全文获取类型
收费全文 | 5212篇 |
免费 | 225篇 |
国内免费 | 13篇 |
学科分类
生物科学 | 5450篇 |
出版年
2023年 | 56篇 |
2022年 | 149篇 |
2021年 | 315篇 |
2020年 | 136篇 |
2019年 | 193篇 |
2018年 | 215篇 |
2017年 | 155篇 |
2016年 | 222篇 |
2015年 | 260篇 |
2014年 | 299篇 |
2013年 | 431篇 |
2012年 | 373篇 |
2011年 | 380篇 |
2010年 | 212篇 |
2009年 | 177篇 |
2008年 | 196篇 |
2007年 | 195篇 |
2006年 | 178篇 |
2005年 | 149篇 |
2004年 | 117篇 |
2003年 | 86篇 |
2002年 | 92篇 |
2001年 | 56篇 |
2000年 | 62篇 |
1999年 | 47篇 |
1998年 | 29篇 |
1997年 | 14篇 |
1996年 | 20篇 |
1995年 | 17篇 |
1993年 | 16篇 |
1992年 | 31篇 |
1991年 | 47篇 |
1990年 | 41篇 |
1989年 | 33篇 |
1988年 | 28篇 |
1987年 | 42篇 |
1986年 | 30篇 |
1985年 | 36篇 |
1984年 | 28篇 |
1983年 | 20篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 23篇 |
1978年 | 24篇 |
1977年 | 13篇 |
1975年 | 14篇 |
1974年 | 13篇 |
1973年 | 20篇 |
1968年 | 12篇 |
排序方式: 共有5450条查询结果,搜索用时 0 毫秒
51.
M Alam M Ahmad A Rasheed M Saleem M K Javaid S Ikram 《Indian journal of experimental biology》1990,28(10):940-942
The metabolic fate of isatin hydrazone (Ia), isatin-3-thiosemicarbazone (Ib), isatin-3-semicarbazone (Ic), isatin-3-phenylhydrazone (Id), isatin oxime (Ie) and 3-hydroxy-3-acetonyl oxindole (II) was studied in rabbits. The compounds were administered orally in the dose of 300 mg/kg body wt. Isatin anthranilic acid, tryptophan and nicotinic acid were identified as the major metabolites excreted in urine. The 3-hydroxy-3-acetonyl oxindole (II) gave on additional metabolite, oxindole. The major metabolites were separated and identified unambiguously on thin layer silica gel plate. Metabolic pathways have been proposed to explain the biotransformation of the compounds investigated. 相似文献
52.
Three enzymes involved in the conversion of 3T3-L2 fibroblasts into fat cells, acetyl CoA carboxylase (ACC), fatty acid synthetase (FAS) and pyruvate carboxylase (PC) have been localized by immunofluorescence techniques. The method enables the identification of cells undergoing the conversion while they are still fibroblastic in appearance, often before the obvious appearance of fat droplets. Specific fluorescence for each enzyme can be seen in "clones" of cells derived from single cells, which may undergo an event during logarithmic growth, which programs the cells to differentiate subsequent to confluence of and addition of induction medium. 相似文献
53.
54.
55.
This investigation reports observations on the growth of Rana cyanophlyctis tadpoles following a whole body gamma-ray exposure. The effect on the body and hind limb size is perhaps the most significant of the period of latency. A dose of 2,000 R serves as a stressor and activates ACTH secretion in the tadpoles. The resultant somatotrophic hormone (STH) inhibition and subsequent recovery during the following days seem an integral part of the radiation syndrome. 相似文献
56.
57.
Ahmad Mokhtarzadeh 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1975,46(1):1-5
Summary F1 plants, monosomic for chromosomes 1A to 7B, from crosses of three lines of Triticum durum var. Khapli with the Chinese series were investigated together with their backcrosses to normal Chinese Spring. The three Khapli lines were designated K1-A, K1-B, and K1-D. Five parameters were analyzed: awn development, glume color, degree of selfing, crossing ability, and seed abortion.Morphological examination of F1 monopentaploid plants revealed that, in the three lines, chromosomes 5A, 1B, 3B, 4B, 5B, and 6B had promotor genes and 2A, 6A, and 2B had inhibitor genes for awn development. Results on glume color suggested the presence of at least three inhibitor genes on 1B, 5B, and 7B, and three promotor genes on 3A, 6A, and 6B chromosomes of Chinese Spring.The first backcross of interspecific hybrids seemed to indicate that some chromosomes (1A, 1B, and 4B) originating from the Khapli lines possessed promotor genes, others (2B and 4A) carried inhibitor genes for seed setting. Similarily, the genetic factor (s) carried by chromosome 5A increased seed abortion whereas those on 2B and 6B reduced it.Self fertility in K1-D hybrids was probably the result of the inhibitor factor (s) on 7A and promotor genes on 3B, 4B, 5B, and 6B chromosomes coming from K1-D. 相似文献
58.
