全文获取类型
收费全文 | 2423篇 |
免费 | 345篇 |
国内免费 | 5篇 |
出版年
2018年 | 23篇 |
2016年 | 46篇 |
2015年 | 60篇 |
2014年 | 73篇 |
2013年 | 79篇 |
2012年 | 125篇 |
2011年 | 113篇 |
2010年 | 61篇 |
2009年 | 47篇 |
2008年 | 87篇 |
2007年 | 95篇 |
2006年 | 86篇 |
2005年 | 84篇 |
2004年 | 81篇 |
2003年 | 77篇 |
2002年 | 64篇 |
2001年 | 70篇 |
2000年 | 70篇 |
1999年 | 64篇 |
1998年 | 30篇 |
1997年 | 36篇 |
1996年 | 29篇 |
1995年 | 29篇 |
1994年 | 29篇 |
1993年 | 28篇 |
1992年 | 49篇 |
1991年 | 50篇 |
1990年 | 46篇 |
1989年 | 51篇 |
1988年 | 63篇 |
1987年 | 44篇 |
1986年 | 54篇 |
1985年 | 52篇 |
1984年 | 40篇 |
1983年 | 46篇 |
1982年 | 33篇 |
1981年 | 27篇 |
1980年 | 26篇 |
1979年 | 45篇 |
1978年 | 30篇 |
1977年 | 34篇 |
1976年 | 25篇 |
1975年 | 24篇 |
1974年 | 18篇 |
1973年 | 38篇 |
1972年 | 28篇 |
1971年 | 33篇 |
1970年 | 27篇 |
1969年 | 20篇 |
1968年 | 26篇 |
排序方式: 共有2773条查询结果,搜索用时 421 毫秒
941.
Sharma S Sud N Wiseman DA Carter AL Kumar S Hou Y Rau T Wilham J Harmon C Oishi P Fineman JR Black SM 《American journal of physiology. Lung cellular and molecular physiology》2008,294(1):L46-L56
Utilizing aortopulmonary vascular graft placement in the fetal lamb, we have developed a model (shunt) of pulmonary hypertension that mimics congenital heart disease with increased pulmonary blood flow. Our previous studies have identified a progressive development of endothelial dysfunction in shunt lambs that is dependent, at least in part, on decreased nitric oxide (NO) signaling. The purpose of this study was to evaluate the possible role of a disruption in carnitine metabolism in shunt lambs and to determine the effect on NO signaling. Our data indicate that at 2 wk of age, shunt lambs have significantly reduced expression (P < 0.05) of the key enzymes in carnitine metabolism: carnitine palmitoyltransferases 1 and 2 as well as carnitine acetyltransferase (CrAT). In addition, we found that CrAT activity was inhibited due to increased nitration. Furthermore, free carnitine levels were significantly decreased whereas acylcarnitine levels were significantly higher in shunt lambs (P < 0.05). We also found that alterations in carnitine metabolism resulted in mitochondrial dysfunction, since shunt lambs had significantly decreased pyruvate, increased lactate, and a reduced pyruvate/lactate ratio. In pulmonary arterial endothelial cells cultured from juvenile lambs, we found that mild uncoupling of the mitochondria led to a decrease in cellular ATP levels and a reduction in both endothelial NO synthase-heat shock protein 90 (eNOS-HSP90) interactions and NO signaling. Similarly, in shunt lambs we found a loss of eNOS-HSP90 interactions that correlated with a progressive decrease in NO signaling. Our data suggest that mitochondrial dysfunction may play a role in the development of endothelial dysfunction and pulmonary hypertension and increased pulmonary blood flow. 相似文献
942.
