全文获取类型
收费全文 | 4451篇 |
免费 | 241篇 |
国内免费 | 160篇 |
专业分类
耳鼻咽喉 | 33篇 |
儿科学 | 49篇 |
妇产科学 | 70篇 |
基础医学 | 1150篇 |
口腔科学 | 96篇 |
临床医学 | 264篇 |
内科学 | 690篇 |
皮肤病学 | 73篇 |
神经病学 | 490篇 |
特种医学 | 62篇 |
外科学 | 648篇 |
综合类 | 279篇 |
预防医学 | 134篇 |
眼科学 | 61篇 |
药学 | 468篇 |
2篇 | |
中国医学 | 68篇 |
肿瘤学 | 215篇 |
出版年
2023年 | 102篇 |
2022年 | 147篇 |
2021年 | 208篇 |
2020年 | 185篇 |
2019年 | 110篇 |
2018年 | 133篇 |
2017年 | 114篇 |
2016年 | 120篇 |
2015年 | 138篇 |
2014年 | 215篇 |
2013年 | 240篇 |
2012年 | 203篇 |
2011年 | 232篇 |
2010年 | 186篇 |
2009年 | 225篇 |
2008年 | 227篇 |
2007年 | 205篇 |
2006年 | 187篇 |
2005年 | 130篇 |
2004年 | 149篇 |
2003年 | 121篇 |
2002年 | 107篇 |
2001年 | 74篇 |
2000年 | 78篇 |
1999年 | 70篇 |
1998年 | 87篇 |
1997年 | 67篇 |
1996年 | 53篇 |
1995年 | 53篇 |
1994年 | 54篇 |
1993年 | 49篇 |
1992年 | 52篇 |
1991年 | 46篇 |
1990年 | 45篇 |
1989年 | 46篇 |
1988年 | 42篇 |
1987年 | 26篇 |
1986年 | 20篇 |
1985年 | 32篇 |
1984年 | 39篇 |
1983年 | 21篇 |
1982年 | 31篇 |
1981年 | 27篇 |
1980年 | 28篇 |
1979年 | 19篇 |
1978年 | 21篇 |
1977年 | 12篇 |
1976年 | 24篇 |
1973年 | 9篇 |
1972年 | 9篇 |
排序方式: 共有4852条查询结果,搜索用时 31 毫秒
71.
Activity-related changes in extracellular K+ concentration ([K+]e), pH (pHe) and extracellular volume were studied by means ofion-selective microelectrodes in the adult rat spinal cord in vivo and in neonatal rat spinal cords isolated from pups 3–14 days of age (P3–P14). Concomitantly with the ionic changes, the extracellular space (ECS) volume fraction (α), ECS tortuosity (λ) and non-specific uptake (k′), three parameters affecting the diffusion of substances in nervous tissue, were studied in the rat spinal cord gray matter. In adult rats, repetitive electrical nerve stimulation (10–100 Hz) elicited increases in [K+]e of about 2.0–3.5 mm, followed by a post-stimulation K+-undershoot and triphasic alkaline-acid-alkaline changes in pHe with a dominating acid shift. The ECS volume in the adult rat occupies about 20% of the tissue, α = 0.20 ± 0.003, λ = 1.62 ± 0.02 and k′ = 4.6 ± 0.4 × 10−3s−1 (n = 39). In contrast, in pups at P3–P6, the [K+]e increased by as much as 6.5 mm at a stimulation frequency of 10 Hz, i.e. K+ ceiling level was elevated, and there was a dominating alkaline shift. An increase in [K+]e as large as 1.3–2.5 mm accompanied by an alkaline shift was evoked by a single electrical stimulus. The K+ ceiling level and alkaline shifts decreased with age, while an acid shift, which was preceded by a small initial alkaline shift, appeared in the second postnatal week. In pups at P1–P2, the spinal cord was X-irradiated to block gliogenesis. The typical decrease in [K+]e ceiling level and the development of the acid shift in pHe at P10–P14 were blocked by X-irradiation. Concomitantly, continuous development of glial fibrillary acidic protein positive reaction was disrupted and densely stained astrocytes in gray matter at P10–P14 revealed astrogliosis.The alkaline, but not the acid, shift was blocked by Mg2+ and picrotoxin (10−6m). Acetazolamide enhanced the alkaline but blocked the acid shift. Furthermore, the acid shift was blocked, and the alkaline shift enhanced, by Ba2+, amiloride and SITS. Application of glutamate or gamma-aminobutyric acid evoked an alkaline shift in the pHe baseline at P3–P14 as well as after X-irradiation. The results suggest that the activity-related acid shifts in pHe are related to membrane transport processes in mature glia, while the alkaline shifts have a postsynaptic origin and are due to activation of ligand-gated ion channels.At P4–P6, the ECS volume was almost double that in adult rats, α = 0.37 ± 0.01 (n = 17), the ECS tortuosity was significantly higher, λ = 1.78 ± 0.02, while the non-specific uptake was not significantly different, k′ = 3.61 ± 0.56 × 10−3 s−1. The α gradually decreased to about 24% at P12. In adult rats, electrical or adequate stimulation evoked a shrinkage of the extracellular space by 20–50%, while no significant changes in ECS volume were found in P3–P6. We conclude that the [K+]e ceiling level, character of the pHe transients, the size of the ECS volume and the activity-related ECS shrinkage are closely related to gliogenesis. 相似文献
72.
