全文获取类型
收费全文 | 72917篇 |
免费 | 4640篇 |
国内免费 | 268篇 |
专业分类
耳鼻咽喉 | 1150篇 |
儿科学 | 2052篇 |
妇产科学 | 1414篇 |
基础医学 | 8217篇 |
口腔科学 | 1513篇 |
临床医学 | 7134篇 |
内科学 | 15030篇 |
皮肤病学 | 1128篇 |
神经病学 | 7004篇 |
特种医学 | 2522篇 |
外国民族医学 | 5篇 |
外科学 | 12547篇 |
综合类 | 879篇 |
一般理论 | 95篇 |
预防医学 | 6192篇 |
眼科学 | 1405篇 |
药学 | 4642篇 |
中国医学 | 112篇 |
肿瘤学 | 4784篇 |
出版年
2023年 | 398篇 |
2022年 | 652篇 |
2021年 | 1784篇 |
2020年 | 944篇 |
2019年 | 1573篇 |
2018年 | 1832篇 |
2017年 | 1323篇 |
2016年 | 1358篇 |
2015年 | 1492篇 |
2014年 | 2298篇 |
2013年 | 3241篇 |
2012年 | 4903篇 |
2011年 | 5098篇 |
2010年 | 2784篇 |
2009年 | 2484篇 |
2008年 | 4504篇 |
2007年 | 4795篇 |
2006年 | 4653篇 |
2005年 | 4608篇 |
2004年 | 4348篇 |
2003年 | 4012篇 |
2002年 | 3711篇 |
2001年 | 608篇 |
2000年 | 553篇 |
1999年 | 680篇 |
1998年 | 759篇 |
1997年 | 684篇 |
1996年 | 607篇 |
1995年 | 540篇 |
1994年 | 530篇 |
1993年 | 448篇 |
1992年 | 443篇 |
1991年 | 429篇 |
1990年 | 367篇 |
1989年 | 353篇 |
1988年 | 334篇 |
1987年 | 312篇 |
1986年 | 332篇 |
1985年 | 407篇 |
1984年 | 475篇 |
1983年 | 403篇 |
1982年 | 544篇 |
1981年 | 509篇 |
1980年 | 469篇 |
1979年 | 241篇 |
1978年 | 296篇 |
1977年 | 287篇 |
1976年 | 229篇 |
1975年 | 237篇 |
1973年 | 195篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
S C Joseph 《Journal of urban health》1988,64(6):506-512
52.
Derivation and spontaneous differentiation of human embryonic stem cells 总被引:16,自引:0,他引:16 下载免费PDF全文
Embryonic stem (ES) cells are unique cells derived from the inner cell mass of the mammalian blastocyst. These cells are immortal and pluripotent, retain their developmental potential after prolonged culture, and can be continuously cultured in an undifferentiated state. Many in vitro differentiation systems have been developed for mouse ES cells, including reproducible methods for mouse ES cell differentiation into haematopoietic and neural precursors, cardiomyocytes, insulin‐secreting cells, endothelial cells and various other cell types. The derivation of new human ES cell lines provides the opportunity to develop unique models for developmental research and for cell therapies. In this review we consider the derivation and spontaneous differentiation of human ES cells. 相似文献
53.
Joseph M. Becker M.D. Peter H. Arger Alan J. Wein A. Richard Kendall 《Urologic radiology》1983,5(1):127-129
A 35-year-old man discovered a 1-cm nodule at the upper pole of the left testicle after blunt focal trauma. While the pain, tenderness, and location suggested hematoma or appendiceal torsion, the demonstration by ultrasound of the size, cystic nature, and extraparenchymal location was consistent with the rarely documented cyst of the tunica albuginea. 相似文献
54.
55.
Joseph M Dhahbi Shelley X Cao Patricia L Mote Brian C Rowley John E Wingo Stephen R Spindler 《The Journal of nutrition》2002,132(1):31-37
Molecular chaperones assist in the biosynthesis and processing of proteins. Most chaperones are induced by physiological stresses. We have shown that dietary energy restriction decreases the mRNA and protein levels of many endoplasmic reticulum chaperones in the livers of mice. Here, we have investigated the response of chaperone mRNA to feeding. Control and 50% energy-restricted C3B10RF1 mice were deprived of food for 24 h, fed, and killed 0, 1.5, 5 or 12 h after feeding. Chaperone mRNAs were strongly induced as early as 1.5 h after feeding in control and energy-restricted mice. The integrated levels of these mRNA over 24 h were significantly lower in energy-restricted mice. The mRNA response to energy intake was mirrored over the course of days in the level of chaperone protein. A similar but smaller response to feeding was found in kidney and muscle. Puromycin and cycloheximide failed to inhibit the feeding response, suggesting that feeding releases chaperone expression from an unstable inhibitor. Studies with dibutyryl-cAMP- and glucagon-supplemented, normal and streptozotocin-diabetic mice suggest that glucagon and insulin may be mediators of the feeding response. Adrenalectomy enhanced the feeding induction, but dexamethasone administration had no effect. Thus, postprandial changes in insulin and glucagon may link chaperone gene expression to feeding, possibly in several tissues including liver. 相似文献
56.
