全文获取类型
收费全文 | 2503篇 |
免费 | 193篇 |
国内免费 | 153篇 |
专业分类
耳鼻咽喉 | 25篇 |
儿科学 | 71篇 |
妇产科学 | 18篇 |
基础医学 | 278篇 |
口腔科学 | 63篇 |
临床医学 | 333篇 |
内科学 | 632篇 |
皮肤病学 | 37篇 |
神经病学 | 176篇 |
特种医学 | 98篇 |
外科学 | 305篇 |
综合类 | 63篇 |
一般理论 | 2篇 |
预防医学 | 115篇 |
眼科学 | 68篇 |
药学 | 241篇 |
中国医学 | 7篇 |
肿瘤学 | 317篇 |
出版年
2024年 | 6篇 |
2023年 | 14篇 |
2022年 | 13篇 |
2021年 | 46篇 |
2020年 | 32篇 |
2019年 | 50篇 |
2018年 | 57篇 |
2017年 | 48篇 |
2016年 | 52篇 |
2015年 | 81篇 |
2014年 | 121篇 |
2013年 | 119篇 |
2012年 | 169篇 |
2011年 | 159篇 |
2010年 | 113篇 |
2009年 | 94篇 |
2008年 | 123篇 |
2007年 | 240篇 |
2006年 | 146篇 |
2005年 | 144篇 |
2004年 | 115篇 |
2003年 | 109篇 |
2002年 | 108篇 |
2001年 | 86篇 |
2000年 | 84篇 |
1999年 | 67篇 |
1998年 | 37篇 |
1997年 | 39篇 |
1996年 | 35篇 |
1995年 | 32篇 |
1994年 | 18篇 |
1993年 | 21篇 |
1992年 | 36篇 |
1991年 | 25篇 |
1990年 | 37篇 |
1989年 | 23篇 |
1988年 | 24篇 |
1987年 | 16篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1971年 | 8篇 |
1970年 | 5篇 |
1967年 | 5篇 |
排序方式: 共有2849条查询结果,搜索用时 0 毫秒
991.
Zhou T Hamer DH Hendrickson WA Sattentau QJ Kwong PD 《Proceedings of the National Academy of Sciences of the United States of America》2005,102(41):14575-14580
The unique ligation properties of metal ions are widely exploited by proteins, with approximately one-third of all proteins estimated to be metalloproteins. Although antibodies use various mechanisms for recognition, to our knowledge, none has ever been characterized that uses an interfacial metal. We previously described a family of CD4-reactive antibodies, the archetype being Q425. CD4:Q425 engagement does not interfere with CD4:HIV-1 gp120 envelope glycoprotein binding, but it blocks subsequent steps required for viral entry. Here, we use surface-plasmon resonance to show that Q425 requires calcium for recognition of CD4. Specifically, Q425 binding of calcium resulted in a 55,000-fold enhancement in affinity for CD4. X-ray crystallographic analyses of Q425 in the presence of Ca(2+), Ba(2+), or EDTA revealed an exposed metal-binding site, partially coordinated by five atoms contributed from four antibody complementarity-determining regions. The results suggest that Q425 recognition of CD4 involves direct ligation of antigen by the Q425-held calcium, with calcium binding each ligating atom of CD4 with approximately 1.5 kcal/mol of binding energy. This energetic contribution, which is greater than that from a typical protein atom, demonstrates how interfacial metal ligation can play a unique role in antigen recognition. 相似文献
992.
993.
