全文获取类型
收费全文 | 12196篇 |
免费 | 1378篇 |
国内免费 | 13篇 |
专业分类
耳鼻咽喉 | 159篇 |
儿科学 | 389篇 |
妇产科学 | 214篇 |
基础医学 | 1760篇 |
口腔科学 | 156篇 |
临床医学 | 1528篇 |
内科学 | 2242篇 |
皮肤病学 | 120篇 |
神经病学 | 1222篇 |
特种医学 | 364篇 |
外科学 | 1627篇 |
综合类 | 460篇 |
一般理论 | 10篇 |
预防医学 | 1381篇 |
眼科学 | 159篇 |
药学 | 836篇 |
中国医学 | 5篇 |
肿瘤学 | 955篇 |
出版年
2021年 | 146篇 |
2020年 | 118篇 |
2019年 | 173篇 |
2018年 | 217篇 |
2017年 | 156篇 |
2016年 | 160篇 |
2015年 | 196篇 |
2014年 | 273篇 |
2013年 | 414篇 |
2012年 | 621篇 |
2011年 | 570篇 |
2010年 | 314篇 |
2009年 | 356篇 |
2008年 | 569篇 |
2007年 | 682篇 |
2006年 | 613篇 |
2005年 | 604篇 |
2004年 | 547篇 |
2003年 | 506篇 |
2002年 | 536篇 |
2001年 | 412篇 |
2000年 | 388篇 |
1999年 | 367篇 |
1998年 | 175篇 |
1997年 | 145篇 |
1996年 | 122篇 |
1995年 | 107篇 |
1994年 | 122篇 |
1993年 | 136篇 |
1992年 | 286篇 |
1991年 | 240篇 |
1990年 | 241篇 |
1989年 | 249篇 |
1988年 | 197篇 |
1987年 | 202篇 |
1986年 | 171篇 |
1985年 | 187篇 |
1984年 | 141篇 |
1983年 | 137篇 |
1982年 | 93篇 |
1979年 | 116篇 |
1978年 | 99篇 |
1977年 | 93篇 |
1976年 | 100篇 |
1975年 | 78篇 |
1974年 | 102篇 |
1973年 | 91篇 |
1972年 | 90篇 |
1971年 | 84篇 |
1970年 | 77篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
K. E. Warnes M. J. Morris M. E. Symonds I. D. Phillips I. J. Clarke J. A. Owens I. C. McMillen 《Journal of neuroendocrinology》1998,10(1):51-57
We have characterized the localization and the ontogenetic changes in Neuropeptide tyrosine (NPY) before birth and investigated the regulation of NPY expression by cortisol and undernutrition in the fetal sheep hypothalamus during late gestation. Using immunohistochemistry, we have identified NPY-containing neurons in the infundibular nucleus and the internal layer of the median eminence in fetal hypothalami collected between 110 and 147 days gestation. NPY projections were also present in the paraventricular nucleus (PVN) of fetal hypothalami at all ages between 110 days gestation and term. There was a significant increase in the amount of immunoreactive NPY/g hypothalamus between 87 and 113 days and 131–140 days gestation and a further significant increase after 141 days gestation. The total hypothalamic content of immunoreactive NPY increased significantly between 87 and 113 days and 141–145 days gestation. The levels of NPY mRNA: 18S rRNA in the mediobasal region of the fetal hypothalamus were significantly higher at 145–146 days gestation than at any earlier gestational age between 116 and 141 days gestation. Cortisol (2.5–3.0 mg/24 h) was infused intrafetally between 109 and 116 days gestation. The ratio of NPY mRNA: 18s rRNA in the mediobasal region of the fetal hypothalamus was significantly higher in the cortisol-infused group when compared with the saline-infused control group at 116 days gestation. Maternal, and hence fetal undernutrition, was induced between 110 and 146 days gestation. At 145–146 days gestation the ratio of NPY mRNA: 18S rRNA in the mediobasal region of the fetal hypothalamus was significantly higher in the undernutrition group when compared with control animals. We have therefore demonstrated that NPY is present in the hypothalamus of the sheep fetus before birth and that hypothalamic NPY content and NPY mRNA increase before delivery. We have also found that glucocorticoids and undernutrition stimulate increases in NPY mRNA levels in the hypothalamus before birth. 相似文献
63.
