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   403篇
  免费   32篇
  435篇
  2024年   1篇
  2022年   1篇
  2021年   3篇
  2020年   1篇
  2019年   4篇
  2018年   1篇
  2017年   6篇
  2016年   6篇
  2015年   11篇
  2014年   15篇
  2013年   20篇
  2012年   19篇
  2011年   32篇
  2010年   13篇
  2009年   14篇
  2008年   18篇
  2007年   24篇
  2006年   42篇
  2005年   17篇
  2004年   32篇
  2003年   14篇
  2002年   11篇
  2001年   12篇
  2000年   11篇
  1999年   12篇
  1998年   6篇
  1997年   2篇
  1996年   3篇
  1995年   2篇
  1994年   3篇
  1992年   15篇
  1991年   12篇
  1990年   9篇
  1989年   6篇
  1988年   7篇
  1987年   6篇
  1986年   4篇
  1985年   4篇
  1984年   4篇
  1983年   3篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1974年   2篇
  1970年   1篇
  1967年   1篇
  1965年   1篇
排序方式: 共有435条查询结果,搜索用时 15 毫秒
111.
112.
A sub-global assessment (SGA) began in Japan in November 2006, and is projected to end in May 2010, when the Tenth Conference of the Parties to the Convention on Biological Diversity (COP10) will be held in Nagoya City. Since May 2008, we have been involved in the evaluation of the Hokkaido Cluster, one of four clusters assessed. This report provides a brief background of the relationships between the Millennium Ecosystem Assessment (MA) and the SGA, and the governance structure of the SGA in Japan. It also describes our efforts in assessing the Hokkaido Cluster and discusses the challenges of SGA at the cluster and national levels. The MA was a 4-year international appraisal of scientific knowledge on world ecosystems and included global and sub-global assessment. After the MA, Japan began a satoyama–satoumi SGA in 2006. This is composed of six teams: the board, a science assessment panel, author groups, local advisory bodies, the board of review editors, and secretariat. Author groups include a national group and groups for four local clusters: Hokkaido, Tohoku, Hoku-shin-etsu, and Western Japan. Work in the Hokkaido Cluster began with a small group in 2008. Authors for the cluster report were selected from among experts on important events regarding satoyama and satoumi in Hokkaido. Generally, Hokkaido has no traditional satoyama–satoumi landscapes created by long-term interactions with the local people. We are now seeking the style of sustainable nature use that is best suited to Hokkaido. The SGA in Japan now faces the challenge of integrating the four cluster assessments according to common indicators.  相似文献   
113.
114.
115.

Background

Each of the pathogenic human retroviruses (HIV-1/2 and HTLV-1) has a nonhuman primate counterpart, and the presence of these retroviruses in humans results from interspecies transmission. The passage of another simian retrovirus, simian foamy virus (SFV), from apes or monkeys to humans has been reported. Mandrillus sphinx, a monkey species living in central Africa, is naturally infected with SFV. We evaluated the natural history of the virus in a free-ranging colony of mandrills and investigated possible transmission of mandrill SFV to humans.

Results

We studied 84 semi-free-ranging captive mandrills at the Primate Centre of the Centre International de Recherches Médicales de Franceville (Gabon) and 15 wild mandrills caught in various areas of the country. The presence of SFV was also evaluated in 20 people who worked closely with mandrills and other nonhuman primates. SFV infection was determined by specific serological (Western blot) and molecular (nested PCR of the integrase region in the polymerase gene) assays. Seropositivity for SFV was found in 70/84 (83%) captive and 9/15 (60%) wild-caught mandrills and in 2/20 (10%) humans. The 425-bp SFV integrase fragment was detected in peripheral blood DNA from 53 captive and 8 wild-caught mandrills and in two personnel. Sequence and phylogenetic studies demonstrated the presence of two distinct strains of mandrill SFV, one clade including SFVs from mandrills living in the northern part of Gabon and the second consisting of SFV from animals living in the south. One man who had been bitten 10 years earlier by a mandrill and another bitten 22 years earlier by a macaque were found to be SFV infected, both at the Primate Centre. The second man had a sequence close to SFVmac sequences. Comparative sequence analysis of the virus from the first man and from the mandrill showed nearly identical sequences, indicating genetic stability of SFV over time.

