全文获取类型
收费全文 | 379071篇 |
免费 | 4367篇 |
国内免费 | 1096篇 |
专业分类
电工技术 | 6605篇 |
综合类 | 284篇 |
化学工业 | 56650篇 |
金属工艺 | 17033篇 |
机械仪表 | 12087篇 |
建筑科学 | 8362篇 |
矿业工程 | 3155篇 |
能源动力 | 9261篇 |
轻工业 | 28184篇 |
水利工程 | 4808篇 |
石油天然气 | 10578篇 |
武器工业 | 28篇 |
无线电 | 41700篇 |
一般工业技术 | 78758篇 |
冶金工业 | 68034篇 |
原子能技术 | 10339篇 |
自动化技术 | 28668篇 |
出版年
2021年 | 3398篇 |
2019年 | 3308篇 |
2018年 | 5747篇 |
2017年 | 5856篇 |
2016年 | 6248篇 |
2015年 | 3745篇 |
2014年 | 6289篇 |
2013年 | 16588篇 |
2012年 | 9925篇 |
2011年 | 13190篇 |
2010年 | 10615篇 |
2009年 | 11968篇 |
2008年 | 12176篇 |
2007年 | 12166篇 |
2006年 | 10400篇 |
2005年 | 9659篇 |
2004年 | 8972篇 |
2003年 | 8826篇 |
2002年 | 8370篇 |
2001年 | 8514篇 |
2000年 | 8184篇 |
1999年 | 8357篇 |
1998年 | 20567篇 |
1997年 | 14512篇 |
1996年 | 11332篇 |
1995年 | 8368篇 |
1994年 | 7481篇 |
1993年 | 7487篇 |
1992年 | 5814篇 |
1991年 | 5679篇 |
1990年 | 5367篇 |
1989年 | 5388篇 |
1988年 | 5257篇 |
1987年 | 4574篇 |
1986年 | 4544篇 |
1985年 | 5196篇 |
1984年 | 4851篇 |
1983年 | 4550篇 |
1982年 | 4087篇 |
1981年 | 4164篇 |
1980年 | 4079篇 |
1979年 | 4148篇 |
1978年 | 4137篇 |
1977年 | 4520篇 |
1976年 | 5685篇 |
1975年 | 3693篇 |
1974年 | 3524篇 |
1973年 | 3633篇 |
1972年 | 3111篇 |
1971年 | 2872篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
OBJECTIVE: A mutant soybean line (A16) low in linolenic acid content (2% of oil by weight) was developed to increase oil oxidative stability. It was unknown whether serum lipid and lipoprotein concentrations in humans would be affected should A16 soybean oil (A16 oil) replace commercial soybean oil in diets. This study was conducted to examine the hypothesis that in free-living normolipidemic women, the consumption of A16 oil at approximately 10% of energy intake (en%) would not affect serum lipids and lipoproteins differently than would the consumption of the same amount of a commercial soybean oil with 7% of linolenic acid content. DESIGN: Fifteen free-living female college students consumed the soybean oil daily with regular meals for 9 weeks in different orders, with each test oil being eaten for 3 weeks. During the study, 13 en% was provided by each test oil and a total of 35 en% was from dietary fat. Serum concentrations of total cholesterol, high-density lipoprotein cholesterol (HDL cholesterol), low-density lipoprotein cholesterol (LDL cholesterol) and triacylglycerides (TAG) were measured. Serum total fatty acid patterns were analyzed as well. RESULTS: Each of the three test oils decreased serum total cholesterol, LDL cholesterol and TAG concentrations from the baseline values. The feeding of A16 and commercial soybean oils decreased serum HDL cholesterol significantly compared with coconut oil (p < 0.05). Dietary inclusion of coconut oil increased serum myristic acid significantly more than did either soybean oil (p < 0.01). Serum arachidonic acid concentrations were significantly greater with A16 consumption than with commercial soybean oil consumption (p < 0.001). CONCLUSION: A16 and commercial soybean oils both diminished serum HDL cholesterol. Although the fatty acid composition differed between the two soybean oils, A16 oil and commercial oil had similar effects on serum concentrations of lipoproteins and lipids. With increased oxidative stability, A16 oil is a good alternative to commercial soybean oil. 相似文献
992.
In this paper, we consider a class of nonlinear fractional order control system with delay in state variable. Existence and uniqueness of solution are shown by using method of steps. The sensitivity of the state and control with respect to the parameters of the system is shown. Finally, analytical results are substantiated by numerical examples. 相似文献
993.
