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   1764篇
  免费   201篇
  国内免费   1篇
  1966篇
  2023年   14篇
  2022年   29篇
  2021年   46篇
  2020年   19篇
  2019年   17篇
  2018年   35篇
  2017年   24篇
  2016年   39篇
  2015年   90篇
  2014年   102篇
  2013年   107篇
  2012年   130篇
  2011年   101篇
  2010年   60篇
  2009年   64篇
  2008年   65篇
  2007年   99篇
  2006年   70篇
  2005年   70篇
  2004年   56篇
  2003年   69篇
  2002年   51篇
  2001年   23篇
  2000年   29篇
  1999年   18篇
  1998年   22篇
  1997年   19篇
  1992年   20篇
  1991年   23篇
  1990年   14篇
  1989年   18篇
  1988年   13篇
  1987年   19篇
  1986年   25篇
  1985年   21篇
  1984年   19篇
  1983年   21篇
  1982年   16篇
  1981年   12篇
  1979年   15篇
  1978年   15篇
  1977年   15篇
  1976年   11篇
  1975年   17篇
  1974年   19篇
  1973年   17篇
  1972年   16篇
  1971年   14篇
  1970年   14篇
  1969年   15篇
排序方式: 共有1966条查询结果,搜索用时 12 毫秒
81.

Purpose

To examine potential associations between body height, cerebrospinal fluid pressure (CSFP), trans-lamina cribrosa pressure difference (TLCPD) and prevalence of open-angle glaucoma (OAG) in a population-based setting.

Methods

The population-based Beijing Eye Study 2011 included 3468 individuals with a mean age of 64.6±9.8 years (range:50–93 years). A detailed ophthalmic examination was performed. Based on a previous study with lumbar cerebrospinal fluid pressure (CSFP) measurements, CSFP was calculated as CSFP[mmHg] = 0.44×Body Mass Index[kg/m2]+0.16×Diastolic Blood Pressure[mmHg]-0.18×Age[Years]-1.91

Results

Data of IOP and CSFP were available for 3353 (96.7%) subjects. Taller body height was associated with higher CSFP (P<0.001; standardized correlation coefficient beta:0.13; regression coefficient B:0.29; 95% confidence interval (CI):0.25,0.33) after adjusting for male gender, urban region of habitation, higher educational level, and pulse rate. If TLCPD instead of CSFP was added, taller body height was associated with lower TLCPD (P<0.001;beta:−0.10;B:−0.20;95%CI:−0.25,−0.15). Correspondingly, higher CSFP was associated with taller body height (P = 0.003;beta:0.02;B:0.01;95%CI:0.00,0.02), after adjusting for age, gender, body mass index, pulse, systolic blood pressure, and blood concentration of cholesterol. If IOP was added to the model, higher CSFP was associated with higher IOP (P<0.001;beta:0.02;B:0.02;95%CI:0.01,0.03). TLCPD was associated with lower body height (P = 0.003;beta:−0.04;B −0.02,95%CI:−0.04,−0.01) after adjusting for age, body mass index, systolic blood pressure, pulse, blood concentrations of triglycerides, axial length, central corneal thickness, corneal curvature radius, and anterior chamber depth. Adding the prevalence of OAG to the multivariate analysis revealed, that taller body height was associated with a lower OAG prevalence (P = 0.03;beta:−0.03;B:−1.20;95%CI:−2.28,−0.12) after adjusting for educational level and gender.

Conclusions

Taller body height was associated with higher CSFP and lower TLCPD (and vice versa), after adjusting for systemic and ocular parameters. Parallel to the associations between a higher prevalence of glaucoma with a lower CSFP or higher TLCPD, taller body height was associated with a lower prevalence of OAG.  相似文献   
82.
Summary Salla disease is an inherited lysosomal storage disorder caused by accumulation of free sialic acid in the lysosomes. Lamp genes, lamp A and lamp B (lysosome associated membrane proteins), are the first known genes encoding for human lysosomal membrane proteins. Absence of linkage in a large group of families shows that lamp genes are not involved in Salla disease. The lamp genes were localized, using Southern hybridization in hamster — human hybrid cell panels, to chromosomes 13 (lamp A) and X (lamp B).  相似文献   
83.
84.

Purpose

To examine whether GNAQ and GNA11 somatic mutations previously identified in uveal melanomas of Caucasians are associated with uveal melanomas in Chinese patients.

