全文获取类型
收费全文 | 6967篇 |
免费 | 527篇 |
国内免费 | 335篇 |
出版年
2024年 | 9篇 |
2023年 | 72篇 |
2022年 | 164篇 |
2021年 | 303篇 |
2020年 | 218篇 |
2019年 | 295篇 |
2018年 | 272篇 |
2017年 | 236篇 |
2016年 | 341篇 |
2015年 | 398篇 |
2014年 | 457篇 |
2013年 | 518篇 |
2012年 | 637篇 |
2011年 | 544篇 |
2010年 | 347篇 |
2009年 | 271篇 |
2008年 | 358篇 |
2007年 | 292篇 |
2006年 | 270篇 |
2005年 | 230篇 |
2004年 | 225篇 |
2003年 | 185篇 |
2002年 | 191篇 |
2001年 | 120篇 |
2000年 | 86篇 |
1999年 | 109篇 |
1998年 | 62篇 |
1997年 | 77篇 |
1996年 | 52篇 |
1995年 | 47篇 |
1994年 | 46篇 |
1993年 | 35篇 |
1992年 | 52篇 |
1991年 | 40篇 |
1990年 | 24篇 |
1989年 | 28篇 |
1988年 | 20篇 |
1987年 | 27篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 23篇 |
1982年 | 7篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有7829条查询结果,搜索用时 359 毫秒
61.
Maninder K. Sohi Tommy Wan Brian J. Sutton Tony Atkinson Max A. Atkinson Jonathan P. Murphy Stephen P. Bottomley Michael G. Gore 《Proteins》1995,23(4):610-612
Protein L is a multi domain cell wall constituent of certain strains of Peptostreptococcus magnus which binds to the variable domain of immunoglobulin κ-light chains. A single immunoglobulin-binding domain of Mr = 9000 from this protein has been isolated and crystallized. The crystals are of space group P42212, with cell dimensions a = b = 66.9 Å, c = 68.3 Å, and diffract to at least 2.2 Å resolution. The asymmetric unit of the crystal contains two molecules of the protein L domain, related by a noncrystallographic 2-fold axis, as revealed by a self-rotation function calculated with native diffraction data. © 1995 Wiley-Liss, Inc. 相似文献
62.
低高径比喷射环流生化反应器流体力学和发酵性能的研究 总被引:5,自引:0,他引:5
对高径比s≤2.5喷射环流生化反应器的流体力学和传质特性进行了系统的研究,选出反应器的最佳结构,关联出氧的体积传递系数(kLa)表达式。在此基础上,进行了谷氨酸发酵试验,摸索出用该设备进行各氨酸发酵的最佳工艺条件,使5批一次性投糖发酵的糖酸转化率达到50%以上。 相似文献
63.
高苯丙氨酸血症大鼠脑内单胺类递质的研究 总被引:3,自引:0,他引:3
以3d龄Sprague-Dawley大鼠腹腔注射苯丙氨酸(Phe)诱导高苯丙氨酸血症,荧光法测定大脑皮层及其突触体中去甲肾上腺素(NE)、多巴胺(DA)和5-羟色胺(5-HT)含量;Y型电迷宫法测其学习记忆能力.结果显示:高苯丙氨酸血症大鼠大脑皮层NE、DA及5-HT含量降低38.6%~67.4%,突触体中NE、DA和5-HT含量降低51.9%~70.2%,学习记忆能力明显低于对照组.结果提示,苯酮尿症智力障碍可能与大脑皮层及其突触体中某些单胺类递质含量降低相关. 相似文献
64.
从青岛采集的多管藻(Polysiphoniaurceolata)中分离得到的R-藻蓝蛋白,在pH=7.0的0.05mol/L磷酸盐-硫酸铵缓冲液中,使用悬滴气相扩散法获得适合X光衍射分析用单晶。经Buerger徘循照相和XRD—100面探测仪分析,R-藻蓝蛋白晶体属于四方晶系,空间群为P41(3)212,晶胞参数:a=b=137.5c=218.5α=β=γ=90°。用等比重梯度柱法测定了晶体和母液的比重分别为1.19和1.09。根据分子量与晶胞体积估算,一个不对称单位含有一个分子,推测它的分子聚集态形式为(αβ)3。 相似文献
65.
