全文获取类型
收费全文 | 49053篇 |
免费 | 3738篇 |
国内免费 | 111篇 |
学科分类
医药卫生 | 52902篇 |
出版年
2024年 | 57篇 |
2023年 | 512篇 |
2022年 | 815篇 |
2021年 | 1814篇 |
2020年 | 1104篇 |
2019年 | 1793篇 |
2018年 | 1896篇 |
2017年 | 1459篇 |
2016年 | 1549篇 |
2015年 | 1627篇 |
2014年 | 2289篇 |
2013年 | 2991篇 |
2012年 | 4482篇 |
2011年 | 4408篇 |
2010年 | 2405篇 |
2009年 | 1989篇 |
2008年 | 3451篇 |
2007年 | 3393篇 |
2006年 | 3154篇 |
2005年 | 2955篇 |
2004年 | 2550篇 |
2003年 | 2135篇 |
2002年 | 1862篇 |
2001年 | 209篇 |
2000年 | 136篇 |
1999年 | 214篇 |
1998年 | 301篇 |
1997年 | 216篇 |
1996年 | 175篇 |
1995年 | 155篇 |
1994年 | 114篇 |
1993年 | 98篇 |
1992年 | 65篇 |
1991年 | 45篇 |
1990年 | 47篇 |
1989年 | 50篇 |
1988年 | 34篇 |
1987年 | 25篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 37篇 |
1983年 | 36篇 |
1982年 | 16篇 |
1981年 | 20篇 |
1980年 | 21篇 |
1978年 | 20篇 |
1977年 | 14篇 |
1976年 | 14篇 |
1975年 | 16篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
In this report, we show that in the human astroglioma cell line D54-MG, both interleukin-1 (IL-1β) and tumor necrosis factor-alpha (TNF-α) enhance C3 gene expression in a time- and dose-dependent manner. Kinetic analysis demonstrates that after 96 h, C3 mRNA levels increase approximately 30-fold and 20-fold in response to IL-1β or TNF-α, respectively. C3 protein production increases proportionally, reaching levels 36-fold and 18-fold higher than untreated controls upon exposure to IL-1β or TNF-α, respectively. D54-MG cells require a minimal 1 h exposure to IL-1β in order to enhance C3 gene expression significantly, while 4 to 8 h are required for TNF-α. Simultaneous treatment of D54-MG cells with IL-1β and interferon-gamma (IFN-γ) resulted in an additive increase in both C3 mRNA and protein expression, a finding not seen with the combination of TNF-α and IFN-γ. Primary rat astrocytes also express increased C3 mRNA levels after 48 h in response to IL-1β (5.3-fold increase) and TNF-α (7-fold increase), while an additive effect was observed upon simultaneous treatment with both IL-1β and IFN-γ. In the central nervous system (CNS), endogenous complement and cytokine production by astrocytes, and enhancement by IFN-γ, a product of activated T cells often seen in the CNS in neural autoimmune disease, may contribute to the pathogenesis of inflammatory demyelinating diseases such as multiple sclerosis. 相似文献
72.
Sherilyn Gross Karen Helm Jennifer J. Gruntmeir Wayne S. Stillman David W. Pyatt Richard D. Irons 《European journal of haematology》1997,59(5):318-326
Abstract: Our current understanding of human haematopoietic stem cell biology is based in part on the characterization of human CD34+ bone marrow cell differentiation in vitro. CD34 is highly expressed on early stem cells and haematopoietic progenitor cells with clonogenic potential and is gradually lost during differentiation and commitment. However, CD71 (transferrin receptor) is expressed at low levels on early stem cells and generally increases during haematopoietic progenitor cell proliferation. We reasoned that the combination of these surface markers would provide a useful framework for the simultaneous analysis of multiple lineage differentiation of CD34+ haematopoietic progenitor cells in liquid culture. In this report, we identify the phenotype of distinct subpopulations of myeloid, erythroid and lymphoid cells in liquid suspension culture using differential expression of CD34 vs. CD71 in combination with specific lineage markers. Freshly isolated human CD34+ bone marrow cells were introduced into suspension culture and monitored over a 6-d period using 3-colour flow cytometry. This is the first demonstration that differential expression of CD34 vs. CD71 can be used to simultaneously monitor differentiation of multiple haematopoietic cell lineages in liquid suspension culture, facilitating the study of cytokine-, drug- or chemical-induced alterations in haematopoietic progenitor cell differentiation in vitro. 相似文献
73.
