全文获取类型
收费全文 | 362篇 |
免费 | 21篇 |
国内免费 | 6篇 |
专业分类
耳鼻咽喉 | 1篇 |
儿科学 | 5篇 |
基础医学 | 36篇 |
口腔科学 | 6篇 |
临床医学 | 22篇 |
内科学 | 42篇 |
皮肤病学 | 2篇 |
神经病学 | 1篇 |
特种医学 | 234篇 |
外科学 | 8篇 |
综合类 | 2篇 |
预防医学 | 4篇 |
眼科学 | 3篇 |
药学 | 11篇 |
肿瘤学 | 12篇 |
出版年
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2014年 | 1篇 |
2012年 | 1篇 |
2011年 | 2篇 |
2010年 | 3篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 2篇 |
2004年 | 3篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 19篇 |
1997年 | 21篇 |
1996年 | 15篇 |
1995年 | 13篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1989年 | 23篇 |
1988年 | 22篇 |
1987年 | 26篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 19篇 |
1980年 | 15篇 |
1979年 | 3篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1974年 | 1篇 |
排序方式: 共有389条查询结果,搜索用时 180 毫秒
101.
Johanna C Dekkers Marieke F van Wier Ingrid JM Hendriksen Jos WR Twisk Willem van Mechelen 《BMC medical research methodology》2008,8(1):69
Background
In population studies, body mass index (BMI) is generally calculated from self-reported body weight and height. The self-report of these anthropometrics is known to be biased, resulting in a misclassification of BMI status. The aim of our study is to evaluate the accuracy of self-reported weight, height and waist circumference among a Dutch overweight (Body Mass Index [BMI] ≥ 25 kg/m2) working population, and to determine to what extent the accuracy was moderated by sex, age, BMI, socio-economic status (SES) and health-related factors. 相似文献102.
Knaggs P; Lambert A; Proudfoot F; Nickson I; Hooper MA; Lenton E; Robertson WR 《Molecular human reproduction》1998,4(2):147-151
The presence of 11beta-hydroxysteroid dehydrogenase (11beta-HSD;
EC1.1.1.146), the enzyme responsible for the interconversion of cortisol
and cortisone, in granulosa-lutein (GL) cells is associated with a poor
outcome in in-vitro fertilization (IVF). We have developed a simple method
of assessing the reductase component of 11beta-HSD in these cells which is
sufficiently rapid to provide data on the enzyme's activity prior to embryo
replacement. Cells were pooled from follicular aspirates and challenged
with cortisone within 2 h of aspiration. Cortisol secretion was then
measured by radioimmunoassay. Conversion of cortisone to cortisol was
linear for up to 3 h and was completely inhibited by glycyrrhetinic acid, a
specific 11beta-HSD inhibitor. Initial velocity rates were determined for
eight cortisone concentrations (range 0.1-8 micromol/l), and the apparent
Km calculated (1.6 +/- 0.4 micromol/l). There was no evidence of
substrate/product inhibition and conversion of cortisone to cortisol was
<2% in all experiments. In subsequent work, cells were challenged with
cortisone (6 micromol/l) for 2 h. Cells challenged for 2 h immediately
following purification from follicular aspirates produced varying amounts
of cortisol (range 25-150 nmol/pooled follicles from each patient, n = 10
patients), while basal outputs were <6 nmol/l. Enzyme activity was also
examined in cells on a per follicle basis from individual patients and
found to vary considerably (e.g. 19, 53 and 36 nmol/l cortisol/1000 cells,
three follicles). Having established the method for assessing
11beta-reductase activity within GL cells, we performed a small prospective
study on a series of 20 patients examining the enzyme activity within 110
individual follicles. 11Beta-reductase activity varied greatly from patient
to patient and from follicle to follicle ranging from <0.024-0.57 nmol
cortisol/microg DNA but at present low patient numbers preclude a
meaningful correlation between enzyme activity and pregnancy rate. In
summary, we have developed a simple, rapid (<8 h) assay for detecting
the reductase activity of 11beta-HSD in GL cells isolated from pooled or
individual follicles. This procedure is sufficiently quick to aid in the
choice of embryo for replacement.
相似文献
103.
