全文获取类型
收费全文 | 2758篇 |
免费 | 89篇 |
国内免费 | 143篇 |
专业分类
系统科学 | 103篇 |
丛书文集 | 82篇 |
教育与普及 | 61篇 |
理论与方法论 | 8篇 |
现状及发展 | 9篇 |
研究方法 | 16篇 |
综合类 | 2711篇 |
出版年
2024年 | 13篇 |
2023年 | 39篇 |
2022年 | 35篇 |
2021年 | 48篇 |
2020年 | 23篇 |
2019年 | 18篇 |
2018年 | 15篇 |
2017年 | 37篇 |
2016年 | 42篇 |
2015年 | 60篇 |
2014年 | 58篇 |
2013年 | 63篇 |
2012年 | 83篇 |
2011年 | 103篇 |
2010年 | 111篇 |
2009年 | 127篇 |
2008年 | 124篇 |
2007年 | 121篇 |
2006年 | 96篇 |
2005年 | 93篇 |
2004年 | 68篇 |
2003年 | 71篇 |
2002年 | 79篇 |
2001年 | 74篇 |
2000年 | 83篇 |
1999年 | 168篇 |
1998年 | 138篇 |
1997年 | 173篇 |
1996年 | 142篇 |
1995年 | 106篇 |
1994年 | 112篇 |
1993年 | 86篇 |
1992年 | 66篇 |
1991年 | 76篇 |
1990年 | 61篇 |
1989年 | 57篇 |
1988年 | 56篇 |
1987年 | 37篇 |
1986年 | 17篇 |
1985年 | 8篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有2990条查询结果,搜索用时 15 毫秒
791.
Ligand-receptor binding revealed by the TNF family member TALL-1 总被引:3,自引:0,他引:3
Liu Y Hong X Kappler J Jiang L Zhang R Xu L Pan CH Martin WE Murphy RC Shu HB Dai S Zhang G 《Nature》2003,423(6935):49-56
The tumour necrosis factor (TNF) ligand TALL-1 and its cognate receptors, BCMA, TACI and BAFF-R, were recently identified as members of the TNF superfamily, which are essential factors contributing to B-cell maturation. The functional, soluble fragment of TALL-1 (sTALL-1) forms a virus-like assembly for its proper function. Here we determine the crystal structures of sTALL-1 complexed with the extracellular domains of BCMA and BAFF-R at 2.6 and 2.5 A, respectively. The single cysteine-rich domain of BCMA and BAFF-R both have saddle-like architectures, which sit on the horseback-like surface formed by four coil regions on each individual sTALL-1 monomer. Three novel structural modules, D2, X2 and N, were revealed from the current structures. Sequence alignments, structural modelling and mutagenesis revealed that one disulphide bridge in BAFF-R is critical for determining the binding specificity of the extracellular domain eBAFF-R to TALL-1 instead of APRIL, a closely related ligand of TALL-1, which was confirmed by binding experiments in vitro. 相似文献
792.
A common feature of the single-walled carbon-nanotube field-effect transistors fabricated to date has been the presence of a Schottky barrier at the nanotube--metal junctions. These energy barriers severely limit transistor conductance in the 'ON' state, and reduce the current delivery capability--a key determinant of device performance. Here we show that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotubes, greatly reduces or eliminates the barriers for transport through the valence band of nanotubes. In situ modification of the electrode work function by hydrogen is carried out to shed light on the nature of the contacts. With Pd contacts, the 'ON' states of semiconducting nanotubes can behave like ohmically contacted ballistic metallic tubes, exhibiting room-temperature conductance near the ballistic transport limit of 4e(2)/h (refs 4-6), high current-carrying capability (approximately 25 micro A per tube), and Fabry-Perot interferences at low temperatures. Under high voltage operation, the current saturation appears to be set by backscattering of the charge carriers by optical phonons. High-performance ballistic nanotube field-effect transistors with zero or slightly negative Schottky barriers are thus realized. 相似文献
793.
在这篇文章中提出了针对状态部分可观下离散事件系统的状态反馈控制综合问题,证明了这个问题的最优解是不存在的,利用谓词Re(G,Q)的性质定义了一种次优解,并给出求解这个次优解的算法. 相似文献
794.
一种基于小波变换方法的图像递进传送方式 总被引:2,自引:0,他引:2
研究利用小波变换方式进行图像的递进传输。方法对图像实行小波变换,然后传递变换后的小波系数,在拉发收端可根据需要对接收到的系数随时地以变换,从而得到原图像的逐级近似。 相似文献
795.
796.
N-phosphoryl-α-amino acids can react to form esters, peptides, phosphoryl ester-exchanged products and phosphoryl group migration products under mild conditions, which are very important in researches on arohebiont. It has been proposed that intramolecular mixed carboxylic-phosphoric anhydrides (IMCPAs) might be the common intermediates of the reactions, which are difficult to be experimentally observed because of their high activity. In this note, it has been revealed, by means of MNDO, that the IMCPAs are situated at the relatively minimal points of the potential surface and can form in a non-synchronous concerted reaction pathway that passes through a transition state with a hydrogen-bond-bridge structure. The results give a successful explanation to the structure and formation of IMCPAs and their ability to promote the various reactions mentioned above. 相似文献
797.
为寻找一种更好的方法,提高股骨颈骨折内固定的治疗效果,笔者应用Hansson钉系统,将2枚带钩的钉以上下平行方式经股骨颈置入股骨头,随机治疗股骨颈骨折患者30例,并进行3~21个月的临床随访观察。结果表明:患肢骨折愈合快、关节功能恢复好,优良率达93%。与其它内固定相比,Hansson钉具有创伤小、操作简便、内固定牢固,符合髋关节生物力学特点,便于推广。 相似文献
798.
799.
讨论了电流变液中介电颗粒在平行板电场中的运动。严格考虑了介电颗粒与极板的相互作用,利用特殊函数得到了封闭的积分表达式。其中偶极矩与一组无穷多个镜象偶极矩之间的相互作用严格表达式,可以方便地用来处理电流变液中颗粒与极板的作用。 相似文献
800.
湖泊水环境中湖流及其风效应研究 总被引:3,自引:0,他引:3
在不规则的三角形网格上,采用改型特征线法处理对流算子;采用集中质量的有限元法处理扩散算子,应用数值求解对流扩散方程的分步杂交法,模拟浅水型湖泊的水力特性,计算了1993年三个季度在不同风应力及入出流作用下的流态、流场分布、水位变化情况. 相似文献