全文获取类型
收费全文 | 28495篇 |
免费 | 2340篇 |
国内免费 | 34篇 |
专业分类
耳鼻咽喉 | 346篇 |
儿科学 | 1018篇 |
妇产科学 | 677篇 |
基础医学 | 3428篇 |
口腔科学 | 576篇 |
临床医学 | 3680篇 |
内科学 | 5246篇 |
皮肤病学 | 441篇 |
神经病学 | 2770篇 |
特种医学 | 1025篇 |
外科学 | 3590篇 |
综合类 | 670篇 |
一般理论 | 46篇 |
预防医学 | 3164篇 |
眼科学 | 505篇 |
药学 | 2126篇 |
2篇 | |
中国医学 | 33篇 |
肿瘤学 | 1526篇 |
出版年
2021年 | 398篇 |
2020年 | 236篇 |
2019年 | 346篇 |
2018年 | 418篇 |
2017年 | 299篇 |
2016年 | 359篇 |
2015年 | 408篇 |
2014年 | 621篇 |
2013年 | 931篇 |
2012年 | 1175篇 |
2011年 | 1327篇 |
2010年 | 760篇 |
2009年 | 557篇 |
2008年 | 1161篇 |
2007年 | 1287篇 |
2006年 | 1268篇 |
2005年 | 1189篇 |
2004年 | 1185篇 |
2003年 | 1024篇 |
2002年 | 966篇 |
2001年 | 963篇 |
2000年 | 980篇 |
1999年 | 776篇 |
1998年 | 292篇 |
1997年 | 271篇 |
1996年 | 237篇 |
1995年 | 241篇 |
1994年 | 215篇 |
1992年 | 687篇 |
1991年 | 705篇 |
1990年 | 656篇 |
1989年 | 601篇 |
1988年 | 597篇 |
1987年 | 552篇 |
1986年 | 563篇 |
1985年 | 541篇 |
1984年 | 425篇 |
1983年 | 418篇 |
1982年 | 269篇 |
1981年 | 252篇 |
1980年 | 228篇 |
1979年 | 423篇 |
1978年 | 309篇 |
1977年 | 267篇 |
1976年 | 241篇 |
1975年 | 229篇 |
1974年 | 299篇 |
1973年 | 261篇 |
1972年 | 233篇 |
1971年 | 227篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Studies on telomere and telomerase biology are fundamental to the understanding of human ageing, and age-related diseases such as cancer. However, human studies are hampered by the lack of fully reflective animal model systems. Here we describe basic studies of telomere length and telomerase activity in sheep tissues and cells. Terminal restriction fragment lengths from sheep tissues ranged from 9 to 23 kb, with telomerase activity present in testis but suppressed in somatic tissues. Sheep fibroblasts had a finite lifespan in culture, after which the cells entered senescence. During in vitro growth the mean terminal restriction fragment lengths decreased in size at a rate of 210 and 350 bp per population doubling (PD). Senescent skin fibroblasts had increased levels of p53 and p21WAF1 compared to young cells. Incubation of senescent cells with siRNA duplexes specific for p53 suppressed p53 expression and allowed the cells to re-enter the cell cycle. Five PDs beyond senescence the siRNA-treated cells reached a second proliferative barrier. This study shows that telomere biology in sheep is similar to that in humans, with senescence in sheep GM03550 fibroblasts being a telomere-driven, p53-(p21WAF1)-dependent process. Therefore sheep may represent an alternative model system for studying telomere biology, replicative senescence, and by implication human ageing. 相似文献
993.
A. K. H. Lim D. J. Nikolic-Paterson F. Y. Ma E. Ozols M. C. Thomas R. A. Flavell R. J. Davis G. H. Tesch 《Diabetologia》2009,52(2):347-358
Aims/hypothesis Obesity and diabetes are associated with increased intracellular p38 mitogen-activated protein kinase (MAPK) signalling, which
may promote tissue inflammation and injury. Activation of p38 MAPK can be induced by either of the immediate upstream kinases,
MAP kinase kinase (MKK)3 or MKK6, and recent evidence suggests that MKK3 has non-redundant roles in the pathology attributed
to p38 MAPK activation. Therefore, this study examined whether MKK3 signalling influences the development of obesity, type
2 diabetes and diabetic nephropathy.
Methods Wild-type and Mkk3 (also known as Map2k3) gene-deficient db/db mice were assessed for the development of obesity, type 2 diabetes and renal injury from 8 to 32 weeks of age.
Results
Mkk3
+/+
db/db and Mkk3
−/−
db/db mice developed comparable obesity and were similar in terms of incidence and severity of type 2 diabetes. At 32 weeks, diabetic
Mkk3
+/+
db/db mice had increased kidney levels of phospho-p38 and MKK3 protein. In comparison, kidney levels of phospho-p38 in diabetic
Mkk3
−/−
db/db mice remained normal, despite a fourfold compensatory increase in MKK6 protein levels. The reduced levels of p38 MAPK signalling
in the diabetic kidneys of Mkk3
−/−
db/db mice was associated with protection against the following: declining renal function, increasing albuminuria, renal hypertrophy,
podocyte loss, mesangial cell activation and glomerular fibrosis. Diabetic Mkk3
−/−
db/db mice were also significantly protected from tubular injury and interstitial fibrosis, which was associated with reduced Ccl2 mRNA expression and interstitial macrophage accumulation.
Conclusions/interpretation MKK3–p38 MAPK signalling is not required for the development of obesity or type 2 diabetes, but plays a distinct pathogenic
role in the progression of diabetic nephropathy in db/db mice. 相似文献
994.
