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   5332篇
  免费   356篇
  国内免费   13篇
耳鼻咽喉   24篇
儿科学   53篇
妇产科学   73篇
基础医学   884篇
口腔科学   136篇
临床医学   529篇
内科学   1070篇
皮肤病学   61篇
神经病学   650篇
特种医学   127篇
外科学   737篇
综合类   92篇
一般理论   14篇
预防医学   362篇
眼科学   49篇
药学   429篇
中国医学   6篇
肿瘤学   405篇
  2021年   75篇
  2020年   34篇
  2019年   80篇
  2018年   127篇
  2017年   89篇
  2016年   87篇
  2015年   94篇
  2014年   136篇
  2013年   223篇
  2012年   336篇
  2011年   357篇
  2010年   201篇
  2009年   200篇
  2008年   314篇
  2007年   321篇
  2006年   323篇
  2005年   332篇
  2004年   272篇
  2003年   267篇
  2002年   253篇
  2001年   98篇
  2000年   75篇
  1999年   79篇
  1998年   50篇
  1997年   60篇
  1996年   49篇
  1995年   45篇
  1994年   44篇
  1993年   46篇
  1992年   48篇
  1991年   49篇
  1990年   45篇
  1989年   45篇
  1988年   47篇
  1987年   58篇
  1986年   51篇
  1985年   51篇
  1984年   40篇
  1983年   32篇
  1981年   23篇
  1980年   26篇
  1979年   59篇
  1978年   42篇
  1977年   40篇
  1976年   26篇
  1973年   32篇
  1972年   30篇
  1971年   25篇
  1970年   27篇
  1969年   30篇
排序方式: 共有5701条查询结果,搜索用时 15 毫秒
1.
ABSTRACT

Purpose

To investigate the expression of IL-11 and its receptor IL-11Rα and to quantify density of CD163+ M2 macrophages in proliferative diabetic retinopathy (PDR).  相似文献   
2.
Zur erfolgreichen Therapie von komplexen Beckenbodenfunktionsstörungen wie Harninkontinenz und Genitalsenkung ist eine individuelle und abgestufte Diagnostik unverzichtbar. Eine Erfassung aller störenden Symptome mit Einschätzung des Leidensdrucks sowie eine urogynäkologische Untersuchung mit verschiedenen Funktionstests sind leicht durchführbar und erfordern keinen technischen Aufwand. Die Einschätzung des Ausmaßes der Beckenbodenschädigung und die Evaluation der Koordinations‑, Relaxations- und Kontraktionsfähigkeit der Levatormuskulatur geben Aufschluss über einen adäquaten Therapiestart. Die Durchführung einer Beckenbodensonographie sollte ebenfalls großzügig erfolgen. Die 2‑D-Sonographie liefert in der Inkontinenzdiagnostik vielfältige und ausreichende Informationen, wie Mobilität der Harnröhre und Lagekontrolle von eingelegten Bändern. Bei Prolapszuständen könnte der 3‑D-Ultraschall durch Detektion tieferer Muskelschichten wertvolle Zusatzbefunde aufzeigen, die eine noch bessere Planung des Operationsverfahrens und Aufklärung der Patientin ermöglichen. Die urodynamische Untersuchung und die Urethrozystoskopie sollten individuell bei Bedarf Einsatz finden.  相似文献   
3.
In this work, Electronic Speckle Pattern Interferometry (ESPI) is presented as a non-invasive tool to study drug transport in controlled release systems. ESPI is shown to be a feasible tool to measure drug film permeability via comparison with an ordinary diaphragm cell. A specially designed cuvette was used in the release study: the polymeric film separated the donor and the receiving chambers of the cuvette to create a diffusion cell with no mixing in the two chambers. Thus, the cuvette mimicked a coated system immersed in a stagnant bulk liquid. Concentration profile data were obtained for the two compartments. Using these data, it was possible to visually discriminate between a film subject only to diffusion and a film subject to diffusion as well as osmotic effects. Moreover, using the concentration profile data collected at different time intervals, it was possible to follow the film properties in terms of drug permeability, thus studying how drug permeability depended on drug concentration. Compared to other measuring techniques, ESPI offers the advantages that no invasive measurements are needed, and that no sampling and calibration are required. Furthermore, the permeability can be measured with no influence of mass transfer in the boundary layers.  相似文献   
4.