Mi-Ju Kim Kun-Pyo Kim Eunhye Choi June-Hyuck Yim Chunpil Choi Hyun-Sun Yun Hee-Yoon Ahn Ji-Young Oh Yunhi Cho 《Nutrients》2021,13(4)
Lactobacillus plantarum CJLP55 has anti-pathogenic bacterial and anti-inflammatory activities in vitro. We investigated the dietary effect of CJLP55 supplement in patients with acne vulgaris, a prevalent inflammatory skin condition. Subjects ingested CJLP55 or placebo (n = 14 per group) supplements for 12 weeks in this double-blind, placebo-controlled randomized study. Acne lesion count and grade, skin sebum, hydration, pH and surface lipids were assessed. Metagenomic DNA analysis was performed on urine extracellular vesicles (EV), which indirectly reflect systemic bacterial flora. Compared to the placebo supplement, CJLP55 supplement improved acne lesion count and grade, decreased sebum triglycerides (TG), and increased hydration and ceramide 2, the major ceramide species that maintains the epidermal lipid barrier for hydration. In addition, CJLP55 supplement decreased the prevalence of Proteobacteria and increased Firmicutes, which were correlated with decreased TG, the major skin surface lipid of sebum origin. CJLP55 supplement further decreased the Bacteroidetes:Firmicutes ratio, a relevant marker of bacterial dysbiosis. No differences in skin pH, other skin surface lipids or urine bacterial EV phylum were noted between CJLP55 and placebo supplements. Dietary Lactobacillus plantarum CJLP55 was beneficial to clinical state, skin sebum, and hydration and urine bacterial EV phylum flora in patients with acne vulgaris. 相似文献
73.
74.
Suhrid Maiti Debaki Ranjan Howlader Prolay Halder Ushasi Bhaumik Moumita Dutta Shanta Dutta Hemanta Koley 《Vaccine》2021,39(2):380-393
Invasive non-typhoidal Salmonella (iNTS) serovars, especially Salmonella Typhimurium (ST) and Salmonella Enteritidis (SE), cause gastroenteritis worldwide. Due to the emergence of multi-drug resistance in iNTS, a broad-spectrum vaccine is urgently needed for the prevention of iNTS infection. Currently, there is no effective licensed vaccine against iNTS available in the market. We have formulated an outer membrane vesicles (OMVs) based bivalent immunogen as a vaccine candidate to generate broad-spectrum protective immunity against both recently circulating prevalent ST and SE. We have isolated OMVs from ST and SE and formulated the immunogen by mixing both OMVs (1:1 ratio). Three doses of bivalent immunogen significantly induced humoral immune responses against lipopolysaccharides (LPSs) and outer membrane proteins (OMPs) as well as a cell-mediated immune response in adult mice. We also observed that proteins of OMVs act as an adjuvant for generation of high levels of anti-LPS antibodies through T cell activation. We then characterized the one-day old suckling mice model for both ST and SE mediated gastroenteritis and used the model for a passive protection study. In the passive protection study, we found the passive transfer of bivalent OMVs immunized sera significantly reduced ST and SE mediated colonization and gastroenteritis symptoms in the colon of suckling mice compared to non-immunized sera recipients. The overall study demonstrated that OMVs based bivalent vaccine could generate broad-spectrum immunity against prevalent iNTS mediated gastroenteritis. This study also established the suckling mice model as a suitable animal model for vaccine study against iNTS mediated gastroenteritis. 相似文献
75.
