全文获取类型
收费全文 | 9374篇 |
免费 | 1359篇 |
国内免费 | 242篇 |
专业分类
耳鼻咽喉 | 31篇 |
儿科学 | 83篇 |
妇产科学 | 23篇 |
基础医学 | 1030篇 |
口腔科学 | 167篇 |
临床医学 | 857篇 |
内科学 | 805篇 |
皮肤病学 | 51篇 |
神经病学 | 1452篇 |
特种医学 | 2502篇 |
外国民族医学 | 4篇 |
外科学 | 370篇 |
综合类 | 913篇 |
预防医学 | 391篇 |
眼科学 | 1108篇 |
药学 | 743篇 |
2篇 | |
中国医学 | 146篇 |
肿瘤学 | 297篇 |
出版年
2024年 | 17篇 |
2023年 | 126篇 |
2022年 | 197篇 |
2021年 | 432篇 |
2020年 | 396篇 |
2019年 | 448篇 |
2018年 | 409篇 |
2017年 | 529篇 |
2016年 | 500篇 |
2015年 | 487篇 |
2014年 | 709篇 |
2013年 | 716篇 |
2012年 | 623篇 |
2011年 | 651篇 |
2010年 | 491篇 |
2009年 | 492篇 |
2008年 | 464篇 |
2007年 | 374篇 |
2006年 | 362篇 |
2005年 | 316篇 |
2004年 | 270篇 |
2003年 | 229篇 |
2002年 | 202篇 |
2001年 | 173篇 |
2000年 | 129篇 |
1999年 | 129篇 |
1998年 | 85篇 |
1997年 | 104篇 |
1996年 | 85篇 |
1995年 | 104篇 |
1994年 | 88篇 |
1993年 | 57篇 |
1992年 | 52篇 |
1991年 | 45篇 |
1990年 | 47篇 |
1989年 | 54篇 |
1988年 | 36篇 |
1987年 | 28篇 |
1986年 | 33篇 |
1985年 | 45篇 |
1984年 | 47篇 |
1983年 | 25篇 |
1982年 | 40篇 |
1981年 | 22篇 |
1980年 | 29篇 |
1979年 | 11篇 |
1978年 | 22篇 |
1977年 | 14篇 |
1976年 | 12篇 |
1975年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
71.
William E. Crowe Nancy K. Wills 《Pflügers Archiv : European journal of physiology》1991,419(3-4):349-357
In this study, we report two developments for studies of ion transport in cultured epithelial cells. First, a convenient method is presented for measuring apparent cell height using fluorescent microbeads as high-contrast landmarks of the apical and basal cell surfaces. The apparent cell height is then used as an indicator to monitor the time course of changes in cell volume in response to osmotic perturbations. Second, an Ussing-type chamber design for the inverted fluorescence microscope is presented, which allows determination of transepithelial electrical properties. Using these two methods, we obtained simultaneous measurements of cell height and transepithelial electrical parameters for cultured renal (A6) epithelium. Cell height was measured by alternately focusing the microscope between microbeads marking the apical and basal surfaces. The distance between these two surfaces was measured electrically from the voltage output of a potentiometer that was mechanically coupled to the fine-focusing knob of the microscope. Following decreases in the bathing solution osmolality, the cell height and transepithelial Na+ transport rate (measured as short-circuit current, I
SC) increased. The increase in cell height preceded changes in I
SC by several minutes, suggesting a lack of direct linkage between changes in cell volume and transepithelial Na+ transport. Both the fluorescent microbead cell height method and the Ussing-type chamber can be used in conjunction with patch-clamp techniques, intracellular microelectrode impalements, or fluorescent probes of intracellular composition. Therefore, this system may be advantageous for studies of epithelial cell volume and channel regulation. 相似文献
72.
James W. Verbsky Mary K. Hintermeyer Pippa M. Simpson Mingen Feng Jody Barbeau Nagarjun Rao Carlyne D. Cool Luis A. Sosa-Lozano Dhiraj Baruah Erin Hammelev Alyssa Busalacchi Amy Rymaszewski Jeff Woodliff Shaoying Chen Mary Bausch-Jurken John M. Routes 《The Journal of allergy and clinical immunology》2021,147(2):704-712.e17
73.
74.
