全文获取类型
收费全文 | 7273篇 |
免费 | 901篇 |
国内免费 | 4篇 |
出版年
2021年 | 78篇 |
2018年 | 89篇 |
2017年 | 75篇 |
2016年 | 111篇 |
2015年 | 156篇 |
2014年 | 210篇 |
2013年 | 281篇 |
2012年 | 307篇 |
2011年 | 289篇 |
2010年 | 186篇 |
2009年 | 171篇 |
2008年 | 257篇 |
2007年 | 229篇 |
2006年 | 236篇 |
2005年 | 203篇 |
2004年 | 212篇 |
2003年 | 226篇 |
2002年 | 202篇 |
2001年 | 223篇 |
2000年 | 219篇 |
1999年 | 195篇 |
1998年 | 94篇 |
1997年 | 92篇 |
1995年 | 89篇 |
1994年 | 91篇 |
1993年 | 75篇 |
1992年 | 174篇 |
1991年 | 170篇 |
1990年 | 160篇 |
1989年 | 154篇 |
1988年 | 163篇 |
1987年 | 139篇 |
1986年 | 124篇 |
1985年 | 161篇 |
1984年 | 121篇 |
1983年 | 116篇 |
1982年 | 108篇 |
1981年 | 87篇 |
1980年 | 91篇 |
1979年 | 138篇 |
1978年 | 91篇 |
1977年 | 92篇 |
1976年 | 96篇 |
1975年 | 89篇 |
1974年 | 105篇 |
1973年 | 95篇 |
1972年 | 85篇 |
1971年 | 77篇 |
1969年 | 71篇 |
1968年 | 64篇 |
排序方式: 共有8178条查询结果,搜索用时 343 毫秒
321.
322.
Immunity to Plasmodium berghei yoelii in mice. II. Specific and nonspecific cellular and humoral responses during the course of infection. 总被引:5,自引:0,他引:5
F I Weinbaum J Weintraub F K Nkrumah C B Evans R E Tigelaar Y J Rosenberg 《Journal of immunology (Baltimore, Md. : 1950)》1978,121(2):629-636
The kinetics of various specific and nonspecific immunologic responses were examined in BALB/c mice infected with 17X nonlethal Plasmodium berghei yoelii (a self-limiting infection). The sequence of events after infection was characterized by rapid sensitization of splenic T cells to malaria antigen and polyclonal B cell activation, followed by a period of depressed splenic proliferative responses in vitro to mitogens (PHA and LPS) and malaria (specific) antigen. At the same time, suppressed primary in vitro splenic PFC responses to trinitrophenyl-aminoethylcarbamylmethyl-Ficoll (TNP-F) were seen. This suppression was an active process requiring adherent cells. During this period, levels of antimalarial antibody also increased exponentially. As the infection was cleared, splenic malaria antigen-specific proliferative responses were again observed and splenic PFC and in vitro mitogen responses returned to preinfection levels after variable periods of time. Both splenic proliferative responses to malaria antigen and antimalarial antibody responses remained persistently elevated. In addition, some responses were examined in mice infected with 17X lethal P.b. yoelii (a fatal infection); in comparison to the early responses of mice infected with the nonlethal substrain, there was a decrease and delay in the development of a splenic T cell response to malaria antigen and a blunted antimalarial antibody response. 相似文献
323.
The present study was done to determine if a progesterone receptor is present in rat pituitary. Cytosol was labeled with 3H-progesterone (3HP) or 3H-RS020 (3HR) and subjected to sucrose-glycerol density-gradient centrifugation. Serum progesterone was measured for correlation with progesterone receptor levels. Two 3HP-binding peaks (4S + 6S) were evident in uterine and pituitary cytosols. The 4S peak was eliminated by competition with unlabeled cortisol leaving a single 6S peak (progesterone receptor). Estradiol (E) priming of the male or female rat increased progesterone receptor levels in pituitary cytosol as demonstrated using 3HP and 3HR, and pituitary progesterone receptor bound 3HR with a higher affinity than 3HP. Following adrenalectomy of gonadectomized rats, progesterone receptor levels were increased in pituitary and uterine cytosol of both E-primed and unprimed groups. An inverse relationship was established between serum progesterone and progesterone receptor levels in the uterus and pituitary suggesting that stressinduced adrenal progesterone secretion significantly influences progesterone receptor levels in the rat. These results demonstrate an estrogen-inducible progesterone receptor in the rat pituitary with properties similar to those of the uterine progesterone receptor. 相似文献
324.
325.
Quantitative electron-paramagnetic-resonance measurements of the electron-transfer components of the photosystem-I reaction centre. The reaction-centre chlorophyll (P700), the primary electron acceptor X and bound iron-sulphur centre A.