Kentaro Ariyoshi Yota Hiroyama Naoya Fujiwara Tomisato Miura Kosuke Kasai Akifumi Nakata Yohei Fujishima Valerie Swee Ting Goh Mitsuaki A Yoshida 《Journal of radiation research》2021,62(1):73
Alopecia is one of the common symptoms after high-dose radiation exposure. In our experiments, neonatal mice that received 7 Gy X-ray exhibited defects in overall hair growth, except for their cheeks. This phenomenon might suggest that some substances were secreted and prevented hair follicle loss in the infant tissues around their cheeks after radiation damage. In this study, we focused on exosome-like vesicles (ELV) secreted from cheek skin tissues and back skin tissues, as control, and examined their radiation protective effects on mouse fibroblast cell lines. We observed that ELV from irradiated cheek skin showed protective effects from radiation. Our results suggest that ELV from radiation-exposed cheek skin tissue is one of the secreted factors that prevent hair follicle loss after high-dose radiation. 相似文献
76.
M. E. Morris G. V. Obrocea M. Avoli 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1996,109(1):71-82
Transient changes in extracellular potassium concentration ([K+]0) and field potentials were evoked by 4-aminopyridine (4-AP; 50–100 M) and recorded with ion-selective microelectrodes in CA1b, CA3b and dentate sectors of adult rat hippocampal slices. Long-lasting field potentials recurred at a frequency of 1/60 s (0.016±0.003 Hz) in association with increases in [K+]0 which were largest and most sustained in the dendritic regions where afferent fibers terminate (dentate>CAl>CA3) and in the hilus. In stratum radiatum of CA1 or stratum moleculare of the dentate these fields had a peak amplitude of 1.4±0.29 mV, duration 8.3±1.6 s, and were accompanied by increases in [K+]0 of 1.8±0.22 mM that lasted 32±5.5 s (n = 17 slices). Interictal epileptiform potentials, which were brief (<0.2 s) and more frequent at 1/3 s (0.30±0.02 Hz) were also present in CA1, CA3 and the hilus and associated with small increases in [K+]0 (0.5 mM, duration 2 s). Interictal activity was blocked by 6-cyano-7-nitroquinoxalone-2,3-dione (CNQX; 5–20 M); the slow, less frequent potentials were resistant to both CNQX and dl-2amino-5-phosphonovaleric acid (APV; 50 M) and reversibly blocked (or attenuated by 80%) by bicuculline methiodide (BMI) (25–100 M). The BMI-sensitive potentials were also abolished by baclofen (100 M), an effect which was reversed by 2-OH-saclofen (100 M). Focal application of KCl or GABA in the absence of 4-AP evoked long-lasting field and [K+]0 potentials which were similar to those evoked by 4-AP but more sustained. The proportional relationship between the amplitudes of field and K+ potentials with GABA closely resembled that observed for 4-AP; in contrast the slope of KCl-evoked responses was lower. Our results demonstrate that in the adult rat hippocampus 4-AP induces in many different regions accumulations of [K+]0 in synchrony with the long-lasting field potentials, which are known to correspond to an intracellular long-lasting depolarization of the pyramidal cells. These changes are smaller than those which occur in the immature rat hippocampus — which may be related to differences in Na-K-ATPase and susceptibility to seizures. These events involve the activation of GABAA receptors, are under the modulatory control of GABAB receptors, and likely arise from the activity of GABAergic interneurons and/or afferent terminals. The long-lasting field potentials appear to reflect mainly the direct depolarizing actions of GABA and to a much more limited extent the associated accumulation of [K+]0. 相似文献
77.
Anselm Frick Ivan Durasin Mechtild Neuweg 《Pflügers Archiv : European journal of physiology》1986,406(4):387-391
Clearance experiments have been performed to study the effects of saline infusion on the reabsorption of inorganic sulfate (SO4) at endogenous levels. Adult female Sprague-Dawley rats on a standard diet were used. Both intact and thyroparathyroidectomized (TPTX) animals were infused with a 130 mmol/l sodium chloride solution at a low (0.15 ml/min) and a high (0.375 ml/min) rate. This increase of the infusion rate decreased the reabsorption of SO4 in both groups of animals significantly. The fractional excretion of SO4 in theintact rats increased from 9.9±5.6 to 18.4±3.6% (mean values±SD,p<0.001) and in theTPTX rats from 5.3±2.5 to 22.4±6.3% (p<0.001). It is concluded that endogenous parathyroid hormone has no major effect on the saline-induced inhibition of reabsorption of SO4.This work was supported by a grant from the Deutsche Forschungsgemeinschaft (Fr 239/9-1) 相似文献
78.
