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   1502篇
  免费   71篇
  国内免费   6篇
耳鼻咽喉   25篇
儿科学   34篇
妇产科学   29篇
基础医学   191篇
口腔科学   14篇
临床医学   192篇
内科学   392篇
皮肤病学   6篇
神经病学   85篇
特种医学   30篇
外科学   173篇
综合类   13篇
一般理论   1篇
预防医学   92篇
眼科学   20篇
药学   189篇
肿瘤学   93篇
  2023年   10篇
  2022年   49篇
  2021年   92篇
  2020年   31篇
  2019年   42篇
  2018年   41篇
  2017年   34篇
  2016年   37篇
  2015年   38篇
  2014年   47篇
  2013年   62篇
  2012年   88篇
  2011年   107篇
  2010年   54篇
  2009年   50篇
  2008年   65篇
  2007年   67篇
  2006年   80篇
  2005年   79篇
  2004年   75篇
  2003年   59篇
  2002年   56篇
  2001年   34篇
  2000年   40篇
  1999年   27篇
  1998年   12篇
  1997年   10篇
  1996年   3篇
  1995年   6篇
  1994年   4篇
  1993年   8篇
  1992年   5篇
  1991年   15篇
  1990年   26篇
  1989年   17篇
  1988年   17篇
  1987年   13篇
  1986年   8篇
  1985年   7篇
  1984年   11篇
  1983年   8篇
  1982年   6篇
  1981年   5篇
  1980年   4篇
  1979年   4篇
  1978年   3篇
  1977年   6篇
  1973年   3篇
  1969年   2篇
  1967年   2篇
排序方式: 共有1579条查询结果,搜索用时 15 毫秒
11.
12.
This study was designed to evaluate the potential effects of acute and chronic daily oral doses of lansoprazole (60 mg) on the disposition of antipyrine, an almost completely metabolized low hepatic extraction compound, and indocyanine green, a hepatically secreted compound with high extraction ratio. The study utilized a randomized, placebo-controlled, double-blind, two-period crossover design. Sixteen of 18 subjects completed all phases of the study. Both antipyrine (10 mg kg(minus sign1)) and indocyanine green (0.5 mg kg(minus sign1)) were administered as single intravenous bolus doses on Days 1 and 7 of lansoprazole or placebo dosing. Acute exposure to lansoprazole had no statistically significant effects on the plasma pharmacokinetics of indocyanine green or antipyrine. After the seventh dose, there was a small but statistically significant reductions in indocyanine green total body clearance (CL), and elimination rate constant of 10.6% and 8%, respectively. Additionally, a small statistically significant reduction (8.6%) in antipyrine volume of distribution was detected. No other plasma antipyrine pharmacokinetic parameters were changed with concomitant lansoprazole administration. About a 12% increase in the recovery of one of the major antipyrine urine metabolites (NORA) was detected. Overall, this study demonstrates little or no effect of lansoprazole on the pharmacokinetics of antipyrine and indocyanine green.  相似文献   
13.
CONTEXT: Given the level of unintended pregnancy in the United States, it is somewhat surprising that hormonal implants and injectables-methods that are long-acting, reversible, highly effective and convenient--have not attained the popularity enjoyed by other medical methods. Knowing the reasons why women have so far spurned these methods might lead to the design and implementation of interventions and targeted social marketing to promote their use. METHODS: Data from the 1993 and 1995 rounds of the National Survey of Women are used to examine the reasons women gave for not having used the implant or injectables, whether they intended to use these methods and how their attitudes toward them may influence their decision to use such methods in the future. Logistic regression models were used to identify the social and demographic characteristics that influence women's decisions not to use these methods. RESULTS: Fewer than 2% of women who were at risk of an unintended pregnancy in 1995 were using the implant, and under 3% were using the injectable. Women gave three major reasons for not using either of these methods: lack of knowledge; fear of side effects or health hazards; and satisfaction with the method they were currently using. Age, education, marital status, parity and current contraceptive method strongly predicted fear of side effects, lack of knowledge and satisfaction with the current method as reasons for not using the implant or the injectable. For example, women aged 30 or older and those with a college education were half as likely as younger women and those with no college education to mention fear of side effects as their main reason for not using the implant. Likewise, single women, women with one or more children and those using a barrier method were 2-3 times as likely as married women, childless women and those using a medical method to attribute nonuse to the implant's side effects. Few women said they intended to use these methods in the next 12 months: 5% for the implant and 10% for the injectable. Single women, women with no college education, women with children, women wanting to have a child (or another child) and women with positive attitudes toward the effect of using an injectable were significantly more likely to say they intended to use the injectable. Nevertheless, substantial proportions of women reported quite negative attitudes about these methods. CONCLUSIONS: The low prevalence of use and the low level of use intention for the implant and for injectables raise questions about the promise for the future of these methods. Each method seems to appeal to certain subgroups of women, however. Thus, if proper interventions and social marketing are targeted to such groups, they may be disabused of misperceptions regarding these methods and possibly become more willing to try them.  相似文献   
14.
