全文获取类型
收费全文 | 1623篇 |
免费 | 75篇 |
国内免费 | 32篇 |
专业分类
耳鼻咽喉 | 7篇 |
儿科学 | 70篇 |
妇产科学 | 44篇 |
基础医学 | 166篇 |
口腔科学 | 34篇 |
临床医学 | 242篇 |
内科学 | 260篇 |
皮肤病学 | 20篇 |
神经病学 | 108篇 |
特种医学 | 71篇 |
外科学 | 156篇 |
综合类 | 66篇 |
一般理论 | 1篇 |
预防医学 | 118篇 |
眼科学 | 19篇 |
药学 | 184篇 |
中国医学 | 1篇 |
肿瘤学 | 163篇 |
出版年
2023年 | 14篇 |
2022年 | 18篇 |
2021年 | 39篇 |
2020年 | 28篇 |
2019年 | 42篇 |
2018年 | 32篇 |
2017年 | 19篇 |
2016年 | 35篇 |
2015年 | 33篇 |
2014年 | 63篇 |
2013年 | 76篇 |
2012年 | 108篇 |
2011年 | 106篇 |
2010年 | 73篇 |
2009年 | 69篇 |
2008年 | 80篇 |
2007年 | 79篇 |
2006年 | 83篇 |
2005年 | 94篇 |
2004年 | 69篇 |
2003年 | 49篇 |
2002年 | 38篇 |
2001年 | 25篇 |
2000年 | 14篇 |
1999年 | 20篇 |
1998年 | 36篇 |
1997年 | 42篇 |
1996年 | 34篇 |
1995年 | 26篇 |
1994年 | 19篇 |
1993年 | 21篇 |
1992年 | 16篇 |
1990年 | 7篇 |
1989年 | 16篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1978年 | 6篇 |
1941年 | 6篇 |
1940年 | 8篇 |
1938年 | 9篇 |
1937年 | 8篇 |
1936年 | 9篇 |
1934年 | 11篇 |
排序方式: 共有1730条查询结果,搜索用时 31 毫秒
1.
2.
3.
4.
5.
6.
Physiologic characterization of endothelin A and B receptor activity in the ovine fetal pulmonary circulation. 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《The Journal of clinical investigation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
To determine the potential contribution of endothelin (ET) to modulation of high pulmonary vascular resistance in the normal fetus, we studied the effects of BQ 123, a selective ET-A receptor antagonist, and sarafoxotoxin S6c (SFX), a selective ET-B receptor agonist, in 31 chronically prepared late gestation fetal lambs. Brief intrapulmonary infusions of BQ 123 (0.1-1.0 mcg/min for 10 min) caused sustained increases in left pulmonary artery flow (Qp) without changing main pulmonary artery (MPA) and aortic (Ao) pressures. In contrast, BQ 123 did not change vascular resistance in a regional systemic circulation (the fetal hindlimb). To determine whether big-endothelin-1 (big-ET-1)-induced pulmonary vasoconstriction is mediated by ET-A receptor stimulation, we studied the effects of big-ET-1 with or without pretreatment with BQ 123. BQ 123 (0.5 mcg/min for 10 min) blocked the rise in total pulmonary resistance caused by big-ET-1. CGS 27830 (100 mcg/min for 10 min), an ET-A and -B receptor antagonist, did not change basal tone but blocked big-ET-1-induced pulmonary vasoconstriction. Brief and prolonged intrapulmonary infusion of SFX (0.1 mcg/min for 10 min) increased Qp twofold without changing MPA or Ao pressures. Nitro-L-arginine (L-NA), a selective endothelium-derived nitric oxide (EDNO) antagonist, blocked vasodilation caused by BQ 123 and SFX. We conclude that: (a) BQ 123 causes sustained fetal pulmonary vasodilation, but did not change vascular resistance in the fetal hindlimb; (b) Big-ET-1-induced pulmonary vasoconstriction may be mediated through ET-A receptor stimulation; and (c) ET-B receptor stimulation causes pulmonary vasodilation through EDNO release. These findings support the hypothesis that endothelin may play a role in modulation of high basal pulmonary vascular resistance in the normal fetus. 相似文献
7.
