全文获取类型
收费全文 | 6720篇 |
免费 | 73篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 39篇 |
综合类 | 3篇 |
化学工业 | 398篇 |
金属工艺 | 53篇 |
机械仪表 | 47篇 |
建筑科学 | 89篇 |
矿业工程 | 7篇 |
能源动力 | 39篇 |
轻工业 | 326篇 |
水利工程 | 16篇 |
石油天然气 | 6篇 |
无线电 | 201篇 |
一般工业技术 | 367篇 |
冶金工业 | 4784篇 |
原子能技术 | 17篇 |
自动化技术 | 404篇 |
出版年
2022年 | 18篇 |
2021年 | 32篇 |
2020年 | 32篇 |
2019年 | 36篇 |
2018年 | 37篇 |
2017年 | 38篇 |
2016年 | 34篇 |
2015年 | 32篇 |
2014年 | 48篇 |
2013年 | 122篇 |
2012年 | 79篇 |
2011年 | 111篇 |
2010年 | 89篇 |
2009年 | 77篇 |
2008年 | 102篇 |
2007年 | 112篇 |
2006年 | 98篇 |
2005年 | 66篇 |
2004年 | 68篇 |
2003年 | 72篇 |
2002年 | 68篇 |
2001年 | 46篇 |
2000年 | 55篇 |
1999年 | 204篇 |
1998年 | 1442篇 |
1997年 | 812篇 |
1996年 | 520篇 |
1995年 | 285篇 |
1994年 | 246篇 |
1993年 | 316篇 |
1992年 | 61篇 |
1991年 | 76篇 |
1990年 | 75篇 |
1989年 | 97篇 |
1988年 | 89篇 |
1987年 | 77篇 |
1986年 | 62篇 |
1985年 | 74篇 |
1984年 | 26篇 |
1983年 | 38篇 |
1982年 | 56篇 |
1981年 | 51篇 |
1980年 | 56篇 |
1979年 | 27篇 |
1978年 | 30篇 |
1977年 | 120篇 |
1976年 | 241篇 |
1975年 | 32篇 |
1972年 | 12篇 |
1963年 | 13篇 |
排序方式: 共有6796条查询结果,搜索用时 0 毫秒
1.
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
2.
3.
Richard Ross 《Information Systems Management》1994,11(3):41-50
Management of distributed environments requires corporate IS managers to shift from being operators of a central utility to facilitators who can recognize the synergy among loosely related groups of users. Success depends on the development of new ways of visualizing and measuring the service delivery process. 相似文献
4.
JS Wefel 《Canadian Metallurgical Quarterly》1995,9(3):335-337
We present a case of a single coronary artery where the right coronary artery (RCA) arose from its proximal part. This rare anomaly was detected during elective coronary angiography in a patient with suspected coronary artery disease. The single coronary artery originated from the left sinus of valsalva, giving rise to RCA proximally and distally dividing into left anterior descending (LAD), ramus intermedius and left circumflex (LCX) arteries. The anginal symptoms in this patient was attributed to a significant stenosis at the proximal LAD which was subsequently dilated by coronary angioplasty. To the best of our knowledge, this is the first reported case of angioplasty of LAD in an anomalous single coronary artery. 相似文献
5.
It is essential in the simulation of power electronics applications to model magnetic components accurately. In addition to modeling the nonlinear hysteresis behavior, eddy currents and winding losses must be included to provide a realistic model. In practice the losses in magnetic components give rise to significant temperature increases which can lead to major changes in the component behavior. In this paper a model of magnetic components is presented which integrates a nonlinear model of hysteresis, electro-magnetic windings and thermal behavior in a single model for use in circuit simulation of power electronics systems. Measurements and simulations are presented which demonstrate the accuracy of the approach for the electrical, magnetic and thermal domains across a variety of operating conditions, including static thermal conditions and dynamic self heating 相似文献
6.
Steven S. Ross 《网络电信》2008,(8):13-13
Perhaps the most powerful claim that advocates of fiber can make,on top of the massive bandwidthfiber makes possible today, is that fiber is future-proof. That is, the fiber that is laid today can be upgraded so that the same strands of glass can carry massively more bandwidth in the future. 相似文献
7.
8.
BACKGROUND: In the Minnesota Colon Cancer Control Study, annual fecal occult blood testing reduced mortality from colorectal cancer by at least 33.4%. Some attribute a large part of this reduction to chance detection of cancers by colonoscopies; rehydration of guaiac test slides greatly increased positivity and consequently the number of colonoscopies performed. This study was conducted to determine how much of the reduction resulted from chance detection. METHODS: We used a mathematical model developed by Lang and Ransohoff to estimate the proportion of the 33.4% mortality attainable by chance alone. Applying the model requires the specification of five parameters: duration of follow-up, rate of compliance with fecal occult blood testing, rate of compliance with colonoscopy, positivity rate, and efficacy of colonoscopy in reducing colorectal cancer mortality. We took values for four of the five parameters directly from the Minnesota study. For the fifth parameter, efficacy of colonoscopy, we selected a value of 60%, based on the conclusions of another study. Whereas the Lang-Ransohoff model selects persons for colonoscopy by chance alone, those with bleeding cancers would also be selected by sensitive fecal occult blood testing. We therefore adjusted the result of the Lang-Ransohoff model for this dual detectability. RESULTS: We found that 16%-25% of the reduction in colorectal cancer deaths effected by fecal occult blood testing in the Minnesota study was due to chance detection; the remainder was due to sensitive detection. CONCLUSION: Chance played a minor role in the detection of colorectal cancers by fecal occult blood testing in the Minnesota study. 相似文献
9.
10.
HJ Lee HK Ha MH Kim YK Jeong PN Kim MG Lee JS Kim DJ Suh SG Lee YI Min YH Auh 《Canadian Metallurgical Quarterly》1997,169(2):517-520
OBJECTIVE: The purpose of this study was to evaluate ERCP and CT findings of ectopic drainage of the common bile duct into the duodenal bulb. CONCLUSION: Although rare, the diagnosis of ectopic drainage of the common bile duct into the duodenal bulb is important to prevent inadvertent damage during biliary tract or gastric surgery and to clarify the cause of chronic peptic ulcers. 相似文献