全文获取类型
收费全文 | 6789篇 |
免费 | 730篇 |
国内免费 | 210篇 |
专业分类
7729篇 |
出版年
2023年 | 49篇 |
2022年 | 133篇 |
2021年 | 216篇 |
2020年 | 146篇 |
2019年 | 161篇 |
2018年 | 184篇 |
2017年 | 113篇 |
2016年 | 218篇 |
2015年 | 335篇 |
2014年 | 367篇 |
2013年 | 447篇 |
2012年 | 507篇 |
2011年 | 483篇 |
2010年 | 334篇 |
2009年 | 274篇 |
2008年 | 323篇 |
2007年 | 285篇 |
2006年 | 304篇 |
2005年 | 254篇 |
2004年 | 260篇 |
2003年 | 203篇 |
2002年 | 178篇 |
2001年 | 157篇 |
2000年 | 160篇 |
1999年 | 133篇 |
1998年 | 63篇 |
1997年 | 60篇 |
1996年 | 50篇 |
1995年 | 51篇 |
1994年 | 53篇 |
1993年 | 55篇 |
1992年 | 89篇 |
1991年 | 95篇 |
1990年 | 72篇 |
1989年 | 72篇 |
1988年 | 80篇 |
1987年 | 69篇 |
1986年 | 64篇 |
1985年 | 73篇 |
1984年 | 59篇 |
1983年 | 48篇 |
1982年 | 41篇 |
1979年 | 38篇 |
1978年 | 41篇 |
1977年 | 27篇 |
1976年 | 28篇 |
1975年 | 27篇 |
1974年 | 34篇 |
1973年 | 31篇 |
1972年 | 26篇 |
排序方式: 共有7729条查询结果,搜索用时 15 毫秒
961.
Research on orchid biology and biotechnology 总被引:1,自引:0,他引:1
Hsiao YY Pan ZJ Hsu CC Yang YP Hsu YC Chuang YC Shih HH Chen WH Tsai WC Chen HH 《Plant & cell physiology》2011,52(9):1467-1486
Orchidaceae constitute one of the largest families of angiosperms. They are one of the most ecological and evolutionary significant plants and have successfully colonized almost every habitat on earth. Because of the significance of plant biology, market needs and the current level of breeding technologies, basic research into orchid biology and the application of biotechnology in the orchid industry are continually endearing scientists to orchids in Taiwan. In this introductory review, we give an overview of the research activities in orchid biology and biotechnology, including the status of genomics, transformation technology, flowering regulation, molecular regulatory mechanisms of floral development, scent production and color presentation. This information will provide a broad scope for study of orchid biology and serve as a starting point for uncovering the mysteries of orchid evolution. 相似文献
962.
A Dzugaj D K Chu H A El-Dorry B L Horecker 《Biochemical and biophysical research communications》1976,70(2):638-646
Digestion of rabbit liver fructose 1,6-bisphosphatase with subtilisin results in a several-fold increase in catalytic activity measured at pH 9.2. This change is due to cleavage of a peptide bond located 60 amino acid residues from the NH2-terminus. The S-peptide and the residual subunit appear as separate peptides in sodium dodecyl sulfate polyacrylamide gel electrophoresis and the S-peptide can be isolated by gel filtration in 9% HCOOH. Under nondissociating conditions, however, the S-peptide remains associated with the protein, and the tetrameric structure and original molecular weight are preserved. Thus the nicking of the peptide chain by subtilisin causes a conformation change that alters the catalytic properties of the enzyme. 相似文献
963.
964.
