全文获取类型
收费全文 | 19788篇 |
免费 | 1556篇 |
国内免费 | 592篇 |
专业分类
耳鼻咽喉 | 76篇 |
儿科学 | 183篇 |
妇产科学 | 189篇 |
基础医学 | 2221篇 |
口腔科学 | 227篇 |
临床医学 | 1483篇 |
内科学 | 4229篇 |
皮肤病学 | 322篇 |
神经病学 | 1103篇 |
特种医学 | 137篇 |
外国民族医学 | 1篇 |
外科学 | 1476篇 |
综合类 | 1330篇 |
现状与发展 | 2篇 |
预防医学 | 368篇 |
眼科学 | 209篇 |
药学 | 5560篇 |
6篇 | |
中国医学 | 282篇 |
肿瘤学 | 2532篇 |
出版年
2024年 | 53篇 |
2023年 | 485篇 |
2022年 | 733篇 |
2021年 | 935篇 |
2020年 | 845篇 |
2019年 | 798篇 |
2018年 | 748篇 |
2017年 | 836篇 |
2016年 | 802篇 |
2015年 | 853篇 |
2014年 | 1056篇 |
2013年 | 2482篇 |
2012年 | 919篇 |
2011年 | 1119篇 |
2010年 | 830篇 |
2009年 | 865篇 |
2008年 | 863篇 |
2007年 | 796篇 |
2006年 | 793篇 |
2005年 | 659篇 |
2004年 | 558篇 |
2003年 | 512篇 |
2002年 | 451篇 |
2001年 | 308篇 |
2000年 | 251篇 |
1999年 | 230篇 |
1998年 | 226篇 |
1997年 | 184篇 |
1996年 | 159篇 |
1995年 | 150篇 |
1994年 | 137篇 |
1993年 | 140篇 |
1992年 | 112篇 |
1991年 | 103篇 |
1990年 | 102篇 |
1989年 | 83篇 |
1988年 | 64篇 |
1987年 | 72篇 |
1986年 | 55篇 |
1985年 | 80篇 |
1984年 | 78篇 |
1983年 | 62篇 |
1982年 | 75篇 |
1981年 | 49篇 |
1980年 | 45篇 |
1979年 | 44篇 |
1978年 | 41篇 |
1977年 | 31篇 |
1976年 | 22篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Eva Díez‐Pea Isabel Quijada‐Garrido Jos Manuel Barrales‐Rienda Ingo Schnell Hans Wolfgang Spiess 《Macromolecular chemistry and physics.》2004,205(4):430-437
Summary: The nature of the pH dependent collapse of poly(methacrylic acid) (PMAA) hydrogels is investigated using recent 1H solid‐state NMR methods. In aqueous solution, PMAA changes from an expanded conformation at high pHs to a compact contracted form at low pHs, where hydrogen bonds play a central role. In solid‐state 1H NMR spectra, recorded under fast magic angle spinning (MAS), dried PMAA samples previously collapsed at low pHs show characteristic signals in the spectral region of the carboxylic acid protons. With the aid of 2D 1H‐1H double‐quantum (DQ) MAS NMR spectra, three signals can be distinguished at 8, 10.5 and 12.5 ppm, which are attributed to free carboxylic groups and two different types of hydrogen bonded forms, respectively. The 12.5 ppm signal arises from the hydrogen bond with the shortest H? H distance, corresponding to the form that is most stable with respect to increasing temperature and pH. The weaker hydrogen‐bonded form (with a signal at 10.5 ppm) requires a slightly lower pH, while the free acid signal (at 8 ppm) emerges under the most acidic medium. Moreover, the stabilities of the hydrogen‐bonded carboxylic acid dimers can be inferred from the proton‐proton distances within the dimers, i.e. (275 ± 5) pm and (295 ± 15) pm for the protons at 12.5 and 10.5 ppm, respectively, which are determined by means of DQ MAS sideband patterns. Both the stability of the hydrogen bonds and the acidity of the protons may be related to the stereochemistry and the conformation of the PMAA chains.