Sud N Wedgwood S Black SM 《American journal of physiology. Lung cellular and molecular physiology》2008,294(3):L582-L591
In this study, we explore the roles of the delta isoform of PKC (PKCdelta) in the regulation of endothelial nitric oxide synthase (eNOS) activity in pulmonary arterial endothelial cells isolated from fetal lambs (FPAECs). Pharmacological inhibition of PKCdelta with either rottlerin or with the peptide, deltaV1-1, acutely attenuated NO production, and this was associated with a decrease in phosphorylation of eNOS at Ser1177 (S1177). The chronic effects of PKCdelta inhibition using either rottlerin or the overexpression of a dominant negative PKCdelta mutant included the downregulation of eNOS gene expression that was manifested by a decrease in both eNOS promoter activity and protein expression after 24 h of treatment. We also found that PKCdelta inhibition blunted Akt activation as observed by a reduction in phosphorylated Akt at position Ser473. Thus, we conclude that PKCdelta is actively involved in the activation of Akt. To determine the effect of Akt on eNOS signaling, we overexpressed a dominant negative mutant of Akt and determined its effect of NO generation, eNOS expression, and phosphorylation of eNOS at S1177. Our results demonstrated that Akt inhibition was associated with decreased NO production that correlated with reduced phosphorylation of eNOS at S1177, and decreased eNOS promoter activity. We next evaluated the effect of endogenously produced NO on eNOS expression by incubating FPAECs with the eNOS inhibitor 2-ethyl-2-thiopseudourea (ETU). ETU significantly inhibited NO production, eNOS promoter activity, and eNOS protein levels. Together, our data indicate involvement of PKCdelta-mediated Akt activation and NO generation in maintaining eNOS expression. 相似文献
943.
Jonathan A. Black Timothy R. Dean Karin Foarde Marc Menetrez 《Mycological Research》2008,112(7):845-851
Highly conserved regions are attractive targets for detection and quantitation by PCR, but designing species-specific primer sets can be difficult. Ultimately, almost all primer sets are designed based upon literature searches in public domain databases, such as the National Center for Biotechnology Information (NCBI). Prudence suggests that the researcher needs to evaluate as many sequences as available for designing species-specific PCR primers. In this report, we aligned 11, 9, and 16 DNA sequences entered for Stachybotrys spp. rRNA, tri5, and β-tubulin regions, respectively. Although we were able to align and determine consensus primer sets for the 9 tri5 and the 16 β-tubulin sequences, there was no consensus sequence that could be derived from alignment of the 11 rRNA sequences. However, by judicious clustering of the sequences that aligned well, we were able to design three sets of primers for the rRNA region of S. chartarum. The two primer sets for tri5 and β-tubulin produced satisfactory PCR results for all four strains of S. chartarum used in this study whereas only one rRNA primer set of three produced similar satisfactory results. Ultimately, we were able to show that rRNA copy number is approximately 2-log greater than for tri5 and β-tubulin in the four strains of S. chartarum tested. 相似文献
944.
David B. Hogan Peter Bailey Sandra Black Anne Carswell Howard Chertkow Barry Clarke Carole Cohen John D. Fisk Dorothy Forbes Malcolm Man-Son-Hing Krista Lanct?t Debra Morgan Lilian Thorpe 《CMAJ》2008,179(8):787-793
Background
The management of mild to moderate dementia presents complex and evolving challenges. Practising physicians are often uncertain about the appropriate approaches to issues such as the disclosure of the diagnosis, driving and caregiver support. In this article, we provide practical guidance on management based on recommendations from the Third Canadian Consensus Conference on the Diagnosis and Treatment of Dementia.Methods
We developed evidence-based guidelines using systematic literature searches, with specific criteria for the selection and quality assessment of articles, and a clear and transparent decision-making process. We selected articles published from January 1996 to December 2005 that dealt with the management of mild to moderate stages of Alzheimer disease and other forms of dementia. Recommendations based on the literature review were drafted and voted on. Consensus required 80% or more agreement by participants. Subsequent to the conference, we searched for additional articles published from January 2006 to April 2008 using the same major keywords and secondary search terms. We graded the strength of evidence using the criteria of the Canadian Task Force on Preventive Health Care.Results
We identified 1615 articles, of which 954 were selected for further study. From a synthesis of the evidence in these studies, we made 48 recommendations for the management of mild to moderate dementia (28) and dementia with a cerebrovascular component (8) as well as recommendations for addressing ethical issues (e.g., disclosure of the diagnosis) (12). The updated literature review did not change these recommendations. In brief, patients and their families should be informed of the diagnosis. Although the specifics of managing comorbid conditions might require modification, standards of care and treatment targets would not change because of a mild dementia. The use of medications with anticholinergic effects should be minimized. There should be proactive planning for driving cessation, since this will be required at some point in the course of progressive dementia. The patient''s ability to drive should be determined primarily on the basis of his or her functional abilities. An important aspect of care is supporting the patient''s primary caregiver.Interpretation
Much has been learned about the care of patients with mild to moderate dementia and the support of their primary caregivers. There is a pressing need for the development, and dissemination, of collaborative systems of care.Articles to date in this series
- Chertkow H. Diagnosis and treatment of dementia: Introduction. Introducing a series based on the Third Canadian Consensus Conference on the Diagnosis and Treatment of Dementia. CMAJ 2008;178:316-21.
