全文获取类型
收费全文 | 8232篇 |
免费 | 453篇 |
国内免费 | 47篇 |
专业分类
耳鼻咽喉 | 104篇 |
儿科学 | 160篇 |
妇产科学 | 190篇 |
基础医学 | 1374篇 |
口腔科学 | 168篇 |
临床医学 | 494篇 |
内科学 | 1848篇 |
皮肤病学 | 224篇 |
神经病学 | 534篇 |
特种医学 | 303篇 |
外科学 | 1354篇 |
综合类 | 25篇 |
预防医学 | 303篇 |
眼科学 | 130篇 |
药学 | 532篇 |
中国医学 | 8篇 |
肿瘤学 | 981篇 |
出版年
2023年 | 45篇 |
2022年 | 78篇 |
2021年 | 131篇 |
2020年 | 77篇 |
2019年 | 107篇 |
2018年 | 120篇 |
2017年 | 106篇 |
2016年 | 150篇 |
2015年 | 147篇 |
2014年 | 170篇 |
2013年 | 219篇 |
2012年 | 358篇 |
2011年 | 385篇 |
2010年 | 203篇 |
2009年 | 200篇 |
2008年 | 364篇 |
2007年 | 399篇 |
2006年 | 409篇 |
2005年 | 354篇 |
2004年 | 378篇 |
2003年 | 372篇 |
2002年 | 358篇 |
2001年 | 332篇 |
2000年 | 344篇 |
1999年 | 301篇 |
1998年 | 118篇 |
1997年 | 94篇 |
1996年 | 61篇 |
1995年 | 54篇 |
1994年 | 39篇 |
1993年 | 46篇 |
1992年 | 192篇 |
1991年 | 156篇 |
1990年 | 184篇 |
1989年 | 195篇 |
1988年 | 199篇 |
1987年 | 161篇 |
1986年 | 147篇 |
1985年 | 132篇 |
1984年 | 106篇 |
1983年 | 83篇 |
1979年 | 56篇 |
1978年 | 38篇 |
1977年 | 43篇 |
1975年 | 34篇 |
1974年 | 42篇 |
1973年 | 50篇 |
1972年 | 43篇 |
1970年 | 47篇 |
1968年 | 36篇 |
排序方式: 共有8732条查询结果,搜索用时 62 毫秒
51.
Z J He K Nakayama 《Proceedings of the National Academy of Sciences of the United States of America》1995,92(24):11155-11159
Although attention plays a significant role in vision, its spatial deployment and spread in the third dimension is not well understood. In visual search experiments we show that we cannot easily focus attention across isodepth loci unless they are part of a well-formed surface with locally coplanar elements. Yet we can easily spread our attention selectively across well-formed surfaces that span an extreme range of stereoscopic depths. In cueing experiments, we show that this spread of attention is, in part, obligatory. Attentional selectivity is reduced when targets and distractors are coplanar with or rest on a common receding stereoscopic plane. We conclude that attention cannot be efficiently allocated to arbitrary depths and extents in space but is linked to and spreads automatically across perceived surfaces. 相似文献
52.
There exists a class of two-dimensional figures (including cumulative gaussian waveforms) whose contours have a limited range of orientations. These figures can appear as highly nonrigid if they undergo pure translation in the image plane. In the case of the cumulative gaussian waveform, it is the region around the inflection point that appears as nonrigid. Motivated by Hildreth's (1984) proposal, we made 5 predictions which were confirmed by the data: (0), rigidity of a figure can be dramatically increased if one attaches line terminators to the figure; (1), moving terminators "on" the figure increase rigidity far more than such terminators "off" the figure; (2) decreasing the velocity of the terminator decreases rigidity; (3) decreasing the distance between the terminator and the inflection point increases rigidity; (4) the effect of a moving terminator can be blocked by interposing a stationary terminator between it and a nonrigidly moving portion of the curve. 相似文献
53.
