全文获取类型
收费全文 | 22634篇 |
免费 | 1534篇 |
国内免费 | 986篇 |
专业分类
25154篇 |
出版年
2024年 | 53篇 |
2023年 | 296篇 |
2022年 | 638篇 |
2021年 | 1022篇 |
2020年 | 678篇 |
2019年 | 909篇 |
2018年 | 898篇 |
2017年 | 684篇 |
2016年 | 973篇 |
2015年 | 1348篇 |
2014年 | 1540篇 |
2013年 | 1776篇 |
2012年 | 1988篇 |
2011年 | 1876篇 |
2010年 | 1047篇 |
2009年 | 921篇 |
2008年 | 1043篇 |
2007年 | 953篇 |
2006年 | 866篇 |
2005年 | 745篇 |
2004年 | 661篇 |
2003年 | 551篇 |
2002年 | 486篇 |
2001年 | 314篇 |
2000年 | 321篇 |
1999年 | 284篇 |
1998年 | 176篇 |
1997年 | 165篇 |
1996年 | 183篇 |
1995年 | 164篇 |
1994年 | 138篇 |
1993年 | 103篇 |
1992年 | 152篇 |
1991年 | 152篇 |
1990年 | 125篇 |
1989年 | 97篇 |
1988年 | 101篇 |
1987年 | 103篇 |
1986年 | 70篇 |
1985年 | 89篇 |
1984年 | 52篇 |
1983年 | 54篇 |
1982年 | 28篇 |
1981年 | 26篇 |
1980年 | 28篇 |
1979年 | 37篇 |
1978年 | 28篇 |
1977年 | 21篇 |
1975年 | 30篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
A disseminated infection with Penicillium marneffei, a rare human pathogen that may infect both healthy and immunocompromised patients, was diagnosed by fine needle aspiration cytology in a patient infected with the human immunodeficiency virus. The presence of yeast-form organisms with an eccentric or central dot and occasional septate and elongated forms highly suggested the diagnosis, which was confirmed on culture. Establishment of the diagnosis is important because this infection is potentially curable. 相似文献
22.
M Gajewski H Laskowska-Bozek S Ma?liński J Ryzewski 《Journal of physiology and pharmacology》1991,42(4):407-415
Isolated, cultured rat neonatal cardiac myocytes were placed in medium supplemented with mitochondrial respiratory inhibitor potassium cyanide which caused a rapid adenosine triphosphate (ATP) depletion. These myocytes with the impaired energy metabolism ("hypoxia-like state") were exposed to unstimulated human neutrophils. Effect of human neutrophils on the myocytes in the "hypoxia-like state" was quantified as a total change in the amount of ATP in cardiac cells. After 5 hours of incubation of neutrophils with the myocytes in the "hypoxia-like state" an additional decrease (of 50 per cent) in ATP content was observed. Since catalase (which destroys hydrogen peroxide) prevented the further decline in ATP level in the myocytes with impaired energy metabolism, it seem that hydrogen peroxide and possibly their products are responsible for this effect. These results suggest that unstimulated human neutrophils after activation by the contact with injured cardiac cells caused further decrease of ATP level in target cells. 相似文献
23.
J Ko?cielak W Ma?liński J Zieleński E Zdebska T Brudzyński H Miller-Podraza B Cedergren 《Biochimica et biophysica acta》1978,530(3):385-393
Major neutral glycosphingolipids were isolated from human plasma and their structures and fatty acid compositions studied. The four neutral glycosphingolipids of plasma were characterized as Glc beta(1 leads to 1)ceramide, Gal beta(1 leads to 1)- ceramide, Gal beta(1 leads to 4) Glc beta (1 leads to 1)ceramide, Gal alpha(1 leads to 4) Gal beta(1 leads to 4) Glc beta(1 leads to 1)ceramide and GalNAc beta(1 leads to 3) Gal (1 leads to 4) Gal (1 leads to 4) Glc beta(1 leads to 1)-ceramide. The glycosphingolipids contained mostly short chain fatty acids of which most prominent was C16. Erythrocyte glucosylceramide and lactosylceramide exhibited similar fatty acid compositions as their plasma counterparts. Triglycosylceramide and globoside of erythrocytes contained almost exclusively long-chain fatty acids. In lactosylceramide obtained from "p" erythrocytes, an accumulation of long-chain fatty acids was found; this accumulation was not observed, however, in lactosylceramide isolated from "p" plasma. It was concluded that plasma and erythrocyte glycosphingolipids are synthesized at separate sites where short- and long-chain fatty acids, respectively, are available. Plasma and erythrocyte glucosylceramide, and probably a fraction of lactosylceramide, exchange between plasma and erythrocyte pools. The latter conclusion is discussed in the light of the relative roles of carbohydrate and lipid moieties of the glycosphingolipids in maintaining their association with erythrocyte membranes. 相似文献
24.