Zia Hossein Ma Joseph K. H. O'Donnell John P. Luzzi Louis A. 《Pharmaceutical research》1991,8(4):502-504
Dimethyl isosorbide (DMI), which is currently under investigation for its potential use as a pharmaceutical vehicle and drug permeation enhancer, is a water-miscible liquid with relatively low viscosity. The solubilization behavior of DMI as a cosolvent for nonpolar drugs was characterized via dielectric constant measurements of binary solvent systems containing DMI and either water, propylene glycol (PG), or polyethylene glycol (PEG). Evidence from the dielectric constant profiles and NMR studies suggest that DMI undergoes complexation with water and PG, but not with PEG, through hydrogen bonding interactions. The solvent complexation exhibited a major effect on the solubilities of prednisone, dexamethasone, and prednisolone in the mixed solvent systems. Maximum solubility of each drug was found to occur near a DMI/water or DMI/PG concentration ratio of 1:2. In the DMI–PEG mixed system, while there is no apparent interaction between DMI and PEG molecules, the solubility of prednisone was found to increase with decreasing dielectric constant. 相似文献
57.
Michael C. Dalsing MD Melissa Kevorkian BS Beth Raper BA Craig Nixon MS Stephen G. Lalka MD Dolores F. Cikrit MD Joseph L. Unthank PhD Malcolm B. Herring MD 《Annals of vascular surgery》1989,3(2):127-133
This study evaluates the potential for endothelial seeding of a collagen-impregnated Dacron graft with or without surface modifiers (fibronectin, heparin) to attach and retain these cells during flow. Human umbilical endothelial cells were harvested, cultured, labeled with Indium111-oxine and seeded onto 30 mm X 4 mm diameter grafts. Six graft surfaces were studied: 1) a collagen-impregnated Dacron graft, HemashieldR (C); 2) C + fibronectin (C + F); 3) C + heparin (C + H); 4) C + F + H; 5) HytrelR + F (Hyt + F); and 6) Hyt + F + H. Radioactive loss determined the percentage attachment and then percentage retention of labeled inoculum after a one-hour in vitro perfusion. Scanning electron and light microscopy demonstrated the endothelium on the graft surface following perfusion. Fibronectin-coated grafts had a significantly higher percentage attachment than those without fibronectin (ANOVA, P less than 0.05). However, the percentage retention following perfusion was similar for all Dacron grafts and statistically inferior to the HytrelR grafts studied (ANOVA, P less than 0.05). SEM evaluation of the C + F + H graft surface was qualitatively the most impressive Dacron surface for seeding, yet was inferior to the HytrelR graft. We conclude that fibronectin benefits the initial attachment of endothelium to collagen-coated Dacron rivaling the HytrelR surface. Fibronectin does not improve percentage retention of the HemashieldR surface during perfusion, therefore, some of its initial benefit is lost. 相似文献
58.
Cancer risk after evaluation for infertility 总被引:3,自引:0,他引:3
L A Brinton L J Melton G D Malkasian A Bond R Hoover 《American journal of epidemiology》1989,129(4):712-722
To evaluate cancer risk by various causes of infertility, the authors conducted a retrospective cohort study among 2,335 women evaluated for infertility at the Mayo Clinic between 1935 and 1964. Most cancers occurred at expected frequencies, with the exception of cancers of the thyroid (standardized incidence ratio (SIR) = 2.6) and other endocrine glands (SIR = 6.7), although analyses were based on small numbers. Patients with progesterone deficiencies (31 per cent of the study subjects) had a 20 per cent higher cancer risk than did those with other causes of infertility, with excesses deriving primarily from cancers of the lung, cervix, ovary, and thyroid and from melanoma. Breast cancer risk, however, was not elevated in either patients with progesterone deficiencies (SIR = 0.9) or patients with other causes of infertility (SIR = 1.0). Examination of other parameters of infertility, including age at evaluation, type of infertility (primary vs. secondary), and years of attempted conception, showed no elevated risks of breast cancer in any subgroup. These results fail to support previous studies that have linked progesterone deficiencies among infertile women to elevated breast cancer risk. However, the data suggest a possible involvement of a progesterone deficiency in the etiology of other cancers, particularly thyroid cancer and melanoma. 相似文献
59.
60.