全文获取类型
收费全文 | 3243篇 |
免费 | 234篇 |
出版年
2023年 | 29篇 |
2021年 | 51篇 |
2020年 | 38篇 |
2019年 | 33篇 |
2018年 | 94篇 |
2017年 | 85篇 |
2016年 | 150篇 |
2015年 | 122篇 |
2014年 | 145篇 |
2013年 | 260篇 |
2012年 | 123篇 |
2011年 | 110篇 |
2010年 | 125篇 |
2009年 | 109篇 |
2008年 | 116篇 |
2007年 | 68篇 |
2006年 | 113篇 |
2005年 | 84篇 |
2004年 | 75篇 |
2003年 | 83篇 |
2002年 | 74篇 |
2001年 | 60篇 |
2000年 | 56篇 |
1999年 | 57篇 |
1998年 | 65篇 |
1997年 | 39篇 |
1996年 | 50篇 |
1995年 | 47篇 |
1994年 | 49篇 |
1993年 | 55篇 |
1992年 | 33篇 |
1991年 | 33篇 |
1989年 | 26篇 |
1988年 | 32篇 |
1987年 | 24篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1981年 | 30篇 |
1980年 | 36篇 |
1978年 | 28篇 |
1975年 | 25篇 |
1974年 | 37篇 |
1973年 | 28篇 |
1972年 | 25篇 |
1971年 | 26篇 |
1969年 | 27篇 |
1966年 | 27篇 |
1963年 | 24篇 |
1962年 | 27篇 |
1960年 | 24篇 |
排序方式: 共有3477条查询结果,搜索用时 468 毫秒
101.
When flax seedlings are decapitated above cotyledons and three days later one of the two cotyledons is removed then the remaining
cotyledon stimulates in four to five days growth of its axillary bud. It has been found that content of endogenous cytokinins
was higher in the stimulated bud as compared with the other one already 12 h after the cotyledon removal.
Flax seedlings decapitated under cotyledons regenerate adventitious buds on thy hypocotyl stump during 5–6 days. The endogenous
fytohormonal preparation of this regeneration was investigated in the 20 mm apical part of the hypocotyl stump. Decrease in
auxin and increase in gibberellins was already found during the first day after decapitation while the level of cytokinins
increased as late as three days after the apex removal. 相似文献
102.
103.
104.
On integrating experimental data published previously, the following picture of the mitochondrial adenine nucleotide (AdN) translocation system is being presented: 1. The AdN translocation system serves not only to transport ATP synthesized within mitochondria into the cytosol but also to transport cytosolic ATP into the mitochondria when oxidative phosphorylation is not functioning. 2. The AdN translocator is coded for by nuclear genes and the mitochondrial protein synthesis is not involved in its formation. 3. The AdN translocation system must be preserved and functioning even in cells which could dispense with oxidative phosphorylation. It assures appropriate concentrations of intramitochondrial ATP. 4. The intramitochondrial ATP is required for normal replication of mitochondrial DNA. Tis supports the view that the mitochondrion is a self-replicating semi-autonomous organelle. 5. The appropriate concentration of ATP must be present in mitochondria to make possible cell growth or multiplication. This points to a direct or indirect role of mitochondria in the control of cell proliferation. 相似文献
105.
Frequency of large granular lymphocytes in peripheral blood of healthy persons and breast cancer patients 总被引:1,自引:0,他引:1
The frequency of large granular lymphocytes (LGL) in the peripheral blood of healthy persons (n = 56) and breast cancer patients (31 cases with stage-I and -II disease and 42 cases with stage-III and -IV disease) was studied. The frequency of LGL in peripheral blood was significantly depressed in cancer patients, and particularly in patients with advanced breast cancer. 相似文献
106.
Miloš Sedlák Jaromír Kaválek Vladimír Machácek Vojeslav Šterba 《Molecules and cells》1992,1(10):170-174
The cyclization reactions of N-methyl-N’-(2-methoxycarbonylphenyl)sulfamide (1a), N-methyl-N-(2-methoxycarbonylphenyl)-sulfamide (2a), and 2-methoxycarbonylphenylsulfamide (3a) were studied in aqueous amine buffers (butylamine, ethanolamine, morpholine, glycinamide). The dependences observed between the rate constants and buffer concentrations show that the reactions are subject to base catalysis in all the three cases, the decomposition of the tetrahedral intermediate being rate limiting. The ratio of the relative rate constants of the base catalyzed cyclizations reactions of the three derivatives is 1a: 2a: 3a = 1: 20000: 100. The logarithm of rate constants of the base catalyzed cyclization reactions was plotted against the pKa values of conjugated acids of the individual amines used as the buffers in the cyclization of compound 1a, and the value of the Brönsted coefficient obtained was about 0.1, which means that the proton transfer from the intermediate to the basic buffer component is thermodynamically favorable. The intermediate is a much weaker base, and the reaction is controlled by diffusion. The slope of an analogous dependence for compound 2a gradually decreases from values near to 0.5 to values near to zero, which means that the intermediate formed from compound 2a (pKa ≈ 9.3) has a pKa value comparable with that of the acid buffer component. 相似文献
107.