An increase in intracellular Na+ during ischaemia has been associated with myocardial injury. In this study, we determined whether inhibition of Na+/K+ ATPase activity contributes to this increase and whether Na+/K+ ATPase activity can be maintained by provision of glucose to perfused rat hearts during low flow, 0.5 ml/min, ischemia. We used 31P NMR spectroscopy to determine changes in myocardial energetics and intracellular and extracellular volumes. 23Na NMR spectroscopy, with DyTTHA3- present as a shift reagent, was used to measure changes in intracellular Na+ and 87Rb NMR spectroscopy was used to estimate Na+/K+ ATPase activity from Rb+ influx rates, Rb+ being an NMR-sensitive congener of K+. In hearts provided with 11 mM glucose throughout ischemia, glycolysis continued and ATP was twofold higher than in hearts without glucose. In the glucose-hearts, Rb+ influx rate was threefold higher, intracellular Na+ was fivefold lower at the end of ischemia and functional recovery during reperfusion was twofold higher. We propose that continuation of glycolysis throughout low flow ischemia allowed maintenance of sufficient Na+/K+ ATPase activity to prevent the increase in intracellular Na+ that would otherwise have led to myocardial injury. 相似文献
64.
A patient with marked exophthalmos secondary to thyroid eye disease
presented for tarsorrhaphy and removal of orbital fat. A single
superolateral peribulbar injection was performed. After injection of 3.5 ml
of local anaesthetic solution, the globe suddenly dislocated anteriorly.
This complication has not been described previously. In patients with
exophthalmos, general anaesthesia should be considered as the method of
choice for ophthalmic procedures.
相似文献
65.
W. Bastain M. J. Boyce L. E. Stafford P. B. Morton D. A. Clarke H. F. Marlow 《European journal of clinical pharmacology》1988,34(5):469-473
Summary The pharmacokinetics of xamoterol, a -adrenoceptor partial agonist under clinical evaluation for the treatment of mild to moderate heart failure, have been studied in 12 healthy male subjects. They received 14 mg i.v. and oral doses of 50 and 200 mg as a tablet and 200 mg as a solution in a 4 way cross-over design.After i.v. dosing the elimination half-life was 7.7 h, the total body clearance was 224 ml·min–1 and the volume of distribution at steady-state (Vss) was 48 l. Sixty-two percent of the dose was recovered unchanged in urine. After oral doses, the absolute bioavailability of xamoterol was shown to be 5% irrespective of whether the dose was administered as a tablet or solution. Peak plasma concentrations occurred at about 2 h for the tablet dose and slightly earlier (1.4 h) for the solution. Peak plasma concentration, AUC and urinary recovery of unchanged drug increased in proportion to dose. The apparent elimination half-life after oral doses (16 h) was significantly longer than that observed after an intravenous dose.Despite the low bioavailability, the degree of inter-subject variability of oral bioavailability was small probably indicating that the controlling factor is the hydrophilic nature of the molecule rather than extensive first pass metabolism or poor dissolution of xamoterol from the tablet formulation. 相似文献
66.
Bronchoalveolar lavage was used to obtain alveolar macrophages (AM) from the lower respiratory tract of healthy normal volunteers. Monoclonal antibody (MoAb) probes specific against macrophage determinants were then applied, in conjunction with density separation techniques, to identify and isolate three relatively homogeneous subpopulations from the AM pool. The MoAbs used, RFD1 and RFD7, have previously been shown to differentiate between "dendritic" cells and mature macrophages, respectively, in normal tissue. In addition to these two phenotypically distinct AM subsets (RFD1+D7- and RFD1-D7+ AM), a third AM subpopulation was isolated, which appeared to express both markers (RFD1+D7+). All three separated macrophage subsets were morphologically similar but exhibited distinct differences in surface receptor expression, enzyme content and physiology. Isolated RFD1+D7- AM (the phenotype of "dendritic" cells) did not adhere to the glass, had weak expression of C3b and FcR1 receptors, low fibronectin content and lysosomal activity; only a small proportion of these cells exhibited phagocytosis. The other two isolated AM subsets adhered to glass, expressed C3b and FcR1 receptors, had high fibronectin and acid phosphatase content, and a large majority exhibited phagocytic capacity; qualitative and quantitative differences in these features existed between the two AM subtypes. Furthermore, a diverse spectrum of hexose monophosphate shunt activity was observed throughout all three AM subpopulations, with the highest activity being recorded in the non-adherent AM. These data support the concept of a dynamic heterogeneity within the AM population. The variation in surface antigen expression and physiological capabilities observed amongst the three isolated AM subsets implies the presence of functionally distinct AM within the human lung, which, during steady-state conditions, may be critically balanced under the influence of stimuli in their local microenvironment. In support, proportional and functional shifts have been witnessed amongst these three AM subpopulations with the advent of disease. 相似文献
67.
