首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   611篇
  免费   45篇
  656篇
  2023年   6篇
  2022年   10篇
  2021年   20篇
  2020年   18篇
  2019年   14篇
  2018年   9篇
  2017年   10篇
  2016年   24篇
  2015年   34篇
  2014年   44篇
  2013年   54篇
  2012年   53篇
  2011年   66篇
  2010年   31篇
  2009年   19篇
  2008年   38篇
  2007年   24篇
  2006年   38篇
  2005年   29篇
  2004年   28篇
  2003年   23篇
  2002年   21篇
  2001年   6篇
  2000年   4篇
  1999年   6篇
  1998年   4篇
  1997年   2篇
  1996年   3篇
  1995年   1篇
  1994年   1篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1985年   2篇
  1982年   1篇
  1978年   1篇
  1976年   1篇
  1973年   1篇
  1970年   2篇
  1966年   1篇
排序方式: 共有656条查询结果,搜索用时 13 毫秒
81.

Background

Economic impact assessment of invasive species requires integration of information on pest entry, establishment and spread, valuation of assets at risk and market consequences at large spatial scales. Here we develop such a framework and demonstrate its application to the pinewood nematode, Bursaphelenchus xylophilus, which threatens the European forestry industry. The effect of spatial resolution on the assessment result is analysed.

Methodology/Principal Findings

Direct economic impacts resulting from wood loss are computed using partial budgeting at regional scale, while impacts on social welfare are computed by a partial equilibrium analysis of the round wood market at EU scale. Substantial impacts in terms of infested stock are expected in Portugal, Spain, Southern France, and North West Italy but not elsewhere in EU in the near future. The cumulative value of lost forestry stock over a period of 22 years (2008–2030), assuming no regulatory control measures, is estimated at €22 billion. The greatest yearly loss of stock is expected to occur in the period 2014–2019, with a peak of three billion euros in 2016, but stabilizing afterwards at 300–800 million euros/year. The reduction in social welfare follows the loss of stock with considerable delay because the yearly harvest from the forest is only 1.8%. The reduction in social welfare for the downstream round wood market is estimated at €218 million in 2030, whereby consumers incur a welfare loss of €357 million, while producers experience a €139 million increase, due to higher wood prices. The societal impact is expected to extend to well beyond the time horizon of the analysis, and long after the invasion has stopped.

