全文获取类型
收费全文 | 1016篇 |
免费 | 59篇 |
国内免费 | 1篇 |
专业分类
1076篇 |
出版年
2023年 | 4篇 |
2022年 | 13篇 |
2021年 | 28篇 |
2020年 | 18篇 |
2019年 | 23篇 |
2018年 | 28篇 |
2017年 | 22篇 |
2016年 | 24篇 |
2015年 | 58篇 |
2014年 | 52篇 |
2013年 | 88篇 |
2012年 | 122篇 |
2011年 | 102篇 |
2010年 | 53篇 |
2009年 | 45篇 |
2008年 | 46篇 |
2007年 | 51篇 |
2006年 | 36篇 |
2005年 | 41篇 |
2004年 | 24篇 |
2003年 | 13篇 |
2002年 | 25篇 |
2001年 | 13篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1970年 | 4篇 |
1964年 | 1篇 |
排序方式: 共有1076条查询结果,搜索用时 0 毫秒
71.
Mahima Chaudhary Anil Kumar Garg Ganesh Kumar Mittal Vishal Mudgal 《Biological trace element research》2010,133(2):217-226
Forty weaned male guinea pigs (Cavia porcellus) of 152.6?±?7.96 g mean body weight were divided into four equal groups and fed a common basal diet comprised of 25% ground cowpea (Vigna unguiculata) hay, 30% ground maize (Zea mays) grain, 22% ground gram (Cicer arietinum) grain, 9.5% deoiled rice (Oryza sativa) bran, 6% soybean (Glycine max) meal, 6% fish meal, 1.5% mineral mixture (without Se), and ascorbic acid at 200 mg/kg to meet their nutrient requirements along with 0, 0.1, 0.2, and 0.3 ppm of organic selenium (Se) in groups I, II, III, and IV, respectively. Experimental feeding lasted for a period of 10 weeks, during which, daily feed intake and weekly body weights were recorded. Intake and digestibility of dry matter, organic matter, ether extract, crude fiber, and nitrogen-free extract as well as uptake of calcium and phosphorus were similar (P?>?0.05) among the four groups. Feed:gain ratio was also similar (P?>?0.05) in the four groups. However, digestibility of crude protein was significantly (P?<?0.001) higher in group II supplemented with 0.1 ppm organic Se as compared to other three group. Intake and absorption of Se was significantly (P?<?0.001) higher in all the Se supplemented groups as compared to control group. Average daily gain (ADG) was significantly (P?<?0.05) higher in group II (3.16 g/day) and III (3.38 g/day) as compared to group I (2.88 g/day). However, ADG in group IV (supplemented 0.3 ppm organic Se) was significantly (P?<?0.05) lower (2.83 g/day) than group II and III, but comparable (P?>?0.05) to group I. Findings of the present experiment suggests that Se requirements of guinea pigs are ≥0.2 ppm, as supplementation of 0.1 ppm organic Se in the diet (having 0.1 ppm Se) not only enhanced their growth rate but also improved the protein utilization. 相似文献
72.
A new flow-structure interaction method is presented, which couples a sharp-interface immersed boundary method flow solver with a finite-element method based solid dynamics solver. The coupled method provides robust and high-fidelity solution for complex flow-structure interaction (FSI) problems such as those involving three-dimensional flow and viscoelastic solids. The FSI solver is used to simulate flow-induced vibrations of the vocal folds during phonation. Both two- and three-dimensional models have been examined and qualitative, as well as quantitative comparisons, have been made with established results in order to validate the solver. The solver is used to study the onset of phonation in a two-dimensional laryngeal model and the dynamics of the glottal jet in a three-dimensional model and results from these studies are also presented. 相似文献
73.
74.
75.
76.
A new family of mononuclear Zn(II) complexes [Zn(Pyimpy)2](ClO4)2 (1), [Zn(Pyimpy)(Cl)2] (2), [Zn(Pyimpy)(SCN)2] (3) and [Zn(Pyimpy)(N3)2] (4) were synthesized using designed tridentate ligand Pyimpy having NNN donors (Pyimpy: (2-((2-phenyl-2-(pyridin-2-l)hydazono)methyl)pyridine)). Complexes were characterized by different spectroscopic studies and it has been found out that all complexes exhibited strong fluorescent emission at room temperature. Molecular structures of [Zn(Pyimpy)2](ClO4)2·C6H5CH3·0.5H2O (1·C6H5CH3·0.5H2O) and [Zn(Pyimpy)(Cl)2]·CH3CN (2·CH3CN) were determined by X-ray crystallography and ligand coordinated Zn(II) ions was described as distorted octahedral and distorted square pyramidal, respectively. DNA binding properties of these complexes were investigated by absorption spectral, fluorescence quenching and circular dichroism spectral studies. 相似文献
77.
