全文获取类型
收费全文 | 1442篇 |
免费 | 155篇 |
国内免费 | 16篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 30篇 |
2021年 | 41篇 |
2020年 | 41篇 |
2019年 | 60篇 |
2018年 | 48篇 |
2017年 | 27篇 |
2016年 | 46篇 |
2015年 | 18篇 |
2014年 | 48篇 |
2013年 | 126篇 |
2012年 | 59篇 |
2011年 | 49篇 |
2010年 | 59篇 |
2009年 | 50篇 |
2008年 | 73篇 |
2007年 | 56篇 |
2006年 | 72篇 |
2005年 | 39篇 |
2004年 | 65篇 |
2003年 | 42篇 |
2002年 | 39篇 |
2001年 | 48篇 |
2000年 | 33篇 |
1999年 | 31篇 |
1998年 | 37篇 |
1997年 | 23篇 |
1996年 | 29篇 |
1995年 | 26篇 |
1994年 | 15篇 |
1993年 | 24篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 18篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1980年 | 22篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有1613条查询结果,搜索用时 578 毫秒
41.
Summary This study investigates the role of the developing diencephalic floor or mesenchymal tissue in the differentiation of ACTH-producing cells.The adenohypophysial primordia of fetal rats on days 12.5 and 13.5 of gestation were treated with collagenase; some primordia were allowed to retain an association with the brain and mesenchyme, but in others the brain and/or mesenchyme were removed. These different combinations of tissues were cultured and examined by immunohistochemical techniques using antisera against pACTH and synthetic -MSH. Removal of mesenchyme alone had little effect on the development of ACTH cells as compared to primordia maintained with brain and mesenchyme. In contrast, removal of the brain with or without mesenchyme on day 12.5 resulted in a marked decrease of ACTH cells accompanied by a mal-growth of adenohypophysial tissue. Such changes were slight when the brain was separated from day 13.5 primordia. Immunoreactive -MSH cells were sparse or absent in all cases.These results suggest that in fetal rats the developing diencephalic floor is essential for differentiation of ACTH cells before day 13.5 of gestation whereas mesenchyme has no apparent effect. 相似文献
42.
43.
Alterations of Inositol Lipid Metabolism of Rat Sciatic Nerve in Streptozotocin-Induced Diabetes 总被引:9,自引:8,他引:1
Abstract: The composition and metabolism of rat sciatic nerve phospholipids were studied 20 weeks after induction of chronic diabetes by intraperitoneal injection of streptozotocin (50 mg/kg). On a wet weight basis the nerves from the diabetic animals showed a 7% decrease in total phospholipid from that of controls and a relative decrease in phosphatidylinositol. Incubations of isolated sciatic nerves of diabetic rats in a medium containing [33 P]orthophosphate gave decreased labeling of phosphatidylinositol and substantial changes in the labeling pattern of phosphatidylinositol phosphate and 4,5-bisphosphate from that of controls. The ratio of label in these polyphosphoinositides decreased from 2.5 for normal nerve to about 1.0 for diabetic nerve within a 2-h incubation period. These metabolic alterations were not observed in acutely diabetic animals 5 days after streptozotocin (100 mg/kg) administration. Because polyphosphoinositides may be involved in the control of membrane permeability during axonal conduction, alterations in their relative amounts or turnover rates could be related to the physiological changes of early diabetic neuropathy. 相似文献
44.
SYNOPSIS. Mature macrogamonts were present in the small intestine of rats 5.5 to 7.5 days postinoculation with Eimeria nieschulzi oocysts; oocysts were present at 6 to 7.5 days. Types I and II wall-forming bodies in macrogamonts began to undergo ultrastructural changes within zygotes to form the outer and inner layers of the oocyst wall. Before and during oocyst wall formation a total of 5 membranes (M1–5) were formed at or near the surface of the zygote. The outer and inner oocyst wall layers formed between M2 and M3, and M4 and M5, respectively. The mature oocyst was loosely surrounded by M1 and M2, had an electron-dense outer layer, 100–275 nm thick, and an electron-lucent inner layer, 160–180 nm thick. It also contained an electron-lucent line consisting of M3 and M4 interposed between the outer and inner layers of the oocyst wall. The micropyle, measuring 935 × 47 nm, was located in the outer layer of the oocyst wall and consisted of 10–14 alternating layers of electron-dense and lucent material. The sporont of mature oocysts was covered by M5, immediately beneath which were M6 and M7. The sporont contained a nucleus and nucleolus, lipid and amylopectin bodies, mitochondria, ribosomes, as well as smooth and rough endoplasmic reticulum. Canaliculi, Golgi complexes, and types I and II wall-forming bodies were absent. 相似文献
45.
Julien Deschênes Jean-Paul Valet Normand Marceau 《In vitro cellular & developmental biology. Plant》1980,16(8):722-729
Summary The two-step collagenase perfusion method originally developed for the high yield isolation of parenchymal cells from adult
rat livers has been adapted to rats of 1 day, 1 week, and 3 weeks of age. The use of this method to isolate hepatocytes from
five or six rats of the respective ages demonstrated its reliability in terms of cell yield, percentage of single cells, and
cell viability. In all cases, hepatocytes attach with high efficiency to fibronectin precoated dishes using serum-free culture
medium. The dynamics of spreading is faster for newborn hepatocytes than adult ones. The functional integrity of these parenchymal
liver cells was assessed by their capacity to secrete albumin and α-fetoprotein in serum-free medium and to express lactate
dehydrogenase activity over a 24-hr period in primary culture.
