全文获取类型
收费全文 | 8916篇 |
免费 | 820篇 |
国内免费 | 273篇 |
专业分类
耳鼻咽喉 | 71篇 |
儿科学 | 114篇 |
妇产科学 | 80篇 |
基础医学 | 1553篇 |
口腔科学 | 99篇 |
临床医学 | 800篇 |
内科学 | 1250篇 |
皮肤病学 | 109篇 |
神经病学 | 499篇 |
特种医学 | 309篇 |
外科学 | 654篇 |
综合类 | 776篇 |
预防医学 | 845篇 |
眼科学 | 56篇 |
药学 | 1118篇 |
1篇 | |
中国医学 | 363篇 |
肿瘤学 | 1312篇 |
出版年
2024年 | 17篇 |
2023年 | 176篇 |
2022年 | 423篇 |
2021年 | 517篇 |
2020年 | 412篇 |
2019年 | 464篇 |
2018年 | 431篇 |
2017年 | 366篇 |
2016年 | 404篇 |
2015年 | 424篇 |
2014年 | 686篇 |
2013年 | 650篇 |
2012年 | 494篇 |
2011年 | 618篇 |
2010年 | 362篇 |
2009年 | 451篇 |
2008年 | 412篇 |
2007年 | 397篇 |
2006年 | 346篇 |
2005年 | 275篇 |
2004年 | 184篇 |
2003年 | 177篇 |
2002年 | 131篇 |
2001年 | 116篇 |
2000年 | 109篇 |
1999年 | 78篇 |
1998年 | 112篇 |
1997年 | 107篇 |
1996年 | 60篇 |
1995年 | 79篇 |
1994年 | 67篇 |
1993年 | 61篇 |
1992年 | 51篇 |
1991年 | 56篇 |
1990年 | 44篇 |
1989年 | 32篇 |
1988年 | 28篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 21篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Lipoblastoma is a relatively rare tumor that occurs in infancy and early childhood and arises from embryonic white fat. Although a benign tumor, lipoblastomas tend to recur and may resemble myxoid liposarcoma. The authors report 26 cases over a 15-year period at Texas Children's Hospital. There was a slight female predilection (14F:12M). The most common symptom was a painless mass with or without increasing size. The trunk, extremities, head and neck, retroperitoneum, inguinal canal, peritoneal cavity, and lung were the tumor sites. Most tumors were circumscribed lipoblastomas and the minority were diffuse infiltrative lipoblastomatosis. Reexcision for residual or recurrent tumor was necessary more frequently in patients with lipoblastomatosis. Histopathologic examination and ultrastructural examination revealed cellular neoplasms composed of immature adipocytes with relatively well-defined septa, frequent lipoblasts, a fine vascular network, and often a myxoid appearance resembling myxoid liposarcoma. Cytogenetics was performed in 4 cases with chromosome 8q abnormality being most common. The major concern with lipoblastoma in children is to completely excise the tumor to avoid leaving residual tumor and to prevent recurrences. Confusion with myxoid liposarcoma, well-differentiated liposarcoma, and typical lipomas may occur. Although asymptomatic, lipoblastomas may cause dysfunction of other organ systems due to mass effect. Complete surgical excision with at least 2 years of follow-up is the preferred therapy. 相似文献
72.
The effect of both intrahypothalamic and systemic administration of guanosine triphosphate (GTP) on lordosis behavior was studied in ovariectomized and ovariectomized-adrenalectomized, estrogen-primed rats (estradiol benzoate, 4 μg). This estrogen dose per se induced only weak or no lordosis behavior. Injection of GTP into the medial hypothalamic area (100 μg in 2.5 μl) elicited lordosis behavior with relatively short latency in 6 out of 7 rats. Systemic administration of GTP in a dose range of 0.8 mg to 5.0 mg to ovariectomized estrogen-primed rats, stimulated intense lordosis behavior in all subjects. Weak lordosis responses were displayed within the first 12 hr after GTP injection, but at 48 hr all rats were highly estrous. Lordosis behavior remained for up to eight days, its duration being related to the dose of GTP administered. GTP (2 mg) induced lordosis behavior in ovariectomized, adrenalectomized estrogen-primed rats, thus excluding the participation of adrenal steroids in this effect. The results are interpreted in terms of the stimulation of adenyl cyclase-cAMP systems by GTP. 相似文献
73.
