全文获取类型
收费全文 | 16718篇 |
免费 | 1340篇 |
国内免费 | 44篇 |
专业分类
耳鼻咽喉 | 147篇 |
儿科学 | 543篇 |
妇产科学 | 322篇 |
基础医学 | 2319篇 |
口腔科学 | 270篇 |
临床医学 | 1624篇 |
内科学 | 3641篇 |
皮肤病学 | 175篇 |
神经病学 | 1361篇 |
特种医学 | 664篇 |
外科学 | 2830篇 |
综合类 | 271篇 |
一般理论 | 20篇 |
预防医学 | 1457篇 |
眼科学 | 400篇 |
药学 | 1026篇 |
1篇 | |
中国医学 | 14篇 |
肿瘤学 | 1017篇 |
出版年
2023年 | 79篇 |
2022年 | 132篇 |
2021年 | 309篇 |
2020年 | 204篇 |
2019年 | 321篇 |
2018年 | 432篇 |
2017年 | 289篇 |
2016年 | 304篇 |
2015年 | 349篇 |
2014年 | 515篇 |
2013年 | 692篇 |
2012年 | 1184篇 |
2011年 | 1150篇 |
2010年 | 649篇 |
2009年 | 570篇 |
2008年 | 1005篇 |
2007年 | 1072篇 |
2006年 | 1073篇 |
2005年 | 1024篇 |
2004年 | 1004篇 |
2003年 | 938篇 |
2002年 | 895篇 |
2001年 | 194篇 |
2000年 | 189篇 |
1999年 | 194篇 |
1998年 | 189篇 |
1997年 | 188篇 |
1996年 | 161篇 |
1995年 | 128篇 |
1994年 | 128篇 |
1993年 | 136篇 |
1992年 | 111篇 |
1991年 | 143篇 |
1990年 | 90篇 |
1989年 | 113篇 |
1988年 | 110篇 |
1987年 | 97篇 |
1986年 | 115篇 |
1985年 | 88篇 |
1984年 | 98篇 |
1983年 | 113篇 |
1982年 | 105篇 |
1981年 | 107篇 |
1980年 | 96篇 |
1979年 | 112篇 |
1978年 | 88篇 |
1977年 | 69篇 |
1976年 | 60篇 |
1975年 | 77篇 |
1974年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
71.
CD1d-restricted invariant natural killer T cell (iNKT cells) have a limited T cell receptor (TCR) repertoire and share characteristics common to T cells and natural killer cells. While intrathymic selection facilitates the production of T cells carrying self major histocompatibility complex-restricted TCRs, natural killer cells carry an appropriate repertoire of self major histocompatibility complex-recognizing receptors to avoid self-reactivity. Here we show that chronic exposure to specific glycolipid antigen resulted in iNKT cell disappearance and thymus-dependent repopulation of iNKT cells with increased expression of inhibitory Ly-49 molecules that resulted in impaired responsiveness. Thymic selection of peripheral Ly-49-expressing iNKT cell repertoire inhibited cytokine production and other functions in vivo. These observations emphasize the acquisition of self-recognizing inhibitory receptors on NKT cells as a previously unknown mechanism of thymic tolerance after chronic antigen exposure. 相似文献
72.
P. Michael Stuart Rita K. Munn Edward DeMoll Jerold G. Woodward 《Human immunology》1995,43(4):269-275
We reported that antigenic preparations from Yersinia enterocolitica stimulate murine T cells in a manner consistent with that of superantigens. As a consequence we examined whether Y. enterocolitica antigenic preparations stimulate human T-cell cultures. Human T cells, enriched from peripheral blood lymphocytes, were stimulated to proliferate in the presence of Y. Enterocolitica cytoplasmic and membrane preparations. This activity has also been shown to be sensitive to protease treatment, indicating the presence of a protein, and when separated by ion-exchange chromatography a single peak of activity is resolved. Furthermore, this proliferation was inhibited, in a dose-dependent manner, by the presence of antibodies directed against MHC class II antigens, indicating a requirement for these molecules. When these cells were stained with a panel of Vβ-specific antibodies to determine if there was an enrichment of a particular Vβ-bearing T-cell subset after stimulation, results indicate a significant enrichment of T cells bearing Vβ3, Vβl2, Vβl4, and Vβl7 over controls. Taken together, these data are consistent with a Y. enterocolitica product acting as a superantigen for human T cells. 相似文献
73.