Part of this work was presented at the 30th Annual Meeting of the Tissue Culture Association, Seattle, June, 1979. 相似文献
46.
Knopf P. M. and Soliman M. 1980. Effects of host endocrine gland removal on the permissive status of laboratory rodents to infection by Schistosoma mansoni. International Journal for Parasitology, 10: 197–204. The capacity of Schistosoma mansoni to complete its life cycle was compared in CD-1 mice (permissive hosts) and Sprague-Dawley rats (nonpermissive hosts) from which the pituitary gland had been removed prior to infection with cercariae. Except for a modest decrease in egg burden, none of the parameters of worm life cycle assessed were affected in hypophysectomized mice. In contrast, all these parameters were affected in hypophysectomized rats, e.g. onset of adult worm elimination was delayed, worm development improved, oviposition increased and miracidia developed. Effects of removal from rats of the thyroid/parathyroid glands on the parasite life cycle were similar to hypophysectomy; adrenalectomy or gonadectomy were without affect. Differences between thyroidectomized and thymectomized rats are discussed. It is concluded that host hormones contribute to the nonpermissive status of rats to Schistosoma mansoni infections. 相似文献
47.
Two groups of 16 rats each were fed the same diet with 12.9 ppm Zn. Nine days after each animal was injected with65Zn for assessing fecal zinc of endogenous origin, zinc intake and excretion were determined for a six-day period at the age
of about five (group I) and nine (II) weeks. At mean growth rates of 5.1 and 5.2 g/day, food consumption per gram of gain
was 2.01 g in group I vs 2.86 g in II. Overall, zinc retention amounted to 21 vs 25 μg Zn/g of gain. Apparent absorption averaged
92 vs 74% of Zn intake (132 vs 189 μg/day), while true absorption averaged 98 vs 92%. It was concluded that endogenous fecal
zinc excretion was limited to the indispensable loss (F
em) in group I (7 μg/day), while it exceeded this minimum loss in group II (33 μg/day). True retention, which reflected total
zinc utilization (true absorption times metabolic efficiency), was derived from apparent absorption plusF
em (11 μg/day for group II according to the greater metabolic body size of the rats). It averaged 98% of Zn intake in group
I vs 80% in group II. The mean metabolic efficiency was 100% vs 87%. The conclusion was that these marked differences between
age groups in utilizing the dietary zinc reflected the efficient homeostatic adjustments in absorption and endogenous excretion
of zinc to the respective zinc supply status. 相似文献
48.
Summary The ventral prostatic secretory epithelial cells in older rats were studied by light and electron microscopy. The cells vary in height in different parts of the same organ, and ultrastructurally they show the presence of a developed secretory apparatus such as well-developed Golgi body and abundant rough endoplasmic reticulum. They also show signs of a depressed secretory activity, involving occasional emiocytosis of apical secretory vacuoles and a paucity of condensing vacuoles in the Golgi region and above it. Further, they are characterized by the frequent occurrence of supra and paranuclear pleomorphic lysosomes. 相似文献
49.
BACKGROUNDS: Recently, potential liver toxicity was discussed with the intake of kava extract preparations (Piper methysticum) as anxiolytic drugs. The aim of this study was to test chronic toxicity in rats by oral application of an ethanolic kava full extract. METHODS: Wistar rats of both sexes were fed 7.3 or 73 mg/kg body weight of ethanolic kava extract for 3 and 6 months. The animals were examined for changes in body weight, hematological and liver parameters, and macroscopical and microscopical histological changes in the major organs. RESULTS: No signs of toxicity could be found. CONCLUSIONS: The results are in accordance with the medical experience regarding the use of kava preparations and the long tradition of kava drinking in the South Pacific island states. Specifically, the results do not back the suspicion of potential liver toxicity. 相似文献
50.
Weixiang He Jianmin Liu Daoquan Liu Jundong Hu Ye Jiang Mingzhou Li Qian Wang Ping Chen Guang Zeng Deqiang Xu Xinghuan Wang Michael E. DiSanto Xinhua Zhang 《Journal of cellular and molecular medicine》2020,24(24):14280
To explore how alterations in the phosphodiesterase type 5 (PDE5) signalling pathway and oxidative stress correlate with changes in the expression of relaxation and contraction molecules and erectile dysfunction (ED) in the corpus cavernosum smooth muscle (CCSM) of spontaneously hypertensive rats (SHR). In this study, SHR and Wistar‐Kyoto (WKY) rats were used. Erectile function was determined by apomorphine test and electrical stimulation (ES) of cavernous nerve. Masson''s trichrome staining and confocal microscopy were performed. Nitric oxide synthase (NOS), PDE5, phosphorylated‐PDE5 and α1‐adrenergic receptor (α1AR) were determined by RT‐PCR and Western blotting while oxidative stress in CC was determined by colorimetric analysis. SHR exhibited obvious ED. CC of SHR showed less SM but more collagen fibres. The expression of NOS isoforms in SHR was significantly decreased while all α1AR isoforms were increased. In addition, PDE5 and phosphorylated‐PDE5 were down‐regulated and its activity attenuated in the hypertensive rats. Meanwhile, the SHR group suffered oxidative stress, which may be modulated by endoplasmic reticulum stress and NADPH oxidase up‐regulation. Dysregulation of NOS and α1AR, histological changes and oxidative stress in CC may be associated with the pathophysiology of hypertension‐induced ED. In addition, PDE5 down‐regulation may lead to the decreased efficacy of PDE5 inhibitors in some hypertensive ED patients and treatment of oxidative stress could be used as a new therapeutic target for this type of ED. 相似文献