Conclusions/Significance

Pinewood nematode has large economic consequences for the conifer forestry industry in the EU. A change in spatial resolution affected the calculated directed losses by 24%, but did not critically affect conclusions.  相似文献   
82.
Correct folding of a nascent polypeptide in the lumen of the endoplasmic reticulum (ER) into a three-dimensional conformation is a crucial step in the stability, intracellular trafficking, and targeting to the final destination of a protein. By transiently and stably expressing human-relevant mutants of Tamm-Horsfall protein in polarized Madin-Darby canine kidney cells, we show here that a cysteine-altering mutation in the evolutionally conserved cysteine-rich domain had more severe defects in ER exit and surface translocation and triggered more apoptosis than a cysteine-altering mutation outside the domain. Both mutants were able to specifically bind and trap the wild-type Tamm-Horsfall protein (THP) and prevent it from exiting the ER and translocating to the cell surface. This explains at least partly why in patients with THP-associated diseases there is a marked urinary reduction of both the mutant and the wild-type THP. Exposure of mutant-expressing cells to low temperature (30 °C), osmolytes (glycerol, trimethylamine N-oxide, and dimethyl sulfoxide), and the Ca(2+)-ATP inhibitor thapsigargin only slightly relieved ER retention and increased surface targeting of the mutants. In contrast, sodium 4-phenylbutyrate and probenecid, the latter a uricosuric drug used clinically to treat gout, markedly reduced ER retention of the mutants and increased their surface translocation and secretion into the culture media. The rescue of the THP mutants was associated with the restoration of the level and subcellular localization of cytosolic chaperone HSP70. Our results reveal intricate mechanistic details that may underlie THP-associated diseases and suggest that novel therapeutics enhancing the refolding of THP mutants may be of important value in therapy.  相似文献   
83.
The aim of this study was to investigate the association between C-reactive protein (CRP) gene polymorphism and metabolic syndrome (MetS) with premature coronary artery disease (PCAD). 116 patients with PCAD (58 with MetS and 58 without MetS) and 119 controls were included in the study. CRP gene + 1059 G>C polymorphism was analyzed by polymerase chain reaction. Serum hs-CRP was measured using high-sensitivity enzyme-linked immunosorbent assay. Carriers of C allele of the CRP + 1059 G>C polymorphism had 3.37 fold increased risk to develop MetS in patients with PCAD. In addition CRP gene and hs-CRP levels were independent risk factors for PCAD and MetS. The present study provides new evidence that the presence of CRP + 1059 G>C polymorphism and hs-CRP levels are independent determinants of PCAD and MetS in Egyptians. The results of our study suggest a synergistic effect of CRP C allele with classical risk factors such as hypertension, obesity, dyslipidemia and MetS.  相似文献   
84.
Cell migration refers to a directional cell movement in response to chemoattractant stimulation. In this work, we developed a cell-migration model by mimicking in vivo migration using optically manipulated chemoattractant-loaded microsources. The model facilitates a quantitative characterization of the relationship among the protrusion force, cell motility, and chemoattractant gradient for the first time (to our knowledge). We verified the correctness of the model using migrating leukemia cancer Jurkat cells. The results show that one can achieve the ideal migrating capacity by choosing the appropriate chemoattractant gradient and concentration at the leading edge of the cell.  相似文献   
85.
The diaphragm muscle of hyperkalemic periodic paralysis (HyperKPP) patients and of the M1592V HyperKPP mouse model rarely suffers from the myotonic and paralytic symptoms that occur in limb muscles. Enigmatically, HyperKPP diaphragm expresses the mutant NaV1.4 channel and, more importantly, has an abnormally high Na+ influx similar to that in extensor digitorum longus (EDL) and soleus, two hindlimb muscles suffering from the robust HyperKPP abnormalities. The objective was to uncover the physiological mechanisms that render HyperKPP diaphragm asymptomatic. A first mechanism involves efficient maintenance of resting membrane polarization in HyperKPP diaphragm at various extracellular K+ concentrations compared with larger membrane depolarizations in HyperKPP EDL and soleus. The improved resting membrane potential (EM) results from significantly increased Na+ K+ pump electrogenic activity, and not from an increased protein content. Action potential amplitude was greater in HyperKPP diaphragm than in HyperKPP soleus and EDL, providing a second mechanism for the asymptomatic behavior of the HyperKPP diaphragm. One suggested mechanism for the greater action potential amplitude is lower intracellular Na+ concentration because of greater Na+ K+ pump activity, allowing better Na+ current during the action potential depolarization phase. Finally, HyperKPP diaphragm had a greater capacity to generate force at depolarized EM compared with wild-type diaphragm. Action potential amplitude was not different between wild-type and HyperKPP diaphragm. There was also no evidence for an increased activity of the Na+–Ca2+ exchanger working in the reverse mode in the HyperKPP diaphragm compared with the wild-type diaphragm. So, a third mechanism remains to be elucidated to fully understand how HyperKPP diaphragm generates more force compared with wild type. Although the mechanism for the greater force at depolarized resting EM remains to be determined, this study provides support for the modulation of the Na+ K+ pump as a component of therapy to alleviate weakness in HyperKPP.  相似文献   
