全文获取类型
收费全文 | 2608篇 |
免费 | 152篇 |
专业分类
2760篇 |
出版年
2023年 | 11篇 |
2022年 | 38篇 |
2021年 | 59篇 |
2020年 | 33篇 |
2019年 | 43篇 |
2018年 | 73篇 |
2017年 | 49篇 |
2016年 | 84篇 |
2015年 | 132篇 |
2014年 | 134篇 |
2013年 | 180篇 |
2012年 | 198篇 |
2011年 | 210篇 |
2010年 | 117篇 |
2009年 | 113篇 |
2008年 | 178篇 |
2007年 | 176篇 |
2006年 | 142篇 |
2005年 | 131篇 |
2004年 | 145篇 |
2003年 | 110篇 |
2002年 | 120篇 |
2001年 | 16篇 |
2000年 | 15篇 |
1999年 | 20篇 |
1998年 | 26篇 |
1997年 | 21篇 |
1996年 | 22篇 |
1995年 | 16篇 |
1994年 | 17篇 |
1993年 | 19篇 |
1992年 | 14篇 |
1991年 | 22篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1964年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有2760条查询结果,搜索用时 15 毫秒
111.
Jianlin Han Marion Jean Christian Roussel Hiroki Moriwaki Vadim A. Soloshonok 《Chirality》2019,31(4):328-335
Herein, we disclose the design of a model Ni(II) complex of glycine Schiff base possessing single‐nitrogen stereogenic center, which was successfully used for high‐performance liquid chromatography (HPLC)‐assisted assessment of its configurational stability. The major finding is that the configurational stability of the Ni(II)‐coordinated nitrogen is profoundly dependent on the reaction conditions used, in particular the solvent, and can range from inconsequential (t½ less than 5 min) to virtually completely stable (t½ 90 y). The discovery reported in this study most likely to be of certain theoretical and synthetic value. 相似文献
112.
113.
114.
In this paper we investigate population dynamics, genealogy and complexity-increase of locally interacting populations of cellular automata-based evolving self-replicating loops (evoloops). We outline experiments indicating that the evolutionary growth in complexity, known to be achievable in principle given the complete genetic accessibility granted by universal construction, may be achievable in practice using much simpler replicating structures. By introducing evoloop populations to hostile environments, we demonstrate that selection pressures toward smaller species can be mediated to enable evolutionary accessibility to larger species, which themselves roam a much more vast portion of genetic state-space. We show that this growth in size results from intrinsically biased genealogy inherent in the rules of the evoloop CA, normally suppressed by selection pressures from direct competition favouring the smallest species. This shows that, in populations of simple self-replicating structures, a limited form of complexity-increase may result from a process which is driven by biased genealogical connectivity--a purely emergent property arising out of bottom-up evolutionary dynamics--and not just by adaptation . Implications of this result are discussed and contrasted with other self-replication studies in Artificial Life and Biology. 相似文献
115.
Nagahata H Higuchi H Teraoka H Takahashi K Takahashi K Kuwabara M Inanami O Kuwabara M 《Immunology and cell biology》2004,82(1):32-37
Stimulant-induced viability of neutrophils, nuclear-fragmentation, increase in intracellular calcium ([Ca2+]i), expression of annexin V on neutrophils and proteolysis of a fluorogenic peptide substrate Ac-DEVD-MCA (acetyl Asp-Glu-Val-Asp alpha-[4-methyl-coumaryl-7-amide]) by neutrophil lysates from five normal calves and three calves with leucocyte adhesion deficiency were determined to evaluate the apoptosis of normal and CD18-deficient neutrophils. Viability was markedly decreased in control neutrophils stimulated with opsonized zymosan (OPZ), compared to CD18-deficient neutrophils at 37 degrees C after incubation periods of 6 and 24 hours. The rate of apoptosis of control neutrophils stimulated with OPZ increased significantly depending on the incubation time, whereas no apparent increase in apoptosis was found in CD18-deficient neutrophils under the same conditions. Aggregated bovine (Agg) IgG-induced apoptosis of control neutrophils was not significantly different from that of CD18-deficient neutrophils. The expression of annexin V on OPZ-stimulated control neutrophils was greater than that of unstimulated ones 6 h after stimulation. No apparent increase in annexin V expression on CD18-deficient neutrophils was found with OPZ stimulation. A delay in apoptosis was demonstrated in CD18-deficient bovine neutrophils and this appeared to be closely associated with lowered signalling via [Ca2+]i, diminished annexin V expression on the cell surface, and decreased caspase 3 activity in lysates. 相似文献
116.
