全文获取类型
收费全文 | 41996篇 |
免费 | 3800篇 |
国内免费 | 4006篇 |
出版年
2024年 | 69篇 |
2023年 | 390篇 |
2022年 | 843篇 |
2021年 | 1931篇 |
2020年 | 1439篇 |
2019年 | 1747篇 |
2018年 | 1729篇 |
2017年 | 1344篇 |
2016年 | 1803篇 |
2015年 | 2555篇 |
2014年 | 3009篇 |
2013年 | 3306篇 |
2012年 | 3926篇 |
2011年 | 3468篇 |
2010年 | 2320篇 |
2009年 | 2057篇 |
2008年 | 2387篇 |
2007年 | 2144篇 |
2006年 | 1808篇 |
2005年 | 1652篇 |
2004年 | 1432篇 |
2003年 | 1364篇 |
2002年 | 1268篇 |
2001年 | 896篇 |
2000年 | 726篇 |
1999年 | 671篇 |
1998年 | 444篇 |
1997年 | 424篇 |
1996年 | 373篇 |
1995年 | 327篇 |
1994年 | 323篇 |
1993年 | 200篇 |
1992年 | 278篇 |
1991年 | 206篇 |
1990年 | 178篇 |
1989年 | 158篇 |
1988年 | 107篇 |
1987年 | 123篇 |
1986年 | 89篇 |
1985年 | 80篇 |
1984年 | 57篇 |
1983年 | 42篇 |
1982年 | 47篇 |
1981年 | 25篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
51.
鲫鱼尾部神经分泌系统显微和亚显微结构的季节性变化 总被引:5,自引:0,他引:5
鲫鱼尾部神经分泌系统的神经分泌细胞和它的轴突中可观察到各种不同电子密度的颗粒。在性腺各个不同的发育阶段,该系统的分泌物具有累积、充满、释放和恢复这样一种周期性变化,由此说明鲫鱼的尾部神经分泌系统和它的生殖有关。 相似文献
52.
异大茴香脑新资源——齿叶黄皮的研究 总被引:2,自引:0,他引:2
齿叶黄皮是生长于广东省北部石灰岩山地的一种芸香科常绿小乔木,其叶富含精油,枝叶经水蒸汽蒸馏出油率为0.7%。精油经毛细管气相色谱、气相色谱/质谱联用、红外吸收光谱、核磁共振波谱等方法分析,确证含异大茴香脑(isoanethole)93.10%。异大茴香脑对霉菌有较强抑菌活性,并可通过异构化一步转变为大茴香脑。 相似文献
53.
Q. L. Zhu 《Histochemistry and cell biology》1987,86(4):385-388
Summary The detection of fibronectin (FN) in osmium-fixed and Araldite-embedded frog skin fragments was studied using a modification of Baskin's procedure (Baskin et al. 1979). Following the removal of Araldite from the semi-thin sections (0.5–1.0 m) with ethanol-NaOH solution, the sections were bleached with hydrogen peroxide. FN was detected by indirect immunoperoxidase method. For precise localization of FN, careful attention was paid to the temperature, antibody concentrations and the quality of the ethanol-NaOH solution. Our results were in agreement with those that we had obtained previously for polyethylene glycol (PEG) sections, suggesting that the present procedure is useful for the detection of FN in Araldite-embedded biological specimens. 相似文献
54.
Sequence homology in the metalloproteins; purple acid phosphatase from beef spleen and uteroferrin from porcine uterus 总被引:1,自引:0,他引:1
D F Hunt J R Yates J Shabanowitz N Z Zhu T Zirino B A Averill S T Daurat-Larroque J G Shewale R M Roberts K Brew 《Biochemical and biophysical research communications》1987,144(3):1154-1160
The primary structures of purple acid phosphatase and uteroferrin, two iron-binding glycoproteins isolated from beef spleen and porcine uterine fluids, respectively, have been examined by a combination of tandem mass spectrometry and classical Edman sequencing methods. Reported here are amino acid sequence data covering more than 90% of the primary structures for these two proteins. The sequence data reveal an unexpectedly high degree of homology, greater than 90%, for these two proteins. 相似文献
55.
