全文获取类型
收费全文 | 1247篇 |
免费 | 173篇 |
国内免费 | 7篇 |
专业分类
耳鼻咽喉 | 4篇 |
儿科学 | 43篇 |
妇产科学 | 17篇 |
基础医学 | 174篇 |
口腔科学 | 70篇 |
临床医学 | 138篇 |
内科学 | 291篇 |
皮肤病学 | 24篇 |
神经病学 | 47篇 |
特种医学 | 143篇 |
外科学 | 122篇 |
综合类 | 89篇 |
预防医学 | 117篇 |
眼科学 | 10篇 |
药学 | 77篇 |
1篇 | |
中国医学 | 1篇 |
肿瘤学 | 59篇 |
出版年
2023年 | 6篇 |
2021年 | 17篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 25篇 |
2017年 | 23篇 |
2016年 | 25篇 |
2015年 | 24篇 |
2014年 | 41篇 |
2013年 | 28篇 |
2012年 | 51篇 |
2011年 | 41篇 |
2010年 | 47篇 |
2009年 | 49篇 |
2008年 | 46篇 |
2007年 | 44篇 |
2006年 | 51篇 |
2005年 | 26篇 |
2004年 | 35篇 |
2003年 | 40篇 |
2002年 | 34篇 |
2001年 | 36篇 |
2000年 | 29篇 |
1999年 | 23篇 |
1998年 | 36篇 |
1997年 | 56篇 |
1996年 | 52篇 |
1995年 | 42篇 |
1994年 | 37篇 |
1993年 | 49篇 |
1992年 | 34篇 |
1991年 | 22篇 |
1990年 | 26篇 |
1989年 | 24篇 |
1988年 | 29篇 |
1987年 | 19篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 21篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 21篇 |
1975年 | 13篇 |
1973年 | 8篇 |
1971年 | 5篇 |
排序方式: 共有1427条查询结果,搜索用时 15 毫秒
1.
Genomes of some parasites contain dozens of alternative and highly diverged surface antigens, of which only a single one is expressed in any cell. Individual cells occasionally change expression of their surface antigen, allowing them to escape immune surveillance. These switches appear to occur in a partly random way, creating a diverse set of antigenic variants. In spite of this diversity, the parasitemia develops as a series of outbreaks, in which each outbreak is dominated by relatively few antigenic types. Host-specific immunity eventually clears the dominant antigenic types, and a new outbreak follows from antigenic types that have apparently been present all along at low frequency. This pattern of sequential dominance by different antigenic types remains unexplained. We review the five most prominent theories, which have developed mainly from studies of the protozoans Trypanosoma and Plasmodium, and the bacterial spirochete Borrelia. The most promising theories depend on some combination of mechanisms to create favored connectivity pathways through the matrix of transitions between variants. Favored pathways may arise from biased switches at the molecular level of gene expression or from biases imposed by immune selection. We illustrate the concept of connectivity pathways by reanalysis of data on transitions between variants from Borrelia hermsii. 相似文献
2.
3.
De Leo V; Morgante G; Lanzetta D; D'Antona D; Bertieri RS 《Human reproduction (Oxford, England)》1997,12(2):357-360
We report the results of administration of danazol after suspension of
gonadotrophin-releasing hormone analogue (GnRHa) therapy for uterine
myomas. A total of 21 women with uterine myomas was treated with 100 mg
danazol for 6 months after GnRHa therapy. Uterine volume and endocrine
status were monitored monthly by ultrasound and assay of plasma
gonadotrophins, oestradiol and progesterone. The results show a rebound of
uterine volume about 30% less than in controls at the end of danazol
therapy. Menstrual cyclicity returned after 65 +/- 3 days in 16 subjects
and five patients remained amenorrhoeic. Hormone assays confirmed renewed
ovarian function in the women whose menstrual periods returned. Bone
mineral content was substantially reduced during GnRHa treatment but
improved significantly during danazol therapy even in the women who
remained amenorrhoeic. These results show the utility of danazol in
prolonging the therapeutic effects of GnRHa. The mechanism by which danazol
inhibits rebound of uterine volume may be due to its antiprogesterone
effects on uterine myomas.
相似文献
4.
We investigated the measurement of phenytoin in plasma by the EMIT method, in the Monarch centrifugal analyzer. When we used the standard protocol supplied by Instrumentation Laboratory, significant drift was observed across a full rotor loaded with 31 replicates of a single specimen. Although the cause remains obscure, the drift was eliminated by using a load-spin-reload-spin procedure. This makes it possible to analyze large batches of samples without excessive use of standards and reagents. 相似文献
5.
6.
7.
The genomic structures of spirochete species are not well characterized, and genetic studies on these organisms have been hampered by lack of a genetic exchange mechanism in these bacteria. In view of these observations, pulsed-field gel electrophoresis was used to examine the genomes of Leptospira species. Live cells, prepared in agarose plugs, were lysed in situ, and the DNA was analyzed under different electrophoretic conditions. Pulsed-field gel electrophoresis of DNA digested with infrequently cutting restriction enzymes showed that the genome of Leptospira interrogans serovar canicola is approximately 3.1 Mb, while that of the saprophytic L. biflexa serovar patoc I is 3.5 Mb. DNA forms of approximately 2,000 and 350 kb which were present in samples from L. interrogans serovars were not readily detected in nonpathogenic serovars. Three distinct populations, designated type alpha, beta, and gamma, of L. interrogans DNA molecules were further analyzed with two-dimensional gel electrophoresis. Evidence suggested that two of these DNA forms, type alpha and gamma, were linear structures. Pulsed-field gel electrophoresis has proven to be a valuable tool with which to size bacterial genomes and to take the first steps toward characterization of a form of leptospiral DNA which behaves as a linear molecule and which may be related to the virulence of L. interrogans. 相似文献
8.
9.
Prior studies have shown that pneumothorax is one of the more difficult entities to diagnose with digitized radiography. This study was designed to test whether increasing resolution from 1.25 to 2.5 line pairs per millimeter (lp/mm) and image processing (edge enhancement from unsharp masking) would increase accuracy and confidence in the diagnosis of pneumothorax, as well as normal cases and other forms of lung disease. Conventional radiographs were digitized with use of a laser reader and then reformatted as film hard copy. Eleven observers read 35 cases reformatted in three different ways (1.25 lp/mm, 2.5 lp/mm, 1.25 lp/mm unsharp mask). The images with finer resolution (2.5 lp/mm) and unsharp mask images were superior to those with coarser resolution (1.25 lp/mm) for the diagnosis of pneumothorax. There was no difference in diagnostic accuracy for normal patients. For abnormalities other than pneumothorax, the unsharp mask images were significantly worse. Confidence in the diagnosis of pneumothorax and other abnormalities was highest with the finest resolution (2.5 lp/mm). 相似文献
10.
The authors report the clinical and laboratory findings of a patient who had severe immune hemolytic anemia due to hydrochlorothiazide (HCTZ). In this case, the HCTZ antibody reacted not only with other thiazide and thiazide-like drugs, but also with a chemically unrelated diuretic, ethacrynic acid. These results indicate that HCTZ antibody activity is not restricted solely to the thiazides and imply that therapy with any of the reactive drugs would be contraindicated for this patient. The serologic screening for drug reactivity may be useful for selecting alternative therapy for patients with drug-induced immune hemolytic anemia. 相似文献