全文获取类型
收费全文 | 1621篇 |
免费 | 86篇 |
国内免费 | 65篇 |
专业分类
耳鼻咽喉 | 6篇 |
儿科学 | 8篇 |
妇产科学 | 2篇 |
基础医学 | 282篇 |
口腔科学 | 5篇 |
临床医学 | 46篇 |
内科学 | 131篇 |
皮肤病学 | 8篇 |
神经病学 | 583篇 |
特种医学 | 75篇 |
外科学 | 35篇 |
综合类 | 135篇 |
预防医学 | 88篇 |
眼科学 | 15篇 |
药学 | 245篇 |
中国医学 | 69篇 |
肿瘤学 | 39篇 |
出版年
2024年 | 4篇 |
2023年 | 10篇 |
2022年 | 28篇 |
2021年 | 26篇 |
2020年 | 26篇 |
2019年 | 17篇 |
2018年 | 26篇 |
2017年 | 36篇 |
2016年 | 33篇 |
2015年 | 30篇 |
2014年 | 90篇 |
2013年 | 73篇 |
2012年 | 90篇 |
2011年 | 88篇 |
2010年 | 72篇 |
2009年 | 78篇 |
2008年 | 64篇 |
2007年 | 50篇 |
2006年 | 44篇 |
2005年 | 34篇 |
2004年 | 37篇 |
2003年 | 41篇 |
2002年 | 33篇 |
2001年 | 24篇 |
2000年 | 33篇 |
1999年 | 23篇 |
1998年 | 33篇 |
1997年 | 26篇 |
1996年 | 26篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 23篇 |
1992年 | 23篇 |
1991年 | 18篇 |
1990年 | 23篇 |
1989年 | 24篇 |
1988年 | 25篇 |
1987年 | 16篇 |
1986年 | 38篇 |
1985年 | 58篇 |
1984年 | 51篇 |
1983年 | 49篇 |
1982年 | 45篇 |
1981年 | 39篇 |
1980年 | 37篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 16篇 |
1976年 | 6篇 |
1975年 | 6篇 |
排序方式: 共有1772条查询结果,搜索用时 15 毫秒
1.
Previous pharmacological studies with the pituitary gland have suggested that acetylcholine (ACh) might be involved in the regulation of intermediate lobe (IL) function. Whether ACh is endogenous to the IL cells or provided from an extrinsic source is unclear. The present experiments tested the possibility that the endocrine cells of the IL may be a source of ACh by measuring certain cholinergic markers in a primary culture of dissociated porcine cells. The endogenous ACh content was readily measurable in both the freshly dissociated IL cells and in 2- or 4-day primary cultures. Choline acetyltransferase activity was also measurable in the freshly dissociated and cultured IL cells and was reduced by 53% in the presence of a specific inhibitor, napthylvinylpyridine (50 μM). IL cells incubated in the presence of [14C]choline (1 μM) were able to synthesize [14C]ACh and the accumulation of the new ACh was inhibited by hemicholinium-3 (30 μM), a competitive inhibitor of high affinity choline uptake at cholinergic nerve terminals. In conclusion, these results demonstrate that the endocrine cells of the IL are capable of synthesizing and storing ACh. 相似文献
2.
蛋黄磷脂中磷脂酰乙醇胺的薄层扫描测定 总被引:2,自引:1,他引:1
将超临界CO2萃取法得到的蛋黄粉中的磷脂经薄层色谱分离,采用双波长薄层扫描仪对其磷脂酰乙醇胺进行测定。平均回收率为97.67%,RSD为2.31%。 相似文献
3.
