全文获取类型
收费全文 | 859篇 |
免费 | 102篇 |
国内免费 | 52篇 |
专业分类
电工技术 | 9篇 |
综合类 | 56篇 |
化学工业 | 287篇 |
金属工艺 | 54篇 |
机械仪表 | 58篇 |
建筑科学 | 46篇 |
矿业工程 | 11篇 |
轻工业 | 63篇 |
水利工程 | 2篇 |
石油天然气 | 14篇 |
武器工业 | 12篇 |
无线电 | 101篇 |
一般工业技术 | 164篇 |
冶金工业 | 24篇 |
原子能技术 | 3篇 |
自动化技术 | 109篇 |
出版年
2024年 | 5篇 |
2023年 | 18篇 |
2022年 | 40篇 |
2021年 | 47篇 |
2020年 | 37篇 |
2019年 | 34篇 |
2018年 | 21篇 |
2017年 | 41篇 |
2016年 | 38篇 |
2015年 | 36篇 |
2014年 | 67篇 |
2013年 | 56篇 |
2012年 | 52篇 |
2011年 | 76篇 |
2010年 | 52篇 |
2009年 | 49篇 |
2008年 | 41篇 |
2007年 | 50篇 |
2006年 | 33篇 |
2005年 | 37篇 |
2004年 | 37篇 |
2003年 | 13篇 |
2002年 | 23篇 |
2001年 | 19篇 |
2000年 | 13篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 13篇 |
1995年 | 12篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1013条查询结果,搜索用时 15 毫秒
1.
Joanna Skrzyde Dorota Borowska-Wykrt Dorota Kwiatkowska 《International journal of molecular sciences》2021,22(8)
This review is devoted to the structure, assembly and function of cuticle. The topics are discussed from the mechanical perspective and whenever the data are available a special attention is paid to the cuticle of perianth organs, i.e., sepals, petals or tepals. The cuticle covering these organs is special in both its structure and function and some of these peculiarities are related to the cuticle mechanics. In particular, strengthening of the perianth surface is often provided by a folded cuticle that functionally resembles profiled plates, while on the surface of the petal epidermis of some plants, the cuticle is the only integral continuous layer. The perianth cuticle is distinguished also by those aspects of its mechanics and development that need further studies. In particular, more investigations are needed to explain the formation and maintenance of cuticle folding, which is typical for the perianth epidermis, and also to elucidate the mechanical properties and behavior of the perianth cuticle in situ. Gaps in our knowledge are partly due to technical problems caused by very small thicknesses of the perianth cuticle but modern tools may help to overcome these obstacles. 相似文献
2.
The determination of a protein''s folding nucleus, i.e. a set of native contacts playing an important role during its folding process, remains an elusive yet essential problem in biochemistry. In this work, we investigate the mechanical properties of 70 protein structures belonging to 14 protein families presenting various folds using coarse-grain Brownian dynamics simulations. The resulting rigidity profiles combined with multiple sequence alignments show that a limited set of rigid residues, which we call the consensus nucleus, occupy conserved positions along the protein sequence. These residues'' side chains form a tight interaction network within the protein''s core, thus making our consensus nuclei potential folding nuclei. A review of experimental and theoretical literature shows that most (above 80%) of these residues were indeed identified as folding nucleus member in earlier studies. 相似文献
3.
Robben J.; der Schueren J.Van; Verhasselt P.; Aert R.; Volckaert G. 《Protein engineering, design & selection : PEDS》1995,8(2):159-165
The deletion of nine residues from the C-terminus of the bacterialchloramphenicol acetyltransferase (CAT) results in depositionof the mutant protein in cytoplasmic inclusion bodies and lossof chloramphenicol resistance in Escherichia coli. This foldingdefect is relieved by C-terminal fusion of the polypeptide withas few as two residues. Based on these observations, efficientpositive selection for the cloning of DNA fragments has beendemonstrated. The cloning vector encodes a C-terminally truncatedCAT protein. Restriction sites in front of the stop codon allowthe insertion of target DNA, resulting in the production ofproperly folded CAT fusion proteins and regained chloramphenicolresistance. The positive selection of recombinants is accomplishedby growth of transformants on chloramphenicol-containing agarplates. The method appears particularly convenient for the cloningof DNA fragments amplified by the PCR because minimal informationto restore CAT folding can be included in the primers. The cloningof random sequences shows that the folding defect can be relievedby fusion to a wide variety of peptides, providing great flexibilityto the positive selection system. This vector may also contributeto the determination of the role of the C-terminus in CAT folding. 相似文献
4.