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
An e.p.r. spectrum of the reduced form of the electron-transport component (X), thought to be the primary electron acceptor of Photosystem I, was obtained. By using line-shape simulations of this component and the free-radical e.p.r. signal I of the oxidized reaction-centre chlorophyll (P700), it was possible to determine the ratio of the number of electron spins to which these signals correspond in Photosystem-I particles under a variety of conditions. On illumination at cryogenic temperatures of Photosystem-I preparations, in which both bound iron-sulphur centres A and B were reduced, the measured ratio of free radical to component X varied between 1.04 and 2.23, with an average value of 1.54 +/- 0.18 where a Gaussian line-shape is assumed for the component-X signal in the simulation. The error in this measurement is estimated to be up to 50%. In a similar way component X and centre A of the bound iron-sulphur protein were quantified, the ratio between these two components varying between 1.26 and 0.61 with an average value of 0.75 +/- 0.06. These results indicate that the quantitative relationship, in terms of net electron spins, between centre A, component X and P700 is of the order to be expected if component X is indeed the primary electron acceptor in Photosystem I and a component of the photosynthetic electron-transport chain. 相似文献
326.
Studies of the antigenicity and immunogenicity of bromelain-pretreated red blood cells 总被引:1,自引:0,他引:1
K O Cox H Baddams A Evans 《The Australian journal of experimental biology and medical science》1977,55(1):27-37
The effects of the proteolytic enzyme bromelain (Br) on the antigenicity and immunogenicity of sheep and mouse red blood cells (RBC) have been investigated. The results presented support the previous claim that there are antigens present on Br RBC that are not present in an exposed form on untreated RBC and that Br RBC have lost some of the antigens present on the surface of normal RBC. The susceptibility of Br RBC to osmotic lysis was very similar to that of normal RBC, implying that the modified RBC were not more fragile than normal RBC. Injection of mice with Br mouse-RBC did not increase the unusually high "background" number of cells producing IgM antibodies against Br mouse-RBC and mice did not mount delayed-type hypersensitivity reactions against Br mouse-RBC, either before or after sensitizing injections of Br mouse-RBC. However, mouse-RBC and Br mouse-RBC elicited similar antibody responses in rabbits and guinea pigs. Although mice appeared unresponsive to Br mouse-RBC injections, delayed-type hypersensitivity responses and antibody production in primary and secondary responses were of similar levels irrespective of whether sheep-RBC or Br sheep-RBC were used as immunogens. From these studies it appears that mice have B-cells producing antibodies against the "new" antigens on Br mouse-RBC, but there are no T-cells that respond to these antigens by way of "helper" activity in antibody production or by way of cell-mediated immune reactions. 相似文献
327.
328.
Janet H. Ransom Charles H. Evans A. Eric Jones Robert A. Zoon Joseph A. DiPaolo 《Cancer immunology, immunotherapy : CII》1983,15(2):126-130
Summary Immunologic prevention of the carcinogenicity of the diagnostic gamma-emitting radionuclide 99mTechnetium (99mTc) by lymphotoxin was evaluated using an in vivo-in vitro assay of carcinogenesis. Pregnant Syrian golden hamsters received 125–2,300 Ci 99mTc/kg body weight by injection, and 7 days later colonies of morphologically transformed cells were quantitated in vitro. The transformation frequency increased directly with the radionuclide concentration, and cells derived from transformed colonies produced tumors in athymic nude mice. The total absorbed 99mTc dose was 0.20 rad following injection of 250 Ci 99mTc/kg hamster body weight; this compares with an exposure of 0.13 rad following injection of 143 Ci 99mTc/kg body weight in humans. Intravenous injection of purified hamster lymphotoxin immediately after 99mTc caused a dose-dependent reduction in the transformation frequency. Transformation was essentially completely prevented (97%) by injection of 8,000 U of lymphotoxin. Thus, the immune system, through the action of lymphotoxin, has the potential to prevent carcinogenesis induced by gamma-radiation from 99mTc. This emphasizes the importance of considering the recipient's immune and other homeostatic mechanisms as part of a complete diagnostic or therapeutic gamma-radiation regimen. 相似文献
329.
330.
Francis L. Marcrina R.Paul Evans Janet Ash Tobian Donna L. Hartley Don B. Clewell Kevin R. Jones 《Gene》1983,25(1):145-150
A novel plasmid vector that is able to replicate both in Escherichia coli and in Streptococcus sanguis is described. This 9.2-kb plasmid, designated pVA856, carries Cmr, Tcr and Emr determinants that are expressed in E. coli. Only the Emr determinant is expressed in S. sanguis. Both the Cmr and the Tcr of pVA856 may be insertionally inactivated. This plasmid affords several different cleavage-ligation strategies for cloning in E. coli followed by subsequent introduction of chimeras in to S. sanguis. In addition, we have modified a previously described E. coli-S. sanguis shuttle plasmid [pVA838; Macrina et al., Gene 19 (1982) 345–353], so that it is unable to replicate in S. sanguis. The utility of such a plasmid for cloning and selecting sequences enabling autonomous replication in S. sanguis is demonstrated. 相似文献