Conclusion

Our results show a high prevalence of SFV infection in a semi-free-ranging colony of mandrills, with the presence of two different strains. We also showed transmission of SFV from a mandrill and a macaque to humans.  相似文献   
116.

Background

General anesthesia is routinely used as a surgical procedure and its safety has been endorsed by clinical outcomes; however, its effects at the molecular level have not been elucidated. General anesthetics influence glucose metabolism in the brain. However, the effects of anesthetics on brain metabolites other than those related to glucose have not been well characterized. We used a pattern recognition analysis of proton nuclear magnetic resonance spectra to visualize the changes in holistic brain metabolic phenotypes in response to the widely used intravenous anesthetic propofol and the volatile anesthetic isoflurane.

Methodology/Principal Findings

Rats were randomized into five groups (n = 7 each group). Propofol and isoflurane were administered to two groups each, for 2 or 6 h. The control group received no anesthesia. Brains were removed directly after anesthesia. Hydrophilic compounds were extracted from excised whole brains and measured by proton nuclear magnetic resonance spectroscopy. All spectral data were processed and analyzed by principal component analysis for comparison of the metabolite profiles. Data were visualized by plotting principal component (PC) scores. In the plots, each point represents an individual sample. The propofol and isoflurane groups were clustered separately on the plots, and this separation was especially pronounced when comparing the 6-h groups. The PC scores of the propofol group were clearly distinct from those of the control group, particularly in the 6-h group, whereas the difference in PC scores was more subtle in the isoflurane group and control groups.

