全文获取类型
收费全文 | 27917篇 |
免费 | 2165篇 |
国内免费 | 441篇 |
专业分类
电工技术 | 253篇 |
综合类 | 846篇 |
化学工业 | 7158篇 |
金属工艺 | 432篇 |
机械仪表 | 679篇 |
建筑科学 | 1136篇 |
矿业工程 | 121篇 |
能源动力 | 679篇 |
轻工业 | 12795篇 |
水利工程 | 286篇 |
石油天然气 | 202篇 |
武器工业 | 18篇 |
无线电 | 498篇 |
一般工业技术 | 2471篇 |
冶金工业 | 267篇 |
原子能技术 | 86篇 |
自动化技术 | 2596篇 |
出版年
2024年 | 213篇 |
2023年 | 605篇 |
2022年 | 1442篇 |
2021年 | 1600篇 |
2020年 | 979篇 |
2019年 | 1109篇 |
2018年 | 976篇 |
2017年 | 1163篇 |
2016年 | 1077篇 |
2015年 | 1183篇 |
2014年 | 1327篇 |
2013年 | 2072篇 |
2012年 | 1507篇 |
2011年 | 1647篇 |
2010年 | 1206篇 |
2009年 | 1226篇 |
2008年 | 1123篇 |
2007年 | 1320篇 |
2006年 | 1191篇 |
2005年 | 993篇 |
2004年 | 857篇 |
2003年 | 684篇 |
2002年 | 631篇 |
2001年 | 436篇 |
2000年 | 409篇 |
1999年 | 444篇 |
1998年 | 387篇 |
1997年 | 290篇 |
1996年 | 397篇 |
1995年 | 306篇 |
1994年 | 318篇 |
1993年 | 244篇 |
1992年 | 234篇 |
1991年 | 174篇 |
1990年 | 107篇 |
1989年 | 116篇 |
1988年 | 88篇 |
1987年 | 92篇 |
1986年 | 57篇 |
1985年 | 73篇 |
1984年 | 57篇 |
1983年 | 41篇 |
1982年 | 25篇 |
1981年 | 13篇 |
1980年 | 48篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Whey is an undurable product. treated very often as a waste which pollutes the natural environment. Whey which is a valuable source of protein, lactose, vitamins and mineral salts should be utilized completely. The present paper is a proposal of whey drying on porous carriers. It is proved experimentally that the proposed drying method guarantees good product quality. 相似文献
42.
43.
C.W.Kenneth Keng 《Energy Economics》1985,7(4):241-258
Because of the huge volume of capital required to construct a modern electric power generating station, investment decisions have to be made with as complete an understanding of the consequences of the decision as possible. This understanding must be provided by the evaluation of future situations. A key consideration in an evaluation is the financial component. This paper attempts to use an econometric method to forecast the construction costs escalation of a standard Canadian nuclear generating station (NGS). A brief review of the history of Canadian nuclear electric power is provided. The major components of the construction costs of a Canadian NGS are studied and summarized. A database is built and indexes are prepared. Based on these indexes, an econometric forecasting model is constructed using an apparently new econometric methodology of forecasting modelling. Forecasts for a period of 40 years are generated and applications (such as alternative scenario forecasts and range forecasts) to uncertainty assessment and/or decision-making are demonstrated. The indexes, the model, and the forecasts and their applications, to the best of the author's knowledge, are the first for Canadian NGS constructions. 相似文献
44.
Kajihara Akiro; Komooka Hitoshi; Kamiya Kenshu; Umeyama Hideaki 《Protein engineering, design & selection : PEDS》1993,6(6):615-620
Bovine pancreatic /S-trypsin (PDB ID-code: 1TPO) which is registeredin the Brookhaven Protein Data Bank (PDB) consists of four exons.The results of homology searches for each exon in the PDB showedthat homologous proteins were tonin (PDB ID-code: 1TON), ratmast cell protease (PDB ID-code: 3RP2_A), kaffikrein A (PDBID-code: 2PKA_B) and kallikrein A (2PKA_B) respectively. Thus,for the three-dimensional structure prediction of 1TPO, a chimeraprotein was constructed from the three proteins mentioned aboveand the 3-D structure prediction was performed using this chimerareference protein. The modelled structure of 1TPO was energeticallyoptimized by molecular mechanics and molecular dynamics simulationand was compared with its X-ray crystal structure registeredin the PDB. The root mean square deviations (r.m.s.d.) of mainchain atoms and the neighbouring active site (5 sphere fromHis57, AsplO2 and Serl95) between the modelled structure andthe X-ray structure were 1.66 and 0.94 respectively. Porcinepancreatic elastase (PDB ID-code: 3EST) which is registeredin the PDB was used as the reference protein and the modelledstructure from 3EST was also compared with the X-ray data. Ther.m.s.d. of main chain atoms and that of the active site were2.14 and 1.18 respectively. These results dearly support thepropriety of this method using the chimera reference protein. 相似文献
45.