Methods

Uveal melanomas treated by primary enucleation in Chinese patients underwent a mutation analysis of GNAQ and GNA11 with sequencing of exon 5 and exon 4.

Results

The study included 50 patients with uveal melanoma and with a mean age of 47.6±13.0 years. During the follow-up of at least 3 years, 20 (40%) patients developed extraocular metastases. The frequencies of GNAQ and GNA11 somatic mutations in uveal melanoma were 18% (9/50) and 20% (10/50), respectively. The mutations occurred exclusively in codon 209 of exon 5. No mutations were detected in exon 4. Mutations affecting codon 209 in GNAQ were c.626A>C(Q209P) (78%) and c.626A>T(Q209L) (22%). Mutations affecting codon 209 in GNA11 were exclusively c.626A>T(Q209L) (100%). In none of the tumors, mutations of BRAF and NRAS were detected. GNAQ/11 mutations were marginally (P = 0.045) associated with optic disc involvement. In Kaplan-Meier analysis, metastasis-free survival was not significantly (P = 0.94) associated with GNAQ/11 mutations.

Conclusions

Mutations of GNAQ and GNA11 can be found in Chinese patients as in Caucasian patients with uveal melanoma, with a higher frequency reported for Caucasian patients.  相似文献   
85.

Background

To investigate the prevalence of depression, suicidal ideations, alcohol and nicotine consumption in adults in an agrarian society mostly unchanged by the effects of urbanization.

Methods

The Central India Eye and Medical Study is a population-based study in rural Central India close to the tribal belt and included 4711 subjects (aged 30+ years). Depression was assessed by the Center for Epidemiologic Studies Depression Scale (CESD), suicidal ideation by six standardized questions, nicotine use by the Fagerstroem Nicotine Tolerance Questionnaire (FTNQ), and alcohol consumption by the Alcohol Use Disorders Identification Test (AUDIT).

Results

Mild to moderate depression (CESD sum score: 15–21) was detected in 1862 (39.6%) individuals (33.5% of men, 44.8 of women), and major depression (CESD sum score >21) in 613 (13.0%) individuals (8.1 of men, 17.3% of women). Suicide attempt was reported by 199 (4.2%) participants and suicidal thoughts during the last 6 months by 238 (5.1%) individuals. There were 887 (18.9%) smokers and smokeless tobacco was consumed by 1968 (41.8%) subjects. Alcohol consumption was reported by 1081 (23.0%) participants; 283 (6.0%) subjects had an AUDIT score ≥8 (hazardous drinking), and 108 (4.63%) subjects a score ≥13 (women) or ≥15 (men) (alcohol dependence).

Conclusions

In rural Central India, prevalence of major depression was comparable to figures reported from other developing countries. Prevalence of smoking and hazardous alcohol consumption was higher than as reported from urban regions. Measures should be taken to address the relatively high prevalence of suicide attempts and thoughts on suicide in rural Central India.  相似文献   
86.
87.
The effect of a panel of monoclonal antibodies and heteroantibodies on T-cell proliferation in various assay systems has been examined. The antibodies tested were directed against T-cell differentiation antigens, HLA-DR antigens, and structures defined by an anti-human VH antiserum. As the test cell system highly purified subpopulations of T-cell growth factor (TCGF)-dependent T-cell lines activated either by mitogen or antigen were used. A survey of the data indicates the following: (1) Mitogenic and antigenic triggering of T lymphocytes are mediated through partly different membrane structures. (2) Antigenic stimulation by purified protein derivative (PPD) as well as polyclonal activation induced by OKT3/anti-Leu 4 monoclonal antibodies can be inhibited by heteroantibodies raised against human immunoglobulin VH fragments thus pointing to a possible connection between the antigens detected by these antisera. (3) There does not seem to be differences between the two major subpopulations of T lymphocytes (i.e., helper/inducer and suppressor/cytotoxic cells) as to how they respond to antigens or mitogens in the investigated assay systems. (4) A clear distinction was found between T blasts specific for PPD and allogeneic cells as compared to cytotoxic T cells (CTL), as the T4 and T8 antigens seem to be functionally important for antigen recognition among CTL but not for the blasts proliferating in response to PPD and allogeneic cells. (5) An inhibitory effect of OKT3/anti-Leu 4, OKIal, and anti-HLA-DR on TCGF-dependent growth was detected, possibly indicating a steric relationship between these antigens and TCGF receptors on mitogen-induced T blasts. (6) Soluble factors obtained after incubating adherent cells with OKIal and anti-HLA-DR antibodies seemed to have an inhibitory effect on overall T-cell proliferation stressing the importance of studying the T-cell activation process at different levels in these kinds of experiments. (7) The results further suggest a complexity in the build up of antigen receptors on the various T-effector cells, perhaps also involving receptors for growth factors, HLA-DR antigens, and receptors for the latter.  相似文献   
88.
The HUPO Brain Proteome Project (HUPO BPP) held its 19th workshop in Dortmund, Germany, from May 22 to 24, 2013. The focus of the spring workshop was on strategies and developments concerning early diagnosis of neurodegenerative diseases  相似文献   
89.

