全文获取类型
收费全文 | 8255篇 |
免费 | 494篇 |
国内免费 | 249篇 |
专业分类
耳鼻咽喉 | 27篇 |
儿科学 | 328篇 |
妇产科学 | 118篇 |
基础医学 | 1269篇 |
口腔科学 | 100篇 |
临床医学 | 726篇 |
内科学 | 1282篇 |
皮肤病学 | 74篇 |
神经病学 | 620篇 |
特种医学 | 284篇 |
外国民族医学 | 2篇 |
外科学 | 431篇 |
综合类 | 983篇 |
现状与发展 | 1篇 |
预防医学 | 392篇 |
眼科学 | 68篇 |
药学 | 1552篇 |
3篇 | |
中国医学 | 228篇 |
肿瘤学 | 510篇 |
出版年
2023年 | 85篇 |
2022年 | 167篇 |
2021年 | 249篇 |
2020年 | 220篇 |
2019年 | 210篇 |
2018年 | 220篇 |
2017年 | 188篇 |
2016年 | 210篇 |
2015年 | 208篇 |
2014年 | 449篇 |
2013年 | 458篇 |
2012年 | 442篇 |
2011年 | 506篇 |
2010年 | 359篇 |
2009年 | 348篇 |
2008年 | 364篇 |
2007年 | 342篇 |
2006年 | 350篇 |
2005年 | 309篇 |
2004年 | 263篇 |
2003年 | 249篇 |
2002年 | 230篇 |
2001年 | 206篇 |
2000年 | 136篇 |
1999年 | 158篇 |
1998年 | 134篇 |
1997年 | 125篇 |
1996年 | 119篇 |
1995年 | 120篇 |
1994年 | 133篇 |
1993年 | 104篇 |
1992年 | 105篇 |
1991年 | 96篇 |
1990年 | 87篇 |
1989年 | 84篇 |
1988年 | 97篇 |
1987年 | 65篇 |
1986年 | 58篇 |
1985年 | 121篇 |
1984年 | 93篇 |
1983年 | 61篇 |
1982年 | 63篇 |
1981年 | 75篇 |
1980年 | 70篇 |
1979年 | 52篇 |
1978年 | 49篇 |
1977年 | 43篇 |
1976年 | 41篇 |
1975年 | 18篇 |
1973年 | 15篇 |
排序方式: 共有8998条查询结果,搜索用时 31 毫秒
51.
The effect of acute infection of mice with lactic dehydrogenase virus (LDV) on two major functions of peritoneal macrophages was tested. Using a macrophage-dependent T cell proliferative assay to test the antigen-presenting capacity of LDV-infected macrophages we found that LDV impairs the capacity of antigen-presenting cells to trigger memory T lymphocytes. Endocytosis of antigen by LDV-infected macrophages was similar to that of uninfected cells. In addition, the proportion of intracellular antigen versus membrane-bound antigen in LDV-infected cells were similar to that observed in uninfected mice. It appears therefore, that the impaired immunogenic effect of LDV-infected macrophages results from reduced immunogenicity of the membrane-bound antigen.Testing the phagocytic activity of peritoneal macrophages we found that the uptake of radiolabeled antibody-coated sheep erythrocytes or bacteria (E. coli) by infected cells was similar to that by uninfected macrophages. In addition, LDV failed to affect the ability of peritoneal macrophages in a nitroblue tetrazolium reduction reaction which serves as an alternative parameter for measuring phagocytic activity. Our results support the assumption that LDV, which probably propagates in the cells of the reticuloendothelial system, impairs some of the immunogenic functions of macrophages and thereby affects macrophage-dependent immune responses. 相似文献
52.
The property of aerobic glycolysis commonly possessed by malignant cells points to a weakness in oxidative metabolism which has been equated in some tumours with partial uncoupling of oxidative phosphorylation. The suggestions are made, first, that this endogenous defect may account for spontaneous cell death
, and, second, that its accentuation would inflict extensive tumour injury upon sensitive neoplasms. Certain drugs not in current use for the treatment of malignant disease are known to be able to interfere selectively with energy metabolism in sensitive tumours to such an extent that widespread necrotisation ensues. The drugs activate an endogenous destructive mechanism that appears to require oxygen. Liminal therapy, the maintenance of continuous destructive pressure on sensitive growths in such a manner that maximal anti-tumour activity in terms of interference with energy production is not achieved at any one time, and under conditions in which the oxygen supply is only partly depleted, is put forward as a possible means of achieving complete and selective tumour destruction
. 相似文献
53.