Conclusions/Significance

The results of the present study showed that propofol and isoflurane exerted differential effects on holistic brain metabolism under anesthesia.  相似文献   
117.
Vascular tone is regulated through the actions of locally produced agents. Among the vasoconstrictors, the most potent agent is endothelin (ET), which exerts its vasoconstrictor actions principally through ET type A (ET(A)) receptors. Of the vasodilators, nitric oxide (NO) seems to be the most important contributor to the acute regulation of vascular tone. Vasculopathy is an important feature of diabetes mellitus (DM). Endogenous ET-mediated vasoconstrictor tone is augmented in diabetic states, and conflicting results persist concerning the NO system in diabetes. The present study investigated the expressions of inducible NO synthases (iNOS) and endothelial NOS (eNOS) in the heart of diabetic animals and the effects of a selective ET(A) receptor antagonist on these alterations. Type I diabetes was induced by intraperitoneal injection of streptozotocin (65 mg/kg) in Sprague-Dawley rats, while control (Con) rats received only citrate buffer. After 1 week, the streptozotocin-administered rats were randomly divided into two groups: the selective ET(A) receptor antagonist-administered group (DM+TA-0201, 1 mg/kg/day, by osmotic minipump for 2 weeks) and the DM+vehicle group (comprising the diabetic rats that received saline). The random blood glucose level was 405 +/- 103 mg/dl in DM animals, and this level was unchanged by ET antagonism. Body weight was more greatly decreased in DM rats than in Con rats, but the left ventricle to body weight ratio was increased in the DM group and was unaffected by ET antagonism. Protein expressions of eNOS and iNOS were assessed in the left ventricular tissues. eNOS expression was significantly increased in DM heart and was greatly inhibited by the treatment with ET antagonist. The expression of iNOS was also increased in early DM heart but was reversed by the ET antagonist. Thus, endothelin antagonism might be beneficial for DM heart by reversing the upregulated eNOS and iNOS expressions.  相似文献   
118.
Endothelin-1 (ET-1) has been implicated in hypertension, heart failure, atherosclerosis, and pulmonary hypertension. In all these conditions, plasma immunoreactive ET-1 levels are elevated, and tissue ET-1 expression is increased. Clinical trials have demonstrated potentially important benefits of ET antagonism among patients with essential hypertension, pulmonary hypertension, and heart failure. It is unknown whether ET antagonism affects the production of ET-1 in stroke-prone spontaneously hypertensive rat (SHRSP) heart at the typical hypertensive stage. The objective of this study was to investigate the effects of ET blockade on the expression levels of plasma and cardiac ET-1 in SHRSPs. SHRSPs were treated for 3 months with SB209670 (ET(A)/ET(B) dual receptor antagonist) or with saline (vehicle) commencing at the prehypertensive stage (age 6 weeks). Plasma and left ventricular ET-1 peptide levels were measured using enzyme-linked immunoabsorbent assay. Compared with age-matched control Wistar-Kyoto rats, peptide levels of ET-1 were significantly upregulated in vehicle-treated SHRSP heart; this upregulation was reversed by long-term ET antagonism. Plasma ET-1 levels were also significantly increased in vehicle-treated SHRSPs and were normalized by ET antagonism. mRNA expression of preproET-1, which is the source of ET-1 peptide production, was significantly increased in vehicle-treated SHRSP heart and was normalized by ET antagonism. Marked cardiac hypertrophy and fibrosis at the histologic level in SHRSPs were ameliorated by ET antagonism, and left ventricular hypertrophy as seen on echocardiography in SHRSPs was suppressed by ET blockade. After ET antagonism, systolic blood pressures were reduced in SHRSPs; diastolic blood pressures were unchanged. The reversal effect of the upregulated ET system in SHRSP heart by ET antagonism might be independent of blood pressure change. By suppressing the upregulated ET system, ET antagonism might be beneficial in arresting cardiac remodeling.  相似文献   
119.
Strength exercise training induces a decrease in arterial distensibility, whereas endurance exercise training causes an increase in arterial distensibility. Endothelin-1 (ET-1), which is produced by vascular endothelial cells, has potent vasoconstrictor and proliferative activity on vascular smooth muscle cells. We hypothesized that endogenous ET-1 participates in alteration of arterial distensibility by different exercise training types (i.e., strength and endurance exercise training). The purpose of the present study was to investigate plasma ET-1 concentration and arterial distensibility in strength- and endurance-trained athletes. Subjects were male strength-trained athletes (discus, hammer, or javelin throwers; 22.2 years; SA), male endurance-trained athletes (long- or middle-distance runners; 20.7 years; EA), and sedentary healthy men (20.6 years; sedentary control, SC). Maximum hand-grip strength was markedly greater in SA compared with EA and SC (55.3 vs. 41.1 vs. 40.5 kg, P < 0.05). Maximum oxygen uptake was markedly greater in EA than in SA and SC (60.9 vs. 43.1 vs. 43.6 ml/kg/min, P < 0.05). Arterial pulse wave velocity (PWV), which is an index of arterial distensibility, was significantly higher in SA than in EA and SC (688 vs. 529 vs. 601 cm/sec, P < 0.05). In EA, PWV was significantly lower in comparison to that in SC (P < 0.05). Thus arterial distensibility was lower in SA than in EA and SC and higher in EA than in SC. Plasma ET-1 concentration was significantly higher in SA compared with EA and SC (1.64 vs. 1.12 vs. 1.24 pg/ml, P < 0.05). Plasma ET-1 concentration tended to be lower in EA than in SC. These results suggest that the difference in plasma ET-1 level may participate in the mechanism underlying different adaptation of arterial distensibility between strength- and endurance-trained athletes.  相似文献   
120.
BACKGROUND: There have been only 4 reported cases of cribriform-morular variant of papillary thyroid carcinoma (CMVPTC) with cytologic findings from fine needle aspiration. In these reports, the cytologic findings do not fully reflect the histologic characteristics of this entity. We report a case of CMVPTC in which a cribriform pattern without colloid and epithelial morules with peculiar nuclear clearing (PNC) were present in smears, thus fulfilling the criteria for a cytologic diagnosis of CMVPTC. Protein truncation tests for APC molecule abnormality indicated the presence of germline mutation in the patient's APC gene. CASE: A 30-year-old woman had multiple thyroid tumors. Aspiration cytology revealed a large number of round to spindle-shaped atypical-cells showing sheet-like, cribriform, follicular, whorl-like and solid, 3-dimensional arrangements. The cribriform and follicular arrangements did not contain colloid in the lumen. The powdery chromatin pattern characteristic of papillary carcinoma was not observed, but there were scattered intranuclear cytoplasmic pseudoinclusions and grooved nuclei. The nuclei of the atypical cells presenting in the whorl formations showed enlargement, thickened nuclear membranes and entirely clear contents, consistent with PNC. Hyalinelike necrotic cells were also observed in the cell clusters or in the background. Histologic and immunohistochemical findings were typical of CMVPTC. CONCLUSION: The cribriform pattern without colloid, fascicular or whorl formation of spindle cells, and morules with PNC are identifiable on cytologic smears and are sufficiently distinctive to allow a cytologic diagnosis of CMVPTC.  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