全文获取类型
收费全文 | 71313篇 |
免费 | 3047篇 |
国内免费 | 112篇 |
专业分类
电工技术 | 601篇 |
综合类 | 65篇 |
化学工业 | 15076篇 |
金属工艺 | 1397篇 |
机械仪表 | 1377篇 |
建筑科学 | 3051篇 |
矿业工程 | 185篇 |
能源动力 | 2111篇 |
轻工业 | 9228篇 |
水利工程 | 767篇 |
石油天然气 | 277篇 |
武器工业 | 5篇 |
无线电 | 3933篇 |
一般工业技术 | 11167篇 |
冶金工业 | 13582篇 |
原子能技术 | 495篇 |
自动化技术 | 11155篇 |
出版年
2023年 | 469篇 |
2022年 | 1128篇 |
2021年 | 1634篇 |
2020年 | 1132篇 |
2019年 | 1435篇 |
2018年 | 1899篇 |
2017年 | 1767篇 |
2016年 | 2004篇 |
2015年 | 1718篇 |
2014年 | 2306篇 |
2013年 | 4783篇 |
2012年 | 3626篇 |
2011年 | 4260篇 |
2010年 | 3346篇 |
2009年 | 3237篇 |
2008年 | 3328篇 |
2007年 | 3151篇 |
2006年 | 2651篇 |
2005年 | 2338篇 |
2004年 | 2043篇 |
2003年 | 1878篇 |
2002年 | 1757篇 |
2001年 | 1197篇 |
2000年 | 1043篇 |
1999年 | 1148篇 |
1998年 | 2940篇 |
1997年 | 2103篇 |
1996年 | 1610篇 |
1995年 | 1144篇 |
1994年 | 1009篇 |
1993年 | 1030篇 |
1992年 | 680篇 |
1991年 | 463篇 |
1990年 | 562篇 |
1989年 | 563篇 |
1988年 | 465篇 |
1987年 | 482篇 |
1986年 | 422篇 |
1985年 | 573篇 |
1984年 | 515篇 |
1983年 | 402篇 |
1982年 | 393篇 |
1981年 | 388篇 |
1980年 | 370篇 |
1979年 | 326篇 |
1978年 | 296篇 |
1977年 | 399篇 |
1976年 | 540篇 |
1975年 | 236篇 |
1973年 | 205篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Three-dimensional models, or pharmacophores, describing Euclidean constraints on the location on small molecules of functional
groups (like hydrophobic groups, hydrogen acceptors and donors, etc.), are often used in drug design to describe the medicinal
activity of potential drugs (or ‘ligands’). This medicinal activity is produced by interaction of the functional groups on
the ligand with a binding site on a target protein. In identifying structure-activity relations of this kind there are three
principal issues: (1) It is often difficult to “align” the ligands in order to identify common structural properties that
may be responsible for activity; (2) Ligands in solution can adopt different shapes (or `conformations’) arising from torsional
rotations about bonds. The 3-D molecular substructure is typically sought on one or more low-energy conformers; and (3) Pharmacophore
models must, ideally, predict medicinal activity on some quantitative scale. It has been shown that the logical representation
adopted by Inductive Logic Programming (ILP) naturally resolves many of the difficulties associated with the alignment and
multi-conformation issues. However, the predictions of models constructed by ILP have hitherto only been nominal, predicting
medicinal activity to be present or absent. In this paper, we investigate the construction of two kinds of quantitative pharmacophoric
models with ILP: (a) Models that predict the probability that a ligand is “active”; and (b) Models that predict the actual
medicinal activity of a ligand. Quantitative predictions are obtained by the utilising the following statistical procedures
as background knowledge: logistic regression and naive Bayes, for probability prediction; linear and kernel regression, for
activity prediction. The multi-conformation issue and, more generally, the relational representation used by ILP results in
some special difficulties in the use of any statistical procedure. We present the principal issues and some solutions. Specifically,
using data on the inhibition of the protease Thermolysin, we demonstrate that it is possible for an ILP program to construct
good quantitative structure-activity models. We also comment on the relationship of this work to other recent developments
in statistical relational learning.