S G Korenman S Viosca D Garza M Guralnik V Place P Campbell S S Davis 《The American journal of medicine》1987,83(3):471-478
The need for improved controlled delivery of testosterone to hypogonadal men stimulated the development of a self-adherent transscrotal testosterone system to provide programmed testosterone delivery through the uniquely permeable scrotal skin. In this short- and long-term efficacy trial, the responses of testosterone and its metabolites to the application of transscrotal testosterone systems of varying testosterone content were compared with the response to 200 mg of testosterone enanthate. Daily transscrotal testosterone system administration resulted in a rapid increase of testosterone and bioavailable, non-sex hormone binding globulin-bound testosterone levels to normal, peaking at two hours, followed by a slow decline over 23 hours, resembling the diurnal variation of endogenous testosterone. One year of daily transscrotal testosterone system therapy demonstrated continued reliable absorption of testosterone and suppression to normal of the luteinizing hormone in two of three patients. There was a greatly disproportionate increase of serum dihydrotestosterone over testosterone, suggesting 5-alpha reduction at the scrotal site. The subjects reported marked subjective improvement. Thus, the transscrotal testosterone system is a novel, effective, and well-tolerated method of delivering testosterone to hypogonadal patients. 相似文献
995.
Leo J. Davis Jr PhD Richard D Hurt MD Robert M Morse MD Peter C. O''Brien PhD 《Alcoholism, clinical and experimental research》1987,11(3):269-273
For a sample of 1156 patients (520 alcoholics and 636 nonalcoholics), discriminant function analyses were performed on the total score, a nine-item version, and a two-item version of the Self-Administered Alcoholism Screening Test (SAAST). With sensitivities set at 90 and 95%, specificities for the total score and nine-item versions ranged from 96.4 to 99.4%. Cross-validation of the nine-item version with the "jackknife" procedure resulted in only one additional misclassification of the 1156 subjects. Separate analyses of the male and female samples revealed that more items entered the discriminant function for women than for men and resulted in a higher, although clinically nonsignificant, percentage of correct classification for women. The results strongly support the use of either the total score or the nine-item version of the SAAST in large-scale screening for alcoholism in a medical patient population. 相似文献
996.
V K Chatterjee J A Ball T M Davis C Proby J M Burrin S R Bloom 《Metabolism: clinical and experimental》1988,37(11):1089-1091
The effect of cholinergic blockade with pirenzepine or atropine on growth hormone (GH) release after galanin administration was investigated in five normal male subjects. The mean peak GH response to an infusion of galanin (40 pmol/kg/min for 40 minutes) was significantly reduced from 17.2 mU/L to 2.9 mU/L (P less than .001) with prior administration of pirenzepine (30 mg IV). When galanin was infused at a higher dose (80 pmol/kg/min), this suppression of release by pirenzepine was partially overcome, with GH rising to a mean peak response of 8.0 mU/L (P less than .05). Repeated administration of atropine (two bolus doses of 0.6 mg IV) also failed to abolish the GH response to this higher dose of galanin in two subjects. It has been proposed that cholinergic pathways control GH release via somatostatin, and this study suggests that galanin may also act by modulating hypothalamic somatostatinergic tone either directly or by facilitating cholinergic transmission. 相似文献
997.
998.
Changes in the density and distribution of Ixodes dammini, Spielman Clifford, Piesman & Corwin were assessed in Wisconsin by examining hunter-killed deer for ticks in 1981 and 1989. Deer examination sites were distributed widely across the state and included 23 sites in 1981 and 15 sites in 1989; 10 sites were visited both years. Between 1981 and 1989, I. dammini became more abundant throughout its range, and I. dammini range expanded into the southwestern portion of Wisconsin. I. dammini was not found in the eastern one-third of the state. When compared with 1981, the 1989 survey revealed significant increases in the proportion of infested deer in the southwest (Arena), higher levels of infestation of individual deer (number of ticks per individual deer) in the central west (Bangor-W. Salem), and significantly less disparity between the proportions of infested male deer and infested female deer in the north (Spooner) compared with sites farther south. These results are consistent with a pattern of I. dammini range expansion from north to south, followed by an increase in population density in the colonized areas. Dermacentor albipictus Packard was present throughout the range of I. dammini and at sites in the northeastern quadrant of Wisconsin where I. dammini was not found. The range of D. albipictus did not change between the survey years, but its population density increased significantly at sites in the north. There is no evidence for interaction between the two tick species that might affect tick distribution or population density, nor can the greater number of I. dammini found in 1989 be attributed to increased tick activity because of warmer weather; temperatures were cooler in 1989 than 1981. 相似文献
999.
Automated instruments for the identification of microorganisms were introduced into clinical microbiology laboratories in the 1970s. During the past two decades, the capabilities and performance characteristics of automated identification systems have steadily progressed and improved. This article explores the development of the various automated identification systems available in the United States and reviews their performance for identification of microorganisms. Observations regarding deficiencies and suggested improvements for these systems are provided. 相似文献
1000.
Holly Hutchinson-Cole Kirk A. Aleck John R. Davis Iris C. Veomett Lynn Hauck 《Clinical genetics》1986,29(1):88-91
A three-month-old female infant with multiple malformations was noted on routine cytogenetic evaluation to have dicentric/ring mosaicism of chromosome 13. Additional cytogenic investigations indicated that the dicentric could be further defined as an isopseudodicentric. Unlike the double chromosome break in the more common ring 13 cases, the mechanism for isopseudodicentric/ring generation is attributed to chromosome and chromatid breaks with subsequent bridging, breaking and fusion. The phenotypic features are those of a combined duplication-deficiency of chromosome 13. 相似文献