Holm-Hansen C Stern B Rustad S Shao J Asjö B 《APMIS : acta pathologica, microbiologica, et immunologica Scandinavica》2000,108(9):608-616
The aim of this study was to determine HIV-1 V3 sequences, in vitro biological characteristics and co-receptor usage of virus isolates from Tanzania. Virus was isolated from 14 of 17 samples investigated. Four of the isolates induced syncytia in MT-2 cells and used the CXCR4 co-receptor, while the remaining 10 isolates used the CCR5 co-receptor characteristic of non-MT-2 tropic viruses. One of the four MT-2 tropic isolates also used the CCR5 and CCR3 co-receptors. Proviral DNA was detected in all 14 isolates and PCR products were subjected to DNA sequencing. Unambiguous V3 amino acid sequences were obtained from 11 amplificates. Phylogenetic analysis indicated that these sequences were divergent and clustered in HIV-1 subtypes A, C or D. Sequences from the viruses that induced syncytia in MT-2 cells presented characteristic V3 phenotype-associated amino acids. Results of co-receptor analysis are in concordance with the isolate phenotype as determined by replication and induction of syncytia in MT-2 cells. The considerable diversity illustrated by a limited number of isolates from Tanzania is in accordance with reports from other regions of Africa. 相似文献
74.
Joseph G. Altin Eloisa B. Pagler Christopher R. Parish 《European journal of immunology》1994,24(2):450-457
Previous studies have reported an association of the cell surface adhesion molecule CD2 with the T cell receptor and with CD45 on mouse and human T lymphocytes. In this study the association of CD2 with cell surface molecules was investigated using cell surface biotinylation of T lymphocytes, coupled with immunoprecipitation using two CD2-specific monoclonal antibodies (mAb) (RM2–5 and 12–15) and analysis by SDS-PAGE. Although both CD2 mAb immunoprecipitated CD2 from lysates of murine lymphocytes, it was found that mAb 12–15, but not RM2–5, co-precipitated two other molecules of 95 and 180 kDa. Subsequent studies revealed that the 95- and 180-kDa molecules were associated with a subspecies of CD2 (? 5%) on thymocytes, the antigen-specific T cell line D10, and splenic T cells but not B cells. Two lines of evidence were obtained consistent with the 95- and 180-kDa molecules being the β and α chains of LFA-1. Firstly, an analysis of 12–15 mAb immunoprecipitates on 4–12% gels under reducing and nonreducing conditions shows that the 95- and 180-kDa molecules have a molecular weight and migration pattern identical to LFA-1. Secondly, depletion of LFA-1 from lysates with LFA-1 mAb abolished the ability of CD2 mAb 12–15 to co-precipitate the 95- and 180-kDa molecules, thereby identifying these as the β and α chains of mouse LFA-1, respectively. These results provide evidence for the first time for an association of LFA-1 and CD2 on mouse T lymphocytes, and suggest that the association occurs with an immunologically distinct subspecies of CD2 molecules. 相似文献
75.
目的:对哮喘症患儿白细胞介素-4(IL-4)近侧启动子区进行克隆并分析其DNA序列的多态性。方法:对40名有明显家族及过敏史哮喘患儿和10名正常儿童,以多聚酶链式反应(PCR)结合单链构象多态性(SSCP)扩增、筛选IL-4近侧启动子片段,进一步构建正常对照和异常条带PCR产物的重组质粒pIL-4-Jx2,并用双脱氧链终止法对重组质粒进行序列测定。结果:在对40名患儿SSCP分析中发现了7组异常条带。DNA测序结果显示有4外变异位点于已知的调控元件之内或毗邻位点,1名病人-229位C被A所替代,该变异恰好位于IL-4正性调节元件-I(PRE-I)之内;2名病人负性调节元件-Ⅱ(NRE-Ⅱ)毗邻C被T所替代,TATA框前增加1个G;1名病人STAT-6元件附近缺少了ATTTT五碱基核苷酸。结论:过敏性哮喘患儿IL-4近侧启动子区DNA序列存在多态性,这可能与IL-4基因异常表达及哮喘的发病有关。 相似文献
76.
系统性红斑狼疮(systemiclupuserythematosus,SLE)是一种复合性多基因的自身免疫性疾病。遗传因素在SLE易感性方面起重要的作用。该文介绍目前已知几个与SLE的易感性有关的遗传基因。通过对这些基因研究,有利于阐明SLE的发病机制,进一步为SLE的预防、诊断和治疗提供重要的依据。 相似文献
77.
