involved on chest radiograph), diabetes,
and prior use of antimicrobial therapy. Twenty-four (8%) patients died, and multivariate analysis showed that older age and
Aboriginal ethnicity were the significant risk factors for death from blastomycosis.
Conclusion Blastomycosis is a cause of serious, potentially life-threatening pulmonary infection in this geographic region.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
66.
67.
Background
Formaldehyde crosslinking is in widespread use as a biological fixative for microscopy and molecular biology. An assumption behind its use is that most biologically meaningful interactions are preserved by crosslinking, but the minimum length of time required for an interaction to become fixed has not been determined.Methodology
Using a unique series of mutations in the DNA binding protein MeCP2, we show that in vivo interactions lasting less than 5 seconds are invisible in the microscope after formaldehyde fixation, though they are obvious in live cells. The stark contrast between live cell and fixed cell images illustrates hitherto unsuspected limitations to the fixation process. We show that chromatin immunoprecipitation, a technique in widespread use that depends on formaldehyde crosslinking, also fails to capture these transient interactions.Conclusions/Significance
Our findings for the first time establish a minimum temporal limitation to crosslink chemistry that has implications for many fields of research. 相似文献68.
Shaista Nisar Eamonn Kelly Pete J. Cullen Stuart J. Mundell 《Traffic (Copenhagen, Denmark)》2010,11(4):508-519
The activity and traffic of G‐protein coupled receptors (GPCRs) is tightly controlled. Recent work from our laboratory has shown that P2Y1 and P2Y12 responsiveness is rapidly and reversibly modulated in human platelets and that the underlying mechanism requires receptor trafficking as an essential part of this process. However, little is known about the molecular mechanisms underlying P2Y receptor traffic. Sorting nexin 1 (SNX1) has been shown to regulate the endosomal sorting of cell surface receptors either to lysosomes where they are downregulated or back to the cell surface. These functions may in part be due to interactions of SNX1 with the mammalian retromer complex. In this study, we investigated the role of SNX1 in P2Y receptor trafficking. We show that P2Y1 receptors recycle via a slow recycling pathway that is regulated by SNX1, whereas P2Y12 receptors return to the cell surface via a rapid route that is SNX1 independent. SNX1 inhibition caused a dramatic increase in the rate of P2Y1 receptor recycling, whereas inhibition of Vps26 and Vps35 known to be present in retromer had no effect, indicating that SNX1 regulation of P2Y1 receptor recycling is retromer independent. In addition, inhibition of SNX4, 6 and 17 proteins did not affect P2Y1 receptor recycling. SNX1 has also been implicated in GPCR degradation; however, we provide evidence that P2Y receptor degradation is SNX1 independent. These data describe a novel function of SNX1 in the regulation of P2Y1 receptor recycling and suggest that SNX1 plays multiple roles in endocytic trafficking of GPCRs. 相似文献
69.
70.
Factor VIII (fVIII) is the plasma protein that is missing or deficient in hemophilia A. In contrast, elevated levels of fVIII are associated with an increased risk of arterial and venous thrombosis. fVIII is activated by thrombin to form a non-covalently linked A1/A2/A3-C1-C2 heterotrimer. At physiological concentrations, fVIIIa decays as a result of A2 subunit dissociation, which may help regulate the balance between hemostasis and thrombosis. A2 subunit dissociation is faster in human fVIIIa than in porcine fVIIIa, which may represent an evolutionary adaptation associated with the development of the upright posture and venous stasis in the lower extremities. To investigate the basis for the different decay kinetics of human and porcine fVIIIa, hybrid fVIII molecules representing all possible combinations of human and porcine A domains were isolated. The kinetics of fVIIIa decay were measured and fit to a model describing a reversible bimolecular reaction in which the dissociation rate constant, k, and dissociation constant, Kd, were the fitted parameters. Substitution of the porcine A1 domain into human fVIIIa produced a dissociation rate constant indistinguishable from porcine fVIIIa. Subsequently, substitution of the second cupredoxin-like A1 subdomain resulted in a dissociation rate constant similar to porcine fVIIIa, whereas substitution of the first cupredoxin-like A1 subdomain resulted in a dissociation rate constant intermediate between human and porcine fVIIIa. We propose that cupredoxin-like A1 subdomains in fVIII contain inter-species differences that are a result of selective pressure on the dissociation rate constant. 相似文献