The effectiveness of protective coatings based on 3-(2,2,3,3,4,4,5,5-octafluoropentyloxy)propyltriethoxysilane (OFTES) in protecting concrete surfaces against water was tested. For the synthesis of OFTES, 2,2,3,3,4,4,5,5-octafluoropentanol, which is a by-product in the synthesis of poly(tetrafluoroethylene), was used. The proposed silane is a cheaper alternative to the fluorinated organosilicon compounds currently used. The coatings were deposited by the sol-gel method. As a result of the creation of chemical bonds between the concrete surface and the silane, a coating was created that permanently increases the hydrophobicity of the concrete. Fluorine chains attached to silicon atoms are an effective barrier that prevents access to water and limits its impact on the concrete surface. As a result of the proposed silanization, the concrete surface obtained a hydrophobic character at contact angles of up to 126°, and the water absorption of the concrete decreased by up to 96%.  相似文献   
15.
Material as well as process variations in the composites industry are reasons to develop methods for in-line monitoring, which would increase reproducibility of the manufacturing process and the final composite products. Fiber Bragg Gratings (FBGs) have shown to be useful for monitoring liquid-composite molding processes, e.g., in terms of online gel point detection. Existing works however, focus on in-plane strain measurements while out-of-plane residual strain prevails. In order to measure out-of-plane strain, FBG inscribed in highly birefringent fiber (HB FBG) can be used. The purpose of this research is the cure stage detection with (a) FBG inscribed in single mode and (b) FBG inscribed in highly-birefringent side-hole fiber in comparison to the reference gel point detected with an in-mold DC sensor. Results reveal that the curing process is better traceable with HB FBG than with regular FBG. Thus, the use of HB FBG can be a good method for the gel point estimation in the RTM process.  相似文献   
16.
This paper presents a photogrammetry-based volume measurement framework for the particle density estimation of Lightweight expanded clay aggregate (LECA). The results are compared with computed tomography (CT) and Archimedes’ method measurements. All of the steps required in order to apply the proposed approach are explained. Next, we discuss how the interpretation of open pores affects the results of volume measurements. We propose to process the shapes obtained from different methods by applying an Ambient Occlusion algorithm with the same threshold, t = 0.175. The difference between the CT and SfM methods is less than 0.006 g/cm3, proving that the photogrammetry-based approach is accurate enough. The Archimedes’ method significantly overestimates the density of the particles. Nevertheless, its accuracy is acceptable for most engineering purposes. Additionally, we evaluate the accuracy of shape reconstruction (in terms of the Hausdorff distance). For 95% of the grain’s surface, the maximum error is between 0.073 mm and 0.129 mm (depending on the grain shape). The presented approach is helpful for measuring the particle density of porous aggregates. The proposed methodology can be utilized in order to estimate intergranular porosity, which is valuable information for the calibration of DEM models.  相似文献   
17.
The present paper investigates the effects of simultaneous mechanical foaming using water and fluxing with a bio-derived agent on the properties of three distinct asphalt binders: 50/70 paving-grade bitumen, 45/80–55 polymer-modified bitumen, and 45/80–80 highly modified asphalt binder. The testing involved classical tests for assessing binder consistency (penetration at 25 °C, ring and ball softening point, Fraass breaking point, and dynamic viscosity) as well as performance tests (high and low Superpave critical temperatures and multiple stress creep recovery). The tests included assessment directly after asphalt binder foaming and were repeated after a 14-day period. It was shown that bitumen foaming had only short-term effects on the asphalt binders, which did not persist in the repeated tests after 14 days. The fluxing agent that was utilized caused significant changes in the consistency of all asphalt binders. The changes in the performance characteristics of the 50/70 and 45/80–55 binders were severe and amounted to a significant decrease in high-temperature performance of these binders. On the other hand, an improvement in all performance characteristics in the case of the 45/80–80 asphalt binder was observed as a result of the applied processes, particularly when measured 14 days after foaming. This study shows that the simultaneous use of foaming and the fluxing additive decreased the dynamic viscosity of the 45/80–80 binder, while improving its properties relating the pavement performance.  相似文献   
18.
19.
20.
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