全文获取类型
收费全文 | 45815篇 |
免费 | 4082篇 |
国内免费 | 32篇 |
出版年
2022年 | 201篇 |
2021年 | 679篇 |
2020年 | 436篇 |
2019年 | 543篇 |
2018年 | 707篇 |
2017年 | 604篇 |
2016年 | 1121篇 |
2015年 | 1888篇 |
2014年 | 2045篇 |
2013年 | 2657篇 |
2012年 | 3202篇 |
2011年 | 3259篇 |
2010年 | 2089篇 |
2009年 | 1765篇 |
2008年 | 2678篇 |
2007年 | 2640篇 |
2006年 | 2418篇 |
2005年 | 2458篇 |
2004年 | 2402篇 |
2003年 | 2295篇 |
2002年 | 2229篇 |
2001年 | 538篇 |
2000年 | 430篇 |
1999年 | 537篇 |
1998年 | 628篇 |
1997年 | 477篇 |
1996年 | 430篇 |
1995年 | 406篇 |
1994年 | 374篇 |
1993年 | 360篇 |
1992年 | 408篇 |
1991年 | 350篇 |
1990年 | 289篇 |
1989年 | 290篇 |
1988年 | 287篇 |
1987年 | 274篇 |
1986年 | 253篇 |
1985年 | 318篇 |
1984年 | 346篇 |
1983年 | 270篇 |
1982年 | 369篇 |
1981年 | 286篇 |
1980年 | 265篇 |
1979年 | 215篇 |
1978年 | 233篇 |
1977年 | 219篇 |
1976年 | 191篇 |
1975年 | 178篇 |
1974年 | 203篇 |
1973年 | 210篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
81.
Ken Walder Carolyn R. Dascaliuc Paul A. Lewandowski Andrew J. Sanigorski Paul Zimmet Greg R. Collier 《Obesity (Silver Spring, Md.)》1997,5(3):193-200
Food intake was restricted to 75% of ad libitum levels in 37 male Psammomys obesus (Israeli Sand Rats) from the ages of 4 (weaning) to 10 weeks. Energy restriction reduced the mean body weight at 10 weeks by 29% compared with 44 ad libitum fed controls. Hyperglycemia was prevented completely in the food-restricted group, and mean blood glucose concentrations were significantly reduced (3.8 ± 0.2 vs. 5.5 ± 0.4 μmol/L; p<0.05) compared with control animals. Plasma insulin concentrations were also decreased significantly compared with ad libitum fed controls (105 ± 13 vs. 241 ± 29 mU/L;p<0.05). Although energy restriction prevented hyperglycemia from developing in 10-week-old P. obesus, 19% of the food restricted animals still developed hyperinsu-linemia. We concluded that hyperphagia between the ages of 4 to 10 weeks may be essential for the development of noninsulin-dependent diabetes mellitus in P. obesus, but that hyperinsulinemia may still occur in the absence of hyperphagia and hyperglycemia, suggesting a significant genetic influence on the development of hyperinsulinemia in this animal model. 相似文献
82.
Effects of Δ8- and Δ9-tetrahydrocannabinol (Δ8- and Δ9-THC) on three experimentally induced seizure models, i.e., audiogenic seizure (AS) test, maximal electroshock seizure (MES) test and pentylenetetrazol (PTZ)-induced seizure test were determined in the audiogenic rat. Both tetrahydrocannabinols possess a dose-related anticonvulsant effect against AS, MES and PTZ-induced maximal seizure. Although anticonvulsant potencies do not significantly differ, Δ8THC is three times more neurotoxic than Δ9THC. In addition, both THC's are without effect on minimal seizure and lethality induced by PTZ. Furthermore, the low protective indexes (TD50/ED50) determined in this study suggest that Δ8 and Δ9 THC may have poor therapeutic potentials as antiepileptic drugs. 相似文献
83.
84.
85.
86.
87.
88.
89.
Hanna Gladh Erika Bergsten Folestad Lars Muhl Monika Ehnman Philip Tannenberg Anna-Lisa Lawrence Christer Betsholtz Ulf Eriksson 《PloS one》2016,11(3)
Platelet-derived growth factor D (PDGF-D) is the most recently discovered member of the PDGF family. PDGF-D signals through PDGF receptor β, but its biological role remains largely unknown. In contrast to other members of the PDGF family of growth factors, which have been extensively investigated using different knockout approaches in mice, PDGF-D has until now not been characterized by gene inactivation in mice. Here, we present the phenotype of a constitutive Pdgfd knockout mouse model (Pdgfd-/-), carrying a LacZ reporter used to visualize Pdgfd promoter activity. Inactivation of the Pdgfd gene resulted in a mild phenotype in C57BL/6 mice, and the offspring was viable, fertile and generally in good health. We show that Pdgfd reporter gene activity was consistently localized to vascular structures in both postnatal and adult tissues. The expression was predominantly arterial, often localizing to vascular bifurcations. Endothelial cells appeared to be the dominating source for Pdgfd, but reporter gene activity was occasionally also found in subpopulations of mural cells. Tissue-specific analyses of vascular structures revealed that NG2-expressing pericytes of the cardiac vasculature were disorganized in Pdgfd-/- mice. Furthermore, Pdgfd-/- mice also had a slightly elevated blood pressure. In summary, the vascular expression pattern together with morphological changes in NG2-expressing cells, and the increase in blood pressure, support a function for PDGF-D in regulating systemic arterial blood pressure, and suggests a role in maintaining vascular homeostasis. 相似文献
90.