全文获取类型
收费全文 | 621893篇 |
免费 | 63087篇 |
国内免费 | 790篇 |
专业分类
685770篇 |
出版年
2018年 | 6683篇 |
2017年 | 6329篇 |
2016年 | 8599篇 |
2015年 | 10834篇 |
2014年 | 13121篇 |
2013年 | 18050篇 |
2012年 | 21302篇 |
2011年 | 22148篇 |
2010年 | 14963篇 |
2009年 | 13462篇 |
2008年 | 19510篇 |
2007年 | 20166篇 |
2006年 | 19065篇 |
2005年 | 18033篇 |
2004年 | 18201篇 |
2003年 | 17147篇 |
2002年 | 16777篇 |
2001年 | 25808篇 |
2000年 | 25552篇 |
1999年 | 20197篇 |
1998年 | 7300篇 |
1997年 | 7166篇 |
1996年 | 6798篇 |
1995年 | 6425篇 |
1994年 | 6140篇 |
1993年 | 6098篇 |
1992年 | 16571篇 |
1991年 | 16703篇 |
1990年 | 16423篇 |
1989年 | 15938篇 |
1988年 | 14794篇 |
1987年 | 13974篇 |
1986年 | 13200篇 |
1985年 | 13144篇 |
1984年 | 10772篇 |
1983年 | 9221篇 |
1982年 | 6777篇 |
1981年 | 6012篇 |
1980年 | 5721篇 |
1979年 | 10048篇 |
1978年 | 8045篇 |
1977年 | 7224篇 |
1976年 | 6833篇 |
1975年 | 8014篇 |
1974年 | 8780篇 |
1973年 | 8562篇 |
1972年 | 7678篇 |
1971年 | 7159篇 |
1970年 | 6072篇 |
1969年 | 5987篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Experiments on conscious rabbits were made to elaborate motor conditioned reflexes through pairing stimuli with electrocutaneous reinforcement applied every 30 s. Neuronal activity in the sensorimotor cortex and putamen was recorded during formation and reproduction of the conditioned reflexes before and after haloperidol injection (0.2 mg/kg i. v.). In the putamen, haloperidol increased the number of neurons exhibiting trace conditioned activity and made the intensity and duration of these processes rise. The changes seen in the sensorimotor cortex were opposite in nature. Inhibition of trace conditioned activity in the sensorimotor cortex depended mainly on the decreased amplitude of the reaction conditioned component. The role of the dopaminergic system in the interaction of the neostriatum and sensorimotor cortex and in formation and reproduction of trace conditioned activity of both the structures is discussed. 相似文献
23.
24.
M S Bortnik A V Skurat I R Eshba T V Bulargina E S Severin 《Biokhimii?a (Moscow, Russia)》1985,50(4):589-594
Changes in the properties of adenylate cyclase from the lungs of tuberculotic guinea pigs were revealed. The number of beta-adrenergic receptors in the lungs was found to be reduced by 30% at the second and by 70% at the third stage of the disease. The degree and the value of Ka for adenylate cyclase activation by isoproterenol remained thereby unchanged. The basal activity of adenylate cyclase was increased by 20% against the control level at the second stage and decreased by 20% at the third stage of the disease. At these periods, the stimulating effects of guanylyl imidodiphosphate, NaF and forskolin on lung adenylate cyclase were diminished. The experimental results point to the significant role of the enzymes of cAMP metabolism and reflect the course of the tuberculosis process in experimental animals. 相似文献
25.
V V Sviridov E V Kozhevnikova 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(9):67-70
The immunization of mice with the protein fraction of B. pertussis strain 305 has made it possible to obtain hybridomas producing monoclonal antibodies to B. pertussis antigens. Ascitic fluids containing monoclonal antibodies react in the ELISA in high titers and actively agglutinate B. pertussis strains 305 and 475. 相似文献
26.
U Mura A M Osman A S Mohamed D Di Martino P L Ipata 《Comparative biochemistry and physiology. B, Comparative biochemistry》1987,87(1):157-160
The preservation of purine ring as purine bases appears to be a common feature of camel liver. Hepatic guanine appears to be actively converted into GMP in the camel rather than further degraded. The limiting step of guanine degradation appears to be the lack of hepatic guanase activity. Higher purine bases over uric acid ratios were found in camel urine with respect to those of zebu. 相似文献
27.
28.
A A Sukhopiatkina O S Bat A V Levitskaia V G Potapova 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(4):80-81
The study of the specific epidemiological and clinical features of Q fever revealed the existence of an active focus of infection among humans due to their contacts with agricultural animals in one of the districts of the region. The focus was manifested by group morbidity among the cattle-tending personnel of a dairy farm. The source of this infection was cattle. The infection was transferred mainly through the air. The disease took a moderately severe course. The study of the rickettsial contamination of humans, animals and ticks suggested the presence of the active epidemic process and made it possible to work out concrete antiepidemic measures. 相似文献
29.
30.
Ernst Wm. Spannhake Terry L. Adams Steven R. Kleeberger 《Prostaglandins & other lipid mediators》1985,30(6):1041-1055
The effects of repeated antigen exposure on the synthesis of mediators by lung tissues are not well understood. To investigate the influence of antigen challenge on the synthesis of prostaglandins by central airway and peripheral lung tissues, fourteen sensitive sheep underwent biweekly exposure to aerosolized antigen (7) or saline (7). Following the fifth exposure, microsomal and high speed supernatant fractions were prepared from trachealis muscle and lung parenchyma. Synthesis of thromboxane (TX) A2, prostaglandin (PG) D2 and PGI2 from the PG endoperoxide intermediate, PGH2, was assayed over a range of substrate concentrations from 3–200 uM. Synthesis of PGI2 by trachealis microsomes was approximately 5-fold greater than that of TXA2. PGI2 and TXA2 production was identical in tracheal preparations from Ascaris- and saline-exposed animals. In parenchymal tissues, where TXA2 production predominated over PGI2 by 9-fold, preparations from Ascaris- exposed animals synthesized 50% more TXA2 than controls at PGH2 concentrations of 25 uM and above, whereas synthesis of PGI2 and PGD2 were similar in preparations from both groups of animals. The density of pulmonary mast cells was decreased by 21% in the Ascaris group, whereas polymorphonuclear leukocyte density was unchanged. These results demonstrate the differential synthesis of TXA2 and PGI2 in central airways and peripheral lung regions of the sheep. They further indicate that repeated exposure of the airways to antigen selectively enhances TXA2 synthesis in the lung periphery of sensitized animals. The site of this increased enzymatic activity, whether in resident cells or newly-infiltrated cells, has not been determined. 相似文献