Meng S Qiao M Foniok T Tuor UI 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2005,166(1):56-60
We hypothesized that the cerebral injury produced by hypoxia-ischemia (HI) in neonatal rats would differ in white compared with gray matter as detected histologically or with magnetic resonance (MR) imaging methods. Maps of T2 and the apparent diffusion coefficient (ADC) of water were acquired in 1-week-old rats at times prior to cerebral HI (right carotid artery occlusion plus 1.5 h of hypoxia), within the last 5–10 min of HI, and 1 h or 24 h after HI. Near the end of HI, ADC decreased and T2 increased in both cortical gray and subcortical white matter within the cingulum of the HI hemisphere. One hour after HI, ADC partially recovered, but T2 remained increased and then increased further by 24 h post-HI. In contrast to the similar MR responses in white and gray matter, histological evidence for irreversible cell damage occurred in white matter earlier than in gray matter within the HI hemisphere. At 1 h post-HI, rarefied or disrupted nerve fibers and an increase in TUNEL-positive cells were observed within white matter in the cingulum, whereas neurons within the cortical gray matter appeared normal. By 24 h post-HI, damage was apparent in both white and gray matter. Thus, MR imaging detected acute tissue edema following cerebral HI in both gray and white matter but did not distinguish between the early irreversible tissue injury detected histologically in white but not gray matter in this rather severe model of neonatal encephalopathy. 相似文献
75.
Churat Tiyapiboonchaiya Jennifer M. Pringle Douglas R. MacFarlane Maria Forsyth Jiazeng Sun 《Macromolecular chemistry and physics.》2003,204(17):2147-2154
Novel polymer electrolyte materials based on a polyelectrolyte‐in‐ionic‐liquid principle are described. A combination of a lithium 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPSLi) and N,N′‐dimethylacrylamide (DMMA) are miscible with the ionic liquid, 1‐ethyl‐3‐methylimidazolium dicyanamide (EMIDCA). EMIDCA has remarkably high conductivity (≥ 2 · 10?2 S · cm?1) at room temperature and acts as a good solvating medium for the polyelectrolyte. At compositions of AMPSLi less than or equal to 75 mol‐% in the copolymer (P(AMPSLi‐co‐DMAA)), the polyelectrolytes in EMIDCA are homogeneous, flexible elastomeric gel materials at 10 ? 15 wt.‐% of total polyelectrolyte. Conductivities higher than 8 · 10?3 S · cm?1 at 30 °C have been achieved. The effects of the monomer composition, polyelectrolyte concentration, temperature and lithium concentration on the ionic conductivity have been studied using thermal and conductivity analysis, and pulsed field gradient nuclear magnetic resonance techniques.
76.
T. GROTMOL J. T. RDNES T. BUANES G. CHRISTENSEN T. LANDSVERK 《Acta physiologica (Oxford, England)》1993,147(4):417-429
The aim of this study was to test whether atrial natriuretic factor (ANF) exerts any effect on human intestinal ion transport, and the porcine intestine was used as a positive control of ANF's effects. Tissues from human proximal (n = 6) and distal (n = 6) colons, and from distal ileum (n = 6) were mounted in Ussing chambers, and short circuit current (Isc) was measured subsequent to serosal application of ANF (10--6 m), 8–Br-cyclic guanosine monophosphate (8–Br-cGMP) (10--4 m), and theophylline (10--2 m). ANF did not affect Isc whereas 8–Br-cGMP increased Isc by 28 (8–53), 16 (3–36), and 16 (5–41) μA cm-2 in the distal colon (DC), proximal colon (PC) and distal ileum (DI), respectively. Likewise, transepithelial potential difference (PD) became more negative by 5.0 (0.6–8.9), 2.5 (0.4–4.0) and 0.9 (0.3–2.3) mV in DC, PC, and DI, respectively, subsequent to addition of 8–Br-cGMP. Isc and PD were further increased by theophylline. Additional radio-isotope flux studies in human colon revealed that ANF did not affect electroneutral sodium and chloride transport either. For comparison, ANF (10--6 m) was administered to large intestinal tissues from young pigs in which ANF induced a significant increase in Isc which was comparable to the 8–Br-cGMP response in humans. The porcine Isc response was partly inhibited by chloride-free solution on the serosal side, by serosal application of bumetanide (10--4 m) and BaCl2 (10--3 m), and mucosal application of the chloride-channel blocker diphenylamine-2–carboxylate (DPC) (10--3 m). Mucosal amiloride (10--5 m) pre-treatment reduced baseline Isc but did not affect the porcine intestinal Isc response to ANF. In vitro radio-autography demonstrated specific binding sites for ANF in porcine distal colon, whereas no apparent labelling was observed in human distal colon. These findings suggest that the lack of effect of ANF on sodium and chloride transport in human distal ileum and colon is probably due to lack of ANF receptors. In the porcine intestine, however, the IS0 response induced by ANF seems to involve stimulation of electrogenic chloride secretion, whereas electrogenic sodium absorption seems unaffected. 相似文献
77.
