全文获取类型
收费全文 | 3626篇 |
免费 | 375篇 |
国内免费 | 554篇 |
专业分类
4555篇 |
出版年
2024年 | 16篇 |
2023年 | 68篇 |
2022年 | 110篇 |
2021年 | 149篇 |
2020年 | 142篇 |
2019年 | 162篇 |
2018年 | 167篇 |
2017年 | 158篇 |
2016年 | 150篇 |
2015年 | 164篇 |
2014年 | 171篇 |
2013年 | 277篇 |
2012年 | 147篇 |
2011年 | 192篇 |
2010年 | 165篇 |
2009年 | 218篇 |
2008年 | 217篇 |
2007年 | 237篇 |
2006年 | 189篇 |
2005年 | 177篇 |
2004年 | 133篇 |
2003年 | 123篇 |
2002年 | 100篇 |
2001年 | 89篇 |
2000年 | 89篇 |
1999年 | 75篇 |
1998年 | 74篇 |
1997年 | 61篇 |
1996年 | 57篇 |
1995年 | 45篇 |
1994年 | 31篇 |
1993年 | 40篇 |
1992年 | 35篇 |
1991年 | 38篇 |
1990年 | 36篇 |
1989年 | 25篇 |
1988年 | 33篇 |
1987年 | 29篇 |
1986年 | 21篇 |
1985年 | 22篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 21篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
排序方式: 共有4555条查询结果,搜索用时 0 毫秒
41.
甘薯品种F3282的浸取液,经硫酸铵分级,甲壳素层析后,再经分子筛过滤,获得在PAGE上呈现单一蛋白质带的甘薯凝集素(Ipomoea Batatas Lectin,IBL)。IBL对鸽、兔、人血等红细胞均有凝集作用,其中对鸽血的凝集活性最高,最低凝集浓度为0.05μg/ml。IBL除凝集红细胞外,还可凝集小鼠脾细胞和肿瘤细胞;其对热相当稳定,90℃加热10min,仍有部分活性;IBL对酸处理较碱处理稳定,但可被阿拉伯糖或乳糖等解除凝集活性。IBL的中性糖含量为5.4%。 相似文献
42.
Malawski GA Hillig RC Monteclaro F Eberspaecher U Schmitz AA Crusius K Huber M Egner U Donner P Müller-Tiemann B 《Protein science : a publication of the Protein Society》2006,15(12):2718-2728
This study describes an efficient multiparallel automated workflow of cloning, expression, purification, and crystallization of a large set of construct variants for isolated protein domains aimed at structure determination by X-ray crystallography. This methodology is applied to MAPKAP kinase 2, a key enzyme in the inflammation pathway and thus an attractive drug target. The study reveals a distinct subset of truncation variants with improved crystallization properties. These constructs distinguish themselves by increased solubility and stability during a parallel automated multistep purification process including removal of the recombinant tag. High-throughput protein melting point analysis characterizes this subset of constructs as particularly thermostable. Both parallel purification screening and melting point determination clearly identify residue 364 as the optimal C terminus for the kinase domain. Moreover, all three constructs that ultimately crystallized feature this C terminus. At the N terminus, only three amino acids differentiate a noncrystallizing from a crystallizing construct. This study addresses the very common issues associated with difficult to crystallize proteins, those of solubility and stability, and the crucial importance of particular residues in the formation of crystal contacts. A methodology is suggested that includes biophysical measurements to efficiently identify and produce construct variants of isolated protein domains which exhibit higher crystallization propensity. 相似文献
43.
Structural and functional characterization of myotoxin, Cr-IV 1, a phospholipase A2 D49 from the venom of the snake Calloselasma rhodostoma 总被引:1,自引:0,他引:1
V.L. Bonfim L.A. Ponce-Soto D. Martins de Souza G.H.M.F. Souza P.A. Baldasso M.N. Eberlin S. Marangoni 《Biologicals》2008,36(3):168-176
A new D49 PLA(2) was purified from the venom of Calloselasma rhodostoma after two chromatographic steps. Molecular exclusion chromatography was done through a Protein-Pack 300 SW column (0.78 cm x 30 cm), eluting with 0.25 M ammonium bicarbonate, pH 7.9, at a flow rate of 0.3 ml/min. Reverse-phase HPLC was then performed on mu-Bondapack C-18. The sample was determined to have a molecular mass of 13,870.94 Da MALDI-TOF by mass spectrometry, and the amino acid composition showed that Cr-IV 1 presented a high content of Lys, Tyr, Gly, Pro, and 14 half-Cys residues, typical of a basic PLA(2). Cr-IV 1 presented a sequence of 122 amino acid residues: DLWEFGQMILKETGSLPFPY YTTYGCYCGV GGRGGKPKDA TDRCCFVHDC CYGKLTGCPK TNDRYSYSRL DYTIVCGEGG PCKQICECDK AAAVCFRENL RTYNKKYRYHLKPFCKEPAE TC and a calculated pI value of 8.0. Cr-IV 1 had PLA(2) activity in the presence of a synthetic chromogenic substrate (4-nitro-3-(octanoyloxy)benzoic acid) and showed a rapid cytolytic effect on mouse skeletal muscle myoblasts and myotubes in culture. In mice, Cr-IV 1 induced myonecrosis and edema upon intramuscular and intravenous injections, respectively. The LD(50) of Cr-IV 1 was determined to be 0.07 mg/k body weight by intracerebroventricular (i.c.v.) injection. The combination of structural and functional information obtained herein classifies Cr-IV 1 as a new member of the D49 PLA(2) family, as it presents the typical behavior of a phospholipase A(2) from this family. 相似文献
44.