82.
B. Pertzov N. Eliakim-Raz H. Atamna A.Z. Trestioreanu D. Yahav L. Leibovici 《Clinical microbiology and infection》2019,25(3):280-289
Objectives
The pleiotropic effect of hydroxymethylglutaryl-CoA reductase inhibitors (statins) might have a beneficial effect in sepsis through several mechanisms. The aim was to assess the efficacy and safety of statins, compared with placebo, for the treatment of sepsis in adults.Methods
We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, 2017, Issue 12), OVID MEDLINE (from 1966 to January 2018), Embase (Ovid SP, from 1974 to January 2018), and LILACS (from 1986 to January 2018). We also searched the trial registries ISRCTN and ClinicalTrials.gov to January 2018. The eligibility criteria were randomized controlled trials comparing the treatment of statins versus placebo in adult patients who were hospitalized due to sepsis. Participants were adults (16 years and older) hospitalized because of sepsis or who developed sepsis during admission. Interventions were treatment with hydroxymethylglutaryl-CoA reductase inhibitors (statins) versus no treatment or placebo. We performed a systematic review of all randomized controlled trials published until January 2018, assessing the efficacy and safety of statins in sepsis treatment. Two primary outcomes were assessed: 30-day overall mortality and deterioration to severe sepsis during management. Secondary outcomes were hospital mortality, need for mechanical ventilation and drug related adverse events.Results
Fourteen trials evaluating 2628 patients were included. Statins did not reduce 30-day all-cause mortality neither in all patients (risk ratio (RR) 0.96, 95% confidence interval (CI) 0.83–1.10), nor in a subgroup of patients with severe sepsis (RR 0.97, 95% CI 0.84–1.12). The certainty of evidence for both outcomes was high. There was no change in the rate of adverse events between study arms (RR 1.24, 95% CI 0.94 to 1.63). The certainty of evidence for this outcome was high.Conclusions
The use of statin therapy in adults for the indication of sepsis is not recommended. 相似文献83.
Miura T Goto M Hosoya N Odawara T Kitamura Y Nakamura T Iwamoto A 《Journal of medical virology》2003,70(4):497-505
Mitochondrial DNA (mtDNA) of peripheral blood mononuclear cells (PBMCs) collected from Human immunodeficiency virus 1 (HIV-1)-infected patients and healthy controls were measured longitudinally using real-time polymerase chain reaction to evaluate the effects of antiretroviral agents on mtDNA synthesis in vivo and to assess the value of monitoring mtDNA in PBMCs to predict adverse events amongst these patients. MtDNA levels in PBMCs were significantly decreased in treatment-naive HIV-1-infected patients compared with healthy people. MtDNA levels were not only significantly correlated with CD4(+) T-cell count, but also inversely correlated with HIV-1 viral load. MtDNA levels in untreated patients and healthy controls were stable during the period of observation. On the other hand, amongst patients treated with regimens containing AZT/3TC or d4T/3TC, mtDNA increased during treatment and recovered to levels comparable to healthy controls. In contrast, mtDNA decreased immediately after the initiation of an AZT/ddC-containing regimen. We did not find a correlation between mtDNA levels and changes in clinical parameters. There was no significant difference in mtDNA levels between patients with and those without lipoatrophy. Furthermore, there was no obvious difference in mtDNA levels amongst those patients exhibiting signs and symptoms of peripheral neuropathy. In conclusion, the decrease in mtDNA levels in PBMCs amongst HIV-1-infected patients and its amelioration by antiretroviral therapy may suggest the influence of direct effects on mitochondria or mtDNA by HIV-1 infection. Further investigations are needed to elucidate the mechanisms contributing to decreased mtDNA and the value of mtDNA measurement in the care of HIV-1-infected individuals. 相似文献
84.