In the retina, amacrine cells modulate the transfer of information from bipolar to ganglion cells. The nature of the modulation depends on the synaptic input and the membrane properties of the cells. In the retina of white bass, we identified a class of bistratified, wide-field amacrine cell characterized by immunopositive labelling for GABA and calmodulin. In isolation, the cells presented resting membrane potentials averaging -69 mV although some cells settled at more depolarized values (-30 mV). Injection of depolarizing current pulses induced oscillatory membrane responses. When elicited from depolarized cells, the oscillations were short-lived (< 40 ms). For the most part, the oscillatory potentials of hyperpolarized cells remained unattenuated throughout the depolarizing pulse. The frequency of the oscillations increased logarithmically with mean membrane potential, ranging from 74 to 140 Hz. Cells exhibiting depolarized membrane potentials oscillated at twice that rate. When the membrane potential of these cells was hyperpolarized to -70 mV, the oscillations became unattenuated and slowed. We found the cells expressed voltage-gated sodium, potassium and calcium currents and calcium-dependent potassium currents. We demonstrate that the oscillatory potentials arose as a result of the interplay between calcium and potassium currents. The cells responded to local application of GABA and glycine, both of which modulate the oscillatory potentials. Glutamate and its analogues depolarized the cell and induced oscillatory potentials. Our results indicate that oscillatory responses of a type of wide-field amacrine cell are an intrinsic feature of the cell and not due to circuit properties.  相似文献   
5.
Atomic absorption spectrometry and x-ray fluorescence have been used to determine the lead content of metatarsal and tibia bone samples. For a range of bone lead levels from 6.5 to 83 micrograms g-1 of ashed bone there is no evidence of a systematic difference between the two techniques of more than 1 microgram g-1. There is, however, some evidence that random differences between the two in vitro analyses applied to the same bone sample are larger than can be accounted for by known measurement uncertainties. Variations in bone composition could account for these differences. Because the x-ray fluorescence technique is applied in an identical way to in vivo analysis, it is concluded that the uncertainties in in vivo measurements are small.  相似文献   
6.
The objective of this study was to assess the in vivo fate of poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA)-based polyplexes after intravenous administration into mice. Circulation kinetics and tissue distribution in terms of plasmid localization and transfection efficiency were assessed. To gain more insight into the observed biodistribution and gene expression profile, the interaction of pDMAEMA-based polyplexes with blood components (erythrocytes and albumin) was investigated in vitro. In the case of i.v. injection of positively charged polyplexes at a dose of 30 microg DNA most of the radioactivity was found in the lungs and the liver 60 min after injection. In the case of pDMAEMA/DNA polyplexes with a negative charge, uptake occurred mainly by the liver. Administration of positively charged complexes at a 30 microg DNA dose resulted in reporter gene expression primarily in the lungs. Injection of negatively charged complexes and naked plasmid did not result in luciferase expression in any of the organs examined. In vitro turbidity experiments showed the induction of a charge dependent aggregation process upon addition of albumin to the polyplexes pointing out to the involvement of aggregate formation in the dominant lung uptake of the positively charged polyplexes. Also, incubations of polyplexes after pre-incubation with a physiological concentration of albumin with washed erythrocytes confirmed that polyplexes induce the formation of extremely large structures. This paper underlines the need for the design of systems with reduced interaction with blood components to promote the delivery of DNA to target tissues outside the lungs.  相似文献   
7.
8.
Therapeutic drug monitoring generally focuses on the plasma compartment only. Differentiation between the total plasma concentration and the free fraction (plasma water) has been described for a number of limited drugs. Besides the plasma compartment, blood has also a cellular fraction which has by far the largest theoretical surface and volume for drug transport. It is with anti-cancer drugs that major progress has been made in the study of partition between the largest cellular blood compartment, i.e., erythrocytes, and the plasma compartment. The aim of the present review is to detail the progress made in predicting what a drug does in the body, i.e., pharmacodynamics including toxicity and plasma and/or red blood cell concentration monitoring. Furthermore, techniques generally used in anti-cancer drug monitoring are highlighted. Data for complex Bayesian statistical approaches and population kinetics studies are beyond the scope of this review, since this is generally limited to the plasma compartment only.  相似文献   
9.
Dysfunction of heart valve prostheses—mechanical as well as biological—is a common problem in cardiac surgery. The reasons for the valve failures are still not well understood. Biological valves especially have an unsatisfactory durability; degeneration and calcification very often lead to the failure of the valves. In our opinion, hidden defects present in the valve material prior to implantation of the valves is a plausible explanation for the dysfunction. Hitherto there has been no technique to detect these defects without destructing the specimen. Holographic interferometry proved to be applicable forin vitro evaluation of mechanical heart valve prostheses. In the present paper we describe application of this method to biological valves. Nine porcine bioprostheses and four fresh porcine aortic valves were investigated by means of holographic interferometry. In eight of nine bioprostheses, the results showed irregularities of the leaflet structure which depend on anomalies of the connective tissue of the leaflets of the valves. To make sure that these findings are not due to normal variations of the morphology, the investigations were carried out with fresh and unfixated porcine aortic valves. In the latter, no such anomalies of the structure were detected. The results obtained confirm the above hypothesis on the origin of the later valve dysfunction. Thus, holographic interferometry tests of bioprostheses prior to their implantation prevent the use of potentially dysfunctional valves.Presented at the 35th World Congress, International College of Angiology, Copenhagen, Denmark, July 1993  相似文献   
10.
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