全文获取类型
收费全文 | 10684篇 |
免费 | 805篇 |
国内免费 | 618篇 |
专业分类
12107篇 |
出版年
2024年 | 21篇 |
2023年 | 142篇 |
2022年 | 279篇 |
2021年 | 432篇 |
2020年 | 297篇 |
2019年 | 345篇 |
2018年 | 360篇 |
2017年 | 295篇 |
2016年 | 481篇 |
2015年 | 632篇 |
2014年 | 748篇 |
2013年 | 817篇 |
2012年 | 983篇 |
2011年 | 911篇 |
2010年 | 562篇 |
2009年 | 490篇 |
2008年 | 585篇 |
2007年 | 540篇 |
2006年 | 461篇 |
2005年 | 415篇 |
2004年 | 361篇 |
2003年 | 346篇 |
2002年 | 317篇 |
2001年 | 138篇 |
2000年 | 136篇 |
1999年 | 116篇 |
1998年 | 84篇 |
1997年 | 82篇 |
1996年 | 69篇 |
1995年 | 56篇 |
1994年 | 63篇 |
1993年 | 49篇 |
1992年 | 62篇 |
1991年 | 55篇 |
1990年 | 51篇 |
1989年 | 37篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 32篇 |
1985年 | 22篇 |
1984年 | 29篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
Marsano RM Milano R Minervini C Moschetti R Caggese C Barsanti P Caizzi R 《Genetica》2003,117(2-3):281-289
The molecular organization of the heterochromatic h39 region of the Drosophila melanogaster second chromosome has been investigated by studying two BAC clones identified both by Southern blotting and by FISH experiments as containing tandem arrays of Bari1, a transposable element present only in this region. Such BAC clones appear to contain different portions of the h39 region since they differ in the DNA sequences flanking the Bari1 repeats on both sides. Thus, the 80 Bari1 copies estimated to be present in the h39 region are split into at least two separated subregions. On the basis of the analysis of the flanking sequences a possible mechanism depending on an aberrant activity of the Bari1 transposase is proposed for the genesis of the heterochromatic tandem arrays of the element. 相似文献
43.
David R. ColemanIV Kumaralal Kaluarachchi Zhiyong Ren Xiaomin Chen John S. McMurray 《International journal of peptide research and therapeutics》2008,14(1):1-9
To answer the question of whether the conformation of the Leu-Pro bond is cis or trans in Ac-pTyr-Leu-Pro-Gln-Thr-Val-NH2 when complexed with the SH2 domain of Stat3, we substituted 2,2-dimethyloxazolidines derived from serine (Ser(ΨMe,Mepro)) and threonine (Thr(ΨMe,Mepro)) for proline. The 2,2-dimethyloxazolidine and 2,2-dimethylthiazolidine pseudoproline (ΨPro) analogs induce predominantly
cis Xxx-ΨPro peptide bonds. As these ΨPro analogs are acid-labile, the phosphopeptides were synthesized using Fmoc-based SPPS
using unprotected phosphotyrosine and 4-hydroxybenzoate as the linker that allowed release from the support by alkaline ammonolysis,
conditions that kept the oxazolidine rings intact. Incorporation of Ser(ΨMe,Mepro) resulted in 69% cis Leu-ΨPro bond content in aqueous solution whereas that for Thr(ΨMe,Mepro) analog was 63%. Affinities for Stat3 were 3–5 fold lower than the lead compound and were inversely correlated with cis content. Thus we conclude that the Leu-Pro peptide bond is trans when the peptide is bound to Stat3. 相似文献
44.
45.
Ren X Zhao L Sivashanmugam A Miao Y Korando L Yang Z Reardon CA Getz GS Brouillette CG Jerome WG Wang J 《Biochemistry》2005,44(45):14907-14919
Apolipoprotein AI (apoAI), the major protein component of HDL, is one of the best predictors of coronary artery disease (CAD), with high apoAI and HDL levels being correlated with low occurrences of CAD. The primary function of apoAI is to recruit phospholipid and cholesterol for assembly of HDL particles. Like other exchangeable apolipoproteins, lipid-free apoAI forms a mixture of different oligomers even at 1.0 mg/mL. This self-association property of the exchangeable apolipoproteins is closely associated with the lipoprotein-binding activity of this protein family. It is unclear if the self-association property of apolipoprotein is required for its lipoprotein-binding activity. We developed a novel method for engineering an oligomeric protein to a monomeric, biologically active protein. Using this method, we generated a monomeric mouse apoAI mutant that is active. This mutant contains the first 216 residues of mouse apoAI and replaces six hydrophobic residues with either polar or smaller hydrophobic residues at the defined positions (V118A/A119S/L121Q/T191S/T195S/T199S). Cross-linking results show that this mutant is greater than 90% monomeric at 8 mg/mL. CD, DSC, and NMR results indicate that the mutant maintains an identical secondary, tertiary structure and stability as those of the wild-type mouse apoAI. Lipid-binding assays suggest that the mutant shares an equal lipoprotein-binding activity as that of the wild-type apoAI. In addition, both the monomeric mutant and the wild-type protein make nearly identical rHDL particles. With this monomeric mouse apoAI, high-quality NMR data has been collected, allowing for the NMR structural determination of lipid-free apoAI. On the basis of these results, we conclude that this apoAI mutant is a monomeric, active apoAI useful for structural determination. 相似文献
46.
