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991.
David Kan 《CAD/CAM与制造业信息化》2008,(5):20-21
随着计算机技术的迅速发展,在工程领域中,有限元分析(FEA)越来越多地用于仿真模拟,来求解真实的工程问题。这些年来,越来越多的工程师、应用数学家和物理学家已经证明这种采用求解偏微分方程(PDE)的方法可以求解许多物理现象,这些偏微 相似文献
992.
Hernandez Prada JA Madden SL Ostrov DA Hernandez MA 《Journal of molecular graphics & modelling》2008,26(8):1365-1369
Intravascular clotting remains a major health problem in the United States, the most prominent being deep vein thrombosis, pulmonary embolism and thromboembolic stroke. Previous reports on the use of pyridine derivatives in cardiovascular drug development encourage us to pursue new types of compounds based on a pyridine scaffold. Eleven pyridine derivatives (oximes, semicarbazones, N-oxides) previously synthesized in our laboratories were tested as anticoagulants on pooled normal plasma using the prothrombin time (PT) protocol. The best anticoagulant within the oxime series was compound AF4, within the oxime N-oxide series was compound AF4-N-oxide, and within the semicarbazone series, compound MD1-30Y. We also used a molecular modeling approach to guide our efforts, and found that there was good correlation between coagulation data and computational energy scores. Molecular docking was performed to target the active site of thrombin with the DOCK v5.2 package. The results of molecular modeling indicate that improvement in anticoagulant activities can be expected by functionalization at the three-position of the pyridine ring and by N-oxide formation. Results reported here prove the suitability of DOCK in the lead optimization process. 相似文献
993.
Extending IP to low-power, wireless personal area networks (LoWPANs) was once considered impractical because these networks are highly constrained and must operate unattended for multiyear lifetimes on modest batteries. Many vendors embraced proprietary protocols, assuming that IP was too resource-intensive to be scaled down to operate on the microcontrollers and low-power wireless links used in LoWPAN settings. However, 6LoWPAN radically alters the calculation by introducing an adaptation layer that enables efficient IPv6 communication over IEEE 802.15.4 LoWPAN links. 相似文献
994.
In this article, efficient computational models for ship motions are presented. These models are used to simulate ship movements
in real time. Compared with traditional approaches, our method possesses the ability to cope with different ship shapes, engines,
and sea conditions without the loss of efficiency. Based on our models, we create a ship motion simulation system for both
entertainment and educational applications. Our system assists users to learn the motions of a ship encountering waves, currents,
and winds. Users can adjust engine powers, rudders, and other ship facilities via a graphical user interface to create their
own ship models. They can also change the environment by altering wave frequencies, wave amplitudes, wave directions, currents,
and winds. Therefore, numerous combinations of ships and the environment are generated and the learning becomes more amusing.
In our system, a ship is treated as a rigid body floating on the sea surface. Its motions compose of 6 degrees of freedom:
pitch, heave, roll, surge, sway, and yaw. These motions are divided into two categories. The first three movements are induced
by sea waves, and the last three ones are caused by propellers, rudders, currents, and winds. Based on Newton’s laws and other
basic physics motion models, we deduce algorithms to compute the magnitudes of the motions. Our methods can be carried out
in real time and possess high fidelity. According to ship theory, the net effects of external forces on the ship hull depend
on the ship shape. Therefore, the behaviors of the ship are influenced by its shape. To enhance our physics models, we classify
ships into three basic types. They are flat ships, thin ships, and slender ships. Each type of ship is associated with some
predefined parameters to specify their characteristics. Users can tune ship behaviors by varying the parameters even though
they have only a little knowledge of ship theory. 相似文献
995.
Richard A. Foulds David M. Saxe Arthur W. JoyceIII Sergei Adamovich 《Virtual Reality》2008,12(2):87-97
The sensory-motor skills of persons with neuromuscular disabilities have been shown to be enhanced by intensive and repetitive
therapeutic interventions. This paper describes a form of low immersion virtual reality and a prototype, open source system
that allow a user with significant physical disability to actively interact with computer-generated objects whose behaviors
promote a game-like interaction. Unlike fully immersive and haptic virtual reality, this approach frees the user from head-mounted
displays and gloves. It extracts the user’s real-time silhouette from the output of a remote video camera and uses that two-dimensional
outline to interact with graphical objects on screen. In contrast to video games that have been modified with specialized
interfaces, this virtual interaction system promotes the repetitive use of goal directed movements of the arms and body, which
are essential to promote cortical reorganization, as well as discourage unwanted changes in muscle tissue that result in contracture.
A prototype system demonstrates the potential of low immersion technology to motivate users and encourage participation in
therapy. It also offers the potential of accommodating the sensory-motor skills of individuals with very significant impairment.