M. Rieu A. Ferry M. C. Martin A. Duvallet 《European journal of applied physiology》1990,61(3-4):223-229
Summary Twelve male and female subjects (eight trained, four untrained) exercised for 30 min on a treadmill at an intensity of maximal O2 consumption (%
O2max) 90.0%, SD 4.7 greater than the anaerobic threshold of 4 mmol ·1–1 (Than =83.6%
O2max, SD 8.9). Time-dependent changes in blood lactate concentration ([lab]) during exercise occurred in two phases: the oxygen uptake (
O2) transient phase (from 0 to 4 min) and the
O2 steady-state phase (4–30 min). During the transient phase, [lab] increased markedly (l.30 mmol · l –1 · min –1, SD 0.13). During the steady-state phase, [lab] increased slightly (0.02 mmol · 1–1 · min–1, SD 0.06) and when individual values were considered, it was seen that there were no time-dependent increases in [lab] in half of the subjects. Following hyperlacticaemia (8.8 mmol -l–1, SD 2.0) induced by a previous 2 min of supramaximal exercise (120%
O2max), [lab] decreased during the
O2 transient (–0.118 mmol · 1–1 · min–1, SD 0.209) and steady-state (–0.088 mmol · 1–1 · min –1, SD 0.103) phases of 30 min exercise (91.4%
O2max, SD 4.8). In conclusion, it was not possible from the Than to determine the maximal [lab] steady state for each subject. In addition, lactate accumulated during previous supramaximal exercise was eliminated during the
O2 transient phase of exercise performed at an intensity above the Than. This effect is probably largely explained by the reduction in oxygen deficit during the transient phase. Under these conditions, the time-course of changes in [lab] during the
O2 steady state was also affected. 相似文献
54.
Succinate dehydrogenase activity was determined in the liver and heart of newborn rats after 3 and 48 hours' exposure to anoxic hypoxia (10% O2) and after 48 hours' starvation. Control determinations were made on newborn animals of corresponding ages, full term foetuses (21 days), infantile (1 and 2 weeks) and full grown animals. Hypoxia for 3 h had no influence on succinate dehydrogenase activity at all in either the heart or liver mitochondria of the newborn animals. After 48 h no difference was observed in the liver between the hypoxic animals and the starved controls of the same age, though starvation itself had resulted in a significant increase in activity, as much as 42%. When liver mitochondrial succinate dehydrogenase in normal mitochondria was activated by preincubation mitochondria with the substrate, the activity increase obtained was greater than that resulting from starvation. The increase in activity in the heart of the hypoxic or starved animals was not significant (< 10%). 相似文献
55.
It was previously proposed that an immunological cross-reaction between two denatured proteins is evidence for an homology betweeen their amino sequence (Arnon &; Maron, 1971; Arnheim et al., 1971) and that detection of such a cross-reaction could then be a rapid method to detect sequence homologies (Zakin et al., 1978). In order to test the possibilities of such a methodology, using proteins of known structure, glyceraldehyde 3-phosphate dehydrogenases from different sources are compared by immunochemical techniques. The antibodies raised against the native enzyme from E. coli K 12 can only recognize the homologous antigen, the glyceraldehyde 3-phosphate dehydrogenase from B. stearothermophilus and to a lesser extent that from halibut. In contrast, the antibodies raised against the denatured enzyme from E. coli K 12 can recognize the glyceraldehyde 3-phosphate dehydrogenases from man, ostrich, chicken, sturgeon, halibut, lobster and yeast, when in their denatured state. The present results show unambiguously that through exposure of buried sequences, the immunochemical detection of sequence homologies among proteins is more discriminating when unfolded proteins are used, rather than native ones. It is also proposed that the use of denatured proteins both as immunogens and antigens would be a useful tool in studying biochemical evolution. 相似文献
56.
Summary The glyceraldehyde-3-phosphate dehydrogenase (gpd) gene of Podospora anserina has been isolated from a genomic library by heterologous hybridization with the corresponding gene of Curvularia lunata. The coding region consists of 1014 nucleotides and is interrupted by a single intron. The amino-acid sequence encoded by the gpd gene shows a high degree of sequence identity with the corresponding gene products of various fungi. Multiple alignments of all fungal GPD sequences so far available resulted in the construction of a phylogenetic tree. The evolutionary relationships of the various fungi belonging to different taxa will be discussed on the basis of these data. Sequence analysis of 1.9 kbp of the 5 non-coding region revealed the presence of typical fungal promoter elements. Utilizing different parts of the 5 regulatory sequence of the Podospora gpd gene, expression vectors containing a dominant selectable marker gene (hygromycin B phosphotransferase) have been constructed for the transformation of P. anserina protoplasts. The use of these homologous gpd regulatory sequences resulted in a significant increase in transformation efficiencies compared to those obtained with vectors in which the selectable marker gene is under the control of the corresponding heterologous promoter of Aspergillus nidulans. 相似文献
57.
Alberto Utrero-Rico Javier Ruiz-Hornillos Cecilia González-Cuadrado Claudia Geraldine Rita Berta Almoguera Pablo Minguez Antonio Herrero-González Mario Fernández-Ruiz Octavio Carretero Juan Carlos Taracido-Fernández Rosario López-Rodriguez Marta Corton José María Aguado Luisa María Villar Carmen Ayuso-García Estela Paz-Artal Rocio Laguna-Goya 《The Journal of allergy and clinical immunology》2021,147(5):1652-1661.e1
58.