Karen A. Baskerville Howard T. Chang Paul Herron 《The Journal of comparative neurology》1993,335(4):552-562
We investigated (1) the topography of projection neurons in the nucleus basalis of Meynert (NBM) with efferents to restricted regions of the primary somatosensory (SI), the second somatosensory (SII), and the primary motor (MI) cortices in the rat; (2) the percentage of these NBM projection neurons that were cholinergic; and (3) the collateralization, if any, of single NBM neurons to different subdivisions within SI, to homotopic areas of SI and SII, and to homotopic areas of SI and MI. Retrograde single-and double-labeling techniques were used to study NBM projections to electrophysiologically identified subdivisions of SI and to homotopic representational areas of SI and SII, and of SI and MI. Choline acetyltransferase immunocytochemistry was done to identify cholinergic NBM neurons. Of the retrogradely labeled NBM neurons that projected to selective subdivisions of SI, SII, and MI, 89%, 87%, and 88%, respectively, were cholinergic. We found a rostral-to-caudal progression of retrogradely labeled NBM neurons following a medial-to-lateral sequence of injections into subdivisions of SI. Overlapping groups of single-labeled NBM neurons were observed after injections of different tracers into adjacent subdivisions within SI or homotopic areas of SI and SII, and of SI and MI. We conclude that NBM innervation to SI, SII, and MI is mostly cholinergic in the rat, that each cortical area receives cholinergic afferents from neurons widely distributed within the NBM, and that each NBM neuron projects to a restricted cortical area without significant collateralization to adjacent subdivisions within SI or to homotopic areas of SI and SII, or SI and MI. © 1993 Wiley-Liss, Inc. 相似文献
4.
目的:比较正常肝组织与肝癌AH 109A,吉田肉瘤中谷氨酸脱氢酶,胆碱氧化酶和葡萄糖-6-磷酸酶的活力对~(67)Ga摄取与积累的影响;方法:制备~(67)Ga枸橼酸溶液给大鼠静注后处死大鼠,制备亚细胞悬液,液闪计数器测定放射活度.结果:~(67)Ga的放射活性在正常肝组织溶酶体中(55%积聚)显著高于肝癌AH109A(32%积聚)和吉田肉瘤(18%)积聚.谷氨酸脱氢酶的活力在正常肝组织,肝癌和吉田肉瘤分别是1830±s 320 U·L~(-1),23±s 6 U·L~(-1)和7±s 2 U·L~(-1);胆碱氧化酶的活力分别是46±s 10 U·L~(-1),25.0±s 0.4 U·L~(-1),2.0±0.4 U·L~(-1);葡萄糖-6-磷酸酶活力分别是2550±s 180 U·L~(-1),84±s 14 U·L~(-1),78±s13 U·L~(-1).结论:正常肝组织中溶酶体酶活力很强,对~(67)Ga的积累起较大作用.癌变组织酶活力降低而作用减弱.吉田肉瘤细胞无肝细胞特点,其溶酶体对~(67)Ga积累作用不大. 相似文献
5.
6.
κ-卡拉胶-魔芋多糖复配胶包埋的啤酒酵母细胞,经冻融处理后用于合成胞嘧啶核苷二磷酸胆碱(CDP-胆碱)。结果表明:250mL摇瓶中加入50mL反应液(葡萄糖400mol/L,CMP10mmol/L,磷酸碍碱50mmol/L,K2HPO4-KH2PO4缓冲液100mmol/L,MgSO410mmol/L,pH=8.0),固定化细胞1200g/L,34℃、150r/min下,反应4h后补加400mmol/L葡萄糖,反应8h可使60%以上的CMP转化为CDP-胆碱。反应液经灭菌和添加辅酶I(NAD^ )后,固定化细胞可连续使用4次,CDP-胆碱转化率维持在40%以上。 相似文献
7.
Murine thymus has been demonstrated to contain both cholinergic receptors and acetylcholinesterase activity. In the present study we have investigated the presence of the enzyme choline acetyltransferase in this organ, which is responsible for the synthesis of acetylcholine. Results reported here demonstrate that (1) an appreciable amount of the enzyme is already present in the thymus on the day of birth; (2) its expression is developmentally regulated; and (3) thymic atrophy, induced in young (2-week-old) and adult (6-week-old) mice by i.p. injection of hydrocortisone for 2 days, is accompanied by significant reduction of choline acetyltransferase activity only in young mice. Altogether these results demonstrate the presence in the murine thymus of functionally relevant markers of the cholinergic system that might interface the interactions between the nervous and immune systems. 相似文献
8.
