全文获取类型
收费全文 | 23154篇 |
免费 | 1476篇 |
国内免费 | 896篇 |
专业分类
化学 | 4119篇 |
晶体学 | 30篇 |
力学 | 815篇 |
综合类 | 188篇 |
数学 | 1942篇 |
物理学 | 2453篇 |
综合类 | 15979篇 |
出版年
2024年 | 50篇 |
2023年 | 192篇 |
2022年 | 434篇 |
2021年 | 421篇 |
2020年 | 530篇 |
2019年 | 394篇 |
2018年 | 352篇 |
2017年 | 508篇 |
2016年 | 543篇 |
2015年 | 668篇 |
2014年 | 1085篇 |
2013年 | 1002篇 |
2012年 | 1242篇 |
2011年 | 1402篇 |
2010年 | 1134篇 |
2009年 | 1248篇 |
2008年 | 1258篇 |
2007年 | 1546篇 |
2006年 | 1386篇 |
2005年 | 1270篇 |
2004年 | 1173篇 |
2003年 | 1121篇 |
2002年 | 936篇 |
2001年 | 809篇 |
2000年 | 733篇 |
1999年 | 590篇 |
1998年 | 528篇 |
1997年 | 410篇 |
1996年 | 398篇 |
1995年 | 363篇 |
1994年 | 318篇 |
1993年 | 281篇 |
1992年 | 250篇 |
1991年 | 210篇 |
1990年 | 174篇 |
1989年 | 167篇 |
1988年 | 128篇 |
1987年 | 113篇 |
1986年 | 51篇 |
1985年 | 34篇 |
1984年 | 17篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
创造民族品牌加强产品竞争能力 总被引:1,自引:1,他引:0
阐述了民族品牌在市场竞争中所面临危急局面 ,提出了创造民族品牌、增强市场竞争能力的一系列措施 ,包括加强工业设计 ,创造品牌文化 ,提升品牌形象与市场地位等 . 相似文献
33.
薛生辉 《江苏技术师范学院学报》2002,8(3):49-51
CI设计的最大特点就在于广泛的参与、实践和应用,对它的教学目的是让学生在全面深入理解设计理念的基础上开展设计实践活动.然而现实中的CI教学往往只偏重于一方面而忽略另一方面,本文就两者的有机结合作了一些尝试. 相似文献
34.
A scheme for vehicle density and velocity estimation in a stretch of highway based on a modified cell transmission model [C.
F. Daganzo, Transportation Research, Part B, 28B(4),269–287, 1994. Elsevier is presented. The scheme is intended for use with on-ramp metering control algorithms, providing
local knowledge of densities and velocities that is helpful to improve on-ramp metering control performance. Estimation of
density is obtained by nonlinear estimators, while velocity estimation is obtained by gradient algorithms. There is one density–velocity
estimator for free traffic flow and other for congested traffic flow. Both estimator schemes work in parallel. The final estimation
of density and velocity results from a convex combination of the predictions of the two estimators. This combination depends
on occupancy or density measurements at the boundaries of the stretch and is produced by a fuzzy inference system. Stability
and convergence of the density and velocity estimation scheme is proved by Lyapunov based techniques. Simulation results comparing
measured and estimated traffic data are presented. They confirm good performance of the estimators.
Research sponsored by grants UNAM PAPIIT IN110403 and CONACYT 47583. 相似文献
35.
Masaaki Harada 《Designs, Codes and Cryptography》2006,38(1):5-16
In this paper, we show that the code generated by the rows of a block-point incidence matrix of a self-orthogonal 3-(56,12,65)
design is a doubly-even self-dual code of length 56. As a consequence, it is shown that an extremal doubly-even self-dual
code of length 56 is generated by the codewords of minimum weight. We also demonstrate that there are more than one thousand
inequivalent extremal doubly-even self-dual [56,28,12] codes. This result shows that there are more than one thousand non-isomorphic
self-orthogonal 3-(56,12,65) designs.
AMS Classification: 94B05, 05B05 相似文献
36.
Parking Capacity and Pricing in Park'n Ride Trips: A Continuous Equilibrium Network Design Problem 总被引:2,自引:0,他引:2
In this paper we consider the problem of designing parking facilities for park'n ride trips. We present a new continuous equilibrium network design problem to decide the capacity and fare of these parking lots at a tactical level. We assume that the parking facilities have already been located and other topological decisions have already been taken.The modeling approach proposed is mathematical programming with equilibrium constraints. In the outer optimization problem, a central Authority evaluates the performance of the transport network for each network design decision. In the inner problem a multimodal traffic assignment with combined modes, formulated as a variational inequality problem, generates the share demand for modes of transportation, and for parking facilities as a function of the design variables of the parking lots. The objective is to make optimal parking investment and pricing decisions in order to minimize the total travel cost in a subnetwork of the multimodal transportation system.We present a new development in model formulation based on the use of generalized parking link cost as a design variable.The bilevel model is solved by a simulated annealing algorithm applied to the continuous and non-negative design decision variables. Numerical tests are reported in order to illustrate the use of the model, and the ability of the approach to solve applications of moderate size. 相似文献
37.
介绍了TLC5 4 9带串行控制的 8位、4 0MHz单通道模数转换器的设计方法。常用的A D转换器件多数是并行输出 ,应用电路成熟 ,而带串行控制的转换器的设计方法少见。本文提出的串行控制单通道模数转换器设计方法在EDA实验系统上得到了验证 ,对相关电路设计具有一定参考价值 相似文献
38.
本文阐述了煤矿井下排水设备的计算机辅助设计中选型程序的编制及绘图,介绍了程序的功能,若干技术问题的处理和绘图方法与要点. 相似文献
39.
在《建筑抗震设计规范(GBJ11-89)》中与底层框架砖房有关的条文规定和大量实际工程设计的基础上,对底部2层框架砖房的抗震设计问题进行探讨。 相似文献
40.