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   4926篇
  免费   264篇
  国内免费   12篇
耳鼻咽喉   42篇
儿科学   148篇
妇产科学   248篇
基础医学   718篇
口腔科学   108篇
临床医学   353篇
内科学   986篇
皮肤病学   70篇
神经病学   422篇
特种医学   135篇
外科学   683篇
综合类   83篇
一般理论   4篇
预防医学   435篇
眼科学   122篇
药学   299篇
中国医学   16篇
肿瘤学   330篇
  2023年   51篇
  2022年   92篇
  2021年   199篇
  2020年   92篇
  2019年   130篇
  2018年   158篇
  2017年   103篇
  2016年   118篇
  2015年   140篇
  2014年   176篇
  2013年   236篇
  2012年   368篇
  2011年   354篇
  2010年   184篇
  2009年   146篇
  2008年   286篇
  2007年   275篇
  2006年   265篇
  2005年   258篇
  2004年   237篇
  2003年   201篇
  2002年   204篇
  2001年   42篇
  2000年   51篇
  1999年   35篇
  1998年   44篇
  1997年   46篇
  1996年   25篇
  1995年   28篇
  1994年   41篇
  1993年   31篇
  1992年   33篇
  1991年   31篇
  1990年   33篇
  1989年   24篇
  1988年   32篇
  1987年   23篇
  1986年   25篇
  1985年   17篇
  1984年   20篇
  1983年   17篇
  1982年   24篇
  1981年   20篇
  1980年   21篇
  1979年   24篇
  1978年   17篇
  1976年   14篇
  1975年   14篇
  1970年   10篇
  1969年   10篇
排序方式: 共有5202条查询结果,搜索用时 0 毫秒
71.
Rectal endometrial stromal sarcoma arising in endometriosis   总被引:3,自引:0,他引:3  
PURPOSE: Endometriosis of the rectovaginal septum can harbor different types of secondary tumors that may involve the rectal wall and protrude into its lumen, thus making diagnosis difficult. Extrauterine low-grade endometrial stromal sarcoma may rarely arise in endometriosis. The purpose of this article was to present the third case of this association. METHOD: This was a clinicopathologic study. RESULTS: A 42-year-old female presented with abdominal pain and fever. Laparotomy revealed a large pelvic mass involving the rectovaginal septum and the colonic wall and which protruded into the lumen forming endoluminal polypoid masses. Concomitant peritoneal nodules and a metastatic paracolic lymph node were also found. Histopathologically, primary endometriotic foci were found in close relationship with an endometrial stromal sarcoma which invaded the rectal wall. The female genital tract had no endometriotic lesions. The patient was treated by surgery and subsequent chemotherapy and was alive and well 20 months later. CONCLUSIONS: Endometriosis and its possible malignant changes should be taken into account in the differential endoscopic diagnosis of rectal masses in females.  相似文献   
72.
Pneumatics is one of the few actuation principles that can be used in an MR environment, since it can produce high forces without affecting imaging quality. However, pneumatic control is challenging, due to the air high compliance and cylinders non-linearities. Furthermore, the system’s properties may change for each subject. Here, we present novel control strategies that adapt to the subject’s individual anatomy and needs while performing accurate periodic gait-like movements with an MRI compatible pneumatically driven robot. In subject-passive mode, an iterative learning controller (ILC) was implemented to reduce the system’s periodic disturbances. To allow the subjects to intend the task by themselves, a zero-force controller minimized the interaction forces between subject and robot. To assist patients who may be too weak, an assist-as-needed controller that adapts the assistance based on online measurement of the subject’s performance was designed. The controllers were experimentally tested. The ILC successfully learned to reduce the variability and tracking errors. The zero-force controller allowed subjects to step in a transparent environment. The assist-as-needed controller adapted the assistance based on individual needs, while still challenged the subjects to perform the task. The presented controllers can provide accurate pneumatic control in MR environments to allow assessments of brain activation.  相似文献   
73.
ObjectivesTo determine the influence of maturational status on the release of cardiac troponin T (cTnT) induced by a bout of 30 min, high-intensity, continuous exercise.DesignQuasi-experimental, cross-sectional study.MethodsSeventy male, young, well trained swimmers (age range 7–18 years, training experience 1–11 years) were classified by maturational stages: Tanner stage I (n = 14), II (n = 15), III (n = 15), IV (n = 13), and V (n = 13). Participants underwent a distance-trial of 30 min continuous swimming, and cTnT was measured before, immediately after and 3 h after exercise. Changes in cTnT over time were compared among groups, and associated with exercise load.ResultsBasal cTnT was higher in Tanner-V (3.8–8.1 ng/L) compared with I (1.55.5 ng/L, p < 0.001), II (1.54.5 ng/L, p < 0.001) and III (1.56.8 ng/L, p = 0.003), and in IV (1.5–6.3 ng/L) compared with II (p = 0.036). Maximal elevations of cTnT from baseline were notable (p < 0.001) and comparable among maturational stages (p = 0.078). The upper reference limit for myocardial injury was exceeded in 35.7% of the participants, without differences among groups (p = 0.18). Baseline cTnT correlated with participant characteristics, and maximal cTnT elevations from baseline with exercise internal load (%HRpeak, rs = 0.34, p =  0.003; %HRmean, rs = 0.28, p = 0.02).ConclusionsMaturational status influences positively absolute pre- and post-exercise cTnT but not its elevation after a bout of 30 min, high-intensity, continuous exercise.  相似文献   
74.
Mosquito samples were collected from rural and urban communities in three selected major towns in Southwestern Nigeria to determine the impact of urbanization on the diversity and abundance of Anopheles species associated with malaria transmission in human habitations. A total of ten Anopheles species were identified in the rural communities, while eight Anopheles species were identified in the urban communities. Out of the ten Anopheles species identified, only four species, Anopheles gambiae (Giles), Anopheles funestus (Giles), Anopheles moucheti (Evans), and Anopheles nili (Theobald), were established to be vectors of malaria occurring in greater than 50 % of the rural communities. Only A. gambiae occurred in all the urban communities, while the other three major vectors occurred in not more than 20 % of the urban communities. Margalef's and Shannon–Wiener indices showed that diversity and species richness were higher in the rural compared to the urban. Comprehensive information on malaria vector abundance and diversity in rapidly changing communities is an important tool in planning and implementing successful vector control programs.  相似文献   
75.
In vivo Raman spectroscopy has been utilized for the non-invasive, non-destructive assessment of tissue pathophysiology for a variety of applications largely through the use of fiber optic probes to interface with samples of interest. Fiber optic probes can be designed to optimize the collection of Raman-scattered photons from application-dependent depths, and this critical consideration should be addressed when planning a study. Herein we investigate four distinct probe geometries for sensitivity to superficial and deep signals through a Monte Carlo model that incorporates Raman scattering and fluorescence. Experimental validation using biological tissues was performed to accurately recapitulate in vivo scenarios. Testing in biological tissues agreed with modeled results and revealed that microlens designs had slightly enhanced performance at shallow depths (< 1 mm), whereas all of the beampath-modified designs yielded more signal from deep within tissue. Simulation based on fluence maps generated using ray-tracing in the absence of optical scattering had drastically different results as a function of depth for each probe compared to the biological simulation. The contrast in simulation results between the non-scattering and biological tissue phantoms underscores the importance of considering the optical properties of a given application when designing a fiber optic probe. The model presented here can be easily extended for optimization of entirely novel probe designs prior to fabrication, reducing time and cost while improving data quality.  相似文献   
76.
77.