Mark Sanford Carolyn Byrne Susan Williams Sandy Atley Jennifer Miller Heather Allin 《Revue canadienne de psychiatrie》2003,48(2):78-86
OBJECTIVE: This study assessed the feasibility and efficacy of a parent-education group for families with young children and a parent with depression. We designed the program to be readily disseminated if shown to be effective. METHOD: We recruited 44 parents with depression from clinics and family doctors in Hamilton, Ontario, and randomly assigned them to receive the parenting program or to a wait-list control group. The outcomes measured included knowledge of depression, parenting, family relationships, depression symptoms, child depressive symptoms, and functioning. We used analysis of covariance to test for posttreatment differences between experimental and control groups. RESULTS: Of the treatment group, 27% dropped out at posttreatment, and 43% by follow-up. Those who dropped out had more severe depression at baseline than did those who completed the program, and there was selective loss of parents with more severe depression in the experimental group. In intention-to-treat analyses at posttreatment, probands in the experimental group reported more improvements on family functioning, parenting sense of competence, and family and parent conflict than did control subjects. Standardized effect sizes (ES) were medium (0.4 to 0.6). When baseline depressive symptom scores were controlled in the analyses, the between-group differences were reduced, showing that selective loss of participants may have influenced the findings. CONCLUSIONS: On balance, the results are encouraging and support the further development and evaluation of the group intervention. However, the study does not provide unequivocal evidence in support of the program. Before it is transferred to other settings, the program needs further modification to improve participation by parents with more severe depression and further evaluation of its effectiveness. 相似文献
74.
Interobserver variability in neonatal cranial ultrasonography 总被引:1,自引:0,他引:1
Jennifer Pinto Nigel Paneth Elias Kazam Ram Kairam Sylvan Wallenstein Walter Rose David Rosenfeld Steven Schonfeld Irving Stein Thomas Witomski 《Paediatric and perinatal epidemiology》1988,2(1):43-58
The reliability of cranial ultrasound diagnosis in the premature neonate was examined using data from an ongoing multicentre study of the epidemiology and long-term consequences of neonatal brain haemorrhage. First week ultrasound films (obtained at 4 hours, 24 hours and 7 days) from 60 study subjects were randomly selected for independent review by two groups of experienced interpreters, and results were recorded separately for observations (i.e. presence or absence of an abnormal echodense area on a film) and interpretations (i.e. presence or absence of haemorrhage or ventricular dilatation) in each hemisphere. Because of deaths in the first week of life, the total number of films examined was 138. Concordance on the presence or absence of an abnormal echodensity was examined for each individual film for three areas of interest: the germinal matrix, the ventricles and the parenchyma. Concordance on the presence or absence of haemorrhage or ventricular dilatation was examined only for the seventh-day film, or the final film prior to death. Finally, concordance was analysed with the diagnostic interpretations grouped into categories thought to differ prognostically for long-term outcome. In general, concordance was poorest for germinal matrix lesions and best for parenchymal lesions. Concordance was lower for observations made on each individual film than it was for interpretation of the final film in each case. Fifty-five of 60 cases (92%) were assigned to the same major prognostic category by both readers. Ultrasound review conferences were held periodically and there was evidence that concordance in ultrasound reading and interpretation improved during the course of the study. 相似文献
75.
76.
77.
78.