- Patterson C, Feightner JW, Garcia A, et al. Diagnosis and treatment of dementia: 1. Risk assessment and primary prevention of Alzheimer disease. CMAJ 2008;178:548-56.
- Feldman HH, Jacova C, Robillard A, et al. Diagnosis and treatment of dementia: 2. Diagnosis. CMAJ 2008;178:825-36.
- Chertkow H, Massoud F, Nasreddine Z, et al. Diagnosis and treatment of dementia: 3. Mild cognitive impairment and cognitive impairment without dementia. CMAJ 2008;178: 1273-85.
945.
Morano LD Bextine BR Garcia DA Maddox SV Gunawan S Vitovsky NJ Black MC 《Current microbiology》2008,56(4):346-351
Xylella fastidiosa is the causative agent of Pierce’s Disease of grape. No published record of X. fastidiosa genetics in Texas exists despite growing financial risk to the U.S. grape industry, a Texas population of the glassy-winged
sharpshooter insect vector (Homalodisca
vitripennis) now spreading in California, and evidence that the bacterium is ubiquitous to southern states. Using sequences of conserved
gyrB and mopB genes, we have established at least two strains in Texas, grape strain and ragweed strain, corresponding genetically with
subsp. piercei and multiplex, respectively. The grape strain in Texas is found in Vitis vinifera varieties, hybrid vines, and wild Vitis near vineyards, whereas the ragweed strain in Texas is found in annuals, shrubs, and trees near vineyards or other areas.
RFLP and QRT PCR techniques were used to differentiate grape and ragweed strains with greater efficiency than sequencing and
are practical for screening numerous X. fastidiosa isolates for clade identity. 相似文献
946.
947.
Djoba Siawaya JF Roberts T Babb C Black G Golakai HJ Stanley K Bapela NB Hoal E Parida S van Helden P Walzl G 《PloS one》2008,3(7):e2535
The recent introduction of fluorescent bead-based technology, allowing the measurement of multiples analytes in a single 25-50 microl sample has revolutionized the study of cytokine responses. However, such multiplex approaches may compromise the ability of these assays to accurately measure actual cytokine levels. This study evaluates the performance of three commercially available multiplex cytokine fluorescent bead-based immunoassays (Bio-Rad's Cytokine 17-plex kit; LINCO Inc's 29-plex kit; and RnD System's Fluorokine-Multi Analyte Profiling (MAP) base kit A and B). The LINCO Inc kit was found to be the most sensitive assay for measuring concentrations of multiple recombinant cytokines in samples that had been spiked with serial dilutions of the standard provided by the manufacturer, followed respectively by the RnD Fluorokine-(MAP) and Bio-Rad 17-plex kits. A positive correlation was found in the levels of IFN-gamma measured in antigen stimulated whole blood culture supernatants by the LINCO Inc 29-plex, RnD Fluorokine-(MAP) and RnD system IFN-gamma Quantikine ELISA kits across a panel of controls and stimulated samples. Researchers should take the limitation of such multiplexed assays into account when planning experiments and the most appropriate use for these tests may currently be as screening tools for the selection of promising markers for analysis by more sensitive techniques. 相似文献
948.