85.
Specificity of blebbistatin, an inhibitor of myosin II 总被引:10,自引:0,他引:10
Limouze J Straight AF Mitchison T Sellers JR 《Journal of muscle research and cell motility》2004,25(4-5):337-341
Blebbistatin is a small molecule inhibitor discovered in a screen for inhibitors of nonmuscle myosin IIA. We have examined
the specificity and potency of the drug by assaying its effects on the actin-activated MgATPase assay of diverse members of
the myosin superfamily. Blebbistatin potently inhibits several striated muscle myosins as well as vertebrate nonmuscle myosin
IIA and IIB with IC50 values ranging from 0.5 to 5 μM. Interestingly, smooth muscle which is highly homologous to vertebrate nonmuscle myosin is
only poorly inhibited (IC50=80 μM). The drug potently inhibits Dictyostelium myosin II, but poorly inhibits Acanthamoeba myosin II. Blebbistatin did not inhibit representative myosin superfamily members from classes I, V, and X.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
86.
K. V. Durikhin 《Bulletin of experimental biology and medicine》1976,81(4):558-561
With edema of the albino mouse paw as experimental model the action of neuraminidase inhibitors on the cholerogenic effect of cholera vibrio culture filtrates (CVCF) was studied. Addition of inhibitors to CVCF was found to depress their biological activity. Since purified neuraminidase preparations from cholera vibrios had no cholerogenic action it was postulated that the region of the cholerogen responsible for fixation on cell membranes is chemically similar to the active center of neuraminidase.Plague Research Institute, Volgograd. (Presented by Academician of the Academy of Medical Sciences of the USSR P. A. Vershilova.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 81, No. 4, pp. 452–454, April, 1976. 相似文献
87.
A simple technique for controlling cell adhesion on glass substrates by surface modification using a commercially available poly(ethylene glycol) (PEG) disilane, which can bind directly to glass in a single step, in combination with photolithographic micropatterning, was developed, characterized, and evaluated for patterning of HepG2 hepatoma cells and 3T3 fibroblasts. The optimal concentration of PEG-disilane for surface modification was 5 mM, and patterning of strongly adherent cells such as HepG2 required the chelation of divalent metal cations in order to inhibit nonspecific binding and cell aggregation. Whereas the average thickness of the PEG-disilane layer was 18±3.5 nm, the perimeters of patterned areas of exposed glass exhibited ridges of average height 857±50 nm, which may have aided in constraining cell spreading and migration. Although unpatterned PEG-treated substrates were hydrophilic (contact angle 46±1°), micropatterned surfaces behaved as if they were somewhat hydrophobic (contact angle 90°), necessitating special protocols for preventing deleterious dewetting of cells. For optimized protocols, the probability of adhesion of HepG2 cells to a patterned area of exposed glass was almost 15 times higher than the probability of adhesion to a PEG-treated background region of equal area. Our technique is useful for short- to intermediate-term patterning of cell or tissue morphology, e.g., for investigation of the effects of cell–cell interactions or cell geometry. 相似文献
88.
