全文获取类型
收费全文 | 1611篇 |
免费 | 178篇 |
国内免费 | 2篇 |
专业分类
1791篇 |
出版年
2022年 | 18篇 |
2021年 | 28篇 |
2020年 | 18篇 |
2019年 | 26篇 |
2018年 | 20篇 |
2017年 | 32篇 |
2016年 | 46篇 |
2015年 | 64篇 |
2014年 | 90篇 |
2013年 | 87篇 |
2012年 | 109篇 |
2011年 | 126篇 |
2010年 | 65篇 |
2009年 | 67篇 |
2008年 | 83篇 |
2007年 | 75篇 |
2006年 | 86篇 |
2005年 | 71篇 |
2004年 | 73篇 |
2003年 | 68篇 |
2002年 | 56篇 |
2001年 | 22篇 |
2000年 | 17篇 |
1999年 | 20篇 |
1998年 | 27篇 |
1997年 | 16篇 |
1996年 | 24篇 |
1995年 | 13篇 |
1994年 | 19篇 |
1993年 | 13篇 |
1992年 | 20篇 |
1991年 | 17篇 |
1990年 | 18篇 |
1989年 | 19篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1974年 | 15篇 |
1973年 | 9篇 |
1972年 | 10篇 |
排序方式: 共有1791条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
The reversible inhibition of respiratory activity could provide a novel approach to the preservation of traditionally hard to store plant germplasm such as clonal materials and recalcitrant seed. The gaseous anesthetic nitrous oxide caused a reversible, dose-dependent, partial inhibition of dioxygen utilization in mitochondrial particles isolated from cell suspension cultures of the salt-tolerant marsh grass Distichlis spicata, with maximal inhibition of 33% after 30 minutes exposure to an atmosphere of 80% nitrous oxide plus 20% oxygen. Respiration of whole cells required longer time to be affected by the anesthetic, and was reversibly inhibited an average of 19% when measured using a differential respirometer. Exposure to 80% nitrous oxide plus 20% oxygen for up to 10 days caused no measurable effect on cell growth.Abbreviations PCV
packed cell volume
- EDTA
sodium ethylenediaminetetraacetic acid
- BSA
bovine serum albumin
- MOPS
3(N-morpholino) propanesulfonic acid
- TMPD
N,N,N',N'-tetramethyl-p-phenylene diamine
- STP
standard temperature and pressure 相似文献
5.
Leigh EG 《Trends in ecology & evolution》1991,6(8):257-262
Adam Smith proposed that individuals can share sufficient interest in their society's welfare to profit by cooperating for its benefit and by jointly suppressing behavior hurtful to it. Similarly, a genome's genes share a common interest in 'honest' meiosis, which ensures that alleles can spread only by benefitting their carriers. Honeybee workers express a common interest in raising their queen's, rather than their half-sisters', eggs by eating eggs laid by half sisters. Can analogous principles explain the evolution of harmony at other levels of biological organization, such as ecosystems or organismic development? 相似文献
6.
R LoBrutto G W Smithers G H Reed W H Orme-Johnson S L Tan J S Leigh 《Biochemistry》1986,25(19):5654-5660
Pulsed electron paramagnetic resonance spectroscopy has been used to detect Mn(II)-ligand superhyperfine couplings in complexes with creatine kinase and in the Mn(II) metalloprotein concanavalin A. Electron spin-echo envelopes from Mn(II), bound in these complexes, are modulated by superhyperfine interactions between Mn(II) and nearby, weakly coupled nuclear spins. The characteristic frequencies of the modulations were obtained by Fourier transformation of the three-pulse, spin-echo envelopes. In transition-state analogue complexes of creatine kinase (enzyme-MnIIADP-anion-creatine), superhyperfine interactions from the directly coordinated nitrogen of the thiocyanate ligand give envelope modulations. The source of the modulations was confirmed by measurements with the 14N and 15N forms of thiocyanate. On the other hand, the nitrogen of coordinated nitrate, which is two bonds removed from the paramagnetic center, does not produce detectable modulations. In spectra for Mn(II) concanavalin A, envelope modulations are detected due to the nitrogen of the coordinated histidine residue. Complexes prepared in 2H2O give strong signals due to weakly coupled 2H. For Mn(II)-doped single crystals of sodium pyrophosphate, signals are observed in the frequency domain spectra that are due to coupling from 31P. Phosphorus signals from the ADP ligand in complexes with creatine kinase show approximately the same coupling constant but have a much broader line width. 相似文献
7.