86.
Since their inception 20 years ago, the biennial blast (Bacterial Locomotion and Signal Transduction) meetings instantly became the place to be for exchanging and sharing the latest developments in the field of bacterial motility and signalling. At the 11th edition, held last January in New Orleans, LA, researchers reported on the myriad of mechanisms involved in bacterial movement, sensing and adaptation, ranging from the molecular level to multicellular behaviour. New insights into bacterial signalling phenomena were gained, revealing previously unsuspected layers of complexity, particularly in mechanisms ensuring signal transduction fidelity and novel links to metabolic processes.  相似文献   
87.
Essential tremor (ET) is a complex genetic disorder for which no causative gene has been found. Recently, a genome-wide association study reported that two variants in the LINGO1 locus were associated to this disease. The aim of the present study was to test if this specific association could be replicated using a French-Canadian cohort of 259 ET patients and 479 ethnically matched controls. Our genotyping results lead us to conclude that no association exists between the key variant rs9652490 and ET (Pcorr = 1.00).  相似文献   
88.
The CCN family of proteins consists of six members with conserved structural features. These proteins play several roles in the physiology and pathology of cells. Among the pathological roles of the CCN family, one of the most important and controversial ones is their role in the expansion and metastasis of cancer. Up to now a number of reports have described the possible role of each CCN family member independently. In this study, we comprehensively analyzed the roles of all six CCN family members in cell growth, migration and invasion of breast cancer cells in vitro and in vivo. As a result, we found the CCN2/CCN3 ratio to be a parameter that is associated with the metastatic phenotype of breast cancer cells that are highly metastatic to the bone. The same analysis with cell lines from oral squamous carcinomas that are not metastatic to the bone further supported our notion. These results suggest the functional significance of the interplay between CCN family members in regulating the phenotype of cancer cells.  相似文献   
89.
We report our experience with an ultrasound system to measure esophageal varix pressure in an in vitro model. The ultrasound system consists of a 12.5 MHz frequency intraluminal ultrasound probe, a water infusion catheter, and a manometry catheter, all contained within a nondistensible latex bag. Esophagi and external jugular veins were harvested from five pigs. The vein and ultrasound system were placed inside the esophagus. One end of the vein was connected to a water reservoir to modulate its pressure; the other end was connected in two different ways to simulate hydrodynamic and hydrostatic flow conditions. The bag was inflated with water until vein occlusion was discernible on the ultrasound images. The influences of vein pressure, vein cross-sectional area and esophageal elasticity on the ultrasound measurement of vein pressure were assessed. A total of 108 trials were performed at nine different vein pressures. Complete vein occlusion occurred when the bag pressure was slightly greater (1.4 +/- 0.7 mmHg) than the vein pressure. For a vein pressure of 25 mmHg, the average occlusion and opening pressures were 27 +/- 0.2 and 25.7 +/- 0.3 mmHg, respectively (P < .05) suggesting that the vein opening pressure on the ultrasound images is more accurate than the vein closing pressure. In conclusion, the ultrasound technique can accurately measure intravariceal pressure in vitro. The bag pressure at the point of vein reopening is the best determinant of the vein pressure.  相似文献   
90.
Cardiovascular disease accounts for significant morbidity and mortality in the elderly. The clinical trial data available to guide therapy in this growing population subset are relatively limited. This review will focus on treatment approaches and recommendations obtained from subgroup analyses of elderly patients from major clinical trials for the management of chronic stable angina, acute coronary syndromes (unstable angina and non-ST-segment elevation myocardial infarction), and coronary revascularization. Recent advances in the treatment of stable angina have shown that use of angiotensin-converting enzyme inhibitors and lipid-lowering therapy as adjunctive measures show benefit in the elderly by reducing the occurrence of death, nonfatal myocardial infarction, and unstable angina. However, if patients experience disabling or unstable anginal symptoms despite effective medical therapy, coronary revascularization must be considered. Several clinical trials have shown a significant reduction in major adverse cardiac events when using intravenous glycoprotein receptor antagonists periprocedurally during percutaneous revascularization approaches in elderly patients with unstable angina or non-ST-segment elevation myocardial infarction, especially when these measures are performed as soon as possible. However, the success of myocardial revascularization by a percutaneous or surgical approach is highly dependent on the patient's associated comorbidities, especially in patients over age 80 years.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号