PT Katzmarzyk WR Leonard MH Crawford RI Sukernik 《American journal of human biology》1994,6(6):783-790
This study presents physical fitness data on two indigenous Siberian populations, the Evenki and Keto. The Canadian Aerobic Test of Fitness (CATF) was utilized to provide estimates of maximal oxygen consumption (V?O2 max) for a sample of 44 subjects (30 males, 14 females) as baseline data for further studies on changing fitness levels and the health problems associated with acculturation. Estimates of V?O2 max average 46.2 ml kg?1 min?1 for males and 33.9 ml kg?1 min?1 for females. These values are comparable to those previously reported for other semisubsistence, cold adapted populations. The Siberian groups are below the Canadian norms in the 15–19 year age range, and thereafter track at about the 50th percentile throughout adulthood. This suggests that the cardiorespiratory systems of adult Evenki and Keto are functionally comparable to the average adult Canadian. © 1994 Wiley-Liss, Inc. 相似文献
104.
Matson PL; Graefling J; Junk SM; Yovich JL; Edirisinghe WR 《Human reproduction (Oxford, England)》1997,12(7):1550-1553
Mouse oocytes and embryos were obtained following ovulation induction of
(C57B16 x CBA) F1 animals. Zonae pellucidae were exposed to alpha-
chymotrypsin in phosphate-buffered medium (PB1) supplemented with 3 mg/ml
bovine serum albumin upon a heated stage (37 degrees C) and were observed
constantly through an inverted microscope. The endpoint of the bioassay was
the limits of the zona no longer being seen clearly at x 200 magnification,
and the time taken for each zona to dissolve was recorded. A dose-dependent
response in dissolution time was clearly seen, with 1% alpha-chymotrypsin
being chosen as the routine working solution. Cryopreservation of 2-cell
mouse embryos using propanediol did not cause zona hardening but induced a
small and significant softening, as gauged by the time taken for zona
dissolution (2181 +/- 167 versus 1864 +/- 82 s). Zona hardening was not
suspected to occur after the freezing of human embryos as there was no
difference in implantation rates per embryo for in-vitro fertilization
(IVF) and intracytoplasmic sperm injection (ICSI) treatment cycles between
fresh [IVF: 63/644 (9.7%); ICSI: 51/330 (15.5%)] and frozen embryos [IVF:
36/458 (7.9%); ICSI: 18/112 (16.1%)]. Conversely, significant hardening of
the zonae of mature oocytes was seen following cryopreservation (747 +/-
393 s) compared with freshly ovulated oocytes (151 +/- 68 s). It is
concluded that (i) the freezing of murine oocytes with propanediol results
in zona hardening, implying a possible benefit of ICSI after the
cryopreservation of human oocytes, and (ii) the cryopreservation of embryos
is not associated with zona hardening or reduced implantation, making
microdissection of the zona in such cases generally unwarranted.
相似文献
105.
The extensive heterogeneity of the gonadotrophin hormones, follicle
stimulating hormone (FSH) and luteinizing hormone (LH), is due primarily to
the heterogeneous nature of their carbohydrate side- chains, in particular
sialic acid residues. In this review, we discuss the role of carbohydrate
chains in receptor binding and activation, biological activity, and
metabolic half-life. The synthesis and secretion of the various glycoforms
of both FSH and LH appear to be under endocrine control with
gonadotrophin-releasing hormone (GnRH), oestradiol and testosterone playing
important roles. Evidence for different glycoforms having variable
biopotency or different encoded functions is increasing, and the production
and secretion of more or less acidic gonadotrophin species in different
physiological states may represent an important mechanism whereby the
pituitary regulates gonadal cell and organ function. This has potential
importance for the development of new pharmaceutical reagents and new
therapeutic regimens in assisted reproduction. It is envisaged that the use
of existing and new forms of FSH/LH will allow patients to be treated in a
more controlled and physiological manner, with treatment regimens
individualized to the needs of the patient.
相似文献
106.