Hideto Kitano Jennifer M Young Jian Cheng Lan Wang Patricia D Hurn Stephanie J Murphy 《Journal of cerebral blood flow and metabolism》2007,27(7):1377-1386
Inhalation anesthetics are effective chemical preconditioning agents in experimental cerebral ischemia. However, previous work has been performed exclusively in male animals. We determined if there is a gender difference in ischemic outcome after isoflurane preconditioning (IsoPC), and if this sex-specific response is linked to differences in Akt phosphorylation or expression of neuronal inducible cell-death putative kinase (NIPK), a negative modulator of Akt activation. Young and middle-aged male and female mice were preconditioned for 4 h with air (sham PC) or 1.0% IsoPC and recovered for 24 h. Cortices were subdissected from preconditioned young male and female mice for measurement of Akt phosphorylation (Western blot) and NIPK mRNA (quantitative polymerase chain reaction). Additional cohorts underwent 2 h of reversible middle cerebral artery occlusion. Lastly, male and female Akt1(+/+) and Akt1(-/-) mice were studied to determine if gender differences in ischemic outcome after IsoPC is Akt1-dependent. Infarction volume was determined at 22 h reperfusion (2,3,5-triphenyltetrazolium chloride). As expected, IsoPC decreased ischemic damage as compared with sham PC in young and middle-aged male mice. In contrast, IsoPC markedly increased infarction in young female mice and had no effect in middle-aged female mice. Cortical phospho-Akt was increased by IsoPC versus sham PC only in male mice. No increase was observed in IsoPC female mice. NIPK mRNA was higher in female mice than in male mice regardless of preconditioning status. Male IsoPC neuroprotection was lost in Akt1-deficient male mice. We conclude that IsoPC is beneficial only in ischemic male brain and that sex differences in IsoPC are mediated through Akt activation and basal NIPK expression. 相似文献
79.
Georgia Robins Sadler Celine Marie Ko Jennifer Alisangco Bradley P Rosbrook Eric Miller Judith Fullerton 《Applied Nursing Research》2007,20(3):152-157
This article discusses issues to be considered by nurse researchers when groups should be used as the unit of randomization. Advantages and disadvantages are presented, with statistical calculations needed to determine the effective sample size. Examples of these concepts are presented using data from the Black Cosmetologists Promoting Health Program. Different hypothetical scenarios and their impact on sample size are also presented. Given the complexity of calculating the sample size when using groups as the unit of randomization, it is advantageous for researchers to work closely with statisticians when designing and implementing studies that anticipate the use of groups as the unit of randomization. 相似文献
80.
The workplace is an important setting for health promotion and provides an ideal opportunity for shaping healthy eating patterns in occupational groups for whom inequalities have been identified (DHSS, 1980). Workplace food/health policies provide an intermediate and pragmatic step towards achieving the dietary targets set out in the Government's white paper Health of the Nation and the most recent COMA report (DoH, 1991,1992). Food/health policies have been widely adopted in the NHS (Gibson & Kallevik, 1990) and preliminary research suggests that they are an effective means of intervention (Wallis & Poulter, 1988; Frost et al., 1991). Industry has been slower to link food and health promotion to a policy making process. Surveys imply that action on healthy eating in companies often originates in the occupational health department and is based on individualistic approaches with little energy being put into preventive activities which would originate in the canteen (Mclnerney & Cooper, 1989; Poulter, 1990). Policies provide a means of balancing the environmental and educational paradigms of health promotion. If food/health policies are to grow in the private sector then industry has to be convinced that the benefits Justify the costs. Some philanthropic employers are motivated by interests other than financial gain, but others are commercially led. There is little hard evidence to demonstrate that any type of employer-sponsored healthy eating initiative provides a favourable return for investment. It has been ‘guesstimates’ and extrapolation from other situations which have provided the justification for UK companies to allocate any resources towards addressing food/health issues. In April 1990 the National Grid Company adopted a comprehensive food/health policy. This paper draws on the experiences in developing and implementing the policy document to discuss the issues around evaluative activity in a commercial setting. Views are expressed on the feasibility of measurement and the value of the informaton collected. One aim of the future should be to research this under-examined area to establish a solid body of information. This would raise the level of debate from one which is currently based on anecdotal evidence to a sounder scientific footing and, therefore, ensure the future growth of such policies in the corporate sector. 相似文献