全文获取类型
收费全文 | 4861篇 |
免费 | 236篇 |
国内免费 | 179篇 |
出版年
2024年 | 11篇 |
2023年 | 59篇 |
2022年 | 85篇 |
2021年 | 115篇 |
2020年 | 113篇 |
2019年 | 111篇 |
2018年 | 127篇 |
2017年 | 110篇 |
2016年 | 101篇 |
2015年 | 120篇 |
2014年 | 220篇 |
2013年 | 273篇 |
2012年 | 125篇 |
2011年 | 217篇 |
2010年 | 128篇 |
2009年 | 241篇 |
2008年 | 255篇 |
2007年 | 237篇 |
2006年 | 238篇 |
2005年 | 223篇 |
2004年 | 223篇 |
2003年 | 192篇 |
2002年 | 170篇 |
2001年 | 95篇 |
2000年 | 81篇 |
1999年 | 113篇 |
1998年 | 124篇 |
1997年 | 102篇 |
1996年 | 87篇 |
1995年 | 79篇 |
1994年 | 87篇 |
1993年 | 56篇 |
1992年 | 65篇 |
1991年 | 64篇 |
1990年 | 80篇 |
1989年 | 58篇 |
1988年 | 52篇 |
1987年 | 60篇 |
1986年 | 35篇 |
1985年 | 68篇 |
1984年 | 58篇 |
1983年 | 27篇 |
1982年 | 43篇 |
1981年 | 40篇 |
1980年 | 23篇 |
1979年 | 27篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1974年 | 6篇 |
排序方式: 共有5276条查询结果,搜索用时 343 毫秒
151.
152.
No differences have been observed in vivo between Lycopersicum peruvianum compatible and incompatible pollen during activation and pollen tube emission and organization, that is until 4 h and 30 min after pollination. During pollen activation the main events are the setting free of rough endoplasmic reticulum (RER) cisterns which were stacked in the mature pollen, the increase in the number of polysomes, and a great activity of the dictyosomes. Immediately after germination of the vegetative nucleus and the generative cell move into the tube, the generative cell diviting to form the male gametes; the tube then becomes organized in four zones. This series of changes is similar to what has already been observed in vitro except that in vitro the generative cell remains undivided and the whole process from seeding to tube organization takes 3 h instead of 4 h and 30 min after pollination, as it does in vivo. Our findings are compatible with the main models of the tube inhibition mechanism proposed till now.Abbreviations RER
rough endoplasmic reticulum
- GC
generative cell
- VN
vegetative nucleus
- GP
germinative pore
Research performed under C.N.R. (Italian National Research Council) program Biology of Reproduction 相似文献
153.
Cationized ferritin was found to inhibit the lateral mobility of intramembrane proteins in turkey erythrocyte membranes and the activation of adenylate cyclase by the (?)-epinephrine-bound β-adrenergic receptor. It was observed that cationized ferritin has only a small direct effect on the β-receptor and on the adenylate cyclase moiety. It is concluded that the cationized ferritin-induced inhibition of the hormone-dependent cyclase activity results from the inhibition of the lateral mobility of the receptor and therefore a decrease in the bimolecular rate of interaction between the receptor and the enzyme. 相似文献
154.
K. Watanabe S. Hakomori M.E. Powell M. Yokota 《Biochemical and biophysical research communications》1980,92(2):638-646
Two amphipathic protein fractions soluble in organic solvents as well as in water have been isolated from the ganglioside fraction of bovine erythrocyte membranes by successive chromatography in chloroform-methanol mixture on DEAE-Sephadex, silicic acid, and α-hydroxypropylated Sephadex G50 (LH60) columns. These two fractions contained a similar low molecular weight protein but with distinctively different amino acid composition. One of these proteins has been characterized by having a strong Paul-Bunnell antigen activity and had a binding affinity to ganglioside. A similar protein without Paul-Bunnell antigen activity was isolated as the major ganglioside-associated protein. 相似文献
155.
1. Respiration rates of broad-bean (Vicia faba) mitochondria were studied as a function of temperature. Arrhenius plots of all membrane-bound enzymes, as obtained with saturating substrate concentrations, revealed a break in the lower temperature range. That break was considered to indicate a phase transition of membrane phospholipids, characteristic for chilling-sensitive plants. A second discontinuity at 30°C occurred only with activities linked to energy conservation. — 2. The activation energies for the oxidation of NAD+-linked substrates differ between states 3 and 4. State 3 respiration of NAD+-linked substrates is the result a superimposition of two branches of electron transport, which can be separated by different sensibilities to rotenone. A characteristic temperature dependency of the respiratory control, as well as a shift of the low temperature break in the Arrhenius plot toward a higher temperature after state 4 to state 3 transition, are calculated to be caused by the superimposition of the two branches. — 3. The temperature dependency of the oxidation of extra-mitochondrial NADH and of succinate differs remarkably from that of the oxidation of matrix-NADH. It has been concluded that the rotenone-resistant oxidation of matrix-NADH and the oxidation of external NADH are mediated via different pathways with individual regulation sites.Abbreviations BSA
bovine serum albumin
- CCCP
carbonylcyanide-m-chlorophenylhydrazone
- TPP
thiaminepyrophosphate 相似文献
156.