Chloe M Mak Yok-Lam Kwong Ching-Wan Lam See-Ching Chan Chung-Mau Lo Sheung-Tak Fan Chee-My Chang Yuk-Kwong Lau Lok-Sun U Sidney Tam 《Amyloid》2007,14(4):293-297
Familial transthyretin amyloidosis (ATTR), caused by mutant transthyretin deposition, is mainly characterized by peripheral neuropathy, autonomic dysfunction, and cardiomyopathy. There are few reports among the Chinese population. We previously described the TTR mutation (Val30Ala) in the first Hong Kong Chinese family with ATTR. In this study, we report the progress of this family and describe another three unrelated Chinese kinships newly diagnosed with ATTR. The second proband presented mainly with peripheral neuropathy, and genetic analysis of the TTR gene showed alanine-to-serine substitution at amino acid 97. The third proband complained of autonomic dysfunction, and a novel missense mutation of glycine-to-glutamate substitution at amino acid 67 was found. The fourth patient presented with peripheral neuropathy and diastolic cardiomyopathy with the mutation threonine-to-lysine at codon 59. Diagnosis was delayed for more than 2 years. We performed DNA analysis in 46 subjects and detected a total of 21 patients, including the four probands, affected with ATTR, 15 of whom were still at a symptom-free stage at the time of writing. We conclude that ATTR remains largely underdiagnosed in the Chinese population. A high clinical suspicion is crucial for a timely diagnosis and can thus lead to a significant decrease in morbidity and mortality. 相似文献
994.
Influence of tumor-promoting phorbol esters on the phosphorylation of membrane proteins in lymphocytes 总被引:1,自引:0,他引:1
Treatment of bovine lymphocytes with 12-O-tetradecanoyl-phorbol-13-acetate(TPA) (108 M) for as little as 5 min significantly altersthe ability of membrane-particulate fractions to phosphorylateproteins using in situ protein kinases and exogenous [-32P]ATP.After 20 min of treatment, the phosphorylation of two proteinswith mol. wts. of 65K and 74K in the isolated membrane-particulatefraction is increased approximately 3035%, whereas thephosphorylation of a 130K protein is almost completely suppressed.The ability of different phorbol esters to alter membrane proteinphosphorylation correlates well with their potency as tumorpromoters in mouse epidermis and as comitogens in phytohemagglutinin-treatedlymphocytes. This phorbol ester response appears to have a lowtemperature coefficient since cells treated with TPA at 4?Calso responded, although at a slower rate. This action of TPAis neither mimicked nor antagonized by dibutyryl cAMP (1 mM);moreover, it is not affected by retinpic acid, an agent whichblocks several other phorbol ester effects in these cells. Inhibitionof protein synthesis with cycloheximide also fails to influencethis response. In contrast, trifluoperazine, an inhibitor ofcalmodulin function and certain lipid-dependent protein kinases,depressed the phosphorylation of the 65K and 74K proteins tobelow the control level. 相似文献
995.
国产沉香化学成分的研究——Ⅴ.三个2-(2-苯乙基)色酮衍生物的分离和鉴定 总被引:1,自引:0,他引:1
自国产沉香(Lignum Aquiarilae sinensis)[瑞香料(Thymeleaceae)植物]乙醇提取物的醋酸乙酯溶解部分经硅胶层析,分寓得到三个2-(2-苯乙基)色酮衍生物。根据光谱(UV,IR,~(13)C NMR,~1H NMR和MS)数据分析确定其中两个为新化合物;其结构分别为5,8-二羟基-2-(2-对甲氧基苯乙基)色酮(2)和6,7-二甲氧基-2-(2-对甲氧基苯乙基)色酮(3)。另外一个为已知化合物5,8-二羟基-2-(2-苯乙基)色酮,(1),是首次从该植物中得到。 相似文献
996.
从人工发酵培养的蜜环菌[Armillaria mellea(Vahl.ex Fr.)Quel.属白蘑科(Tricholometaceae)真菌]菌丝体的石油醚提取物中,经硅胶层析分离得到一新的倍半萜醇芳香酸酯类化合物,命名为蜜环菌癸素(armillaripin)。根据光谱(UV,IR,~1HNMR,~(13)CNMR和MS)分析推测其化学结构,并进一步用X-线衍射晶体解析法确证其结构和其相对构型。 相似文献
997.
998.
