全文获取类型
收费全文 | 1810篇 |
免费 | 126篇 |
国内免费 | 48篇 |
专业分类
耳鼻咽喉 | 5篇 |
儿科学 | 93篇 |
妇产科学 | 15篇 |
基础医学 | 208篇 |
口腔科学 | 16篇 |
临床医学 | 244篇 |
内科学 | 642篇 |
皮肤病学 | 46篇 |
神经病学 | 150篇 |
特种医学 | 151篇 |
外科学 | 142篇 |
综合类 | 59篇 |
预防医学 | 79篇 |
眼科学 | 11篇 |
药学 | 74篇 |
中国医学 | 3篇 |
肿瘤学 | 46篇 |
出版年
2021年 | 16篇 |
2018年 | 24篇 |
2017年 | 18篇 |
2016年 | 18篇 |
2015年 | 30篇 |
2014年 | 38篇 |
2013年 | 40篇 |
2012年 | 57篇 |
2011年 | 68篇 |
2010年 | 62篇 |
2009年 | 51篇 |
2008年 | 58篇 |
2007年 | 95篇 |
2006年 | 74篇 |
2005年 | 72篇 |
2004年 | 57篇 |
2003年 | 39篇 |
2002年 | 51篇 |
2001年 | 56篇 |
2000年 | 33篇 |
1999年 | 39篇 |
1998年 | 51篇 |
1997年 | 52篇 |
1996年 | 64篇 |
1995年 | 37篇 |
1994年 | 38篇 |
1993年 | 28篇 |
1992年 | 35篇 |
1991年 | 27篇 |
1990年 | 30篇 |
1989年 | 54篇 |
1988年 | 36篇 |
1987年 | 38篇 |
1986年 | 41篇 |
1985年 | 29篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 24篇 |
1981年 | 19篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1978年 | 32篇 |
1977年 | 30篇 |
1976年 | 23篇 |
1975年 | 23篇 |
1974年 | 18篇 |
1973年 | 21篇 |
1972年 | 24篇 |
1971年 | 22篇 |
1968年 | 17篇 |
排序方式: 共有1984条查询结果,搜索用时 31 毫秒
11.
H J Alter J S Epstein S G Swenson M J VanRaden J W Ward R A Kaslow J E Menitove H G Klein S G Sandler M H Sayers 《The New England journal of medicine》1990,323(19):1312-1317
BACKGROUND. We performed a multicenter study in 1989 to determine whether screening whole-blood donors for human immunodeficiency virus type 1 (HIV-1) p24 antigen would improve transfusion safety by identifying carriers of the virus who are seronegative for HIV-1 antibody. METHODS. More than 500,000 donations were tested at 13 U.S. blood centers with test kits from two manufacturers. Units found repeatedly reactive were retested in a central laboratory; if the results were positive, they were confirmed by a neutralization assay. A subgroup of units was also tested for HIV-1 by the polymerase chain reaction. Selected donors confirmed or not confirmed as having p24 antigen were contacted for follow-up interviews to identify risk factors and undergo retesting for HIV-1 markers. RESULTS. Positive tests for p24 antigen were confirmed by neutralization in five donors (0.001 percent of all donations tested), all of whom were also positive for HIV-1 antibody and HIV-1 by polymerase chain reaction. Three of the antigen-positive donors had other markers of infectious disease that would have resulted in the exclusion of their blood; two had risk factors for HIV-1 that should have led to self-exclusion. Of 220 blood units with repeatedly reactive p24 antigen whose presence could not be confirmed by neutralization (0.04 percent of the donations studied), none were positive for HIV-1 antibody, HIV-1 by polymerase chain reaction (120 units tested), or virus culture (76 units tested)--attesting to the specificity of confirmatory neutralization. CONCLUSIONS. The finding that no donation studied was positive for p24 antigen and negative for HIV-1 antibody suggests that screening donors for p24 antigen with tests of the current level of sensitivity would not add substantially to the safety of the U.S. blood supply. 相似文献
12.
Induction of a differentiated ciliated cell phenotype in primary cultures of Fallopian tube epithelium 总被引:5,自引:1,他引:5
Human Fallopian tubal epithelial cells in culture lose morphological
features associated with the epithelium in situ and the extent to which
they retain their in-vivo phenotype or function is unknown. In order to
address this question, immunocytochemical markers were identified which
distinguish secretory (HMFG2+, LhS28-) from ciliated (HMFG2-, LhS28+)
epithelial cells in tissue sections of Fallopian tube. These markers were
used to analyse the phenotype of tubal cells in vitro. Primary cultures of
human tubal epithelial cells were seeded onto glass and grown to confluence
before addition of oestradiol-17beta. In the absence of hormone, tubal
epithelial cells expressed cytokeratins and nuclear receptors for oestrogen
and progesterone and adopted a homogeneous (HMFG2+, LhS28-) secretory cell
phenotype. Following the addition of oestradiol-17beta, a proportion of
cells became positive for LhS28. The induction of a ciliated epithelial
cell phenotype was confirmed by scanning electron microscopy, where on
permeable collagen membranes, approximately one-third of tubal epithelial
cells became ciliated in the presence of oestradiol-17beta. We suggest that
in vitro, tubal epithelial cells adopt an immature secretory-like phenotype
and that oestrogen can induce differentiation to a ciliated epithelial cell
phenotype.
相似文献
13.
