全文获取类型
收费全文 | 12335篇 |
免费 | 1519篇 |
国内免费 | 2347篇 |
出版年
2024年 | 44篇 |
2023年 | 192篇 |
2022年 | 442篇 |
2021年 | 645篇 |
2020年 | 587篇 |
2019年 | 621篇 |
2018年 | 607篇 |
2017年 | 492篇 |
2016年 | 567篇 |
2015年 | 830篇 |
2014年 | 957篇 |
2013年 | 946篇 |
2012年 | 1119篇 |
2011年 | 1031篇 |
2010年 | 775篇 |
2009年 | 659篇 |
2008年 | 751篇 |
2007年 | 684篇 |
2006年 | 618篇 |
2005年 | 492篇 |
2004年 | 481篇 |
2003年 | 470篇 |
2002年 | 432篇 |
2001年 | 314篇 |
2000年 | 219篇 |
1999年 | 229篇 |
1998年 | 133篇 |
1997年 | 103篇 |
1996年 | 99篇 |
1995年 | 104篇 |
1994年 | 72篇 |
1993年 | 64篇 |
1992年 | 62篇 |
1991年 | 56篇 |
1990年 | 45篇 |
1989年 | 49篇 |
1988年 | 31篇 |
1987年 | 24篇 |
1986年 | 23篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1977年 | 6篇 |
1975年 | 4篇 |
1956年 | 3篇 |
1950年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 984 毫秒
991.
Different strategies, including palladium electrodeposition (Pd(CV)), Pd sputtering (Pd(S)) and Nafion-solubilized carbon nanotube casting (Nafion/CNT), were used to modify screen-printed carbon electrodes (SPCEs) for the fabrication of amperometric enzyme biosensors. The electrochemical properties of the bare and modified SPCEs and the optimal conditions for surface modification were determined. The electrochemical response of the bare SPCE to H(2)O(2) under the potential of 0.3 V could be improved about 100-fold by Pd modification by electrodeposition or sputtering. By contrast, the electrochemical response of the bare SPCE was enhanced by only about 11-fold by Nafion/CNT casting. Moreover, the Pd(CV)-SPCEs exhibited better reproducibility of electrochemical response (a relative standard deviation (R.S.D.)<6.0%) than freshly prepared Pd(S)-SPCEs (R.S.D.>10%). The glucose biosensor fabricated from Pd-modified electrodes could be stored for up to 108 days without loosing significant activity. The Pd(CV)-SPCE also showed very reliable signal characteristics upon 50 consecutively repeated measurements of ascorbic acid. The electrocatalytic detection of the Pd-SPCE was combined with additional advantages of resistance to surface fouling and hence good stability. In conclusion, this study demonstrated that deposition of Pd thin film on SPCEs by electrodeposition or sputtering provided superior enhancement of electrochemical properties compared to Nafion/CNT-SPCEs. Despite their high electrochemical response, Pd(S)-SPCEs required an activation process to improve stability and Pd(CV)-SPCEs suffered from poor between electrode reproducibility. 相似文献
992.
记述了采自中国台湾斑腿蝗科外斑腿蝗属Xenocatantops Dirsh,1953的2新种.台湾外斑腿蝗X.taiwanensis sp.nov.近似Xenocatantops sauteri(Ramme,1941),区别特征为前翅较长,超过后足股节中部,到达肛上板的中点;颜面隆起具纵沟,两侧近平行,中部微缩狭;前胸腹板突圆柱形,端圆形.长翅外斑腿蝗X.longipennis sp.nov.近似Xenocatantops luteitibia Zheng et Jiang,2002,区别特征为后足股节粗壮,长为最宽处的3.7倍;触角中段一节的长为宽的1.1~1.3倍;前胸背板缺小黑点.并附外斑腿蝗属中国已知种的检索表.模式标本保存于国立自然科学博物馆,台中. 相似文献
993.
红树林植物海芒果的化学成分研究 总被引:2,自引:0,他引:2
用硅胶柱层析和凝胶柱层析对红树林植物海芒果(Cerbera manghas)的乙酸乙酯提取物进行分离纯化,从中分离得到11个化合物;通过波谱学数据并与已知化合物数据作比较,它们分别鉴定为cyclocerberidol(1)、cerberidol(2)、(Z)-ligustilide(3)、coniferaldehyde(4)、ethyl(2E)-3-(4-methoxyphenyl)-2-propenoate(5)、p-hydroxyphenylethyl anisate(6)、nodakenin(7)、isoimperatorin(8)、theviridoside(9)、cycloolivil(10)及3β-acetyl-lupeol(11)。化合物3-8及11为首次从该植物中分得。 相似文献
994.