Solubilization of hemoglobin S by other hemoglobins. 总被引:2,自引:2,他引:2
R E Benesch R Edalji R Benesch S Kwong 《Proceedings of the National Academy of Sciences of the United States of America》1980,77(9):5130-5134
The polymerization of mixtures of Hb S with hemoglobins A, A2, and F has been investigated by analysis of the proportions of S and non-S hemoglobin both in the supernate and in the pellet after centrifugation. In all cases the non-S hemoglobin was incorporated into the polymer even in the absence of hybrids in the order A > A2 > F. The solubility of Hb S is substantially increased by the other hemoglobins, especially by Hb F, which would account for its antisickling effect. It appears that the excluded volume effect of the other hemoglobin on Hb S is largely counterbalanced by the solubilizing effect arising from the interaction between the two hemoglobins in solution. The ability of hybrid hemoglobins to gel was demonstrated directly with tetramers in which alpha beta s dimers were covalently linked to alpha beta A, alpha delta A2, and alpha gamma F dimers. 相似文献
999.
Early glial responses after acute elevated intraocular pressure in rats 总被引:16,自引:0,他引:16
PURPOSE: To study the responses of glial cells to a short-term elevation in intraocular pressure (IOP) in rats. METHODS: Adult Sprague-Dawley albino rats, 45 to 55 days old, were given India ink intracamerally. After 7 days, 200 spots of laser burn over 360 degrees were delivered by an Argon laser (620-637 nm; 200 mW; 200 mm; 0.2 seconds) aimed at the ink deposits in the trabecular meshwork. IOP was recorded and eye tissues at 12 hours and 1, 3, 5, 7, or 14 days after laser were examined by immunohistochemistry with antibodies against glial fibrillary acidic protein (GFAP), vimentin, S-100, ED1, and OX42. To evaluate neuronal loss, the number of cells in the retinal ganglion cell layer (RGCL) was counted on flat preparations of retinas at various times after elevation of IOP. RESULTS: Significant elevation of IOP from 1 to 7 days and loss of cells in the RGCL from 3 days onward were noted after trabecular laser photocoagulation. In the inner retina, there was a gradual and sustained increase in GFAP and S-100 immunoreactivity, but only a transient increase in vimentin immunoreactivity. No remarkable changes in GFAP, vimentin, and S-100 immunoreactivity were noted at the optic nerve head (ONH). ED1- and OX42-labeled cells were noted in the choroidal plexus, the parapapillary region of the optic nerve, and the ONH from 3 days onward, whereas expression in the retina was unremarkable. CONCLUSIONS: There is differential expression of glial cell markers in the retina and the ONH, with early loss of cells in the RGCL in response to the elevation of IOP. Macroglia such as astrocytes and Müller cells may be involved in the pathophysiology of retinal ganglion cell death or retinal repair, and activated microglial/phagocytic cells may play an important role in modulating the changes in the ONH that occur with the elevation of IOP. 相似文献
1000.
蜜环菌菌丝体化学成分的研究——Ⅶ.丙酮提取物中化学成分的分离与鉴定 总被引:6,自引:0,他引:6
自人工液体发酵生产的白磨科(Tricholomataceae)蜜环菌[Armiilaria meilea(Vahl.exFr.)Quel.]菌丝体的丙酮提取物中分离得到八个化合物,其中三个为原伊鲁烷型倍半萜醇芳香酸酯类化合物。根据光谱(UV,IR,1H-NMR,13C-NMR,2D-NMR和MS)分析,其中一个为已知物4′-methylmelledonal(Ⅰ),两个为新化合物即密环菌丑素(armillaritin)和蜜环菌寅素(armillarivin),其结构分别为式Ⅱ和Ⅲ。另外五个为已知物赤藓醇(D-erythritol),甘露醇(Dmannitol),杜鹃花酸(azclaic acid)、苔藓酸(orsellinic acid)和甘油醇-α-单油酸酯(glycerin-α-monooleate)。 相似文献