全文获取类型
收费全文 | 4500篇 |
免费 | 533篇 |
国内免费 | 2篇 |
出版年
2021年 | 40篇 |
2020年 | 28篇 |
2019年 | 48篇 |
2018年 | 49篇 |
2017年 | 35篇 |
2016年 | 81篇 |
2015年 | 121篇 |
2014年 | 137篇 |
2013年 | 193篇 |
2012年 | 274篇 |
2011年 | 269篇 |
2010年 | 148篇 |
2009年 | 158篇 |
2008年 | 208篇 |
2007年 | 228篇 |
2006年 | 231篇 |
2005年 | 234篇 |
2004年 | 229篇 |
2003年 | 195篇 |
2002年 | 205篇 |
2001年 | 101篇 |
2000年 | 101篇 |
1999年 | 102篇 |
1998年 | 74篇 |
1997年 | 54篇 |
1996年 | 58篇 |
1995年 | 63篇 |
1994年 | 43篇 |
1993年 | 44篇 |
1992年 | 88篇 |
1991年 | 65篇 |
1990年 | 74篇 |
1989年 | 75篇 |
1988年 | 83篇 |
1987年 | 67篇 |
1986年 | 68篇 |
1985年 | 65篇 |
1984年 | 53篇 |
1983年 | 37篇 |
1982年 | 48篇 |
1981年 | 37篇 |
1980年 | 36篇 |
1979年 | 45篇 |
1978年 | 39篇 |
1976年 | 26篇 |
1975年 | 31篇 |
1974年 | 28篇 |
1973年 | 23篇 |
1972年 | 27篇 |
1968年 | 22篇 |
排序方式: 共有5035条查询结果,搜索用时 15 毫秒
1.
2.
3.
The direct binding of porcine pancreatic phospholipase A2 and its zymogen to 1,2-bis(heptanylcarbamoyl)-rac-glycerol 3-sulfate was studied by optical detection of triplet-state magnetic resonance spectroscopy in zero applied magnetic field. The zero-field splittings of the single Trp3 residue undergo significant changes upon binding of phospholipase A2 to lipid. Shifts in zero-field splittings, characterized mainly by a reduction of the E parameter from 1.215 to 1.144 GHz, point to large changes in the Trp3 local environment which accompany the complexing of phospholipase A2 with lipid. This may be attributed to Stark effects caused by the binding of a charged group near Trp3 in the enzyme-lipid complex. The cofactor, Ca2+, which is strongly bound to the enzyme active site, has an influence on the bonding, as reflected by smaller zero-field splitting shifts. A relatively small change in the Trp environment was observed for the interaction of the zymogen with lipid. 相似文献
4.
5.
G C Randall 《Journal of developmental physiology》1988,10(1):77-83
The role of cortisol as a factor controlling the deposition of glycogen in the pig fetus was examined by infusing either a low dose (1 mg/day) or a high dose (3 mg/day) of cortisol into chronically-catheterized hypophysectomized fetal pigs for five days beginning on day 100-104 of gestation. After infusion, liver glycogen was significantly higher (P less than 0.05) and lung glycogen significantly lower (P less than 0.05) than in uninfused hypophysectomized litter mates although concentrations were significantly different from intact litter mates (P less than 0.05). Although skeletal and cardiac muscle content increased after infusion this difference was not significant. Changes in tissue glycogen content were similar for both the low and high rates of infusion. These observations indicate that exogenous cortisol alone is able to stimulate liver glycogen deposition and reverse the effect of hypophysectomy. Although other factors may be necessary for maximal response this suggests that cortisol is an important stimulant for liver glycogen deposition in the fetal pig. The effect of cortisol on muscle glycogen was equivocal suggesting that other hormones may play a more important role in this tissue. 相似文献
6.
7.
The RNA helicases encoded by melanoma differentiation-associated gene 5 (mda-5) and retinoic acid-inducible gene I (RIG-I) detect foreign cytoplasmic RNA molecules generated during the course of a virus infection, and their activation leads to induction of type I interferon synthesis. Paramyxoviruses limit the amount of interferon produced by infected cells through the action of their V protein, which binds to and inhibits mda-5. Here we show that activation of both mda-5 and RIG-I by double-stranded RNA (dsRNA) leads to the formation of homo-oligomers through self-association of the helicase domains. We identify a region within the helicase domain of mda-5 that is targeted by all paramyxovirus V proteins and demonstrate that they inhibit activation of mda-5 by blocking dsRNA binding and consequent self-association. In addition to this commonly targeted domain, some paramyxovirus V proteins target additional regions of mda-5. In contrast, V proteins cannot bind to RIG-I and consequently have no effect on the ability of RIG-I to bind dsRNA or to form oligomers. 相似文献
8.
9.
de Haas P. G. 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1947,17(13-15):402-411
Theoretical and Applied Genetics - 相似文献
10.
D L Epstein G A Nolen J L Randall S A Christ E J Read J A Stober M K Smith 《Teratology》1992,46(3):225-235
Dichloroacetic acid (DCA) is a by-product of the chlorine disinfection of water and may occur in treated water at levels exceeding 100 micrograms/L. Previous studies revealed teratogenic effects, particularly heart malformations, at high doses (900-2,400 mg/kg given on days 6-15 of pregnancy). In a series of three studies, groups of 7-10 Long-Evans rats were dosed with 1,900 mg/kg of DCA on days 6-8, 9-11, or 12-15; with 2,400 mg/kg on days 10, 11, 12, or 13; and with 3,500 mg/kg on days 9, 10, 11, 12, or 13, in an attempt to determine the most sensitive period and further characterize the heart defect. In a fourth study, six dams were treated with 1,900 mg/kg of DCA days 6-15 of pregnancy, and 56 fetuses were harvested for light microscopy of the heart. Eight control fetuses from four litters were also examined. No heart malformations were seen in the groups treated with 1,900 mg/kg DCA days 6-8 but were present in the group treated on days 9-11 and 12-15, with the higher incidence occurring on days 12-15. Single doses of 2,400 mg/kg DCA given on days 10, 11, 12, or 13 resulted in a much lower incidence of cardiac malformations, which occurred only on days 10 and 12. The high dose of DCA (3,500 mg/kg) did not increase the incidence of heart defects but showed that dosing on day 9 as well as on days 10 and 12 would produce the defect. The defects seen were characterized as high interventricular septal defects (H-IVSD). Light microscopy showed that the defect was caudal to the semilunar valves, with the anterior right wall of the aorta communicating with the right ventricle. Another aspect of the defect is at the level of the semilunar valves, with the right cusp or sinus of Valsalva in communication with the right ventricle. The defects are discussed more fully and methods for further study suggested. 相似文献