首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4273篇
  免费   350篇
  国内免费   12篇
耳鼻咽喉   67篇
儿科学   139篇
妇产科学   83篇
基础医学   614篇
口腔科学   58篇
临床医学   493篇
内科学   800篇
皮肤病学   77篇
神经病学   551篇
特种医学   169篇
外科学   577篇
综合类   14篇
预防医学   489篇
眼科学   29篇
药学   255篇
中国医学   12篇
肿瘤学   208篇
  2024年   7篇
  2023年   80篇
  2022年   99篇
  2021年   225篇
  2020年   132篇
  2019年   166篇
  2018年   236篇
  2017年   160篇
  2016年   164篇
  2015年   182篇
  2014年   227篇
  2013年   263篇
  2012年   414篇
  2011年   379篇
  2010年   181篇
  2009年   164篇
  2008年   254篇
  2007年   212篇
  2006年   231篇
  2005年   206篇
  2004年   142篇
  2003年   143篇
  2002年   107篇
  2001年   12篇
  2000年   12篇
  1999年   18篇
  1998年   9篇
  1997年   7篇
  1996年   17篇
  1995年   9篇
  1994年   8篇
  1993年   9篇
  1992年   4篇
  1985年   5篇
  1983年   5篇
  1981年   4篇
  1976年   4篇
  1942年   5篇
  1939年   3篇
  1932年   3篇
  1928年   5篇
  1926年   7篇
  1923年   8篇
  1922年   6篇
  1921年   5篇
  1913年   3篇
  1912年   6篇
  1911年   7篇
  1910年   3篇
  1874年   3篇
排序方式: 共有4635条查询结果,搜索用时 15 毫秒
51.
Objective Elevated plasma homocysteine has been implicated in vascular changes compatible with atherosis and endothelial dysfunction similar to the vascular changes of the placenta in preeclampsia. Previous reports have indicated an increased incidence of hyperohomocysteinemia in preeclamptic patients. The aim of this study was to examine the association of homocysteine levels and preeclampsia in our patients. Study design Prospective study of 28 preeclamptic patients that were matched with 26 normal controls of the same gestational age. Results The preeclamptic group had an increased incidence of cesarean sections (75%), of growth retarded fetuses (50%), intrauterine deaths (7%) and placental abruptions (7%). Mean levels of homocysteine were significantly elevated in the preeclamptic than in control group (11.11 vs. 6.40 μmol/l, P < 0.001). There were no differences between the groups regarding the levels of folic acid (11.12 vs. 9.73 ng/ml, P = 0.55) and vitamin B12 (295.76 vs. 356.15 pg/ml, P = 0.43). Conclusion It is concluded that in our study homocysteine levels are significantly elevated in patients with preeclampsia compared with control group, while no vitamin deficiencies were observed.  相似文献   
52.
1. It may be concluded that, under the conditions of the experiments and within the limits of accuracy of the method, the temporary multiplication of fibroblasts cultivated in the plasma of an adult animal is not due to the serum. It may be attributed to the presence of a small amount of embryonic juice within the tissue itself. 2. The indefinite multiplication of fibroblasts in a medium composed of adult plasma and of embryonic juice is due neither to the serum nor to the fibrin. It depends entirely on substances contained in the embryonic juice. 3. There is a definite relation between the rate of growth and the concentration of the embryonic juice in the medium.  相似文献   
53.
It may be concluded that the degree of dilution of the culture medium has a marked influence on the rate of growth of splenic tissue. The maximum acceleration was obtained in a medium composed of three volumes of normal plasma and two volumes of distilled water. The growth in this hypotonic plasma was very much larger than in normal plasma. On the contrary, the growth of the spleen in hypertonic plasma was always less than in normal plasma. In other experiments, we found that in diluted plasma there was also an acceleration of the growth of the skin, the heart, and the liver of chickens. The skin of adult frogs also grew more actively in this plasma. The optimum degree of dilution varied according to the nature of the tissues and to the species of the animals. While the plasma containing two fifths distilled water produced the largest growth of splenic tissue, a slightly less diluted medium was more favorable for the liver and the heart, and generally for the skin also. The action of hypertonic plasma varied also in a large measure. While the spleen did not grow at all in the medium containing 0.0124 and 0.0144 sodium chlorid, the skin, on the other hand, could stand a high concentration of the sodium chlorid. Even its growth was activated in media containing 0.0094 and 0.0124 sodium chlorid and was greater than with normal plasma. The spleen of kittens was very easily affected by the changes of the dilution of the plasma, while the skin of the frog presented its best growth in plasma containing one half distilled water. Marked variations in the sensitiveness of tissues to hypertonic and hypotonic media will probably be observed in animals of different species. From these experiments, three conclusions can be drawn: namely, that certain laws of growth, discovered by Loeb, in lower organisms are true also for higher organisms; that normal plasma is not the optimum medium for the growth of tissue; and that each tissue has probably its optimum medium. The growth of the spleen is, without doubt, considerably modified by the variations of the dilution and perhaps of the osmotic tension of the plasma. It is possible then that the influence of osmotic tension, discovered by Loeb, in the growth of certain organisms, is a general law applicable as well to higher forms of life— frogs, cats, and chickens—as to lower organisms—tubularia and sea-urchins. In placing tubularia in different dilutions of sea-water and distilled water, Loeb found that the greatest rate of regeneration was observed when two volumes of distilled water were added to three volumes of sea-water. But fertilized eggs of sea-urchins were more sensitive to the action of hypertonic plasma, and they all died in a dilution of sea-water with two fifths distilled water. If only one fifth distilled water was added to the sea-water they developed normally. We found that the cells of certain tissues of the chicken follow a similar rule, since the maximal growth of the spleen is obtained in plasma containing two fifths distilled water, while other tissues grow better in a less hypotonic medium. Normal plasma is certainly not the ideal medium for the growth of tissues, since slight modifications of the tension, the alkalinity, or the addition of certain inorganic salts to normal plasma, increase the rate of the growth of tissues.  相似文献   
54.
The thyroid gland of mammals can be cultivated outside the body. The proliferated elements consist of connective tissue and epithelial cells, the former predominating. The cells survive in cultures for two weeks or longer, which period can be increased by secondary and sometimes by tertiary cultivations. It is to be noted that the method of growing in vitro organs such as the thyroid gland may come to be used with advantage in the study of the substances concerned with the internal secretion of certain glands.  相似文献   
55.
56.
57.
The major therapeutic goal for immune thrombocytopenic purpura (ITP) is to restore normal platelet counts using drugs to promote platelet production or by interfering with mechanisms responsible for platelet destruction. Eighty percent of patients with ITP possess anti–integrin αIIbβ3 IgG autoantibodies that cause platelet opsonization and phagocytosis. The spleen is considered the primary site of autoantibody production by autoreactive B cells and platelet destruction. The immediate failure in approximately 50% of patients to recover a normal platelet count after anti-CD20 rituximab-mediated B cell depletion and splenectomy suggests that autoreactive, rituximab-resistant, IgG-secreting B cells (IgG-SCs) reside in other anatomical compartments. We analyzed more than 3,300 single IgG-SCs from spleen, bone marrow, and/or blood of 27 patients with ITP, revealing high interindividual variability in affinity for αIIbβ3, with variations over 3 logs. IgG-SC dissemination and range of affinities were, however, similar for each patient. Longitudinal analysis of autoreactive IgG-SCs upon treatment with the anti-CD38 mAb daratumumab demonstrated variable outcomes, from complete remission to failure with persistence of high-affinity anti–αIIbβ3 IgG-SCs in the bone marrow. This study demonstrates the existence and dissemination of high-affinity autoreactive plasma cells in multiple anatomical compartments of patients with ITP that may cause the failure of current therapies.  相似文献   
58.