Mitochondrial antigens as targets of cellular and humoral auto-immunity in primary biliary cirrhosis 总被引:3,自引:0,他引:3
Ichiki Y Selmi C Shimoda S Ishibashi H Gordon SC Gershwin ME 《Clinical reviews in allergy & immunology》2005,28(2):83-91
Several factors point toward an auto-immune pathogenesis for primary biliary cirrhosis (PBC), mostly based on the presence
of serum auto-antibodies to mitochondrial antigens (AMAs) and autoreactive T cells (both helper and cytotoxic). Interestingly,
epitopes recognized by AMA and T-cell clones are located within overlapping areas of the antigens. Moreover, a role for an
imbalance in cytokine pattern and for natural-killer lymphocytes has also been proposed. Despite several experimental reports,
no clear evidence is available regarding the interaction of these factors leading to bile duct destruction. This article reviews
the current reports regarding the auto-immune reaction against mitochondrial auto-antigens in PBC. 相似文献
59.
Pre‐conditioning activates adenosine utilization in a cost‐effective way during myocardial ischaemia
G. Wikstrm M. Kavianipour G. Ronquist A. Waldenstrm 《Acta physiologica (Oxford, England)》2001,173(2):185-194
During pre‐conditioning the interstitial concentration of adenosine, in contrast to lactate, presents a die‐away curve‐pattern for every successive episode of ischaemia. This die‐away pattern might not necessarily be attributed to diminished adenosine production. The present study was undertaken to investigate whether pre‐conditioning alters the metabolic turnover of adenosine as observed by the lactate production during ischaemia. Interstitial levels of metabolites in pre‐conditioned (n=21) and non‐preconditioned (n=21) porcine hearts were monitored with microdialysis probes inserted in both ischaemic and non‐ischaemic tissue in an open chest heart model. Three subgroups perturbated with either plain microdialysis buffer (control), buffer containing adenosine (375 μM ), or buffer containing deoxyadenosine (375 μM ) were studied. All animals were subjected to 90 min of equilibrium microdialysis before 40 min of regional myocardial ischaemia and 120 min of reperfusion. Pre‐conditioning consisted of four repetitive episodes of 10 min of ischaemia and 20 min of reperfusion. Significantly higher levels of inosine and lactate were found in the ischaemic tissue of the pre‐conditioned subgroup receiving adenosine (P < 0.05) compared with the other two subgroups receiving deoxyadenosine and plain buffer, respectively. This difference was only valid for pre‐conditioned ischaemic myocardium, and hence equal amounts of inosine and lactate were produced in the non‐preconditioned ischaemic myocardium regardless of the presence of adenosine or deoxyadenosine. In the non‐ischaemic myocardium baseline levels of metabolites were measured in all subgroups. Pre‐conditioning favoured degradation of exogenous adenosine to inosine successively ending up in enhanced lactate production. This was probably because of the involvement of the hexose monophosphate pathway in the pre‐conditioned ischaemic myocardium. This route may therefore be supplementary in energy metabolism as a metabolic flow can be started by adenosine ending up in lactate without initial adenosine 5′‐triphosphate (ATP) investment. Utilization of adenosine in this way may also explain the successive die‐away pattern of adenosine seen in consecutive pre‐conditioning cycles. 相似文献
60.
Martin D. Hoffman Kara M. Kassay Anne I. Zeni Philip S. Clifford 《European journal of applied physiology》1996,74(6):541-547
The primary purpose of this study was to determine if the aerobic demand for production of specified power outputs is altered
by distribution of work between the arms and legs compared with when all the work is performed by the legs. Because of the
important exercise training implications, a secondary purpose of this study was to determine if the exercising muscle mass
affects the cardiorespiratory demands at specified rating of perceived exertion (RPE) levels and blood lactate concentrations.
Nine healthy adults completed leg cycling and combined arm and leg exercise on an Airdyne using a discontinuous protocol.
Repeated measures ANOVA revealed that oxygen uptake for the combined arm and leg exercise averaged 0.04 l·min−1 greater (p<0.05) than for leg cycling at the same external power outputs. However, RPE levels at specified power outputs were lower
(p<0.05) with combined arm and leg exercise than leg cycling. At specified RPE levels and blood lactate concentrations, oxygen
uptake and heart rate values were higher (p<0.05) for combined arm and leg exercise than leg cycling. From these findings we conclude that: (1) the addition of arm exercise
to leg cycling results in a reduction in RPE, but a minimal increase in oxygen consumption to perform a given power output,
and (2) if training intensity is established by RPE or blood lactate concentration, use of a muscle mass larger than that
used in leg cycling should allow a greater cardiorespiratory training effect. 相似文献