8.
9.
Role for [corrected] Agrobacterium tumefaciens ChvA protein in export of beta-1,2-glucan. 总被引:23,自引:15,他引:8 下载免费PDF全文
G A Cangelosi G Martinetti J A Leigh C C Lee C Theines E W Nester 《Journal of bacteriology》1989,171(3):1609-1615
Functional chvA and chvB genes are required for attachment of Agrobacterium tumefaciens to plant cells, an early step in crown gall tumor formation. Strains defective in these loci do not secrete normal amounts of cyclic beta-1,2-glucan. Whereas chvB is required for beta-1,2-glucan synthesis, the role of chvA in glucan synthesis or export has not been clearly defined. We found that cultures of chvA mutants contained as much neutral beta-1,2-glucan in the cell pellets as did the wild type, with no detectable accumulation of glucan in the culture supernatant. The cytoplasm of chvA mutant cells contained over three times more soluble beta-1,2-glucan than did the cytoplasm of the wild-type parent. Unlike the wild type, chvA mutants contained no detectable periplasmic glucan. The amino acid sequence of chvA is highly homologous to the sequences of bacterial and eucaryotic export proteins, as observed previously in the case of ndvA, a rhizobial homolog of chvA. Strong sequence homology within this family of export proteins is concentrated in the carboxy-terminal portions of the proteins, but placement of consensus ATP-binding sites, internal signal sequences, and hydrophobic domains are conserved over their entire lengths. These data suggest a model for beta-1,2-glucan synthesis in A. tumefaciens in which glucan is synthesized inside the inner membrane with the participation of ChvB and transported across the inner membrane with the participation of ChvA. 相似文献
10.
The characteristics of Cl– transport in isolated tonoplast vesicles from red-beet (Beta vulgaris L.) storage tissue have been investigated using the Cl–-sensitive fluorescent probe, 6-methoxy-1-(3-sulfonatopropyl)-quinolinium (SPQ). The imposition of (inside) positive diffusion potentials, generated with K+ and valinomycin, increased the initial rate of Cl– transport, demonstrating that Cl– could be electrically driven into the vesicles. Chloride influx was unaffected by SO
4
2-
, but was competitively blocked by NO
3
–
, indicating that both Cl– and NO
3
–
may be transported by the same porter. In some preparations, increases in free-Ca2+ concentration from 10–8 to 10–5 mol·dm–3 caused a significant decrease in Cl– influx, which may indicate that cytosolic Ca2+ concentration has a role in controlling Cl– fluxes at the tonoplast. However, this effect was only seen in about 50% of membrane preparations and some doubt remains over its physiological significance. A range of compounds known to block anion transport in other systems was tested, and some partially blocked Cl– transport. However, many of these inhibitors interfered with SPQ fluorescence and so only irreversible effects could be tested. The results are discussed in the context of recent advances made using the patch-clamp technique on isolated vacuoles.Abbreviations and Symbols BTP
1,3-bis[tris(hydroxymethyl)-methylamino]propane
- DTT
dithiothreitol
- EDTA
ethylenediaminetetraacetic acid
-
membrane potential
- pH
pH gradient
- SPQ
6-methoxy-1-(3-sulfonatopropyl)quinolinium
- Tricine
N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl] glycine 相似文献