Occlusion and the solution to the aperture problem for motion 总被引:5,自引:0,他引:5
The "aperture problem" indicates that a local reading of the velocity of an oriented contour is inherently ambiguous, insufficient by itself to recover the velocity of image points. In Wallach's "barber pole" display consisting of moving diagonal lines within an elongated rectangular aperture, it has been suggested that the unambiguous motion of edge-terminators along the longer edges of the aperture propagates towards the motion-ambiguous center part of drifting stripes. This results in the perception of a surface moving in the direction of the longer axis of the aperture. By manipulating the stereoscopic disparity of a striped pattern relative to the aperture plane, we found that the disambiguating effects of terminators could be abolished if the striped pattern was in uncrossed disparity relative to the aperture plane. Also, the motion in 3 separate horizontally oriented, and vertically aligned apertures which would otherwise be seen as moving horizontally, was seen as "linked" together and moving vertically. This occurred only when the horizontally oriented segments separating these apertures were stereoscopically coded so that they appeared as occluders in front. These findings suggest that accidental or "extrinsic" terminators created by occluding edges are treated differently from real or "intrinsic" terminators, and that the real-world constraint of occlusion is thus implemented in the ambiguity-solving processes for motion. 相似文献
54.
Motoko Yanase Hideto Tanaka Teruo Nakayama 《European journal of applied physiology》1989,58(4):446-451
Summary In female rats, rectal temperature (T
re), tail vasomotor response, oxygen uptake
, and carbon dioxide production
were measured in proestrus and estrus stages during treadmill running at two different speeds at an ambient temperature (T
a) of 24° C. Experiments were performed at 2.00–6.00 a.m., when the difference inT
re was greatest between the two stages;T
re at rest in the estrus stage was 0.54° C higher than in the proestrus stage. In a mild warm environment, thresholdT
re for a rise in tail skin temperature (T
tail) was also higher in the estrus stage than in the proestrus stage. In contrast, no difference was seen in the thresholdT
re and steady stateT
re at the end of exercise between proestrus and estrus stages. These values were higher at the higher work intensity.
was also similar between the two stages, except in the second 5 min after the beginning of exercise, when
was greater andT
re rose more steeply in the proestrus stage. These data indicate that deep body temperature during exercise is regulated at a certain level depending on the work intensity and is not influenced by the estrus cycle.This study was supported in part by a Grant-in Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (Grant No. 62480114) 相似文献
55.
Aonuma M Saeki Y Akimoto T Nakayama Y Hattori C Yoshitake Y Nishikawa K Shibuya M Tanaka NG 《International journal of experimental pathology》1999,80(5):271-281
To elucidate the role of vascular endothelial growth factor (VEGF), an endothelial cell-specific mitogen, in tumour angiogenesis and malignant progression, an expression vector harboring human VEGF cDNA was stably transfected into three human cancer cell lines with poor VEGF productivity. Though their in vitro growth rate and intrinsic productivity of another angiogenic factor, basic fibroblast growth factor (bFGF), were not changed by transfection, those clones with higher VEGF production were endowed with tumorigenic and angiogenic potentials as follows: firstly, nontumorigenic, lung carcinoma QG90 cells having lower bFGF productivity acquired tumorigenicity as well as significant in vivo angiogenesis-inducing ability, secondly, tumorigenic colorectal carcinoma RPMI4788 cells having higher potency for bFGF production could form more vascularized solid tumour with faster growth rate and thirdly, oestrogen-dependent breast carcinoma MCF-7 cells, which did not produce detectable bFGF, acquired tumorigenicity even in the absence of oestrogen and the solid tumour growth rate was remarkably enhanced, accompanied with increased vascularization, in the presence of oestrogen. These results suggest that tumour progression closely depends on angiogenesis, and VEGF significantly contributes to malignant progression of a variety of tumour cells through its potent angiogenic activity, independent on the bFGF productivity of tumour cells. 相似文献
56.
Alipov G Nakayama T Ito M Kawai K Naito S Nakashima M Niino D Sekine I 《Histopathology》2005,47(2):202-208
AIMS: The high incidence of clinically diagnosed prostatic cancer is exceeded by the frequency of tumours detected at autopsy. The Ets-1 proto-oncogene is expressed by a variety of malignant and normal tissues. Therefore, in this study, expression of Ets-1 protein was investigated in 'latent' prostatic cancer detected at autopsy, compared with benign prostatic hyperplasia, normal prostatic tissues and clinical prostatic cancer. METHODS AND RESULTS: Using immunohistochemistry, we analysed Ets-1 expression in 95 prostatic specimens including 19 cases of latent prostatic carcinoma (LPC) and 55 cases of clinical prostatic carcinoma (CPC), 11 cases of benign prostatic hyperplasia (BPH) and 10 cases of normal prostate (NP). Differences in the incidence of LPC and CPC suggest different courses for the biological progression of prostatic cancer. There was a significant difference in the degree of Ets-1 expression in CPC and LPC (P < 0.05). Ets-1 was not expressed in BPH and NP, but in malignant cases (57 of 74; 77.0%) commonly demonstrated immunoreactivity in the tumour cells. In our study the expression of Ets-1 between benign and malignant, and well, moderately and poorly differentiated adenocarcinomas of prostatic cancer showed significant differences. The presence of Ets-1 mRNA was confirmed by in-situ hybridization in human prostatic tissues. CONCLUSION: Our results suggest that Ets-1 might play an important role in carcinogenesis and/or the progression of human prostatic carcinomas. 相似文献
57.