The behaviors of the computer-generated graphics can be altered to allow use by those with very limited range of motion and/or
motor control. These behaviors can be adjusted to provide a continuing challenge as the user’s skills improve. This prototype
is described in terms of functional capabilities that include a silhouette extraction from a video image, and generation of
graphical objects that interact with the silhouette. The work is extended with a discussion of a more sophisticated region
of interest detection algorithm that can select specific parts of the body. 相似文献
996.
Gregory Larson Deryl Snyder David Vanden Abeele Tanja Clees 《Computing and Visualization in Science》2008,11(1):27-40
Single- and multi-level iterative methods for sparse linear systems are applied to unsteady flow simulations via implementation
into a direct numerical simulation solver for incompressible turbulent flows on unstructured meshes. The performance of these
solution methods, implemented in the well-established SAMG and ML packages, are quantified in terms of computational speed
and memory consumption, with a direct sparse LU solver (SuperLU) used as a reference. The classical test case of unsteady
flow over a circular cylinder at low Reynolds numbers is considered, employing a series of increasingly fine anisotropic meshes.
As expected, the memory consumption increases dramatically with the considered problem size for the direct solver. Surprisingly,
however, the computation times remain reasonable. The speed and memory usage of pointwise algebraic and smoothed aggregation
multigrid solvers are found to exhibit near-linear scaling. As an alternative to multi-level solvers, a single-level ILUT-preconditioned
GMRES solver with low drop tolerance is also considered. This solver is found to perform sufficiently well only on small meshes.
Even then, it is outperformed by pointwise algebraic multigrid on all counts. Finally, the effectiveness of pointwise algebraic
multigrid is illustrated by considering a large three-dimensional direct numerical simulation case using a novel parallelization
approach on a large distributed memory computing cluster. 相似文献
997.
The convergence analysis of multigrid methods for boundary element equations arising from negative-order pseudo-differential operators is quite different from the usual finite element multigrid analysis for elliptic partial differential equations. In this paper, we study the convergence of geometrical multigrid methods for solving large-scale, data-sparse boundary element equations. In particular, we investigate multigrid methods for \(\mathcal{H}\)-matrices arising from the adaptive cross approximation to the single layer potential operator. 相似文献
998.
Voting systems have become controversial in the years following the multiple election disasters that occurred in the United States during and after 2000. Of particular note were the electronic voting (e-voting) systems that were widely deployed to replace the pre-scored punch-card systems, systems that had have been frequently judged to be central to the problem in the 2000 Florida general election. The (premature) deployment of e-voting machines stimulated a new field of security and privacy research around the subject of elections, a subject that has turned out to be more complex and deeper than anyone would have predicted a decade ago. Here we present a sample of some of the finest recent work on election technology from authors on three continents. 相似文献
999.
Leveraging online communities in fostering adaptive schools 总被引:1,自引:0,他引:1
David Hung Kenneth Y. T. Lim Der-Thanq Victor Chen Thiam Seng Koh 《International Journal of Computer-Supported Collaborative Learning》2008,3(4):373-386
There has long been a call for schools to prepare students for the twenty-first century where skills and dispositions differ
significantly from much of what has historically characterized formal education. The knowledge based economy calls for policy
and pedagogical efforts that would transform schools. Schools are to foster communities of learners. This paper suggests that
para-communities may be points of leverage in the fostering of adaptive schools. A critical analysis is done on the differences
between para-communities (such as online communities) and schools; and an argument is made that they each serve differing
goals and should be left distinct because they achieve different societal and economic demands. 相似文献
1000.
Considerate home notification systems: a field study of acceptability of notifications in the home 总被引:2,自引:2,他引:0
Martijn H. Vastenburg David V. Keyson Huib de Ridder 《Personal and Ubiquitous Computing》2008,12(8):555-566
A field study in ten homes was conducted to understand what influences users’ acceptability of notifications in the home environment.
The key finding is that perceived message urgency is the primary indicator of acceptability of notifications in the home—if
people think a message is urgent, they want the message to be shown immediately, regardless of what they are doing at the
time of notification. The study also shows that the acceptability of low-urgent and medium-urgent messages could be improved
by taking into account mental activity load at the time of notification. No effect of physical activity was found on acceptability.
The results suggest that to improve the scheduling of notifications in the home, notification systems need a mechanism assessing
both the message urgency and the mental activity load, whereas physical activity can be ignored. From a methodological point
of view, it is difficult to measure acceptability of notifications in a realistic setting, given the need to balance experimental
control with realistic context. The present paper suggests a way to introduce controlled notifications and subjective measurements
of acceptability in homes. 相似文献