Removal efficiency of gold from a solution of pure tetrachloroaurate ions was investigated using microbial fuel cell (MFC) technology. The effects of type of catholyte solution and initial gold concentration on the removal efficiency were considered. Due to its presence at high levels in the gold wastewater, the effect of copper ions on the removal efficiency of the gold ions was also studied. The effects of pH and initial biomass concentration on the gold removal efficiency was also determined. The results showed that after 5 h contact time, 95% of gold removal efficiency from a wastewater containing 250 ppm of initial gold ions at ambient temperature using 80 g/L yeast concentration was achieved. After 48 h of the cell''s operation under the same condition, 98.86% of AuCl4 – ions were successfully removed from the solution. At initial gold concentration in the waste solution of 250 ppm, pH 2, and initial yeast concentration of 80 g/L, 100% removal efficiency of the gold was achieved. On the other hand, the most suitable condition for copper removal was found at a pH of 5.2, where 53% removal efficiency from the waste solution was accomplished. 相似文献
59.
We have analyzed, by means of density functional theory calculations and the embedded cluster model, the adsorption and spin-state
properties of Cr, Ni, Mo, and Pt deposited on a MgO crystal. We considered deposition at the Mg2+ site of a defect-free surface and at Li+ and Na+ sites of impurity-containing surfaces. To avoid artificial polarization effects, clusters of moderate sizes with no border
anions were embedded in simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces. The interaction
between a transition metal atom and a surface results from a competition between Hund's rule for the adsorbed atom and the
formation of a chemical bond at the interface. We found that the adsorption energies of the metal atoms are significantly
enhanced by the cation impurities, and the adsorption energies of the low-spin states of spin-quenched complexes are always
more favorable than those of the high-spin states. Spin polarization effects tend to preserve the spin states of the adsorbed
atoms relative to those of the isolated atoms. The metal–support interactions stabilize the low-spin states of the adsorbed
metals with respect to the isolated metals, but the effect is not always enough to quench the spin. Spin quenching occurs
for Cr and Mo complexes at the Mg2+ site of the pure surface and at Li+ and Na+ sites of the impurity-containing surfaces. Variations of the spin-state properties of free metals and of the adsorption and
spin-state properties of metal complexes are correlated with the energies of the frontier orbitals. The electrostatic potential
energy curves provide further understanding of the nature of the examined properties. 相似文献
60.
Mahboob Ahmad Malik M. Ahmad Rifat Hamid M. Z. Abdin Saleem Javed 《Mycotoxin Research》2013,29(1):39-45
Aflatoxins are one of the most important secondary metabolites. These extrolites are produced by a number of Aspergillus fungi. In this study, we demonstrate the effect of media components and enhanced aflatoxin yield shown by A. flavus using response surface methodology in response to different nutrients. Different components of a chemically defined media that influence the aflatoxin production were monitored using Plackett–Burman experimental design and further optimized by Box–Behnken factorial design of response surface methodology in liquid culture. Interactions were studied with five variables, namely sorbitol, fructose, ammonium sulfate, KH2PO4, and MgSO4.7H2O. Maximum aflatoxin production was envisaged in medium containing 4.94 g/l sorbitol, 5.56 g/l fructose, 0.62 g/l ammonium sulfate, 1.33 g/l KH2PO4, and 0.65 g/l MgSO4·7H2O using response surface plots and the point prediction tool of the DESIGN EXPERT 8.1.0 (Stat-Ease, USA) software. However, a production of 5.25 μg/ml aflatoxin production was obtained, which was in agreement with the prediction observed in verification experiment. The other component (MgSO4.7H2O) was found to be an insignificant variable. 相似文献