Heather F. Armitage Andrea J. Britton René van der Wal Imogen S. K. Pearce Des B. A. Thompson Sarah J. Woodin 《Global Change Biology》2012,18(1):290-300
Ecosystems are subject to multiple, natural and anthropogenic environmental influences, including nitrogen (N) deposition, land use and climate. Assessment of the relative importance of these influences on biodiversity and ecosystem functioning is crucial for guiding policy and management decisions to mitigate global change; yet, few studies consider multiple drivers. In the UK, ongoing loss of the internationally important arctic/alpine moss‐sedge community, Racomitrium heath, has been linked to elevated N deposition, high grazing pressures and their combination; however, the relative importance of these drivers remains unclear. We used environmental gradients across the habitat's European distribution (UK, Faroes, Norway and Iceland) to investigate the relative impact of N deposition and grazing pressure, as well as climate, on the condition of the dominant moss species, Racomitrium lanuginosum. Key variables including tissue chemistry, growth and cover were measured at 36 sites, and multiple linear regressions were used to examine the relative importance of the drivers across sites. Our results clearly show that regional variation in the condition of R. lanuginosum across Europe is primarily associated with the impacts of N deposition, with climate (air temperature) and grazing pressure playing secondary roles. In contrast to previous experimental studies, we found moss growth to be stimulated by elevated N deposition; this apparent discrepancy may result from the use of artificially high N concentrations in many experiments. Despite increased growth rates, we found that moss mat depth and cover declined in response to N deposition. Our results suggest that this is due to increased decomposition of material in the moss mat, which ultimately leads to loss of moss cover and habitat degradation. This study clearly demonstrates both the key role of N deposition in degradation of Racomitrium heath and the importance of observational studies along natural gradients for testing predictions from experimental studies in the real world. 相似文献
47.
48.
该研究以宁夏贺兰山东麓酿酒葡萄种植区栽培面积最大的‘赤霞珠’为材料,在前期完成从果实形成至成熟不同发育时期的转录组测序以及关键有机酸含量测定基础上,进一步通过转录因子结合位点预测、差异表达基因分析、加权基因共表达网络关联分析(WGCNA),逐步筛选出与‘赤霞珠’果实苹果酸生物合成相关功能基因特异结合的、影响苹果酸生物合成的相应转录因子,并对其进行qRT PCR验证,以揭示这些关键功能基因及其关键转录因子在葡萄不同种植区、果实不同发育时期存在的相互调控作用机制,为以后培育优质酿酒葡萄提供新的理论依据与思路。结果表明:(1)GC/MS分析发现, ‘赤霞珠’果实在4个发育时期的延胡索酸和苹果酸含量变化趋势基本一致,两种酸含量均从果实硬果期到绿果期逐步升至最高(3.63和626.53 μg/g),之后缓慢下降,经转色期到成熟期后逐渐降至最低(2.14和244.26 μg/g),而草酰乙酸的变化趋势却相反,在硬果期含量最高(315.54 μg/g),经绿果期、转色期到成熟期逐渐降至最低值(126.11 μg/g)。(2)‘赤霞珠’果实发育时期样本转录组测序共获得可能与苹果酸生物合成途径12种功能基因结合的转录因子6 411个,其中延胡索酸水化酶(FH)的3个功能基因有86个转录因子,苹果酸脱氢酶(MDH)的10个功能基因有717个转录因子。(3)转录组测序数据及其与有机酸含量WGCNA关联结果的Veen分析确定了‘赤霞珠’果实成熟过程中与苹果酸生物合成相关度最高的3个FH基因(VIT_14s0060g01700、VIT_13s0019g03330、VIT_07s0005g00880)、2个MDH基因(VIT_10s0003g01000、VIT_13s0019g05250)及相应的18个关键转录因子。(4)qRT PCR验证及相关性分析表明, FH基因VIT_13s0019g03330与其转录因子VIT_01s0011g06200、VIT_08s0056g01230以及MDH基因VIT_13s0019g05250与其转录因子VIT_06s0004g04960、VIT_10s0003g02070的表达水平与苹果酸的积累存在显著正相关关系,推测这4个关键转录因子可能通过调控功能基因的转录,综合影响‘赤霞珠’果实苹果酸的生物合成。 相似文献
49.