Laura Pirastru Mohamed Darwish Fong Lam Chu Fran?ois Perreault Louka Sirois Lekha Sleno Radovan Popovic 《Journal of applied phycology》2012,24(1):117-124
Under stress conditions, some microalgae up-regulate certain biosynthetic pathways, leading to the accumulation of specific
compounds. For example, changing nutrient composition can induce stress in algae’s physiological activities, which may trigger
an intense increase in carotenoid production. In this study, the change of photosynthetic functions and carotenoid production
in the green microalga Scenedesmus sp. was investigated when algal cultures were exposed to conditions including limited nitrogen content with the addition
of sodium acetate. Microalgal cultures were treated for 18 days under higher irradiance conditions. We observed a decrease
of chlorophyll content induced concomitantly with a decline of photosystem II and I photochemistry. At the same time, an important
increase in carotenoid content was detected. By using high-performance liquid chromatographic analysis, we found that the
secondary carotenoids astaxanthin and canthaxanthin were accumulated compared to controls. During the process of carotenoid
accumulation, chlorophyll degradation was found in addition to a strong decrease in photosynthetic electron transport. Such
changes may be associated with the structural reorganization of the photosynthetic apparatus and can be a useful indicator
of secondary carotenoid accumulation in algal cultures. 相似文献
965.
Jen Chun Kuan Chang Chieh Wu Chien An Sun Chi Ming Chu Fu Gong Lin Chih Hsiung Hsu Po-Chieh Kan Shih-Chieh Lin Tsan Yang Yu-Ching Chou 《PloS one》2015,10(3)
Accumulating evidence has suggested the requirement for further stratification of patients in the same tumor stage according to molecular factors. We evaluate the combination of cancer stage and DNA methylation status as an indicator of the risk of recurrence and mortality among patients with colorectal cancer (CRC). A cohort study of 215 patients with CRC (mean age 64.32 years; 50.5% of men) from Tri-Service General Hospital in Taiwan examined the association between cancer stage and risk of CRC recurrence and mortality. A Cox proportional hazard model was used to analyze patient methylation status and clinical information at study entry, and their associations with CRC recurrence and mortality during follow-up. The advanced stage patients with p16, hMLH1, and MGMT methylation were associated with higher risk of CRC recurrence compared with the local stage patients with unmethylation status in tumor tissues, with adjusted hazard ratios (HRs) (95% confidence interval [CI]) of 9.64 (2.92–31.81), 8.29 (3.40–20.22), and 11.83 (3.49–40.12), respectively. When analyzing normal tissues, we observed similar risk of CRC recurrence with adjusted HRs (95% CI) of 10.85 (4.06–28.96), 9.04 (3.79–21.54), and 12.61 (4.90–32.44), respectively. For combined analyses, the risk of recurrence in the patients in advanced stage with DNA methylation in both normal and tumor tissues, compared with local stage with unmethylation, was increased with adjusted HR (95% CI) of 9.37 (3.36–26.09). In the advanced stage patients, methylation status and tissue subtype were associated with increased risk of 5-year cumulative CRC recurrence (p < 0.001). This study demonstrates that clustering DNA methylation status according to cancer stage and tissue subtype is critical for the assessment of risk of recurrence in CRC patients and also indicated an underlying mechanism. 相似文献
966.
967.
Yellow-green foliage cultivars of four vegetables grown outdoors, i.e., Chinese mustard (Brassica rapa), Chinese kale (Brassica oleracea var. alboglabra), sweet potato (Ipomoea batatas) and Chinese amaranth (Amaranthus tricolor), had lower chlorophyll (Chl) (a+b) (29–36% of green cultivars of the same species), total carotenoids (46–62%) and ascorbate (72–90%) contents per leaf area.
Furthermore, yellow-green cultivars had smaller photosystem II (PSII) antenna size (65–70%) and lower photosynthetic capacity
(52–63%), but higher Chl a/b (107–156%) and from low (60%) to high (129%) ratios of de-epoxidized xanthophyll cycle pigments per Chl a content. Potential quantum efficiency of PSII (Fv/Fm) of all overnight dark-adapted leaves was ca. 0.8, with no significant difference between yellow-green and green cultivars of the same species. However, yellow-green
cultivars displayed a higher degree of photoinhibition (lower Fv/Fm after illumination) when they were exposed to high irradiance.