45.
Engineering enzymes with improved catalytic properties in non-natural environments have been concerned with their diverse industrial and biotechnological applications. Immobilization represents a promising but straightforward route, and immobilized biocatalysts often display higher activities and stabilities compared to free enzymes. Owing to their unique physicochemical characteristics, including the high-specific surface area, exceptional chemical, electrical, and mechanical properties, efficient enzyme loading, and multivalent functionalization, nano-based materials are postulated as suitable carriers for biomolecules or enzyme immobilization. Enzymes immobilized on nanomaterial-based supports are more robust, stable, and recoverable than their pristine counterparts, and are even used for continuous catalytic processes. Furthermore, the unique intrinsic properties of nanomaterials, particularly nanoparticles, also confer the immobilized enzymes to be used for their broader applications. Herein, an effort has been made to present novel potentialities of multi-point enzyme immobilization in the current biotechnological sector. Various nano-based platforms for enzyme/biomolecule immobilization are discussed in the second part of the review. In summary, recent developments in the use of nanomaterials as new carriers to construct robust nano-biocatalytic systems are reviewed, and future trends are pointed out in this article. 相似文献
46.
sp10基因在精卵识别过程中起着重要作用 .从家兔睾丸cDNA文库中克隆了家兔的sp10基因 (rsp10 ) ,cDNA序列全长 12 82bp ,包含 10 0 5bp开放阅读框 .由开放阅读框推测出的氨基酸序列与人、狒狒、狐和小鼠的SP10氨基酸序列之间存在较高水平的同源性 ,同源性分别为 70 %、69%、68%和 61% .在大肠杆菌中表达rsp10基因 ,获得重组rSP10 .用重组rSP10免疫雌性母兔 ,得到rSP10专一性多抗 .对精子膜蛋白进行免疫印迹分析发现 ,rsp10基因在家兔睾丸中的表达呈现多态性 .rsp10基因在GenBank的登录号为 :AF2 51558. 相似文献
47.
Partial migration in inexperienced pied avocets Recurvirostra avosetta: distribution pattern and correlates 下载免费PDF全文
Rémi Chambon Sébastien Dugravot Jean‐Marc Paillisson Jean‐Christophe Lemesle Frédéric Ysnel Guillaume Gélinaud 《Journal of avian biology》2018,49(6)
Birds exhibit a range of wintering behaviour from strictly migrant to strictly resident species. In partially migrating ones, some birds overwinter within their breeding region (resident birds) while others, although breeding in the same area, winter far away (migrant birds). Accordingly, choosing a wintering region is a key stage in the annual life cycle of birds, notably for inexperienced first‐year individuals. The present study aimed to investigate this issue, and more specifically to study the distribution pattern during winter and factors influencing the wintering behaviour of first‐year pied avocets Recurvirostra avosetta. Based on a 10‐yr ringing study carried out on five of the major French breeding colonies distributed along the Atlantic coast, we showed the coexistence of different wintering tactics. The resident tactic was predominant (approximately 86% of the 575 birds re‐sighted), while the other birds adopted migration. Among resident individuals, two different tactics occurred: 43% of birds overwintered within their natal colony, whereas the others wintered in another site located at relatively close proximity along the French Atlantic coast. Hatching date was a consistent predictor of all wintering tactics. More specifically, the probability of migrating was the highest for early‐hatched birds, and for resident ones, the probability of wintering within their natal colony rather than in another French site was the highest for both median‐ and late‐hatched individuals. In addition, a colony effect was demonstrated for resident birds. Several biological interpretations, including social system, variations in both individual body condition and habitat quality, were put forward to explain these correlates. 相似文献
48.
一种基于单分子纳米操纵的有序化测序策略 总被引:1,自引:0,他引:1
尽管包括人类在内的许多生物物种的基因组测序工作已经完成,但由于现有测序技术的限制,大部分复杂基因组还存在很多大大小小的缺口.缺口的填补以及对其他重复序列区域的测序迫切需要全新的思路和技术.基于在DNA单分子定位切割和拾取方面的实验进展,提出了一种基于原子力显微镜纳米操纵技术的单分子有序化测序策略.计算机模拟的结果表明,这一方法和策略是可行的,有助于解决目前测序工作中所遇到的一些棘手问题. 相似文献
49.
50.