全文获取类型
收费全文 | 4690篇 |
免费 | 343篇 |
国内免费 | 215篇 |
专业分类
耳鼻咽喉 | 13篇 |
儿科学 | 65篇 |
妇产科学 | 17篇 |
基础医学 | 394篇 |
口腔科学 | 1278篇 |
临床医学 | 252篇 |
内科学 | 789篇 |
皮肤病学 | 30篇 |
神经病学 | 183篇 |
特种医学 | 74篇 |
外科学 | 167篇 |
综合类 | 606篇 |
现状与发展 | 1篇 |
预防医学 | 187篇 |
眼科学 | 80篇 |
药学 | 922篇 |
中国医学 | 143篇 |
肿瘤学 | 47篇 |
出版年
2024年 | 7篇 |
2023年 | 69篇 |
2022年 | 221篇 |
2021年 | 275篇 |
2020年 | 142篇 |
2019年 | 142篇 |
2018年 | 134篇 |
2017年 | 134篇 |
2016年 | 177篇 |
2015年 | 191篇 |
2014年 | 282篇 |
2013年 | 383篇 |
2012年 | 308篇 |
2011年 | 342篇 |
2010年 | 277篇 |
2009年 | 228篇 |
2008年 | 207篇 |
2007年 | 195篇 |
2006年 | 157篇 |
2005年 | 151篇 |
2004年 | 135篇 |
2003年 | 125篇 |
2002年 | 96篇 |
2001年 | 90篇 |
2000年 | 54篇 |
1999年 | 61篇 |
1998年 | 77篇 |
1997年 | 49篇 |
1996年 | 53篇 |
1995年 | 43篇 |
1994年 | 58篇 |
1993年 | 42篇 |
1992年 | 43篇 |
1991年 | 38篇 |
1990年 | 20篇 |
1989年 | 31篇 |
1988年 | 27篇 |
1987年 | 26篇 |
1986年 | 23篇 |
1985年 | 23篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有5248条查询结果,搜索用时 250 毫秒
1.
2.
Solid-state reactions between sodium hydride and sodium hydroxide are unusual among hydride-hydroxide systems since hydrogen can be stored reversibly. In order to understand the relationship between hydrogen uptake/release properties and phase/structure evolution, the dehydrogenation and hydrogenation behavior of the Na-O-H system has been investigated in detail both ex- and in-situ. Simultaneous thermogravimetric-differential thermal analysis coupled to mass spectrometry (TG-DTA-MS) experiments of NaH-NaOH composites reveal two principal features: Firstly, an H2 desorption event occurring between 240 and 380 °C and secondly an additional endothermic process at around 170 °C with no associated weight change. In-situ high-resolution synchrotron powder X-ray diffraction showed that NaOH appears to form a solid solution with NaH yielding a new cubic complex hydride phase below 200 °C. The Na-H-OH phase persists up to the maximum temperature of the in-situ diffraction experiment shortly before dehydrogenation occurs. The present work suggests that not only is the inter-phase synergic interaction of protic hydrogen (in NaOH) and hydridic hydrogen (in NaH) important in the dehydrogenation mechanism, but that also an intra-phase Hδ+… Hδ– interaction may be a crucial step in the desorption process. 相似文献
3.
4.
Pten基因敲除对过氧化物酶家族表达和活性氧水平的影响 总被引:2,自引:0,他引:2
目的:探讨Pten基因敲除后对过氧化物酶家族(Peroxiredoxins,Prdxs)水平和活性氧水平的影响.方法:采用Western印迹和化学/荧光发光分析法分别检测了在Pten / MEF和Pten-/-MEF细胞中PRDXs的表达和细胞内活性氧水平.结果:Western印迹结果显示,与Pten / MEF细胞相比,Pten-/-MEF细胞PRDX Ⅰ,Ⅱ,Ⅴ,Ⅵ蛋白水平下调,PRDX Ⅲ不变,PRDX Ⅳ上调.DCFH探针标记后流式结果显示Pten-/-MEF 细胞活性氧荧光值显著高于对照Pten / MEF细胞(P<0.05).结论:Pten基因敲除引起数种PRDXs表达下调,细胞内活性氧水平增高. 相似文献
5.
6.