Chaim Brautbar Isac Cohen Esther Kahana Milton Alter Fritz Jørgensen Lars Lamm 《Tissue antigens》1977,10(4):291-302
The distribution of 24 HLA antigens of the A and B loci was investigated in 197 Israeli Jewish patients with multiple sclerosis (MS) from various Jewish ethnic origins including central and eastern Europe, countries bordering the Mediterranean, the Middle East and from native-born Israelis. The results were compared with the HLA antigen frequencies in a control sample of 455 unrelated individuals representing the general Jewish population. The frequency of HLA-Bw40 among all MS patients (15%) was significantly greater (P less than 0.001) than among the controls (7%). In contrast to the findings in MS patients from other populations, there was no increased frequency of A3 and B7 and Dw2 was present in only one out of 28 patients. The study showed a similar distribution of HLA-A and -B locus antigens, especially of Bw40, in Jews of diverse ethnic origins represented in the control group. 相似文献
14.
Clinical profiling of recombinant follicle stimulating hormone (rFSH; Puregon): relationship between serum FSH and efficacy 总被引:9,自引:0,他引:9
Single-dose and multiple-rising dose studies of recombinantfollicle stimulating hormone (rFSH) in hypogonadotrophic maleand female volunteers demonstrated that the rate of FSH absorptionafter i.m. injection is higher in men than in women. In theabsence of endogenous FSH, a correlation between serum FSH andbody weight became apparent. The elimination half-life of rFSHwas not different between the sexes and was comparable withurinary FSH. However, the in-vitro bio:immuno ratio of serumFSH was significantly higher after the administration of rFSHthan after urinary FSH. When rFSH was administered daily witha fixed dose, steady state levels were reached within 3-5 days.Serum FSH concentrations increased in a dose-dependent mannerwhen the daily dose was increased weekly over 3 weeks from 75to 225 IU. In hypogonadotrophic women, rFSH induced normal folliculargrowth whereas oestrogen synthesis was impaired. In women pituitarysuppressed by a high-dose oral contraceptive, the daily administrationof 150 IU rFSH for 1 week induced more and larger antral folliclesthan the same regimen with urinary FSH, whereas the serum immunoactiveFSH concentrations measured 24 h after each dosing were similar.It is concluded that even though equal or lower serum immunoactiveFSH concentrations were obtained following the administrationof rFSH compared with urinary FSH, circulating bioactivity FSHconcentrations were higher. Therefore, the conventional ideathat serum immunoreactive FSH correlates positively with themagnitude of the ovarian response should be reconsidered. 相似文献
15.
16.
Idiopathic torsion dystonia (ITD) has long been considered to be genetically determined, but the pattern of inheritance has been unclear. It has been suggested that inheritance may differ in Jews and non-Jews. In the present study, data gathered in a nationwide survey of ITD in Israel were analysed. Between 1969 and 1980, 47 patients were collected, of whom 40 were of European origin. In these European Jews, the ITD frequency was about 1:23 000 live births, which was five-fold greater than in Jews of Afro-Asian origin. Assuming that all cases fit the same genetic model, an X linked or a simple autosomal recessive model of inheritance did not agree well with our data. An autosomal dominant model with low penetrance could have accounted for our observations and would yield an ITD gene frequency in European Jews of 3 to 4:100 000. In view of the increased ages of their fathers, the isolated cases may have included some new mutations. Multifactorial inheritance was also possible. However, it may be inappropriate to assume that all cases have the same genetic basis, or even that all are inherited. 相似文献
17.
Multiple sclerosis and childhood infections 总被引:1,自引:0,他引:1
M Alter Z X Zhang Z Davanipour E Sobel J Zibulewski G Schwartz G Friday 《Neurology》1986,36(10):1386-1389
Migration from an area where MS is common to an area where it is rare (and vice versa) affects the risk of MS, provided migration occurs in childhood. A childhood infection might explain this effect. Therefore, the age pattern of infectious diseases in different regions was examined. A higher proportion of children showed positive titers to many viral diseases early in life in areas where MS is rare compared with those where MS is common. Also, mortality rates from a variety of infectious diseases correlated negatively with the MS mortality. Thus, infection early in life may "protect" against MS, and conversely, later infection, when the immune system has partially matured, may increase risk. MS may be an age-dependent, host-immune response to childhood infection. 相似文献
18.
There has been significant advance in our understanding of CJD and similar spongiform encephalopathies in recent years. The range in clinical expression of the disease is better appreciated, and the existence of "atypical" cases of CJD is increasingly recognized. New ideas about the possible modes of natural transmission have been derived from case-control studies in different parts of the world. 相似文献
19.
20.
Ionizing radiation is a carcinogen that induces oxidative DNA damage. 8-
Hydroxy-2'-deoxyguanosine (8-OHdG) is a relatively abundant, mutagenic
lesion that is widely regarded as a reliable index of oxidative DNA damage.
The purpose of this study was to examine the effects of X- radiation on
levels of 8-OHdG in the context of an experimental model for breast cancer
in which chronic radiation exposure has been shown to be carcinogenic in
Sprague-Dawley rats. A secondary objective of this study was to determine
if the use of phenol during DNA isolation affected the concentration of
8-OHdG subsequently measured. Our results indicate that a profoundly
carcinogenic dose of radiation induced a small but significant increase in
8-OHdG concentration in mammary gland DNA, and that the use of a
phenol-based versus a salt-based method of DNA isolation had no significant
impact on the levels of 8-OHdG detected in either control or irradiated
tissue.
相似文献