56.
The molecular cloning and nucleotide sequencing of bovine kidney alkaline phosphatase is reported. The homology with the human enzyme is about 90% at both the nucleotide and amino acid levels. The only significant sequence differences occur at the respective C termini. The high degree of homology also extends into the 5' and 3' untranslated regions of the two cDNAs. 相似文献
57.
58.
Valerie Vreeland Suzanne R. Morse Robert H. Robichaux Kathleen L. Miller Sui-Sheng T. Hua Watson M. Laetsch 《Planta》1989,177(4):435-446
Carbohydrate-hybridization probes (Vreeland and Laetsch, 1989, Planta (177, 423–434) were used to localize the homogalacturonan (pectate) component of pectins in the cell walls of leaves and soybean root nodules. Leaves of two species of the dicotyledon Dubautia were compared; these species contain much pectin but differ in their tissue water relations with respect to their cell-wall properties. Maturation of the primary cell walls in nodules was studied in the Bradyrhizobium japonicum-Glycine max symbiosis. Probe labelling was based on the divalent-cation-mediated association between pectate in tissue sections and fluorescein-conjugated pectate fragments. Pectate was also labelled by mixed-dimer formation with fluorescent polyguluronate derived from alginate. The specificity of the probe for unesterified polygalacturonate was indicated by increased cell-wall labelling after chemical or enzymatic deesterification of tissue sections, in contrast to elimination of labelling by chemical esterification. Postfixation of tissue sections improved retention of soluble pectate. Pectate differences were found in the leaves among cell types, in degree of esterification, and between plant species. The cell walls of soybean nodules were strongly labelled by the pectate probe in nodules one week and three weeks after infection. Pectate was more highly esterified in the central infected zone than in the surrouding cortex. Within the infected zone, walls of uninfected cells and infected cells were similarly labelled by the pectate probe. The results indicate that the pectate molecular probe provides detailed information on pectate distribution at the cellular level for investigations of cell-wall structure, development and physiology.Abbreviations EDTA
ethylenedinitrilotetraacetic acid (ethylenediaminetetraacetic acid)
- NMR
nuclear magnetic resonance spectroscopy
- TTB
1,3,5-triazido-2,4,6-trinitrobenene 相似文献
59.
S. Honecker B. Bisping Zhu Yang H. -J. Rehm 《Applied microbiology and biotechnology》1989,31(1):17-24
Summary Immobilized cells of Aspergillus niger needed a lower initial sucrose concentration than free cells in order to obtain maximal yields of citric acid production. High sucrose concentrations led to reduced yields and increased polyol formation (glycerol, erythritol, arabitol). Continuous fermentation with media containing low sugar concentrations prevented the formation of polyols. The change from nitrogen-limited to phosphate-limited precultivation of immobilized spores significantly increased the productivity of the mycelium. The ratio of citric acid to residual sugar in the effluent distinctly lay in the direction of citric acid. Inside the alginate beads mainly large bulbous cells were observed. 相似文献
60.
P Favard N Favard Q L Zhu J Bourguet J P Lechaire 《Biology of the cell / under the auspices of the European Cell Biology Organization》1989,66(1-2):99-106
We have developed a technique for recovering apical membranous sheets from amphibian urinary bladders by gelatin stripping. The tissue is mounted on a lucite support and the apical surface is first stuck onto a gelatin-coated glass slide at 30 degrees C. This sandwich is then chilled on ice and the bladder is pulled away from the slide. Preliminary results indicate that this simple technique could be used to remove membranous apical sheets of various sizes, almost devoid of cytoplasmic contamination and without significant damage to the underlying cell structures. The method could also be adapted to prepare perforated cells and to study the cohesive forces between the different layers of the tissue. 相似文献