全文获取类型
收费全文 | 4956篇 |
免费 | 199篇 |
国内免费 | 680篇 |
出版年
2023年 | 41篇 |
2022年 | 35篇 |
2021年 | 73篇 |
2020年 | 103篇 |
2019年 | 91篇 |
2018年 | 79篇 |
2017年 | 108篇 |
2016年 | 118篇 |
2015年 | 99篇 |
2014年 | 137篇 |
2013年 | 431篇 |
2012年 | 145篇 |
2011年 | 220篇 |
2010年 | 154篇 |
2009年 | 306篇 |
2008年 | 317篇 |
2007年 | 312篇 |
2006年 | 301篇 |
2005年 | 234篇 |
2004年 | 232篇 |
2003年 | 211篇 |
2002年 | 176篇 |
2001年 | 173篇 |
2000年 | 154篇 |
1999年 | 138篇 |
1998年 | 128篇 |
1997年 | 103篇 |
1996年 | 94篇 |
1995年 | 95篇 |
1994年 | 96篇 |
1993年 | 87篇 |
1992年 | 95篇 |
1991年 | 57篇 |
1990年 | 91篇 |
1989年 | 55篇 |
1988年 | 59篇 |
1987年 | 72篇 |
1986年 | 63篇 |
1985年 | 45篇 |
1984年 | 55篇 |
1983年 | 15篇 |
1982年 | 20篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1979年 | 28篇 |
1978年 | 21篇 |
1977年 | 24篇 |
1976年 | 17篇 |
1974年 | 21篇 |
1973年 | 20篇 |
排序方式: 共有5835条查询结果,搜索用时 921 毫秒
991.
豫东平原杨\|农复合系统凋落物的数量、组成及其动态 总被引:3,自引:0,他引:3
农林复合系统的凋落物既是维持植被系统和土壤系统养分循环的关键,也是维持农林复合系统结构和功能的重要因子.通过对豫东平原农区4年生、9年生和12年生3个不同林龄杨-农复合系统杨树凋落物的数量、组成及季节动态的研究来为深入研究农林复合系统对大气中CO2的调节作用以及碳循环机理提供参考数据.结果表明,4a杨-农复合系统年凋落物总量为11 18 t·hm-2;9a杨-农间作复合系统年凋落物总量为12.86 t·hm-2;12a杨-农复合系统年凋落物总量为13.75 t·hm-2.3个不同林龄的杨-农复合系统凋落物总量月变化模式较为相似,均在8月和11月份出现峰值,而以11月份数量最大.其季节变化模式则为秋季>冬季>夏季>春季. 相似文献
992.
从山西太原水稻田土壤中,分离得到一株能以甲烷为唯一碳源和能源生长的菌株C611。通过生理生化特征及16SrDNA序列分析,该菌株初步鉴定为克雷伯氏菌(Klebsiella sp.)。采用响应面法优化了该菌株利用甲烷的培养条件,得到最佳培养条件为:温度24.4oC、接种量为6.7%、甲烷含量25%。以C611固定化细菌和溶氧响应仪为体系,采用电化学法研究了不同含量甲烷的响应时间以及溶氧变化与甲烷含量的关系。结果表明,菌株C611能利用甲烷,该反应体系对0~10%甲烷气体测定的响应时间小于100s;溶氧消耗量与通入甲烷气体含量呈线性关系,拟合系数(R2)为0.9994。以3%甲烷气体样品进行8次测量,测定平均值为3.09%,RSD为3.48%,相对误差为3%。表明该反应体系重现性良好,为该菌株进一步研究甲烷传感器奠定基础。 相似文献
993.
革兰氏阴性菌Acinetobacter sp.ADP1可以利用水杨酸作为惟一的碳源和能源生长,与这一代谢过程相关的基因为sal基因.利用sal基因启动子与细菌荧光素酶基因(lux)编码区融合而构建的工程菌Acinetobacter ADPWH_lux,通过定量测定活细胞发光度可以检测出salR基因在不同离子环境中的活性.本试验测定了不同浓度梯度的10种金属离子对处于指数期和稳定期的细菌的salR基因活性的影响.发光度检测表明重金属离子均会抑制指数期和稳定期的细菌的发光能力.RT-PCR试验也证明,凡能够抑制细菌发光能力的离子,均会抑制细菌的salA基因的转录. 相似文献
994.