催产素在脊髓水平对电针镇痛的影响 总被引:3,自引:0,他引:3
采用玻璃微电极胞外记录和脊髓表面给药的方法观察了催产素(OT)、抗催产素血清(AOTS)以及电针穴位对背角神经元伤害性诱发放电的影响。结果表明:电针穴位或脊髓表面施加OT可部分抑制脊髓背角神经元的伤害性诱发放电;在电针的基础上施加OT则明显加强电针的抑制效应;相反,用AOTS预处理后,电针的抑制作用放取消。提示OT在脊髓水平参与了对痛觉信息的调制,并与一定频率的针刺镇痛有关。 相似文献
66.
Chicken egg yolk was found to contain a unique glycosphingolipid pattern not seen in other types of tissue or cell. These glycosphingolipids were isolated in pure form and their structures established by sequential enzymic hydrolysis and permethylation analysis. The major gangliosides in chicken egg yolk are N-acetylneuraminosylgalactosylceramide, N-acetylneuraminosyl-lactosylceramide and di-N-acetylneuraminosyl-lactosylceramide. The only neutral glycosphingolipid found in chicken egg yolk is galactosylceramide. 相似文献
67.
Summary An ultrastructural analysis is presented of the cuticular and neural structures formed by the prothoracic leg and wing imaginal discs of maleDrosophila melanogaster larvae during culture in vitro with 0.2 g/ml of -ecdysone. A pupal cuticle, and subsequently an imaginal cuticle with a well-defined epicuticle and a laminated endocuticle is formed. The ultrastructure of the epidermis and of cuticular structures such as bristles, trichomes, apodemes, and tracheoles is very similar to that found in situ. Dendrites and nerve cell bodies are formed in vitro, and sensory axons form nerve bundles similar to those of normal appendages in situ, despite their isolation from the central nervous system. It is concluded that at the ultrastructural level, differentiation in vitro closely parallels the normal course of development. 相似文献
68.
A. Ian Scott S.L. Lee W. Wan 《Biochemical and biophysical research communications》1977,75(4):1004-1009
The “ajmalicine synthetase” system of has been partially purified from callus, seedlings and mature plants. On gel filtration of the cell-free extract, four β-D-glucosidase isozymes were observed in seedlings and plants. Only two were present in the callus. A protein peak at 55,000 daltons in all three materials was capable of synthesizing ajmalicine from tryptamine and secologanin in the presence of NADPH. This “ajmalicine synthetase” rapidly lost its ability to synthsize ajmalicine, but retained the β-glucosidase activity. 相似文献
69.
The structural filament network of the nucleus is prepared while still connected to the cytoskeleton. The relatively gentle procedure removes about 98% of the DNA and at least 86% of the histones. The matrix is bounded by an outer nuclear lamina connected to the cytoskeletal framework, as well as the inner filaments. The filaments range in diameter from 3 to 22 nm, and are organized in a three-dimensional anastomosing network in which nucleoli are enmeshed. The nuclear matrix is separated from the cytoskeletal framework by a double detergent and then partitioned into a chromatin fraction and a matrix fraction by nuclease and high salt. Two-dimensional gel electrophoresis shows that the proteins of the cytoskeleton, chromatin and nuclear matrix are very different. A major protein found in all fractions cofocuses with actin. Vimentin is largely associated with the nuclear matrix, probably as a corona external of filaments. 相似文献
70.
A relatively stable enzyme system that converts versiconal hemiacetal acetate to versicolorin A was isolated from the soluble fraction of the homogenized cells of Aspergillus parasiticus ATCC 15517. The cell-free preparation did not require oxygen or oxidized nicotinamide adenine dinucleotide phosphate for activity, nor did it require dithiothreitol, polyclar (polyvinyl pyrrolidone), or glycerol for stabilization of activity. It was susceptible to inhibition by dichlorvos and cysteine. Isotope tracer studies revealed involvement of several intermediates in the conversion of versiconal hemiacetal acetate to versicolorin A. These findings confirm the biogenetic relationship of versiconal hemiacetal acetate and versicolorin A, and they confirm that the bisfuran ring structure in aflatoxins and related fungal metabolites is derived from the hemiacetal structure of versiconal hemiacetal acetate. 相似文献