Hong ZHU 《Frontiers of Computer Science in China》2012,6(1):40-56
Meta-modelling plays an important role in model driven software development.In this paper,a graphic extension of BNF (GEBNF) is proposed to define the abstract syntax of graphic modelling languages.Fro... 相似文献
46.
47.
48.
The performance of a venturi scrubber in the removal of tar from gas in updraft gasification has been studied. The gasifier has been operated with a husk feed rate of 1.6 × 10?4 kg/s. The venturi scrubber has been operated at a superficial gas velocity of 56.4 m/s at the throat. A wide variety of scrubbing liquids having surface tensions ranging from 0.026 to 0.072 N/m have been used. The Qg/Ql, has been varied in the range of 1000–8000. The tar separation efficiency η has been found to vary from 51 to 98.5%. A mathematical model, assuming steady-state operation, has been developed considering very high pseudosolubility of tar in the scrubbing liquids. The predicted values of η have been compared with experimental results. The model satisfactorily explains the tar removal efficiency of the venturi for Qg/Ql values ranging from 4000 to 8000 for all scrubbing liquids. The following correlation has been developed for predicting venturi scrubber efficiency: . 相似文献
49.
Quantification of secondary structure prediction improvement using multiple alignments 总被引:9,自引:0,他引:9
Levin Jonathan M.; Pascarella Stefano; Argos Patrick; Garnier Jean 《Protein engineering, design & selection : PEDS》1993,6(8):849-854
The use of multiple sequence alignments for secondary structurepredictions is analysed. Seven different protein families, containingonly sequences of known structure, were considered to providea range of alignment and prediction conditions. Using alignmentsobtained by spatial superposition of main chain atoms in knowntertiary protein structures allowed a mean of 8% in secondarystructure prediction accuracy, when compared to those obtainedfrom the individual sequences. Substitution of these alignmentsby those determined directly from an automated sequence alignmentalgorithm showed variations in the prediction accuracy whichcorrelated with the quality of the multiple alignments and distanceof the primary sequence. Secondary structure predictions canbe reliably improved using alignments from an automatic alignmentprocedure with a mean increase of 6.87percnt;, giving an overallprediction accuracy of 68.5%, if there is a minimum of 25% sequenceidentity between all sequences in a family. 相似文献
50.
An evaluation of the performance of an automated procedure for comparative modelling of protein tertiary structure 总被引:6,自引:0,他引:6
A 3-D model of a protein can be constructed from its amino acidsequence and the 3-D structures of one or more homologues byannealing three sets of fragments: the structurally conservedregions, structurally variable regions and the side chains.The method encoded in the computer program COMPOSER was assessedby generating 3-D models of eight proteins whose crystal structuresare already known and for which 3-D structures of homologuesare available. In the structurally conserved regions, differencesbetween modelled and X-ray structures are smaller than the differencesbetween the X-ray structures of the modelled protein and thehomologues used to build the model. When several homologuesare used, the contributions of the known structures are weighted,preferably by the square of sequence similarity; this is especiallyimportant when the similarities of the homologues to the modelledstructure differ greatly. The collar extensionapproach, in which a similar region of different length in ahomologue is used to extend the framework, can result in a moreaccurate model. If known homologues comprise more than one relatedgroup of proteins and they are both distantly related to theunknown, then alignment of the sequence to be modelled witheach group of homologues facilitates identification of structurallyconserved regions of the unknown and leads to an improved model.Models have root mean square differences (r.m.s.d.s) with thestructures defined by X-ray analysis of between 0.73 and 1.56Å for all C atoms, for seven of the eight models. Forthe model of mucor pepsin, where the closest homologue has 33%sequence identity and 20% of the residues are in structurallyvariable regions, the r.m.s.d. for the framework region is 1.71Å and the r.m.s.d. for all C atoms is 3.47 Â. 相似文献