全文获取类型
收费全文 | 4659篇 |
免费 | 264篇 |
国内免费 | 109篇 |
专业分类
耳鼻咽喉 | 19篇 |
儿科学 | 51篇 |
妇产科学 | 36篇 |
基础医学 | 1019篇 |
口腔科学 | 92篇 |
临床医学 | 308篇 |
内科学 | 675篇 |
皮肤病学 | 71篇 |
神经病学 | 401篇 |
特种医学 | 66篇 |
外国民族医学 | 1篇 |
外科学 | 144篇 |
综合类 | 346篇 |
预防医学 | 197篇 |
眼科学 | 23篇 |
药学 | 1325篇 |
中国医学 | 144篇 |
肿瘤学 | 114篇 |
出版年
2023年 | 44篇 |
2022年 | 52篇 |
2021年 | 111篇 |
2020年 | 100篇 |
2019年 | 102篇 |
2018年 | 98篇 |
2017年 | 103篇 |
2016年 | 133篇 |
2015年 | 116篇 |
2014年 | 208篇 |
2013年 | 313篇 |
2012年 | 166篇 |
2011年 | 210篇 |
2010年 | 162篇 |
2009年 | 199篇 |
2008年 | 214篇 |
2007年 | 199篇 |
2006年 | 192篇 |
2005年 | 178篇 |
2004年 | 191篇 |
2003年 | 132篇 |
2002年 | 137篇 |
2001年 | 134篇 |
2000年 | 100篇 |
1999年 | 103篇 |
1998年 | 91篇 |
1997年 | 80篇 |
1996年 | 74篇 |
1995年 | 99篇 |
1994年 | 83篇 |
1993年 | 88篇 |
1992年 | 86篇 |
1991年 | 74篇 |
1990年 | 70篇 |
1989年 | 56篇 |
1988年 | 58篇 |
1987年 | 73篇 |
1986年 | 49篇 |
1985年 | 57篇 |
1984年 | 70篇 |
1983年 | 57篇 |
1982年 | 34篇 |
1981年 | 39篇 |
1980年 | 32篇 |
1979年 | 28篇 |
1978年 | 18篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1974年 | 7篇 |
1971年 | 1篇 |
排序方式: 共有5032条查询结果,搜索用时 15 毫秒
21.
F. W. BACH 《Acta anaesthesiologica Scandinavica》1997,41(1):133-140
We have known the endogenous opioid peptide β-endorphin for 20 years. Surprisingly, our knowledge of the physiological role of this peptide and its receptors in modulation of pain perception is still fragmentary. Whereas most studies have tried to elucidate the physiological role of β-endorphin by reversing evoked responses by the opioid antagonist naloxone, this review focuses on quantification of release of β-endorphin in the brain as the approach to define physiological and pathophysiological roles of β-endorphin in relation to nociception. Using a lateral ventricle-cisterna magna perfusion model in the anesthetized rat, it was shown that depolarization of neurons in the arcuate nucleus of the hypothalamus, where β-endorphin is produced, was followed by release of β-endorphin to the cerebrospinal fluid compartment. Intense activation of spinal nociceptive pathways by intrathecal capsaicin injections also led to β-endorphin release. It is concluded that there may still be good reason to quantify β-endorphin in human cerebrospinal fluid to elucidate the role of β-endorphin in pain perception. 相似文献
22.
23.
本文观察了15例慢性肾功能衰竭病人透析前后的血浆心钠素浓度改变.患者透析前血浆心钠素浓度较正常人明显增高(P相似文献
24.
LARBI EL-MASDOURI ANDR AUBRY GUY BOUSSARD MICHEL MARRAUD 《Chemical biology & drug design》1992,40(6):482-486
The similar conformations and interaction modes of Ac-DL-Leu-Nme2 and Ac-Δ-Leu-NMe2 molecules in the solid state allow the comparison of their geometrical parameters. The most evident variations are essentially restricted to the α,β-unsaturated side-chain which adopts the Z-disposition. The dimensions of the peptide backbone are much less sensitive to α,β-unsaturation, with a small shortening by 0.04 Å and 0.02 Å of the N-Cα and Cα-C′ bonds, respectively, and an increase by 6° of the N-Cα- C′ bond angle. The ethylenic and amide groups in the Δ-Leu derivative are far from coplanarity, and a significant electronic conjugation of the π-orbital is likely to be rejected. 相似文献
25.
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
26.
27.