Dr M. C. T. Denyer M. Riehle S. T. Britland A. Offenhauser 《Medical & biological engineering & computing》1998,36(5):638-644
There are a range of techniques that can be used to assay bioactive compound. One potentially promising technique is a system
consisting of microfabricated extracellular recording devices over which electrogenic cells can be grown. To date, research
in this area has concentrated on the use of neurons as an electrogenic cell type. However, these cells have limitations. Only
small extracellular potentials have been recorded from mammalian neurons cultured over microfabricated electrode arrays. Although
such potentials may be of use in assays examining the effects of bio-active compound analogues on firing frequency, they are
of little use for more detailed pharmacological studies involving analyses of signal shape. What is required is a system from
which much larger extracellular potentials can be recorded. This preliminary study reports on a system based on cardiac myocytes
cultured over microfabricated metal microelectrode arrays, from which potentials with a mean amplitude of 16.9 μV can be reliably
recorded, which can be reversibly blocked with μmoll−1 concentrations of the sodium ion channel blocker lidocaine. Less common potentials with amplitudes of up to 3.5 mV were also
recorded. It is demonstrated that cardiac myocytes cultured over microfabricated micro-electrode arrays can be used in assays
of cardioactive compound analogues. 相似文献
79.
The uptake of the -amino acid taurine by rat renal brush border membrane vesicles (BBMV) adapts to changes in dietary sulfur amino acid intake. Initial rateV
max upregulates after ingestion of a low methionine and taurine diet (LTD) and downregulates after a high taurine diet (HTD). This is reflected in vivo by hypotaurinuria after a LTD (90% reduction in excretion) and an 18-fold increase in urine taurine after a HTD. This study was performed to determine whether taurine efflux from BBMV is adaptively regulated by external taurine concentration or by diet. Vesicles were preloaded with varying concentrations of radiolabelled and unlabelled taurine and a 150 mM concentration of various salts. Efflux conditions were: taurine and 150 mM salt inside and 150 mM salt outside. The efflux of five concentrations of taurine (10–500 M) was linear over 6 min, reached equilibrium by 21 min, and was dependent upon intravesicular taurine content. The kinetic characteristics of efflux (E) were significantly different from influx (I):K
m=109.8±5.8 (E) versus 23.6±4.2 (I),P<0.001 [time of linearity=360 s (E) vs. 20 s (I)]. Efflux of taurine was dependent on the presence of both sodium and chloride in the system, but neither external taurine content (0,100 M, 1,000 M) nor external -alanine altered initial efflux. Feeding rats a normal diet, LTD, or fasting altered taurine uptake but not efflux. Efflux does not appear to play a role in the adaptive regulation of taurine transport found in all mammalian species. 相似文献
80.
A series of multilamellar liposome dispersions was prepared from lipids of soy phosphatidylcholine or hydrogenated soy phosphatidylcholine containing from 0 to 30 mol% of either cholesterol, steary-lamine, or dipalmitoyl phosphatidylglycerol. The liposome dispersions were aerosolized with a Collison nebulizer for 80 min at an output flow rate of 4.7 liters of air/min. The effects of nebulization on the vesicles were determined by monitoring the release of encapsulated 5,6-carboxyfluorescein (CF) from dispersions containing 200 µg of total CF, of which 93.1 ± 2.4% (N = 18) was initially encapsulated. In all experiments CF was released from the liposomes while being aerosolized, and this ranged from a mean of 12.7 ± 3.8 to 60.9 ± 1.9% of the encapsulated CF, depending upon the lipid composition. The lipid concentration in the dispersions did not affect the rate or percentage release of CF over a range of 0.5 to 50 mg per nebulized dispersion. If liposomes are to be used as drug carriers in an inhalation aerosol a lipid composition should be employed which will minimize the release of encapsulated drug caused by nebulization. 相似文献