Sukhumaporn Sukkhum Shinji Tokuyama Vichien Kitpreechavanich 《Biotechnology and Bioprocess Engineering》2009,14(3):302-306
The fermentation process for a poly (L-lactide) (PLA)-degrading enzyme production by a newly isolate of thermophilic PLA-degrading
Actinomadura sp. T16-1 was investigated. The strain produced 33.9 U/mL of enzyme activity after cultivation at 50°C under shaking of 150
rpm for 96 h in a medium consisting of (w/v) 0.05% PLA film, 0.2% gelatin, 0.4% (NH4)2SO4, 0.4% K2HPO4, 0.2 % KH2PO4, and 0.02% MgSO4 · 7H2O. The optimal concentration of PLA film and gelatin obtained by response surface methodology (RSM) for the highest production
of PLA-degrading enzyme was 0.035% (w/v) and 0.238% (w/v), respectively. Under these conditions, the model predicted 40.4
U/mL of PLA-degrading activity and the verification of the optimization showed 44.6 U/mL of PLA-degrading enzymatic activity
in the flasks experiment. The maximum PLA-degrading activity reached 150 U/mL within 72 h cultivation in the 3-L airlift fermenter. 相似文献
995.
Vishal V. Dawkar Umesh U. Jadhav Amar A. Telke Sanjay P. Govindwar 《Biotechnology and Bioprocess Engineering》2009,14(3):361-368
Peroxidase was purified by an ion exchange chromatography followed by gel filtration chromatography from dye degrading Bacillus sp. strain VUS. The optimum pH and temperature of the enzyme activity was 3.0 and 65°C, respectively. This enzyme showed
more activity with n-propanol than other substrates tested viz. xylidine, 3-(3,4-dihydroxy phenyl) Lalanine (L-DOPA), hydroxyquinone, ethanol, indole, and veratrole. Km value of the enzyme
was 0.076 mM towards n-propanol under standard assay conditions. Peroxidase was more active in presence of the metal ions like Li2+, Co2+, K2+, Zn2+, and Cu2+ where as it showed less activity in the presence of Ca2+ and Mn2+. Inhibitors like ethylenediamine tetraacetic acid (EDTA), glutamine, and phenylalanine inhibited the enzyme partially, while
sodium azide (NaN3) completely. The crude as well as the purified peroxidase was able to decolourize different industrial dyes. This enzyme
decolourized various textile dyes and enhanced percent decolourization in the presence of redox mediators. Aniline was the
most effective redox mediator than other mediators tested. Gas chromatography-Mass spectrometry (GC-MS) confirmed the formation
of 7-Acetylamino-4-hydroxy-naphthalene-2-sulphonic acid as the final product of Reactive Orange 16 indicating asymmetric cleavage
of the dye. 相似文献
996.
A new species of Amphidinium, A. cupulatisquama Tamura et Horiguchi, from sand samples from Ikei Island, Okinawa Prefecture in subtropical Japan, is described based on light, scanning and transmission electron microscopy and the partial sequencing of the large subunit rDNA gene. The species has a typical morphology for the genus, but is distinguished from previously described species by having a combination of the following characteristics: (i) a relatively large cell (over 30 µm in length); (ii) possessing an eyespot on the dorsal side of the cingulum; (iii) the longitudinal flagellum emerging from a point close to the cingulum; (iv) cell division taking place in the motile phase; and (v) possessing body scales. This is the third species of this genus to possess body scales. The body scales of A. cupulatisquama are uniform and cup‐shaped in side view and elliptical in face view. Their dimensions are 136.4 nm by 91.0 nm by 81.8 nm high. In side view, the scale is seen to have a thick lower half and a thin upper half. This scale type is very different from those of previously reported Amphidinium species (HG114 and HG115). The molecular tree indicated that A. cupulatisquama and the two other strains of body scale‐bearing Amphidinium are distantly related within the Amphidinium clade. 相似文献
997.
A review of East Asian frog flounders, genus Pleuronichthys (family Pleuronectidae), recognized Pleuronichthys japonicus sp. nov. and P. cornutus (Temminck and Schlegel 1846). Pleuronichthys japonicus sp. nov. is characterized by small, dark, rounded spots or marbled markings on the ocular side of the body, rounded cycloid
scales somewhat irregularly arranged, usually 12 abdominal vertebrae, 67–80 (modally 75) dorsal-fin rays, 48–59 (modally 55)
anal-fin rays, and a short branch of the supratemporal lateral line usually present on both sides. Pleuronichthys cornutus is characterized by densely distributed small, dark, irregular spots on the ocular side of the body, elongate cycloid scales
somewhat regularly arranged, usually 13 abdominal vertebrae, 72–88 (modally 77) dorsal-fin rays, 52–65 (modally 58) anal-fin
rays, and a branch of the supratemporal lateral line usually absent on both sides. Whereas P. cornutus is distributed from Miyagi Prefecture (Tohoku District) southward along the Pacific coast of Japan to the Bungo Channel,
from Akita Prefecture (Tohoku District) southward along the Sea of Japan coast through the Tsushima Strait to the East China
Sea, Yellow and Bohai Seas, the Taiwan Strait, and northern Chinese coast of the South China Sea, P. japonicus is distributed from southern Hokkaido southward along the Sea of Japan and Pacific coasts of Japan to the southern East China
Sea. Geographic variations were found in caudal vertebrae and anal-fin ray counts, and caudal-peduncle depth in P. cornutus, and in ocular side body coloration, body depth, and head length in P. japonicus. Pleuronichthys lighti Wu 1929 was regarded as a junior synonym of P. cornutus. 相似文献
998.
