全文获取类型
收费全文 | 1553篇 |
免费 | 111篇 |
出版年
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 29篇 |
2020年 | 12篇 |
2019年 | 25篇 |
2018年 | 39篇 |
2017年 | 27篇 |
2016年 | 31篇 |
2015年 | 66篇 |
2014年 | 82篇 |
2013年 | 79篇 |
2012年 | 123篇 |
2011年 | 129篇 |
2010年 | 61篇 |
2009年 | 58篇 |
2008年 | 135篇 |
2007年 | 108篇 |
2006年 | 103篇 |
2005年 | 94篇 |
2004年 | 80篇 |
2003年 | 101篇 |
2002年 | 80篇 |
2001年 | 19篇 |
2000年 | 17篇 |
1999年 | 19篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1975年 | 2篇 |
1971年 | 3篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1664条查询结果,搜索用时 15 毫秒
961.
We studied the effects of increase in the number of surface arginines on the enzyme activity and stability of Trichoderma reesei endo-1,4-beta-xylanase II. The number of arginines was increased in two mutant series. The first set contained six arginines on different sides of the protein surface. These arginines had no significant effect on the thermostability. However, the optimal pH region became narrower. Another series of five arginines was engineered into the 'Ser/Thr surface', formed of part of the double-layered beta-sheet located on one side of the 'right-hand-like' xylanase. These mutations shifted the activity profile to the alkaline region by approximately 0.5-1.0 pH units. In addition, the arginines on the Ser/Thr surface increased the enzyme activity at high temperature, although the enzyme stability in the absence of substrate decreased significantly at 50-55 degrees C. In the presence of the substrate, the thermostability increased 4-5-fold at 60-65 degrees C. Thus, the substrate neutralized the destabilizing effect of Ser/Thr surface arginines and revealed a stabilizing effect of the same mutations. The stabilizing effect of arginines at high temperatures was seen clearly only when five arginines were introduced into the Ser/Thr surface. 相似文献
962.
Tadasu Emoto Masaaki Kurasaki Shinji Oikawa Mika Suzuki-Kurasaki Masashi Okabe Futoshi Yamasaki Yutaka Kojima 《Biochemical genetics》1996,34(5-6):239-251
The sequence of six amino acid residues -Ser-Cys-Cys-Ser-Cys-Cys- is present in all mammalian metallothionein sequences and
has been highly conserved during evolution, although the metallothioneins have divergent primary sequences. To determine whether
two serines in the sequence play a crucial role in metalbinding of metallothioneins, a mutant metallothionein with these two
serines replaced by leucines was obtained using anEscherichia coli expression system. The expressed protein was analyzed for its chemical and spectroscopic properties. It was confirmed that
the mutant metallothionein (MT) bound cadmium through a metal-thiolate complex and that there was no strong difference between
the mutant and the wild-type MTs in retaining the metal-binding cluster. However, the metal-binding cluster of the mutant
metallothionein was more unstable than that of the wild-type metallothionein. The two conservative serines could play a role
in the stability of metal-binding ligands. 相似文献
963.
Keita Tamura Mika Sakamoto Yasuhiro Tanizawa Takako Mochizuki Shuji Matsushita Yoshihiro Kato Takeshi Ishikawa Keisuke Okuhara Yasukazu Nakamura Hidemasa Bono 《DNA research》2023,30(1)
Perilla frutescens (Lamiaceae) is an important herbal plant with hundreds of bioactive chemicals, among which perillaldehyde and rosmarinic acid are the two major bioactive compounds in the plant. The leaves of red perilla are used as traditional Kampo medicine or food ingredients. However, the medicinal and nutritional uses of this plant could be improved by enhancing the production of valuable metabolites through the manipulation of key enzymes or regulatory genes using genome editing technology. Here, we generated a high-quality genome assembly of red perilla domesticated in Japan. A near-complete chromosome-level assembly of P. frutescens was generated contigs with N50 of 41.5 Mb from PacBio HiFi reads. 99.2% of the assembly was anchored into 20 pseudochromosomes, among which seven pseudochromosomes consisted of one contig, while the rest consisted of less than six contigs. Gene annotation and prediction of the sequences successfully predicted 86,258 gene models, including 76,825 protein-coding genes. Further analysis showed that potential targets of genome editing for the engineering of anthocyanin pathways in P. frutescens are located on the late-stage pathways. Overall, our genome assembly could serve as a valuable reference for selecting target genes for genome editing of P. frutescens. 相似文献
964.