Editors: Tamás Horváth and Akihiro Yamamoto 相似文献
82.
The effects of parameter uncertainty on optimal policy have been a matter of interest for academics, and even for some policymakers,
for a long time. Two lines of literature have developed analytical results on this matter. The first line uses static models
and the second dynamic models. In this dynamic line most of the results are confined to models with a single state and a single
control variable.
In this paper we want to encourage the analysis of more general dynamic cases. To do so, the results in the dynamic line are
extended from one-state and one-control finite horizon models to models with a pair of control variables. We then discuss
some of the hurdles which must be surmounted for the results to be made more general and suggests some lines for further research.
JEL classification: C61; E61 相似文献
83.
84.
Hambleton P.J. Ng B.K. Plimmer S.A. David J.P.R. Rees G.J. 《Electron Devices, IEEE Transactions on》2003,50(2):347-351
The nonlocal enhancement in the velocities of charge carriers to ionization is shown to outweigh the opposing effects of dead space, increasing the avalanche speed of short avalanche photodiodes (APDs) over the predictions of a conventional local model which ignores both of these effects. The trends in the measured gain-bandwidth product of two short InAlAs APDs reported in the literature support this result. Relatively large speed benefits are predicted to result from further small reductions in the lengths of short multiplication regions. 相似文献
85.
An Imhoff tank was reconstructed into a 250 m3 UASB reactor in order to treat a malting plant wastewater. The UASB was inoculated with sludge from an anaerobic lagoon used for slaughterhouse wastewater treatment. After two months of operation the reactor achieved full load with an HRT of 17 h, a COD removal higher than 80% and a biogas production of 300 m3/day (77% average methane content), with an organic loading rate of 3.6 kgCOD/m3.d (0.24 kgCOD/kgVSS.d). A yield coefficient of 0.09 gVSS/gCODrem was found from a mass balance. The fat present in the inoculated sludge (48 mg/gSSV) did not affect the start up performance. Sludge from the inoculum with high content of fat (270 mg/gSSV), was separated by flotation in the first week of operation. The COD removal efficiency was scarcely influenced by the reactor operation temperature (17-25 degrees C). 相似文献
86.
87.
A.S. Fomichev I. David S.M. Lukyanov Yu.E. Penionzhkevich N.K. Skobelev O.B. Tarasov 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1994,350(3):605-607
The mass and charge identification of secondary particles with Z < 4 by a large CsI(T1) scintillation detector is performed using pulse shape analysis and time-of-flight methods. The dependence of the light output on E, A and Z is studied in the energy range of 1–20 MeV/A and special attention is paid to the integration time of the photomultiplier anode signal. It is found that the behaviour of the calibration curves strongly depends on the choice of the integration time interval. 相似文献
88.
89.
F Abadía-Molina R Calvente R Carmona R Luján F Abadía-Fenoll 《Canadian Metallurgical Quarterly》1993,8(2):297-304
In this study chick embryo optic cups at HH stage 13 of development were analyzed under normal conditions and after inoculation with colchicine for 1, 2, 4, and 8 h. Several changes were seen after these periods of treatment: 1) modifications of the structure, with thicker regions in the cup and a general decrease in the total volume according to the duration of exposure to the drug (about 4 times less than normal, 5,035 x 10(3) microns 3 vs 1,334 x 10(3) microns 3 after 8 h of treatment); 2) enlargement of the ventricular cavity and its closure, due to failure of approximation of retinal and pigmentary layers; 3) failure of lens development, with delay and impairment of pit formation and deformation of all structures; lens volume was less than normal (about 4 times less, 2,148 x 10(3) microns 3 vs 658 x 10(3) microns 3 after 8 h of treatment); 4) a general segregation of the cells making up the structure, principally in the more active proliferating zones. The local alterations found are described. 相似文献
90.