Tsuruta H Tamura J Yamagata H Aizono Y 《Bioscience, biotechnology, and biochemistry》2004,68(2):440-443
Protein-tyrosine phosphatase [EC 3.1.3.48] from a psychrophile, Shewanella sp. shows high activity at low temperatures and has the conserved amino acid sequence of protein-Ser/Thr-phosphatases. Site-directed mutagenesis with the conserved amino acid residues indicated that His148 could be important as a general acid catalyst and Asp115 assists the protonation with His148 of the leaving group of a substrate, and that Asp76 and Asp112 were involved in binding to magnesium ions. 相似文献
117.
Elmasri H Winkler C Liedtke D Sasado T Morinaga C Suwa H Niwa K Henrich T Hirose Y Yasuoka A Yoda H Watanabe T Deguchi T Iwanami N Kunimatsu S Osakada M Loosli F Quiring R Carl M Grabher C Winkler S Del Bene F Wittbrodt J Abe K Takahama Y Takahashi K Katada T Nishina H Kondoh H Furutani-Seiki M 《Mechanisms of development》2004,121(7-8):659-671
The metameric structure of the vertebrate trunk is generated by repeated formation of somites from the unsegmented presomitic mesoderm (PSM). We report the initial characterization of nine different mutants affecting segmentation that were isolated in a large-scale mutagenesis screen in Medaka (Oryzias latipes). Four mutants were identified that show a complete or partial absence of somites or somite boundaries. In addition, five mutations were found that cause fused somites or somites with irregular sizes and shapes. In situ hybridization analysis using specific markers involved in the segmentation clock and antero-posterior (A-P) polarity of somites revealed that the nine mutants can be compiled into two groups. In group 1, mutants exhibit defects in tailbud formation and PSM prepatterning, whereas A-P identity in the somites is defective in group 2 mutants. Three mutants (planlos, pll; schnelles ende, sne; samidare, sam) have characteristic phenotypes that are similar to those in zebrafish mutants affected in the Delta/Notch signaling pathway. The majority of mutants, however, exhibit somitic phenotypes distinct from those found in zebrafish, such as individually fused somites and irregular somite sizes. Thus, these Medaka mutants can be expected to provide clues to uncovering novel components essential for somitogenesis. 相似文献
118.
Endothelin-1 (ET-1), a 21-amino acid peptide secreted by the epithelium and core mesenchyme in the branchial arches as well as vascular endothelium, is involved in craniofacial and cardiovascular development through endothelin receptor type-A (EdnrA) expressed in the neural crest-derived ectomesenchyme. Here we show that ET-1(-/-) mutant mice exhibit a homeotic-like transformation of the lower jaw to an upper jaw. Most of the maxillary arch-derived components are duplicated and replaced mandibular arch-derived structures, resulting in a mirror image of the upper and lower jaws in the ET-1(-/-) mutant. As for hyoid arch-derivatives, the ventral structures are severely affected in comparison to the dorsal ones in the ET-1(-/-) mutant. Correspondingly, the expression of Dlx5 and Dlx6, Distalless-related homeobox genes determining the ventral identity of the anterior branchial arches, and of the mandibular marker gene Pitx1 is significantly downregulated in the ET-1(-/-) mutant, whereas the expression of Dlx2 and the maxillary marker gene Prx2 is unaffected or rather upregulated. These findings indicate that the ET-1/EdnrA signaling may contribute to the dorsoventral axis patterning of the branchial arch system as a mediator of the regional intercellular interactions. 相似文献
119.
Nagamune H Ohkura K Sukeno A Cowan G Mitchell TJ Ito W Ohnishi O Hattori K Yamato M Hirota K Miyake Y Maeda T Kourai H 《Microbiology and immunology》2004,48(9):677-692
Intermedilysin is a pore-forming cytolysin belonging to the streptolysin O gene family known as the 'Cholesterol-binding/dependent cytolysins' and is unique within the family in that it is highly humanspecific. This specificity suggests interaction with a component of human cells other than cholesterol, the proposed receptor for the other toxins of the gene family. Indeed, intermedilysin showed no significant degree of affinity to free or liposome-embedded cholesterol. Characterization of intermedilysin undecapeptide mutants revealed that this lack of affinity to cholesterol was a result of the substitutions of intermedilysin in this region. Absorption assays with erythrocyte membranes from various animals, competitive inhibition with domain 4 of intermedilysin and liposome-binding assays of streptolysin O and intermedilysin indicated that cell membrane binding is the human-specific step of intermedilysin action, that the host cell membrane-binding site is located within domain 4 in common with other members of the family and that the receptor for this toxin is not cholesterol. The species specificity of undecapeptide mutants of intermedilysin and streptolysin O and chimeric mutants between intermedilysin and streptolysin O, and intermedilysin and pneumolysin indicated that domain 4 of intermedilysin determines the human-specific action step and the cell-binding site of domain 4 lies within the 56 amino acids of the C-terminal, excluding the undecapeptide region. 相似文献
120.