全文获取类型
收费全文 | 100844篇 |
免费 | 6782篇 |
国内免费 | 6989篇 |
出版年
2024年 | 145篇 |
2023年 | 1583篇 |
2022年 | 1981篇 |
2021年 | 3320篇 |
2020年 | 3139篇 |
2019年 | 4281篇 |
2018年 | 3622篇 |
2017年 | 2807篇 |
2016年 | 2840篇 |
2015年 | 3526篇 |
2014年 | 6021篇 |
2013年 | 7685篇 |
2012年 | 4908篇 |
2011年 | 6027篇 |
2010年 | 4745篇 |
2009年 | 5284篇 |
2008年 | 5528篇 |
2007年 | 5693篇 |
2006年 | 5286篇 |
2005年 | 4702篇 |
2004年 | 4220篇 |
2003年 | 3583篇 |
2002年 | 3246篇 |
2001年 | 2327篇 |
2000年 | 1863篇 |
1999年 | 1831篇 |
1998年 | 1709篇 |
1997年 | 1406篇 |
1996年 | 1325篇 |
1995年 | 1225篇 |
1994年 | 1153篇 |
1993年 | 839篇 |
1992年 | 792篇 |
1991年 | 659篇 |
1990年 | 547篇 |
1989年 | 418篇 |
1988年 | 399篇 |
1987年 | 359篇 |
1986年 | 289篇 |
1985年 | 377篇 |
1984年 | 554篇 |
1983年 | 381篇 |
1982年 | 405篇 |
1981年 | 295篇 |
1980年 | 235篇 |
1979年 | 215篇 |
1978年 | 187篇 |
1977年 | 152篇 |
1976年 | 130篇 |
1975年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
972.
973.
Yoshiko Kikuchi Yoshio Oka Mariko Kobayashi Yukifumi Uesono Akio Toh-e Akihiko Kikuchi 《Molecular & general genetics : MGG》1994,245(1):107-116
A new temperature-sensitive mutant of Saccharomyces cerevisiae was isolated. Arrested cells grown at the nonpermissive temperature were of dumb-bell shape and contained large vacuoles. A DNA fragment was cloned based on its ability to complement this temperature sensitivity. The HTR1 gene encodes a putative protein of 93 kDa without significant homology to any known proteins. The gene was mapped between ade5 and lys5 on the left arm of chromosome VII. The phenotype of the gene disruptant appeared to be strain-specific; disruption of the gene in strain W303 caused the cells to become temperature sensitive. The arrested phenotype here was similar to that of the original is mutant and cells in G2/M phase predominated at high temperature. Another disruptant in a strain YPH background grew slowly at high temperature due to slow progression through G2/M phase, and morphologically abnormal (elongated) cells accumulated. A single-copy suppressor that alleviated the temperature-sensitive defects in both strains was identified as MCS1/SSD1. The wild-type strains W303 and YPH are known to carry defective MCS1/SSD1 alleles; hence HTR1 may function redundantly with MCS1/SSD1 to suppress the temperature-sensitive phenotypes. In addition, based on a halo bioassay, the disruptant strains appeared to be defective in recovery from, or adaptive response to G1 arrest mediated by mating pheromone, even at the permissive temperature. Thus the gene has at least two functions and is designated HTR1 (required for high temperature growth and recovery from G1 arrest induced by mating pheromone). 相似文献
974.
The Saccharomyces cerevisiae DIS2S1/GLC7 gene encodes a type 1 protein phosphatase indispensable for cell proliferation. We found that introduction of a multicopy DIS2S1 plasmid impaired growth of cells with reduced activity of the cAMP-dependent protein kinase. In order to understand further the interaction between the two enzymes, a temperature-sensitive mutation in the DIS2S1 gene was isolated. The mutant accumulated less glycogen than wild type at the permissive temperature, indicating that activity of the Dis2s1 protein phosphatase is attenuated by the mutation. Furthermore, the dis2s1
ts mutation was shown to be suppressed by a multicopy plasmid harboring PDE2, a gene for cAMP phosphodiesterase. These results indicate that the Ras-cAMP pathway interacts genetically with the DIS2S1/GLC7 gene. 相似文献
975.
976.