965.
Naama Yahalom-Mack Dafna Langgut Omri Dvir Ofir Tirosh Adi Eliyahu-Behar Yigal Erel Boaz Langford Amos Frumkin Mika Ullman Uri Davidovich 《PloS one》2015,10(12)
In the deepest section of a large complex cave in the northern Negev desert, Israel, a bi-conical lead object was found logged onto a wooden shaft. Associated material remains and radiocarbon dating of the shaft place the object within the Late Chalcolithic period, at the late 5th millennium BCE. Based on chemical and lead isotope analysis, we show that this unique object was made of almost pure metallic lead, likely smelted from lead ores originating in the Taurus range in Anatolia. Either the finished object, or the raw material, was brought to the southern Levant, adding another major component to the already-rich Late Chalcolithic metallurgical corpus known to-date. The paper also discusses possible uses of the object, suggesting that it may have been used as a spindle whorl, at least towards its deposition. 相似文献
966.
Markku Talja Martti Klinga Mika Polamo Erkki Aitola Markku Leskelä 《Inorganica chimica acta》2005,358(4):1061-1067
Three 2-phenylaminopyridine (Ap) complexes of types ApTiCl3 and Ap2TiCl2 were characterized with X-ray diffraction. The complexes were studied as polymerization catalysts using MAO as cocatalyst. In ethylene polymerization, the catalysts showed moderate activities between 65 and 285 kg PE mol−1 Ti−1 h−1 and the molecular weight distributions were between 2.5 and 4.2, and the molar masses were between 135 000 and 804 000 kg/mol. 相似文献
967.
Mika Bendiksby Sabrina Mazzoni Marte H. Jørgensen Håkon Holien 《Journal of Biogeography》2014,41(11):2020-2031
968.
969.
Dafna Ben Bashat Moran Artzi Haim Ben Ami Orna Aizenstein Deborah T. Blumenthal Felix Bokstein Benjamin W. Corn Zvi Ram Avraham A. Kanner Biatris Lifschitz-Mercer Irit Solar Tsafrir Kolatt Mika Palmon Yifat Edrei Rinat Abramovitch 《PloS one》2012,7(11)
Blood oxygenation level dependence (BOLD) imaging under either hypercapnia or hyperoxia has been used to study neuronal activation and for assessment of various brain pathologies. We evaluated the benefit of a combined protocol of BOLD imaging during both hyperoxic and hypercapnic challenges (termed hemodynamic response imaging (HRI)). Nineteen healthy controls and seven patients with primary brain tumors were included: six with glioblastoma (two newly diagnosed and four with recurrent tumors) and one with atypical-meningioma. Maps of percent signal intensity changes (ΔS) during hyperoxia (carbogen; 95%O2+5%CO2) and hypercapnia (95%air+5%CO2) challenges and vascular reactivity mismatch maps (VRM; voxels that responded to carbogen with reduced/absent response to CO2) were calculated. VRM values were measured in white matter (WM) and gray matter (GM) areas of healthy subjects and used as threshold values in patients. Significantly higher response to carbogen was detected in healthy subjects, compared to hypercapnia, with a GM/WM ratio of 3.8 during both challenges. In patients with newly diagnosed/treatment-naive tumors (n = 3), increased response to carbogen was detected with substantially increased VRM response (compared to threshold values) within and around the tumors. In patients with recurrent tumors, reduced/absent response during both challenges was demonstrated. An additional finding in 2 of 4 patients with recurrent glioblastoma was a negative response during carbogen, distant from tumor location, which may indicate steal effect. In conclusion, the HRI method enables the assessment of blood vessel functionality and reactivity. Reference values from healthy subjects are presented and preliminary results demonstrate the potential of this method to complement perfusion imaging for the detection and follow up of angiogenesis in patients with brain tumors. 相似文献
970.