全文获取类型
收费全文 | 10484篇 |
免费 | 563篇 |
国内免费 | 4篇 |
专业分类
11051篇 |
出版年
2022年 | 54篇 |
2021年 | 117篇 |
2020年 | 56篇 |
2019年 | 84篇 |
2018年 | 119篇 |
2017年 | 111篇 |
2016年 | 156篇 |
2015年 | 253篇 |
2014年 | 308篇 |
2013年 | 624篇 |
2012年 | 521篇 |
2011年 | 465篇 |
2010年 | 303篇 |
2009年 | 302篇 |
2008年 | 489篇 |
2007年 | 456篇 |
2006年 | 462篇 |
2005年 | 434篇 |
2004年 | 436篇 |
2003年 | 450篇 |
2002年 | 398篇 |
2001年 | 415篇 |
2000年 | 410篇 |
1999年 | 340篇 |
1998年 | 147篇 |
1997年 | 110篇 |
1996年 | 91篇 |
1995年 | 87篇 |
1994年 | 80篇 |
1993年 | 85篇 |
1992年 | 245篇 |
1991年 | 252篇 |
1990年 | 197篇 |
1989年 | 180篇 |
1988年 | 183篇 |
1987年 | 158篇 |
1986年 | 148篇 |
1985年 | 148篇 |
1984年 | 122篇 |
1983年 | 108篇 |
1982年 | 89篇 |
1981年 | 59篇 |
1980年 | 58篇 |
1979年 | 90篇 |
1978年 | 84篇 |
1977年 | 62篇 |
1976年 | 57篇 |
1975年 | 49篇 |
1973年 | 58篇 |
1970年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Escherichia coli disruptants defective in the yaeM gene, which is located at 4.2 min on the chromosome map, were constructed and characterized. The disruptants showed auxotrophy for 2-C-methylerythritol, a free alcohol of 2-C-methyl-D-erythritol 4-phosphate that is a biosynthetic precursor in the nonmevalonate pathway. This result clearly shows that the yaeM gene is indeed involved in this pathway in E. coli. 相似文献
3.
T Kaidoh S Natsuume-Sakai M Takahashi 《Journal of immunology (Baltimore, Md. : 1950)》1981,126(2):463-467
A simple, 3-step method was described for purification of murine C4 binding protein (C4-bp), a recently recognized serum protein that functions as one of the regulatory proteins of the complement system. The method consists of 1) affinity chromatography using TNBS-BGG-conjugated Sepharose beads, 2) gel filtration on a Sepharose 6B column, and 3) heparin-Sepharose chromatography. By this method, milligram quantities of C4-bp can be easily purified by more than 500-fold from EDTA-serum of various mouse strains, and the whole purification process can be completed within 1 wk. The overall yield of C4-bp is about 15%. The C4-bp thus prepared is homogeneous as judged by SDS-polyacrylamide gel electrophoresis and immunelectrophoresis. The purified mouse C4-bp showed physicochemical properties very similar to those described for human C4-bp. Like human C4-bp, mouse C4-bp is composed of several apparently identical subunits of the m.w. of 80,000. However unlike the human counterpart, the subunits of mouse C4-bp are not linked by disulfide bonds but are connected by non-covalent forces that can be disrupted by SDS. The purified mouse C4-bp retained binding affinity for C4 and showed unaltered antigenicity. Immunization of rabbits with the purified mouse C4-bp resulted in the production of potent and monospecific antisera. 相似文献
4.
5.
Akihisa Hattori 《Journal of Ethology》2006,24(1):51-57
The distribution patterns of the leathery sea anemone, Heteractis crispa, which contains an algal endosymbiont (zooxanthellae) and anemonefish, were investigated in relation to size distribution on a shallow fringing reef (3.2 ha, 0–4 m depth) in Okinawa, Japan. Individual growth and movements were also examined. Large individuals (>1,000 cm2) inhabited reef edges up to a depth of 4 m, while small anemone (<500 cm2) inhabited shallow reefs including inner reef flats. Individuals rarely moved, and their sizes were significantly correlated with their water depths. Growth of small anemones was negatively correlated with their distance from the reef edge, suggesting that reef edges provide more prey and lower levels of physiological stress. This study suggested that deep reef edges are suitable habitats for H. crispa. Large anemones were inhabited by large Amphiprion perideraion or large Amphiprion clarkii, both of which are effective defenders against anemone predators. Anemones that settle in deep reef edges may enjoy a higher survival rate and attain a large size because of their symbiotic relationship with anemonefish. However, early settlers do not harbor anemonefish. Their mortality rate would be higher in the deep edges than in shallow edges, the complicated topography of which provides refuge. 相似文献
6.
7.
8.
9.
Hisao Tsukamoto Yoshihiro Kubo David L. Farrens Mitsumasa Koyanagi Akihisa Terakita Yuji Furutani 《The Journal of biological chemistry》2015,290(45):27176-27187
Melanopsins play a key role in non-visual photoreception in mammals. Their close phylogenetic relationship to the photopigments in invertebrate visual cells suggests they have evolved to acquire molecular characteristics that are more suited for their non-visual functions. Here we set out to identify such characteristics by comparing the molecular properties of mammalian melanopsin to those of invertebrate melanopsin and visual pigment. Our data show that the Schiff base linking the chromophore retinal to the protein is more susceptive to spontaneous cleavage in mammalian melanopsins. We also find this stability is highly diversified between mammalian species, being particularly unstable for human melanopsin. Through mutagenesis analyses, we find that this diversified stability is mainly due to parallel amino acid substitutions in extracellular regions. We propose that the different stability of the retinal attachment in melanopsins may contribute to functional tuning of non-visual photoreception in mammals. 相似文献
10.
N Nakagata K Matsumoto M Anzai A Takahashi Y Takahashi Y Matsuzaki K Miyata 《Jikken dobutsu》1992,41(4):537-540
Spermatozoa of a homozygous transgenic mouse, in which the firefly luciferase gene was expressed under the control of beta-actin promoter, were frozen at -196 degrees C. One fourth of the frozen sperm was later thawed and used for in vitro fertilization. Thirty-six of 65 oocytes (55.4%) developed to the 2-cell stage. All the 2-cell embryos were transferred to the oviducts of pseudopregnant recipients and 23 young (63.9%, 23/36) were born. All of young analyzed carried the transgene and showed the luciferase gene expression. 相似文献