5.
6.
针对具有方位谱混叠现象的斜视聚束式合成孔径雷达(SAR)成像问题,本文研究了一种基于去调频技术的成像方法.文中首先分析了斜视聚束SAR中的方位谱混叠现象,从理论上找出了斜视角影响方位粗聚焦的根本原因.基于分析结果,引入了回波信号非线性相位校正预处理法,彻底消除了斜视角的影响,从而得到正确的粗聚焦结果.然后基于斜视成像模型,推导了预处理回波信号的方位粗聚焦和精聚焦处理过程.在精聚焦的方位滤波处理中,针对非线性相位校正预处理导致的场景聚焦深度限制问题,提出了一种改进的非线性调频变标(NLCS)算法,实现了回波信号的高精度方位压缩.仿真实验结果证明了文中理论分析的正确性和所提方法的有效性. 相似文献
7.
针对平面结构标签在使用过程中经常发生弯曲形变的问题,研究一种柔性标签发生圆弧形弯曲和垂直折叠形变时天线性能的变化以及对RFID系统识读距离的影响。介绍柔性标签天线的研究现状,分析影响RFID系统识读距离的关键因素,通过示意图阐述弯曲天线模型的建模方法,基于HFSS仿真分析阻抗、增益和辐射效率等的变化规律。通过实际测量验证了RFID系统识读距离的仿真结果及该方法的可行性。 相似文献
8.
Sun Shaojian; Brem Rachel; Chan Hue Sun; Dill Ken A. 《Protein engineering, design & selection : PEDS》1995,8(12):1205-1213
We present two methods for designing amino acid sequences ofproteins that will fold to have good hydrophobic cores. Giventhe coordinates of the desired target protein or polymer structure,the methods generate sequences of hydrophobic (H) and polar(P) monomers that are intended to fold to these structures.One method designs hydrophobic inside, polar outside; the otherminimizes an energy function in a sequence evolution process.The sequences generated by these methods agree at the levelof 6080% of the sequence positions in 20 proteins inthe Protein Data Bank. A major challenge in protein design isto create sequences that can fold uniquely, i.e. to a singleconformation rather than to many. While an earlier lattice-basedsequence evolution method was shown not to design unique folders,our method generates unique folders in lattice model tests.These methods may also be useful in designing other types offoldable polymer not based on amino acids 相似文献
9.
The far infra-red spectrum of a poly(vinyl chloride) sample prepared by the urea clathrate (UC) route has been measured at various temperatures in the range 60 to 320 K. The results, taken in conjunction with those for two less highly ordered polymers, indicate that a revision of the assignments of earlier workers, based on normal coordinate calculations and on the measured spectra of secondary alkyl chlorides such as 2-chlorobutane, is required. The band at 65 cm?1 is attributed to a lattice mode and is not indicative of weak hydrogen bonds of the type CH…ClC. However, it is suggested that the band at 185 cm?1, which is particularly clear and sharp with the UC polymer, probably originates from an interaction of this type, occurring specifically at tight chain folds. 相似文献
10.
It has been demonstrated using CD that ethanol induces importantsecondary structure changes of ß-lactoglobulin. CDspectra indicate that ß-lactoglobulin secondary structure,which is mainly composed of ß-strands, becomes mostly-helical under the influence of the solvent polarity changes.The midpoint of ß-strand/-helix transition in ß-lactoglobulinis observed at dielectric constant {small tilde}60 (35% ethanol;v/v). According to CD measurements, the ethanol-dependent secondarystructure changes are reversible. The alkylation of lysines-NH2 in ß-lactoglobulin weakens the central ß-barrelstructure, since the ß-strand/-helix transition midpointof alkylated ß-lactoglobulin is shifted to lower ethanolconcentration (25% ethanol; v/v). ß-Lactoglobulinstructural changes are triggering the dissociation of the ß-lactoglobulin- retinol complex as judged from complete quenching of its fluorescencein ethanol concentration >30% (v/v). However, in 20% ethanol(v/v), ß-lactoglobulin still retains most of its nativesecondary structure as shown by CD and, in this condition, oneß-lactoglobulin molecule binds an additional secondretinol molecule. This suggests that the highly populated speciesobserved around 20% ethanol (v/v) might represent an intermediatestate able to bind two molecules of retinol. 相似文献