ISABELLA L. KARLE JUDITH L. FLIPPEN-ANDERSON THEODOR WIELAND 《Chemical biology & drug design》1989,33(6):422-427
The synthetic perhydrogenated symmetric analog of the cyclic decapeptide antamanide is biologically inactive, although the conformation of the molecule and the crystal packing are very similar to that of the active symmetric analog of antamanide. In fact, the same conformation for the molecule has now been found in six polymorphs of uncomplexed antamanide and its analogs. The differences between the active and inactive antamanide analogs are displayed dramatically in the conformations of their metal ion (Na+ or Li+) complexes, thus suggesting strongly that for physiological activity antamanide is not in the conformation assumed by the uncomplexed molecule, but rather in the conformation assumed by the complexed state of natural antamanide. The present structure crystallizes in space group P212121 with a = 20.515(14) Å, b = 21.316(16) Å, c = 17.128(16) Å and four peptide molecules in the unit cell. There are three cocrystallized water molecules at full occupancy intrinsic to the peptide, and several more water molecules or other solvent molecules at partial occupancy. The formula of the peptide is C66 H106 N10O10· 4-H2O·2X. 相似文献
7.
8.
SEVERO SALVADORI REMO GUERRINI PIERO ANDREA BOREA ROBERTO TOMATIS 《Chemical biology & drug design》1992,40(5):437-444
The synthesis of pseudotetrapeptides H-Tyr-D-Ala-Phe-NH-(CH2)2-NH2 (1a), H-Tyr-D-Ala-Phe-ψ(CH2-NH)-Gly-NH2 (2a), H-Tyr-D-Ala-ψ(CH2-NH)-Phe-Gly-NH2 (3a), and H-Tyr-ψ(CH2-NH)-D-Ala-Phe-Gly-NH2 (4a), representing the N-terminal tetrapeptide sequence of dermorphin, in which amide bonds are replaced by CH2-NH bond, is described. N-acetyl-Tyr and desamino-Tyr pseudopeptide analogs (1-4b), (1-3c) are also described. The analogs were assayed in binding studies based on displacement of μ and δ-receptor selective radiolabels from rat brain membrane and in a bioassay using guinea pig ileum (GPI). Pseudopeptides in which the C-terminal (1a) or D-Ala-Phe (3a) amide bond are substituted, exhibit higher μ-affinities and μ-receptor selectivity than the corresponding Phe-Gly or Tyr-D-Ala analogs (2a, 4a). Acetyl-and desamino-Tyr pseudopeptide analogs (1-4b) and (1-3c) did not exhibit μ and δ-opioid receptor affinity at nM concentration. The relevance of the single peptide replacement and of its association to acetylation or amino group elimination of Tyr, is discussed on the basis of a receptor model for μ and δ opioids. 相似文献
9.
3种常用低温灭菌方法研究现状 总被引:5,自引:2,他引:3
阐述了环氧乙烷低温灭菌法、低温蒸汽甲醛灭菌法、过氧化氢等离子体灭菌法的灭菌机制、主要特点及应用范围。 相似文献
10.
The previously described cyclic delta opioid receptor-selective tetrapeptide H-Tyr-d -Cys-Phe-d -Pen-OH (JOM-13) was modified at residue 3 by incorporation of both natural and unnatural amino acids with varying steric, electronic, and lipophilic properties. Effects on mu and delta opioid receptor binding affinities were evaluated by testing the compounds for displacement of radiolabeled receptor-selective ligands in a guinea pig brain receptor binding assay. Results obtained with the bulky aromatic 1-Nal3 and 2-Nal3 substitutions suggest that the shape of the receptor subsite with which the side chain of the internal aromatic residue interacts differs for delta and mu receptors. This subsite of either receptor can accommodate the transverse steric bulk of the 1-Nal3 side chain but only the delta receptor can readily accept the more elongated 2-Nal3 side chain. Several analogs with pi-excessive heteroaromatic side chains in residue 3 were examined. In general, these analogs display diminished binding to mu and delta receptors, consistent with previous findings for analogs with residue 3 substitutions of modified electronic character. Several analogs with alkyl side chains in residue 3 were also examined. While delta receptor binding affinity is severely diminished with Val3, Ile3, and Leu3 substitutions, Cha3 substitution is very well tolerated, indicating that, contrary to the widely held belief, an aromatic side chain in this portion of the ligand is not required for delta receptor binding. Where possible, comparison of results in this delta-selective tetrapeptide series with those reported for analogous modification in the cyclic delta-selective pentapeptide [d -Pen2, d -Pen5]enkephalin (DPDPE) and linear pentapeptide enkephalins reveals similar trends. 相似文献