Guidot David M. Linas Stuart L. Repine Michael J. Shanley Paul F. Fisher Halee S. Repine John E. 《Inflammation》1994,18(5):537-545
Hearts from rats treated with interleukin-1 (IL-1) intraperitoneally developed a rapid (6 h after IL-1), transient increase in neutrophils, tissue hydrogen peroxide (H2O2), and oxidized glutathione (GSSG) levels, and a subsequent (36 h after IL-1) increase in myocardial glucose-6-phosphate dehydrogenase (G6PD) activity and tolerance to ischemia-reperfusion. In the present investigation, we found that rats treated similarly with IL-1 had increased numbers of neutrophils in their kidneys, which were comparable to myocardial neutrophil increases, but did not develop increased renal tissue H2O2 or GSSG levels acutely (6 h after IL-1) or increased G6PD activity or resistance to ischemia-reperfusion injury later (36 h after IL-1). Our findings indicate that IL-1 treatment increased neutrophil accumulation in rat kidneys but did not increase oxidative stress, antioxidant enzyme activity, or resistance to ischemia-reperfusion injury. We conclude that organ-to-organ differences exist with respect to IL-1-induced tolerance. 相似文献
74.
75.
Characterization of an antigen secreted by Chlamydia-infected cell culture. 总被引:4,自引:0,他引:4 下载免费PDF全文
A soluble genus-specific chlamydial antigen has been isolated from the supernatants of cultures infected with Chlamydia trachomatis and from other sources. The antigen is a glycolipid that is secreted during the infective cycle. This exoglycolipid can be hydrolysed and fractionated into polysaccharide and lipid components. Both fractions retain antigenic activity. An immunodominant antigenic determinant of the lipid component contains fatty acids of C17 and C18:1. The polysaccharide immunodominant epitope gives rise to gulose when derivatives are formed. The secretion of the antigen into the media supernatant, the presence of gulose and the observed molecular weight are consistent with properties of alginate secreted by Gram-negative bacteria. Chemical analyses and SDS-PAGE indicate that the exoglycolipid is markedly different from LPS. 相似文献
76.
77.
The avian ciliary ganglion contains two populations of parasympathetic cells, termed the ciliary and choroid neurons. We have estimated the quantal contents of nicotinic excitatory postsynaptic potentials in both populations of neurons by several methods. The singly innervated ciliary neurons have quantal contents of 15–30. In contrast, the multiply innervated choroid cells have quantal contents of 4–7. Quantal conductance was also determined, using a parallel conductance model which takes into account the capacitance of the cell membrane. This analysis indicates that in both populations of neurons one quantum activates approximately 100 postsynaptic receptors.
It is concluded that in autonomie ganglia singly innervated cells demonstrate a larger quantal content, consistent with a higher safety factor for neurotransmission, while quantal content in multiply innervated cells is generally much lower, allowing for considerable summation of presynaptic inputs. Further, in autonomic neurons many fewer postsynaptic receptors are activated by a single quantum than is the case at the neuromuscular junction. 相似文献
78.