We have studied the role of electrical activity in the elimination of axonal targeting errors, which is a normal process in brain development. The experiments were focused on the isthmo-optic nucleus (ION), which, in adults, projects in topographical order on the contralateral retina. During embryogenesis, however, a few isthmo-optic neurons project to the ipsilateral retina, and many project to topographically inappropriate parts of the contralateral one; both kinds of targeting error are known to be eliminated by the deaths of the parent neurons. We injected tetrodotoxin (TTX) intraocularly at embryonic days 13 and 15 and, on the latter, applied a retrograde label to the retina of the same eye. Embryos were fixed at embryonic day 17. In some embryos, the label was a peripherally placed fleck of the carbocyanine dye "diI"; the resulting retrogradely labeled neurons in the contralateral ION were much more widely scattered in the TTX-injected embryos than in controls (errors in topography). In other embryos, the label was a solution of rhodamine-B-isothiocyanate (RITC) injected into the vitreous body; this yielded several ipsilaterally labeled isthmo-optic neurons in the TTX-injected embryos, but virtually none in the controls. The numbers of both kinds of aberrantly projecting neuron approached those previously reported near the beginning of the ION's period of neuronal death. We conclude that electrical activity plays an important role in the elimination of axonal targeting errors in the chick embryo's isthmo-optic system. 相似文献
68.
69.
Yu Y Harris RI Yang JL Anderson HC Walsh WR 《Journal of biomedical materials research. Part A》2004,70(1):122-128
Differential expression of multiple osteogenic factors may be responsible for the different osteoinductivity of osteosarcoma cell lines. We compared in vivo osteoinductivity of human osteosarcoma cell lines (Saos-2 vs. U-2 OS) in nude mice, and their in vitro expression of various osteogenic factors of protein level by quantitative immunocytochemistry and mRNA level by RT-PCR and/or in situ hybridization. Saos-2 cells, but not U-2 OS, were osteoinductive in vivo. Significantly higher expression (independent t-test, all p < 0.005) of osteogenic factors were observed in Saos-2 cells compared with U-2 OS, which included bone morphogenetic proteins (particularly BMPs-2, 3, 4, and 7), transforming growth factor-beta (TGF-beta), BMP receptor (BMPR)-1A, receptor-regulated Smads (R-Smads), Smads 1, 2, and 5, and common-mediator Smad (Co-Smad), Smad 4. In contrast, U-2 OS cells expressed higher levels of inhibitory Smad 6 (I-Smad) protein than Saos-2 cells (p < 0.001). These results suggest that a combination of osteogenic factors (BMPs, TGF-beta, BMPRs, and R/Co-Smads) against I-Smad may play important roles in the Saos-2 cell osteoinductivity. This may have a clinical implication in selecting key osteogenic factors for combined therapy for bone defect diseases. The characterized cell lines can be used as positive and negative controls for the assessments of both in vitro and in vivo bone formation capabilities of designed tissues or biomaterials. 相似文献
70.
Clarke B Gordon M Moodley M Naidoo R Chetty R 《International journal of surgical pathology》2003,11(4):253-260
Cervical cancer is the most common gynecologic malignancy of the developing world. The oncogenic role of human papilloma virus (HPV) is well known. Attention is now focusing on the complicit genetic changes, which allow progression of these tumors. Regarding these changes, deletion of tumor suppressor genes (loss of heterozygosity [LOH]) is the preferred pathway of progression with only a subset manifesting microsatellite instability (MSI). Implicated loci include 3p14.1-22. Several studies suggest that the mutator phenotype in cervical cancer may correlate with higher grade tumors, more advanced disease stage, and poor outcome. Unlike colorectal cancer, in which an inverse relationship has been demonstrated between microsatellite instability and loss of heterozygosity, cervical cancers expressing MSI have been found to coexpress LOH at other loci. In this study we analyzed 8-microsatellite loci including p53, DCC, APC, the MMR gene hMLH1 and 2 regions of interest on chromosome 3 in a high-risk population group in which HPV infection is endemic. 相似文献