Purpose

To examine a potential association between longitudinal changes in intraocular pressure (IOP), arterial blood pressure and body mass index (BMI) in a population-based setting.

Methods

The longitudinal population-based Beijing Eye Study included 2355 subjects with an age of 45+ years who were examined in 2006 and in 2011. The participants underwent a detailed ophthalmic examination including tonometry and measurement of arterial blood pressure and BMI.

Results

Data on IOP, arterial blood pressure and BMI measured in 2006 and in 2011 were available for 2257 (95.8%) subjects with a mean age of 59.5±9.7 years. The mean change in IOP was −1.25±2.26 mm Hg, mean change in mean blood pressure −7.4±12.1 mmHg, and mean change in BMI was 0.01±2.04 kg/m2. In multivariate analysis, the 5-year change in IOP was significantly associated with a higher change in mean blood pressure (P<0.001; standardized regression coefficient Beta:0.11; regression coefficient B:0.02; 95% confidence interval (CI):0.01,0.03) after adjusting for younger age (P<0.001;Beta:−0.18;B:−0.04;95% CI:−0.05,−0.03), shorter body stature (P = 0.002;Beta:−0.06;B:−0.06;95% CI:−0.03,−0.01), thicker central corneal thickness (P<0.001;Beta:0.19;B:0.02;95% CI:0.01,0.02), deeper anterior chamber depth (P = 0.01;Beta:0.05;B:0.33;95% CI:0.07,0.60), and lower intraocular pressure at baseline (P<0.001;Beta:−0.56;B:−0.42;95% CI:−0.45,−0.39). If the analysis included only longitudinal parameters, the change in IOP was significantly associated with a higher change in mean arterial blood pressure (P<0.001;Beta:0.10;B:0.02;95% CI:0.01,0.03) and a higher change in body mass index (P<0.04;Beta:0.04;B:0.04;95% CI:0.01,0.09).

Conclusions

In the 5-year follow-up of our population-based sample, a change in IOP was associated with a corresponding change in arterial blood pressure and with a corresponding change in body mass index. These longitudinal data support the notion of a physiological relationship between arterial blood pressure, intraocular pressure and body mass index. These findings may be of interest for the discussion of the pathogenesis of glaucomatous optic neuropathy.  相似文献   
90.
The end-Triassic biodiversity crisis was one of the most severe mass extinctions in the history of animal life. However, the extent to which the loss of taxonomic diversity was coupled with a reduction in organismal abundance remains to be quantified. Further, the temporal relationship between organismal abundance and local marine redox conditions is lacking in carbonate sections. To address these questions, we measured skeletal grain abundance in shallow-marine limestones by point counting 293 thin sections from four stratigraphic sections across the Triassic/Jurassic boundary in the Lombardy Basin and Apennine Platform of western Tethys. Skeletal abundance decreased abruptly across the Triassic/Jurassic boundary in all stratigraphic sections. The abundance of skeletal organisms remained low throughout the lower-middle Hettangian strata and began to rebound during the late Hettangian and early Sinemurian. A two-way ANOVA indicates that sample age (p < .01, η2 = 0.30) explains more of the variation in skeletal abundance than the depositional environment or paleobathymetry (p < .01, η2 = 0.15). Measured I/Ca ratios, a proxy for local shallow-marine redox conditions, show this same pattern with the lowest I/Ca ratios occurring in the early Hettangian. The close correspondence between oceanic water column oxygen levels and skeletal abundance indicates a connection between redox conditions and benthic organismal abundance across the Triassic/Jurassic boundary. These findings indicate that the end-Triassic mass extinction reduced not only the biodiversity but also the carrying capacity for skeletal organisms in early Hettangian ecosystems, adding to evidence that mass extinction of species generally leads to mass rarity among survivors.  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