No significant differences in the acetylene-reducing activity and evolution of H2 and CO2 nodulated roots ofPisum sativum inoculated with soilRhizobium populations from two soils with different acidities (Ruzyně soil 7.6; Lukavec soil 4.9) were observed.Rhizobium population from Lukavec soil formed nodules, exhibiting a higher H2 evolution. Co-inoculation with the Hup+ strain 128C30 (7×107 cells per seedling) eliminated, to some extent, the effect of soil populations on physiological activity.
Translated by Č. Novotny 相似文献
108.
Distance measurements using paramagnetic ion-induced relaxation in the saturation transfer electron spin resonance of spin-labeled biomolecules: Application to phospholipid bilayers and interdigitated gel phases 下载免费PDF全文
The saturation transfer electron spin resonance (STESR) spectra of spin-labeled phosphatidylcholines in gel phase lipid bilayers are shown to be sensitive to dipolar spin-spin interactions with paramagnetic ions in the aqueous phase. The reciprocal integrated intensity of the STESR spectrum is linearly dependent on aqueous Ni2+ ion concentration, hence, confirming the expectation that the STESR intensity is directly proportional to the spin-lattice relaxation time of the spin label. The gradient of the relaxation rate with respect to Ni2+ ion concentration decreases strongly with the position of the nitroxide group down the sn-2 chain of the spin-labeled lipid and is consistent with a 1/R3 dependence on the distance, R, from the bilayer surface. The values derived for the dimensions of the bilayer and lipid molecules in the case of dipalmitoyl phosphatidylcholine (DPPC) are in good agreement with those available from x-ray diffraction studies. Allowance for the multibilayer nature of the DPPC dispersions gives an estimate of the water layer thickness that is also consistent with results from x-ray diffraction. The profile of the paramagnetic ion-induced relaxation is drastically changed with DPPC dispersions in glycerol for which the lipid chains are known to be interdigitated in the gel phase. The terminal methyl groups of the lipid chains are located approximately in register with the C-3 atoms of the sn-2 chain of the oppositely oriented lipid molecules in the interdigitated phase. The thickness of the lipid layer and the effective thickness of the lipid polar group are reduced by ~40% in the interdigitated phase as compared with the bilayer phase. The calibrations of the distance dependence established by use of spin labels at defined chain positions should be applicable to STESR measurements on other biological systems. 相似文献
109.
Darja Barlič Maganja Borut Štrukelj Jože Pungerčar Franc Gubenšek Vito Turk Igor Kregar 《Plant molecular biology》1992,20(2):311-313
A genomic DNA clone encoding an aspartic proteinase inhibitor of potato was isolated from a lambda EMBL3 phage library using the aspartic proteinase inhibitor cDNA as a hybridization probe. The gene has all characteristic sequences normally found in eucaryotic genes. Typical CAAT and TATA box sequences were found in the 5-upstream region. In this part are also two putative regulatory AGGA box sequences located. In the genomic sequence there are no intron sequences interrupting the coding region. An open reading frame of the gene encodes a precursor protein of 217 amino acids which shows high percent identity with the aspartic proteinase inhibitor cDNA. 相似文献
110.
Racemization of the aqua-{N-salicylidene-(S)-alaninato}copper(II) by reaction with potassium cyanate
Copper(II) N-salicylidene-(S)-alaninate trihydrate reacting as the S-enantiomeric parent compound with KOCN in hot diluted methanol yielded by slow crystallisation from the cooled reaction mixture (in the course of 1 day) the racemic product K[Cu{sal-(RS)-ala}(NCO)]. The parameters of the axial type EPR spectrum in X-band region and the LF band position in the electronic spectrum are typical of an axially distorted square pyramidal coordination of the Cu(II) atom in this complex. The spectral properties of the complex cuprate prepared and its basal crystallographic data are consistent with those of the earlier studied15 K2[Cu2{sal-(RS)-ala}2(μ-NCO)2] synthetized by using [Cu{sal-(RS)-ala}(H2O)].H2O as the racemic parent complex in the reaction mixture with KOCN. 相似文献