全文获取类型
收费全文 | 45431篇 |
免费 | 3157篇 |
国内免费 | 2061篇 |
专业分类
50649篇 |
出版年
2024年 | 97篇 |
2023年 | 814篇 |
2022年 | 1132篇 |
2021年 | 1537篇 |
2020年 | 1484篇 |
2019年 | 1973篇 |
2018年 | 1633篇 |
2017年 | 1106篇 |
2016年 | 1237篇 |
2015年 | 1608篇 |
2014年 | 2483篇 |
2013年 | 3220篇 |
2012年 | 1751篇 |
2011年 | 2272篇 |
2010年 | 1690篇 |
2009年 | 1976篇 |
2008年 | 2009篇 |
2007年 | 2104篇 |
2006年 | 1886篇 |
2005年 | 1790篇 |
2004年 | 1611篇 |
2003年 | 1389篇 |
2002年 | 1335篇 |
2001年 | 1130篇 |
2000年 | 938篇 |
1999年 | 859篇 |
1998年 | 819篇 |
1997年 | 751篇 |
1996年 | 716篇 |
1995年 | 674篇 |
1994年 | 636篇 |
1993年 | 591篇 |
1992年 | 562篇 |
1991年 | 535篇 |
1990年 | 401篇 |
1989年 | 408篇 |
1988年 | 377篇 |
1987年 | 307篇 |
1986年 | 260篇 |
1985年 | 324篇 |
1984年 | 399篇 |
1983年 | 231篇 |
1982年 | 305篇 |
1981年 | 294篇 |
1980年 | 230篇 |
1979年 | 210篇 |
1978年 | 152篇 |
1977年 | 104篇 |
1976年 | 112篇 |
1974年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Satoko Iwahori Daisuke Kohmon Junya Kobayashi Yuhei Tani Takashi Yugawa Kenshi Komatsu 《Cell cycle (Georgetown, Tex.)》2014,13(3):471-481
Ataxia-telangiectasia mutated (ATM) plays crucial roles in DNA damage responses, especially with regard to DNA double-strand breaks (DSBs). However, it appears that ATM can be activated not only by DSB, but also by some changes in chromatin architecture, suggesting potential ATM function in cell cycle control. Here, we found that ATM is involved in timely degradation of Cdt1, a critical replication licensing factor, during the unperturbed S phase. At least in certain cell types, degradation of p27Kip1 was also impaired by ATM inhibition. The novel ATM function for Cdt1 regulation was dependent on its kinase activity and NBS1. Indeed, we found that ATM is moderately phosphorylated at Ser1981 during the S phase. ATM silencing induced partial reduction in levels of Skp2, a component of SCFSkp2 ubiquitin ligase that controls Cdt1 degradation. Furthermore, Skp2 silencing resulted in Cdt1 stabilization like ATM inhibition. In addition, as reported previously, ATM silencing partially prevented Akt phosphorylation at Ser473, indicative of its activation, and Akt inhibition led to modest stabilization of Cdt1. Therefore, the ATM-Akt-SCFSkp2 pathway may partly contribute to the novel ATM function. Finally, ATM inhibition rendered cells hypersensitive to induction of re-replication, indicating importance for maintenance of genome stability. 相似文献
22.
23.
24.
Cell division in cell suspension cultures can be completely blocked by the growth retardant tetcyclacis at a concentration of 10-4 mol l-1. In rice cells it has been demonstrated that the growth inhibition can be completely overcome by application of cholesterol independent of the duration of pretreatment with tetcyclacis. In suspension cultures of maize and soybean, too, the effect of tetcyclacis on cell division was neutralized by adding cholesterol. Other plant sterols, stigmasterol, campesterol and sitosterol were active in a decreasing order. Modifications in the cholesterol perhydro-cyclopentanophenanthrene-ring system indicate that the hydroxyl group at C-3 and the double bond between C-5 and C-6 in ring B are required for the activity. In contrast, gibberellic acid as well as ent-kaurenoic acid could not compensate retardant effects. Likewise, tetcyclasis did not change the level of gibberellins in rice cells as shown by radioimmunoassay. Thus, it is concluded that in cell suspension cultures sterols play a more important role in cell division than gibberellins.Abbreviation GAx
gibberelin Ax 相似文献
25.