L. Giovannelli F. Casamenti G. Pepeu 《Journal of neural transmission (Vienna, Austria : 1996)》1998,105(8-9):935-948
Summary. A unilateral quisqualic acid lesion was placed in the nucleus basalis magnocellularis of 3- and 24-month-old rats, and the
animals were sacrificed at different times post-surgery. The morphology and the number of the cholinergic neurons of the nucleus
basalis were analyzed by means of immunohistochemistry for cholineacetyltransferase, in order to evaluate the size and severity
of the lesion. Immunohistochemistry for the immediate early gene c-fos was also performed in order to clarify its role in
the process of neurodegeneration following the excitotoxin injection. The DNA laddering and TUNEL techniques were used to
define the type of cell death involved. At short times (4 hr) the lesion induced alterations in the morphology of cholinergic
neurons of the nucleus basalis. Subsequently, a significant decrease in the number of neurons was found in comparison to the
contralateral unlesioned side. In the older animals the loss of cholineacetyltransferase immunoreactivity had an earlier onset
(4 hr) than in the young (24 hr). C-fos expression was induced by the lesion and not by saline injection in the nucleus basalis
and in neighbouring areas of the brain as early as 4 hr after surgery. The c-fos protein was no longer present by 24 hr. Furthermore,
the c-fos gene product was consistently absent from the nuclei of cholinergic cells. The aged animals exhibited a slower and
smaller increase in c-fos as measured by counting the labelled nuclei in the injected area. Analysis of DNA fragmentation
did not provide any evidence for apoptosis as the type of cell death involved in the cholinergic degeneration. These results
indicate that the c-fos protein might have a protective role in the response to excitotoxic lesions. Furthermore, we have
shown that the aged brain displays a reduced ability to produce a c-fos-mediated plastic response to the lesion.
Received December 17, 1997; accepted February 17, 1998 相似文献
9.
The effect of intramuscular administration of a mixture of gangliosides (21% GM1, 39.7% GD1a,, 16% GD1b, 19% GT1 in a daily dose of 50 mg per kg upon the time course of changes in hippocampal acetylcholinesterase and choline acetyltransferase activities after extensive medioventral septal lesions in the rat was checked on days 3, 5, 18 and 50 after the operation. Following the early decrease in the enzyme activities to about 25% of control due to degeneration, a gradual recovery up to about 50% of control activity at the 50th day was found. When gangliosides were administered, the recovery in the activity of both enzymes was more pronounced. The ratio of the enzyme activities from the animals injected with gangliosides to that from uninjected animals was 1.45 and 1.48 on the 18th day and 1.62 and 1.50 on the 50th day after the operation, for choline acetyltransferase and acetylcholinesterase activity, respectively. Since no significant effect of ganglioside injection was seen at early postoperative times i.e. on days 3 and 5, the effects seen on days 18 and 50 seem to be specifically due to facilitation of the recovery processes and not to retardation of the degeneration processes.Assuming that the spontaneous recovery of cholinergic enzyme activity reflects reinnervation of the hippocampus through collateral sprouting, gangliosides would seem to facilitate the regrowth of new cholinergic nerve terminals. 相似文献
10.
The problem of synaptosome formation in the electric organ of Torpedo has been re-investigated using tissue from juvenile fish. This tissue is softer than adult material and can be easily homogenized in an Aldridge-type homogenizer. Homogenates so prepared contain a significant number of synaptosome-like structures which can be purified by differential and density gradient centrifugation. The purified particles are enriched in acetylcholine and choline acetyltransferase; they also contain lactate dehydrogenase activity, most of which is in an occluded form. The structure of these particles as revealed by electron microscopy is unusual in that they have no post-synaptic adhesions, relatively few synaptic vesicles and no intraterminal mitochondria. Because of their unusual morphology we have named these particles nerve terminal sacs (T-sacs). A high-affinity, hemicholinium-3 sensitive choline uptake system with an apparent Km of 1–3 μm is associated with the T-sacs. 相似文献