Virus-induced cytokines regulate circulating lymphocyte levels during primary SIV infections 总被引:1,自引:0,他引:1
Rosenberg YJ; Cafaro A; Brennan T; Greenhouse JG; Villinger F; Ansari AA; Brown C; McKinnon K; Bellah S; Yalley-Ogunro J; Elkins WR; Gartner S; Lewis MG 《International immunology》1997,9(5):703-712
Decline in blood CD4+ lymphocytes during primary symptomatic infections
with HIV is usually attributed to viral killing, and has not been
considered in terms of altered lymphocyte migration and sequestration. We
therefore sought to examine whether CD4+ cell loss from blood of macaques
undergoing an acute primary SIV infection might be due to increased
synthesis of cytokines, known to profoundly affect lymphocyte trafficking,
rather than to direct lymphocyte destruction by virus. The findings
indicate that rapid lymphocyte depletion following acute infection is not
selective for CD4+ cells, correlates precisely with increased plasma
IFN-gamma and tumor necrosis factor-alpha levels, and is reversible.
CD4/CD8 ratios in lymph nodes with high viral burdens remain relatively
unchanged despite lymphocyte loss from blood. Levels of cytokine mRNA
measured in lymphoid organs reflect neither cytokine plasma levels nor
their potential to induce sequestration. These results support a model of
cytokine-induced lymphocyte extravasation to account for the acute
HIV/SIV-induced CD4+ cell lymphopenia and raise questions regarding the
extent to which altered lymphocyte migration plays a role in the gradual
CD4+ cell depletion throughout infection.
相似文献
107.
Trinucleotide expansion mutations in the cartilage oligomeric matrix protein (COMP) gene 总被引:6,自引:1,他引:5
Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) are
two human autosomal dominant skeletal dysplasias characterized by variable
short stature, joint laxity and early-onset degenerative joint disease.
Both disorders can result from mut-ations in the gene for cartilage
oligomeric matrix protein (COMP), an extracellular matrix glycoprotein.
About one-third of PSACH cases result from heterozygosity for deletion of
one codon within a very short triplet repeat, (GAC)5, which encodes five
consecutive aspartic acid residues within the calmodulin-like region of the
COMP protein. We have identified two expansion mut-ations in this repeat:
an MED patient carrying a (GAC)6allele and a PSACH patient carrying a
(GAC)7allele. These are among the shortest disease-causing triplet repeat
expansion mutations described thus far, and are the first identified in a
GAC repeat. A unique feature of this sequence is that expansion as well as
shortening of the repeat can cause the same disease. In cartilage, both
patients have rough endoplasmic reticulum inclusions in chondrocytes. The
inclusions are also present in tendon tissue and can be reproduced in
cultured tendon cells, suggesting that the pathophysiology of disease is
similar in both cartilage and tendon.
相似文献
108.
The potential of magnetic resonance (MR) imaging to demonstrate the mediastinal veins was evaluated retrospectively in 25 patients with no evidence of a venous abnormality, 28 patients who had narrowing or occlusion of a mediastinal vein, and two patients who had a venous anomaly. In patients with venous occlusion, the MR images graphically demonstrated the sites and extent. MR images also demonstrated slow flow within venous structures proximal to the obstruction. Generally, venous collaterals in the mediastinum and chest wall were better seen with contrast material-enhanced computed tomography scans. The marked contrast on MR images between the signal void of normal vascular structures, the moderate signal intensity of tumor, and the high signal intensity of a thrombus or slowly flowing blood allows ready detection of venous occlusion and may suggest the nature of the occlusion. 相似文献
109.
Detection of pulmonary nodules using spin-echo magnetic resonance (MR) imaging was compared with detection using computed tomography (CT). Of the 25 patients studied independently by two radiologists, no lung nodules were detected in 11 (CT or MR), ten had a single nodule, and four had multiple nodules. The lesions not seen using CT or MR were less than 1.3 cm in diameter. The greater spatial resolution of CT enabled better detection of nodules close to the diaphragm, the pleura, or to each other, whereas the better contrast resolution of MR enabled the detection of several nodules close to blood vessels. With MR, nodules were best seen on images with long repetition times (2.0 sec). Most pulmonary nodules are seen using both CT and MR. CT generally enables the detection of more small nodules than MR does, and some low-density nodules near blood vessels are better displayed using MR. 相似文献
110.