全文获取类型
收费全文 | 252177篇 |
免费 | 8451篇 |
国内免费 | 4228篇 |
专业分类
耳鼻咽喉 | 2050篇 |
儿科学 | 7934篇 |
妇产科学 | 3842篇 |
基础医学 | 24422篇 |
口腔科学 | 3124篇 |
临床医学 | 22000篇 |
内科学 | 41491篇 |
皮肤病学 | 2327篇 |
神经病学 | 19531篇 |
特种医学 | 12242篇 |
外国民族医学 | 22篇 |
外科学 | 35651篇 |
综合类 | 15937篇 |
现状与发展 | 17篇 |
一般理论 | 4篇 |
预防医学 | 24733篇 |
眼科学 | 4591篇 |
药学 | 18125篇 |
80篇 | |
中国医学 | 5485篇 |
肿瘤学 | 21248篇 |
出版年
2024年 | 245篇 |
2023年 | 1043篇 |
2022年 | 2627篇 |
2021年 | 3612篇 |
2020年 | 2746篇 |
2019年 | 2304篇 |
2018年 | 24095篇 |
2017年 | 19694篇 |
2016年 | 21714篇 |
2015年 | 4715篇 |
2014年 | 5614篇 |
2013年 | 5836篇 |
2012年 | 14233篇 |
2011年 | 28328篇 |
2010年 | 24246篇 |
2009年 | 16072篇 |
2008年 | 24660篇 |
2007年 | 26383篇 |
2006年 | 5157篇 |
2005年 | 6045篇 |
2004年 | 6159篇 |
2003年 | 6736篇 |
2002年 | 4516篇 |
2001年 | 1516篇 |
2000年 | 1396篇 |
1999年 | 894篇 |
1998年 | 589篇 |
1997年 | 631篇 |
1996年 | 367篇 |
1995年 | 359篇 |
1994年 | 326篇 |
1993年 | 196篇 |
1992年 | 189篇 |
1991年 | 226篇 |
1990年 | 225篇 |
1989年 | 145篇 |
1988年 | 110篇 |
1987年 | 84篇 |
1986年 | 60篇 |
1985年 | 54篇 |
1984年 | 43篇 |
1983年 | 35篇 |
1982年 | 34篇 |
1980年 | 49篇 |
1974年 | 28篇 |
1938年 | 60篇 |
1937年 | 30篇 |
1934年 | 30篇 |
1932年 | 56篇 |
1930年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
22.
A Well-Balanced Positivity-Preserving Quasi-Lagrange Moving Mesh DG Method for the Shallow Water Equations 下载免费PDF全文
A high-order, well-balanced, positivity-preserving quasi-Lagrange moving
mesh DG method is presented for the shallow water equations with non-flat bottom
topography. The well-balance property is crucial to the ability of a scheme to simulate perturbation waves over the lake-at-rest steady state such as waves on a lake or
tsunami waves in the deep ocean. The method combines a quasi-Lagrange moving
mesh DG method, a hydrostatic reconstruction technique, and a change of unknown
variables. The strategies in the use of slope limiting, positivity-preservation limiting,
and change of variables to ensure the well-balance and positivity-preserving properties are discussed. Compared to rezoning-type methods, the current method treats
mesh movement continuously in time and has the advantages that it does not need to
interpolate flow variables from the old mesh to the new one and places no constraint
for the choice of a update scheme for the bottom topography on the new mesh. A selection of one- and two-dimensional examples are presented to demonstrate the well-balance property, positivity preservation, and high-order accuracy of the method and
its ability to adapt the mesh according to features in the flow and bottom topography. 相似文献
23.
24.
25.
Konrad Matyja Anna Małachowska-Jutsz Anna K. Mazur Kazimierz Grabas 《Ecotoxicology (London, England)》2016,25(5):924-939
Dehydrogenase activity is frequently used to assess the general condition of microorganisms in soil and activated sludge. Many studies have investigated the inhibition of dehydrogenase activity by various compounds, including heavy metal ions. However, the time after which the measurements are carried out is often chosen arbitrarily. Thus, it can be difficult to estimate how the toxic effects of compounds vary during the reaction and when the maximum of the effect would be reached. Hence, the aim of this study was to create simple and useful mathematical model describing changes in dehydrogenase activity during exposure to substances that inactivate enzymes. Our model is based on the Lagergrens pseudo-first-order equation, the rate of chemical reactions, enzyme activity, and inactivation and was created to describe short-term changes in dehydrogenase activity. The main assumption of our model is that toxic substances cause irreversible inactivation of enzyme units. The model is able to predict the maximum direct toxic effect (MDTE) and the time to reach this maximum (TMDTE). In order to validate our model, we present two examples: inactivation of dehydrogenase in microorganisms in soil and activated sludge. The model was applied successfully for cadmium and copper ions. Our results indicate that the predicted MDTE and TMDTE are more appropriate than EC50 and IC50 for toxicity assessments, except for long exposure times. 相似文献
26.
27.
28.
Contraceptive use is an important strategy for the prevention of unwanted pregnancy and avoidance of induced abortion. Of all the contraception methods, emergency contraceptive (EC) offers the last chance to achieve this. However, few studies have documented the use of EC among young people in Ghana. This study explored knowledge and usage of EC as well as the factors associated with it among University of Cape Coast students. Data were obtained on the knowledge and usage of ECs among University of Cape Coast students in 2013. Logistic regression analysis was used to investigate the association between students’ socio-demographic characteristics and EC knowledge and use. More male students (72 %) than females (59 %) were sexually active. Fifty-seven percent of the respondents had ever heard of EC and 36 % had ever used EC. Although males were more likely to be sexually active, females were more likely to have knowledge of EC use compared to males. The study underscores the need to increase awareness regarding EC among University students in order to offer them the opportunity that EC provides if other forms of contraceptives are missed. 相似文献
29.
30.
Recent studies have reported an association between gastroesophageal reflux disease (GERD) and atrial fibrillation (AF). The objective of the present study was to evaluate whether AF is one of the risk factors for GERD occurrence.In this hospital-based, retrospective, case–control study, the patients were classified into 2 groups. The patients diagnosed with new AF were assigned to the AF group (n = 1612); those diagnosed without AF and GERD were assigned to the control group (n = 1612). The subjects in the control group were selected from outpatients of total healthcare center without a history of AF or GERD, and matched for age and gender. We evaluated the incidence of GERD and risk factors for GERD occurrence between the 2 groups.The number of patients experiencing occurrence of GERD during the follow-up period was significantly higher in the AF group than those in the control group, respectively (129 patients vs 98 subjects, P = 0.037). The incidence of GERD was significantly higher in the AF group than in the control group by Kaplan–Meier analysis with log-rank test (P = 0.008). The AF group''s adjusted hazard ratio of GERD occurrence against that of the control group was 1.37 (95% confidence interval [CI]: 1.16–1.57; P = 0.009) according to Cox''s proportional hazard model.The presence of AF appears to increase the incidence of GERD and may be considered a risk factor for the development of GERD. Further, large prospective and cohort studies will be required to better establish the correlation of GERD with AF. 相似文献