Although vegetables used in this study are of either temperate or tropical origin and include both C3 and C4 plants, data from all cultivars combined revealed that Fv/Fm after illumination still showed a significant positive linear regression with xanthophyll cycledependent energy quenching
(qE) and a negative linear regression with photoinhibitory quenching (qI). Fv/Fm was, however, not correlated with nonphotochemical quenching (NPQ). Yet, a higher degree of photoinhibition in yellow-green
cultivars could recover during the night darkness period, suggesting that the repair of PSII in yellow-green cultivars would
allow them to grow normally in the field. 相似文献
968.
Genetic Modulation of the Overexpression of Tailoring Genes eryK and eryG Leading to the Improvement of Erythromycin A Purity and Production in Saccharopolyspora erythraea Fermentation 下载免费PDF全文
Yun Chen Wei Deng Jiequn Wu Jiangchao Qian Ju Chu Yingping Zhuang Siliang Zhang Wen Liu 《Applied microbiology》2008,74(6):1820-1828
969.
The mtDNA of Cycas taitungensis is a circular molecule of 414,903 bp, making it 2- to 6-fold larger than the known mtDNAs of charophytes and bryophytes, but similar to the average of 7 elucidated angiosperm mtDNAs. It is characterized by abundant RNA editing sites (1,084), more than twice the number found in the angiosperm mtDNAs. The A + T content of Cycas mtDNA is 53.1%, the lowest among known land plants. About 5% of the Cycas mtDNA is composed of a novel family of mobile elements, which we designated as "Bpu sequences." They share a consensus sequence of 36 bp with 2 terminal direct repeats (AAGG) and a recognition site for the Bpu 10I restriction endonuclease (CCTGAAGC). Comparison of the Cycas mtDNA with other plant mtDNAs revealed many new insights into the biology and evolution of land plant mtDNAs. For example, the noncoding sequences in mtDNAs have drastically expanded as land plants have evolved, with abrupt increases appearing in the bryophytes, and then in the seed plants. As a result, the genomic organizations of seed plant mtDNAs are much less compact than in other plants. Also, the Cycas mtDNA appears to have been exempted from the frequent gene loss observed in angiosperm mtDNAs. Similar to the angiosperms, the 3 Cycas genes nad1, nad2, and nad5 are disrupted by 5 group II intron squences, which have brought the genes into trans-splicing arrangements. The evolutionary origin and invasion/duplication mechanism of the Bpu sequences in Cycas mtDNA are hypothesized and discussed. 相似文献
970.
Jun Chu Zhihong Zhang Ying Zheng Jie Yang Lingsong Qin Jinling Lu Zhen-Li Huang Shaoqun Zeng Qingming Luo 《Biosensors & bioelectronics》2009,25(1):234-239
Fluorescent protein (FP) has enabled the analysis of biomolecular interactions in living cells, and bimolecular fluorescence complementation (BiFC) represents one of the newly developed imaging technologies to directly visualize protein–protein interactions in living cells. Although 10 different FPs that cover a broad range of spectra have been demonstrated to support BiFC, only Cerulean (cyan FP variant), Citrine and Venus (yellow FP variants)-based BiFC systems can be used under 37 °C physiological temperature. The sensitivity of two mRFP-based red BiFC systems to higher temperatures (i.e., 37 °C) limits their applications in most mammalian cell-based studies. Here we report that mLumin, a newly isolated far-red fluorescent protein variant of mKate with an emission maximum of 621 nm, enables BiFC analysis of protein–protein interactions at 37 °C in living mammalian cells. Furthermore, the combination of mLumin with Cerulean- and Venus-based BiFC systems allows for simultaneous visualization of three pairs of protein–protein interactions in the same cell. The mLumin-based BiFC system will facilitate simultaneous visualization of multiple protein–protein interactions in living cells and offer the potential to visualize protein–protein interactions in living animals. 相似文献