Objective

To determine whether stratification of complexity models in congenital heart surgery (RACHS-1, Aristotle basic score and STS-EACTS mortality score) fit to our center and determine the best method of discriminating hospital mortality.

Methods

Surgical procedures in congenital heart diseases in patients under 18 years of age were allocated to the categories proposed by the stratification of complexity methods currently available. The outcome hospital mortality was calculated for each category from the three models. Statistical analysis was performed to verify whether the categories presented different mortalities. The discriminatory ability of the models was determined by calculating the area under the ROC curve and a comparison between the curves of the three models was performed.

Results

360 patients were allocated according to the three methods. There was a statistically significant difference between the mortality categories: RACHS-1 (1) - 1.3%, (2) - 11.4%, (3)-27.3%, (4) - 50 %, (P<0.001); Aristotle basic score (1) - 1.1%, (2) - 12.2%, (3) - 34%, (4) - 64.7%, (P<0.001); and STS-EACTS mortality score (1) - 5.5 %, (2) - 13.6%, (3) - 18.7%, (4) - 35.8%, (P<0.001). The three models had similar accuracy by calculating the area under the ROC curve: RACHS-1- 0.738; STS-EACTS-0.739; Aristotle- 0.766.

Conclusion

The three models of stratification of complexity currently available in the literature are useful with different mortalities between the proposed categories with similar discriminatory capacity for hospital mortality.  相似文献   
78.
79.
80.
Generation of morphological diversity remains a challenge for evolutionary biologists because it is unclear how an ultimately finite number of genes involved in initial pattern formation integrates with morphogenesis. Ideally, models used to search for the simplest developmental principles on how genes produce form should account for both developmental process and evolutionary change. Here we present a model reproducing the morphology of mammalian teeth by integrating experimental data on gene interactions and growth into a morphodynamic mechanism in which developing morphology has a causal role in patterning. The model predicts the course of tooth-shape development in different mammalian species and also reproduces key transitions in evolution. Furthermore, we reproduce the known expression patterns of several genes involved in tooth development and their dynamics over developmental time. Large morphological effects frequently can be achieved by small changes, according to this model, and similar morphologies can be produced by different changes. This finding may be consistent with why predicting the morphological outcomes of molecular experiments is challenging. Nevertheless, models incorporating morphology and gene activity show promise for linking genotypes to phenotypes.  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