Ann E. Aust Michael R. Antczak Veronica M. Maher J. Justin McCormick 《Journal of cellular biochemistry》1981,16(3):269-279
Human cells that appear capable of metabolizing various classes of carcinogens have been identified using one of two methods: metabolism of tritiated benzo(a)pyrene to aqueous-acetone soluble forms or inhibition of cellular DNA synthesis. Each of the assay systems was optimized and the results on 15 human epithelial cell lines were compared. One or more cell lines were found to activate each of four classes of carcinogens examined: polycyclic hydrocarbons, aromatic amines, heterocyclic hydrocarbons, and nitrosamines. Cells that appeared capable of metabolizing polycyclic hydrocarbons or aromatic amines by these methods were also found to produce metabolites which were cytotoxic to cocultivated human xeroderma pigmentosum fibroblasts after a 48-hr exposure to the carcinogen. 相似文献
157.
Photosynthetic induction in wheat protoplasts and chloroplasts. Autocatalysis and light activation of enzymes 总被引:1,自引:0,他引:1
Abstract Unlike wheat chloroplasts, wheat protoplasts showed a pronounced restoration of the induction phase after a short period of darkness. This difference was used to investigate the relative roles of light-induced reductive activation of enzymes and the auto-catalytic increase in the level of substrates in the control of the rate of photosynthesis during induction. Light activation and dark inactivation of ribulose 5-phosphate kinase, fructose 1,6-biphosphatase and NADP+-specific glyceraldehydephosphate dehydrogenase were measured. In this respect there was no appreciable difference between protoplasts and chloroplasts. In contrast, the level of photosynthetic intermediates remained constant in darkened isolated chloroplasts, but declined rapidly in chloroplasts isolated from darkened protoplasts. When fructose 1,6-bisphosphatase was pre-activated by treating protoplasts with dithiothreitol the lag was only slightly shortened. These results are discussed in terms of control of the rate of the photosynthesis during the lag by substrates rather than limitation imposed by activity of any of the enzymes measured. 相似文献
158.
Erich Kessler 《Archives of microbiology》1977,113(1-2):139-141
Five physiological and biochemical characters, which had proved to be valuable for the taxonomy of the genus Chlorella, were studied in the genus Prototheca. There is no hydrogenase activity and no liquefaction of gelatin. Most strains are very acidtolerant (limit of growth at pH 2.0 or 2.5) and very salt-tolerant (limit of growth at 4 or 5% NaCl). Two strains grow well at 38°C. The 16 strains, which were previously assigned to seven taxa, fall into four different groups. Our results tend to support the assumption that Prototheca might be related to Chlorella protothecoides. 相似文献
159.
Opposing effects of human peripheral blood lymphocytes on the growth of cultured leukemia cell lines
Natural killing of two human leukemia cell lines (K562 and Molt 4) in a soft-agar, clonagenic assay was shown to be the result of two opposite yet concurrent processes: target cell colony stimulation and inhibition. The stimulatory effect was demonstrable when the effector lymphocytes and target cells were separated in contiguous agar layers, suggesting mediation by a soluble factor. Similarly, stimulation occurred when the effector lymphocytes and target cells were combined at low effector-target cell ratios that do not favor direct cell contact. Target colony inhibition was found to be dominant when large E:T ratios were employed. Both target-effector binding and natural killing were significantly reduced in medium devoid of divalent cations. 相似文献
160.
NLR蛋白是存在于植物和动物中的一个免疫受体大家族, 具有核苷酸结合域并富含亮氨酸重复序列。植物NLR通过识别病原菌特异效应子开启免疫信号转导。第1个植物NLR抗性蛋白于25年前克隆, 但其激活机制仍不清楚, 至今仍未获得一个完整的NLR蛋白结构。最近, 柴继杰、周俭民和王宏伟实验室合作解析了第一个植物完整NLR ZAR1激活前后的结构, 研究成果以两篇论文形式发表在“科学”杂志上, 填补了NLR介导的免疫信号转导研究领域的空白。该文简要总结了相关研究进展, 讨论了NLR免疫信号转导研究领域尚需解决的问题。 相似文献