Aims: Isolation and characterization of an agarase-producing bacterium Agarivorans sp. HZ105.
Methods and Results: An agarase-producing bacterium strain HZ105 had been isolated from marine sediment sample. Based on phylogenetic analysis of the 16S rRNA gene sequence and phenotypic analysis, as well as biochemical analyses, this strain was named Agarivorans sp. HZ105. Effect of pH, NaCl on the growth and agarase production of strain HZ105 was studied. Strain HZ105 produced three extracellular agarases which were purified to homogeneity from bands in the PAGE gel. Two agarases of these three had a molecular mass of 54, 58 kDa, respectively. And the MS and MS/MS spectra were used to identify the agarases.
Conclusions: The MS spectra result showed that the agarases of strain HZ105 should be beta-agarase and belong to the family 50 of glycosyl hydrolases. The agarases could keep stable activity at room temperature.
Significance and Impact of the Study: The strain HZ105 was useful to produce stable agarases. The solution produced by agar's degradation in the agar plates was first reported to be used for purification of agarase. Agarases were purified to homogeneity directly from the PAGE gel without stained by Coomassie brilliant blue. 相似文献
Methods and Results: An agarase-producing bacterium strain HZ105 had been isolated from marine sediment sample. Based on phylogenetic analysis of the 16S rRNA gene sequence and phenotypic analysis, as well as biochemical analyses, this strain was named Agarivorans sp. HZ105. Effect of pH, NaCl on the growth and agarase production of strain HZ105 was studied. Strain HZ105 produced three extracellular agarases which were purified to homogeneity from bands in the PAGE gel. Two agarases of these three had a molecular mass of 54, 58 kDa, respectively. And the MS and MS/MS spectra were used to identify the agarases.
Conclusions: The MS spectra result showed that the agarases of strain HZ105 should be beta-agarase and belong to the family 50 of glycosyl hydrolases. The agarases could keep stable activity at room temperature.
Significance and Impact of the Study: The strain HZ105 was useful to produce stable agarases. The solution produced by agar's degradation in the agar plates was first reported to be used for purification of agarase. Agarases were purified to homogeneity directly from the PAGE gel without stained by Coomassie brilliant blue. 相似文献
999.
A comparison of fructosyltransferase (EC 2.4.1.9) production by Aureobasidium sp. ATCC 20524 in batch and two step batch cultures was investigated in a 1-l stirred tank reactor using a sucrose supply of 200 g/l. Results showed that the innovative cultivation in two step of Aureobasidium sp. produced more fructosyltransferase (FFase) than the single batch culture at the same sucrose concentration with a maximal enzyme production of 523 U/ml, which was 80.5% higher than the one obtained in the batch culture. The production of fructooligosaccharides (FOSs) was also analyzed; their concentration reached a maximum value of 160 g/l the first day in the two-step culture and 127 g/l in the single-batch mode. The use of the two-step batch culture with Aureobasidium sp. ATCC 20524 in allowing the microorganism to grow up prior to the induction of sucrose (second step), proved to be a powerful method for producing fructosyltransferase and FOSs. 相似文献
1000.
A salt-tolerant alkaliphilic actinomycete, Mit-1 was isolated from Mithapur, coastal region of Gujarat, India. The strain
was identified as Streptomyces clavuligerus and based on 16S rRNA gene sequence (EU146061) homology; it was related to Streptomyces sp. (AY641538.1). The organism could grow with up to 15% salt and pH 11, optimally at 5% and pH 9. It was able to tolerate
and secrete alkaline protease in the presence of a number of organic solvents including xylene, ethanol, acetone, butanol,
benzene and chloroform. Besides, it could also utilize these solvents as the sole source of carbon with significant enzyme
production. However, the organism produced spongy cell mass with all solvents and an orange brown soluble pigment was evident
with benzene and xylene. Further, the enzyme secretion increased by 50-fold in the presence of butanol. With acetone and ethanol;
the enzyme was highly active at 60–80°C and displayed optimum activity at 70°C. The protease was significantly stable and
catalyzed the reaction in the presence of xylene, acetone and butanol. However, ethanol and benzene affected the catalysis
of the enzyme adversely. Crude enzyme preparation was more stable at 37°C in solvents as compared to partially purified and
purified enzymes. The study holds significance as only few salt-tolerant alkaliphilic actinomycetes are explored and information
on their enzymatic potential is still scares. To the best of our knowledge this is the first report on organic solvent tolerant
protease from salt-tolerant alkaliphilic actinomycetes. 相似文献