Enrique Hilario Emilia Rodeño Josu Simón Francisco J. Alvarez Salvador F. Aliño 《Virchows Archiv : an international journal of pathology》1992,421(6):485-490
Summary The growth and vascularization patterns of B16 melanoma colonies in the liver and lungs were measured and compared by histological techniques and dye diffusion patterns after injection of the fluorochrome Hoechst 33342. In the liver, the fluorescent pattern of dye diffusion revealed that uninodular tumours measuring up to 146 n in diameter were not functionally vascularized. However, when the nodules fused to give rise to multinodular tumours measuring between 256 and 366 n in diameter, a reticular dye diffusion pattern revealed functional tumour vascularization. In the lungs, subpleural, parenchymal and peritubular (i.e. surrounding blood vessels and airways) tumours were observed. The two former classes were vascularized down to thicknesses and diameters of 49 and 24 m respectively. In contrast, dye diffusion was never seen in peritubular tumour cuffs up to 609 m in thickness. The results indicate differences in vascularization patterns in B16 tumours in the liver and lungs, and differences between tumours growing in different sites within the lungs. If these results are applicable to metastases in these two organs, they indicate potential diffusion-mediated resistance to chemotherapy, and potential hypoxia-mediated resistance to radiotherapy of both metastases and micrometastases. 相似文献
78.
Peter Knoppien 《Behavior genetics》1987,17(4):409-425
Virgin males (or females) of some species ofDrosophila, when stored singly, are known to be superior in mating to males (or females) stored in groups. This may create a spurious rare-male effect on some occasions. When no account is taken of this storage effect in an experimental setup designed to show rare-male mating advantage, bias in favor of a raremale effect may result. It is shown that merely by storing the rare males singly and the common males in groups, with males not differing in any other respect, a very strong spurious rare-male effect can be produced. Similarly, it is shown that a spurious rare-female effect is possible too. It is proposed that the very strong rare-male effect for pepperment scent as found by Dal Molin [(1979).Am. Nat.
113:951–954] is merely a result of such a bias. The relevance for natural populations of the mating advantage associated with the single housing condition is discussed. In the experiments designed to show a spurious rare-male effect, mating chambers of two different sizes were used. It is shown that sexual selection is more severe in the small chambers, for both males and females. 相似文献
79.
80.
The parameters that characterize the intricate water diffusion in tumors may serve to reveal their distinct pathology. Specifically, the application of diffusion magnetic resonance imaging (MRI) can aid in characterizing breast cancer, as well as monitoring response to therapy. We present here a non-invasive, quantitative MRI investigation, at high spatial resolution, of water diffusion in hormonal dependent MCF7 breast tumors implanted orthotopically in immunodeficient mice. Distinctive MRI protocols were designed in this study, utilizing a broad range of diffusion times and diffusion gradient strengths. Application of these protocols allowed water diffusion in the tissue extracellular and intracellular compartments to be distinguished, and the effect of restricted diffusion and water exchange on the water diffusion in these compartments to be evaluated. Pixel-by-pixel analysis yielded parametric maps of the estimated volume fraction and apparent diffusion coefficient of each compartment. The diffusion of the water in the extracellular microenvironment was approximately two fold slower than that of free water, and in the intracellular compartment was about one order of magnitude slower than that of free water and demonstrated restriction of water diffusion at long diffusion times. Mapping of the water fraction in each compartment was further employed to monitor changes during tumor progression and to assess tumor response to hormonal manipulation with a new antiestrogenic drug, tamoxifen methiodide (TMI). It was found that, in parallel to the growth arrest by this drug, the volume fraction of the slowly diffusing water increased, suggesting a TMI-induced cell swelling. This study can serve as a basis for extending diffusion breast MRI in the clinical setting. 相似文献