全文获取类型
收费全文 | 693篇 |
免费 | 43篇 |
国内免费 | 16篇 |
专业分类
耳鼻咽喉 | 6篇 |
儿科学 | 35篇 |
妇产科学 | 6篇 |
基础医学 | 104篇 |
口腔科学 | 16篇 |
临床医学 | 85篇 |
内科学 | 123篇 |
皮肤病学 | 5篇 |
神经病学 | 28篇 |
特种医学 | 107篇 |
外科学 | 88篇 |
综合类 | 41篇 |
一般理论 | 1篇 |
预防医学 | 42篇 |
眼科学 | 6篇 |
药学 | 36篇 |
中国医学 | 1篇 |
肿瘤学 | 22篇 |
出版年
2021年 | 8篇 |
2019年 | 8篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 10篇 |
2015年 | 15篇 |
2014年 | 17篇 |
2013年 | 21篇 |
2012年 | 30篇 |
2011年 | 12篇 |
2010年 | 30篇 |
2009年 | 18篇 |
2008年 | 13篇 |
2007年 | 27篇 |
2006年 | 13篇 |
2005年 | 14篇 |
2003年 | 12篇 |
2002年 | 16篇 |
2001年 | 6篇 |
2000年 | 18篇 |
1999年 | 21篇 |
1998年 | 27篇 |
1997年 | 27篇 |
1996年 | 26篇 |
1995年 | 20篇 |
1994年 | 21篇 |
1993年 | 20篇 |
1992年 | 8篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 30篇 |
1988年 | 21篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 12篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 8篇 |
1971年 | 13篇 |
1970年 | 6篇 |
1969年 | 7篇 |
1968年 | 10篇 |
1967年 | 6篇 |
排序方式: 共有752条查询结果,搜索用时 15 毫秒
1.
Sonoelasticity imaging of prostate cancer: in vitro results 总被引:2,自引:0,他引:2
2.
On authorship and acknowledgments 总被引:2,自引:0,他引:2
3.
M S Leboff G E Fuleihan J E Angell S Chung K Curtis 《Journal of bone and mineral research》1992,7(7):841-846
Although single-photon absorptiometry (SPA) has been the predominant tool used to assess bone mineral density (BMD) in the forearm, the development of dual-energy x-ray absorptiometry (DEXA) provides the benefits of greater source stability, reduced scanning time, and improved image resolution compared to SPA. In the present study we used the DEXA bone densitometer (Hologic, Inc., Waltham, MA) to (1) measure BMD in the one-third radius and ultradistal radius; (2) examine the reproducibility of these BMD measurements; and (3) compare the BMD at the one-third radius with SPA (SP2, Lunar Corp., Madison, WI). In 65 normal women (ages 22-74 years) we examined changes in the forearm DEXA BMD with age, revealing significant quadratic regression equations. The reproducibility of DEXA BMD (mean +/- SEM) in 7 normal subjects aged 22-50 years is 0.85 +/- 0.16% for the predominantly cortical one-third radius site and 0.97 +/- 0.15% for the more trabecular ultradistal site. The regression relationship between DEXA and SPA of the one-third radius in 26 subjects (ages 22-68 years) is DEXA BMD = 0.105 + 0.826 (SPA BMD); R = 0.97, R2 = 0.94, p less than 0.0001. Bone densitometry of the forearm using DEXA may be performed relatively rapidly, providing reproducibility and image resolution that are generally superior to those observed with SPA. 相似文献
4.
Screening for early ovarian cancer 总被引:5,自引:0,他引:5
5.
Trimethyltin (TMT) was used as a positive control neurotoxicant to evaluate a repeated acquisition procedure for the 8-arm radial maze. Ten male Long-Evans rats were trained to collect a single food pellet at the end of each baited arm on each trial of a daily 12-trial test session. Four of the eight arms were baited on all trials of a given session. The set of four baited arms was changed each day: thus the rats were required to learn a new set of baited arms in each session. In trained rats, error frequencies (entries into unbaited arms) declined from about 4 on Trial 1 to less than 1 on Trials 4-12 in each session: this within-session error reduction thus defined an acquisition baseline which was evaluated for its sensitivity to TMT. Learning was impaired after 7 mg/kg (iv) TMT, as shown by a slower decline in within-session error frequencies in all treated rats. Errors and response times were elevated for 5 weeks after TMT but returned to control levels thereafter. Histological examination of hippocampi showed damage in all treated rats 18 weeks after treatment; however, no significant relationship between degree of damage and behavioral effect was observed. Analysis of errors showed that TMT more strongly impaired the rats' ability to avoid arms in the current unbaited set than those baited arms already entered on a given trial (i.e., working memory). These dissociations between behavior and hippocampal morphology in terms of time course, magnitude of effect across animals, and error type suggest that performance of this task does not depend upon hippocampal integrity, as do other tasks involving spatial working memory. Recovery of function in this kind of task may shed light on processes of neural plasticity after exposure to neurotoxic compounds. 相似文献
6.