The amplification of hepatitis B virus (HBV) DNA sequences in sera for molecular epidemiology of HBV is an important application of the polymerase chain reaction (PCR) with regard to HBV. To simplify the PCR for this purpose, the optimal concentrations of SDS and detergents for carrying out the proteinase K digestion and the amplification of DNA by Taq polymerase were evaluated. It was found that by using 1% deoxycholic acid as detergent for the proteinase K step and diluting the digest 10 times before carrying out the PCR, the phenol extraction of DNA became superfluous. The sensitivity of this procedure equalled that of PCR after phenol extraction on comparable amounts of serum. Four pairs of oligonucleotide primers were compared for amplification of HBV DNA sequences in 48 sera previously subtyped with respect to hepatitis B surface antigen (HBsAg), and in eight sera with different genotypes of HBV, representing the subtypes of HBsAg P1 to P8, defined at an international meeting [Couroucé-Pauty et al.: "HBs Antigen Subtypes." Basel: Karger, 1976]. Two primer pairs, selected from conserved regions in the X and S genes of HBV, gave a positive PCR with sera harbouring all the eight different strains of HBV, resulting in DNA fragments consistent with the sizes deduced from genome sequence data. Two other primer pairs were selected in order to discriminate genotypes with regard to differences between d/y and w/r strains.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
78.
S. W. Schneider J. Lärmer R. M. Henderson H. Oberleithner 《Pflügers Archiv : European journal of physiology》1998,435(3):362-367
Proteins are usually identified by their molecular weights, and atomic force microscopy (AFM) produces images of single molecules
in three dimensions. We have used AFM to measure the molecular volumes of a number of proteins and to determine any correlation
with their known molecular weights. We used native proteins (the TATA-binding protein Tbp, a fusion protein of glutathione-S-transferase and the renal potassium channel protein ROMK1, the immunoglobulins IgG and IgM, and the vasodilator-stimulated
phosphoprotein VASP) and also denatured proteins (the red blood cell proteins actin, Band 3 and spectrin separated by SDS-gel
electrophoresis and isolated from nitrocellulose). Proteins studied had molecular weights between 38 and 900 kDa and were
imaged attached to a mica substrate. We found that molecular weight increased with an increasing molecular volume (correlation
coefficient = 0.994). Thus, the molecular volumes measured with AFM compare well with the calculated volumes of the individual
proteins. The degree of resolution achieved (lateral 5 nm, vertical 0.2 nm) depended upon the firm attachment of the proteins
to the mica. This was aided by coating the mica with suitable detergent and by imaging using the AFM tapping mode which minimizes
any lateral force applied to the protein. We conclude that single (native and denatured) proteins can be imaged by AFM in
three dimensions and identified by their specific molecular volumes. This new approach permits detection of the number of
monomers of a homomultimeric protein and study of single proteins under physiological conditions at the molecular level.
Received: 14 February 1997 / Received after revision: 8 September 1997 / Accepted: 8 September 1997 相似文献
79.
Usual human livers contain two major ALDH isozymes, i.e., cytosolic ALDH1 and mitochondrial ALDH2, while approximately 50% of Orientals are "atypical" and have only the ALDH1 and are missing the ALDH2. Instead, the atypical livers contain an enzymatically inactive but immunologically cross-reactive material (CRM) corresponding to the ALDH2 component. Some Orientals are found to be atypical also in the ALDH1 locus, i.e., they are missing the enzymatically active ALDH1 but contain a large amount of CRM corresponding to the ALDH1 component. cDNA for ALDH1 and that for ALDH2 were cloned and their nucleotide sequences were determined. The amino acid sequences of ALDH1 and ALDH2 were deduced from their cDNA sequences. The molecular abnormality of the inactive ALDH2(2) is found to be the substitution of Glu at the 14th position from the COOH-terminal of the protein by Lys which resulted from G----A transition in the gene. 相似文献
80.
Ad F. Roffel Willy G. in't Hout Rokus A. de Zeeuw Johan Zaagsma 《Naunyn-Schmiedeberg's archives of pharmacology》1987,335(5):593-595
Summary We have characterized the muscarine receptors in bovine tracheal and left ventricular membranes using 3H-dexetimide/pirenzepine and 3H-dexetimide/AF-DX 116 competition studies. Pirenzepinc exhibited low (M2) affinity binding to both preparations; K
d was 590 nM in left ventricle and 463 nM in trachea. AF-DX 116 exhibited high (M2) affinity binding to left ventricle (K
d = 95.6 nM); in tracheal membranes it bound with high (M2) affinity (K
d = 40.7 nM) to 74% of the receptors and with low (M3) affinity (K
d = 2.26 M) to 26% of the receptors. It is concluded that bovine tracheal muscle membranes contain a heterogeneous population of muscarine binding sites, the majority having M2 (heart) subtype characteristics and being located on the smooth muscle membranes; a minority having M3 (exocrine gland) subtype characteristics and presumed to be located in submucosal glands. This is the first report of high affinity binding of AF-DX 116 to non-cardiac peripheral muscarine receptors.
Send offprint requests to A. F. Roffel at the above address 相似文献