Objective

To estimate the impact of global strategies, such as pooled procurement arrangements, third-party price negotiation and differential pricing, on reducing the price of antiretrovirals (ARVs), which currently hinders universal access to HIV/AIDS treatment.

Methods

We estimated the impact of global strategies to reduce ARV prices using data on 7253 procurement transactions (July 2002–October 2007) from databases hosted by WHO and the Global Fund to Fight AIDS, Tuberculosis and Malaria.

Findings

For 19 of 24 ARV dosage forms, we detected no association between price and volume purchased. For the other five ARVs, high-volume purchases were 4–21% less expensive than medium- or low-volume purchases. Nine of 13 generic ARVs were priced 6–36% lower when purchased under the Clinton Foundation HIV/AIDS Initiative (CHAI). Fifteen of 18 branded ARVs were priced 23–498% higher for differentially priced purchases compared with non-CHAI generic purchases. However, two branded, differentially priced ARVs were priced 63% and 73% lower, respectively, than generic non-CHAI equivalents.

Conclusion

Large purchase volumes did not necessarily result in lower ARV prices. Although current plans for pooled procurement will further increase purchase volumes, savings are uncertain and should be balanced against programmatic costs. Third-party negotiation by CHAI resulted in lower generic ARV prices. Generics were less expensive than differentially priced branded ARVs, except where little generic competition exists. Alternative strategies for reducing ARV prices, such as streamlining financial management systems, improving demand forecasting and removing barriers to generics, should be explored.  相似文献   
59.
From March 2020 through May 2021, nightlife venues were shut down and large gatherings were deemed illegal in New York City (NYC) due to COVID-19. This study sought to determine the extent of risky party attendance during the COVID-19 shutdown among people who attend electronic dance music parties in NYC. During the first four months that venues were permitted to reopen (June through September 2021), time–space sampling was used to survey adults (n = 278) about their party attendance during the first year of the shutdown (March 2020–March 2021). We examined prevalence and correlates of attendance and mask-wearing at such parties. A total of 43.9% attended private parties with more than 10 people, 27.3% attended nightclubs, and 20.5% attended other parties such as raves. Among those who attended any, 32.3% never wore a mask and 19.3% reported attending parties in which no one wore a mask. Past-year ecstasy use was associated with increased risk for attending private (aPR = 1.51, 95% CI: 1.00–2.28) or other parties (aPR = 2.75, 95% CI: 1.48–5.13), and use of 2C series drugs was associated with increased risk for attending nightclubs (aPR = 2.67, 95% CI: 1.24–5.77) or other parties (aPR = 2.50, 95% CI: 1.06–5.87). Attending >10 parties was associated with increased risk for never wearing a mask (aPR = 2.74, 95% CI: 1.11–6.75) and for no other attendees wearing masks (aPR = 4.22, 95% CI: 1.26–14.07). Illegal dance parties continued in NYC during the COVID-19 shutdown. Prevention and harm reduction efforts to mitigate risk of COVID-19 transmission during such shutdowns are sorely needed.  相似文献   
60.
By employing a common protocol and data from electronic health registries in Denmark, Navarre (Spain), Norway and Portugal, we estimated vaccine effectiveness (VE) against hospitalisation due to COVID-19 in individuals aged ≥ 65 years old, without previous documented infection, between October 2021 and March 2022. VE was higher in 65–79-year-olds compared with ≥ 80-year-olds and in those who received a booster compared with those who were primary vaccinated. VE remained high (ca 80%) between ≥ 12 and < 24 weeks after the first booster administration, and after Omicron became dominant.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号