Single nucleotide polymorphisms in chicken <Emphasis Type="Italic">lmbr1</Emphasis> gene were associated with chicken growth and carcass traits
下载免费PDF全文
![点击此处可从《中国科学C辑(英文版)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Huang YanQun Du XiaoHui Deng XueMei Qiu XiangPin Wang ChunKao Chen Wen Li Ning Wu ChangXin 《中国科学C辑(英文版)》2007,50(1):62-69
Lmbr1 is the key candidate gene controlling vertebrate limb development, but its effects on animal growth and carcass traits have
never been reported. In this experiment, lmbr1 was taken as the candidate gene affecting chicken growth and carcass traits. T/C and G/A mutations located in exon 16 and
one A/C mutation located in intron 5 of chicken lmbr1 were detected from Silky, White Plymouth Rock broilers and their F2 crossing chickens by PCR-SSCP and sequencing methods. The analysis of variance (ANOVA) results suggests that T/C polymorphism
of exon 16 had significant association with eviscerated yield rate (EYR), gizzard rate (GR), shank and claw rate (SCR) and
shank girth (SG); A/C polymorphism of intron 5 was significantly associated with SCR, liver rate and head-neck weight (HNW),
while both sites had no significant association with other growth and carcass traits. These results demonstrate that lmbr1 gene could be a genetic locus or linked to a major gene significantly affecting these growth and carcass traits in chicken. 相似文献
995.
996.
997.
998.
No information to date is available on the structure of fish major histocompatibility complex (MHC) class I and beta2-microglobulin (beta2m) proteins. In the present study, grass carp (Ctenopharyngodon idellus) MHC class I (Ctid-MHC I) and beta(2)-microglobulin (Ctid-beta2m) genes were expressed as soluble maltose binding protein (MBP)-proteins and purified in a pMAL-p2X/Escherichia coli TB1 system. The expressed proteins were purified on amylase affinity columns followed by DEAE-Sepharose. The purified products were identified by Western blotting with anti-MBP polyclonal antibodies. The MBP-Ctid-MHC I and MBP-Ctid-beta2m were cleaved separately with Factor Xa, mixed together and purified on DEAE-Sepharose. The secondary structures were analyzed by circular dichroism (CD) spectrophotometry. The three-dimensional (3D) structure of their peptide-binding domain (PBD) was modeled based sequence homology. The sequence lengths of the alpha-helix, beta-sheet, turn, and random coil in the Ctid-MHC I protein were 79aa, 75aa, 20aa, and 99aa, respectively. In the 97aa of Ctid-beta2m, the contents of the alpha-helix, beta-sheet, turn, and random coil were 0aa, 41aa, 12aa, and 44aa, respectively. The Ctid-beta2m protein displayed a typical beta-sheet. Homology modeling of the Ctid-MHC I and Ctid-beta2m proteins demonstrated similarities with the structure of human MHC class I proteins. 相似文献
999.
Accurately determining a cryoEM particle's alignment parameters is crucial to high resolution single particle 3-D reconstruction. We developed Multi-Path Simulated Annealing, a Monte-Carlo type of optimization algorithm, for globally aligning the center and orientation of a particle simultaneously. A consistency criterion was developed to ensure the alignment parameters are correct and to remove some bad particles from a large pool of images of icosahedral particles. Without using any a priori model, this procedure is able to reconstruct a structure from a random initial model. Combining the procedure above with a new empirical double threshold particle selection method, we are able to pick tens of best quality particles to reconstruct a subnanometer resolution map from scratch. Using the best 62 particles of rice dwarf virus, the reconstruction reached 9.6A resolution at which four helices of the P3A subunit of RDV are resolved. Furthermore, with the 284 best particles, the reconstruction is improved to 7.9A resolution, and 21 of 22 helices and six of seven beta sheets are resolved. 相似文献
1000.
H.-C. Chang D. C. Agrawal C.-L. Kuo J.-L. Wen C.-C. Chen H.-S. Tsay 《In vitro cellular & developmental biology. Plant》2007,43(2):133-139
This study reports spore germination, early gametophyte development and change in the reproductive phase of Drynaria fortunei, a medicinal fern, in response to changes in pH and light spectra. Germination of D. fortunei spores occurred on a wide range of pH from 3.7 to 9.7. The highest germination (63.3%) occurred on ½ strength Murashige and Skoog basal medium supplemented with 2% sucrose at pH 7.7 under white light condition. Among the different light spectra tested, red, far-red, blue, and white light resulted in 71.3, 42.3, 52.7, and 71.0% spore germination, respectively. There were no morphological differences among gametophytes grown under white and blue light. Elongated or filamentous but multiseriate gametophytes developed under red light, whereas under far-red light gametophytes grew as uniseriate filaments consisting of mostly elongated cells. Different light spectra influenced development of antheridia and archegonia in the gametophytes. Gametophytes gave rise to new gametophytes and developed antheridia and archegonia after they were transferred to culture flasks. After these gametophytes were transferred to plastic tray cells with potting mix of tree fern trunk fiber mix (TFTF mix) and peatmoss the highest number of sporophytes was found. Sporophytes grown in pots developed rhizomes. 相似文献