Sodium and calcium currents shape action potentials in immature mouse inner hair cells 总被引:3,自引:12,他引:3
Walter Marcotti Stuart L. Johnson Alfons Rüsch Corné J. Kros 《The Journal of physiology》2003,552(3):743-761
Before the onset of hearing at postnatal day 12, mouse inner hair cells (IHCs) produce spontaneous and evoked action potentials. These spikes are likely to induce neurotransmitter release onto auditory nerve fibres. Since immature IHCs express both α1D (Cav 1.3) Ca2+ and Na+ currents that activate near the resting potential, we examined whether these two conductances are involved in shaping the action potentials. Both had extremely rapid activation kinetics, followed by fast and complete voltage-dependent inactivation for the Na+ current, and slower, partially Ca2+ -dependent inactivation for the Ca2+ current. Only the Ca2+ current is necessary for spontaneous and induced action potentials, and 29 % of cells lacked a Na+ current. The Na+ current does, however, shorten the time to reach the action-potential threshold, whereas the Ca2+ current is mainly involved, together with the K+ currents, in determining the speed and size of the spikes. Both currents increased in size up to the end of the first postnatal week. After this, the Ca2+ current reduced to about 30 % of its maximum size and persisted in mature IHCs. The Na+ current was downregulated around the onset of hearing, when the spiking is also known to disappear. Although the Na+ current was observed as early as embryonic day 16.5, its role in action-potential generation was only evident from just after birth, when the resting membrane potential became sufficiently negative to remove a sizeable fraction of the inactivation (half inactivation was at −71 mV). The size of both currents was positively correlated with the developmental change in action-potential frequency. 相似文献
79.
John P. McCarthy Marcas M. Bamman Janice M. Yelle Adrian D. LeBlanc Roger M. Rowe Michael C. Greenisen Stuart M. C. Lee Elisabeth R. Spector Suzanne M. Fortney 《European journal of applied physiology》1997,76(1):32-40
Resistance exercise has been suggested to increase blood volume, increase the sensitivity of the carotid baroreceptor cardiac reflex response (BARO), and decrease leg compliance, all factors that are expected to improve orthostatic tolerance. To further test these hypotheses, cardiovascular responses to standing and to pre-syncopal limited lower body negative pressure (LBNP) were measured in two groups of sedentary men before and after a 12-week period of either exercise (n = 10) or no exercise (control, n = 9). Resistance exercise training consisted of nine isotonic exercises, four sets of each, 3 days per week, stressing all major muscle groups. After exercise training, leg muscle volumes increased (P?0.05) by 4–14%, lean body mass increased (P = 0.00) by 2.0 (0.5)?kg, leg compliance and BARO were not significantly altered, and the maximal LBNP tolerated without pre-syncope was not significantly different. Supine resting heart rate was reduced (P = 0.03) without attenuating the heart rate or blood pressure responses during the stand test or LBNP. Also, blood volume (125I and 51Cr) and red cell mass were increased (P?0.02) by 2.8% and 3.9%, respectively. These findings indicate that intense resistance exercise increases blood volume but does not consistently improve orthostatic tolerance. 相似文献
80.
Helicobacter pylori does not require Lewis X or Lewis Y expression to colonize C3H/HeJ mice 下载免费PDF全文
Takata T El-Omar E Camorlinga M Thompson SA Minohara Y Ernst PB Blaser MJ 《Infection and immunity》2002,70(6):3073-3079
Helicobacter pylori strains frequently express Lewis X (Le(x)) and/or Le(y) on their cell surfaces as constituents of the O antigens of their lipopolysaccharide molecules. To assess the effect of Le(x) and Le(y) expression on the ability of H. pylori to colonize the mouse stomach and to adhere to epithelial cells, isogenic mutants were created in which fucT1 alone or fucT1 and fucT2, which encode the fucosyl transferases necessary for Le(x) and Le(y) expression, were deleted. C3H/HeJ mice were experimentally challenged with either wild-type 26695 H. pylori or its isogenic mutants. All strains, whether passaged in the laboratory or recovered after mouse passage, colonized the mice well and without consistent differences. During colonization by the mutants, there was no reversion to wild type. Similarly, adherence to AGS and KatoIII cells was unaffected by the mutations. Together, these findings indicate that Le expression is not necessary for mouse gastric colonization or for H. pylori adherence to epithelial cells. 相似文献