Hiromi Maekawa Tomoko Nakagawa Yoko Uno Kenji Kitamura Chikashi Shimoda 《Molecular & general genetics : MGG》1994,244(5):456-464
When the fission yeastSchizosaccharomyces pombe is starved for nitrogen, the cells are arrested in the G1 phase, enter the G0 phase and initiate sexual development. Theste13 mutant, however, fails to undergo a G1 arrest when starved for nitrogen and since this mutant phenotype is not suppressed by a mutation in adenylyl cyclase (cyr1), it would appear thatste13
+ either acts independently of the decrease in the cellular cAMP level induced by starvation for nitrogen, or functions downstream of this controlling event. We have used functional complementation to clone theste13
+ gene from anS. pombe genomic library and show that its disruption is not lethal, indicating that, while the gene is required for sexual development, it is not essential for cell growth. Nucleotide sequencing predicts thatste13
+ should encode a protein of 485 amino acids in which the consensus motifs of ATP-dependent RNA helicases of the DEAD box family are completely conserved. Point mutations introduced into these consensus motifs abolished theste13
+ functions. The predicted Ste13 protein is 72% identical to theDrosophila melanogaster Me31B protein over a stretch of 391 amino acids. ME31B is a developmentally regulated gene that is expressed preferentially in the female germline and may be required for oogenesis. Expression of ME31B cDNA inS. pombe suppresses theste13 mutation. These two evolutionarily conserved genes encoding putative RNA helicases may play a pivotal role in sexual development. 相似文献
977.
Indrioi Benediktsson Claudia P. Spampinato Carlos S. Andreo Otto Schieder 《Physiologia plantarum》1994,90(3):445-450
Clastogenic agents, i.e. agents that can induce chromosome or DNA breakage, have been shown to enhance the rale of direct gene transfer to protoplasts. The effect was analysed at the enzymatic level using protoplast homogenates as well as intact protoplasts. For that purpose existing procedures were modified to enable measurement of DNA polymerase in vivo. In the system used, external DNA was able to enter the cells without the addition of membrane-permeabilizing compounds. When comparing total DNA polymerase activity of protoplasts irradiated with X-rays or UV-light with that of untreated cells we did not observe significant differences. Incubation of protoplasts with high doses of bleomycin affected total DNA polymerase activity negatively. but dideoxythymidine triphosphate-sensitive activity was not influenced. We conclude that the DNA strand-breaks induced by low doses of X-rays. UV-light or bleomycin do not increase the total or the repair-DNA polymerase activity and. therefore. that the increase in the transformation rates after DNA strand-breaking is not preceded by enhanced DNA polymerase activity. 相似文献
978.
Endogenous gibberellins (GAs) were extracted and purified from apical buds of Eucalyptus nitens (Deane and Maid.) Maid. and the cambial region of E. globulus (Labill.). then analysed by capillary gas chromatography-mass spectrometry. GA1 GA19 GA20 and GA29 were identified by full scan mass spectra. Kovats retention indices and high resolution selected ion monitoring. Using deuterated internal standards. GA1 . GA19 . GA20 and putative GA29 and GA53 were quantified in the apical buds, while GA4 . GA8 . GA9 and GA44 were shown to be either absent or present at very low levels. From the cambial region. GA1 and GA20 were quantified at levels of 0.30 ng (g fresh weight)-1 and 8.8 ng (g fresh weight)-1 respectively. These data suggest that the early 13-hydroxylation pathway is the dominant pathway for GA biosynthesis in Eucalyptus . 相似文献
979.
980.
Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol], a triazole growth retardant, increased the 1-aminocyclopropane-1-carboxylic acid (ACC) level and resulted in reduced ethylene production, estimated as ethylene release in a closed system or by vacuum-extraction, in the primary leaves of Phaseolus vulgaris L. cv. Juliska seedlings exposed to light. At the light/dark transition, a definite enhancement of the endogenous ethylene level was observed by vacuum-extraction of primary leaves of treated plants and the ethylene deficiency of retardant-treated leaves ceased. The concentration of ACC after the light/dark transition followed the pattern for ethylene, and the increase in ACC content was paralleled by a decrease in malonyl-ACC.
It is concluded that the internal level of ethylene is not necessarily lower in the primary leaves of paclobutrazol-treated bean plants, but under special environmental conditions in vivo it may reach that of the control. 相似文献
It is concluded that the internal level of ethylene is not necessarily lower in the primary leaves of paclobutrazol-treated bean plants, but under special environmental conditions in vivo it may reach that of the control. 相似文献