The present study examines the effects of 30 mg/kg butachlor on the cyanobacterial diversity of rice fields in Eastern Uttar Pradesh and Western Bihar in India. A total of 40 samples were grouped into three classes [(i) acidic, (ii) neutral, and (iii) alkaline soils], based on physicochemical and principle component analyses. Acidic soils mainly harbored Westillopsis, Trichormus, Anabaenopsis, and unicellular cyanobacteria; whereas Nostoc, Anabaena, Calothrix, Tolypothrix, and Aulosira were found in neutral and alkaline soils. Molecular characterization using 16S rRNA PCR and DGGE revealed the presence of 13 different phylotypes of cyanobacteria in these samples. Butachlor treatment of the soil samples led to the disappearance of 5 and the emergence of 2 additional phylotypes. A total of 40 DGGE bands showed significant reproducible changes upon treatment with butachlor. Phylogenetic analyses divided the phylotypes into five major clusters exhibiting interesting links with soil pH. Aulosira, Anabaena, Trichormus, and Anabaenopsis were sensitive to butachlor treatment, whereas uncultured cyanobacteria, a chroococcalean member, Westillopsis, Nostoc, Calothrix, Tolypothrix, Rivularia, Gloeotrichia, Fischerella, Leptolyngbya, and Cylindrospermum, appeared to be tolerant against butachlor at their native soil pH. Butachlor-induced inhibition of nitrogen fixation was found to be 65% (maximum) and 33% (minimum) in the soil samples of pH 9.23 and 5.20, respectively. In conclusion, low butachlor doses may prove beneficial in paddy fields having a neutral to alkaline soil pH. 相似文献
78.
Nidhi Verma Aparna Pandey Santwana Tiwari Sheo Mohan Prasad 《Biochemistry and Biophysics Reports》2021
Calcium (Ca2+) and nitric oxide (NO) are potentially active and multitasking signaling molecules which are known to regulate abiotic stresses in plants, but their interactive role in the acquisition of metal stress tolerance in cyanobacteria remains elusive. In current study the signaling role of Ca2+ (800 μM) and NO (10 μM SNP) on key physiological and biochemical attributes of the agriculturally and economically important cyanobacterium Nostoc muscorum ATCC 27893 subjected to Ni stress (2 μM) was examined. Results revealed that Ni at elevated level caused severe damages to the test organism but exogenous supplementation of Ca2+ and NO efficiently mitigated its toxic effects and up-regulated the growth, pigment contents, rate of photosynthesis (whole cell oxygen evolution and Chl a fluorescence indices: Kinetic traits: ΦP0, Ψ0, ΦE0 and PIABS, along with Fv/F0), nitrogen metabolism (NO3 ̄ and NO2 ̄ uptake, nitrate:NR and NiR; and ammonia:GS and GOGAT; assimilating enzymes), and boosted the enzymatic (SOD, POD, CAT and GST) along with non-enzymatic (proline, cysteine and NP-SH) antioxidants. Whereas the increased values of energy flux traits: (ABS/RC, TR0/RC, DI0/RC and ET0/RC) along with F0/Fv, rate of respiration, oxidative stress biomarkers (SOR, H2O2 and MDA), and activity of GDH enzyme exhibited lowering trends with application of Ca2+ and NO. Further, addition of EGTA (Ca2+ scavenger) and PTIO (NO scavenger) reversed the positive impacts of Ca2+ and NO and worsened the toxicity of Ni on test cyanobacterium, but the damages were more pronounced under PTIO application that demonstrated Ca2+ mediated signaling role of NO in Ni toxicity alleviation. 相似文献
79.
A mathematical model is developed and validated to predict the depth of cut in potato tuber slabs as a function of laser power and travel speed. The model considers laser processing parameters such as input power, spot size and exposure time as well as the properties of the material being cut such as specific heat, thermal conductivity, surface reflectance, etc. The model also considers the phase change of water in potato and the ignition temperature of the solid portion. The composition of the potato tuber is assumed to be of water and solid. The model also assumes that the ablation process is accomplished through ejection of liquid water, debris and water vapour, and combustion of solid. A CO2 laser operating in c.w. mode was chosen for the experimental work because water absorbs laser energy highly at 10.6 μm, and CO2 laser units with relatively high output power are available. Slabs of potato tuber were chosen to be laser processed since potato contains high moisture and large amounts of relatively homogeneous tissue. The results of the preliminary calculations and experiments concluded that the model is able to predict the depth of cut in potato tuber parenchyma when subjected to a CO2 laser beam. 相似文献
80.
Sultan M Piccini I Balzereit D Herwig R Saran NG Lehrach H Reeves RH Yaspo ML 《Genome biology》2007,8(5):R91