《Cell reports》2020,30(5):1504-1514.e7
- Download : Download high-res image (117KB)
- Download : Download full-size image
26.
Masaru Kubota Ying-Wei Lin Keigo Hamahata Machiko Sawada Seiji Koishi Haruyo Hirota Yoshihiro Wakazono 《Mutation Research - Genetic Toxicology and Environmental Mutagenesis》2000,470(2):21
The occurrence of a second neoplasm is one of the major obstacles in cancer chemotherapy. The elucidation of the genotoxic effects induced by anti-cancer drugs is considered to be helpful in identifying the degree of cancer risk. Numerous investigations on cancer patients after chemotherapy have demonstrated: (i) an increase in the in vivo somatic cell mutant frequency (Mf) at three genetic loci, including hypoxanthine–guanine phosphoribosyl-transferase (hprt), glycophorin A (GPA), and the T-cell receptor (TCR), and (ii) alterations in the mutational spectra of hprt mutants. However, the time required for and the degree of such changes are quite variable among patients even if they have received the same chemotherapy, suggesting the existence of underlying genetic factor(s). Accordingly, some cancer patients prior to chemotherapy as well as patients with cancer-prone syndrome have been found to show an elevated Mf. Based on the information obtained from somatic cell mutation assays, an individualized chemotherapy should be considered in order to minimize the risk of a second neoplasm. 相似文献
27.
Sven Skog Viola Eriksson Eva Eliasson 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,672(1):33-44
Suspension cultures of ‘Chang liver’ cells were synchronized by preincubation in a glutamine-deficient medium or by thymidine blockade. Specific arginase activity varied in the synchronized cultures, being high when the number of S-phase cells was maximal. A relationship between high arginase activity and a high percentage of (S+G2) cells was also found when unsynchronized cells were separated by velocity sedimentation. The increase in arginase activity near the G1/S border was totally inhibited in the presence of cycloheximide. The rate of decrease in activity after addition of the drug indicated that the variations in the rate of synthesis of the enzyme, while the rate of degradation was more or less constant, corresponding to 4–6% per h. The role of arginase in cells lacking a urea cycle and the regulation of arginase activity in ‘Chang liver’ cells is discussed. 相似文献
28.
《Cell reports》2020,30(7):2065-2074.e4
- Download : Download high-res image (155KB)
- Download : Download full-size image
29.
Giovanni Murtas 《Systems and synthetic biology》2010,4(2):85-93
One of the major properties of the semi-synthetic minimal cell, as a model for early living cells, is the ability to self-reproduce
itself, and the reproduction of the boundary layer or vesicle compartment is part of this process. A minimal bio-molecular
mechanism based on the activity of one single enzyme, the FAS-B (Fatty Acid Synthase) Type I enzyme from Brevibacterium ammoniagenes, is encapsulated in 1-palmitoyl-2oleoyl-sn-glycero-3-phosphatidylcholine (POPC) liposomes to control lipid synthesis. Consequently molecules of palmitic acid released
from the FAS catalysis, within the internal lumen, move toward the membrane compartment and become incorporated into the phospholipid
bilayer. As a result the vesicle membranes change in lipid composition and liposome growth can be monitored. Here we report
the first experiments showing vesicles growth by catalysis of one enzyme only that produces cell boundary from within. This
is the prototype of the simplest autopoietic minimal cell. 相似文献
30.
《植物生理与分子生物学学报》1997,(3)
植物在不同的逆境条件下可以生成一类受脱落酸(ABA)诱导的蛋白质[脱落酸响应蛋白(ABAresPonsiveProtein,RABpr。tein)](Bray1993)。RAB蛋白分布在不同的物种之中,许多[如Lea(Lateembryogen-。isabundant)蛋白(Dure1993)]形成于植物胚胎成熟失水过程中,但也有一些是植物受到不同逆境处理后在营养器官内所形成的「如脱水蛋白(Dehrdrin)](Dure1993)。已发现的70余个RAB蛋白中,有30余个属于脱水蛋白。(Close等1993)RAB蛋白在植物体内的功能目前尚不了解(Bray1993)。由蛋白质的氨基酸组成分析表明,这些… 相似文献