Stabilizing manipulators during the transition from free to constraint motion is an important issue in contact task control design. This paper documents the development, theoretical analysis and experimental evaluation of a Lyapunov-based control scheme to regulate the impacts of a hydraulic actuator that comes in contact with a nonmoving environment. Upon sensing a nonzero force, the controller positions the actuator at the location where the force was first sensed, exerting minimal force on the environment. The scheme does not require continuous measurement of force or velocity during the short period of impacts, making it very useful for practical cases. Furthermore, no knowledge of the impact dynamics, friction effects, servovalve dynamics, or hydraulic parameters is required for control action. Stability of the control scheme is verified via analytical analyses. Due to the discontinuous friction model and the discontinuous nature of the proposed control law, the control system is nonsmooth. The existence, continuation and uniqueness of Filippov's solution to the system are, therefore, investigated. The extension of LaSalle's invariance principle to nonsmooth systems is next employed to prove that all the solution trajectories converge to the equilibria. The controller is finally tested experimentally to verify its practicality and effectiveness in collisions with hard and soft environments and with various approach velocities. 相似文献
994.
A recursive orthogonal least squares (ROLS) algorithm for multi-input, multi-output systems is developed in this paper and is applied to updating the weighting matrix of a radial basis function network. An illustrative example is given, to demonstrate the effectiveness of the algorithm for eliminating the effects of ill-conditioning in the training data, in an application of neural modelling of a multi-variable chemical process. Comparisons with results from using standard least squares algorithms, in batch and recursive form, show that the ROLS algorithm can significantly improve the neural modelling accuracy. The ROLS algorithm can also be applied to a large data set with much lower requirements on computer memory than the batch OLS algorithm. 相似文献
995.
Transform image processing is done in nonoverlapping blocks and a block of (4 × 4) or a (8 × 8) subpicture size is reasonable in terms of both mean-square error and subjective picture quality. It is therefore desirable to search for a fast transform which is efficient for data of small sequence length. This paper presents a modified slant and a modified slant Haar transform. Computational operations are increased by 2 additions and 4 multiplications only as compared to conventional slant and slant Haar transforms. Performance evaluation based on a first-order stationary Markov process signal such as variance distribution, mean-square error estimate due to scalar Wiener filtering of signal corrupted by white noise and decorrelation property establish the superiority of the transforms. Comparative study of results on a monochrome picture are encouraging. 相似文献
996.
A. B. Al’shin E. A. Al’shina A. G. Limonov 《Mathematical Models and Computer Simulations》2010,2(4):493-503
Rosenbrock methods are known to be good in numerical modeling of stiff problems. In this work, a new symbolic algorithm is
proposed for automating the derivation of order conditions for two-stage Rosenbrock schemes with complex coefficients. Software
implementation of the proposed algorithm is discussed in detail. 相似文献
997.
Automated recovery of system features and their designs from program source codes is important in reverse engineering and system comprehension. It also helps in the testing of software. An error that is made by users in an input to an execution of a transaction and discovered only after the completion of the execution is called a posttransaction user-input error (PTUIE) of the transaction. For a transaction in any database application, usually, it is essential to-provide transactions for correcting the effect that could result from any PTUIE of the transaction. We discover some probable properties that exist between the control flow graph of a transaction and the control flow graphs of transactions for correcting PTUIE of the former transaction. Through recognizing these properties, we present a novel approach for the automated approximate recovery of provisions and designs for transactions to correct PTUIE of transactions in a database application. The approach recognizes these properties through analyzing the source codes of transactions in the database application statically. 相似文献
998.
Triangulation of planar regions with applications 总被引:24,自引:0,他引:24
999.
Fischer B. Buhmann J.M. 《IEEE transactions on pattern analysis and machine intelligence》2003,25(4):513-518
Perceptual grouping organizes image parts in clusters based on psychophysically plausible similarity measures. We propose a novel grouping method in this paper, which stresses connectedness of image elements via mediating elements rather than favoring high mutual similarity. This grouping principle yields superior clustering results when objects are distributed on low-dimensional extended manifolds in a feature space, and not as local point clouds. In addition to extracting connected structures, objects are singled out as outliers when they are too far away from any cluster structure. The objective function for this perceptual organization principle is optimized by a fast agglomerative algorithm. We report on perceptual organization experiments where small edge elements are grouped to smooth curves. The generality of the method is emphasized by results from grouping textured images with texture gradients in an unsupervised fashion. 相似文献
1000.
This investigation was prompted by Asch's (1952) discussion of the personal and social significance of yielding to group pressure. For the person, yielding requires the inhibition of overt and perhaps implicit responses to objective situational requirements. For the group, malignant processes may arise and develop, unchecked by those members in whom goals of personal security predominate over group goals. In the present study, the view was taken that both meanings of yielding are assigned positive value in two separate ideologies concerning the group-individual relation. One of these is termed "conformity" and the other is "rugged individualism." In the study, group pressure was simulated by announcing bogus group judgments to small groups of Ss whose apparent task was to match one of three lines of variable length with a standard line. Questionnaires were used to measure variables, which were: the ideology of conformity (IC), the ideology of rugged individualism (RI), ethnocentrism (E), and authoritarianism (F). The questionnaires were administered to 91 college students, both day school and evening. It was found that the correlation with the F scale was .48 (P 相似文献