Adult Trogoderma glabrum females assume stationary postures characterized by abdominal elevation and partial exposure of the ovipositor segments. The postural activity was studied in relation to sex pheromone production and was designated calling, or sex pheromone-releasing behaviour because it was accompanied by an increase in the rate of release of sex pheromone(s). Calling was largely restricted to an 8 hr interval centered toward the middle of a 16 hr photophase. Mating frequency and female pheromone content increased during the same interval. Because females extracted during the calling period yielded at least 10 times more pheromone than extracts prepared at other times, and because pheromone activity released during one calling period was estimated to be at least 10-fold higher than that which could be extracted from whole females several hours prior to the start of calling, heightened production of active pheromone(s) was postulated to occur during calling. Functional significance of the calling posture is discussed in relation to sex pheromone gland location. 相似文献
25.
Metabolic effects of vasopressin, glucagan and adrenalin were compared, in intact rats, especially in regard to time courses of effects. Hyperglycaemia was transient in response to vasopressin, prolonged following adrenalin, and, suprisingly, was not discernible after glucagon, except in response to a very large dose. Vasopressin decreased and adrenalin increased, the plasma free fatty acid concentration; both hormones decreased the triacylglycerol level. Muscle glycogen concentrations, measured in heart, diaphragm and skeletal muscle, exhibited small changes, with complex time courses, following hormone administration. Vasopressin brought about a rapid but transient activation of heaptic glycogen phosphorylase which resembled that due to adrenalin. The activation by glucagon of phosphorylase was greater and more prolonged, despite the absence of hyperglycaemia. In response to vasopressin, there was in increase in plasma insulin. Incorporation of 14C from [14C]glucose into glycogen or fatty acids was not influenced by vasopressin. Taken together, these results may be explained by rapid metabolic action of vasopressin on hepatic glycogenolysis, whereas adrenalin has multiple prolonged actions. 相似文献
26.
Models of learning based on the plastic properties of the "placing reaction" in cats] 总被引:1,自引:0,他引:1
B I Kotliar V I Ma?orov E I Savchenko 《Zhurnal vysshe? nervno? deiatelnosti imeni I P Pavlova》1975,25(5):967-973
A possibility of functional reorganization of initial sensorimotor connections of the forepaw has been shown on seven cats. The main initial relationships between the afferent tactile input and motor output for the ulnar joint of the cat forepaw are as follows: tactile stimulation of the dorsal surface of the paw produces a flexion in the ulnar joint ("placing reaction"), and that of the ventral surface, an extension of the paw in the ulnar joint ("magnetic reflex"); simultaneous tactile stimulation of the ventral surface of the paw blocks the "placing reaction" evoked by a touch of the dorsal side. Extinction was produced of the above unconditioned connections and elaboration of a new "cross" connection consisting in that tactile stimulation of the ventral side of the paw resulted in flexion in the ulnar joint. 相似文献
27.
Shuai Ma Shuhui Sun Jiaming Li Yanling Fan Jing Qu Liang Sun Si Wang Yiyuan Zhang Shanshan Yang Zunpeng Liu Zeming Wu Sheng Zhang Qiaoran Wang Aihua Zheng Shuguang Duo Yang Yu Juan Carlos Izpisua Belmonte Piu Chan Qi Zhou Moshi Song Weiqi Zhang Guang-Hui Liu 《Cell research》2021,(4):415-432
Aging is a major risk factor for many diseases,especially in highly prevalent cardiopulmonary comorbidities and infectious diseases including Coronavirus Diseas... 相似文献
28.
29.
A PCR-Based Method for Monitoring Legionella pneumophila in Water Samples Detects Viable but Noncultivable Legionellae That Can Recover Their Cultivability 下载免费PDF全文
30.