Shintaroh Kubo Shun Kai Yang Corbin S Black Daniel Dai Melissa Valente-Paterno Jacek Gaertig Muneyoshi Ichikawa Khanh Huy Bui 《EMBO reports》2021,22(9)
Cilia are thin microtubule‐based protrusions of eukaryotic cells. The swimming of ciliated protists and sperm cells is propelled by the beating of cilia. Cilia propagate the flow of mucus in the trachea and protect the human body from viral infections. The main force generators of ciliary beating are the outer dynein arms (ODAs) which attach to the doublet microtubules. The bending of cilia is driven by the ODAs'' conformational changes caused by ATP hydrolysis. Here, we report the native ODA complex structure attaching to the doublet microtubule by cryo‐electron microscopy. The structure reveals how the ODA complex is attached to the doublet microtubule via the docking complex in its native state. Combined with coarse‐grained molecular dynamic simulations, we present a model of how the attachment of the ODA to the doublet microtubule induces remodeling and activation of the ODA complex. 相似文献
949.
Control of nematode parasites with reduced reliance on the use of anthelmintics was studied in 16 ewes with suckling twin
lambs on contaminated pasture in Denmark. Ewes and lambs were treated with albendazole at turn-out 3 May. Ewes were removed
from the groups on 26 July, and lambs were slaughtered on 11 October. The animals were allocated to 4 groups of 8 lambs and
their 4 ewes. Group TS was treated with albendazole at weeks 3, 6 and 8 after turnout and set-stocked; group TM was similarly
treated but moved to clean pasture in conjunction with the last drenching; group US was untreated and set-stocked, and group
UM was left untreated but moved to clean pasture week 8 after turn-out. Supplementary feed was offered in June and August
due to scarcity of pasture. Strategic treatments of ewes and lambs weeks 3, 6 and 8 after turn-out, with or without a move
to clean pasture, were highly effective in controlling nematode infections for most of the season. This was reflected in better
weight gains and carcass characteristics in the treated compared to untreated lambs, resulting in an average increase in the
value of the product by 36%. The effect of moving without treatment (UM) on faecal egg counts was limited but peak pasture
infectivity was reduced to less than 10% compared to the set-stocked group and weight gains of lambs were significantly better
despite poor feed availability in late season. The study showed that under set-stocked conditions repeated anthelmintic treatments
of both ewes and lambs in early season may ensure sufficient nematode control whereas moving animals to clean pasture without
dosing was less efficient. The latter may, however, still be a viable option in organic and other production systems where
routine use of anthelmintics is banned, particularly if weaning and moving are combined or a second move is performed. 相似文献
950.
U2 as well as U1 small nuclear ribonucleoproteins are involved in premessenger RNA splicing 总被引:166,自引:0,他引:166
Two different experimental approaches have provided evidence that both U2 and U1 snRNPs function in pre-mRNA splicing. When the U2 snRNPs in a nuclear extract are selectively degraded using ribonuclease H and either of two deoxyoligonucleotides complementary to U2 RNA, splicing activity is abolished. Mixing an extract in which U2 has been degraded with one in which U1 has been degraded recovers activity. Use of anti-(U2)RNP autoantibodies demonstrates that U2 snRNPs associate with the precursor RNA during in vitro splicing. At 60 min, but not at 0 min, into the reaction intron fragments that include the branch-point sequence are immunoprecipitated by anti-(U2)RNP. At all times, U1 snRNPs bind the 5' splice site of the pre-mRNA. Possible interactions of the U2 snRNP with the U1 snRNP and with the pre-mRNA during splicing are considered. 相似文献