Juvenile hyaline fibromatosis: A report of two unrelated adult sibling cases and a literature review
Hideto Senzaki Yasuhiko Kiyozuka Yoshiko Uemura Nobuaki Shikata Satoshi Ueda Airo Tsubura 《Pathology international》1998,48(3):230-236
Two unrelated adult sibling cases (36- and 32-year-old females) of Juvenile hyaline fibromatosis are presented. The parents of one of these patients were non-consanguineous but natives of a small Island, and one elder sister among four siblings was affected with the same disease. The parents of the other patient were consanguineous, and one other sibling suffered from the identical disease. Both patients presented with multiple subcutaneous nodules, which they had had since infancy, and had undergone numerous surgical excisions. Light microscopy examination of skin lesions from both patients showed identical histology; an abundance of a homogenous, amorphous, eosinophlllc extracellular matrix in which spindle-shaped cells were embedded. Electron microscopically, the spindle-shaped cells had hypertrophic Golgi apparatus and dilated, rough endoplasmlc reticulum. Fine flbrillar and granular material-filled structures, the contents of which were occasionally released into the extracellular matrix, were also seen, immunohistochemically, the spindle-shaped cells were vlmentin-positive but negative for α-smooth muscle actln and S-100 protein, and the hyaline ground substance was positive for type I and type III collagen but negative for type II and type IV collagen and tenascin. Matrix metalloprotelnase-1, -2, and -9, and tissue inhibitor of matrix metalloproteinase (TlMP)-2 was positive but TIMP-1 was negative. A review of 39 cases of juvenile hyaline fibromatosis In the literature is also presented. In summary, skin lesions may be the most outstanding symptoms of juvenile hyaline fibromatosis, but joint contracture and gingival hypertrophy precede the skin manifestation. 相似文献
89.
Harvey M.B.; Leco K.J.; Arcellana-Panlilio M.Y.; Zhang X.; Edwards D.R.; Schultz G.A. 《Human reproduction (Oxford, England)》1995,10(3):712-718
Several growth factor ligand and receptor gene products havebeen shown to play roles during preimplantation mammalian development.Genes for insulin-like growth factors (IGFs), transforming growthfactors (TGFs), fibroblast growth factor (FGF), platelet-derivedgrowth factor (PDGF) and receptors for insulin, IGF, PDGF, TGFand epidermal growth factor (EGF) are expressed by early embryosof several species including mouse, rat, cow and sheep. Rolesof growth factors during early development have been demonstratedby addition of purified growth factors to culture medium orby molecular genetic techniques that interfere with gene expression.In this way, it has been shown that successful development ofthe blastocyst is dependent on the action of epidermal growthfactor (EGF) and leukaemia inhibitory factor (LIF). Recent experimentsshow that both LIF and EGF stimulate secretion of urokinase-typeplasminogen activator (uPA) and gelatinase B/ matrix metalloproteinase-9(MMP-9) in day 7 mouse blastocyst outgrowths. At the same time,tissue inhibitors of MMPs (TIMPs) are also expressed by embryonic,decidual and uterine tissues during the implantation process.It appears that LIF may act directly or indirectly, by inducingthe expression of other cytokines, to regulate the temporaland spatial production and activity of proteases and proteaseinhibitors to create a favourable environment for implantation. 相似文献
90.
Summary Ionic channel properties of acetylcholine receptors located in, in the vicinity of, or far away from a frog neuromuscular
junction were investigated by noise analysis of drug induced current fluctuations. For drugs applied to the junction, in certain
cases two Lorentzian curves were necessary to describe the data. It is postulated that the reason for this observation is
that a contribution from perijunctional receptors was being observed. The conductance of a single channel in the junction
was independent of the nature of the agonist and had an average value of 17.9 pS (temperature range 8–25°C, solution buffered
with Tris). After denervation for 21 days the conductance γ was 7.5 pS at extrajunctional locations. In the close neighbourhood
of the junction (perijunctional receptors) values were found between 4 and 19 pS.
The mean value of the open channel life-time τ in the endplate exposed to acetylcholine was 2.4 ms at 8–11°C. This value was
0.90 ms with carbachol, 0.50 ms with succinylcholine, 0.28 ms with decamethonium and 0.45 ms with nicotine. The receptors
outside the endplate exhibited τ-values which at a given temperature were 2–3 times larger than those at the endplate. Raising
the temperature to 23°C reduced all τ-values by factors of 2–3. It is concluded that at least two types of ACh-receptors with
different properties exist in the muscle membrane, possibly produced by ACh-receptive units in different states of aggregation.
This work was supported by the Deutsche Forschungsgemeinschaft, SFB 38, Project N 相似文献