The dose of (-)deprenyl (2.0 mg/kg/day, sc, for 3 weeks) which significantly increased activities of superoxide dismutase (SOD) and catalase in the striatum of young male rats significantly reduced these activities in young female rats but did not change the SOD activity in old female rats. In order to clarify these effects, different doses of the drug were continuously infused sc for 3 weeks in three groups of rats (young males and young and old females). When a 10-fold smaller dose (0.2 mg/kg/day) was applied in young female rats, activities of both SOD and catalase were significantly increased, while a higher dose of 0.5 mg/kg/day was ineffective and a lower dose of 0.1 mg/kg/day was substantially less effective. In old female rats, doses of both 0.5 and 1.0 mg/kg/day were equally effective in elevating activities of SOD and catalase, while a lower dose of 0.1 mg/kg/day was less effective. The activity of glutathione peroxidase (GSH Px) remained unchanged in all groups, except for a significant decrease in the activity of non-selenium-dependent GSH Px in both young and old female rats given the highest drug dose (2.0 mg/kg/day). Furthermore, activities of all three enzymes remained unchanged in the hippocampus in most groups. The results indicate that (-)deprenyl significantly increases activities of both SOD and catalase in the striatum, but not in hippocampus of rats, and that the optimal dose is very different depending on the sex and age of the animal. 相似文献
8.
Relative carriage rates of nuclear dehydrogenating clostridia in two populations of different colorectal cancer risk
下载免费PDF全文
![点击此处可从《Journal of clinical pathology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Carriage of nuclear dehydrogenating clostridia has been associated with colon cancer and implicated in its aetiology. This study has compared the carriage of these organisms in a British population at high risk for the development of colon cancer with a low risk Nigerian population. Clostridia were found in all of the stools from both populations. Nuclear dehydrogenating clostridia were only found in the stools of the British subjects (32%). These results support the suggestion that the carriage rate of nuclear dehydrogenating clostridia in a population is related to the risk of colon cancer. 相似文献
9.
Development of hatching blastocysts from immature human oocytes following in-vitro maturation and fertilization using a co-culture system 总被引:8,自引:0,他引:8
Hwu YM; Lee RK; Chen CP; Su JT; Chen YW; Lin SP 《Human reproduction (Oxford, England)》1998,13(7):1916-1921
Recently, in-vitro maturation (IVM) of immature human oocytes recovered
from non-stimulated follicles has been applied in the treatment of
infertility. However, in previous reports, very few embryos cultured in
conventional medium have reached the expanded blastocyst stage following
in-vitro maturation and fertilization (IVM/IVF). The objective of this
study was to investigate whether the developmental competence of human
embryos following IVM/IVF could be enhanced by the use of a human ampullary
cell co-culture system. Immature human oocytes were aspirated from small
follicles at Caesarean section and then cultured in medium containing human
menopausal gonadotrophin for 36 to 48 h, followed by insemination. Zygotes
were randomly cultured either in conventional culture medium alone or in
the co-culture system. Of 48 embryos cultured in conventional medium alone,
all arrested at the 2-16- cell stage on day 3 after insemination. Of 46
embryos cultured in the co-culture system, 26 embryos (56.5%) arrested at
the 2-16-cell stage. Six embryos (13%) developed to the morula stage.
Fourteen embryos (30.4%) developed to expanded blastocysts and two
blastocysts were hatching on day 7 after insemination. We conclude that
co-culture significantly enhances the development of blastocysts in embryos
resulting from IVM/IVF.
相似文献
10.
Limited information is available on the upregulation of endogenous antioxidant enzymes by means of administering various pharmaceuticals and/or chemicals. It has been reported that ursodeoxycholic acid (UDCA), a bile acid originally identified from black bear bile (a Chinese medicine, Yutan) increased glutathione S-transferase (GST) activities in mouse livers, resulting in a decrease in systemic lethal toxicity of orally challenged 1-2-dichloro-4-nitrobenzene (DCNB). Also, ursolic acid found in herbal medicines (e.g. leaves of loquat) was reported to increase catalase (CAT) activities in mouse liver. Interestingly, the chemical structures of these two compounds are surprisingly similar to each other, despite the difference in their original sources. These results suggest that in the future, more and more compounds will be found to have effects on increasing endogenous antioxidant enzyme activities. Deprenyl is a monoamine oxidase B inhibitor but also possesses many other different pharmacological activities. Among these various pharmacological effects of deprenyl, a possible causal relationship between two effects of deprenyl, namely the prolongation of the survival of animals and upregulation of antioxidant enzymes in selective brain regions, has been postulated by the authors. In at least four different animal species (rats, mice, hamsters and dogs), a significant prolongation of survival by chronic administration of the drug has been reported by different groups including that of the authors. This group has reported that repeated administration of the drug for 2-3 weeks can significantly increase activities of both types of superoxide dismutase (SODs) (Cu, Zn-, and Mn-SODs) as well as of CAT selectively in brain dopaminergic regions. Both effects are dose dependent but excessive dosages become less effective and even cause an adverse effect (i.e. a decrease in enzyme activities and shortening of life span). The parallelism of the dose-effect relationship between the two phenomena suggests that modification of SOD and CAT levels is one possible mechanism for deprenyl's ability to prolong the life span of animals. 相似文献