58.
Ebihara T Endo R Ishiguro N Nakayama T Sawada H Kikuta H 《Journal of clinical microbiology》2004,42(12):5944-5946
Human metapneumovirus (hMPV) is one of the major pathogens of respiratory illness. Reinfection with hMPV occurs frequently throughout life. We describe an infant who was infected with two different hMPV strains during a period of only 1 month. 相似文献
59.
Kiyoshi A Ishikawa T Hayashi K Iwatsuki Y Ishii K Nakayama K 《Pflügers Archiv : European journal of physiology》2003,447(2):142-149
Rhythmical contractions accompanied by an increase in cytosolic Ca2+ concentrations were produced in ring preparations of endothelium-denuded pulmonary arteries from monocrotaline-treated rats, but not in those from vehicle-treated rats, 2-3 h after a resting tension of 15 mN (150-180% of the initial wall length of the artery) was applied. The rhythmical contractions were abolished by nicardipine and ryanodine. Cyclopiazonic acid reduced the relaxation phase of the rhythmical contractions, finally leading to a sustained contraction. Similarly, apamin caused a sustained contraction, whereas charybdotoxin increased the amplitude of the rhythmical contractions. Glibenclamide had no apparent effects on them. Indomethacin and the prostaglandin H2/thromboxane A2 receptor antagonist SQ29548 abolished the rhythmical contractions and reduced the tension, but the thromboxane synthase inhibitor ozagrel had no effect. These results suggest that optimal stretch induces rhythmical contractions in the pulmonary arteries of monocrotaline-induced pulmonary hypertensive rats, to which both Ca2+ influx through voltage-operated Ca2+ channels and Ca2+ release from the endoplasmic reticulum seem to contribute. It is also suggested that small-conductance Ca(2+)-activated K+ channels participate in the relaxation phase of rhythmical contractions. Furthermore, prostaglandin H2 released from nonendothelial cells is likely to play a pivotal role in the induction of rhythmical contractions. 相似文献
60.
Osamu Sakai Yasuhide Nakayama Yasushi Nemoto Yoshihiro Okamoto Taiji Watanabe Keiichi Kanda Hitoshi Yaku 《Journal of artificial organs》2005,8(2):119-124
A novel sutureless vascular connecting system, an assembly with a delivery rod, an introducing sheath, and a connecting device, was developed for easy implantation of small-caliber vascular grafts less than 2 mm in internal diameter. A microporous stainless tube (length 2 mm, external diameter 1.6 mm, wall thickness 65 µm, pore diameter 400 µm, pore-to-pore distance 500 µm) was designed to serve as a connecting device. The feasibility of the system was tested using two types of preliminary animal experiments. One animal model consisted of graft implantation into the rat abdominal aorta (1.5 mm in diameter). The connecting device was inserted into the proximal and distal ends of the aorta through the introducing sheath by pushing the delivery rod with the connecting device placed over it. Subsequently, the aortic segments were inserted into both ends of model grafts made of segmented polyurethane (1.8 mm in internal diameter) and were fixed with banding silk threads from the exterior. The procedure was completed within 20 min without requiring specialized microsurgery techniques. Blood leakage and obstruction did not occur. The second model consisted of an end-to-end anastomosis between rabbit common carotid arteries (2 mm in diameter), which was performed within several minutes of blood flow interruption. Scanning electron microscopy demonstrated that the luminal surface of the device was fully covered with endothelial cells (ECs) after 1 week as a result of transluminal ingrowth of native ECs through the micropores in the device. This endothelialization may prevent early thrombus-induced occlusion. This simple and “easy-to-learn” technique will promote the development of small-caliber arterial grafts, and furthermore, it may have potential for clinical application. 相似文献