7.
The vascularity of 49 renal masses (26 malignant and 23 benign lesions) was investigated with duplex Doppler ultrasound. Doppler signals obtained at the margins of renal masses were defined as "tumor signals" when the Doppler-shifted frequency of the lesion exceeded the frequency shift in the ipsilateral main renal artery. These exceeded 2.5 kHz with a 3-MHz insonating frequency. Among the 26 renal masses that subsequently proved to be malignant, tumor signals were obtained in 15 of 18 (83%) untreated renal cell carcinomas, in three of four Wilms tumors, and in two patients with metastases to the kidney, but not in the one patient with lymphoma. None of the 23 benign renal masses demonstrated tumor signals. Tumor vascularity in malignant lesions gives rise to abnormal, high-velocity, Doppler-shifted signals that can help in the differential diagnosis of renal masses. 相似文献
8.
Cytogenetic analysis of unfertilized human oocytes 总被引:3,自引:1,他引:3
R R Angell W Ledger E L Yong L Harkness D T Baird 《Human reproduction (Oxford, England)》1991,6(4):568-573
Cytogenetic studies were carried out on 180 oocytes that appeared unfertilized after in-vitro fertilization. The majority of the 135 that were informative had grossly haploid second meiotic metaphases, two were grossly diploid, and five had a variety of different abnormalities. Twenty-one oocytes were abnormally fertilized and included prematurely condensed sperm chromosomes. The frequency of this phenomenon varied according to the stimulation protocol, those oocytes maturing longer in vivo showing less propensity to abnormal fertilizations. Thirteen per cent of the analysable haploid metaphases were hyperhaploid but none contained extra whole chromosomes. The extra components were a single chromatid (one case), or two single chromatids replacing a whole chromosome (four cases). The data suggest that the chromatids arose as a result of premature centromere division at meiosis I, and that this may be a major mechanism for trisomy formation rather than non-disjunction of whole bivalents at meiosis I, as generally believed. 相似文献
9.
William R. Brody William W. Angell Jon C. Kosek 《The American journal of pathology》1972,66(1):111-130
The histologic fate of venous grafts used for coronary artery bypass has been observed with light and electron microscopy in dogs. Endothelial damage and thrombosis were chiefly limited to the first postoperative week. The muscular media uniformly suffered extensive necrosis and inflammatory cell infiltration during the first week. Its smooth muscle cells either hypertrophied, died or underwent apparent fibroblastic transformation, with eventual fibrous replacement, to a variable degree, of the vein wall. Vascular wall ischemia due to interruption of vasa vasorum during transplantation appears to initiate these medial changes. Much more slowly, intimal thickening by myointimal cells and collagen may reduce the graft lumen to a variable extent. 相似文献
10.
Detection of reactive oxygen species (ROS) and apoptosis in human fragmented embryos 总被引:8,自引:2,他引:8
Yang HW; Hwang KJ; Kwon HC; Kim HS; Choi KW; Oh KS 《Human reproduction (Oxford, England)》1998,13(4):998-1002
In human in-vitro fertilization (IVF)-embryo transfer, the in-vitro culture
environment differs from in-vivo conditions in that the oxygen
concentration is higher, and in such conditions the mouse embryos show a
higher concentration of reactive oxygen species (ROS) in simple culture
media. ROS are believed to cause damage to cell membranes and DNA
fragmentation in somatic cells. This study was conducted to ascertain the
level of H2O2 concentration within embryos and the morphological features
of cell damage induced by H2O2. A total of 62 human oocytes and embryos (31
fragmented, 15 non-fragmented embryos, 16 unfertilized oocytes) was
obtained from the IVF-embryo transfer programme. The relative intensity of
H2O2 concentrations within embryos was measured using
2',7'-dichlorodihydrofluorescein diacetate by Quanti cell 500 fluorescence
imaging and DNA fragmentation was observed with transmission electron
microscopy and an in-situ apoptosis detection kit. The H2O2 concentrations
were significantly higher in fragmented embryos (72.21 +/- 9.62, mean +/-
SEM) compared to non-fragmented embryos (31.30 +/- 3.50, P < 0.05) and
unfertilized oocytes (30.75 +/- 2.67, P < 0.05). Apoptosis was observed
only in fragmented embryos, and was absent in non-fragmented embryos.
Electron microscopic findings confirmed apoptotic bodies and cytoplasmic
condensation in the fragmented blastomeres. We conclude that there is a
direct relationship between increased H2O2 concentration and apoptosis, and
that further studies should be undertaken to confirm these findings.
相似文献