ALEKSANDRA MISICKA ANDRZEJ W. LIPKOWSKI ROBERT HORVATH PEG DAVIS FRANK PORRECA HENRY I. YAMAMURA VICTOR J. HRUBY 《Chemical biology & drug design》1994,44(1):80-84
Further efforts to correlate the topography of the bioactive structures of DPDPE and the deltorphins, two δ-opioid receptor active peptide families, are reported. A number of DPLPE-deltorphin chimeric peptides have been synthesized in which the C-terminal dipeptide δ-address of the deltorphins (-Val-GlyNH2, -Nle-GlyNH2) have been linked to the highly δ-opioid selective cyclic peptides DPDPE or DPLPE. These studies demonstrate that a major structural feature determining high potency of hybrid analogues is the chirality of the amino acid residue in position 5. The radioligand binding assays have revealed a decrease in potency (compared to DPDPE) at §-receptors when the C-terminal dipeptides were added to DPDPE. On the other hand, chimeric peptides of DPLPE with these same C-terminal dipeptides retained high δ-selectivity and affinity. Similar results were obtained using the mouse vas deferens (MVD) and guinea pig ileum (GPI) bioassays. The importance of the hydrophilicity of amino acids in positions 2 and 5 for δ-selectivity is consistent with the previous finding for DPLPE and DPDPE. On the other hand, the replacement of phenylalanine-4 with p-chlorophenylalanine-4 did not increase δ-selectivity as in DPDPE. These findings suggest that the δ-receptor interacts with hybridized enkephalins and deltorphins somewhat differently than with DPDPE. 相似文献
28.
The peptide Leu-Asp-Asp-Ser-Lys-Arg-Val-Ala-Lys-Arg-Lys-Leu-Ile-Glu, which corresponds to sequence 124 to 137 of c-erb-A protein, was synthesized and tested as substrate for protein kinase C (PKC). Although a typical recognition sequence for PKC, consisting of a cluster of basic residues, is found on the C-terminus side of serine, its phosphorylation was totally prevented by the presence of the two acidic residues on the amino-terminus side. Three analogs in which aspartyl residues were successively replaced with alanine were studied and the influence of the acidic side chain in modulating phosphorylation by PKC was thus possible to determine. The results show that the presence of a single aspartyl residue located in positions i-1 or i-2 with respect to the phosphorylable residue can almost totally abolish the positive effect of a highly favorable cluster of basic residues. These observations highlight the role of negative substrate specificity determinants in settling the protein substrate profile of protein kinase C. 相似文献
29.
David M VOSS Kelvin L LYNN Adrian L BUTTIMORE Eric A ESPINER 《Nephrology (Carlton, Vic.)》1995,1(6):577-581
Summary: We studied changes in blood pressure (BP) and plasma hormones (atrial natriuretic peptide [ANP], brain natriuretic peptide [BNP], endothelin [ET], angiotensin [AII] and renin [PRA]) in four stable haemodialysis patients 48 h after a routine dialysis (basal stat), after volume expansion (4–7% above dry bodyweight) for 4 days then 48 h later following ultrafiltration. Blood pressure rose and plasma AII and PRA values fell with volume expansion and returned to baseline at the end of the study. Endothelin values were unchanged. Plasma ANP and BNP rose similarly in three patients and returned to near baseline levels after ultrafiltration. Sustained volume expansion over 4 days in dialysis patients is associated with an increase in BP, a marked elevation in plasma ANP and BNP but without change in ET. 相似文献
30.
Glutaminase has been considered to be a synthesizing enzyme of transmitter glutamate in pyramidal neurons of the cerebral cortex. In the present study, an attempt was made to examine with a double immunofluorescence method whether or not nonpyramidal neurons of the cerebral cortex are immunoreactive for glutaminase. Glutaminase was stained with mouse anti-glutaminase IgM and FITC-labeled anti-[mouse IgM] antibody. In the same section, parvalbumin (PA), calbindin (CB), choline acetyltransferase (CAT), vasoactive intestinal polypeptide (VIP), corticotropin releasing factor (CRF), cholecystokinin (CCK), somatostatin (SS), or neuropeptide Y (NPY) was visualized as a marker for nonpyramidal neurons with an antibody to each substance, biotinylated secondary antibody and Texas Red-labeled avidin. Virtually no glutaminase immunoreactivity was seen in PA-, CB-, CAT-, VIP-, CRF-, CCK-, SS-, or NPY-immunoreactive neuronal perikarya in the neocortex and mesocortex (cingulate and retrosplenial cortices), although it was detected in a few PA-, CB-, VIP-, CCK-, SS-, or NPY-immunoreactive nonpyramidal neurons in the piriform, entorhinal, and hippocampal cortices. PA- and CB-positive neurons have been reported to constitute the major population of GABAergic neurons in the cerebral cortex. Thus, the present results, together with the previous reports, suggest that most GABAergic, cholinergic and peptidergic nonpyramidal neurons in the neo- and mesocortex do not contain glutaminase. 相似文献